libdispatch-703.50.37.tar.gz

[apple/libdispatch.git] / src / source.c

/*
 * Copyright (c) 2008-2016 Apple Inc. All rights reserved.
 *
 * @APPLE_APACHE_LICENSE_HEADER_START@
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * @APPLE_APACHE_LICENSE_HEADER_END@
 */

#include "internal.h"
#if HAVE_MACH
#include "protocol.h"
#include "protocolServer.h"
#endif

#define DKEV_DISPOSE_IMMEDIATE_DELETE 0x1
#define DKEV_UNREGISTER_DISCONNECTED 0x2
#define DKEV_UNREGISTER_REPLY_REMOVE 0x4
#define DKEV_UNREGISTER_WAKEUP 0x8

static pthread_priority_t
_dispatch_source_compute_kevent_priority(dispatch_source_t ds);
static void _dispatch_source_handler_free(dispatch_source_t ds, long kind);
static void _dispatch_source_merge_kevent(dispatch_source_t ds,
                const _dispatch_kevent_qos_s *ke);
static bool _dispatch_kevent_register(dispatch_kevent_t *dkp,
                pthread_priority_t pp, uint32_t *flgp);
static long _dispatch_kevent_unregister(dispatch_kevent_t dk, uint32_t flg,
                unsigned int options);
static long _dispatch_kevent_resume(dispatch_kevent_t dk, uint32_t new_flags,
                uint32_t del_flags);
static void _dispatch_kevent_drain(_dispatch_kevent_qos_s *ke);
static void _dispatch_kevent_merge(_dispatch_kevent_qos_s *ke);
static void _dispatch_timers_kevent(_dispatch_kevent_qos_s *ke);
static void _dispatch_timers_unregister(dispatch_source_t ds,
                dispatch_kevent_t dk);
static void _dispatch_timers_update(dispatch_source_t ds);
static void _dispatch_timer_aggregates_check(void);
static void _dispatch_timer_aggregates_register(dispatch_source_t ds);
static void _dispatch_timer_aggregates_update(dispatch_source_t ds,
                unsigned int tidx);
static void _dispatch_timer_aggregates_unregister(dispatch_source_t ds,
                unsigned int tidx);
static inline unsigned long _dispatch_source_timer_data(
                dispatch_source_refs_t dr, unsigned long prev);
static void _dispatch_kq_deferred_update(const _dispatch_kevent_qos_s *ke);
static long _dispatch_kq_immediate_update(_dispatch_kevent_qos_s *ke);
static void _dispatch_memorypressure_init(void);
#if HAVE_MACH
static void _dispatch_mach_host_calendar_change_register(void);
#if DISPATCH_EVFILT_MACHPORT_PORTSET_FALLBACK
static void _dispatch_mach_recv_msg_buf_init(void);
static kern_return_t _dispatch_kevent_machport_resume(dispatch_kevent_t dk,
                uint32_t new_flags, uint32_t del_flags);
#endif
static kern_return_t _dispatch_kevent_mach_notify_resume(dispatch_kevent_t dk,
                uint32_t new_flags, uint32_t del_flags);
static void _dispatch_mach_kevent_merge(_dispatch_kevent_qos_s *ke);
static mach_msg_size_t _dispatch_kevent_mach_msg_size(
                _dispatch_kevent_qos_s *ke);
#else
static inline void _dispatch_mach_host_calendar_change_register(void) {}
static inline void _dispatch_mach_recv_msg_buf_init(void) {}
#endif
static const char * _evfiltstr(short filt);
#if DISPATCH_DEBUG
static void dispatch_kevent_debug(const char *verb,
                const _dispatch_kevent_qos_s *kev, int i, int n,
                const char *function, unsigned int line);
#define DISPATCH_ASSERT_ON_MANAGER_QUEUE() \
        dispatch_assert(_dispatch_queue_get_current() == &_dispatch_mgr_q)
#else
static inline void
dispatch_kevent_debug(const char *verb, const _dispatch_kevent_qos_s *kev,
                int i, int n, const char *function, unsigned int line)
{
        (void)verb; (void)kev; (void)i; (void)n; (void)function; (void)line;
}
#define DISPATCH_ASSERT_ON_MANAGER_QUEUE()
#endif
#define _dispatch_kevent_debug(verb, _kev) \
                dispatch_kevent_debug(verb, _kev, 0, 1, __FUNCTION__, __LINE__)
#define _dispatch_kevent_debug_n(verb, _kev, i, n) \
                dispatch_kevent_debug(verb, _kev, i, n, __FUNCTION__, __LINE__)
#ifndef DISPATCH_MGR_QUEUE_DEBUG
#define DISPATCH_MGR_QUEUE_DEBUG 0
#endif
#if DISPATCH_MGR_QUEUE_DEBUG
#define _dispatch_kevent_mgr_debug _dispatch_kevent_debug
#else
static inline void
_dispatch_kevent_mgr_debug(_dispatch_kevent_qos_s* kev DISPATCH_UNUSED) {}
#endif

#pragma mark -
#pragma mark dispatch_source_t

dispatch_source_t
dispatch_source_create(dispatch_source_type_t type, uintptr_t handle,
                unsigned long mask, dispatch_queue_t dq)
{
        // ensure _dispatch_evfilt_machport_direct_enabled is initialized
        _dispatch_root_queues_init();
        const _dispatch_kevent_qos_s *proto_kev = &type->ke;
        dispatch_source_t ds;
        dispatch_kevent_t dk;

        // input validation
        if (type == NULL || (mask & ~type->mask)) {
                return DISPATCH_BAD_INPUT;
        }
        if (type->mask && !mask) {
                // expect a non-zero mask when the type declares one ... except
                switch (type->ke.filter) {
                case DISPATCH_EVFILT_TIMER:
                        break; // timers don't need masks
                case DISPATCH_EVFILT_MACH_NOTIFICATION:
                        break; // type->init handles zero mask as a legacy case
                default:
                        // otherwise reject as invalid input
                        return DISPATCH_BAD_INPUT;
                }
        }

        switch (type->ke.filter) {
        case EVFILT_SIGNAL:
                if (handle >= NSIG) {
                        return DISPATCH_BAD_INPUT;
                }
                break;
        case EVFILT_FS:
#if DISPATCH_USE_MEMORYSTATUS
        case EVFILT_MEMORYSTATUS:
#endif
        case DISPATCH_EVFILT_CUSTOM_ADD:
        case DISPATCH_EVFILT_CUSTOM_OR:
                if (handle) {
                        return DISPATCH_BAD_INPUT;
                }
                break;
        case DISPATCH_EVFILT_TIMER:
                if ((handle == 0) != (type->ke.ident == 0)) {
                        return DISPATCH_BAD_INPUT;
                }
                break;
        default:
                break;
        }

        ds = _dispatch_alloc(DISPATCH_VTABLE(source),
                        sizeof(struct dispatch_source_s));
        // Initialize as a queue first, then override some settings below.
        _dispatch_queue_init(ds->_as_dq, DQF_NONE, 1, true);
        ds->dq_label = "source";
        ds->do_ref_cnt++; // the reference the manager queue holds

        switch (type->ke.filter) {
        case DISPATCH_EVFILT_CUSTOM_OR:
                dk = DISPATCH_KEV_CUSTOM_OR;
                break;
        case DISPATCH_EVFILT_CUSTOM_ADD:
                dk = DISPATCH_KEV_CUSTOM_ADD;
                break;
        default:
                dk = _dispatch_calloc(1ul, sizeof(struct dispatch_kevent_s));
                dk->dk_kevent = *proto_kev;
                dk->dk_kevent.ident = handle;
                dk->dk_kevent.flags |= EV_ADD|EV_ENABLE;
                dk->dk_kevent.fflags |= (uint32_t)mask;
                dk->dk_kevent.udata = (_dispatch_kevent_qos_udata_t)dk;
                TAILQ_INIT(&dk->dk_sources);

                ds->ds_pending_data_mask = dk->dk_kevent.fflags;
                ds->ds_ident_hack = (uintptr_t)dk->dk_kevent.ident;
                if (EV_UDATA_SPECIFIC & proto_kev->flags) {
                        dk->dk_kevent.flags |= EV_DISPATCH;
                        ds->ds_is_direct_kevent = true;
                        ds->ds_needs_rearm = true;
                }
                break;
        }
        ds->ds_dkev = dk;

        if ((EV_DISPATCH|EV_ONESHOT) & proto_kev->flags) {
                ds->ds_needs_rearm = true;
        } else if (!(EV_CLEAR & proto_kev->flags)) {
                // we cheat and use EV_CLEAR to mean a "flag thingy"
                ds->ds_is_adder = true;
        }
        // Some sources require special processing
        if (type->init != NULL) {
                type->init(ds, type, handle, mask);
        }
        dispatch_assert(!(ds->ds_is_level && ds->ds_is_adder));
        if (!ds->ds_is_custom_source && (dk->dk_kevent.flags & EV_VANISHED)) {
                // see _dispatch_source_merge_kevent
                dispatch_assert(!(dk->dk_kevent.flags & EV_ONESHOT));
                dispatch_assert(dk->dk_kevent.flags & EV_DISPATCH);
                dispatch_assert(dk->dk_kevent.flags & EV_UDATA_SPECIFIC);
        }

        if (fastpath(!ds->ds_refs)) {
                ds->ds_refs = _dispatch_calloc(1ul,
                                sizeof(struct dispatch_source_refs_s));
        }
        ds->ds_refs->dr_source_wref = _dispatch_ptr2wref(ds);

        if (slowpath(!dq)) {
                dq = _dispatch_get_root_queue(_DISPATCH_QOS_CLASS_DEFAULT, true);
        } else {
                _dispatch_retain(dq);
        }
        ds->do_targetq = dq;
        _dispatch_object_debug(ds, "%s", __func__);
        return ds;
}

void
_dispatch_source_dispose(dispatch_source_t ds)
{
        _dispatch_object_debug(ds, "%s", __func__);
        _dispatch_source_handler_free(ds, DS_REGISTN_HANDLER);
        _dispatch_source_handler_free(ds, DS_EVENT_HANDLER);
        _dispatch_source_handler_free(ds, DS_CANCEL_HANDLER);
        free(ds->ds_refs);
        _dispatch_queue_destroy(ds->_as_dq);
}

void
_dispatch_source_xref_dispose(dispatch_source_t ds)
{
        dx_wakeup(ds, 0, DISPATCH_WAKEUP_FLUSH);
}

long
dispatch_source_testcancel(dispatch_source_t ds)
{
        return (bool)(ds->dq_atomic_flags & DSF_CANCELED);
}

unsigned long
dispatch_source_get_mask(dispatch_source_t ds)
{
        unsigned long mask = ds->ds_pending_data_mask;
        if (ds->ds_vmpressure_override) {
                mask = NOTE_VM_PRESSURE;
        }
#if TARGET_IPHONE_SIMULATOR
        else if (ds->ds_memorypressure_override) {
                mask = NOTE_MEMORYSTATUS_PRESSURE_WARN;
        }
#endif
        return mask;
}

uintptr_t
dispatch_source_get_handle(dispatch_source_t ds)
{
        unsigned int handle = (unsigned int)ds->ds_ident_hack;
#if TARGET_IPHONE_SIMULATOR
        if (ds->ds_memorypressure_override) {
                handle = 0;
        }
#endif
        return handle;
}

unsigned long
dispatch_source_get_data(dispatch_source_t ds)
{
        unsigned long data = ds->ds_data;
        if (ds->ds_vmpressure_override) {
                data = NOTE_VM_PRESSURE;
        }
#if TARGET_IPHONE_SIMULATOR
        else if (ds->ds_memorypressure_override) {
                data = NOTE_MEMORYSTATUS_PRESSURE_WARN;
        }
#endif
        return data;
}

DISPATCH_ALWAYS_INLINE
static inline void
_dispatch_source_merge_data2(dispatch_source_t ds,
                pthread_priority_t pp, unsigned long val)
{
        _dispatch_kevent_qos_s kev = {
                .fflags = (typeof(kev.fflags))val,
                .data = (typeof(kev.data))val,
#if DISPATCH_USE_KEVENT_QOS
                .qos = (_dispatch_kevent_priority_t)pp,
#endif
        };
#if !DISPATCH_USE_KEVENT_QOS
        (void)pp;
#endif

        dispatch_assert(ds->ds_dkev == DISPATCH_KEV_CUSTOM_OR ||
                        ds->ds_dkev == DISPATCH_KEV_CUSTOM_ADD);
        _dispatch_kevent_debug("synthetic data", &kev);
        _dispatch_source_merge_kevent(ds, &kev);
}

void
dispatch_source_merge_data(dispatch_source_t ds, unsigned long val)
{
        _dispatch_source_merge_data2(ds, 0, val);
}

void
_dispatch_source_merge_data(dispatch_source_t ds, pthread_priority_t pp,
                unsigned long val)
{
        _dispatch_source_merge_data2(ds, pp, val);
}

#pragma mark -
#pragma mark dispatch_source_handler

DISPATCH_ALWAYS_INLINE
static inline dispatch_continuation_t
_dispatch_source_get_handler(dispatch_source_refs_t dr, long kind)
{
        return os_atomic_load(&dr->ds_handler[kind], relaxed);
}
#define _dispatch_source_get_event_handler(dr) \
        _dispatch_source_get_handler(dr, DS_EVENT_HANDLER)
#define _dispatch_source_get_cancel_handler(dr) \
        _dispatch_source_get_handler(dr, DS_CANCEL_HANDLER)
#define _dispatch_source_get_registration_handler(dr) \
        _dispatch_source_get_handler(dr, DS_REGISTN_HANDLER)

DISPATCH_ALWAYS_INLINE
static inline dispatch_continuation_t
_dispatch_source_handler_alloc(dispatch_source_t ds, void *func, long kind,
                bool block)
{
        // sources don't propagate priority by default
        const dispatch_block_flags_t flags =
                        DISPATCH_BLOCK_HAS_PRIORITY | DISPATCH_BLOCK_NO_VOUCHER;
        dispatch_continuation_t dc = _dispatch_continuation_alloc();
        if (func) {
                uintptr_t dc_flags = 0;

                if (kind != DS_EVENT_HANDLER) {
                        dc_flags |= DISPATCH_OBJ_CONSUME_BIT;
                }
                if (block) {
#ifdef __BLOCKS__
                        _dispatch_continuation_init(dc, ds, func, 0, flags, dc_flags);
#endif /* __BLOCKS__ */
                } else {
                        dc_flags |= DISPATCH_OBJ_CTXT_FETCH_BIT;
                        _dispatch_continuation_init_f(dc, ds, ds->do_ctxt, func,
                                        0, flags, dc_flags);
                }
                _dispatch_trace_continuation_push(ds->_as_dq, dc);
        } else {
                dc->dc_flags = 0;
                dc->dc_func = NULL;
        }
        return dc;
}

DISPATCH_NOINLINE
static void
_dispatch_source_handler_dispose(dispatch_continuation_t dc)
{
#ifdef __BLOCKS__
        if (dc->dc_flags & DISPATCH_OBJ_BLOCK_BIT) {
                Block_release(dc->dc_ctxt);
        }
#endif /* __BLOCKS__ */
        if (dc->dc_voucher) {
                _voucher_release(dc->dc_voucher);
                dc->dc_voucher = VOUCHER_INVALID;
        }
        _dispatch_continuation_free(dc);
}

DISPATCH_ALWAYS_INLINE
static inline dispatch_continuation_t
_dispatch_source_handler_take(dispatch_source_t ds, long kind)
{
        return os_atomic_xchg(&ds->ds_refs->ds_handler[kind], NULL, relaxed);
}

DISPATCH_ALWAYS_INLINE
static inline void
_dispatch_source_handler_free(dispatch_source_t ds, long kind)
{
        dispatch_continuation_t dc = _dispatch_source_handler_take(ds, kind);
        if (dc) _dispatch_source_handler_dispose(dc);
}

DISPATCH_ALWAYS_INLINE
static inline void
_dispatch_source_handler_replace(dispatch_source_t ds, long kind,
                dispatch_continuation_t dc)
{
        if (!dc->dc_func) {
                _dispatch_continuation_free(dc);
                dc = NULL;
        } else if (dc->dc_flags & DISPATCH_OBJ_CTXT_FETCH_BIT) {
                dc->dc_ctxt = ds->do_ctxt;
        }
        dc = os_atomic_xchg(&ds->ds_refs->ds_handler[kind], dc, release);
        if (dc) _dispatch_source_handler_dispose(dc);
}

DISPATCH_NOINLINE
static void
_dispatch_source_set_handler_slow(void *context)
{
        dispatch_source_t ds = (dispatch_source_t)_dispatch_queue_get_current();
        dispatch_assert(dx_type(ds) == DISPATCH_SOURCE_KEVENT_TYPE);

        dispatch_continuation_t dc = context;
        long kind = (long)dc->dc_data;
        dc->dc_data = NULL;
        _dispatch_source_handler_replace(ds, kind, dc);
}

DISPATCH_NOINLINE
static void
_dispatch_source_set_handler(dispatch_source_t ds, long kind,
                dispatch_continuation_t dc)
{
        dispatch_assert(dx_type(ds) == DISPATCH_SOURCE_KEVENT_TYPE);
        if (_dispatch_queue_try_inactive_suspend(ds->_as_dq)) {
                _dispatch_source_handler_replace(ds, kind, dc);
                return dx_vtable(ds)->do_resume(ds, false);
        }
        _dispatch_ktrace1(DISPATCH_PERF_post_activate_mutation, ds);
        if (kind == DS_REGISTN_HANDLER) {
                _dispatch_bug_deprecated("Setting registration handler after "
                                "the source has been activated");
        }
        dc->dc_data = (void *)kind;
        _dispatch_barrier_trysync_or_async_f(ds->_as_dq, dc,
                        _dispatch_source_set_handler_slow);
}

#ifdef __BLOCKS__
void
dispatch_source_set_event_handler(dispatch_source_t ds,
                dispatch_block_t handler)
{
        dispatch_continuation_t dc;
        dc = _dispatch_source_handler_alloc(ds, handler, DS_EVENT_HANDLER, true);
        _dispatch_source_set_handler(ds, DS_EVENT_HANDLER, dc);
}
#endif /* __BLOCKS__ */

void
dispatch_source_set_event_handler_f(dispatch_source_t ds,
                dispatch_function_t handler)
{
        dispatch_continuation_t dc;
        dc = _dispatch_source_handler_alloc(ds, handler, DS_EVENT_HANDLER, false);
        _dispatch_source_set_handler(ds, DS_EVENT_HANDLER, dc);
}

void
_dispatch_source_set_event_handler_continuation(dispatch_source_t ds,
                dispatch_continuation_t dc)
{
        _dispatch_trace_continuation_push(ds->_as_dq, dc);
        _dispatch_source_set_handler(ds, DS_EVENT_HANDLER, dc);
}

#ifdef __BLOCKS__
void
dispatch_source_set_cancel_handler(dispatch_source_t ds,
                dispatch_block_t handler)
{
        dispatch_continuation_t dc;
        dc = _dispatch_source_handler_alloc(ds, handler, DS_CANCEL_HANDLER, true);
        _dispatch_source_set_handler(ds, DS_CANCEL_HANDLER, dc);
}
#endif /* __BLOCKS__ */

void
dispatch_source_set_cancel_handler_f(dispatch_source_t ds,
                dispatch_function_t handler)
{
        dispatch_continuation_t dc;
        dc = _dispatch_source_handler_alloc(ds, handler, DS_CANCEL_HANDLER, false);
        _dispatch_source_set_handler(ds, DS_CANCEL_HANDLER, dc);
}

#ifdef __BLOCKS__
void
dispatch_source_set_registration_handler(dispatch_source_t ds,
                dispatch_block_t handler)
{
        dispatch_continuation_t dc;
        dc = _dispatch_source_handler_alloc(ds, handler, DS_REGISTN_HANDLER, true);
        _dispatch_source_set_handler(ds, DS_REGISTN_HANDLER, dc);
}
#endif /* __BLOCKS__ */

void
dispatch_source_set_registration_handler_f(dispatch_source_t ds,
        dispatch_function_t handler)
{
        dispatch_continuation_t dc;
        dc = _dispatch_source_handler_alloc(ds, handler, DS_REGISTN_HANDLER, false);
        _dispatch_source_set_handler(ds, DS_REGISTN_HANDLER, dc);
}

#pragma mark -
#pragma mark dispatch_source_invoke

static void
_dispatch_source_registration_callout(dispatch_source_t ds, dispatch_queue_t cq,
                dispatch_invoke_flags_t flags)
{
        dispatch_continuation_t dc;

        dc = _dispatch_source_handler_take(ds, DS_REGISTN_HANDLER);
        if (ds->dq_atomic_flags & (DSF_CANCELED | DQF_RELEASED)) {
                // no registration callout if source is canceled rdar://problem/8955246
                return _dispatch_source_handler_dispose(dc);
        }
        if (dc->dc_flags & DISPATCH_OBJ_CTXT_FETCH_BIT) {
                dc->dc_ctxt = ds->do_ctxt;
        }
        _dispatch_continuation_pop(dc, cq, flags);
}

static void
_dispatch_source_cancel_callout(dispatch_source_t ds, dispatch_queue_t cq,
                dispatch_invoke_flags_t flags)
{
        dispatch_continuation_t dc;

        dc = _dispatch_source_handler_take(ds, DS_CANCEL_HANDLER);
        ds->ds_pending_data_mask = 0;
        ds->ds_pending_data = 0;
        ds->ds_data = 0;
        _dispatch_source_handler_free(ds, DS_EVENT_HANDLER);
        _dispatch_source_handler_free(ds, DS_REGISTN_HANDLER);
        if (!dc) {
                return;
        }
        if (!(ds->dq_atomic_flags & DSF_CANCELED)) {
                return _dispatch_source_handler_dispose(dc);
        }
        if (dc->dc_flags & DISPATCH_OBJ_CTXT_FETCH_BIT) {
                dc->dc_ctxt = ds->do_ctxt;
        }
        _dispatch_continuation_pop(dc, cq, flags);
}

static void
_dispatch_source_latch_and_call(dispatch_source_t ds, dispatch_queue_t cq,
                dispatch_invoke_flags_t flags)
{
        unsigned long prev;

        dispatch_source_refs_t dr = ds->ds_refs;
        dispatch_continuation_t dc = _dispatch_source_get_handler(dr, DS_EVENT_HANDLER);
        prev = os_atomic_xchg2o(ds, ds_pending_data, 0, relaxed);
        if (ds->ds_is_level) {
                ds->ds_data = ~prev;
        } else if (ds->ds_is_timer && ds_timer(dr).target && prev) {
                ds->ds_data = _dispatch_source_timer_data(dr, prev);
        } else {
                ds->ds_data = prev;
        }
        if (!dispatch_assume(prev) || !dc) {
                return;
        }
        _dispatch_continuation_pop(dc, cq, flags);
        if (ds->ds_is_timer && (ds_timer(dr).flags & DISPATCH_TIMER_AFTER)) {
                _dispatch_source_handler_free(ds, DS_EVENT_HANDLER);
                dispatch_release(ds); // dispatch_after sources are one-shot
        }
}

static void
_dispatch_source_kevent_unregister(dispatch_source_t ds)
{
        _dispatch_object_debug(ds, "%s", __func__);
        uint32_t flags = (uint32_t)ds->ds_pending_data_mask;
        dispatch_kevent_t dk = ds->ds_dkev;
        dispatch_queue_flags_t dqf = _dispatch_queue_atomic_flags(ds->_as_dq);
        if (ds->ds_is_custom_source) {
                ds->ds_dkev = NULL;
                goto done;
        }

        if (ds->ds_is_direct_kevent &&
                        ((dqf & DSF_DELETED) || !(ds->ds_is_installed))) {
                dk->dk_kevent.flags |= EV_DELETE; // already deleted
                dk->dk_kevent.flags &= ~(EV_ADD|EV_ENABLE|EV_VANISHED);
        }
        if (dk->dk_kevent.filter == DISPATCH_EVFILT_TIMER) {
                ds->ds_dkev = NULL;
                if (ds->ds_is_installed) {
                        _dispatch_timers_unregister(ds, dk);
                }
        } else if (!ds->ds_is_direct_kevent) {
                ds->ds_dkev = NULL;
                dispatch_assert((bool)ds->ds_is_installed);
                TAILQ_REMOVE(&dk->dk_sources, ds->ds_refs, dr_list);
                _dispatch_kevent_unregister(dk, flags, 0);
        } else {
                unsigned int dkev_dispose_options = 0;
                if (ds->ds_needs_rearm && !(dqf & DSF_ARMED)) {
                        dkev_dispose_options |= DKEV_DISPOSE_IMMEDIATE_DELETE;
                } else if (dx_type(ds) == DISPATCH_MACH_CHANNEL_TYPE) {
                        if (!ds->ds_is_direct_kevent) {
                                dkev_dispose_options |= DKEV_DISPOSE_IMMEDIATE_DELETE;
                        }
                }
                long r = _dispatch_kevent_unregister(dk, flags, dkev_dispose_options);
                if (r == EINPROGRESS) {
                        _dispatch_debug("kevent-source[%p]: deferred delete kevent[%p]",
                                        ds, dk);
                        _dispatch_queue_atomic_flags_set(ds->_as_dq, DSF_DEFERRED_DELETE);
                        return; // deferred unregistration
#if DISPATCH_KEVENT_TREAT_ENOENT_AS_EINPROGRESS
                } else if (r == ENOENT) {
                        _dispatch_debug("kevent-source[%p]: ENOENT delete kevent[%p]",
                                        ds, dk);
                        _dispatch_queue_atomic_flags_set(ds->_as_dq, DSF_DEFERRED_DELETE);
                        return; // potential concurrent EV_DELETE delivery rdar://22047283
#endif
                } else {
                        dispatch_assume_zero(r);
                }
                ds->ds_dkev = NULL;
                _TAILQ_TRASH_ENTRY(ds->ds_refs, dr_list);
        }
done:
        dqf = _dispatch_queue_atomic_flags_set_and_clear_orig(ds->_as_dq,
                        DSF_DELETED, DSF_ARMED | DSF_DEFERRED_DELETE | DSF_CANCEL_WAITER);
        if (dqf & DSF_CANCEL_WAITER) {
                _dispatch_wake_by_address(&ds->dq_atomic_flags);
        }
        ds->ds_is_installed = true;
        ds->ds_needs_rearm = false; // re-arm is pointless and bad now
        _dispatch_debug("kevent-source[%p]: disarmed kevent[%p]", ds, dk);
        _dispatch_release(ds); // the retain is done at creation time
}

DISPATCH_ALWAYS_INLINE
static bool
_dispatch_source_tryarm(dispatch_source_t ds)
{
        dispatch_queue_flags_t oqf, nqf;
        return os_atomic_rmw_loop2o(ds, dq_atomic_flags, oqf, nqf, relaxed, {
                if (oqf & (DSF_DEFERRED_DELETE | DSF_DELETED)) {
                        // the test is inside the loop because it's convenient but the
                        // result should not change for the duration of the rmw_loop
                        os_atomic_rmw_loop_give_up(break);
                }
                nqf = oqf | DSF_ARMED;
        });
}

static bool
_dispatch_source_kevent_resume(dispatch_source_t ds, uint32_t new_flags)
{
        switch (ds->ds_dkev->dk_kevent.filter) {
        case DISPATCH_EVFILT_TIMER:
                _dispatch_timers_update(ds);
                _dispatch_queue_atomic_flags_set(ds->_as_dq, DSF_ARMED);
                _dispatch_debug("kevent-source[%p]: rearmed kevent[%p]", ds,
                                ds->ds_dkev);
                return true;
#if HAVE_MACH
        case EVFILT_MACHPORT:
                if ((ds->ds_pending_data_mask & DISPATCH_MACH_RECV_MESSAGE) &&
                                !ds->ds_is_direct_kevent) {
                        new_flags |= DISPATCH_MACH_RECV_MESSAGE; // emulate EV_DISPATCH
                }
                break;
#endif
        }
        if (unlikely(!_dispatch_source_tryarm(ds))) {
                return false;
        }
        if (unlikely(_dispatch_kevent_resume(ds->ds_dkev, new_flags, 0))) {
                _dispatch_queue_atomic_flags_set_and_clear(ds->_as_dq, DSF_DELETED,
                                DSF_ARMED);
                return false;
        }
        _dispatch_debug("kevent-source[%p]: armed kevent[%p]", ds, ds->ds_dkev);
        return true;
}

static void
_dispatch_source_kevent_register(dispatch_source_t ds, pthread_priority_t pp)
{
        dispatch_assert_zero((bool)ds->ds_is_installed);
        switch (ds->ds_dkev->dk_kevent.filter) {
        case DISPATCH_EVFILT_TIMER:
                // aggressively coalesce background/maintenance QoS timers
                // <rdar://problem/12200216&27342536>
                pp = _dispatch_source_compute_kevent_priority(ds);
                if (_dispatch_is_background_priority(pp)) {
                        ds_timer(ds->ds_refs).flags |= DISPATCH_TIMER_BACKGROUND;
                }
                _dispatch_timers_update(ds);
                _dispatch_queue_atomic_flags_set(ds->_as_dq, DSF_ARMED);
                _dispatch_debug("kevent-source[%p]: armed kevent[%p]", ds, ds->ds_dkev);
                return;
        }
        uint32_t flags;
        bool do_resume = _dispatch_kevent_register(&ds->ds_dkev, pp, &flags);
        TAILQ_INSERT_TAIL(&ds->ds_dkev->dk_sources, ds->ds_refs, dr_list);
        ds->ds_is_installed = true;
        if (do_resume || ds->ds_needs_rearm) {
                if (unlikely(!_dispatch_source_kevent_resume(ds, flags))) {
                        _dispatch_source_kevent_unregister(ds);
                }
        } else {
                _dispatch_queue_atomic_flags_set(ds->_as_dq, DSF_ARMED);
        }
        _dispatch_object_debug(ds, "%s", __func__);
}

static void
_dispatch_source_set_event_handler_context(void *ctxt)
{
        dispatch_source_t ds = ctxt;
        dispatch_continuation_t dc = _dispatch_source_get_event_handler(ds->ds_refs);

        if (dc && (dc->dc_flags & DISPATCH_OBJ_CTXT_FETCH_BIT)) {
                dc->dc_ctxt = ds->do_ctxt;
        }
}

static pthread_priority_t
_dispatch_source_compute_kevent_priority(dispatch_source_t ds)
{
        pthread_priority_t p = ds->dq_priority & ~_PTHREAD_PRIORITY_FLAGS_MASK;
        dispatch_queue_t tq = ds->do_targetq;
        pthread_priority_t tqp = tq->dq_priority & ~_PTHREAD_PRIORITY_FLAGS_MASK;

        while (unlikely(tq->do_targetq)) {
                if (unlikely(tq == &_dispatch_mgr_q)) {
                        return _PTHREAD_PRIORITY_EVENT_MANAGER_FLAG;
                }
                if (unlikely(_dispatch_queue_is_thread_bound(tq))) {
                        // thread bound hierarchies are weird, we need to install
                        // from the context of the thread this hierarchy is bound to
                        return 0;
                }
                if (unlikely(DISPATCH_QUEUE_IS_SUSPENDED(tq))) {
                        // this queue may not be activated yet, so the queue graph may not
                        // have stabilized yet
                        _dispatch_ktrace1(DISPATCH_PERF_delayed_registration, ds);
                        return 0;
                }
                if (unlikely(!_dispatch_queue_has_immutable_target(tq))) {
                        if (!_dispatch_is_in_root_queues_array(tq->do_targetq)) {
                                // we're not allowed to dereference tq->do_targetq
                                _dispatch_ktrace1(DISPATCH_PERF_delayed_registration, ds);
                                return 0;
                        }
                }
                if (!(tq->dq_priority & _PTHREAD_PRIORITY_INHERIT_FLAG)) {
                        if (p < tqp) p = tqp;
                }
                tq = tq->do_targetq;
                tqp = tq->dq_priority & ~_PTHREAD_PRIORITY_FLAGS_MASK;
        }

        if (unlikely(!tqp)) {
                // pthread root queues opt out of QoS
                return 0;
        }
        return _dispatch_priority_inherit_from_root_queue(p, tq);
}

void
_dispatch_source_finalize_activation(dispatch_source_t ds)
{
        dispatch_continuation_t dc;

        if (unlikely(ds->ds_is_direct_kevent &&
                        (_dispatch_queue_atomic_flags(ds->_as_dq) & DSF_CANCELED))) {
                return _dispatch_source_kevent_unregister(ds);
        }

        dc = _dispatch_source_get_event_handler(ds->ds_refs);
        if (dc) {
                if (_dispatch_object_is_barrier(dc)) {
                        _dispatch_queue_atomic_flags_set(ds->_as_dq, DQF_BARRIER_BIT);
                }
                ds->dq_priority = dc->dc_priority & ~_PTHREAD_PRIORITY_FLAGS_MASK;
                if (dc->dc_flags & DISPATCH_OBJ_CTXT_FETCH_BIT) {
                        _dispatch_barrier_async_detached_f(ds->_as_dq, ds,
                                        _dispatch_source_set_event_handler_context);
                }
        }

        // call "super"
        _dispatch_queue_finalize_activation(ds->_as_dq);

        if (ds->ds_is_direct_kevent && !ds->ds_is_installed) {
                pthread_priority_t pp = _dispatch_source_compute_kevent_priority(ds);
                if (pp) _dispatch_source_kevent_register(ds, pp);
        }
}

DISPATCH_ALWAYS_INLINE
static inline dispatch_queue_t
_dispatch_source_invoke2(dispatch_object_t dou, dispatch_invoke_flags_t flags,
                uint64_t *owned, struct dispatch_object_s **dc_ptr DISPATCH_UNUSED)
{
        dispatch_source_t ds = dou._ds;
        dispatch_queue_t retq = NULL;
        dispatch_queue_t dq = _dispatch_queue_get_current();

        if (_dispatch_queue_class_probe(ds)) {
                // Intentionally always drain even when on the manager queue
                // and not the source's regular target queue: we need to be able
                // to drain timer setting and the like there.
                retq = _dispatch_queue_serial_drain(ds->_as_dq, flags, owned, NULL);
        }

        // This function performs all source actions. Each action is responsible
        // for verifying that it takes place on the appropriate queue. If the
        // current queue is not the correct queue for this action, the correct queue
        // will be returned and the invoke will be re-driven on that queue.

        // The order of tests here in invoke and in wakeup should be consistent.

        dispatch_source_refs_t dr = ds->ds_refs;
        dispatch_queue_t dkq = &_dispatch_mgr_q;

        if (ds->ds_is_direct_kevent) {
                dkq = ds->do_targetq;
        }

        if (!ds->ds_is_installed) {
                // The source needs to be installed on the kevent queue.
                if (dq != dkq) {
                        return dkq;
                }
                _dispatch_source_kevent_register(ds, _dispatch_get_defaultpriority());
        }

        if (unlikely(DISPATCH_QUEUE_IS_SUSPENDED(ds))) {
                // Source suspended by an item drained from the source queue.
                return ds->do_targetq;
        }

        if (_dispatch_source_get_registration_handler(dr)) {
                // The source has been registered and the registration handler needs
                // to be delivered on the target queue.
                if (dq != ds->do_targetq) {
                        return ds->do_targetq;
                }
                // clears ds_registration_handler
                _dispatch_source_registration_callout(ds, dq, flags);
        }

        dispatch_queue_flags_t dqf = _dispatch_queue_atomic_flags(ds->_as_dq);
        bool prevent_starvation = false;

        if ((dqf & DSF_DEFERRED_DELETE) &&
                        ((dqf & DSF_DELETED) || !(dqf & DSF_ARMED))) {
unregister_event:
                // DSF_DELETE: Pending source kevent unregistration has been completed
                // !DSF_ARMED: event was delivered and can safely be unregistered
                if (dq != dkq) {
                        return dkq;
                }
                _dispatch_source_kevent_unregister(ds);
                dqf = _dispatch_queue_atomic_flags(ds->_as_dq);
        }

        if (!(dqf & (DSF_CANCELED | DQF_RELEASED)) && ds->ds_pending_data) {
                // The source has pending data to deliver via the event handler callback
                // on the target queue. Some sources need to be rearmed on the kevent
                // queue after event delivery.
                if (dq == ds->do_targetq) {
                        _dispatch_source_latch_and_call(ds, dq, flags);
                        dqf = _dispatch_queue_atomic_flags(ds->_as_dq);

                        // starvation avoidance: if the source triggers itself then force a
                        // re-queue to give other things already queued on the target queue
                        // a chance to run.
                        //
                        // however, if the source is directly targetting an overcommit root
                        // queue, this would requeue the source and ask for a new overcommit
                        // thread right away.
                        prevent_starvation = dq->do_targetq ||
                                        !(dq->dq_priority & _PTHREAD_PRIORITY_OVERCOMMIT_FLAG);
                        if (prevent_starvation && ds->ds_pending_data) {
                                retq = ds->do_targetq;
                        }
                } else {
                        // there is no point trying to be eager, the next thing to do is
                        // to deliver the event
                        return ds->do_targetq;
                }
        }

        if ((dqf & (DSF_CANCELED | DQF_RELEASED)) && !(dqf & DSF_DEFERRED_DELETE)) {
                // The source has been cancelled and needs to be uninstalled from the
                // kevent queue. After uninstallation, the cancellation handler needs
                // to be delivered to the target queue.
                if (!(dqf & DSF_DELETED)) {
                        if (dq != dkq) {
                                return dkq;
                        }
                        _dispatch_source_kevent_unregister(ds);
                        dqf = _dispatch_queue_atomic_flags(ds->_as_dq);
                        if (unlikely(dqf & DSF_DEFERRED_DELETE)) {
                                if (!(dqf & DSF_ARMED)) {
                                        goto unregister_event;
                                }
                                // we need to wait for the EV_DELETE
                                return retq;
                        }
                }
                if (dq != ds->do_targetq && (_dispatch_source_get_event_handler(dr) ||
                                _dispatch_source_get_cancel_handler(dr) ||
                                _dispatch_source_get_registration_handler(dr))) {
                        retq = ds->do_targetq;
                } else {
                        _dispatch_source_cancel_callout(ds, dq, flags);
                        dqf = _dispatch_queue_atomic_flags(ds->_as_dq);
                }
                prevent_starvation = false;
        }

        if (ds->ds_needs_rearm && !(dqf & DSF_ARMED)) {
                // The source needs to be rearmed on the kevent queue.
                if (dq != dkq) {
                        return dkq;
                }
                if (unlikely(dqf & DSF_DEFERRED_DELETE)) {
                        // no need for resume when we can directly unregister the kevent
                        goto unregister_event;
                }
                if (prevent_starvation) {
                        // keep the old behavior to force re-enqueue to our target queue
                        // for the rearm. It is inefficient though and we should
                        // improve this <rdar://problem/24635615>.
                        //
                        // if the handler didn't run, or this is a pending delete
                        // or our target queue is a global queue, then starvation is
                        // not a concern and we can rearm right away.
                        return ds->do_targetq;
                }
                if (unlikely(!_dispatch_source_kevent_resume(ds, 0))) {
                        dqf = _dispatch_queue_atomic_flags(ds->_as_dq);
                        goto unregister_event;
                }
        }

        return retq;
}

DISPATCH_NOINLINE
void
_dispatch_source_invoke(dispatch_source_t ds, dispatch_invoke_flags_t flags)
{
        _dispatch_queue_class_invoke(ds->_as_dq, flags, _dispatch_source_invoke2);
}

void
_dispatch_source_wakeup(dispatch_source_t ds, pthread_priority_t pp,
                dispatch_wakeup_flags_t flags)
{
        // This function determines whether the source needs to be invoked.
        // The order of tests here in wakeup and in invoke should be consistent.

        dispatch_source_refs_t dr = ds->ds_refs;
        dispatch_queue_wakeup_target_t dkq = DISPATCH_QUEUE_WAKEUP_MGR;
        dispatch_queue_wakeup_target_t tq = DISPATCH_QUEUE_WAKEUP_NONE;
        dispatch_queue_flags_t dqf = _dispatch_queue_atomic_flags(ds->_as_dq);
        bool deferred_delete = (dqf & DSF_DEFERRED_DELETE);

        if (ds->ds_is_direct_kevent) {
                dkq = DISPATCH_QUEUE_WAKEUP_TARGET;
        }

        if (!ds->ds_is_installed) {
                // The source needs to be installed on the kevent queue.
                tq = dkq;
        } else if (_dispatch_source_get_registration_handler(dr)) {
                // The registration handler needs to be delivered to the target queue.
                tq = DISPATCH_QUEUE_WAKEUP_TARGET;
        } else if (deferred_delete && ((dqf & DSF_DELETED) || !(dqf & DSF_ARMED))) {
                // Pending source kevent unregistration has been completed
                // or EV_ONESHOT event can be acknowledged
                tq = dkq;
        } else if (!(dqf & (DSF_CANCELED | DQF_RELEASED)) && ds->ds_pending_data) {
                // The source has pending data to deliver to the target queue.
                tq = DISPATCH_QUEUE_WAKEUP_TARGET;
        } else if ((dqf & (DSF_CANCELED | DQF_RELEASED)) && !deferred_delete) {
                // The source needs to be uninstalled from the kevent queue, or the
                // cancellation handler needs to be delivered to the target queue.
                // Note: cancellation assumes installation.
                if (!(dqf & DSF_DELETED)) {
                        tq = dkq;
                } else if (_dispatch_source_get_event_handler(dr) ||
                                _dispatch_source_get_cancel_handler(dr) ||
                                _dispatch_source_get_registration_handler(dr)) {
                        tq = DISPATCH_QUEUE_WAKEUP_TARGET;
                }
        } else if (ds->ds_needs_rearm && !(dqf & DSF_ARMED)) {
                // The source needs to be rearmed on the kevent queue.
                tq = dkq;
        }
        if (!tq && _dispatch_queue_class_probe(ds)) {
                tq = DISPATCH_QUEUE_WAKEUP_TARGET;
        }

        if (tq) {
                return _dispatch_queue_class_wakeup(ds->_as_dq, pp, flags, tq);
        } else if (pp) {
                return _dispatch_queue_class_override_drainer(ds->_as_dq, pp, flags);
        } else if (flags & DISPATCH_WAKEUP_CONSUME) {
                return _dispatch_release_tailcall(ds);
        }
}

void
dispatch_source_cancel(dispatch_source_t ds)
{
        _dispatch_object_debug(ds, "%s", __func__);
        // Right after we set the cancel flag, someone else
        // could potentially invoke the source, do the cancellation,
        // unregister the source, and deallocate it. We would
        // need to therefore retain/release before setting the bit
        _dispatch_retain(ds);

        dispatch_queue_t q = ds->_as_dq;
        if (_dispatch_queue_atomic_flags_set_orig(q, DSF_CANCELED) & DSF_CANCELED) {
                _dispatch_release_tailcall(ds);
        } else {
                dx_wakeup(ds, 0, DISPATCH_WAKEUP_FLUSH | DISPATCH_WAKEUP_CONSUME);
        }
}

void
dispatch_source_cancel_and_wait(dispatch_source_t ds)
{
        dispatch_queue_flags_t old_dqf, dqf, new_dqf;
        pthread_priority_t pp;

        if (unlikely(_dispatch_source_get_cancel_handler(ds->ds_refs))) {
                DISPATCH_CLIENT_CRASH(ds, "Source has a cancel handler");
        }

        _dispatch_object_debug(ds, "%s", __func__);
        os_atomic_rmw_loop2o(ds, dq_atomic_flags, old_dqf, new_dqf, relaxed, {
                new_dqf = old_dqf | DSF_CANCELED;
                if (old_dqf & DSF_CANCEL_WAITER) {
                        os_atomic_rmw_loop_give_up(break);
                }
                if ((old_dqf & DSF_STATE_MASK) == DSF_DELETED) {
                        // just add DSF_CANCELED
                } else if ((old_dqf & DSF_DEFERRED_DELETE) || !ds->ds_is_direct_kevent){
                        new_dqf |= DSF_CANCEL_WAITER;
                }
        });
        dqf = new_dqf;

        if (old_dqf & DQF_RELEASED) {
                DISPATCH_CLIENT_CRASH(ds, "Dispatch source used after last release");
        }
        if ((old_dqf & DSF_STATE_MASK) == DSF_DELETED) {
                return;
        }
        if (dqf & DSF_CANCEL_WAITER) {
                goto override;
        }

        // simplified version of _dispatch_queue_drain_try_lock
        // that also sets the DIRTY bit on failure to lock
        dispatch_lock_owner tid_self = _dispatch_tid_self();
        uint64_t xor_owner_and_set_full_width = tid_self |
                        DISPATCH_QUEUE_WIDTH_FULL_BIT | DISPATCH_QUEUE_IN_BARRIER;
        uint64_t old_state, new_state;

        os_atomic_rmw_loop2o(ds, dq_state, old_state, new_state, seq_cst, {
                new_state = old_state;
                if (likely(_dq_state_is_runnable(old_state) &&
                                !_dq_state_drain_locked(old_state))) {
                        new_state &= DISPATCH_QUEUE_DRAIN_PRESERVED_BITS_MASK;
                        new_state ^= xor_owner_and_set_full_width;
                } else if (old_dqf & DSF_CANCELED) {
                        os_atomic_rmw_loop_give_up(break);
                } else {
                        // this case needs a release barrier, hence the seq_cst above
                        new_state |= DISPATCH_QUEUE_DIRTY;
                }
        });

        if (unlikely(_dq_state_is_suspended(old_state))) {
                if (unlikely(_dq_state_suspend_cnt(old_state))) {
                        DISPATCH_CLIENT_CRASH(ds, "Source is suspended");
                }
                // inactive sources have never been registered and there is no need
                // to wait here because activation will notice and mark the source
                // as deleted without ever trying to use the fd or mach port.
                return dispatch_activate(ds);
        }

        if (likely(_dq_state_is_runnable(old_state) &&
                        !_dq_state_drain_locked(old_state))) {
                // same thing _dispatch_source_invoke2() does when handling cancellation
                dqf = _dispatch_queue_atomic_flags(ds->_as_dq);
                if (!(dqf & (DSF_DEFERRED_DELETE | DSF_DELETED))) {
                        _dispatch_source_kevent_unregister(ds);
                        dqf = _dispatch_queue_atomic_flags(ds->_as_dq);
                        if (likely((dqf & DSF_STATE_MASK) == DSF_DELETED)) {
                                _dispatch_source_cancel_callout(ds, NULL, DISPATCH_INVOKE_NONE);
                        }
                }
                _dispatch_try_lock_transfer_or_wakeup(ds->_as_dq);
        } else if (unlikely(_dq_state_drain_locked_by(old_state, tid_self))) {
                DISPATCH_CLIENT_CRASH(ds, "dispatch_source_cancel_and_wait "
                                "called from a source handler");
        } else {
override:
                pp = _dispatch_get_priority() & _PTHREAD_PRIORITY_QOS_CLASS_MASK;
                if (pp) dx_wakeup(ds, pp, DISPATCH_WAKEUP_OVERRIDING);
                dispatch_activate(ds);
        }

        dqf = _dispatch_queue_atomic_flags(ds->_as_dq);
        while (unlikely((dqf & DSF_STATE_MASK) != DSF_DELETED)) {
                if (unlikely(!(dqf & DSF_CANCEL_WAITER))) {
                        if (!os_atomic_cmpxchgvw2o(ds, dq_atomic_flags,
                                        dqf, dqf | DSF_CANCEL_WAITER, &dqf, relaxed)) {
                                continue;
                        }
                        dqf |= DSF_CANCEL_WAITER;
                }
                _dispatch_wait_on_address(&ds->dq_atomic_flags, dqf, DLOCK_LOCK_NONE);
                dqf = _dispatch_queue_atomic_flags(ds->_as_dq);
        }
}

static void
_dispatch_source_merge_kevent(dispatch_source_t ds,
                const _dispatch_kevent_qos_s *ke)
{
        _dispatch_object_debug(ds, "%s", __func__);
        dispatch_wakeup_flags_t flags = 0;
        dispatch_queue_flags_t dqf;
        pthread_priority_t pp = 0;

        if (ds->ds_needs_rearm || (ke->flags & (EV_DELETE | EV_ONESHOT))) {
                // once we modify the queue atomic flags below, it will allow concurrent
                // threads running _dispatch_source_invoke2 to dispose of the source,
                // so we can't safely borrow the reference we get from the knote udata
                // anymore, and need our own
                flags = DISPATCH_WAKEUP_CONSUME;
                _dispatch_retain(ds); // rdar://20382435
        }

        if ((ke->flags & EV_UDATA_SPECIFIC) && (ke->flags & EV_ONESHOT) &&
                        !(ke->flags & EV_DELETE)) {
                dqf = _dispatch_queue_atomic_flags_set_and_clear(ds->_as_dq,
                                DSF_DEFERRED_DELETE, DSF_ARMED);
                if (ke->flags & EV_VANISHED) {
                        _dispatch_bug_kevent_client("kevent", _evfiltstr(ke->filter),
                                        "monitored resource vanished before the source "
                                        "cancel handler was invoked", 0);
                }
                _dispatch_debug("kevent-source[%p]: %s kevent[%p]", ds,
                                (ke->flags & EV_VANISHED) ? "vanished" :
                                "deferred delete oneshot", (void*)ke->udata);
        } else if ((ke->flags & EV_DELETE) || (ke->flags & EV_ONESHOT)) {
                dqf = _dispatch_queue_atomic_flags_set_and_clear(ds->_as_dq,
                                DSF_DELETED, DSF_ARMED);
                _dispatch_debug("kevent-source[%p]: delete kevent[%p]",
                                ds, (void*)ke->udata);
                if (ke->flags & EV_DELETE) goto done;
        } else if (ds->ds_needs_rearm) {
                dqf = _dispatch_queue_atomic_flags_clear(ds->_as_dq, DSF_ARMED);
                _dispatch_debug("kevent-source[%p]: disarmed kevent[%p] ",
                                ds, (void*)ke->udata);
        } else {
                dqf = _dispatch_queue_atomic_flags(ds->_as_dq);
        }

        if (dqf & (DSF_CANCELED | DQF_RELEASED)) {
                goto done; // rdar://20204025
        }
#if HAVE_MACH
        if (ke->filter == EVFILT_MACHPORT &&
                        dx_type(ds) == DISPATCH_MACH_CHANNEL_TYPE) {
                DISPATCH_INTERNAL_CRASH(ke->flags,"Unexpected kevent for mach channel");
        }
#endif

        unsigned long data;
        if ((ke->flags & EV_UDATA_SPECIFIC) && (ke->flags & EV_ONESHOT) &&
                        (ke->flags & EV_VANISHED)) {
                // if the resource behind the ident vanished, the event handler can't
                // do anything useful anymore, so do not try to call it at all
                //
                // Note: if the kernel doesn't support EV_VANISHED we always get it
                // back unchanged from the flags passed at EV_ADD (registration) time
                // Since we never ask for both EV_ONESHOT and EV_VANISHED for sources,
                // if we get both bits it was a real EV_VANISHED delivery
                os_atomic_store2o(ds, ds_pending_data, 0, relaxed);
#if HAVE_MACH
        } else if (ke->filter == EVFILT_MACHPORT) {
                data = DISPATCH_MACH_RECV_MESSAGE;
                os_atomic_store2o(ds, ds_pending_data, data, relaxed);
#endif
        } else if (ds->ds_is_level) {
                // ke->data is signed and "negative available data" makes no sense
                // zero bytes happens when EV_EOF is set
                dispatch_assert(ke->data >= 0l);
                data = ~(unsigned long)ke->data;
                os_atomic_store2o(ds, ds_pending_data, data, relaxed);
        } else if (ds->ds_is_adder) {
                data = (unsigned long)ke->data;
                os_atomic_add2o(ds, ds_pending_data, data, relaxed);
        } else if (ke->fflags & ds->ds_pending_data_mask) {
                data = ke->fflags & ds->ds_pending_data_mask;
                os_atomic_or2o(ds, ds_pending_data, data, relaxed);
        }

done:
#if DISPATCH_USE_KEVENT_QOS
        pp = ((pthread_priority_t)ke->qos) & ~_PTHREAD_PRIORITY_FLAGS_MASK;
#endif
        dx_wakeup(ds, pp, flags | DISPATCH_WAKEUP_FLUSH);
}

#pragma mark -
#pragma mark dispatch_kevent_t

#define DSL_HASH(x) ((x) & (DSL_HASH_SIZE - 1))

DISPATCH_CACHELINE_ALIGN
static TAILQ_HEAD(, dispatch_kevent_s) _dispatch_sources[DSL_HASH_SIZE];

static void
_dispatch_kevent_init()
{
        unsigned int i;
        for (i = 0; i < DSL_HASH_SIZE; i++) {
                TAILQ_INIT(&_dispatch_sources[i]);
        }
}

static inline uintptr_t
_dispatch_kevent_hash(uint64_t ident, short filter)
{
        uint64_t value;
#if HAVE_MACH
        value = (filter == EVFILT_MACHPORT ||
                        filter == DISPATCH_EVFILT_MACH_NOTIFICATION ?
                        MACH_PORT_INDEX(ident) : ident);
#else
        value = ident;
        (void)filter;
#endif
        return DSL_HASH((uintptr_t)value);
}

static dispatch_kevent_t
_dispatch_kevent_find(uint64_t ident, short filter)
{
        uintptr_t hash = _dispatch_kevent_hash(ident, filter);
        dispatch_kevent_t dki;

        TAILQ_FOREACH(dki, &_dispatch_sources[hash], dk_list) {
                if (dki->dk_kevent.ident == ident && dki->dk_kevent.filter == filter) {
                        break;
                }
        }
        return dki;
}

static void
_dispatch_kevent_insert(dispatch_kevent_t dk)
{
        if (dk->dk_kevent.flags & EV_UDATA_SPECIFIC) return;
        uintptr_t hash = _dispatch_kevent_hash(dk->dk_kevent.ident,
                        dk->dk_kevent.filter);
        TAILQ_INSERT_TAIL(&_dispatch_sources[hash], dk, dk_list);
}

// Find existing kevents, and merge any new flags if necessary
static bool
_dispatch_kevent_register(dispatch_kevent_t *dkp, pthread_priority_t pp,
                uint32_t *flgp)
{
        dispatch_kevent_t dk = NULL, ds_dkev = *dkp;
        uint32_t new_flags;
        bool do_resume = false;

        if (!(ds_dkev->dk_kevent.flags & EV_UDATA_SPECIFIC)) {
                dk = _dispatch_kevent_find(ds_dkev->dk_kevent.ident,
                                ds_dkev->dk_kevent.filter);
        }
        if (dk) {
                // If an existing dispatch kevent is found, check to see if new flags
                // need to be added to the existing kevent
                new_flags = ~dk->dk_kevent.fflags & ds_dkev->dk_kevent.fflags;
                dk->dk_kevent.fflags |= ds_dkev->dk_kevent.fflags;
                free(ds_dkev);
                *dkp = dk;
                do_resume = new_flags;
        } else {
                dk = ds_dkev;
#if DISPATCH_USE_KEVENT_WORKQUEUE
                if (!_dispatch_kevent_workqueue_enabled) {
                        // do nothing
                } else if (!(dk->dk_kevent.flags & EV_UDATA_SPECIFIC)) {
                        dk->dk_kevent.qos = _PTHREAD_PRIORITY_EVENT_MANAGER_FLAG;
                } else {
                        pp &= (~_PTHREAD_PRIORITY_FLAGS_MASK |
                                        _PTHREAD_PRIORITY_OVERCOMMIT_FLAG);
                        if (!pp) pp = _PTHREAD_PRIORITY_EVENT_MANAGER_FLAG;
                        _dispatch_assert_is_valid_qos_class(pp);
                        dk->dk_kevent.qos = (_dispatch_kevent_priority_t)pp;
                }
#else
                (void)pp;
#endif
                _dispatch_kevent_insert(dk);
                new_flags = dk->dk_kevent.fflags;
                do_resume = true;
        }
        // Re-register the kevent with the kernel if new flags were added
        // by the dispatch kevent
        if (do_resume) {
                dk->dk_kevent.flags |= EV_ADD;
        }
        *flgp = new_flags;
        return do_resume;
}

static long
_dispatch_kevent_resume(dispatch_kevent_t dk, uint32_t new_flags,
                uint32_t del_flags)
{
        long r;
        bool oneshot;
        if (dk->dk_kevent.flags & EV_DELETE) {
                return 0;
        }
        switch (dk->dk_kevent.filter) {
        case DISPATCH_EVFILT_TIMER:
        case DISPATCH_EVFILT_CUSTOM_ADD:
        case DISPATCH_EVFILT_CUSTOM_OR:
                // these types not registered with kevent
                return 0;
#if HAVE_MACH
        case DISPATCH_EVFILT_MACH_NOTIFICATION:
                return _dispatch_kevent_mach_notify_resume(dk, new_flags, del_flags);
#if DISPATCH_EVFILT_MACHPORT_PORTSET_FALLBACK
        case EVFILT_MACHPORT:
                if (!(dk->dk_kevent.flags & EV_UDATA_SPECIFIC)) {
                        return _dispatch_kevent_machport_resume(dk, new_flags, del_flags);
                }
                // fall through
#endif
#endif // HAVE_MACH
        default:
                // oneshot dk may be freed by the time we return from
                // _dispatch_kq_immediate_update if the event was delivered (and then
                // unregistered) concurrently.
                oneshot = (dk->dk_kevent.flags & EV_ONESHOT);
                r = _dispatch_kq_immediate_update(&dk->dk_kevent);
                if (r && (dk->dk_kevent.flags & EV_ADD) &&
                                (dk->dk_kevent.flags & EV_UDATA_SPECIFIC)) {
                        dk->dk_kevent.flags |= EV_DELETE;
                        dk->dk_kevent.flags &= ~(EV_ADD|EV_ENABLE|EV_VANISHED);
                } else if (!oneshot && (dk->dk_kevent.flags & EV_DISPATCH)) {
                        // we can safely skip doing this for ONESHOT events because
                        // the next kq update we will do is _dispatch_kevent_dispose()
                        // which also clears EV_ADD.
                        dk->dk_kevent.flags &= ~(EV_ADD|EV_VANISHED);
                }
                return r;
        }
        (void)new_flags; (void)del_flags;
}

static long
_dispatch_kevent_dispose(dispatch_kevent_t dk, unsigned int options)
{
        long r = 0;
        switch (dk->dk_kevent.filter) {
        case DISPATCH_EVFILT_TIMER:
        case DISPATCH_EVFILT_CUSTOM_ADD:
        case DISPATCH_EVFILT_CUSTOM_OR:
                if (dk->dk_kevent.flags & EV_UDATA_SPECIFIC) {
                        free(dk);
                } else {
                        // these sources live on statically allocated lists
                }
                return r;
        }
        if (!(dk->dk_kevent.flags & EV_DELETE)) {
                dk->dk_kevent.flags |= EV_DELETE;
                dk->dk_kevent.flags &= ~(EV_ADD|EV_ENABLE|EV_VANISHED);
                if (options & DKEV_DISPOSE_IMMEDIATE_DELETE) {
                        dk->dk_kevent.flags |= EV_ENABLE;
                }
                switch (dk->dk_kevent.filter) {
#if HAVE_MACH
                case DISPATCH_EVFILT_MACH_NOTIFICATION:
                        r = _dispatch_kevent_mach_notify_resume(dk, 0,dk->dk_kevent.fflags);
                        break;
#if DISPATCH_EVFILT_MACHPORT_PORTSET_FALLBACK
                case EVFILT_MACHPORT:
                        if (!(dk->dk_kevent.flags & EV_UDATA_SPECIFIC)) {
                                r = _dispatch_kevent_machport_resume(dk,0,dk->dk_kevent.fflags);
                                break;
                        }
                        // fall through
#endif
#endif
                default:
                        if (options & DKEV_DISPOSE_IMMEDIATE_DELETE) {
                                _dispatch_kq_deferred_update(&dk->dk_kevent);
                        } else {
                                r = _dispatch_kq_immediate_update(&dk->dk_kevent);
                        }
                        break;
                }
                if (options & DKEV_DISPOSE_IMMEDIATE_DELETE) {
                        dk->dk_kevent.flags &= ~EV_ENABLE;
                }
        }
        if (dk->dk_kevent.flags & EV_UDATA_SPECIFIC) {
                bool deferred_delete = (r == EINPROGRESS);
#if DISPATCH_KEVENT_TREAT_ENOENT_AS_EINPROGRESS
                if (r == ENOENT) deferred_delete = true;
#endif
                if (deferred_delete) {
                        // deferred EV_DELETE or concurrent concurrent EV_DELETE delivery
                        dk->dk_kevent.flags &= ~EV_DELETE;
                        dk->dk_kevent.flags |= EV_ENABLE;
                        return r;
                }
        } else {
                uintptr_t hash = _dispatch_kevent_hash(dk->dk_kevent.ident,
                                dk->dk_kevent.filter);
                TAILQ_REMOVE(&_dispatch_sources[hash], dk, dk_list);
        }
        free(dk);
        return r;
}

static long
_dispatch_kevent_unregister(dispatch_kevent_t dk, uint32_t flg,
                unsigned int options)
{
        dispatch_source_refs_t dri;
        uint32_t del_flags, fflags = 0;
        long r = 0;

        if (TAILQ_EMPTY(&dk->dk_sources) ||
                        (dk->dk_kevent.flags & EV_UDATA_SPECIFIC)) {
                r = _dispatch_kevent_dispose(dk, options);
        } else {
                TAILQ_FOREACH(dri, &dk->dk_sources, dr_list) {
                        dispatch_source_t dsi = _dispatch_source_from_refs(dri);
                        uint32_t mask = (uint32_t)dsi->ds_pending_data_mask;
                        fflags |= mask;
                }
                del_flags = flg & ~fflags;
                if (del_flags) {
                        dk->dk_kevent.flags |= EV_ADD;
                        dk->dk_kevent.fflags &= ~del_flags;
                        r = _dispatch_kevent_resume(dk, 0, del_flags);
                }
        }
        return r;
}

DISPATCH_NOINLINE
static void
_dispatch_kevent_proc_exit(_dispatch_kevent_qos_s *ke)
{
        // EVFILT_PROC may fail with ESRCH when the process exists but is a zombie
        // <rdar://problem/5067725>. As a workaround, we simulate an exit event for
        // any EVFILT_PROC with an invalid pid <rdar://problem/6626350>.
        _dispatch_kevent_qos_s fake;
        fake = *ke;
        fake.flags &= ~EV_ERROR;
        fake.flags |= EV_ONESHOT;
        fake.fflags = NOTE_EXIT;
        fake.data = 0;
        _dispatch_kevent_debug("synthetic NOTE_EXIT", ke);
        _dispatch_kevent_merge(&fake);
}

DISPATCH_NOINLINE
static void
_dispatch_kevent_error(_dispatch_kevent_qos_s *ke)
{
        _dispatch_kevent_qos_s *kev = NULL;

        if (ke->flags & EV_DELETE) {
                if (ke->flags & EV_UDATA_SPECIFIC) {
                        if (ke->data == EINPROGRESS) {
                                // deferred EV_DELETE
                                return;
                        }
#if DISPATCH_KEVENT_TREAT_ENOENT_AS_EINPROGRESS
                        if (ke->data == ENOENT) {
                                // deferred EV_DELETE
                                return;
                        }
#endif
                }
                // for EV_DELETE if the update was deferred we may have reclaimed
                // our dispatch_kevent_t, and it is unsafe to dereference it now.
        } else if (ke->udata) {
                kev = &((dispatch_kevent_t)ke->udata)->dk_kevent;
                ke->flags |= kev->flags;
        }

#if HAVE_MACH
        if (ke->filter == EVFILT_MACHPORT && ke->data == ENOTSUP &&
                        (ke->flags & EV_ADD) && _dispatch_evfilt_machport_direct_enabled &&
                        kev && (kev->fflags & MACH_RCV_MSG)) {
                DISPATCH_INTERNAL_CRASH(ke->ident,
                                "Missing EVFILT_MACHPORT support for ports");
        }
#endif

        if (ke->data) {
                // log the unexpected error
                _dispatch_bug_kevent_client("kevent", _evfiltstr(ke->filter),
                                !ke->udata ? NULL :
                                ke->flags & EV_DELETE ? "delete" :
                                ke->flags & EV_ADD ? "add" :
                                ke->flags & EV_ENABLE ? "enable" : "monitor",
                                (int)ke->data);
        }
}

static void
_dispatch_kevent_drain(_dispatch_kevent_qos_s *ke)
{
        if (ke->filter == EVFILT_USER) {
                _dispatch_kevent_mgr_debug(ke);
                return;
        }
        if (slowpath(ke->flags & EV_ERROR)) {
                if (ke->filter == EVFILT_PROC && ke->data == ESRCH) {
                        _dispatch_debug("kevent[0x%llx]: ESRCH from EVFILT_PROC: "
                                        "generating fake NOTE_EXIT", (unsigned long long)ke->udata);
                        return _dispatch_kevent_proc_exit(ke);
                }
                _dispatch_debug("kevent[0x%llx]: handling error",
                                (unsigned long long)ke->udata);
                return _dispatch_kevent_error(ke);
        }
        if (ke->filter == EVFILT_TIMER) {
                _dispatch_debug("kevent[0x%llx]: handling timer",
                                (unsigned long long)ke->udata);
                return _dispatch_timers_kevent(ke);
        }
#if HAVE_MACH
        if (ke->filter == EVFILT_MACHPORT) {
                _dispatch_debug("kevent[0x%llx]: handling mach port",
                                (unsigned long long)ke->udata);
                return _dispatch_mach_kevent_merge(ke);
        }
#endif
        return _dispatch_kevent_merge(ke);
}

DISPATCH_NOINLINE
static void
_dispatch_kevent_merge(_dispatch_kevent_qos_s *ke)
{
        dispatch_kevent_t dk = (void*)ke->udata;
        dispatch_source_refs_t dri, dr_next;

        TAILQ_FOREACH_SAFE(dri, &dk->dk_sources, dr_list, dr_next) {
                _dispatch_source_merge_kevent(_dispatch_source_from_refs(dri), ke);
        }
}

#pragma mark -
#pragma mark dispatch_source_timer

#if DISPATCH_USE_DTRACE
static dispatch_source_refs_t
                _dispatch_trace_next_timer[DISPATCH_TIMER_QOS_COUNT];
#define _dispatch_trace_next_timer_set(x, q) \
                _dispatch_trace_next_timer[(q)] = (x)
#define _dispatch_trace_next_timer_program(d, q) \
                _dispatch_trace_timer_program(_dispatch_trace_next_timer[(q)], (d))
#define _dispatch_trace_next_timer_wake(q) \
                _dispatch_trace_timer_wake(_dispatch_trace_next_timer[(q)])
#else
#define _dispatch_trace_next_timer_set(x, q)
#define _dispatch_trace_next_timer_program(d, q)
#define _dispatch_trace_next_timer_wake(q)
#endif

#define _dispatch_source_timer_telemetry_enabled() false

DISPATCH_NOINLINE
static void
_dispatch_source_timer_telemetry_slow(dispatch_source_t ds,
                dispatch_clock_t clock, struct dispatch_timer_source_s *values)
{
        if (_dispatch_trace_timer_configure_enabled()) {
                _dispatch_trace_timer_configure(ds, clock, values);
        }
}

DISPATCH_ALWAYS_INLINE
static inline void
_dispatch_source_timer_telemetry(dispatch_source_t ds, dispatch_clock_t clock,
                struct dispatch_timer_source_s *values)
{
        if (_dispatch_trace_timer_configure_enabled() ||
                        _dispatch_source_timer_telemetry_enabled()) {
                _dispatch_source_timer_telemetry_slow(ds, clock, values);
                asm(""); // prevent tailcall
        }
}

static inline unsigned long
_dispatch_source_timer_data(dispatch_source_refs_t dr, unsigned long prev)
{
        // calculate the number of intervals since last fire
        unsigned long data, missed;
        uint64_t now;
        now = _dispatch_time_now(DISPATCH_TIMER_CLOCK(_dispatch_source_timer_idx(dr)));
        missed = (unsigned long)((now - ds_timer(dr).last_fire) /
                        ds_timer(dr).interval);
        // correct for missed intervals already delivered last time
        data = prev - ds_timer(dr).missed + missed;
        ds_timer(dr).missed = missed;
        return data;
}

struct dispatch_set_timer_params {
        dispatch_source_t ds;
        struct dispatch_timer_source_s values;
        dispatch_clock_t clock;
};

static void
_dispatch_source_set_timer3(void *context)
{
        // Called on the _dispatch_mgr_q
        struct dispatch_set_timer_params *params = context;
        dispatch_source_t ds = params->ds;
        dispatch_timer_source_refs_t dt = (dispatch_timer_source_refs_t)ds->ds_refs;

        params->values.flags = ds_timer(dt).flags;
        if (params->clock == DISPATCH_CLOCK_WALL) {
                params->values.flags |= DISPATCH_TIMER_WALL_CLOCK;
#if HAVE_MACH
                _dispatch_mach_host_calendar_change_register();
#endif
        } else {
                params->values.flags &= ~(unsigned long)DISPATCH_TIMER_WALL_CLOCK;
        }
        ds_timer(dt) = params->values;
        ds->ds_ident_hack = _dispatch_source_timer_idx(ds->ds_refs);
        // Clear any pending data that might have accumulated on
        // older timer params <rdar://problem/8574886>
        ds->ds_pending_data = 0;

        dispatch_resume(ds);
        if (_dispatch_source_tryarm(ds)) {
                // Re-arm in case we got disarmed because of pending set_timer suspension
                _dispatch_debug("kevent-source[%p]: rearmed kevent[%p]", ds, dt);
                // Must happen after resume to avoid getting disarmed due to suspension
                _dispatch_timers_update(ds);
        }
        dispatch_release(ds);
        free(params);
}

static void
_dispatch_source_set_timer2(void *context)
{
        // Called on the source queue
        struct dispatch_set_timer_params *params = context;
        dispatch_suspend(params->ds);
        _dispatch_barrier_async_detached_f(&_dispatch_mgr_q, params,
                        _dispatch_source_set_timer3);
}

DISPATCH_NOINLINE
static struct dispatch_set_timer_params *
_dispatch_source_timer_params(dispatch_source_t ds, dispatch_time_t start,
                uint64_t interval, uint64_t leeway)
{
        struct dispatch_set_timer_params *params;
        params = _dispatch_calloc(1ul, sizeof(struct dispatch_set_timer_params));
        params->ds = ds;

        if (interval == 0) {
                // we use zero internally to mean disabled
                interval = 1;
        } else if ((int64_t)interval < 0) {
                // 6866347 - make sure nanoseconds won't overflow
                interval = INT64_MAX;
        }
        if ((int64_t)leeway < 0) {
                leeway = INT64_MAX;
        }
        if (start == DISPATCH_TIME_NOW) {
                start = _dispatch_absolute_time();
        } else if (start == DISPATCH_TIME_FOREVER) {
                start = INT64_MAX;
        }

        if ((int64_t)start < 0) {
                // wall clock
                start = (dispatch_time_t)-((int64_t)start);
                params->clock = DISPATCH_CLOCK_WALL;
        } else {
                // absolute clock
                interval = _dispatch_time_nano2mach(interval);
                if (interval < 1) {
                        // rdar://problem/7287561 interval must be at least one in
                        // in order to avoid later division by zero when calculating
                        // the missed interval count. (NOTE: the wall clock's
                        // interval is already "fixed" to be 1 or more)
                        interval = 1;
                }
                leeway = _dispatch_time_nano2mach(leeway);
                params->clock = DISPATCH_CLOCK_MACH;
        }
        params->values.target = start;
        params->values.deadline = (start < UINT64_MAX - leeway) ?
                        start + leeway : UINT64_MAX;
        params->values.interval = interval;
        params->values.leeway = (interval == INT64_MAX || leeway < interval / 2) ?
                        leeway : interval / 2;
        return params;
}

DISPATCH_ALWAYS_INLINE
static inline void
_dispatch_source_set_timer(dispatch_source_t ds, dispatch_time_t start,
                uint64_t interval, uint64_t leeway, bool source_sync)
{
        if (slowpath(!ds->ds_is_timer) ||
                        slowpath(ds_timer(ds->ds_refs).flags & DISPATCH_TIMER_INTERVAL)) {
                DISPATCH_CLIENT_CRASH(ds, "Attempt to set timer on a non-timer source");
        }

        struct dispatch_set_timer_params *params;
        params = _dispatch_source_timer_params(ds, start, interval, leeway);

        _dispatch_source_timer_telemetry(ds, params->clock, &params->values);
        // Suspend the source so that it doesn't fire with pending changes
        // The use of suspend/resume requires the external retain/release
        dispatch_retain(ds);
        if (source_sync) {
                return _dispatch_barrier_trysync_or_async_f(ds->_as_dq, params,
                                _dispatch_source_set_timer2);
        } else {
                return _dispatch_source_set_timer2(params);
        }
}

void
dispatch_source_set_timer(dispatch_source_t ds, dispatch_time_t start,
                uint64_t interval, uint64_t leeway)
{
        _dispatch_source_set_timer(ds, start, interval, leeway, true);
}

void
_dispatch_source_set_runloop_timer_4CF(dispatch_source_t ds,
                dispatch_time_t start, uint64_t interval, uint64_t leeway)
{
        // Don't serialize through the source queue for CF timers <rdar://13833190>
        _dispatch_source_set_timer(ds, start, interval, leeway, false);
}

void
_dispatch_source_set_interval(dispatch_source_t ds, uint64_t interval)
{
#define NSEC_PER_FRAME (NSEC_PER_SEC/60)
// approx 1 year (60s * 60m * 24h * 365d)
#define FOREVER_NSEC 31536000000000000ull

        dispatch_source_refs_t dr = ds->ds_refs;
        const bool animation = ds_timer(dr).flags & DISPATCH_INTERVAL_UI_ANIMATION;
        if (fastpath(interval <= (animation ? FOREVER_NSEC/NSEC_PER_FRAME :
                        FOREVER_NSEC/NSEC_PER_MSEC))) {
                interval *= animation ? NSEC_PER_FRAME : NSEC_PER_MSEC;
        } else {
                interval = FOREVER_NSEC;
        }
        interval = _dispatch_time_nano2mach(interval);
        uint64_t target = _dispatch_absolute_time() + interval;
        target = (target / interval) * interval;
        const uint64_t leeway = animation ?
                        _dispatch_time_nano2mach(NSEC_PER_FRAME) : interval / 2;
        ds_timer(dr).target = target;
        ds_timer(dr).deadline = target + leeway;
        ds_timer(dr).interval = interval;
        ds_timer(dr).leeway = leeway;
        dispatch_clock_t clock = DISPATCH_TIMER_CLOCK(ds->ds_ident_hack);
        _dispatch_source_timer_telemetry(ds, clock, &ds_timer(dr));
}

#pragma mark -
#pragma mark dispatch_timers

#define DISPATCH_TIMER_STRUCT(refs) \
        uint64_t target, deadline; \
        TAILQ_HEAD(, refs) dt_sources

typedef struct dispatch_timer_s {
        DISPATCH_TIMER_STRUCT(dispatch_timer_source_refs_s);
} *dispatch_timer_t;

#define DISPATCH_TIMER_INITIALIZER(tidx) \
        [tidx] = { \
                .target = UINT64_MAX, \
                .deadline = UINT64_MAX, \
                .dt_sources = TAILQ_HEAD_INITIALIZER( \
                                _dispatch_timer[tidx].dt_sources), \
        }
#define DISPATCH_TIMER_INIT(kind, qos) \
                DISPATCH_TIMER_INITIALIZER(DISPATCH_TIMER_INDEX( \
                DISPATCH_CLOCK_##kind, DISPATCH_TIMER_QOS_##qos))

struct dispatch_timer_s _dispatch_timer[] =  {
        DISPATCH_TIMER_INIT(WALL, NORMAL),
        DISPATCH_TIMER_INIT(WALL, CRITICAL),
        DISPATCH_TIMER_INIT(WALL, BACKGROUND),
        DISPATCH_TIMER_INIT(MACH, NORMAL),
        DISPATCH_TIMER_INIT(MACH, CRITICAL),
        DISPATCH_TIMER_INIT(MACH, BACKGROUND),
};
#define DISPATCH_TIMER_COUNT \
                ((sizeof(_dispatch_timer) / sizeof(_dispatch_timer[0])))

#if __linux__
#define DISPATCH_KEVENT_TIMER_UDATA(tidx) \
                (void*)&_dispatch_kevent_timer[tidx]
#else
#define DISPATCH_KEVENT_TIMER_UDATA(tidx) \
                (uintptr_t)&_dispatch_kevent_timer[tidx]
#endif
#ifdef __LP64__
#define DISPATCH_KEVENT_TIMER_UDATA_INITIALIZER(tidx) \
                .udata = DISPATCH_KEVENT_TIMER_UDATA(tidx)
#else // __LP64__
// dynamic initialization in _dispatch_timers_init()
#define DISPATCH_KEVENT_TIMER_UDATA_INITIALIZER(tidx) \
                .udata = 0
#endif // __LP64__
#define DISPATCH_KEVENT_TIMER_INITIALIZER(tidx) \
        [tidx] = { \
                .dk_kevent = { \
                        .ident = tidx, \
                        .filter = DISPATCH_EVFILT_TIMER, \
                        DISPATCH_KEVENT_TIMER_UDATA_INITIALIZER(tidx), \
                }, \
                .dk_sources = TAILQ_HEAD_INITIALIZER( \
                                _dispatch_kevent_timer[tidx].dk_sources), \
        }
#define DISPATCH_KEVENT_TIMER_INIT(kind, qos) \
                DISPATCH_KEVENT_TIMER_INITIALIZER(DISPATCH_TIMER_INDEX( \
                DISPATCH_CLOCK_##kind, DISPATCH_TIMER_QOS_##qos))

struct dispatch_kevent_s _dispatch_kevent_timer[] = {
        DISPATCH_KEVENT_TIMER_INIT(WALL, NORMAL),
        DISPATCH_KEVENT_TIMER_INIT(WALL, CRITICAL),
        DISPATCH_KEVENT_TIMER_INIT(WALL, BACKGROUND),
        DISPATCH_KEVENT_TIMER_INIT(MACH, NORMAL),
        DISPATCH_KEVENT_TIMER_INIT(MACH, CRITICAL),
        DISPATCH_KEVENT_TIMER_INIT(MACH, BACKGROUND),
        DISPATCH_KEVENT_TIMER_INITIALIZER(DISPATCH_TIMER_INDEX_DISARM),
};
#define DISPATCH_KEVENT_TIMER_COUNT \
                ((sizeof(_dispatch_kevent_timer) / sizeof(_dispatch_kevent_timer[0])))

#define DISPATCH_KEVENT_TIMEOUT_IDENT_MASK (~0ull << 8)
#define DISPATCH_KEVENT_TIMEOUT_INITIALIZER(tidx, note) \
        [tidx] = { \
                .ident = DISPATCH_KEVENT_TIMEOUT_IDENT_MASK|(tidx), \
                .filter = EVFILT_TIMER, \
                .flags = EV_ONESHOT, \
                .fflags = NOTE_ABSOLUTE|NOTE_NSECONDS|NOTE_LEEWAY|(note), \
        }
#define DISPATCH_KEVENT_TIMEOUT_INIT(kind, qos, note) \
                DISPATCH_KEVENT_TIMEOUT_INITIALIZER(DISPATCH_TIMER_INDEX( \
                DISPATCH_CLOCK_##kind, DISPATCH_TIMER_QOS_##qos), note)

_dispatch_kevent_qos_s _dispatch_kevent_timeout[] = {
        DISPATCH_KEVENT_TIMEOUT_INIT(WALL, NORMAL, NOTE_MACH_CONTINUOUS_TIME),
        DISPATCH_KEVENT_TIMEOUT_INIT(WALL, CRITICAL, NOTE_MACH_CONTINUOUS_TIME | NOTE_CRITICAL),
        DISPATCH_KEVENT_TIMEOUT_INIT(WALL, BACKGROUND, NOTE_MACH_CONTINUOUS_TIME | NOTE_BACKGROUND),
        DISPATCH_KEVENT_TIMEOUT_INIT(MACH, NORMAL, 0),
        DISPATCH_KEVENT_TIMEOUT_INIT(MACH, CRITICAL, NOTE_CRITICAL),
        DISPATCH_KEVENT_TIMEOUT_INIT(MACH, BACKGROUND, NOTE_BACKGROUND),
};
#define DISPATCH_KEVENT_TIMEOUT_COUNT \
                ((sizeof(_dispatch_kevent_timeout) / sizeof(_dispatch_kevent_timeout[0])))
static_assert(DISPATCH_KEVENT_TIMEOUT_COUNT == DISPATCH_TIMER_INDEX_COUNT - 1,
                "should have a kevent for everything but disarm (ddt assumes this)");

#define DISPATCH_KEVENT_COALESCING_WINDOW_INIT(qos, ms) \
                [DISPATCH_TIMER_QOS_##qos] = 2ull * (ms) * NSEC_PER_MSEC

static const uint64_t _dispatch_kevent_coalescing_window[] = {
        DISPATCH_KEVENT_COALESCING_WINDOW_INIT(NORMAL, 75),
        DISPATCH_KEVENT_COALESCING_WINDOW_INIT(CRITICAL, 1),
        DISPATCH_KEVENT_COALESCING_WINDOW_INIT(BACKGROUND, 100),
};

#define _dispatch_timers_insert(tidx, dra, dr, dr_list, dta, dt, dt_list) ({ \
        typeof(dr) dri = NULL; typeof(dt) dti; \
        if (tidx != DISPATCH_TIMER_INDEX_DISARM) { \
                TAILQ_FOREACH(dri, &dra[tidx].dk_sources, dr_list) { \
                        if (ds_timer(dr).target < ds_timer(dri).target) { \
                                break; \
                        } \
                } \
                TAILQ_FOREACH(dti, &dta[tidx].dt_sources, dt_list) { \
                        if (ds_timer(dt).deadline < ds_timer(dti).deadline) { \
                                break; \
                        } \
                } \
                if (dti) { \
                        TAILQ_INSERT_BEFORE(dti, dt, dt_list); \
                } else { \
                        TAILQ_INSERT_TAIL(&dta[tidx].dt_sources, dt, dt_list); \
                } \
        } \
        if (dri) { \
                TAILQ_INSERT_BEFORE(dri, dr, dr_list); \
        } else { \
                TAILQ_INSERT_TAIL(&dra[tidx].dk_sources, dr, dr_list); \
        } \
        })

#define _dispatch_timers_remove(tidx, dk, dra, dr, dr_list, dta, dt, dt_list) \
        ({ \
        if (tidx != DISPATCH_TIMER_INDEX_DISARM) { \
                TAILQ_REMOVE(&dta[tidx].dt_sources, dt, dt_list); \
        } \
        TAILQ_REMOVE(dk ? &(*(dk)).dk_sources : &dra[tidx].dk_sources, dr, \
                        dr_list); })

#define _dispatch_timers_check(dra, dta) ({ \
        unsigned int timerm = _dispatch_timers_mask; \
        bool update = false; \
        unsigned int tidx; \
        for (tidx = 0; tidx < DISPATCH_TIMER_COUNT; tidx++) { \
                if (!(timerm & (1 << tidx))){ \
                        continue; \
                } \
                dispatch_timer_source_refs_t dr = (dispatch_timer_source_refs_t) \
                                TAILQ_FIRST(&dra[tidx].dk_sources); \
                dispatch_timer_source_refs_t dt = (dispatch_timer_source_refs_t) \
                                TAILQ_FIRST(&dta[tidx].dt_sources); \
                uint64_t target = dr ? ds_timer(dr).target : UINT64_MAX; \
                uint64_t deadline = dr ? ds_timer(dt).deadline : UINT64_MAX; \
                if (target != dta[tidx].target) { \
                        dta[tidx].target = target; \
                        update = true; \
                } \
                if (deadline != dta[tidx].deadline) { \
                        dta[tidx].deadline = deadline; \
                        update = true; \
                } \
        } \
        update; })

static bool _dispatch_timers_reconfigure, _dispatch_timer_expired;
static unsigned int _dispatch_timers_mask;
static bool _dispatch_timers_force_max_leeway;

static void
_dispatch_timers_init(void)
{
#ifndef __LP64__
        unsigned int tidx;
        for (tidx = 0; tidx < DISPATCH_TIMER_COUNT; tidx++) {
                _dispatch_kevent_timer[tidx].dk_kevent.udata =
                                DISPATCH_KEVENT_TIMER_UDATA(tidx);
        }
#endif // __LP64__
        if (slowpath(getenv("LIBDISPATCH_TIMERS_FORCE_MAX_LEEWAY"))) {
                _dispatch_timers_force_max_leeway = true;
        }
}

static inline void
_dispatch_timers_unregister(dispatch_source_t ds, dispatch_kevent_t dk)
{
        dispatch_source_refs_t dr = ds->ds_refs;
        unsigned int tidx = (unsigned int)dk->dk_kevent.ident;

        if (slowpath(ds_timer_aggregate(ds))) {
                _dispatch_timer_aggregates_unregister(ds, tidx);
        }
        _dispatch_timers_remove(tidx, dk, _dispatch_kevent_timer, dr, dr_list,
                        _dispatch_timer, (dispatch_timer_source_refs_t)dr, dt_list);
        if (tidx != DISPATCH_TIMER_INDEX_DISARM) {
                _dispatch_timers_reconfigure = true;
                _dispatch_timers_mask |= 1 << tidx;
        }
}

// Updates the ordered list of timers based on next fire date for changes to ds.
// Should only be called from the context of _dispatch_mgr_q.
static void
_dispatch_timers_update(dispatch_source_t ds)
{
        dispatch_kevent_t dk = ds->ds_dkev;
        dispatch_source_refs_t dr = ds->ds_refs;
        unsigned int tidx;

        DISPATCH_ASSERT_ON_MANAGER_QUEUE();

        // Do not reschedule timers unregistered with _dispatch_kevent_unregister()
        if (slowpath(!dk)) {
                return;
        }
        // Move timers that are disabled, suspended or have missed intervals to the
        // disarmed list, rearm after resume resp. source invoke will reenable them
        if (!ds_timer(dr).target || DISPATCH_QUEUE_IS_SUSPENDED(ds) ||
                        ds->ds_pending_data) {
                tidx = DISPATCH_TIMER_INDEX_DISARM;
                _dispatch_queue_atomic_flags_clear(ds->_as_dq, DSF_ARMED);
                _dispatch_debug("kevent-source[%p]: disarmed kevent[%p]", ds,
                                ds->ds_dkev);
        } else {
                tidx = _dispatch_source_timer_idx(dr);
        }
        if (slowpath(ds_timer_aggregate(ds))) {
                _dispatch_timer_aggregates_register(ds);
        }
        if (slowpath(!ds->ds_is_installed)) {
                ds->ds_is_installed = true;
                if (tidx != DISPATCH_TIMER_INDEX_DISARM) {
                        _dispatch_queue_atomic_flags_set(ds->_as_dq, DSF_ARMED);
                        _dispatch_debug("kevent-source[%p]: rearmed kevent[%p]", ds,
                                        ds->ds_dkev);
                }
                _dispatch_object_debug(ds, "%s", __func__);
                ds->ds_dkev = NULL;
                free(dk);
        } else {
                _dispatch_timers_unregister(ds, dk);
        }
        if (tidx != DISPATCH_TIMER_INDEX_DISARM) {
                _dispatch_timers_reconfigure = true;
                _dispatch_timers_mask |= 1 << tidx;
        }
        if (dk != &_dispatch_kevent_timer[tidx]){
                ds->ds_dkev = &_dispatch_kevent_timer[tidx];
        }
        _dispatch_timers_insert(tidx, _dispatch_kevent_timer, dr, dr_list,
                        _dispatch_timer, (dispatch_timer_source_refs_t)dr, dt_list);
        if (slowpath(ds_timer_aggregate(ds))) {
                _dispatch_timer_aggregates_update(ds, tidx);
        }
}

static inline void
_dispatch_timers_run2(dispatch_clock_now_cache_t nows, unsigned int tidx)
{
        dispatch_source_refs_t dr;
        dispatch_source_t ds;
        uint64_t now, missed;

        now = _dispatch_time_now_cached(DISPATCH_TIMER_CLOCK(tidx), nows);
        while ((dr = TAILQ_FIRST(&_dispatch_kevent_timer[tidx].dk_sources))) {
                ds = _dispatch_source_from_refs(dr);
                // We may find timers on the wrong list due to a pending update from
                // dispatch_source_set_timer. Force an update of the list in that case.
                if (tidx != ds->ds_ident_hack) {
                        _dispatch_timers_update(ds);
                        continue;
                }
                if (!ds_timer(dr).target) {
                        // No configured timers on the list
                        break;
                }
                if (ds_timer(dr).target > now) {
                        // Done running timers for now.
                        break;
                }
                // Remove timers that are suspended or have missed intervals from the
                // list, rearm after resume resp. source invoke will reenable them
                if (DISPATCH_QUEUE_IS_SUSPENDED(ds) || ds->ds_pending_data) {
                        _dispatch_timers_update(ds);
                        continue;
                }
                // Calculate number of missed intervals.
                missed = (now - ds_timer(dr).target) / ds_timer(dr).interval;
                if (++missed > INT_MAX) {
                        missed = INT_MAX;
                }
                if (ds_timer(dr).interval < INT64_MAX) {
                        ds_timer(dr).target += missed * ds_timer(dr).interval;
                        ds_timer(dr).deadline = ds_timer(dr).target + ds_timer(dr).leeway;
                } else {
                        ds_timer(dr).target = UINT64_MAX;
                        ds_timer(dr).deadline = UINT64_MAX;
                }
                _dispatch_timers_update(ds);
                ds_timer(dr).last_fire = now;

                unsigned long data;
                data = os_atomic_add2o(ds, ds_pending_data,
                                (unsigned long)missed, relaxed);
                _dispatch_trace_timer_fire(dr, data, (unsigned long)missed);
                dx_wakeup(ds, 0, DISPATCH_WAKEUP_FLUSH);
                if (ds_timer(dr).flags & DISPATCH_TIMER_AFTER) {
                        _dispatch_source_kevent_unregister(ds);
                }
        }
}

DISPATCH_NOINLINE
static void
_dispatch_timers_run(dispatch_clock_now_cache_t nows)
{
        unsigned int tidx;
        for (tidx = 0; tidx < DISPATCH_TIMER_COUNT; tidx++) {
                if (!TAILQ_EMPTY(&_dispatch_kevent_timer[tidx].dk_sources)) {
                        _dispatch_timers_run2(nows, tidx);
                }
        }
}

#define DISPATCH_TIMERS_GET_DELAY_ALL (~0u)

static inline unsigned int
_dispatch_timers_get_delay(dispatch_clock_now_cache_t nows,
                struct dispatch_timer_s timer[],
                uint64_t *delay, uint64_t *leeway, unsigned int query)
{
        unsigned int tidx, ridx = DISPATCH_TIMER_COUNT, minidx, maxidx;
        uint64_t tmp, delta = INT64_MAX, dldelta = INT64_MAX;

        if (query == DISPATCH_TIMERS_GET_DELAY_ALL) {
                minidx = 0;
                maxidx = DISPATCH_TIMER_COUNT - 1;
        } else {
                minidx = maxidx = query;
        }

        for (tidx = minidx; tidx <= maxidx; tidx++) {
                dispatch_clock_t clock = DISPATCH_TIMER_CLOCK(tidx);
                uint64_t target = timer[tidx].target;
                if (target >= INT64_MAX) {
                        continue;
                }
                uint64_t deadline = timer[tidx].deadline;
                if (query != DISPATCH_TIMERS_GET_DELAY_ALL) {
                        // Timer pre-coalescing <rdar://problem/13222034>
                        unsigned int qos = DISPATCH_TIMER_QOS(tidx);
                        uint64_t window = _dispatch_kevent_coalescing_window[qos];
                        uint64_t latest = deadline > window ? deadline - window : 0;
                        dispatch_source_refs_t dri;
                        TAILQ_FOREACH(dri, &_dispatch_kevent_timer[tidx].dk_sources,
                                        dr_list) {
                                tmp = ds_timer(dri).target;
                                if (tmp > latest) break;
                                target = tmp;
                        }
                }
                uint64_t now = _dispatch_time_now_cached(clock, nows);
                if (target <= now) {
                        delta = 0;
                        break;
                }
                tmp = target - now;
                if (clock != DISPATCH_CLOCK_WALL) {
                        tmp = _dispatch_time_mach2nano(tmp);
                }
                if (tmp < INT64_MAX && tmp < delta) {
                        ridx = tidx;
                        delta = tmp;
                }
                dispatch_assert(target <= deadline);
                tmp = deadline - now;
                if (clock != DISPATCH_CLOCK_WALL) {
                        tmp = _dispatch_time_mach2nano(tmp);
                }
                if (tmp < INT64_MAX && tmp < dldelta) {
                        dldelta = tmp;
                }
        }
        *delay = delta;
        *leeway = delta && delta < INT64_MAX ? dldelta - delta : INT64_MAX;
        return ridx;
}


#ifdef __linux__
// in linux we map the _dispatch_kevent_qos_s  to struct kevent instead
// of struct kevent64. We loose the kevent.ext[] members and the time
// out is based on relavite msec based time vs. absolute nsec based time.
// For now we make the adjustments right here until the solution
// to either extend libkqueue with a proper kevent64 API or removing kevent
// all together and move to a lower API (e.g. epoll or kernel_module.
// Also leeway is ignored.

static void
_dispatch_kevent_timer_set_delay(_dispatch_kevent_qos_s *ke, uint64_t delay,
                uint64_t leeway, dispatch_clock_now_cache_t nows)
{
        // call to update nows[]
        _dispatch_time_now_cached(DISPATCH_CLOCK_WALL, nows);
#ifdef KEVENT_NSEC_NOT_SUPPORTED
        // adjust nsec based delay to msec based and ignore leeway
        delay /= 1000000L;
        if ((int64_t)(delay) <= 0) {
                delay = 1; // if value <= 0 the dispatch will stop
        }
#else
        ke->fflags |= NOTE_NSECONDS;
#endif
        ke->data = (int64_t)delay;
}

#else
static void
_dispatch_kevent_timer_set_delay(_dispatch_kevent_qos_s *ke, uint64_t delay,
                uint64_t leeway, dispatch_clock_now_cache_t nows)
{
        delay += _dispatch_time_now_cached(DISPATCH_CLOCK_WALL, nows);
        if (slowpath(_dispatch_timers_force_max_leeway)) {
                ke->data = (int64_t)(delay + leeway);
                ke->ext[1] = 0;
        } else {
                ke->data = (int64_t)delay;
                ke->ext[1] = leeway;
        }
}
#endif // __linux__

static bool
_dispatch_timers_program2(dispatch_clock_now_cache_t nows,
                _dispatch_kevent_qos_s *ke, unsigned int tidx)
{
        bool poll;
        uint64_t delay, leeway;

        _dispatch_timers_get_delay(nows, _dispatch_timer, &delay, &leeway, tidx);
        poll = (delay == 0);
        if (poll || delay == UINT64_MAX) {
                _dispatch_trace_next_timer_set(NULL, DISPATCH_TIMER_QOS(tidx));
                if (!ke->data) {
                        return poll;
                }
                ke->data = 0;
                ke->flags |= EV_DELETE;
                ke->flags &= ~(EV_ADD|EV_ENABLE);
        } else {
                _dispatch_trace_next_timer_set(
                                TAILQ_FIRST(&_dispatch_kevent_timer[tidx].dk_sources), DISPATCH_TIMER_QOS(tidx));
                _dispatch_trace_next_timer_program(delay, DISPATCH_TIMER_QOS(tidx));
                _dispatch_kevent_timer_set_delay(ke, delay, leeway, nows);
                ke->flags |= EV_ADD|EV_ENABLE;
                ke->flags &= ~EV_DELETE;
#if DISPATCH_USE_KEVENT_WORKQUEUE
                if (_dispatch_kevent_workqueue_enabled) {
                        ke->qos = _PTHREAD_PRIORITY_EVENT_MANAGER_FLAG;
                }
#endif
        }
        _dispatch_kq_deferred_update(ke);
        return poll;
}

DISPATCH_NOINLINE
static bool
_dispatch_timers_program(dispatch_clock_now_cache_t nows)
{
        bool poll = false;
        unsigned int tidx, timerm = _dispatch_timers_mask;
        for (tidx = 0; tidx < DISPATCH_KEVENT_TIMEOUT_COUNT; tidx++) {
                if (!(timerm & 1 << tidx)){
                        continue;
                }
                poll |= _dispatch_timers_program2(nows, &_dispatch_kevent_timeout[tidx],
                                tidx);
        }
        return poll;
}

DISPATCH_NOINLINE
static bool
_dispatch_timers_configure(void)
{
        _dispatch_timer_aggregates_check();
        // Find out if there is a new target/deadline on the timer lists
        return _dispatch_timers_check(_dispatch_kevent_timer, _dispatch_timer);
}

#if HAVE_MACH
static void
_dispatch_timers_calendar_change(void)
{
        unsigned int qos;

        // calendar change may have gone past the wallclock deadline
        _dispatch_timer_expired = true;
        for (qos = 0; qos < DISPATCH_TIMER_QOS_COUNT; qos++) {
                _dispatch_timers_mask |=
                                1 << DISPATCH_TIMER_INDEX(DISPATCH_CLOCK_WALL, qos);
        }
}
#endif

static void
_dispatch_timers_kevent(_dispatch_kevent_qos_s *ke)
{
        dispatch_assert(ke->data > 0);
        dispatch_assert((ke->ident & DISPATCH_KEVENT_TIMEOUT_IDENT_MASK) ==
                        DISPATCH_KEVENT_TIMEOUT_IDENT_MASK);
        unsigned int tidx = ke->ident & ~DISPATCH_KEVENT_TIMEOUT_IDENT_MASK;
        dispatch_assert(tidx < DISPATCH_KEVENT_TIMEOUT_COUNT);
        dispatch_assert(_dispatch_kevent_timeout[tidx].data != 0);
        _dispatch_kevent_timeout[tidx].data = 0; // kevent deleted via EV_ONESHOT
        _dispatch_timer_expired = true;
        _dispatch_timers_mask |= 1 << tidx;
        _dispatch_trace_next_timer_wake(DISPATCH_TIMER_QOS(tidx));
}

static inline bool
_dispatch_mgr_timers(void)
{
        dispatch_clock_now_cache_s nows = { };
        bool expired = slowpath(_dispatch_timer_expired);
        if (expired) {
                _dispatch_timers_run(&nows);
        }
        bool reconfigure = slowpath(_dispatch_timers_reconfigure);
        if (reconfigure || expired) {
                if (reconfigure) {
                        reconfigure = _dispatch_timers_configure();
                        _dispatch_timers_reconfigure = false;
                }
                if (reconfigure || expired) {
                        expired = _dispatch_timer_expired = _dispatch_timers_program(&nows);
                        expired = expired || _dispatch_mgr_q.dq_items_tail;
                }
                _dispatch_timers_mask = 0;
        }
        return expired;
}

#pragma mark -
#pragma mark dispatch_timer_aggregate

typedef struct {
        TAILQ_HEAD(, dispatch_timer_source_aggregate_refs_s) dk_sources;
} dispatch_timer_aggregate_refs_s;

typedef struct dispatch_timer_aggregate_s {
        DISPATCH_QUEUE_HEADER(queue);
        TAILQ_ENTRY(dispatch_timer_aggregate_s) dta_list;
        dispatch_timer_aggregate_refs_s
                        dta_kevent_timer[DISPATCH_KEVENT_TIMER_COUNT];
        struct {
                DISPATCH_TIMER_STRUCT(dispatch_timer_source_aggregate_refs_s);
        } dta_timer[DISPATCH_TIMER_COUNT];
        struct dispatch_timer_s dta_timer_data[DISPATCH_TIMER_COUNT];
        unsigned int dta_refcount;
} DISPATCH_QUEUE_ALIGN dispatch_timer_aggregate_s;

typedef TAILQ_HEAD(, dispatch_timer_aggregate_s) dispatch_timer_aggregates_s;
static dispatch_timer_aggregates_s _dispatch_timer_aggregates =
                TAILQ_HEAD_INITIALIZER(_dispatch_timer_aggregates);

dispatch_timer_aggregate_t
dispatch_timer_aggregate_create(void)
{
        unsigned int tidx;
        dispatch_timer_aggregate_t dta = _dispatch_alloc(DISPATCH_VTABLE(queue),
                        sizeof(struct dispatch_timer_aggregate_s));
        _dispatch_queue_init(dta->_as_dq, DQF_NONE,
                        DISPATCH_QUEUE_WIDTH_MAX, false);
        dta->do_targetq = _dispatch_get_root_queue(
                        _DISPATCH_QOS_CLASS_USER_INITIATED, true);
        //FIXME: aggregates need custom vtable
        //dta->dq_label = "timer-aggregate";
        for (tidx = 0; tidx < DISPATCH_KEVENT_TIMER_COUNT; tidx++) {
                TAILQ_INIT(&dta->dta_kevent_timer[tidx].dk_sources);
        }
        for (tidx = 0; tidx < DISPATCH_TIMER_COUNT; tidx++) {
                TAILQ_INIT(&dta->dta_timer[tidx].dt_sources);
                dta->dta_timer[tidx].target = UINT64_MAX;
                dta->dta_timer[tidx].deadline = UINT64_MAX;
                dta->dta_timer_data[tidx].target = UINT64_MAX;
                dta->dta_timer_data[tidx].deadline = UINT64_MAX;
        }
        return (dispatch_timer_aggregate_t)_dispatch_introspection_queue_create(
                        dta->_as_dq);
}

typedef struct dispatch_timer_delay_s {
        dispatch_timer_t timer;
        uint64_t delay, leeway;
} *dispatch_timer_delay_t;

static void
_dispatch_timer_aggregate_get_delay(void *ctxt)
{
        dispatch_timer_delay_t dtd = ctxt;
        dispatch_clock_now_cache_s nows = { };
        _dispatch_timers_get_delay(&nows, dtd->timer, &dtd->delay, &dtd->leeway,
                        DISPATCH_TIMERS_GET_DELAY_ALL);
}

uint64_t
dispatch_timer_aggregate_get_delay(dispatch_timer_aggregate_t dta,
                uint64_t *leeway_ptr)
{
        struct dispatch_timer_delay_s dtd = {
                .timer = dta->dta_timer_data,
        };
        dispatch_sync_f(dta->_as_dq, &dtd, _dispatch_timer_aggregate_get_delay);
        if (leeway_ptr) {
                *leeway_ptr = dtd.leeway;
        }
        return dtd.delay;
}

static void
_dispatch_timer_aggregate_update(void *ctxt)
{
        dispatch_timer_aggregate_t dta = (void*)_dispatch_queue_get_current();
        dispatch_timer_t dtau = ctxt;
        unsigned int tidx;
        for (tidx = 0; tidx < DISPATCH_TIMER_COUNT; tidx++) {
                dta->dta_timer_data[tidx].target = dtau[tidx].target;
                dta->dta_timer_data[tidx].deadline = dtau[tidx].deadline;
        }
        free(dtau);
}

DISPATCH_NOINLINE
static void
_dispatch_timer_aggregates_configure(void)
{
        dispatch_timer_aggregate_t dta;
        dispatch_timer_t dtau;
        TAILQ_FOREACH(dta, &_dispatch_timer_aggregates, dta_list) {
                if (!_dispatch_timers_check(dta->dta_kevent_timer, dta->dta_timer)) {
                        continue;
                }
                dtau = _dispatch_calloc(DISPATCH_TIMER_COUNT, sizeof(*dtau));
                memcpy(dtau, dta->dta_timer, sizeof(dta->dta_timer));
                _dispatch_barrier_async_detached_f(dta->_as_dq, dtau,
                                _dispatch_timer_aggregate_update);
        }
}

static inline void
_dispatch_timer_aggregates_check(void)
{
        if (fastpath(TAILQ_EMPTY(&_dispatch_timer_aggregates))) {
                return;
        }
        _dispatch_timer_aggregates_configure();
}

static void
_dispatch_timer_aggregates_register(dispatch_source_t ds)
{
        dispatch_timer_aggregate_t dta = ds_timer_aggregate(ds);
        if (!dta->dta_refcount++) {
                TAILQ_INSERT_TAIL(&_dispatch_timer_aggregates, dta, dta_list);
        }
}

DISPATCH_NOINLINE
static void
_dispatch_timer_aggregates_update(dispatch_source_t ds, unsigned int tidx)
{
        dispatch_timer_aggregate_t dta = ds_timer_aggregate(ds);
        dispatch_timer_source_aggregate_refs_t dr;
        dr = (dispatch_timer_source_aggregate_refs_t)ds->ds_refs;
        _dispatch_timers_insert(tidx, dta->dta_kevent_timer, dr, dra_list,
                        dta->dta_timer, dr, dta_list);
}

DISPATCH_NOINLINE
static void
_dispatch_timer_aggregates_unregister(dispatch_source_t ds, unsigned int tidx)
{
        dispatch_timer_aggregate_t dta = ds_timer_aggregate(ds);
        dispatch_timer_source_aggregate_refs_t dr;
        dr = (dispatch_timer_source_aggregate_refs_t)ds->ds_refs;
        _dispatch_timers_remove(tidx, (dispatch_timer_aggregate_refs_s*)NULL,
                        dta->dta_kevent_timer, dr, dra_list, dta->dta_timer, dr, dta_list);
        if (!--dta->dta_refcount) {
                TAILQ_REMOVE(&_dispatch_timer_aggregates, dta, dta_list);
        }
}

#pragma mark -
#pragma mark dispatch_kqueue

static int _dispatch_kq;

#if DISPATCH_DEBUG_QOS && DISPATCH_USE_KEVENT_WORKQUEUE
#define _dispatch_kevent_assert_valid_qos(ke)  ({ \
                if (_dispatch_kevent_workqueue_enabled) { \
                        const _dispatch_kevent_qos_s *_ke = (ke); \
                        if (_ke->flags & (EV_ADD|EV_ENABLE)) { \
                                _dispatch_assert_is_valid_qos_class(\
                                                (pthread_priority_t)_ke->qos); \
                                dispatch_assert(_ke->qos); \
                        } \
                } \
        })
#else
#define _dispatch_kevent_assert_valid_qos(ke)  ((void)ke)
#endif


static void
_dispatch_kq_init(void *context DISPATCH_UNUSED)
{
        _dispatch_fork_becomes_unsafe();
#if DISPATCH_USE_KEVENT_WORKQUEUE
        _dispatch_kevent_workqueue_init();
        if (_dispatch_kevent_workqueue_enabled) {
                int r;
                const _dispatch_kevent_qos_s kev[] = {
                        [0] = {
                                .ident = 1,
                                .filter = EVFILT_USER,
                                .flags = EV_ADD|EV_CLEAR,
                                .qos = _PTHREAD_PRIORITY_EVENT_MANAGER_FLAG,
                        },
                        [1] = {
                                .ident = 1,
                                .filter = EVFILT_USER,
                                .fflags = NOTE_TRIGGER,
                        },
                };
                _dispatch_kq = -1;
retry:
                r = kevent_qos(-1, kev, 2, NULL, 0, NULL, NULL,
                                KEVENT_FLAG_WORKQ|KEVENT_FLAG_IMMEDIATE);
                if (slowpath(r == -1)) {
                        int err = errno;
                        switch (err) {
                        case EINTR:
                                goto retry;
                        default:
                                DISPATCH_CLIENT_CRASH(err,
                                                "Failed to initalize workqueue kevent");
                                break;
                        }
                }
                return;
        }
#endif // DISPATCH_USE_KEVENT_WORKQUEUE
#if DISPATCH_USE_MGR_THREAD
        static const _dispatch_kevent_qos_s kev = {
                .ident = 1,
                .filter = EVFILT_USER,
                .flags = EV_ADD|EV_CLEAR,
        };

        _dispatch_fork_becomes_unsafe();
#if DISPATCH_USE_GUARDED_FD
        guardid_t guard = (uintptr_t)&kev;
        _dispatch_kq = guarded_kqueue_np(&guard, GUARD_CLOSE | GUARD_DUP);
#else
        _dispatch_kq = kqueue();
#endif
        if (_dispatch_kq == -1) {
                int err = errno;
                switch (err) {
                case EMFILE:
                        DISPATCH_CLIENT_CRASH(err, "kqueue() failure: "
                                        "process is out of file descriptors");
                        break;
                case ENFILE:
                        DISPATCH_CLIENT_CRASH(err, "kqueue() failure: "
                                        "system is out of file descriptors");
                        break;
                case ENOMEM:
                        DISPATCH_CLIENT_CRASH(err, "kqueue() failure: "
                                        "kernel is out of memory");
                        break;
                default:
                        DISPATCH_INTERNAL_CRASH(err, "kqueue() failure");
                        break;
                }
        }
        (void)dispatch_assume_zero(kevent_qos(_dispatch_kq, &kev, 1, NULL, 0, NULL,
                        NULL, 0));
        _dispatch_queue_push(_dispatch_mgr_q.do_targetq, &_dispatch_mgr_q, 0);
#endif // DISPATCH_USE_MGR_THREAD
}

DISPATCH_NOINLINE
static long
_dispatch_kq_update(const _dispatch_kevent_qos_s *ke, int n)
{
        int i, r;
        _dispatch_kevent_qos_s kev_error[n];
        static dispatch_once_t pred;
        dispatch_once_f(&pred, NULL, _dispatch_kq_init);

        for (i = 0; i < n; i++) {
                if (ke[i].filter != EVFILT_USER || DISPATCH_MGR_QUEUE_DEBUG) {
                        _dispatch_kevent_debug_n("updating", ke + i, i, n);
                }
        }

        unsigned int flags = KEVENT_FLAG_ERROR_EVENTS;
#if DISPATCH_USE_KEVENT_WORKQUEUE
        if (_dispatch_kevent_workqueue_enabled) {
                flags |= KEVENT_FLAG_WORKQ;
        }
#endif

retry:
        r = kevent_qos(_dispatch_kq, ke, n, kev_error, n, NULL, NULL, flags);
        if (slowpath(r == -1)) {
                int err = errno;
                switch (err) {
                case EINTR:
                        goto retry;
                case EBADF:
                        DISPATCH_CLIENT_CRASH(err, "Do not close random Unix descriptors");
                        break;
                default:
                        (void)dispatch_assume_zero(err);
                        break;
                }
                return err;
        }
        for (i = 0, n = r; i < n; i++) {
                if (kev_error[i].flags & EV_ERROR) {
                        _dispatch_kevent_debug("returned error", &kev_error[i]);
                        _dispatch_kevent_drain(&kev_error[i]);
                        r = (int)kev_error[i].data;
                } else {
                        _dispatch_kevent_mgr_debug(&kev_error[i]);
                        r = 0;
                }
        }
        return r;
}

DISPATCH_ALWAYS_INLINE
static void
_dispatch_kq_update_all(const _dispatch_kevent_qos_s *kev, int n)
{
        (void)_dispatch_kq_update(kev, n);
}

DISPATCH_ALWAYS_INLINE
static long
_dispatch_kq_update_one(const _dispatch_kevent_qos_s *kev)
{
        return _dispatch_kq_update(kev, 1);
}

static inline bool
_dispatch_kevent_maps_to_same_knote(const _dispatch_kevent_qos_s *e1,
                const _dispatch_kevent_qos_s *e2)
{
        return e1->filter == e2->filter &&
                        e1->ident == e2->ident &&
                        e1->udata == e2->udata;
}

static inline int
_dispatch_deferred_event_find_slot(dispatch_deferred_items_t ddi,
                const _dispatch_kevent_qos_s *ke)
{
        _dispatch_kevent_qos_s *events = ddi->ddi_eventlist;
        int i;

        for (i = 0; i < ddi->ddi_nevents; i++) {
                if (_dispatch_kevent_maps_to_same_knote(&events[i], ke)) {
                        break;
                }
        }
        return i;
}

static void
_dispatch_kq_deferred_update(const _dispatch_kevent_qos_s *ke)
{
        dispatch_deferred_items_t ddi = _dispatch_deferred_items_get();
        int slot;

        _dispatch_kevent_assert_valid_qos(ke);
        if (ddi) {
                if (unlikely(ddi->ddi_nevents == ddi->ddi_maxevents)) {
                        _dispatch_deferred_items_set(NULL);
                        _dispatch_kq_update_all(ddi->ddi_eventlist, ddi->ddi_nevents);
                        ddi->ddi_nevents = 0;
                        _dispatch_deferred_items_set(ddi);
                }
                if (ke->filter != EVFILT_USER || DISPATCH_MGR_QUEUE_DEBUG) {
                        _dispatch_kevent_debug("deferred", ke);
                }
                bool needs_enable = false;
                slot = _dispatch_deferred_event_find_slot(ddi, ke);
                if (slot == ddi->ddi_nevents) {
                        ddi->ddi_nevents++;
                } else if (ke->flags & EV_DELETE) {
                        // <rdar://problem/26202376> when deleting and an enable is pending,
                        // we must merge EV_ENABLE to do an immediate deletion
                        needs_enable = (ddi->ddi_eventlist[slot].flags & EV_ENABLE);
                }
                ddi->ddi_eventlist[slot] = *ke;
                if (needs_enable) {
                        ddi->ddi_eventlist[slot].flags |= EV_ENABLE;
                }
        } else {
                _dispatch_kq_update_one(ke);
        }
}

static long
_dispatch_kq_immediate_update(_dispatch_kevent_qos_s *ke)
{
        dispatch_deferred_items_t ddi = _dispatch_deferred_items_get();
        int slot, last;

        _dispatch_kevent_assert_valid_qos(ke);
        if (ddi) {
                _dispatch_kevent_qos_s *events = ddi->ddi_eventlist;
                slot = _dispatch_deferred_event_find_slot(ddi, ke);
                if (slot < ddi->ddi_nevents) {
                        // <rdar://problem/26202376> when deleting and an enable is pending,
                        // we must merge EV_ENABLE to do an immediate deletion
                        if ((ke->flags & EV_DELETE) && (events[slot].flags & EV_ENABLE)) {
                                ke->flags |= EV_ENABLE;
                        }
                        last = --ddi->ddi_nevents;
                        if (slot != last) {
                                events[slot] = events[last];
                        }
                }
        }
        return _dispatch_kq_update_one(ke);
}

#pragma mark -
#pragma mark dispatch_mgr

DISPATCH_NOINLINE
static void
_dispatch_mgr_queue_poke(dispatch_queue_t dq DISPATCH_UNUSED,
                pthread_priority_t pp DISPATCH_UNUSED)
{
        static const _dispatch_kevent_qos_s kev = {
                .ident = 1,
                .filter = EVFILT_USER,
                .fflags = NOTE_TRIGGER,
        };

#if DISPATCH_DEBUG && DISPATCH_MGR_QUEUE_DEBUG
        _dispatch_debug("waking up the dispatch manager queue: %p", dq);
#endif
        _dispatch_kq_deferred_update(&kev);
}

void
_dispatch_mgr_queue_wakeup(dispatch_queue_t dq, pthread_priority_t pp,
                dispatch_wakeup_flags_t flags)
{
        if (flags & DISPATCH_WAKEUP_FLUSH) {
                os_atomic_or2o(dq, dq_state, DISPATCH_QUEUE_DIRTY, release);
        }

        if (_dispatch_queue_get_current() == &_dispatch_mgr_q) {
                return;
        }

        if (!_dispatch_queue_class_probe(&_dispatch_mgr_q)) {
                return;
        }

        _dispatch_mgr_queue_poke(dq, pp);
}

DISPATCH_NOINLINE
static void
_dispatch_event_init(void)
{
        _dispatch_kevent_init();
        _dispatch_timers_init();
#if DISPATCH_EVFILT_MACHPORT_PORTSET_FALLBACK
        _dispatch_mach_recv_msg_buf_init();
#endif
        _dispatch_memorypressure_init();
        _voucher_activity_debug_channel_init();
}

#if DISPATCH_USE_MGR_THREAD
DISPATCH_NOINLINE
static void
_dispatch_mgr_init(void)
{
        uint64_t owned = DISPATCH_QUEUE_SERIAL_DRAIN_OWNED;
        _dispatch_queue_set_current(&_dispatch_mgr_q);
        if (_dispatch_queue_drain_try_lock(&_dispatch_mgr_q,
                        DISPATCH_INVOKE_STEALING, NULL) != owned) {
                DISPATCH_INTERNAL_CRASH(0, "Locking the manager should not fail");
        }
        _dispatch_mgr_priority_init();
        _dispatch_event_init();
}

DISPATCH_NOINLINE
static bool
_dispatch_mgr_wait_for_event(dispatch_deferred_items_t ddi, bool poll)
{
        int r;
        dispatch_assert((size_t)ddi->ddi_maxevents < countof(ddi->ddi_eventlist));

retry:
        r = kevent_qos(_dispatch_kq, ddi->ddi_eventlist, ddi->ddi_nevents,
                        ddi->ddi_eventlist + ddi->ddi_maxevents, 1, NULL, NULL,
                        poll ? KEVENT_FLAG_IMMEDIATE : KEVENT_FLAG_NONE);
        if (slowpath(r == -1)) {
                int err = errno;
                switch (err) {
                case EINTR:
                        goto retry;
                case EBADF:
                        DISPATCH_CLIENT_CRASH(err, "Do not close random Unix descriptors");
                        break;
                default:
                        (void)dispatch_assume_zero(err);
                        break;
                }
        }
        ddi->ddi_nevents = 0;
        return r > 0;
}

DISPATCH_NOINLINE DISPATCH_NORETURN
static void
_dispatch_mgr_invoke(void)
{
        dispatch_deferred_items_s ddi;
        bool poll;

        ddi.ddi_magic = DISPATCH_DEFERRED_ITEMS_MAGIC;
        ddi.ddi_stashed_pp = _PTHREAD_PRIORITY_EVENT_MANAGER_FLAG;
        ddi.ddi_nevents = 0;
        ddi.ddi_maxevents = 1;

        _dispatch_deferred_items_set(&ddi);

        for (;;) {
                _dispatch_mgr_queue_drain();
                poll = _dispatch_mgr_timers();
                poll = poll || _dispatch_queue_class_probe(&_dispatch_mgr_q);
                if (_dispatch_mgr_wait_for_event(&ddi, poll)) {
                        _dispatch_kevent_qos_s *ke = ddi.ddi_eventlist + ddi.ddi_maxevents;
                        _dispatch_kevent_debug("received", ke);
                        _dispatch_kevent_drain(ke);
                }
        }
}
#endif // DISPATCH_USE_MGR_THREAD

DISPATCH_NORETURN
void
_dispatch_mgr_thread(dispatch_queue_t dq DISPATCH_UNUSED,
                dispatch_invoke_flags_t flags DISPATCH_UNUSED)
{
#if DISPATCH_USE_KEVENT_WORKQUEUE
        if (_dispatch_kevent_workqueue_enabled) {
                DISPATCH_INTERNAL_CRASH(0, "Manager queue invoked with "
                                "kevent workqueue enabled");
        }
#endif
#if DISPATCH_USE_MGR_THREAD
        _dispatch_mgr_init();
        // never returns, so burn bridges behind us & clear stack 2k ahead
        _dispatch_clear_stack(2048);
        _dispatch_mgr_invoke();
#endif
}

#if DISPATCH_USE_KEVENT_WORKQUEUE

#define DISPATCH_KEVENT_WORKER_IS_NOT_MANAGER ((pthread_priority_t)(~0ul))

DISPATCH_ALWAYS_INLINE
static inline pthread_priority_t
_dispatch_kevent_worker_thread_init(dispatch_deferred_items_t ddi)
{
        uint64_t owned = DISPATCH_QUEUE_SERIAL_DRAIN_OWNED;

        ddi->ddi_magic = DISPATCH_DEFERRED_ITEMS_MAGIC;
        ddi->ddi_nevents = 0;
        ddi->ddi_maxevents = countof(ddi->ddi_eventlist);
        ddi->ddi_stashed_pp = _PTHREAD_PRIORITY_EVENT_MANAGER_FLAG;

        pthread_priority_t pp = _dispatch_get_priority();
        if (!(pp & _PTHREAD_PRIORITY_EVENT_MANAGER_FLAG)) {
                // If this thread does not have the event manager flag set, don't setup
                // as the dispatch manager and let the caller know to only process
                // the delivered events.
                //
                // Also add the NEEDS_UNBIND flag so that
                // _dispatch_priority_compute_update knows it has to unbind
                pp &= _PTHREAD_PRIORITY_OVERCOMMIT_FLAG | ~_PTHREAD_PRIORITY_FLAGS_MASK;
                pp |= _PTHREAD_PRIORITY_NEEDS_UNBIND_FLAG;
                _dispatch_thread_setspecific(dispatch_priority_key,
                                        (void *)(uintptr_t)pp);
                ddi->ddi_stashed_pp = 0;
                return DISPATCH_KEVENT_WORKER_IS_NOT_MANAGER;
        }

        if ((pp & _PTHREAD_PRIORITY_SCHED_PRI_FLAG) ||
                        !(pp & ~_PTHREAD_PRIORITY_FLAGS_MASK)) {
                // When the phtread kext is delivering kevents to us, and pthread
                // root queues are in use, then the pthread priority TSD is set
                // to a sched pri with the _PTHREAD_PRIORITY_SCHED_PRI_FLAG bit set.
                //
                // Given that this isn't a valid QoS we need to fixup the TSD,
                // and the best option is to clear the qos/priority bits which tells
                // us to not do any QoS related calls on this thread.
                //
                // However, in that case the manager thread is opted out of QoS,
                // as far as pthread is concerned, and can't be turned into
                // something else, so we can't stash.
                pp &= (pthread_priority_t)_PTHREAD_PRIORITY_FLAGS_MASK;
        }
        // Managers always park without mutating to a regular worker thread, and
        // hence never need to unbind from userland, and when draining a manager,
        // the NEEDS_UNBIND flag would cause the mutation to happen.
        // So we need to strip this flag
        pp &= ~(pthread_priority_t)_PTHREAD_PRIORITY_NEEDS_UNBIND_FLAG;
        _dispatch_thread_setspecific(dispatch_priority_key, (void *)(uintptr_t)pp);

        // ensure kevents registered from this thread are registered at manager QoS
        pthread_priority_t old_dp = _dispatch_set_defaultpriority(
                        (pthread_priority_t)_PTHREAD_PRIORITY_EVENT_MANAGER_FLAG, NULL);
        _dispatch_queue_set_current(&_dispatch_mgr_q);
        if (_dispatch_queue_drain_try_lock(&_dispatch_mgr_q,
                        DISPATCH_INVOKE_STEALING, NULL) != owned) {
                DISPATCH_INTERNAL_CRASH(0, "Locking the manager should not fail");
        }
        static int event_thread_init;
        if (!event_thread_init) {
                event_thread_init = 1;
                _dispatch_event_init();
        }
        return old_dp;
}

DISPATCH_ALWAYS_INLINE DISPATCH_WARN_RESULT
static inline bool
_dispatch_kevent_worker_thread_reset(pthread_priority_t old_dp)
{
        dispatch_queue_t dq = &_dispatch_mgr_q;
        uint64_t orig_dq_state;

        _dispatch_queue_drain_unlock(dq, DISPATCH_QUEUE_SERIAL_DRAIN_OWNED,
                        &orig_dq_state);
        _dispatch_reset_defaultpriority(old_dp);
        _dispatch_queue_set_current(NULL);
        return _dq_state_is_dirty(orig_dq_state);
}

DISPATCH_NOINLINE
void
_dispatch_kevent_worker_thread(_dispatch_kevent_qos_s **events, int *nevents)
{
        _dispatch_introspection_thread_add();

        if (!events && !nevents) {
                // events for worker thread request have already been delivered earlier
                return;
        }

        _dispatch_kevent_qos_s *ke = *events;
        int n = *nevents;
        if (!dispatch_assume(n) || !dispatch_assume(*events)) return;

        dispatch_deferred_items_s ddi;
        pthread_priority_t old_dp = _dispatch_kevent_worker_thread_init(&ddi);

        _dispatch_deferred_items_set(&ddi);
        for (int i = 0; i < n; i++) {
                _dispatch_kevent_debug("received", ke);
                _dispatch_kevent_drain(ke++);
        }

        if (old_dp != DISPATCH_KEVENT_WORKER_IS_NOT_MANAGER) {
                _dispatch_mgr_queue_drain();
                bool poll = _dispatch_mgr_timers();
                if (_dispatch_kevent_worker_thread_reset(old_dp)) {
                        poll = true;
                }
                if (poll) _dispatch_mgr_queue_poke(&_dispatch_mgr_q, 0);
        }
        _dispatch_deferred_items_set(NULL);

        if (ddi.ddi_stashed_pp & _PTHREAD_PRIORITY_PRIORITY_MASK) {
                *nevents = 0;
                if (ddi.ddi_nevents) {
                        _dispatch_kq_update_all(ddi.ddi_eventlist, ddi.ddi_nevents);
                }
                ddi.ddi_stashed_pp &= _PTHREAD_PRIORITY_QOS_CLASS_MASK;
                return _dispatch_root_queue_drain_deferred_item(ddi.ddi_stashed_dq,
                                ddi.ddi_stashed_dou, ddi.ddi_stashed_pp);
#ifndef WORKQ_KEVENT_EVENT_BUFFER_LEN
        } else if (ddi.ddi_nevents > *nevents) {
                *nevents = 0;
                _dispatch_kq_update_all(ddi.ddi_eventlist, ddi.ddi_nevents);
#endif
        } else {
                *nevents = ddi.ddi_nevents;
                dispatch_static_assert(__builtin_types_compatible_p(typeof(**events),
                                typeof(*ddi.ddi_eventlist)));
                memcpy(*events, ddi.ddi_eventlist,
                         (size_t)ddi.ddi_nevents * sizeof(*ddi.ddi_eventlist));
        }
}
#endif // DISPATCH_USE_KEVENT_WORKQUEUE

#pragma mark -
#pragma mark dispatch_memorypressure

#if DISPATCH_USE_MEMORYPRESSURE_SOURCE
#define DISPATCH_MEMORYPRESSURE_SOURCE_TYPE DISPATCH_SOURCE_TYPE_MEMORYPRESSURE
#define DISPATCH_MEMORYPRESSURE_SOURCE_MASK ( \
                DISPATCH_MEMORYPRESSURE_NORMAL | \
                DISPATCH_MEMORYPRESSURE_WARN | \
                DISPATCH_MEMORYPRESSURE_CRITICAL | \
                DISPATCH_MEMORYPRESSURE_PROC_LIMIT_WARN | \
                DISPATCH_MEMORYPRESSURE_PROC_LIMIT_CRITICAL)
#define DISPATCH_MEMORYPRESSURE_MALLOC_MASK ( \
                DISPATCH_MEMORYPRESSURE_WARN | \
                DISPATCH_MEMORYPRESSURE_CRITICAL | \
                DISPATCH_MEMORYPRESSURE_PROC_LIMIT_WARN | \
                DISPATCH_MEMORYPRESSURE_PROC_LIMIT_CRITICAL)
#endif

#if DISPATCH_USE_MEMORYPRESSURE_SOURCE
static dispatch_source_t _dispatch_memorypressure_source;

static void
_dispatch_memorypressure_handler(void *context DISPATCH_UNUSED)
{
#if DISPATCH_USE_MEMORYPRESSURE_SOURCE
        unsigned long memorypressure;
        memorypressure = dispatch_source_get_data(_dispatch_memorypressure_source);

        if (memorypressure & DISPATCH_MEMORYPRESSURE_NORMAL) {
                _dispatch_memory_warn = false;
                _dispatch_continuation_cache_limit = DISPATCH_CONTINUATION_CACHE_LIMIT;
#if VOUCHER_USE_MACH_VOUCHER
                if (_firehose_task_buffer) {
                        firehose_buffer_clear_bank_flags(_firehose_task_buffer,
                                        FIREHOSE_BUFFER_BANK_FLAG_LOW_MEMORY);
                }
#endif
        }
        if (memorypressure & DISPATCH_MEMORYPRESSURE_WARN) {
                _dispatch_memory_warn = true;
                _dispatch_continuation_cache_limit =
                                DISPATCH_CONTINUATION_CACHE_LIMIT_MEMORYPRESSURE_PRESSURE_WARN;
#if VOUCHER_USE_MACH_VOUCHER
                if (_firehose_task_buffer) {
                        firehose_buffer_set_bank_flags(_firehose_task_buffer,
                                        FIREHOSE_BUFFER_BANK_FLAG_LOW_MEMORY);
                }
#endif
        }
        if (memorypressure & DISPATCH_MEMORYPRESSURE_MALLOC_MASK) {
                malloc_memory_event_handler(memorypressure & DISPATCH_MEMORYPRESSURE_MALLOC_MASK);
        }
#endif
}

static void
_dispatch_memorypressure_init(void)
{
        _dispatch_memorypressure_source = dispatch_source_create(
                        DISPATCH_MEMORYPRESSURE_SOURCE_TYPE, 0,
                        DISPATCH_MEMORYPRESSURE_SOURCE_MASK,
                        _dispatch_get_root_queue(_DISPATCH_QOS_CLASS_DEFAULT, true));
        dispatch_source_set_event_handler_f(_dispatch_memorypressure_source,
                        _dispatch_memorypressure_handler);
        dispatch_activate(_dispatch_memorypressure_source);
}
#else
static inline void _dispatch_memorypressure_init(void) {}
#endif // DISPATCH_USE_MEMORYPRESSURE_SOURCE

#pragma mark -
#pragma mark dispatch_mach

#if HAVE_MACH

#if DISPATCH_DEBUG && DISPATCH_MACHPORT_DEBUG
#define _dispatch_debug_machport(name) \
                dispatch_debug_machport((name), __func__)
#else
#define _dispatch_debug_machport(name) ((void)(name))
#endif

// Flags for all notifications that are registered/unregistered when a
// send-possible notification is requested/delivered
#define _DISPATCH_MACH_SP_FLAGS (DISPATCH_MACH_SEND_POSSIBLE| \
                DISPATCH_MACH_SEND_DEAD|DISPATCH_MACH_SEND_DELETED)
#define _DISPATCH_MACH_RECV_FLAGS (DISPATCH_MACH_RECV_MESSAGE| \
                DISPATCH_MACH_RECV_MESSAGE_DIRECT| \
                DISPATCH_MACH_RECV_MESSAGE_DIRECT_ONCE)
#define _DISPATCH_MACH_RECV_DIRECT_FLAGS ( \
                DISPATCH_MACH_RECV_MESSAGE_DIRECT| \
                DISPATCH_MACH_RECV_MESSAGE_DIRECT_ONCE)

#define _DISPATCH_IS_POWER_OF_TWO(v) (!(v & (v - 1)) && v)
#define _DISPATCH_HASH(x, y) (_DISPATCH_IS_POWER_OF_TWO(y) ? \
                (MACH_PORT_INDEX(x) & ((y) - 1)) : (MACH_PORT_INDEX(x) % (y)))

#define _DISPATCH_MACHPORT_HASH_SIZE 32
#define _DISPATCH_MACHPORT_HASH(x) \
                _DISPATCH_HASH((x), _DISPATCH_MACHPORT_HASH_SIZE)

#ifndef MACH_RCV_VOUCHER
#define MACH_RCV_VOUCHER 0x00000800
#endif
#define DISPATCH_MACH_RCV_TRAILER MACH_RCV_TRAILER_CTX
#define DISPATCH_MACH_RCV_OPTIONS ( \
                MACH_RCV_MSG | MACH_RCV_LARGE | MACH_RCV_LARGE_IDENTITY | \
                MACH_RCV_TRAILER_ELEMENTS(DISPATCH_MACH_RCV_TRAILER) | \
                MACH_RCV_TRAILER_TYPE(MACH_MSG_TRAILER_FORMAT_0)) | \
                MACH_RCV_VOUCHER

#define DISPATCH_MACH_NOTIFICATION_ARMED(dk) ((dk)->dk_kevent.ext[0])

static void _dispatch_kevent_mach_msg_recv(_dispatch_kevent_qos_s *ke,
                mach_msg_header_t *hdr);
static void _dispatch_kevent_mach_msg_destroy(_dispatch_kevent_qos_s *ke,
                mach_msg_header_t *hdr);
static void _dispatch_source_merge_mach_msg(dispatch_source_t ds,
                dispatch_source_refs_t dr, dispatch_kevent_t dk,
                _dispatch_kevent_qos_s *ke, mach_msg_header_t *hdr,
                mach_msg_size_t siz);
static kern_return_t _dispatch_mach_notify_update(dispatch_kevent_t dk,
                uint32_t new_flags, uint32_t del_flags, uint32_t mask,
                mach_msg_id_t notify_msgid, mach_port_mscount_t notify_sync);
static void _dispatch_mach_notify_source_invoke(mach_msg_header_t *hdr);
static void _dispatch_mach_reply_kevent_unregister(dispatch_mach_t dm,
                dispatch_mach_reply_refs_t dmr, unsigned int options);
static void _dispatch_mach_notification_kevent_unregister(dispatch_mach_t dm);
static void _dispatch_mach_msg_recv(dispatch_mach_t dm,
                dispatch_mach_reply_refs_t dmr, _dispatch_kevent_qos_s *ke,
                mach_msg_header_t *hdr, mach_msg_size_t siz);
static void _dispatch_mach_merge_notification_kevent(dispatch_mach_t dm,
                const _dispatch_kevent_qos_s *ke);
static inline mach_msg_option_t _dispatch_mach_checkin_options(void);

static const size_t _dispatch_mach_recv_msg_size =
                DISPATCH_MACH_RECEIVE_MAX_INLINE_MESSAGE_SIZE;
static const size_t dispatch_mach_trailer_size =
                sizeof(dispatch_mach_trailer_t);
static mach_port_t _dispatch_mach_notify_port;
static dispatch_source_t _dispatch_mach_notify_source;

static inline void*
_dispatch_kevent_mach_msg_buf(_dispatch_kevent_qos_s *ke)
{
        return (void*)ke->ext[0];
}

static inline mach_msg_size_t
_dispatch_kevent_mach_msg_size(_dispatch_kevent_qos_s *ke)
{
        // buffer size in the successful receive case, but message size (like
        // msgh_size) in the MACH_RCV_TOO_LARGE case, i.e. add trailer size.
        return (mach_msg_size_t)ke->ext[1];
}

static void
_dispatch_source_type_mach_recv_direct_init(dispatch_source_t ds,
        dispatch_source_type_t type DISPATCH_UNUSED,
        uintptr_t handle DISPATCH_UNUSED,
        unsigned long mask DISPATCH_UNUSED)
{
        ds->ds_pending_data_mask = DISPATCH_MACH_RECV_MESSAGE_DIRECT;
#if DISPATCH_EVFILT_MACHPORT_PORTSET_FALLBACK
        if (_dispatch_evfilt_machport_direct_enabled) return;
        ds->ds_dkev->dk_kevent.fflags = DISPATCH_MACH_RECV_MESSAGE_DIRECT;
        ds->ds_dkev->dk_kevent.flags &= ~(EV_UDATA_SPECIFIC|EV_VANISHED);
        ds->ds_is_direct_kevent = false;
#endif
}

static const
struct dispatch_source_type_s _dispatch_source_type_mach_recv_direct = {
        .ke = {
                .filter = EVFILT_MACHPORT,
                .flags = EV_VANISHED|EV_DISPATCH|EV_UDATA_SPECIFIC,
                .fflags = DISPATCH_MACH_RCV_OPTIONS,
        },
        .init = _dispatch_source_type_mach_recv_direct_init,
};

#if DISPATCH_EVFILT_MACHPORT_PORTSET_FALLBACK
static mach_port_t _dispatch_mach_portset,  _dispatch_mach_recv_portset;
static _dispatch_kevent_qos_s _dispatch_mach_recv_kevent = {
        .filter = EVFILT_MACHPORT,
        .flags = EV_ADD|EV_ENABLE|EV_DISPATCH,
        .fflags = DISPATCH_MACH_RCV_OPTIONS,
};

static void
_dispatch_mach_recv_msg_buf_init(void)
{
        if (_dispatch_evfilt_machport_direct_enabled) return;
        mach_vm_size_t vm_size = mach_vm_round_page(
                        _dispatch_mach_recv_msg_size + dispatch_mach_trailer_size);
        mach_vm_address_t vm_addr = vm_page_size;
        kern_return_t kr;

        while (slowpath(kr = mach_vm_allocate(mach_task_self(), &vm_addr, vm_size,
                        VM_FLAGS_ANYWHERE))) {
                if (kr != KERN_NO_SPACE) {
                        DISPATCH_CLIENT_CRASH(kr,
                                        "Could not allocate mach msg receive buffer");
                }
                _dispatch_temporary_resource_shortage();
                vm_addr = vm_page_size;
        }
        _dispatch_mach_recv_kevent.ext[0] = (uintptr_t)vm_addr;
        _dispatch_mach_recv_kevent.ext[1] = vm_size;
}
#endif

DISPATCH_NOINLINE
static void
_dispatch_source_merge_mach_msg_direct(dispatch_source_t ds,
                _dispatch_kevent_qos_s *ke, mach_msg_header_t *hdr)
{
        dispatch_continuation_t dc = _dispatch_source_get_event_handler(ds->ds_refs);
        dispatch_queue_t cq = _dispatch_queue_get_current();

        // see firehose_client_push_notify_async
        _dispatch_queue_set_current(ds->_as_dq);
        dc->dc_func(hdr);
        _dispatch_queue_set_current(cq);
        if (hdr != _dispatch_kevent_mach_msg_buf(ke)) {
                free(hdr);
        }
}

dispatch_source_t
_dispatch_source_create_mach_msg_direct_recv(mach_port_t recvp,
                const struct dispatch_continuation_s *dc)
{
        dispatch_source_t ds;
        ds = dispatch_source_create(&_dispatch_source_type_mach_recv_direct,
                        recvp, 0, &_dispatch_mgr_q);
        os_atomic_store(&ds->ds_refs->ds_handler[DS_EVENT_HANDLER],
                        (dispatch_continuation_t)dc, relaxed);
        return ds;
}

static void
_dispatch_mach_notify_port_init(void *context DISPATCH_UNUSED)
{
        kern_return_t kr;
#if HAVE_MACH_PORT_CONSTRUCT
        mach_port_options_t opts = { .flags = MPO_CONTEXT_AS_GUARD | MPO_STRICT };
#ifdef __LP64__
        const mach_port_context_t guard = 0xfeed09071f1ca7edull;
#else
        const mach_port_context_t guard = 0xff1ca7edull;
#endif
        kr = mach_port_construct(mach_task_self(), &opts, guard,
                        &_dispatch_mach_notify_port);
#else
        kr = mach_port_allocate(mach_task_self(), MACH_PORT_RIGHT_RECEIVE,
                        &_dispatch_mach_notify_port);
#endif
        DISPATCH_VERIFY_MIG(kr);
        if (slowpath(kr)) {
                DISPATCH_CLIENT_CRASH(kr,
                                "mach_port_construct() failed: cannot create receive right");
        }

        static const struct dispatch_continuation_s dc = {
                .dc_func = (void*)_dispatch_mach_notify_source_invoke,
        };
        _dispatch_mach_notify_source = _dispatch_source_create_mach_msg_direct_recv(
                        _dispatch_mach_notify_port, &dc);
        dispatch_assert(_dispatch_mach_notify_source);
        dispatch_activate(_dispatch_mach_notify_source);
}

static mach_port_t
_dispatch_get_mach_notify_port(void)
{
        static dispatch_once_t pred;
        dispatch_once_f(&pred, NULL, _dispatch_mach_notify_port_init);
        return _dispatch_mach_notify_port;
}

#if DISPATCH_EVFILT_MACHPORT_PORTSET_FALLBACK
static void
_dispatch_mach_recv_portset_init(void *context DISPATCH_UNUSED)
{
        kern_return_t kr;

        kr = mach_port_allocate(mach_task_self(), MACH_PORT_RIGHT_PORT_SET,
                        &_dispatch_mach_recv_portset);
        DISPATCH_VERIFY_MIG(kr);
        if (slowpath(kr)) {
                DISPATCH_CLIENT_CRASH(kr,
                                "mach_port_allocate() failed: cannot create port set");
        }
        _dispatch_kevent_qos_s *ke = &_dispatch_mach_recv_kevent;
        dispatch_assert(_dispatch_kevent_mach_msg_buf(ke));
        dispatch_assert(dispatch_mach_trailer_size ==
                        REQUESTED_TRAILER_SIZE_NATIVE(MACH_RCV_TRAILER_ELEMENTS(
                        DISPATCH_MACH_RCV_TRAILER)));
        ke->ident = _dispatch_mach_recv_portset;
#if DISPATCH_USE_KEVENT_WORKQUEUE
        if (_dispatch_kevent_workqueue_enabled) {
                ke->qos = _PTHREAD_PRIORITY_EVENT_MANAGER_FLAG;
        }
#endif
        _dispatch_kq_immediate_update(&_dispatch_mach_recv_kevent);
}

static mach_port_t
_dispatch_get_mach_recv_portset(void)
{
        static dispatch_once_t pred;
        dispatch_once_f(&pred, NULL, _dispatch_mach_recv_portset_init);
        return _dispatch_mach_recv_portset;
}

static void
_dispatch_mach_portset_init(void *context DISPATCH_UNUSED)
{
        _dispatch_kevent_qos_s kev = {
                .filter = EVFILT_MACHPORT,
                .flags = EV_ADD,
        };
#if DISPATCH_USE_KEVENT_WORKQUEUE
        if (_dispatch_kevent_workqueue_enabled) {
                kev.qos = _PTHREAD_PRIORITY_EVENT_MANAGER_FLAG;
        }
#endif

        kern_return_t kr;

        kr = mach_port_allocate(mach_task_self(), MACH_PORT_RIGHT_PORT_SET,
                        &_dispatch_mach_portset);
        DISPATCH_VERIFY_MIG(kr);
        if (slowpath(kr)) {
                DISPATCH_CLIENT_CRASH(kr,
                                "mach_port_allocate() failed: cannot create port set");
        }
        kev.ident = _dispatch_mach_portset;
        _dispatch_kq_immediate_update(&kev);
}

static mach_port_t
_dispatch_get_mach_portset(void)
{
        static dispatch_once_t pred;
        dispatch_once_f(&pred, NULL, _dispatch_mach_portset_init);
        return _dispatch_mach_portset;
}

static kern_return_t
_dispatch_mach_portset_update(dispatch_kevent_t dk, mach_port_t mps)
{
        mach_port_t mp = (mach_port_t)dk->dk_kevent.ident;
        kern_return_t kr;

        _dispatch_debug_machport(mp);
        kr = mach_port_move_member(mach_task_self(), mp, mps);
        if (slowpath(kr)) {
                DISPATCH_VERIFY_MIG(kr);
                switch (kr) {
                case KERN_INVALID_RIGHT:
                        if (mps) {
                                _dispatch_bug_mach_client("_dispatch_kevent_machport_enable: "
                                                "mach_port_move_member() failed ", kr);
                                break;
                        }
                        //fall through
                case KERN_INVALID_NAME:
#if DISPATCH_DEBUG
                        _dispatch_log("Corruption: Mach receive right 0x%x destroyed "
                                        "prematurely", mp);
#endif
                        break;
                default:
                        (void)dispatch_assume_zero(kr);
                        break;
                }
        }
        return mps ? kr : 0;
}

static kern_return_t
_dispatch_kevent_machport_resume(dispatch_kevent_t dk, uint32_t new_flags,
                uint32_t del_flags)
{
        kern_return_t kr = 0;
        dispatch_assert_zero(new_flags & del_flags);
        if ((new_flags & _DISPATCH_MACH_RECV_FLAGS) ||
                        (del_flags & _DISPATCH_MACH_RECV_FLAGS)) {
                mach_port_t mps;
                if (new_flags & _DISPATCH_MACH_RECV_DIRECT_FLAGS) {
                        mps = _dispatch_get_mach_recv_portset();
                } else if ((new_flags & DISPATCH_MACH_RECV_MESSAGE) ||
                                ((del_flags & _DISPATCH_MACH_RECV_DIRECT_FLAGS) &&
                                (dk->dk_kevent.fflags & DISPATCH_MACH_RECV_MESSAGE))) {
                        mps = _dispatch_get_mach_portset();
                } else {
                        mps = MACH_PORT_NULL;
                }
                kr = _dispatch_mach_portset_update(dk, mps);
        }
        return kr;
}
#endif // DISPATCH_EVFILT_MACHPORT_PORTSET_FALLBACK

static kern_return_t
_dispatch_kevent_mach_notify_resume(dispatch_kevent_t dk, uint32_t new_flags,
                uint32_t del_flags)
{
        kern_return_t kr = 0;
        dispatch_assert_zero(new_flags & del_flags);
        if ((new_flags & _DISPATCH_MACH_SP_FLAGS) ||
                        (del_flags & _DISPATCH_MACH_SP_FLAGS)) {
                // Requesting a (delayed) non-sync send-possible notification
                // registers for both immediate dead-name notification and delayed-arm
                // send-possible notification for the port.
                // The send-possible notification is armed when a mach_msg() with the
                // the MACH_SEND_NOTIFY to the port times out.
                // If send-possible is unavailable, fall back to immediate dead-name
                // registration rdar://problem/2527840&9008724
                kr = _dispatch_mach_notify_update(dk, new_flags, del_flags,
                                _DISPATCH_MACH_SP_FLAGS, MACH_NOTIFY_SEND_POSSIBLE,
                                MACH_NOTIFY_SEND_POSSIBLE == MACH_NOTIFY_DEAD_NAME ? 1 : 0);
        }
        return kr;
}

#if DISPATCH_EVFILT_MACHPORT_PORTSET_FALLBACK
DISPATCH_NOINLINE
static void
_dispatch_kevent_machport_drain(_dispatch_kevent_qos_s *ke)
{
        mach_port_t name = (mach_port_name_t)ke->data;
        dispatch_kevent_t dk;

        _dispatch_debug_machport(name);
        dk = _dispatch_kevent_find(name, EVFILT_MACHPORT);
        if (!dispatch_assume(dk)) {
                return;
        }
        _dispatch_mach_portset_update(dk, MACH_PORT_NULL); // emulate EV_DISPATCH

        _dispatch_kevent_qos_s kev = {
                .ident = name,
                .filter = EVFILT_MACHPORT,
                .flags = EV_ADD|EV_ENABLE|EV_DISPATCH,
                .fflags = DISPATCH_MACH_RECV_MESSAGE,
                .udata = (uintptr_t)dk,
        };
        _dispatch_kevent_debug("synthetic", &kev);
        _dispatch_kevent_merge(&kev);
}
#endif

DISPATCH_NOINLINE
static void
_dispatch_kevent_mach_msg_drain(_dispatch_kevent_qos_s *ke)
{
        mach_msg_header_t *hdr = _dispatch_kevent_mach_msg_buf(ke);
        mach_msg_size_t siz;
        mach_msg_return_t kr = (mach_msg_return_t)ke->fflags;

        if (!fastpath(hdr)) {
                DISPATCH_INTERNAL_CRASH(kr, "EVFILT_MACHPORT with no message");
        }
        if (fastpath(!kr)) {
                _dispatch_kevent_mach_msg_recv(ke, hdr);
                goto out;
        } else if (kr != MACH_RCV_TOO_LARGE) {
                goto out;
        } else if (!ke->data) {
                DISPATCH_INTERNAL_CRASH(0, "MACH_RCV_LARGE_IDENTITY with no identity");
        }
        if (slowpath(ke->ext[1] > (UINT_MAX - dispatch_mach_trailer_size))) {
                DISPATCH_INTERNAL_CRASH(ke->ext[1],
                                "EVFILT_MACHPORT with overlarge message");
        }
        siz = _dispatch_kevent_mach_msg_size(ke) + dispatch_mach_trailer_size;
        hdr = malloc(siz);
        if (!dispatch_assume(hdr)) {
                // Kernel will discard message too large to fit
                hdr = NULL;
                siz = 0;
        }
        mach_port_t name = (mach_port_name_t)ke->data;
        const mach_msg_option_t options = ((DISPATCH_MACH_RCV_OPTIONS |
                        MACH_RCV_TIMEOUT) & ~MACH_RCV_LARGE);
        kr = mach_msg(hdr, options, 0, siz, name, MACH_MSG_TIMEOUT_NONE,
                        MACH_PORT_NULL);
        if (fastpath(!kr)) {
                _dispatch_kevent_mach_msg_recv(ke, hdr);
                goto out;
        } else if (kr == MACH_RCV_TOO_LARGE) {
                _dispatch_log("BUG in libdispatch client: "
                                "_dispatch_kevent_mach_msg_drain: dropped message too "
                                "large to fit in memory: id = 0x%x, size = %u",
                                hdr->msgh_id, _dispatch_kevent_mach_msg_size(ke));
                kr = MACH_MSG_SUCCESS;
        }
        if (hdr != _dispatch_kevent_mach_msg_buf(ke)) {
                free(hdr);
        }
out:
        if (slowpath(kr)) {
                _dispatch_bug_mach_client("_dispatch_kevent_mach_msg_drain: "
                                "message reception failed", kr);
        }
}

DISPATCH_NOINLINE
static void
_dispatch_mach_kevent_merge(_dispatch_kevent_qos_s *ke)
{
        if (unlikely(!(ke->flags & EV_UDATA_SPECIFIC))) {
#if DISPATCH_EVFILT_MACHPORT_PORTSET_FALLBACK
                if (ke->ident == _dispatch_mach_recv_portset) {
                        _dispatch_kevent_mach_msg_drain(ke);
                        return _dispatch_kq_deferred_update(&_dispatch_mach_recv_kevent);
                } else if (ke->ident == _dispatch_mach_portset) {
                        return _dispatch_kevent_machport_drain(ke);
                }
#endif
                return _dispatch_kevent_error(ke);
        }

        dispatch_kevent_t dk = (dispatch_kevent_t)ke->udata;
        dispatch_source_refs_t dr = TAILQ_FIRST(&dk->dk_sources);
        bool is_reply = (dk->dk_kevent.flags & EV_ONESHOT);
        dispatch_source_t ds = _dispatch_source_from_refs(dr);

        if (_dispatch_kevent_mach_msg_size(ke)) {
                _dispatch_kevent_mach_msg_drain(ke);
                if (is_reply) {
                        // _dispatch_kevent_mach_msg_drain() should have deleted this event
                        dispatch_assert(ke->flags & EV_DELETE);
                        return;
                }

                if (!(ds->dq_atomic_flags & DSF_CANCELED)) {
                        // re-arm the mach channel
                        ke->fflags = DISPATCH_MACH_RCV_OPTIONS;
                        ke->data = 0;
                        ke->ext[0] = 0;
                        ke->ext[1] = 0;
                        return _dispatch_kq_deferred_update(ke);
                }
        } else if (is_reply) {
                DISPATCH_INTERNAL_CRASH(ke->flags, "Unexpected EVFILT_MACHPORT event");
        }
        if (unlikely((ke->flags & EV_VANISHED) &&
                        (dx_type(ds) == DISPATCH_MACH_CHANNEL_TYPE))) {
                DISPATCH_CLIENT_CRASH(ke->flags,
                                "Unexpected EV_VANISHED (do not destroy random mach ports)");
        }
        return _dispatch_kevent_merge(ke);
}

static void
_dispatch_kevent_mach_msg_recv(_dispatch_kevent_qos_s *ke,
                mach_msg_header_t *hdr)
{
        dispatch_source_refs_t dri;
        dispatch_kevent_t dk;
        mach_port_t name = hdr->msgh_local_port;
        mach_msg_size_t siz = hdr->msgh_size + dispatch_mach_trailer_size;

        if (!dispatch_assume(hdr->msgh_size <= UINT_MAX -
                        dispatch_mach_trailer_size)) {
                _dispatch_bug_client("_dispatch_kevent_mach_msg_recv: "
                                "received overlarge message");
                return _dispatch_kevent_mach_msg_destroy(ke, hdr);
        }
        if (!dispatch_assume(name)) {
                _dispatch_bug_client("_dispatch_kevent_mach_msg_recv: "
                                "received message with MACH_PORT_NULL port");
                return _dispatch_kevent_mach_msg_destroy(ke, hdr);
        }
        _dispatch_debug_machport(name);
        if (ke->flags & EV_UDATA_SPECIFIC) {
                dk = (void*)ke->udata;
        } else {
                dk = _dispatch_kevent_find(name, EVFILT_MACHPORT);
        }
        if (!dispatch_assume(dk)) {
                _dispatch_bug_client("_dispatch_kevent_mach_msg_recv: "
                                "received message with unknown kevent");
                return _dispatch_kevent_mach_msg_destroy(ke, hdr);
        }
        TAILQ_FOREACH(dri, &dk->dk_sources, dr_list) {
                dispatch_source_t dsi = _dispatch_source_from_refs(dri);
                if (dsi->ds_pending_data_mask & _DISPATCH_MACH_RECV_DIRECT_FLAGS) {
                        return _dispatch_source_merge_mach_msg(dsi, dri, dk, ke, hdr, siz);
                }
        }
        _dispatch_bug_client("_dispatch_kevent_mach_msg_recv: "
                        "received message with no listeners");
        return _dispatch_kevent_mach_msg_destroy(ke, hdr);
}

static void
_dispatch_kevent_mach_msg_destroy(_dispatch_kevent_qos_s *ke,
                mach_msg_header_t *hdr)
{
        if (hdr) {
                mach_msg_destroy(hdr);
                if (hdr != _dispatch_kevent_mach_msg_buf(ke)) {
                        free(hdr);
                }
        }
}

static void
_dispatch_source_merge_mach_msg(dispatch_source_t ds, dispatch_source_refs_t dr,
                dispatch_kevent_t dk, _dispatch_kevent_qos_s *ke,
                mach_msg_header_t *hdr, mach_msg_size_t siz)
{
        if (dx_type(ds) == DISPATCH_SOURCE_KEVENT_TYPE) {
                return _dispatch_source_merge_mach_msg_direct(ds, ke, hdr);
        }
        dispatch_mach_reply_refs_t dmr = NULL;
        if (dk->dk_kevent.flags & EV_ONESHOT) {
                dmr = (dispatch_mach_reply_refs_t)dr;
        }
        return _dispatch_mach_msg_recv((dispatch_mach_t)ds, dmr, ke, hdr, siz);
}

DISPATCH_NOINLINE
static void
_dispatch_mach_notify_merge(mach_port_t name, uint32_t flag, bool final)
{
        dispatch_source_refs_t dri, dr_next;
        dispatch_kevent_t dk;
        bool unreg;

        dk = _dispatch_kevent_find(name, DISPATCH_EVFILT_MACH_NOTIFICATION);
        if (!dk) {
                return;
        }

        // Update notification registration state.
        dk->dk_kevent.data &= ~_DISPATCH_MACH_SP_FLAGS;
        _dispatch_kevent_qos_s kev = {
                .ident = name,
                .filter = DISPATCH_EVFILT_MACH_NOTIFICATION,
                .flags = EV_ADD|EV_ENABLE,
                .fflags = flag,
                .udata = (uintptr_t)dk,
        };
        if (final) {
                // This can never happen again
                unreg = true;
        } else {
                // Re-register for notification before delivery
                unreg = _dispatch_kevent_resume(dk, flag, 0);
        }
        DISPATCH_MACH_NOTIFICATION_ARMED(dk) = 0;
        TAILQ_FOREACH_SAFE(dri, &dk->dk_sources, dr_list, dr_next) {
                dispatch_source_t dsi = _dispatch_source_from_refs(dri);
                if (dx_type(dsi) == DISPATCH_MACH_CHANNEL_TYPE) {
                        dispatch_mach_t dm = (dispatch_mach_t)dsi;
                        _dispatch_mach_merge_notification_kevent(dm, &kev);
                        if (unreg && dm->dm_dkev) {
                                _dispatch_mach_notification_kevent_unregister(dm);
                        }
                } else {
                        _dispatch_source_merge_kevent(dsi, &kev);
                        if (unreg) {
                                _dispatch_source_kevent_unregister(dsi);
                        }
                }
                if (!dr_next || DISPATCH_MACH_NOTIFICATION_ARMED(dk)) {
                        // current merge is last in list (dk might have been freed)
                        // or it re-armed the notification
                        return;
                }
        }
}

static kern_return_t
_dispatch_mach_notify_update(dispatch_kevent_t dk, uint32_t new_flags,
                uint32_t del_flags, uint32_t mask, mach_msg_id_t notify_msgid,
                mach_port_mscount_t notify_sync)
{
        mach_port_t previous, port = (mach_port_t)dk->dk_kevent.ident;
        typeof(dk->dk_kevent.data) prev = dk->dk_kevent.data;
        kern_return_t kr, krr = 0;

        // Update notification registration state.
        dk->dk_kevent.data |= (new_flags | dk->dk_kevent.fflags) & mask;
        dk->dk_kevent.data &= ~(del_flags & mask);

        _dispatch_debug_machport(port);
        if ((dk->dk_kevent.data & mask) && !(prev & mask)) {
                _dispatch_debug("machport[0x%08x]: registering for send-possible "
                                "notification", port);
                previous = MACH_PORT_NULL;
                krr = mach_port_request_notification(mach_task_self(), port,
                                notify_msgid, notify_sync, _dispatch_get_mach_notify_port(),
                                MACH_MSG_TYPE_MAKE_SEND_ONCE, &previous);
                DISPATCH_VERIFY_MIG(krr);

                switch(krr) {
                case KERN_INVALID_NAME:
                case KERN_INVALID_RIGHT:
                        // Suppress errors & clear registration state
                        dk->dk_kevent.data &= ~mask;
                        break;
                default:
                        // Else, we don't expect any errors from mach. Log any errors
                        if (dispatch_assume_zero(krr)) {
                                // log the error & clear registration state
                                dk->dk_kevent.data &= ~mask;
                        } else if (dispatch_assume_zero(previous)) {
                                // Another subsystem has beat libdispatch to requesting the
                                // specified Mach notification on this port. We should
                                // technically cache the previous port and message it when the
                                // kernel messages our port. Or we can just say screw those
                                // subsystems and deallocate the previous port.
                                // They should adopt libdispatch :-P
                                kr = mach_port_deallocate(mach_task_self(), previous);
                                DISPATCH_VERIFY_MIG(kr);
                                (void)dispatch_assume_zero(kr);
                                previous = MACH_PORT_NULL;
                        }
                }
        } else if (!(dk->dk_kevent.data & mask) && (prev & mask)) {
                _dispatch_debug("machport[0x%08x]: unregistering for send-possible "
                                "notification", port);
                previous = MACH_PORT_NULL;
                kr = mach_port_request_notification(mach_task_self(), port,
                                notify_msgid, notify_sync, MACH_PORT_NULL,
                                MACH_MSG_TYPE_MOVE_SEND_ONCE, &previous);
                DISPATCH_VERIFY_MIG(kr);

                switch (kr) {
                case KERN_INVALID_NAME:
                case KERN_INVALID_RIGHT:
                case KERN_INVALID_ARGUMENT:
                        break;
                default:
                        if (dispatch_assume_zero(kr)) {
                                // log the error
                        }
                }
        } else {
                return 0;
        }
        if (slowpath(previous)) {
                // the kernel has not consumed the send-once right yet
                (void)dispatch_assume_zero(
                                _dispatch_send_consume_send_once_right(previous));
        }
        return krr;
}

static void
_dispatch_mach_host_notify_update(void *context DISPATCH_UNUSED)
{
        static int notify_type = HOST_NOTIFY_CALENDAR_SET;
        kern_return_t kr;
        _dispatch_debug("registering for calendar-change notification");
retry:
        kr = host_request_notification(_dispatch_get_mach_host_port(),
                        notify_type, _dispatch_get_mach_notify_port());
        // Fallback when missing support for newer _SET variant, fires strictly more.
        if (kr == KERN_INVALID_ARGUMENT &&
                notify_type != HOST_NOTIFY_CALENDAR_CHANGE){
                notify_type = HOST_NOTIFY_CALENDAR_CHANGE;
                goto retry;
        }
        DISPATCH_VERIFY_MIG(kr);
        (void)dispatch_assume_zero(kr);
}

static void
_dispatch_mach_host_calendar_change_register(void)
{
        static dispatch_once_t pred;
        dispatch_once_f(&pred, NULL, _dispatch_mach_host_notify_update);
}

static void
_dispatch_mach_notify_source_invoke(mach_msg_header_t *hdr)
{
        mig_reply_error_t reply;
        dispatch_assert(sizeof(mig_reply_error_t) == sizeof(union
                __ReplyUnion___dispatch_libdispatch_internal_protocol_subsystem));
        dispatch_assert(sizeof(mig_reply_error_t) < _dispatch_mach_recv_msg_size);
        boolean_t success = libdispatch_internal_protocol_server(hdr, &reply.Head);
        if (!success && reply.RetCode == MIG_BAD_ID &&
                        (hdr->msgh_id == HOST_CALENDAR_SET_REPLYID ||
                         hdr->msgh_id == HOST_CALENDAR_CHANGED_REPLYID)) {
                _dispatch_debug("calendar-change notification");
                _dispatch_timers_calendar_change();
                _dispatch_mach_host_notify_update(NULL);
                success = TRUE;
                reply.RetCode = KERN_SUCCESS;
        }
        if (dispatch_assume(success) && reply.RetCode != MIG_NO_REPLY) {
                (void)dispatch_assume_zero(reply.RetCode);
        }
        if (!success || (reply.RetCode && reply.RetCode != MIG_NO_REPLY)) {
                mach_msg_destroy(hdr);
        }
}

kern_return_t
_dispatch_mach_notify_port_deleted(mach_port_t notify DISPATCH_UNUSED,
                mach_port_name_t name)
{
#if DISPATCH_DEBUG
        _dispatch_log("Corruption: Mach send/send-once/dead-name right 0x%x "
                        "deleted prematurely", name);
#endif

        _dispatch_debug_machport(name);
        _dispatch_mach_notify_merge(name, DISPATCH_MACH_SEND_DELETED, true);

        return KERN_SUCCESS;
}

kern_return_t
_dispatch_mach_notify_dead_name(mach_port_t notify DISPATCH_UNUSED,
                mach_port_name_t name)
{
        kern_return_t kr;

        _dispatch_debug("machport[0x%08x]: dead-name notification", name);
        _dispatch_debug_machport(name);
        _dispatch_mach_notify_merge(name, DISPATCH_MACH_SEND_DEAD, true);

        // the act of receiving a dead name notification allocates a dead-name
        // right that must be deallocated
        kr = mach_port_deallocate(mach_task_self(), name);
        DISPATCH_VERIFY_MIG(kr);
        //(void)dispatch_assume_zero(kr);

        return KERN_SUCCESS;
}

kern_return_t
_dispatch_mach_notify_send_possible(mach_port_t notify DISPATCH_UNUSED,
                mach_port_name_t name)
{
        _dispatch_debug("machport[0x%08x]: send-possible notification", name);
        _dispatch_debug_machport(name);
        _dispatch_mach_notify_merge(name, DISPATCH_MACH_SEND_POSSIBLE, false);

        return KERN_SUCCESS;
}

#pragma mark -
#pragma mark dispatch_mach_t

#define DISPATCH_MACH_RETURN_IMMEDIATE_SEND_RESULT 0x1
#define DISPATCH_MACH_REGISTER_FOR_REPLY 0x2
#define DISPATCH_MACH_WAIT_FOR_REPLY 0x4
#define DISPATCH_MACH_OWNED_REPLY_PORT 0x8
#define DISPATCH_MACH_OPTIONS_MASK 0xffff

#define DM_SEND_STATUS_SUCCESS 0x1
#define DM_SEND_STATUS_RETURNING_IMMEDIATE_SEND_RESULT 0x2

DISPATCH_ENUM(dispatch_mach_send_invoke_flags, uint32_t,
        DM_SEND_INVOKE_NONE            = 0x0,
        DM_SEND_INVOKE_FLUSH           = 0x1,
        DM_SEND_INVOKE_NEEDS_BARRIER   = 0x2,
        DM_SEND_INVOKE_CANCEL          = 0x4,
        DM_SEND_INVOKE_CAN_RUN_BARRIER = 0x8,
        DM_SEND_INVOKE_IMMEDIATE_SEND  = 0x10,
);
#define DM_SEND_INVOKE_IMMEDIATE_SEND_MASK \
                ((dispatch_mach_send_invoke_flags_t)DM_SEND_INVOKE_IMMEDIATE_SEND)

static inline pthread_priority_t _dispatch_mach_priority_propagate(
                mach_msg_option_t options);
static mach_port_t _dispatch_mach_msg_get_remote_port(dispatch_object_t dou);
static mach_port_t _dispatch_mach_msg_get_reply_port(dispatch_object_t dou);
static void _dispatch_mach_msg_disconnected(dispatch_mach_t dm,
                mach_port_t local_port, mach_port_t remote_port);
static inline void _dispatch_mach_msg_reply_received(dispatch_mach_t dm,
                dispatch_mach_reply_refs_t dmr, mach_port_t local_port);
static dispatch_mach_msg_t _dispatch_mach_msg_create_reply_disconnected(
                dispatch_object_t dou, dispatch_mach_reply_refs_t dmr);
static bool _dispatch_mach_reconnect_invoke(dispatch_mach_t dm,
                dispatch_object_t dou);
static inline mach_msg_header_t* _dispatch_mach_msg_get_msg(
                dispatch_mach_msg_t dmsg);
static void _dispatch_mach_send_push(dispatch_mach_t dm, dispatch_object_t dou,
                pthread_priority_t pp);

static dispatch_mach_t
_dispatch_mach_create(const char *label, dispatch_queue_t q, void *context,
                dispatch_mach_handler_function_t handler, bool handler_is_block)
{
        dispatch_mach_t dm;
        dispatch_mach_refs_t dr;

        dm = _dispatch_alloc(DISPATCH_VTABLE(mach),
                        sizeof(struct dispatch_mach_s));
        _dispatch_queue_init(dm->_as_dq, DQF_NONE, 1, true);

        dm->dq_label = label;
        dm->do_ref_cnt++; // the reference _dispatch_mach_cancel_invoke holds

        dr = _dispatch_calloc(1ul, sizeof(struct dispatch_mach_refs_s));
        dr->dr_source_wref = _dispatch_ptr2wref(dm);
        dr->dm_handler_func = handler;
        dr->dm_handler_ctxt = context;
        dm->ds_refs = dr;
        dm->dm_handler_is_block = handler_is_block;

        dm->dm_refs = _dispatch_calloc(1ul,
                        sizeof(struct dispatch_mach_send_refs_s));
        dm->dm_refs->dr_source_wref = _dispatch_ptr2wref(dm);
        dm->dm_refs->dm_disconnect_cnt = DISPATCH_MACH_NEVER_CONNECTED;
        TAILQ_INIT(&dm->dm_refs->dm_replies);

        if (slowpath(!q)) {
                q = _dispatch_get_root_queue(_DISPATCH_QOS_CLASS_DEFAULT, true);
        } else {
                _dispatch_retain(q);
        }
        dm->do_targetq = q;
        _dispatch_object_debug(dm, "%s", __func__);
        return dm;
}

dispatch_mach_t
dispatch_mach_create(const char *label, dispatch_queue_t q,
                dispatch_mach_handler_t handler)
{
        dispatch_block_t bb = _dispatch_Block_copy((void*)handler);
        return _dispatch_mach_create(label, q, bb,
                        (dispatch_mach_handler_function_t)_dispatch_Block_invoke(bb), true);
}

dispatch_mach_t
dispatch_mach_create_f(const char *label, dispatch_queue_t q, void *context,
                dispatch_mach_handler_function_t handler)
{
        return _dispatch_mach_create(label, q, context, handler, false);
}

void
_dispatch_mach_dispose(dispatch_mach_t dm)
{
        _dispatch_object_debug(dm, "%s", __func__);
        dispatch_mach_refs_t dr = dm->ds_refs;
        if (dm->dm_handler_is_block && dr->dm_handler_ctxt) {
                Block_release(dr->dm_handler_ctxt);
        }
        free(dr);
        free(dm->dm_refs);
        _dispatch_queue_destroy(dm->_as_dq);
}

void
dispatch_mach_connect(dispatch_mach_t dm, mach_port_t receive,
                mach_port_t send, dispatch_mach_msg_t checkin)
{
        dispatch_mach_send_refs_t dr = dm->dm_refs;
        dispatch_kevent_t dk;
        uint32_t disconnect_cnt;
        dispatch_source_type_t type = &_dispatch_source_type_mach_recv_direct;

        dm->ds_is_direct_kevent = (bool)_dispatch_evfilt_machport_direct_enabled;
        if (MACH_PORT_VALID(receive)) {
                dk = _dispatch_calloc(1ul, sizeof(struct dispatch_kevent_s));
                dk->dk_kevent = type->ke;
                dk->dk_kevent.ident = receive;
                dk->dk_kevent.flags |= EV_ADD|EV_ENABLE|EV_VANISHED;
                dk->dk_kevent.udata = (uintptr_t)dk;
                TAILQ_INIT(&dk->dk_sources);
                dm->ds_dkev = dk;
                dm->ds_pending_data_mask = DISPATCH_MACH_RECV_MESSAGE_DIRECT;
                dm->ds_needs_rearm = dm->ds_is_direct_kevent;
                if (!dm->ds_is_direct_kevent) {
                        dk->dk_kevent.fflags = DISPATCH_MACH_RECV_MESSAGE_DIRECT;
                        dk->dk_kevent.flags &= ~(EV_UDATA_SPECIFIC|EV_VANISHED);
                }
                _dispatch_retain(dm); // the reference the manager queue holds
        }
        dr->dm_send = send;
        if (MACH_PORT_VALID(send)) {
                if (checkin) {
                        dispatch_retain(checkin);
                        checkin->dmsg_options = _dispatch_mach_checkin_options();
                        dr->dm_checkin_port = _dispatch_mach_msg_get_remote_port(checkin);
                }
                dr->dm_checkin = checkin;
        }
        // monitor message reply ports
        dm->ds_pending_data_mask |= DISPATCH_MACH_RECV_MESSAGE_DIRECT_ONCE;
        dispatch_assert(DISPATCH_MACH_NEVER_CONNECTED - 1 ==
                        DISPATCH_MACH_NEVER_INSTALLED);
        disconnect_cnt = os_atomic_dec2o(dr, dm_disconnect_cnt, release);
        if (unlikely(disconnect_cnt != DISPATCH_MACH_NEVER_INSTALLED)) {
                DISPATCH_CLIENT_CRASH(disconnect_cnt, "Channel already connected");
        }
        _dispatch_object_debug(dm, "%s", __func__);
        return dispatch_activate(dm);
}

// assumes low bit of mach port names is always set
#define DISPATCH_MACH_REPLY_PORT_UNOWNED 0x1u

static inline void
_dispatch_mach_reply_mark_reply_port_owned(dispatch_mach_reply_refs_t dmr)
{
        dmr->dmr_reply &= ~DISPATCH_MACH_REPLY_PORT_UNOWNED;
}

static inline bool
_dispatch_mach_reply_is_reply_port_owned(dispatch_mach_reply_refs_t dmr)
{
        mach_port_t reply_port = dmr->dmr_reply;
        return reply_port ? !(reply_port & DISPATCH_MACH_REPLY_PORT_UNOWNED) :false;
}

static inline mach_port_t
_dispatch_mach_reply_get_reply_port(dispatch_mach_reply_refs_t dmr)
{
        mach_port_t reply_port = dmr->dmr_reply;
        return reply_port ? (reply_port | DISPATCH_MACH_REPLY_PORT_UNOWNED) : 0;
}

static inline bool
_dispatch_mach_reply_tryremove(dispatch_mach_t dm,
                dispatch_mach_reply_refs_t dmr)
{
        bool removed;
        _dispatch_unfair_lock_lock(&dm->dm_refs->dm_replies_lock);
        if ((removed = _TAILQ_IS_ENQUEUED(dmr, dmr_list))) {
                TAILQ_REMOVE(&dm->dm_refs->dm_replies, dmr, dmr_list);
                _TAILQ_MARK_NOT_ENQUEUED(dmr, dmr_list);
        }
        _dispatch_unfair_lock_unlock(&dm->dm_refs->dm_replies_lock);
        return removed;
}

DISPATCH_NOINLINE
static void
_dispatch_mach_reply_waiter_unregister(dispatch_mach_t dm,
                dispatch_mach_reply_refs_t dmr, unsigned int options)
{
        dispatch_mach_msg_t dmsgr = NULL;
        bool disconnected = (options & DKEV_UNREGISTER_DISCONNECTED);
        if (options & DKEV_UNREGISTER_REPLY_REMOVE) {
                _dispatch_unfair_lock_lock(&dm->dm_refs->dm_replies_lock);
                if (unlikely(!_TAILQ_IS_ENQUEUED(dmr, dmr_list))) {
                        DISPATCH_INTERNAL_CRASH(0, "Could not find reply registration");
                }
                TAILQ_REMOVE(&dm->dm_refs->dm_replies, dmr, dmr_list);
                _TAILQ_MARK_NOT_ENQUEUED(dmr, dmr_list);
                _dispatch_unfair_lock_unlock(&dm->dm_refs->dm_replies_lock);
        }
        if (disconnected) {
                dmsgr = _dispatch_mach_msg_create_reply_disconnected(NULL, dmr);
        } else if (dmr->dmr_voucher) {
                _voucher_release(dmr->dmr_voucher);
                dmr->dmr_voucher = NULL;
        }
        _dispatch_debug("machport[0x%08x]: unregistering for sync reply%s, ctxt %p",
                        _dispatch_mach_reply_get_reply_port(dmr),
                        disconnected ? " (disconnected)" : "", dmr->dmr_ctxt);
        if (dmsgr) {
                return _dispatch_queue_push(dm->_as_dq, dmsgr, dmsgr->dmsg_priority);
        }
        dispatch_assert(!(options & DKEV_UNREGISTER_WAKEUP));
}

DISPATCH_NOINLINE
static void
_dispatch_mach_reply_kevent_unregister(dispatch_mach_t dm,
                dispatch_mach_reply_refs_t dmr, unsigned int options)
{
        dispatch_mach_msg_t dmsgr = NULL;
        bool replies_empty = false;
        bool disconnected = (options & DKEV_UNREGISTER_DISCONNECTED);
        if (options & DKEV_UNREGISTER_REPLY_REMOVE) {
                _dispatch_unfair_lock_lock(&dm->dm_refs->dm_replies_lock);
                if (unlikely(!_TAILQ_IS_ENQUEUED(dmr, dmr_list))) {
                        DISPATCH_INTERNAL_CRASH(0, "Could not find reply registration");
                }
                TAILQ_REMOVE(&dm->dm_refs->dm_replies, dmr, dmr_list);
                _TAILQ_MARK_NOT_ENQUEUED(dmr, dmr_list);
                replies_empty = TAILQ_EMPTY(&dm->dm_refs->dm_replies);
                _dispatch_unfair_lock_unlock(&dm->dm_refs->dm_replies_lock);
        }
        if (disconnected) {
                dmsgr = _dispatch_mach_msg_create_reply_disconnected(NULL, dmr);
        } else if (dmr->dmr_voucher) {
                _voucher_release(dmr->dmr_voucher);
                dmr->dmr_voucher = NULL;
        }
        uint32_t flags = DISPATCH_MACH_RECV_MESSAGE_DIRECT_ONCE;
        dispatch_kevent_t dk = dmr->dmr_dkev;
        _dispatch_debug("machport[0x%08x]: unregistering for reply%s, ctxt %p",
                        (mach_port_t)dk->dk_kevent.ident,
                        disconnected ? " (disconnected)" : "", dmr->dmr_ctxt);
        if (!dm->ds_is_direct_kevent) {
                dmr->dmr_dkev = NULL;
                TAILQ_REMOVE(&dk->dk_sources, (dispatch_source_refs_t)dmr, dr_list);
                _dispatch_kevent_unregister(dk, flags, 0);
        } else {
                long r = _dispatch_kevent_unregister(dk, flags, options);
                if (r == EINPROGRESS) {
                        _dispatch_debug("machport[0x%08x]: deferred delete kevent[%p]",
                                        (mach_port_t)dk->dk_kevent.ident, dk);
                        dispatch_assert(options == DKEV_UNREGISTER_DISCONNECTED);
                        // dmr must be put back so that the event delivery finds it, the
                        // replies lock is held by the caller.
                        TAILQ_INSERT_HEAD(&dm->dm_refs->dm_replies, dmr, dmr_list);
                        if (dmsgr) {
                                dmr->dmr_voucher = dmsgr->dmsg_voucher;
                                dmsgr->dmsg_voucher = NULL;
                                dispatch_release(dmsgr);
                        }
                        return; // deferred unregistration
                }
                dispatch_assume_zero(r);
                dmr->dmr_dkev = NULL;
                _TAILQ_TRASH_ENTRY(dmr, dr_list);
        }
        free(dmr);
        if (dmsgr) {
                return _dispatch_queue_push(dm->_as_dq, dmsgr, dmsgr->dmsg_priority);
        }
        if ((options & DKEV_UNREGISTER_WAKEUP) && replies_empty &&
                        (dm->dm_refs->dm_disconnect_cnt ||
                        (dm->dq_atomic_flags & DSF_CANCELED))) {
                dx_wakeup(dm, 0, DISPATCH_WAKEUP_FLUSH);
        }
}

DISPATCH_NOINLINE
static void
_dispatch_mach_reply_waiter_register(dispatch_mach_t dm,
                dispatch_mach_reply_refs_t dmr, mach_port_t reply_port,
                dispatch_mach_msg_t dmsg, mach_msg_option_t msg_opts)
{
        dmr->dr_source_wref = _dispatch_ptr2wref(dm);
        dmr->dmr_dkev = NULL;
        dmr->dmr_reply = reply_port;
        if (msg_opts & DISPATCH_MACH_OWNED_REPLY_PORT) {
                _dispatch_mach_reply_mark_reply_port_owned(dmr);
        } else {
                if (dmsg->dmsg_voucher) {
                        dmr->dmr_voucher = _voucher_retain(dmsg->dmsg_voucher);
                }
                dmr->dmr_priority = (dispatch_priority_t)dmsg->dmsg_priority;
                // make reply context visible to leaks rdar://11777199
                dmr->dmr_ctxt = dmsg->do_ctxt;
        }

        _dispatch_debug("machport[0x%08x]: registering for sync reply, ctxt %p",
                        reply_port, dmsg->do_ctxt);
        _dispatch_unfair_lock_lock(&dm->dm_refs->dm_replies_lock);
        if (unlikely(_TAILQ_IS_ENQUEUED(dmr, dmr_list))) {
                DISPATCH_INTERNAL_CRASH(dmr->dmr_list.tqe_prev, "Reply already registered");
        }
        TAILQ_INSERT_TAIL(&dm->dm_refs->dm_replies, dmr, dmr_list);
        _dispatch_unfair_lock_unlock(&dm->dm_refs->dm_replies_lock);
}

DISPATCH_NOINLINE
static void
_dispatch_mach_reply_kevent_register(dispatch_mach_t dm, mach_port_t reply_port,
                dispatch_mach_msg_t dmsg)
{
        dispatch_kevent_t dk;
        dispatch_mach_reply_refs_t dmr;
        dispatch_source_type_t type = &_dispatch_source_type_mach_recv_direct;
        pthread_priority_t mp, pp;

        dk = _dispatch_calloc(1ul, sizeof(struct dispatch_kevent_s));
        dk->dk_kevent = type->ke;
        dk->dk_kevent.ident = reply_port;
        dk->dk_kevent.flags |= EV_ADD|EV_ENABLE|EV_ONESHOT;
        dk->dk_kevent.udata = (uintptr_t)dk;
        TAILQ_INIT(&dk->dk_sources);
        if (!dm->ds_is_direct_kevent) {
                dk->dk_kevent.fflags = DISPATCH_MACH_RECV_MESSAGE_DIRECT_ONCE;
                dk->dk_kevent.flags &= ~(EV_UDATA_SPECIFIC|EV_VANISHED);
        }

        dmr = _dispatch_calloc(1ul, sizeof(struct dispatch_mach_reply_refs_s));
        dmr->dr_source_wref = _dispatch_ptr2wref(dm);
        dmr->dmr_dkev = dk;
        dmr->dmr_reply = reply_port;
        if (dmsg->dmsg_voucher) {
                dmr->dmr_voucher = _voucher_retain(dmsg->dmsg_voucher);
        }
        dmr->dmr_priority = (dispatch_priority_t)dmsg->dmsg_priority;
        // make reply context visible to leaks rdar://11777199
        dmr->dmr_ctxt = dmsg->do_ctxt;

        pp = dm->dq_priority & ~_PTHREAD_PRIORITY_FLAGS_MASK;
        if (pp && dm->ds_is_direct_kevent) {
                mp = dmsg->dmsg_priority & ~_PTHREAD_PRIORITY_FLAGS_MASK;
                if (pp < mp) pp = mp;
                pp |= dm->dq_priority & _PTHREAD_PRIORITY_OVERCOMMIT_FLAG;
        } else {
                pp = _PTHREAD_PRIORITY_EVENT_MANAGER_FLAG;
        }

        _dispatch_debug("machport[0x%08x]: registering for reply, ctxt %p",
                        reply_port, dmsg->do_ctxt);
        uint32_t flags;
        bool do_resume = _dispatch_kevent_register(&dmr->dmr_dkev, pp, &flags);
        TAILQ_INSERT_TAIL(&dmr->dmr_dkev->dk_sources, (dispatch_source_refs_t)dmr,
                        dr_list);
        _dispatch_unfair_lock_lock(&dm->dm_refs->dm_replies_lock);
        if (unlikely(_TAILQ_IS_ENQUEUED(dmr, dmr_list))) {
                DISPATCH_INTERNAL_CRASH(dmr->dmr_list.tqe_prev, "Reply already registered");
        }
        TAILQ_INSERT_TAIL(&dm->dm_refs->dm_replies, dmr, dmr_list);
        _dispatch_unfair_lock_unlock(&dm->dm_refs->dm_replies_lock);
        if (do_resume && _dispatch_kevent_resume(dmr->dmr_dkev, flags, 0)) {
                return _dispatch_mach_reply_kevent_unregister(dm, dmr,
                                DKEV_UNREGISTER_DISCONNECTED|DKEV_UNREGISTER_REPLY_REMOVE);
        }
}

DISPATCH_NOINLINE
static void
_dispatch_mach_notification_kevent_unregister(dispatch_mach_t dm)
{
        DISPATCH_ASSERT_ON_MANAGER_QUEUE();
        dispatch_kevent_t dk = dm->dm_dkev;
        dm->dm_dkev = NULL;
        TAILQ_REMOVE(&dk->dk_sources, (dispatch_source_refs_t)dm->dm_refs,
                        dr_list);
        dm->ds_pending_data_mask &= ~(unsigned long)
                        (DISPATCH_MACH_SEND_POSSIBLE|DISPATCH_MACH_SEND_DEAD);
        _dispatch_kevent_unregister(dk,
                        DISPATCH_MACH_SEND_POSSIBLE|DISPATCH_MACH_SEND_DEAD, 0);
}

DISPATCH_NOINLINE
static void
_dispatch_mach_notification_kevent_register(dispatch_mach_t dm,mach_port_t send)
{
        DISPATCH_ASSERT_ON_MANAGER_QUEUE();
        dispatch_kevent_t dk;

        dk = _dispatch_calloc(1ul, sizeof(struct dispatch_kevent_s));
        dk->dk_kevent = _dispatch_source_type_mach_send.ke;
        dk->dk_kevent.ident = send;
        dk->dk_kevent.flags |= EV_ADD|EV_ENABLE;
        dk->dk_kevent.fflags = DISPATCH_MACH_SEND_POSSIBLE|DISPATCH_MACH_SEND_DEAD;
        dk->dk_kevent.udata = (uintptr_t)dk;
        TAILQ_INIT(&dk->dk_sources);

        dm->ds_pending_data_mask |= dk->dk_kevent.fflags;

        uint32_t flags;
        bool do_resume = _dispatch_kevent_register(&dk,
                        _PTHREAD_PRIORITY_EVENT_MANAGER_FLAG, &flags);
        TAILQ_INSERT_TAIL(&dk->dk_sources,
                        (dispatch_source_refs_t)dm->dm_refs, dr_list);
        dm->dm_dkev = dk;
        if (do_resume && _dispatch_kevent_resume(dm->dm_dkev, flags, 0)) {
                _dispatch_mach_notification_kevent_unregister(dm);
        }
}

static mach_port_t
_dispatch_get_thread_reply_port(void)
{
        mach_port_t reply_port, mrp = _dispatch_get_thread_mig_reply_port();
        if (mrp) {
                reply_port = mrp;
                _dispatch_debug("machport[0x%08x]: borrowed thread sync reply port",
                                reply_port);
        } else {
                reply_port = mach_reply_port();
                _dispatch_set_thread_mig_reply_port(reply_port);
                _dispatch_debug("machport[0x%08x]: allocated thread sync reply port",
                                reply_port);
        }
        _dispatch_debug_machport(reply_port);
        return reply_port;
}

static void
_dispatch_clear_thread_reply_port(mach_port_t reply_port)
{
        mach_port_t mrp = _dispatch_get_thread_mig_reply_port();
        if (reply_port != mrp) {
                if (mrp) {
                        _dispatch_debug("machport[0x%08x]: did not clear thread sync reply "
                                        "port (found 0x%08x)", reply_port, mrp);
                }
                return;
        }
        _dispatch_set_thread_mig_reply_port(MACH_PORT_NULL);
        _dispatch_debug_machport(reply_port);
        _dispatch_debug("machport[0x%08x]: cleared thread sync reply port",
                        reply_port);
}

static void
_dispatch_set_thread_reply_port(mach_port_t reply_port)
{
        _dispatch_debug_machport(reply_port);
        mach_port_t mrp = _dispatch_get_thread_mig_reply_port();
        if (mrp) {
                kern_return_t kr = mach_port_mod_refs(mach_task_self(), reply_port,
                                MACH_PORT_RIGHT_RECEIVE, -1);
                DISPATCH_VERIFY_MIG(kr);
                dispatch_assume_zero(kr);
                _dispatch_debug("machport[0x%08x]: deallocated sync reply port "
                                "(found 0x%08x)", reply_port, mrp);
        } else {
                _dispatch_set_thread_mig_reply_port(reply_port);
                _dispatch_debug("machport[0x%08x]: restored thread sync reply port",
                                reply_port);
        }
}

static inline mach_port_t
_dispatch_mach_msg_get_remote_port(dispatch_object_t dou)
{
        mach_msg_header_t *hdr = _dispatch_mach_msg_get_msg(dou._dmsg);
        mach_port_t remote = hdr->msgh_remote_port;
        return remote;
}

static inline mach_port_t
_dispatch_mach_msg_get_reply_port(dispatch_object_t dou)
{
        mach_msg_header_t *hdr = _dispatch_mach_msg_get_msg(dou._dmsg);
        mach_port_t local = hdr->msgh_local_port;
        if (!MACH_PORT_VALID(local) || MACH_MSGH_BITS_LOCAL(hdr->msgh_bits) !=
                        MACH_MSG_TYPE_MAKE_SEND_ONCE) return MACH_PORT_NULL;
        return local;
}

static inline void
_dispatch_mach_msg_set_reason(dispatch_mach_msg_t dmsg, mach_error_t err,
                unsigned long reason)
{
        dispatch_assert_zero(reason & ~(unsigned long)code_emask);
        dmsg->dmsg_error = ((err || !reason) ? err :
                         err_local|err_sub(0x3e0)|(mach_error_t)reason);
}

static inline unsigned long
_dispatch_mach_msg_get_reason(dispatch_mach_msg_t dmsg, mach_error_t *err_ptr)
{
        mach_error_t err = dmsg->dmsg_error;

        dmsg->dmsg_error = 0;
        if ((err & system_emask) == err_local && err_get_sub(err) == 0x3e0) {
                *err_ptr = 0;
                return err_get_code(err);
        }
        *err_ptr = err;
        return err ? DISPATCH_MACH_MESSAGE_SEND_FAILED : DISPATCH_MACH_MESSAGE_SENT;
}

static void
_dispatch_mach_msg_recv(dispatch_mach_t dm, dispatch_mach_reply_refs_t dmr,
                _dispatch_kevent_qos_s *ke, mach_msg_header_t *hdr, mach_msg_size_t siz)
{
        _dispatch_debug_machport(hdr->msgh_remote_port);
        _dispatch_debug("machport[0x%08x]: received msg id 0x%x, reply on 0x%08x",
                        hdr->msgh_local_port, hdr->msgh_id, hdr->msgh_remote_port);
        bool canceled = (dm->dq_atomic_flags & DSF_CANCELED);
        if (!dmr && canceled) {
                // message received after cancellation, _dispatch_mach_kevent_merge is
                // responsible for mach channel source state (e.g. deferred deletion)
                return _dispatch_kevent_mach_msg_destroy(ke, hdr);
        }
        dispatch_mach_msg_t dmsg;
        voucher_t voucher;
        pthread_priority_t priority;
        void *ctxt = NULL;
        if (dmr) {
                _voucher_mach_msg_clear(hdr, false); // deallocate reply message voucher
                voucher = dmr->dmr_voucher;
                dmr->dmr_voucher = NULL; // transfer reference
                priority = dmr->dmr_priority;
                ctxt = dmr->dmr_ctxt;
                unsigned int options = DKEV_DISPOSE_IMMEDIATE_DELETE;
                options |= DKEV_UNREGISTER_REPLY_REMOVE;
                options |= DKEV_UNREGISTER_WAKEUP;
                if (canceled) options |= DKEV_UNREGISTER_DISCONNECTED;
                _dispatch_mach_reply_kevent_unregister(dm, dmr, options);
                ke->flags |= EV_DELETE; // remember that unregister deleted the event
                if (canceled) return;
        } else {
                voucher = voucher_create_with_mach_msg(hdr);
                priority = _voucher_get_priority(voucher);
        }
        dispatch_mach_msg_destructor_t destructor;
        destructor = (hdr == _dispatch_kevent_mach_msg_buf(ke)) ?
                        DISPATCH_MACH_MSG_DESTRUCTOR_DEFAULT :
                        DISPATCH_MACH_MSG_DESTRUCTOR_FREE;
        dmsg = dispatch_mach_msg_create(hdr, siz, destructor, NULL);
        if (hdr == _dispatch_kevent_mach_msg_buf(ke)) {
                _dispatch_ktrace2(DISPATCH_MACH_MSG_hdr_move, (uint64_t)hdr, (uint64_t)dmsg->dmsg_buf);
        }
        dmsg->dmsg_voucher = voucher;
        dmsg->dmsg_priority = priority;
        dmsg->do_ctxt = ctxt;
        _dispatch_mach_msg_set_reason(dmsg, 0, DISPATCH_MACH_MESSAGE_RECEIVED);
        _dispatch_voucher_debug("mach-msg[%p] create", voucher, dmsg);
        _dispatch_voucher_ktrace_dmsg_push(dmsg);
        return _dispatch_queue_push(dm->_as_dq, dmsg, dmsg->dmsg_priority);
}

DISPATCH_ALWAYS_INLINE
static inline dispatch_mach_msg_t
_dispatch_mach_msg_reply_recv(dispatch_mach_t dm,
                dispatch_mach_reply_refs_t dmr, mach_port_t reply_port)
{
        if (slowpath(!MACH_PORT_VALID(reply_port))) {
                DISPATCH_CLIENT_CRASH(reply_port, "Invalid reply port");
        }
        void *ctxt = dmr->dmr_ctxt;
        mach_msg_header_t *hdr, *hdr2 = NULL;
        void *hdr_copyout_addr;
        mach_msg_size_t siz, msgsiz = 0;
        mach_msg_return_t kr;
        mach_msg_option_t options;
        siz = mach_vm_round_page(_dispatch_mach_recv_msg_size +
                        dispatch_mach_trailer_size);
        hdr = alloca(siz);
        for (mach_vm_address_t p = mach_vm_trunc_page(hdr + vm_page_size);
                        p < (mach_vm_address_t)hdr + siz; p += vm_page_size) {
                *(char*)p = 0; // ensure alloca buffer doesn't overlap with stack guard
        }
        options = DISPATCH_MACH_RCV_OPTIONS & (~MACH_RCV_VOUCHER);
retry:
        _dispatch_debug_machport(reply_port);
        _dispatch_debug("machport[0x%08x]: MACH_RCV_MSG %s", reply_port,
                        (options & MACH_RCV_TIMEOUT) ? "poll" : "wait");
        kr = mach_msg(hdr, options, 0, siz, reply_port, MACH_MSG_TIMEOUT_NONE,
                        MACH_PORT_NULL);
        hdr_copyout_addr = hdr;
        _dispatch_debug_machport(reply_port);
        _dispatch_debug("machport[0x%08x]: MACH_RCV_MSG (size %u, opts 0x%x) "
                        "returned: %s - 0x%x", reply_port, siz, options,
                        mach_error_string(kr), kr);
        switch (kr) {
        case MACH_RCV_TOO_LARGE:
                if (!fastpath(hdr->msgh_size <= UINT_MAX -
                                dispatch_mach_trailer_size)) {
                        DISPATCH_CLIENT_CRASH(hdr->msgh_size, "Overlarge message");
                }
                if (options & MACH_RCV_LARGE) {
                        msgsiz = hdr->msgh_size + dispatch_mach_trailer_size;
                        hdr2 = malloc(msgsiz);
                        if (dispatch_assume(hdr2)) {
                                hdr = hdr2;
                                siz = msgsiz;
                        }
                        options |= MACH_RCV_TIMEOUT;
                        options &= ~MACH_RCV_LARGE;
                        goto retry;
                }
                _dispatch_log("BUG in libdispatch client: "
                                "dispatch_mach_send_and_wait_for_reply: dropped message too "
                                "large to fit in memory: id = 0x%x, size = %u", hdr->msgh_id,
                                hdr->msgh_size);
                break;
        case MACH_RCV_INVALID_NAME: // rdar://problem/21963848
        case MACH_RCV_PORT_CHANGED: // rdar://problem/21885327
        case MACH_RCV_PORT_DIED:
                // channel was disconnected/canceled and reply port destroyed
                _dispatch_debug("machport[0x%08x]: sync reply port destroyed, ctxt %p: "
                                "%s - 0x%x", reply_port, ctxt, mach_error_string(kr), kr);
                goto out;
        case MACH_MSG_SUCCESS:
                if (hdr->msgh_remote_port) {
                        _dispatch_debug_machport(hdr->msgh_remote_port);
                }
                _dispatch_debug("machport[0x%08x]: received msg id 0x%x, size = %u, "
                                "reply on 0x%08x", hdr->msgh_local_port, hdr->msgh_id,
                                hdr->msgh_size, hdr->msgh_remote_port);
                siz = hdr->msgh_size + dispatch_mach_trailer_size;
                if (hdr2 && siz < msgsiz) {
                        void *shrink = realloc(hdr2, msgsiz);
                        if (shrink) hdr = hdr2 = shrink;
                }
                break;
        default:
                dispatch_assume_zero(kr);
                break;
        }
        _dispatch_mach_msg_reply_received(dm, dmr, hdr->msgh_local_port);
        hdr->msgh_local_port = MACH_PORT_NULL;
        if (slowpath((dm->dq_atomic_flags & DSF_CANCELED) || kr)) {
                if (!kr) mach_msg_destroy(hdr);
                goto out;
        }
        dispatch_mach_msg_t dmsg;
        dispatch_mach_msg_destructor_t destructor = (!hdr2) ?
                        DISPATCH_MACH_MSG_DESTRUCTOR_DEFAULT :
                        DISPATCH_MACH_MSG_DESTRUCTOR_FREE;
        dmsg = dispatch_mach_msg_create(hdr, siz, destructor, NULL);
        if (!hdr2 || hdr != hdr_copyout_addr) {
                _dispatch_ktrace2(DISPATCH_MACH_MSG_hdr_move, (uint64_t)hdr_copyout_addr, (uint64_t)_dispatch_mach_msg_get_msg(dmsg));
        }
        dmsg->do_ctxt = ctxt;
        return dmsg;
out:
        free(hdr2);
        return NULL;
}

static inline void
_dispatch_mach_msg_reply_received(dispatch_mach_t dm,
                dispatch_mach_reply_refs_t dmr, mach_port_t local_port)
{
        bool removed = _dispatch_mach_reply_tryremove(dm, dmr);
        if (!MACH_PORT_VALID(local_port) || !removed) {
                // port moved/destroyed during receive, or reply waiter was never
                // registered or already removed (disconnected)
                return;
        }
        mach_port_t reply_port = _dispatch_mach_reply_get_reply_port(dmr);
        _dispatch_debug("machport[0x%08x]: unregistered for sync reply, ctxt %p",
                        reply_port, dmr->dmr_ctxt);
        if (_dispatch_mach_reply_is_reply_port_owned(dmr)) {
                _dispatch_set_thread_reply_port(reply_port);
                if (local_port != reply_port) {
                        DISPATCH_CLIENT_CRASH(local_port,
                                        "Reply received on unexpected port");
                }
                return;
        }
        mach_msg_header_t *hdr;
        dispatch_mach_msg_t dmsg;
        dmsg = dispatch_mach_msg_create(NULL, sizeof(mach_msg_header_t),
                        DISPATCH_MACH_MSG_DESTRUCTOR_DEFAULT, &hdr);
        hdr->msgh_local_port = local_port;
        dmsg->dmsg_voucher = dmr->dmr_voucher;
        dmr->dmr_voucher = NULL;  // transfer reference
        dmsg->dmsg_priority = dmr->dmr_priority;
        dmsg->do_ctxt = dmr->dmr_ctxt;
        _dispatch_mach_msg_set_reason(dmsg, 0, DISPATCH_MACH_REPLY_RECEIVED);
        return _dispatch_queue_push(dm->_as_dq, dmsg, dmsg->dmsg_priority);
}

static inline void
_dispatch_mach_msg_disconnected(dispatch_mach_t dm, mach_port_t local_port,
                mach_port_t remote_port)
{
        mach_msg_header_t *hdr;
        dispatch_mach_msg_t dmsg;
        dmsg = dispatch_mach_msg_create(NULL, sizeof(mach_msg_header_t),
                        DISPATCH_MACH_MSG_DESTRUCTOR_DEFAULT, &hdr);
        if (local_port) hdr->msgh_local_port = local_port;
        if (remote_port) hdr->msgh_remote_port = remote_port;
        _dispatch_mach_msg_set_reason(dmsg, 0, DISPATCH_MACH_DISCONNECTED);
        _dispatch_debug("machport[0x%08x]: %s right disconnected", local_port ?
                        local_port : remote_port, local_port ? "receive" : "send");
        return _dispatch_queue_push(dm->_as_dq, dmsg, dmsg->dmsg_priority);
}

static inline dispatch_mach_msg_t
_dispatch_mach_msg_create_reply_disconnected(dispatch_object_t dou,
                dispatch_mach_reply_refs_t dmr)
{
        dispatch_mach_msg_t dmsg = dou._dmsg, dmsgr;
        mach_port_t reply_port = dmsg ? dmsg->dmsg_reply :
                        _dispatch_mach_reply_get_reply_port(dmr);
        voucher_t v;

        if (!reply_port) {
                if (!dmsg) {
                        v = dmr->dmr_voucher;
                        dmr->dmr_voucher = NULL; // transfer reference
                        if (v) _voucher_release(v);
                }
                return NULL;
        }

        if (dmsg) {
                v = dmsg->dmsg_voucher;
                if (v) _voucher_retain(v);
        } else {
                v = dmr->dmr_voucher;
                dmr->dmr_voucher = NULL; // transfer reference
        }

        if ((dmsg && (dmsg->dmsg_options & DISPATCH_MACH_WAIT_FOR_REPLY) &&
                        (dmsg->dmsg_options & DISPATCH_MACH_OWNED_REPLY_PORT)) ||
                        (dmr && !dmr->dmr_dkev &&
                        _dispatch_mach_reply_is_reply_port_owned(dmr))) {
                if (v) _voucher_release(v);
                // deallocate owned reply port to break _dispatch_mach_msg_reply_recv
                // out of waiting in mach_msg(MACH_RCV_MSG)
                kern_return_t kr = mach_port_mod_refs(mach_task_self(), reply_port,
                                MACH_PORT_RIGHT_RECEIVE, -1);
                DISPATCH_VERIFY_MIG(kr);
                dispatch_assume_zero(kr);
                return NULL;
        }

        mach_msg_header_t *hdr;
        dmsgr = dispatch_mach_msg_create(NULL, sizeof(mach_msg_header_t),
                        DISPATCH_MACH_MSG_DESTRUCTOR_DEFAULT, &hdr);
        dmsgr->dmsg_voucher = v;
        hdr->msgh_local_port = reply_port;
        if (dmsg) {
                dmsgr->dmsg_priority = dmsg->dmsg_priority;
                dmsgr->do_ctxt = dmsg->do_ctxt;
        } else {
                dmsgr->dmsg_priority = dmr->dmr_priority;
                dmsgr->do_ctxt = dmr->dmr_ctxt;
        }
        _dispatch_mach_msg_set_reason(dmsgr, 0, DISPATCH_MACH_DISCONNECTED);
        _dispatch_debug("machport[0x%08x]: reply disconnected, ctxt %p",
                        hdr->msgh_local_port, dmsgr->do_ctxt);
        return dmsgr;
}

DISPATCH_NOINLINE
static void
_dispatch_mach_msg_not_sent(dispatch_mach_t dm, dispatch_object_t dou)
{
        dispatch_mach_msg_t dmsg = dou._dmsg, dmsgr;
        mach_msg_header_t *msg = _dispatch_mach_msg_get_msg(dmsg);
        mach_msg_option_t msg_opts = dmsg->dmsg_options;
        _dispatch_debug("machport[0x%08x]: not sent msg id 0x%x, ctxt %p, "
                        "msg_opts 0x%x, kvoucher 0x%08x, reply on 0x%08x",
                        msg->msgh_remote_port, msg->msgh_id, dmsg->do_ctxt,
                        msg_opts, msg->msgh_voucher_port, dmsg->dmsg_reply);
        unsigned long reason = (msg_opts & DISPATCH_MACH_REGISTER_FOR_REPLY) ?
                        0 : DISPATCH_MACH_MESSAGE_NOT_SENT;
        dmsgr = _dispatch_mach_msg_create_reply_disconnected(dmsg, NULL);
        _dispatch_mach_msg_set_reason(dmsg, 0, reason);
        _dispatch_queue_push(dm->_as_dq, dmsg, dmsg->dmsg_priority);
        if (dmsgr) _dispatch_queue_push(dm->_as_dq, dmsgr, dmsgr->dmsg_priority);
}

DISPATCH_NOINLINE
static uint32_t
_dispatch_mach_msg_send(dispatch_mach_t dm, dispatch_object_t dou,
                dispatch_mach_reply_refs_t dmr, pthread_priority_t pp,
                dispatch_mach_send_invoke_flags_t send_flags)
{
        dispatch_mach_send_refs_t dr = dm->dm_refs;
        dispatch_mach_msg_t dmsg = dou._dmsg, dmsgr = NULL;
        voucher_t voucher = dmsg->dmsg_voucher;
        mach_voucher_t ipc_kvoucher = MACH_VOUCHER_NULL;
        uint32_t send_status = 0;
        bool clear_voucher = false, kvoucher_move_send = false;
        mach_msg_header_t *msg = _dispatch_mach_msg_get_msg(dmsg);
        bool is_reply = (MACH_MSGH_BITS_REMOTE(msg->msgh_bits) ==
                        MACH_MSG_TYPE_MOVE_SEND_ONCE);
        mach_port_t reply_port = dmsg->dmsg_reply;
        if (!is_reply) {
                dr->dm_needs_mgr = 0;
                if (unlikely(dr->dm_checkin && dmsg != dr->dm_checkin)) {
                        // send initial checkin message
                        if (dm->dm_dkev && slowpath(_dispatch_queue_get_current() !=
                                        &_dispatch_mgr_q)) {
                                // send kevent must be uninstalled on the manager queue
                                dr->dm_needs_mgr = 1;
                                goto out;
                        }
                        if (unlikely(!_dispatch_mach_msg_send(dm,
                                        dr->dm_checkin, NULL, pp, DM_SEND_INVOKE_NONE))) {
                                goto out;
                        }
                        dr->dm_checkin = NULL;
                }
        }
        mach_msg_return_t kr = 0;
        mach_msg_option_t opts = 0, msg_opts = dmsg->dmsg_options;
        if (!(msg_opts & DISPATCH_MACH_REGISTER_FOR_REPLY)) {
                mach_msg_priority_t msg_priority = MACH_MSG_PRIORITY_UNSPECIFIED;
                opts = MACH_SEND_MSG | (msg_opts & ~DISPATCH_MACH_OPTIONS_MASK);
                if (!is_reply) {
                        if (dmsg != dr->dm_checkin) {
                                msg->msgh_remote_port = dr->dm_send;
                        }
                        if (_dispatch_queue_get_current() == &_dispatch_mgr_q) {
                                if (slowpath(!dm->dm_dkev)) {
                                        _dispatch_mach_notification_kevent_register(dm,
                                                        msg->msgh_remote_port);
                                }
                                if (fastpath(dm->dm_dkev)) {
                                        if (DISPATCH_MACH_NOTIFICATION_ARMED(dm->dm_dkev)) {
                                                goto out;
                                        }
                                        opts |= MACH_SEND_NOTIFY;
                                }
                        }
                        opts |= MACH_SEND_TIMEOUT;
                        if (dmsg->dmsg_priority != _voucher_get_priority(voucher)) {
                                ipc_kvoucher = _voucher_create_mach_voucher_with_priority(
                                                voucher, dmsg->dmsg_priority);
                        }
                        _dispatch_voucher_debug("mach-msg[%p] msg_set", voucher, dmsg);
                        if (ipc_kvoucher) {
                                kvoucher_move_send = true;
                                clear_voucher = _voucher_mach_msg_set_mach_voucher(msg,
                                                ipc_kvoucher, kvoucher_move_send);
                        } else {
                                clear_voucher = _voucher_mach_msg_set(msg, voucher);
                        }
                        if (pp && _dispatch_evfilt_machport_direct_enabled) {
                                opts |= MACH_SEND_OVERRIDE;
                                msg_priority = (mach_msg_priority_t)pp;
                        }
                }
                _dispatch_debug_machport(msg->msgh_remote_port);
                if (reply_port) _dispatch_debug_machport(reply_port);
                if (msg_opts & DISPATCH_MACH_WAIT_FOR_REPLY) {
                        if (msg_opts & DISPATCH_MACH_OWNED_REPLY_PORT) {
                                _dispatch_clear_thread_reply_port(reply_port);
                        }
                        _dispatch_mach_reply_waiter_register(dm, dmr, reply_port, dmsg,
                                        msg_opts);
                }
                kr = mach_msg(msg, opts, msg->msgh_size, 0, MACH_PORT_NULL, 0,
                                msg_priority);
                _dispatch_debug("machport[0x%08x]: sent msg id 0x%x, ctxt %p, "
                                "opts 0x%x, msg_opts 0x%x, kvoucher 0x%08x, reply on 0x%08x: "
                                "%s - 0x%x", msg->msgh_remote_port, msg->msgh_id, dmsg->do_ctxt,
                                opts, msg_opts, msg->msgh_voucher_port, reply_port,
                                mach_error_string(kr), kr);
                if (unlikely(kr && (msg_opts & DISPATCH_MACH_WAIT_FOR_REPLY))) {
                        _dispatch_mach_reply_waiter_unregister(dm, dmr,
                                        DKEV_UNREGISTER_REPLY_REMOVE);
                }
                if (clear_voucher) {
                        if (kr == MACH_SEND_INVALID_VOUCHER && msg->msgh_voucher_port) {
                                DISPATCH_CLIENT_CRASH(kr, "Voucher port corruption");
                        }
                        mach_voucher_t kv;
                        kv = _voucher_mach_msg_clear(msg, kvoucher_move_send);
                        if (kvoucher_move_send) ipc_kvoucher = kv;
                }
        }
        if (kr == MACH_SEND_TIMED_OUT && (opts & MACH_SEND_TIMEOUT)) {
                if (opts & MACH_SEND_NOTIFY) {
                        _dispatch_debug("machport[0x%08x]: send-possible notification "
                                        "armed", (mach_port_t)dm->dm_dkev->dk_kevent.ident);
                        DISPATCH_MACH_NOTIFICATION_ARMED(dm->dm_dkev) = 1;
                } else {
                        // send kevent must be installed on the manager queue
                        dr->dm_needs_mgr = 1;
                }
                if (ipc_kvoucher) {
                        _dispatch_kvoucher_debug("reuse on re-send", ipc_kvoucher);
                        voucher_t ipc_voucher;
                        ipc_voucher = _voucher_create_with_priority_and_mach_voucher(
                                        voucher, dmsg->dmsg_priority, ipc_kvoucher);
                        _dispatch_voucher_debug("mach-msg[%p] replace voucher[%p]",
                                        ipc_voucher, dmsg, voucher);
                        if (dmsg->dmsg_voucher) _voucher_release(dmsg->dmsg_voucher);
                        dmsg->dmsg_voucher = ipc_voucher;
                }
                goto out;
        } else if (ipc_kvoucher && (kr || !kvoucher_move_send)) {
                _voucher_dealloc_mach_voucher(ipc_kvoucher);
        }
        if (!(msg_opts & DISPATCH_MACH_WAIT_FOR_REPLY) && !kr && reply_port &&
                        !(dm->ds_dkev && dm->ds_dkev->dk_kevent.ident == reply_port)) {
                if (!dm->ds_is_direct_kevent &&
                                _dispatch_queue_get_current() != &_dispatch_mgr_q) {
                        // reply receive kevent must be installed on the manager queue
                        dr->dm_needs_mgr = 1;
                        dmsg->dmsg_options = msg_opts | DISPATCH_MACH_REGISTER_FOR_REPLY;
                        goto out;
                }
                _dispatch_mach_reply_kevent_register(dm, reply_port, dmsg);
        }
        if (unlikely(!is_reply && dmsg == dr->dm_checkin && dm->dm_dkev)) {
                _dispatch_mach_notification_kevent_unregister(dm);
        }
        if (slowpath(kr)) {
                // Send failed, so reply was never registered <rdar://problem/14309159>
                dmsgr = _dispatch_mach_msg_create_reply_disconnected(dmsg, NULL);
        }
        _dispatch_mach_msg_set_reason(dmsg, kr, 0);
        if ((send_flags & DM_SEND_INVOKE_IMMEDIATE_SEND) &&
                        (msg_opts & DISPATCH_MACH_RETURN_IMMEDIATE_SEND_RESULT)) {
                // Return sent message synchronously <rdar://problem/25947334>
                send_status |= DM_SEND_STATUS_RETURNING_IMMEDIATE_SEND_RESULT;
        } else {
                _dispatch_queue_push(dm->_as_dq, dmsg, dmsg->dmsg_priority);
        }
        if (dmsgr) _dispatch_queue_push(dm->_as_dq, dmsgr, dmsgr->dmsg_priority);
        send_status |= DM_SEND_STATUS_SUCCESS;
out:
        return send_status;
}

#pragma mark -
#pragma mark dispatch_mach_send_refs_t

static void _dispatch_mach_cancel(dispatch_mach_t dm);
static void _dispatch_mach_send_barrier_drain_push(dispatch_mach_t dm,
                pthread_priority_t pp);

DISPATCH_ALWAYS_INLINE
static inline pthread_priority_t
_dm_state_get_override(uint64_t dm_state)
{
        dm_state &= DISPATCH_MACH_STATE_OVERRIDE_MASK;
        return (pthread_priority_t)(dm_state >> 32);
}

DISPATCH_ALWAYS_INLINE
static inline uint64_t
_dm_state_override_from_priority(pthread_priority_t pp)
{
        uint64_t pp_state = pp & _PTHREAD_PRIORITY_QOS_CLASS_MASK;
        return pp_state << 32;
}

DISPATCH_ALWAYS_INLINE
static inline bool
_dm_state_needs_override(uint64_t dm_state, uint64_t pp_state)
{
        return (pp_state > (dm_state & DISPATCH_MACH_STATE_OVERRIDE_MASK));
}

DISPATCH_ALWAYS_INLINE
static inline uint64_t
_dm_state_merge_override(uint64_t dm_state, uint64_t pp_state)
{
        if (_dm_state_needs_override(dm_state, pp_state)) {
                dm_state &= ~DISPATCH_MACH_STATE_OVERRIDE_MASK;
                dm_state |= pp_state;
                dm_state |= DISPATCH_MACH_STATE_DIRTY;
                dm_state |= DISPATCH_MACH_STATE_RECEIVED_OVERRIDE;
        }
        return dm_state;
}

#define _dispatch_mach_send_push_update_tail(dr, tail) \
                os_mpsc_push_update_tail(dr, dm, tail, do_next)
#define _dispatch_mach_send_push_update_head(dr, head) \
                os_mpsc_push_update_head(dr, dm, head)
#define _dispatch_mach_send_get_head(dr) \
                os_mpsc_get_head(dr, dm)
#define _dispatch_mach_send_unpop_head(dr, dc, dc_next) \
                os_mpsc_undo_pop_head(dr, dm, dc, dc_next, do_next)
#define _dispatch_mach_send_pop_head(dr, head) \
                os_mpsc_pop_head(dr, dm, head, do_next)

DISPATCH_ALWAYS_INLINE
static inline bool
_dispatch_mach_send_push_inline(dispatch_mach_send_refs_t dr,
                dispatch_object_t dou)
{
        if (_dispatch_mach_send_push_update_tail(dr, dou._do)) {
                _dispatch_mach_send_push_update_head(dr, dou._do);
                return true;
        }
        return false;
}

DISPATCH_NOINLINE
static bool
_dispatch_mach_send_drain(dispatch_mach_t dm, dispatch_invoke_flags_t flags,
                dispatch_mach_send_invoke_flags_t send_flags)
{
        dispatch_mach_send_refs_t dr = dm->dm_refs;
        dispatch_mach_reply_refs_t dmr;
        dispatch_mach_msg_t dmsg;
        struct dispatch_object_s *dc = NULL, *next_dc = NULL;
        pthread_priority_t pp = _dm_state_get_override(dr->dm_state);
        uint64_t old_state, new_state;
        uint32_t send_status;
        bool needs_mgr, disconnecting, returning_send_result = false;

again:
        needs_mgr = false; disconnecting = false;
        while (dr->dm_tail) {
                dc = _dispatch_mach_send_get_head(dr);
                do {
                        dispatch_mach_send_invoke_flags_t sf = send_flags;
                        // Only request immediate send result for the first message
                        send_flags &= ~DM_SEND_INVOKE_IMMEDIATE_SEND_MASK;
                        next_dc = _dispatch_mach_send_pop_head(dr, dc);
                        if (_dispatch_object_has_type(dc,
                                        DISPATCH_CONTINUATION_TYPE(MACH_SEND_BARRIER))) {
                                if (!(send_flags & DM_SEND_INVOKE_CAN_RUN_BARRIER)) {
                                        goto partial_drain;
                                }
                                _dispatch_continuation_pop(dc, dm->_as_dq, flags);
                                continue;
                        }
                        if (_dispatch_object_is_slow_item(dc)) {
                                dmsg = ((dispatch_continuation_t)dc)->dc_data;
                                dmr = ((dispatch_continuation_t)dc)->dc_other;
                        } else if (_dispatch_object_has_vtable(dc)) {
                                dmsg = (dispatch_mach_msg_t)dc;
                                dmr = NULL;
                        } else {
                                if ((dm->dm_dkev || !dm->ds_is_direct_kevent) &&
                                                (_dispatch_queue_get_current() != &_dispatch_mgr_q)) {
                                        // send kevent must be uninstalled on the manager queue
                                        needs_mgr = true;
                                        goto partial_drain;
                                }
                                if (unlikely(!_dispatch_mach_reconnect_invoke(dm, dc))) {
                                        disconnecting = true;
                                        goto partial_drain;
                                }
                                continue;
                        }
                        _dispatch_voucher_ktrace_dmsg_pop(dmsg);
                        if (unlikely(dr->dm_disconnect_cnt ||
                                        (dm->dq_atomic_flags & DSF_CANCELED))) {
                                _dispatch_mach_msg_not_sent(dm, dmsg);
                                continue;
                        }
                        send_status = _dispatch_mach_msg_send(dm, dmsg, dmr, pp, sf);
                        if (unlikely(!send_status)) {
                                goto partial_drain;
                        }
                        if (send_status & DM_SEND_STATUS_RETURNING_IMMEDIATE_SEND_RESULT) {
                                returning_send_result = true;
                        }
                } while ((dc = next_dc));
        }

        os_atomic_rmw_loop2o(dr, dm_state, old_state, new_state, release, {
                if (old_state & DISPATCH_MACH_STATE_DIRTY) {
                        new_state = old_state;
                        new_state &= ~DISPATCH_MACH_STATE_DIRTY;
                        new_state &= ~DISPATCH_MACH_STATE_RECEIVED_OVERRIDE;
                        new_state &= ~DISPATCH_MACH_STATE_PENDING_BARRIER;
                } else {
                        // unlock
                        new_state = 0;
                }
        });
        goto out;

partial_drain:
        // if this is not a complete drain, we must undo some things
        _dispatch_mach_send_unpop_head(dr, dc, next_dc);

        if (_dispatch_object_has_type(dc,
                        DISPATCH_CONTINUATION_TYPE(MACH_SEND_BARRIER))) {
                os_atomic_rmw_loop2o(dr, dm_state, old_state, new_state, release, {
                        new_state = old_state;
                        new_state |= DISPATCH_MACH_STATE_DIRTY;
                        new_state |= DISPATCH_MACH_STATE_PENDING_BARRIER;
                        new_state &= ~DISPATCH_MACH_STATE_UNLOCK_MASK;
                });
        } else {
                os_atomic_rmw_loop2o(dr, dm_state, old_state, new_state, release, {
                        new_state = old_state;
                        if (old_state & (DISPATCH_MACH_STATE_DIRTY |
                                        DISPATCH_MACH_STATE_RECEIVED_OVERRIDE)) {
                                new_state &= ~DISPATCH_MACH_STATE_DIRTY;
                                new_state &= ~DISPATCH_MACH_STATE_RECEIVED_OVERRIDE;
                                new_state &= ~DISPATCH_MACH_STATE_PENDING_BARRIER;
                        } else {
                                new_state |= DISPATCH_MACH_STATE_DIRTY;
                                new_state &= ~DISPATCH_MACH_STATE_UNLOCK_MASK;
                        }
                });
        }

out:
        if (old_state & DISPATCH_MACH_STATE_RECEIVED_OVERRIDE) {
                // Ensure that the root queue sees that this thread was overridden.
                _dispatch_set_defaultpriority_override();
        }

        if (unlikely(new_state & DISPATCH_MACH_STATE_UNLOCK_MASK)) {
                os_atomic_thread_fence(acquire);
                pp = _dm_state_get_override(new_state);
                goto again;
        }

        if (new_state & DISPATCH_MACH_STATE_PENDING_BARRIER) {
                pp = _dm_state_get_override(new_state);
                _dispatch_mach_send_barrier_drain_push(dm, pp);
        } else {
                if (needs_mgr || dr->dm_needs_mgr) {
                        pp = _dm_state_get_override(new_state);
                } else {
                        pp = 0;
                }
                if (!disconnecting) dx_wakeup(dm, pp, DISPATCH_WAKEUP_FLUSH);
        }
        return returning_send_result;
}

DISPATCH_NOINLINE
static void
_dispatch_mach_send_invoke(dispatch_mach_t dm,
                dispatch_invoke_flags_t flags,
                dispatch_mach_send_invoke_flags_t send_flags)
{
        dispatch_lock_owner tid_self = _dispatch_tid_self();
        uint64_t old_state, new_state;
        pthread_priority_t pp_floor;

        uint64_t canlock_mask = DISPATCH_MACH_STATE_UNLOCK_MASK;
        uint64_t canlock_state = 0;

        if (send_flags & DM_SEND_INVOKE_NEEDS_BARRIER) {
                canlock_mask |= DISPATCH_MACH_STATE_PENDING_BARRIER;
                canlock_state = DISPATCH_MACH_STATE_PENDING_BARRIER;
        } else if (!(send_flags & DM_SEND_INVOKE_CAN_RUN_BARRIER)) {
                canlock_mask |= DISPATCH_MACH_STATE_PENDING_BARRIER;
        }

        if (flags & DISPATCH_INVOKE_MANAGER_DRAIN) {
                pp_floor = 0;
        } else {
                // _dispatch_queue_class_invoke will have applied the queue override
                // (if any) before we get here. Else use the default base priority
                // as an estimation of the priority we already asked for.
                pp_floor = dm->_as_dq->dq_override;
                if (!pp_floor) {
                        pp_floor = _dispatch_get_defaultpriority();
                        pp_floor &= _PTHREAD_PRIORITY_QOS_CLASS_MASK;
                }
        }

retry:
        os_atomic_rmw_loop2o(dm->dm_refs, dm_state, old_state, new_state, acquire, {
                new_state = old_state;
                if (unlikely((old_state & canlock_mask) != canlock_state)) {
                        if (!(send_flags & DM_SEND_INVOKE_FLUSH)) {
                                os_atomic_rmw_loop_give_up(break);
                        }
                        new_state |= DISPATCH_MACH_STATE_DIRTY;
                } else {
                        if (likely(pp_floor)) {
                                pthread_priority_t pp = _dm_state_get_override(old_state);
                                if (unlikely(pp > pp_floor)) {
                                        os_atomic_rmw_loop_give_up({
                                                _dispatch_wqthread_override_start(tid_self, pp);
                                                // Ensure that the root queue sees
                                                // that this thread was overridden.
                                                _dispatch_set_defaultpriority_override();
                                                pp_floor = pp;
                                                goto retry;
                                        });
                                }
                        }
                        new_state |= tid_self;
                        new_state &= ~DISPATCH_MACH_STATE_DIRTY;
                        new_state &= ~DISPATCH_MACH_STATE_RECEIVED_OVERRIDE;
                        new_state &= ~DISPATCH_MACH_STATE_PENDING_BARRIER;
                }
        });

        if (unlikely((old_state & canlock_mask) != canlock_state)) {
                return;
        }
        if (send_flags & DM_SEND_INVOKE_CANCEL) {
                _dispatch_mach_cancel(dm);
        }
        _dispatch_mach_send_drain(dm, flags, send_flags);
}

DISPATCH_NOINLINE
void
_dispatch_mach_send_barrier_drain_invoke(dispatch_continuation_t dc,
                dispatch_invoke_flags_t flags)
{
        dispatch_mach_t dm = (dispatch_mach_t)_dispatch_queue_get_current();
        uintptr_t dc_flags = DISPATCH_OBJ_CONSUME_BIT;
        dispatch_thread_frame_s dtf;

        DISPATCH_COMPILER_CAN_ASSUME(dc->dc_priority == DISPATCH_NO_PRIORITY);
        DISPATCH_COMPILER_CAN_ASSUME(dc->dc_voucher == DISPATCH_NO_VOUCHER);
        // hide the mach channel (see _dispatch_mach_barrier_invoke comment)
        _dispatch_thread_frame_stash(&dtf);
        _dispatch_continuation_pop_forwarded(dc, DISPATCH_NO_VOUCHER, dc_flags,{
                _dispatch_mach_send_invoke(dm, flags,
                                DM_SEND_INVOKE_NEEDS_BARRIER | DM_SEND_INVOKE_CAN_RUN_BARRIER);
        });
        _dispatch_thread_frame_unstash(&dtf);
}

DISPATCH_NOINLINE
static void
_dispatch_mach_send_barrier_drain_push(dispatch_mach_t dm,
                pthread_priority_t pp)
{
        dispatch_continuation_t dc = _dispatch_continuation_alloc();

        dc->do_vtable = DC_VTABLE(MACH_SEND_BARRRIER_DRAIN);
        dc->dc_func = NULL;
        dc->dc_ctxt = NULL;
        dc->dc_voucher = DISPATCH_NO_VOUCHER;
        dc->dc_priority = DISPATCH_NO_PRIORITY;
        return _dispatch_queue_push(dm->_as_dq, dc, pp);
}

DISPATCH_NOINLINE
static void
_dispatch_mach_send_push(dispatch_mach_t dm, dispatch_continuation_t dc,
                pthread_priority_t pp)
{
        dispatch_mach_send_refs_t dr = dm->dm_refs;
        uint64_t pp_state, old_state, new_state, state_flags = 0;
        dispatch_lock_owner owner;
        bool wakeup;

        // <rdar://problem/25896179> when pushing a send barrier that destroys
        // the last reference to this channel, and the send queue is already
        // draining on another thread, the send barrier may run as soon as
        // _dispatch_mach_send_push_inline() returns.
        _dispatch_retain(dm);
        pp_state = _dm_state_override_from_priority(pp);

        wakeup = _dispatch_mach_send_push_inline(dr, dc);
        if (wakeup) {
                state_flags = DISPATCH_MACH_STATE_DIRTY;
                if (dc->do_vtable == DC_VTABLE(MACH_SEND_BARRIER)) {
                        state_flags |= DISPATCH_MACH_STATE_PENDING_BARRIER;
                }
        }

        if (state_flags) {
                os_atomic_rmw_loop2o(dr, dm_state, old_state, new_state, release, {
                        new_state = _dm_state_merge_override(old_state, pp_state);
                        new_state |= state_flags;
                });
        } else {
                os_atomic_rmw_loop2o(dr, dm_state, old_state, new_state, relaxed, {
                        new_state = _dm_state_merge_override(old_state, pp_state);
                        if (old_state == new_state) {
                                os_atomic_rmw_loop_give_up(break);
                        }
                });
        }

        pp = _dm_state_get_override(new_state);
        owner = _dispatch_lock_owner((dispatch_lock)old_state);
        if (owner) {
                if (_dm_state_needs_override(old_state, pp_state)) {
                        _dispatch_wqthread_override_start_check_owner(owner, pp,
                                        &dr->dm_state_lock.dul_lock);
                }
                return _dispatch_release_tailcall(dm);
        }

        dispatch_wakeup_flags_t wflags = 0;
        if (state_flags & DISPATCH_MACH_STATE_PENDING_BARRIER) {
                _dispatch_mach_send_barrier_drain_push(dm, pp);
        } else if (wakeup || dr->dm_disconnect_cnt ||
                        (dm->dq_atomic_flags & DSF_CANCELED)) {
                wflags = DISPATCH_WAKEUP_FLUSH | DISPATCH_WAKEUP_CONSUME;
        } else if (old_state & DISPATCH_MACH_STATE_PENDING_BARRIER) {
                wflags = DISPATCH_WAKEUP_OVERRIDING | DISPATCH_WAKEUP_CONSUME;
        }
        if (wflags) {
                return dx_wakeup(dm, pp, wflags);
        }
        return _dispatch_release_tailcall(dm);
}

DISPATCH_NOINLINE
static bool
_dispatch_mach_send_push_and_trydrain(dispatch_mach_t dm,
                dispatch_object_t dou, pthread_priority_t pp,
                dispatch_mach_send_invoke_flags_t send_flags)
{
        dispatch_mach_send_refs_t dr = dm->dm_refs;
        dispatch_lock_owner tid_self = _dispatch_tid_self();
        uint64_t pp_state, old_state, new_state, canlock_mask, state_flags = 0;
        dispatch_lock_owner owner;

        pp_state = _dm_state_override_from_priority(pp);
        bool wakeup = _dispatch_mach_send_push_inline(dr, dou);
        if (wakeup) {
                state_flags = DISPATCH_MACH_STATE_DIRTY;
        }

        if (unlikely(dr->dm_disconnect_cnt ||
                        (dm->dq_atomic_flags & DSF_CANCELED))) {
                os_atomic_rmw_loop2o(dr, dm_state, old_state, new_state, release, {
                        new_state = _dm_state_merge_override(old_state, pp_state);
                        new_state |= state_flags;
                });
                dx_wakeup(dm, pp, DISPATCH_WAKEUP_FLUSH);
                return false;
        }

        canlock_mask = DISPATCH_MACH_STATE_UNLOCK_MASK |
                        DISPATCH_MACH_STATE_PENDING_BARRIER;
        if (state_flags) {
                os_atomic_rmw_loop2o(dr, dm_state, old_state, new_state, seq_cst, {
                        new_state = _dm_state_merge_override(old_state, pp_state);
                        new_state |= state_flags;
                        if (likely((old_state & canlock_mask) == 0)) {
                                new_state |= tid_self;
                                new_state &= ~DISPATCH_MACH_STATE_DIRTY;
                                new_state &= ~DISPATCH_MACH_STATE_RECEIVED_OVERRIDE;
                                new_state &= ~DISPATCH_MACH_STATE_PENDING_BARRIER;
                        }
                });
        } else {
                os_atomic_rmw_loop2o(dr, dm_state, old_state, new_state, acquire, {
                        new_state = _dm_state_merge_override(old_state, pp_state);
                        if (new_state == old_state) {
                                os_atomic_rmw_loop_give_up(return false);
                        }
                        if (likely((old_state & canlock_mask) == 0)) {
                                new_state |= tid_self;
                                new_state &= ~DISPATCH_MACH_STATE_DIRTY;
                                new_state &= ~DISPATCH_MACH_STATE_RECEIVED_OVERRIDE;
                                new_state &= ~DISPATCH_MACH_STATE_PENDING_BARRIER;
                        }
                });
        }

        owner = _dispatch_lock_owner((dispatch_lock)old_state);
        if (owner) {
                if (_dm_state_needs_override(old_state, pp_state)) {
                        _dispatch_wqthread_override_start_check_owner(owner, pp,
                                        &dr->dm_state_lock.dul_lock);
                }
                return false;
        }

        if (old_state & DISPATCH_MACH_STATE_PENDING_BARRIER) {
                dx_wakeup(dm, pp, DISPATCH_WAKEUP_OVERRIDING);
                return false;
        }

        // Ensure our message is still at the head of the queue and has not already
        // been dequeued by another thread that raced us to the send queue lock.
        // A plain load of the head and comparison against our object pointer is
        // sufficient.
        if (unlikely(!(wakeup && dou._do == dr->dm_head))) {
                // Don't request immediate send result for messages we don't own
                send_flags &= ~DM_SEND_INVOKE_IMMEDIATE_SEND_MASK;
        }
        return _dispatch_mach_send_drain(dm, DISPATCH_INVOKE_NONE, send_flags);
}

static void
_dispatch_mach_merge_notification_kevent(dispatch_mach_t dm,
                const _dispatch_kevent_qos_s *ke)
{
        if (!(ke->fflags & dm->ds_pending_data_mask)) {
                return;
        }
        _dispatch_mach_send_invoke(dm, DISPATCH_INVOKE_MANAGER_DRAIN,
                        DM_SEND_INVOKE_FLUSH);
}

#pragma mark -
#pragma mark dispatch_mach_t

static inline mach_msg_option_t
_dispatch_mach_checkin_options(void)
{
        mach_msg_option_t options = 0;
#if DISPATCH_USE_CHECKIN_NOIMPORTANCE
        options = MACH_SEND_NOIMPORTANCE; // <rdar://problem/16996737>
#endif
        return options;
}


static inline mach_msg_option_t
_dispatch_mach_send_options(void)
{
        mach_msg_option_t options = 0;
        return options;
}

DISPATCH_ALWAYS_INLINE
static inline pthread_priority_t
_dispatch_mach_priority_propagate(mach_msg_option_t options)
{
#if DISPATCH_USE_NOIMPORTANCE_QOS
        if (options & MACH_SEND_NOIMPORTANCE) return 0;
#else
        (void)options;
#endif
        return _dispatch_priority_propagate();
}

DISPATCH_NOINLINE
static bool
_dispatch_mach_send_msg(dispatch_mach_t dm, dispatch_mach_msg_t dmsg,
                dispatch_continuation_t dc_wait, mach_msg_option_t options)
{
        dispatch_mach_send_refs_t dr = dm->dm_refs;
        if (slowpath(dmsg->do_next != DISPATCH_OBJECT_LISTLESS)) {
                DISPATCH_CLIENT_CRASH(dmsg->do_next, "Message already enqueued");
        }
        dispatch_retain(dmsg);
        pthread_priority_t priority = _dispatch_mach_priority_propagate(options);
        options |= _dispatch_mach_send_options();
        dmsg->dmsg_options = options;
        mach_msg_header_t *msg = _dispatch_mach_msg_get_msg(dmsg);
        dmsg->dmsg_reply = _dispatch_mach_msg_get_reply_port(dmsg);
        bool is_reply = (MACH_MSGH_BITS_REMOTE(msg->msgh_bits) ==
                        MACH_MSG_TYPE_MOVE_SEND_ONCE);
        dmsg->dmsg_priority = priority;
        dmsg->dmsg_voucher = _voucher_copy();
        _dispatch_voucher_debug("mach-msg[%p] set", dmsg->dmsg_voucher, dmsg);

        uint32_t send_status;
        bool returning_send_result = false;
        dispatch_mach_send_invoke_flags_t send_flags = DM_SEND_INVOKE_NONE;
        if (options & DISPATCH_MACH_RETURN_IMMEDIATE_SEND_RESULT) {
                send_flags = DM_SEND_INVOKE_IMMEDIATE_SEND;
        }
        if (is_reply && !dmsg->dmsg_reply && !dr->dm_disconnect_cnt &&
                        !(dm->dq_atomic_flags & DSF_CANCELED)) {
                // replies are sent to a send-once right and don't need the send queue
                dispatch_assert(!dc_wait);
                send_status = _dispatch_mach_msg_send(dm, dmsg, NULL, 0, send_flags);
                dispatch_assert(send_status);
                returning_send_result = !!(send_status &
                                DM_SEND_STATUS_RETURNING_IMMEDIATE_SEND_RESULT);
        } else {
                _dispatch_voucher_ktrace_dmsg_push(dmsg);
                priority &= _PTHREAD_PRIORITY_QOS_CLASS_MASK;
                dispatch_object_t dou = { ._dmsg = dmsg };
                if (dc_wait) dou._dc = dc_wait;
                returning_send_result = _dispatch_mach_send_push_and_trydrain(dm, dou,
                                priority, send_flags);
        }
        if (returning_send_result) {
                _dispatch_voucher_debug("mach-msg[%p] clear", dmsg->dmsg_voucher, dmsg);
                if (dmsg->dmsg_voucher) _voucher_release(dmsg->dmsg_voucher);
                dmsg->dmsg_voucher = NULL;
                dmsg->do_next = DISPATCH_OBJECT_LISTLESS;
                dispatch_release(dmsg);
        }
        return returning_send_result;
}

DISPATCH_NOINLINE
void
dispatch_mach_send(dispatch_mach_t dm, dispatch_mach_msg_t dmsg,
                mach_msg_option_t options)
{
        dispatch_assert_zero(options & DISPATCH_MACH_OPTIONS_MASK);
        options &= ~DISPATCH_MACH_OPTIONS_MASK;
        bool returned_send_result = _dispatch_mach_send_msg(dm, dmsg, NULL,options);
        dispatch_assert(!returned_send_result);
}

DISPATCH_NOINLINE
void
dispatch_mach_send_with_result(dispatch_mach_t dm, dispatch_mach_msg_t dmsg,
                mach_msg_option_t options, dispatch_mach_send_flags_t send_flags,
                dispatch_mach_reason_t *send_result, mach_error_t *send_error)
{
        if (unlikely(send_flags != DISPATCH_MACH_SEND_DEFAULT)) {
                DISPATCH_CLIENT_CRASH(send_flags, "Invalid send flags");
        }
        dispatch_assert_zero(options & DISPATCH_MACH_OPTIONS_MASK);
        options &= ~DISPATCH_MACH_OPTIONS_MASK;
        options |= DISPATCH_MACH_RETURN_IMMEDIATE_SEND_RESULT;
        bool returned_send_result = _dispatch_mach_send_msg(dm, dmsg, NULL,options);
        unsigned long reason = DISPATCH_MACH_NEEDS_DEFERRED_SEND;
        mach_error_t err = 0;
        if (returned_send_result) {
                reason = _dispatch_mach_msg_get_reason(dmsg, &err);
        }
        *send_result = reason;
        *send_error = err;
}

static inline
dispatch_mach_msg_t
_dispatch_mach_send_and_wait_for_reply(dispatch_mach_t dm,
                dispatch_mach_msg_t dmsg, mach_msg_option_t options,
                bool *returned_send_result)
{
        mach_port_t reply_port = _dispatch_mach_msg_get_reply_port(dmsg);
        if (!reply_port) {
                // use per-thread mach reply port <rdar://24597802>
                reply_port = _dispatch_get_thread_reply_port();
                mach_msg_header_t *hdr = _dispatch_mach_msg_get_msg(dmsg);
                dispatch_assert(MACH_MSGH_BITS_LOCAL(hdr->msgh_bits) ==
                                MACH_MSG_TYPE_MAKE_SEND_ONCE);
                hdr->msgh_local_port = reply_port;
                options |= DISPATCH_MACH_OWNED_REPLY_PORT;
        }

        dispatch_mach_reply_refs_t dmr;
#if DISPATCH_DEBUG
        dmr = _dispatch_calloc(1, sizeof(*dmr));
#else
        struct dispatch_mach_reply_refs_s dmr_buf = { };
        dmr = &dmr_buf;
#endif
        struct dispatch_continuation_s dc_wait = {
                .dc_flags = DISPATCH_OBJ_SYNC_SLOW_BIT,
                .dc_data = dmsg,
                .dc_other = dmr,
                .dc_priority = DISPATCH_NO_PRIORITY,
                .dc_voucher = DISPATCH_NO_VOUCHER,
        };
        dmr->dmr_ctxt = dmsg->do_ctxt;
        *returned_send_result = _dispatch_mach_send_msg(dm, dmsg, &dc_wait,options);
        if (options & DISPATCH_MACH_OWNED_REPLY_PORT) {
                _dispatch_clear_thread_reply_port(reply_port);
        }
        dmsg = _dispatch_mach_msg_reply_recv(dm, dmr, reply_port);
#if DISPATCH_DEBUG
        free(dmr);
#endif
        return dmsg;
}

DISPATCH_NOINLINE
dispatch_mach_msg_t
dispatch_mach_send_and_wait_for_reply(dispatch_mach_t dm,
                dispatch_mach_msg_t dmsg, mach_msg_option_t options)
{
        bool returned_send_result;
        dispatch_mach_msg_t reply;
        dispatch_assert_zero(options & DISPATCH_MACH_OPTIONS_MASK);
        options &= ~DISPATCH_MACH_OPTIONS_MASK;
        options |= DISPATCH_MACH_WAIT_FOR_REPLY;
        reply = _dispatch_mach_send_and_wait_for_reply(dm, dmsg, options,
                        &returned_send_result);
        dispatch_assert(!returned_send_result);
        return reply;
}

DISPATCH_NOINLINE
dispatch_mach_msg_t
dispatch_mach_send_with_result_and_wait_for_reply(dispatch_mach_t dm,
                dispatch_mach_msg_t dmsg, mach_msg_option_t options,
                dispatch_mach_send_flags_t send_flags,
                dispatch_mach_reason_t *send_result, mach_error_t *send_error)
{
        if (unlikely(send_flags != DISPATCH_MACH_SEND_DEFAULT)) {
                DISPATCH_CLIENT_CRASH(send_flags, "Invalid send flags");
        }
        bool returned_send_result;
        dispatch_mach_msg_t reply;
        dispatch_assert_zero(options & DISPATCH_MACH_OPTIONS_MASK);
        options &= ~DISPATCH_MACH_OPTIONS_MASK;
        options |= DISPATCH_MACH_WAIT_FOR_REPLY;
        options |= DISPATCH_MACH_RETURN_IMMEDIATE_SEND_RESULT;
        reply = _dispatch_mach_send_and_wait_for_reply(dm, dmsg, options,
                        &returned_send_result);
        unsigned long reason = DISPATCH_MACH_NEEDS_DEFERRED_SEND;
        mach_error_t err = 0;
        if (returned_send_result) {
                reason = _dispatch_mach_msg_get_reason(dmsg, &err);
        }
        *send_result = reason;
        *send_error = err;
        return reply;
}

DISPATCH_NOINLINE
static bool
_dispatch_mach_disconnect(dispatch_mach_t dm)
{
        dispatch_mach_send_refs_t dr = dm->dm_refs;
        bool disconnected;
        if (dm->dm_dkev) {
                _dispatch_mach_notification_kevent_unregister(dm);
        }
        if (MACH_PORT_VALID(dr->dm_send)) {
                _dispatch_mach_msg_disconnected(dm, MACH_PORT_NULL, dr->dm_send);
        }
        dr->dm_send = MACH_PORT_NULL;
        if (dr->dm_checkin) {
                _dispatch_mach_msg_not_sent(dm, dr->dm_checkin);
                dr->dm_checkin = NULL;
        }
        _dispatch_unfair_lock_lock(&dm->dm_refs->dm_replies_lock);
        dispatch_mach_reply_refs_t dmr, tmp;
        TAILQ_FOREACH_SAFE(dmr, &dm->dm_refs->dm_replies, dmr_list, tmp) {
                TAILQ_REMOVE(&dm->dm_refs->dm_replies, dmr, dmr_list);
                _TAILQ_MARK_NOT_ENQUEUED(dmr, dmr_list);
                if (dmr->dmr_dkev) {
                        _dispatch_mach_reply_kevent_unregister(dm, dmr,
                                        DKEV_UNREGISTER_DISCONNECTED);
                } else {
                        _dispatch_mach_reply_waiter_unregister(dm, dmr,
                                        DKEV_UNREGISTER_DISCONNECTED);
                }
        }
        disconnected = TAILQ_EMPTY(&dm->dm_refs->dm_replies);
        _dispatch_unfair_lock_unlock(&dm->dm_refs->dm_replies_lock);
        return disconnected;
}

static void
_dispatch_mach_cancel(dispatch_mach_t dm)
{
        _dispatch_object_debug(dm, "%s", __func__);
        if (!_dispatch_mach_disconnect(dm)) return;
        if (dm->ds_dkev) {
                mach_port_t local_port = (mach_port_t)dm->ds_dkev->dk_kevent.ident;
                _dispatch_source_kevent_unregister(dm->_as_ds);
                if ((dm->dq_atomic_flags & DSF_STATE_MASK) == DSF_DELETED) {
                        _dispatch_mach_msg_disconnected(dm, local_port, MACH_PORT_NULL);
                }
        } else {
                _dispatch_queue_atomic_flags_set_and_clear(dm->_as_dq, DSF_DELETED,
                                DSF_ARMED | DSF_DEFERRED_DELETE);
        }
}

DISPATCH_NOINLINE
static bool
_dispatch_mach_reconnect_invoke(dispatch_mach_t dm, dispatch_object_t dou)
{
        if (!_dispatch_mach_disconnect(dm)) return false;
        dispatch_mach_send_refs_t dr = dm->dm_refs;
        dr->dm_checkin = dou._dc->dc_data;
        dr->dm_send = (mach_port_t)dou._dc->dc_other;
        _dispatch_continuation_free(dou._dc);
        (void)os_atomic_dec2o(dr, dm_disconnect_cnt, relaxed);
        _dispatch_object_debug(dm, "%s", __func__);
        _dispatch_release(dm); // <rdar://problem/26266265>
        return true;
}

DISPATCH_NOINLINE
void
dispatch_mach_reconnect(dispatch_mach_t dm, mach_port_t send,
                dispatch_mach_msg_t checkin)
{
        dispatch_mach_send_refs_t dr = dm->dm_refs;
        (void)os_atomic_inc2o(dr, dm_disconnect_cnt, relaxed);
        if (MACH_PORT_VALID(send) && checkin) {
                dispatch_retain(checkin);
                checkin->dmsg_options = _dispatch_mach_checkin_options();
                dr->dm_checkin_port = _dispatch_mach_msg_get_remote_port(checkin);
        } else {
                checkin = NULL;
                dr->dm_checkin_port = MACH_PORT_NULL;
        }
        dispatch_continuation_t dc = _dispatch_continuation_alloc();
        dc->dc_flags = DISPATCH_OBJ_CONSUME_BIT;
        // actually called manually in _dispatch_mach_send_drain
        dc->dc_func = (void*)_dispatch_mach_reconnect_invoke;
        dc->dc_ctxt = dc;
        dc->dc_data = checkin;
        dc->dc_other = (void*)(uintptr_t)send;
        dc->dc_voucher = DISPATCH_NO_VOUCHER;
        dc->dc_priority = DISPATCH_NO_PRIORITY;
        _dispatch_retain(dm); // <rdar://problem/26266265>
        return _dispatch_mach_send_push(dm, dc, 0);
}

DISPATCH_NOINLINE
mach_port_t
dispatch_mach_get_checkin_port(dispatch_mach_t dm)
{
        dispatch_mach_send_refs_t dr = dm->dm_refs;
        if (slowpath(dm->dq_atomic_flags & DSF_CANCELED)) {
                return MACH_PORT_DEAD;
        }
        return dr->dm_checkin_port;
}

DISPATCH_NOINLINE
static void
_dispatch_mach_connect_invoke(dispatch_mach_t dm)
{
        dispatch_mach_refs_t dr = dm->ds_refs;
        _dispatch_client_callout4(dr->dm_handler_ctxt,
                        DISPATCH_MACH_CONNECTED, NULL, 0, dr->dm_handler_func);
        dm->dm_connect_handler_called = 1;
}

DISPATCH_NOINLINE
void
_dispatch_mach_msg_invoke(dispatch_mach_msg_t dmsg,
                dispatch_invoke_flags_t flags)
{
        dispatch_thread_frame_s dtf;
        dispatch_mach_refs_t dr;
        dispatch_mach_t dm;
        mach_error_t err;
        unsigned long reason = _dispatch_mach_msg_get_reason(dmsg, &err);
        _dispatch_thread_set_self_t adopt_flags = DISPATCH_PRIORITY_ENFORCE|
                        DISPATCH_VOUCHER_CONSUME|DISPATCH_VOUCHER_REPLACE;

        // hide mach channel
        dm = (dispatch_mach_t)_dispatch_thread_frame_stash(&dtf);
        dr = dm->ds_refs;
        dmsg->do_next = DISPATCH_OBJECT_LISTLESS;
        _dispatch_voucher_ktrace_dmsg_pop(dmsg);
        _dispatch_voucher_debug("mach-msg[%p] adopt", dmsg->dmsg_voucher, dmsg);
        (void)_dispatch_adopt_priority_and_set_voucher(dmsg->dmsg_priority,
                        dmsg->dmsg_voucher, adopt_flags);
        dmsg->dmsg_voucher = NULL;
        dispatch_invoke_with_autoreleasepool(flags, {
                if (slowpath(!dm->dm_connect_handler_called)) {
                        _dispatch_mach_connect_invoke(dm);
                }
                _dispatch_client_callout4(dr->dm_handler_ctxt, reason, dmsg, err,
                                dr->dm_handler_func);
        });
        _dispatch_thread_frame_unstash(&dtf);
        _dispatch_introspection_queue_item_complete(dmsg);
        dispatch_release(dmsg);
}

DISPATCH_NOINLINE
void
_dispatch_mach_barrier_invoke(dispatch_continuation_t dc,
                dispatch_invoke_flags_t flags)
{
        dispatch_thread_frame_s dtf;
        dispatch_mach_t dm = dc->dc_other;
        dispatch_mach_refs_t dr;
        uintptr_t dc_flags = (uintptr_t)dc->dc_data;
        unsigned long type = dc_type(dc);

        // hide mach channel from clients
        if (type == DISPATCH_CONTINUATION_TYPE(MACH_RECV_BARRIER)) {
                // on the send queue, the mach channel isn't the current queue
                // its target queue is the current one already
                _dispatch_thread_frame_stash(&dtf);
        }
        dr = dm->ds_refs;
        DISPATCH_COMPILER_CAN_ASSUME(dc_flags & DISPATCH_OBJ_CONSUME_BIT);
        _dispatch_continuation_pop_forwarded(dc, dm->dq_override_voucher, dc_flags,{
                dispatch_invoke_with_autoreleasepool(flags, {
                        if (slowpath(!dm->dm_connect_handler_called)) {
                                _dispatch_mach_connect_invoke(dm);
                        }
                        _dispatch_client_callout(dc->dc_ctxt, dc->dc_func);
                        _dispatch_client_callout4(dr->dm_handler_ctxt,
                                        DISPATCH_MACH_BARRIER_COMPLETED, NULL, 0,
                                        dr->dm_handler_func);
                });
        });
        if (type == DISPATCH_CONTINUATION_TYPE(MACH_RECV_BARRIER)) {
                _dispatch_thread_frame_unstash(&dtf);
        }
}

DISPATCH_NOINLINE
void
dispatch_mach_send_barrier_f(dispatch_mach_t dm, void *context,
                dispatch_function_t func)
{
        dispatch_continuation_t dc = _dispatch_continuation_alloc();
        uintptr_t dc_flags = DISPATCH_OBJ_CONSUME_BIT;
        pthread_priority_t pp;

        _dispatch_continuation_init_f(dc, dm, context, func, 0, 0, dc_flags);
        dc->dc_data = (void *)dc->dc_flags;
        dc->dc_other = dm;
        dc->do_vtable = DC_VTABLE(MACH_SEND_BARRIER);
        _dispatch_trace_continuation_push(dm->_as_dq, dc);
        pp = _dispatch_continuation_get_override_priority(dm->_as_dq, dc);
        return _dispatch_mach_send_push(dm, dc, pp);
}

DISPATCH_NOINLINE
void
dispatch_mach_send_barrier(dispatch_mach_t dm, dispatch_block_t barrier)
{
        dispatch_continuation_t dc = _dispatch_continuation_alloc();
        uintptr_t dc_flags = DISPATCH_OBJ_CONSUME_BIT;
        pthread_priority_t pp;

        _dispatch_continuation_init(dc, dm, barrier, 0, 0, dc_flags);
        dc->dc_data = (void *)dc->dc_flags;
        dc->dc_other = dm;
        dc->do_vtable = DC_VTABLE(MACH_SEND_BARRIER);
        _dispatch_trace_continuation_push(dm->_as_dq, dc);
        pp = _dispatch_continuation_get_override_priority(dm->_as_dq, dc);
        return _dispatch_mach_send_push(dm, dc, pp);
}

DISPATCH_NOINLINE
void
dispatch_mach_receive_barrier_f(dispatch_mach_t dm, void *context,
                dispatch_function_t func)
{
        dispatch_continuation_t dc = _dispatch_continuation_alloc();
        uintptr_t dc_flags = DISPATCH_OBJ_CONSUME_BIT;

        _dispatch_continuation_init_f(dc, dm, context, func, 0, 0, dc_flags);
        dc->dc_data = (void *)dc->dc_flags;
        dc->dc_other = dm;
        dc->do_vtable = DC_VTABLE(MACH_RECV_BARRIER);
        return _dispatch_continuation_async(dm->_as_dq, dc);
}

DISPATCH_NOINLINE
void
dispatch_mach_receive_barrier(dispatch_mach_t dm, dispatch_block_t barrier)
{
        dispatch_continuation_t dc = _dispatch_continuation_alloc();
        uintptr_t dc_flags = DISPATCH_OBJ_CONSUME_BIT;

        _dispatch_continuation_init(dc, dm, barrier, 0, 0, dc_flags);
        dc->dc_data = (void *)dc->dc_flags;
        dc->dc_other = dm;
        dc->do_vtable = DC_VTABLE(MACH_RECV_BARRIER);
        return _dispatch_continuation_async(dm->_as_dq, dc);
}

DISPATCH_NOINLINE
static void
_dispatch_mach_cancel_invoke(dispatch_mach_t dm, dispatch_invoke_flags_t flags)
{
        dispatch_mach_refs_t dr = dm->ds_refs;

        dispatch_invoke_with_autoreleasepool(flags, {
                if (slowpath(!dm->dm_connect_handler_called)) {
                        _dispatch_mach_connect_invoke(dm);
                }
                _dispatch_client_callout4(dr->dm_handler_ctxt,
                                DISPATCH_MACH_CANCELED, NULL, 0, dr->dm_handler_func);
        });
        dm->dm_cancel_handler_called = 1;
        _dispatch_release(dm); // the retain is done at creation time
}

DISPATCH_NOINLINE
void
dispatch_mach_cancel(dispatch_mach_t dm)
{
        dispatch_source_cancel(dm->_as_ds);
}

static void
_dispatch_mach_install(dispatch_mach_t dm, pthread_priority_t pp)
{
        uint32_t disconnect_cnt;

        if (dm->ds_dkev) {
                _dispatch_source_kevent_register(dm->_as_ds, pp);
        }
        if (dm->ds_is_direct_kevent) {
                pp &= (~_PTHREAD_PRIORITY_FLAGS_MASK |
                                _PTHREAD_PRIORITY_DEFAULTQUEUE_FLAG |
                                _PTHREAD_PRIORITY_OVERCOMMIT_FLAG);
                // _dispatch_mach_reply_kevent_register assumes this has been done
                // which is unlike regular sources or queues, the DEFAULTQUEUE flag
                // is used so that the priority of that channel doesn't act as a floor
                // QoS for incoming messages (26761457)
                dm->dq_priority = (dispatch_priority_t)pp;
        }
        dm->ds_is_installed = true;
        if (unlikely(!os_atomic_cmpxchgv2o(dm->dm_refs, dm_disconnect_cnt,
                        DISPATCH_MACH_NEVER_INSTALLED, 0, &disconnect_cnt, release))) {
                DISPATCH_INTERNAL_CRASH(disconnect_cnt, "Channel already installed");
        }
}

void
_dispatch_mach_finalize_activation(dispatch_mach_t dm)
{
        if (dm->ds_is_direct_kevent && !dm->ds_is_installed) {
                dispatch_source_t ds = dm->_as_ds;
                pthread_priority_t pp = _dispatch_source_compute_kevent_priority(ds);
                if (pp) _dispatch_mach_install(dm, pp);
        }

        // call "super"
        _dispatch_queue_finalize_activation(dm->_as_dq);
}

DISPATCH_ALWAYS_INLINE
static inline dispatch_queue_t
_dispatch_mach_invoke2(dispatch_object_t dou, dispatch_invoke_flags_t flags,
                uint64_t *owned, struct dispatch_object_s **dc_ptr DISPATCH_UNUSED)
{
        dispatch_mach_t dm = dou._dm;
        dispatch_queue_t retq = NULL;
        dispatch_queue_t dq = _dispatch_queue_get_current();

        // This function performs all mach channel actions. Each action is
        // responsible for verifying that it takes place on the appropriate queue.
        // If the current queue is not the correct queue for this action, the
        // correct queue will be returned and the invoke will be re-driven on that
        // queue.

        // The order of tests here in invoke and in wakeup should be consistent.

        dispatch_mach_send_refs_t dr = dm->dm_refs;
        dispatch_queue_t dkq = &_dispatch_mgr_q;

        if (dm->ds_is_direct_kevent) {
                dkq = dm->do_targetq;
        }

        if (slowpath(!dm->ds_is_installed)) {
                // The channel needs to be installed on the kevent queue.
                if (dq != dkq) {
                        return dkq;
                }
                _dispatch_mach_install(dm, _dispatch_get_defaultpriority());
        }

        if (_dispatch_queue_class_probe(dm)) {
                if (dq == dm->do_targetq) {
                        retq = _dispatch_queue_serial_drain(dm->_as_dq, flags, owned, NULL);
                } else {
                        retq = dm->do_targetq;
                }
        }

        dispatch_queue_flags_t dqf = _dispatch_queue_atomic_flags(dm->_as_dq);

        if (dr->dm_tail) {
                bool requires_mgr = dr->dm_needs_mgr || (dr->dm_disconnect_cnt &&
                                (dm->dm_dkev || !dm->ds_is_direct_kevent));
                if (!(dm->dm_dkev && DISPATCH_MACH_NOTIFICATION_ARMED(dm->dm_dkev)) ||
                                (dqf & DSF_CANCELED) || dr->dm_disconnect_cnt) {
                        // The channel has pending messages to send.
                        if (unlikely(requires_mgr && dq != &_dispatch_mgr_q)) {
                                return retq ? retq : &_dispatch_mgr_q;
                        }
                        dispatch_mach_send_invoke_flags_t send_flags = DM_SEND_INVOKE_NONE;
                        if (dq != &_dispatch_mgr_q) {
                                send_flags |= DM_SEND_INVOKE_CAN_RUN_BARRIER;
                        }
                        _dispatch_mach_send_invoke(dm, flags, send_flags);
                }
        } else if (dqf & DSF_CANCELED) {
                // The channel has been cancelled and needs to be uninstalled from the
                // manager queue. After uninstallation, the cancellation handler needs
                // to be delivered to the target queue.
                if ((dqf & DSF_STATE_MASK) == (DSF_ARMED | DSF_DEFERRED_DELETE)) {
                        // waiting for the delivery of a deferred delete event
                        return retq;
                }
                if ((dqf & DSF_STATE_MASK) != DSF_DELETED) {
                        if (dq != &_dispatch_mgr_q) {
                                return retq ? retq : &_dispatch_mgr_q;
                        }
                        _dispatch_mach_send_invoke(dm, flags, DM_SEND_INVOKE_CANCEL);
                        dqf = _dispatch_queue_atomic_flags(dm->_as_dq);
                        if (unlikely((dqf & DSF_STATE_MASK) != DSF_DELETED)) {
                                // waiting for the delivery of a deferred delete event
                                // or deletion didn't happen because send_invoke couldn't
                                // acquire the send lock
                                return retq;
                        }
                }
                if (!dm->dm_cancel_handler_called) {
                        if (dq != dm->do_targetq) {
                                return retq ? retq : dm->do_targetq;
                        }
                        _dispatch_mach_cancel_invoke(dm, flags);
                }
        }

        return retq;
}

DISPATCH_NOINLINE
void
_dispatch_mach_invoke(dispatch_mach_t dm, dispatch_invoke_flags_t flags)
{
        _dispatch_queue_class_invoke(dm, flags, _dispatch_mach_invoke2);
}

void
_dispatch_mach_wakeup(dispatch_mach_t dm, pthread_priority_t pp,
                dispatch_wakeup_flags_t flags)
{
        // This function determines whether the mach channel needs to be invoked.
        // The order of tests here in probe and in invoke should be consistent.

        dispatch_mach_send_refs_t dr = dm->dm_refs;
        dispatch_queue_wakeup_target_t dkq = DISPATCH_QUEUE_WAKEUP_MGR;
        dispatch_queue_wakeup_target_t tq = DISPATCH_QUEUE_WAKEUP_NONE;
        dispatch_queue_flags_t dqf = _dispatch_queue_atomic_flags(dm->_as_dq);

        if (dm->ds_is_direct_kevent) {
                dkq = DISPATCH_QUEUE_WAKEUP_TARGET;
        }

        if (!dm->ds_is_installed) {
                // The channel needs to be installed on the kevent queue.
                tq = dkq;
                goto done;
        }

        if (_dispatch_queue_class_probe(dm)) {
                tq = DISPATCH_QUEUE_WAKEUP_TARGET;
                goto done;
        }

        if (_dispatch_lock_is_locked(dr->dm_state_lock.dul_lock)) {
                // Sending and uninstallation below require the send lock, the channel
                // will be woken up when the lock is dropped <rdar://15132939&15203957>
                _dispatch_queue_reinstate_override_priority(dm, (dispatch_priority_t)pp);
                goto done;
        }

        if (dr->dm_tail) {
                bool requires_mgr = dr->dm_needs_mgr || (dr->dm_disconnect_cnt &&
                                (dm->dm_dkev || !dm->ds_is_direct_kevent));
                if (!(dm->dm_dkev && DISPATCH_MACH_NOTIFICATION_ARMED(dm->dm_dkev)) ||
                                (dqf & DSF_CANCELED) || dr->dm_disconnect_cnt) {
                        if (unlikely(requires_mgr)) {
                                tq = DISPATCH_QUEUE_WAKEUP_MGR;
                        } else {
                                tq = DISPATCH_QUEUE_WAKEUP_TARGET;
                        }
                } else {
                        // can happen when we can't send because the port is full
                        // but we should not lose the override
                        _dispatch_queue_reinstate_override_priority(dm,
                                        (dispatch_priority_t)pp);
                }
        } else if (dqf & DSF_CANCELED) {
                if ((dqf & DSF_STATE_MASK) == (DSF_ARMED | DSF_DEFERRED_DELETE)) {
                        // waiting for the delivery of a deferred delete event
                } else if ((dqf & DSF_STATE_MASK) != DSF_DELETED) {
                        // The channel needs to be uninstalled from the manager queue
                        tq = DISPATCH_QUEUE_WAKEUP_MGR;
                } else if (!dm->dm_cancel_handler_called) {
                        // the cancellation handler needs to be delivered to the target
                        // queue.
                        tq = DISPATCH_QUEUE_WAKEUP_TARGET;
                }
        }

done:
        if (tq) {
                return _dispatch_queue_class_wakeup(dm->_as_dq, pp, flags, tq);
        } else if (pp) {
                return _dispatch_queue_class_override_drainer(dm->_as_dq, pp, flags);
        } else if (flags & DISPATCH_WAKEUP_CONSUME) {
                return _dispatch_release_tailcall(dm);
        }
}

#pragma mark -
#pragma mark dispatch_mach_msg_t

dispatch_mach_msg_t
dispatch_mach_msg_create(mach_msg_header_t *msg, size_t size,
                dispatch_mach_msg_destructor_t destructor, mach_msg_header_t **msg_ptr)
{
        if (slowpath(size < sizeof(mach_msg_header_t)) ||
                        slowpath(destructor && !msg)) {
                DISPATCH_CLIENT_CRASH(size, "Empty message");
        }
        dispatch_mach_msg_t dmsg = _dispatch_alloc(DISPATCH_VTABLE(mach_msg),
                        sizeof(struct dispatch_mach_msg_s) +
                        (destructor ? 0 : size - sizeof(dmsg->dmsg_msg)));
        if (destructor) {
                dmsg->dmsg_msg = msg;
        } else if (msg) {
                memcpy(dmsg->dmsg_buf, msg, size);
        }
        dmsg->do_next = DISPATCH_OBJECT_LISTLESS;
        dmsg->do_targetq = _dispatch_get_root_queue(_DISPATCH_QOS_CLASS_DEFAULT,
                        false);
        dmsg->dmsg_destructor = destructor;
        dmsg->dmsg_size = size;
        if (msg_ptr) {
                *msg_ptr = _dispatch_mach_msg_get_msg(dmsg);
        }
        return dmsg;
}

void
_dispatch_mach_msg_dispose(dispatch_mach_msg_t dmsg)
{
        if (dmsg->dmsg_voucher) {
                _voucher_release(dmsg->dmsg_voucher);
                dmsg->dmsg_voucher = NULL;
        }
        switch (dmsg->dmsg_destructor) {
        case DISPATCH_MACH_MSG_DESTRUCTOR_DEFAULT:
                break;
        case DISPATCH_MACH_MSG_DESTRUCTOR_FREE:
                free(dmsg->dmsg_msg);
                break;
        case DISPATCH_MACH_MSG_DESTRUCTOR_VM_DEALLOCATE: {
                mach_vm_size_t vm_size = dmsg->dmsg_size;
                mach_vm_address_t vm_addr = (uintptr_t)dmsg->dmsg_msg;
                (void)dispatch_assume_zero(mach_vm_deallocate(mach_task_self(),
                                vm_addr, vm_size));
                break;
        }}
}

static inline mach_msg_header_t*
_dispatch_mach_msg_get_msg(dispatch_mach_msg_t dmsg)
{
        return dmsg->dmsg_destructor ? dmsg->dmsg_msg :
                        (mach_msg_header_t*)dmsg->dmsg_buf;
}

mach_msg_header_t*
dispatch_mach_msg_get_msg(dispatch_mach_msg_t dmsg, size_t *size_ptr)
{
        if (size_ptr) {
                *size_ptr = dmsg->dmsg_size;
        }
        return _dispatch_mach_msg_get_msg(dmsg);
}

size_t
_dispatch_mach_msg_debug(dispatch_mach_msg_t dmsg, char* buf, size_t bufsiz)
{
        size_t offset = 0;
        offset += dsnprintf(&buf[offset], bufsiz - offset, "%s[%p] = { ",
                        dx_kind(dmsg), dmsg);
        offset += dsnprintf(&buf[offset], bufsiz - offset, "xrefcnt = 0x%x, "
                        "refcnt = 0x%x, ", dmsg->do_xref_cnt + 1, dmsg->do_ref_cnt + 1);
        offset += dsnprintf(&buf[offset], bufsiz - offset, "opts/err = 0x%x, "
                        "msgh[%p] = { ", dmsg->dmsg_options, dmsg->dmsg_buf);
        mach_msg_header_t *hdr = _dispatch_mach_msg_get_msg(dmsg);
        if (hdr->msgh_id) {
                offset += dsnprintf(&buf[offset], bufsiz - offset, "id 0x%x, ",
                                hdr->msgh_id);
        }
        if (hdr->msgh_size) {
                offset += dsnprintf(&buf[offset], bufsiz - offset, "size %u, ",
                                hdr->msgh_size);
        }
        if (hdr->msgh_bits) {
                offset += dsnprintf(&buf[offset], bufsiz - offset, "bits <l %u, r %u",
                                MACH_MSGH_BITS_LOCAL(hdr->msgh_bits),
                                MACH_MSGH_BITS_REMOTE(hdr->msgh_bits));
                if (MACH_MSGH_BITS_OTHER(hdr->msgh_bits)) {
                        offset += dsnprintf(&buf[offset], bufsiz - offset, ", o 0x%x",
                                        MACH_MSGH_BITS_OTHER(hdr->msgh_bits));
                }
                offset += dsnprintf(&buf[offset], bufsiz - offset, ">, ");
        }
        if (hdr->msgh_local_port && hdr->msgh_remote_port) {
                offset += dsnprintf(&buf[offset], bufsiz - offset, "local 0x%x, "
                                "remote 0x%x", hdr->msgh_local_port, hdr->msgh_remote_port);
        } else if (hdr->msgh_local_port) {
                offset += dsnprintf(&buf[offset], bufsiz - offset, "local 0x%x",
                                hdr->msgh_local_port);
        } else if (hdr->msgh_remote_port) {
                offset += dsnprintf(&buf[offset], bufsiz - offset, "remote 0x%x",
                                hdr->msgh_remote_port);
        } else {
                offset += dsnprintf(&buf[offset], bufsiz - offset, "no ports");
        }
        offset += dsnprintf(&buf[offset], bufsiz - offset, " } }");
        return offset;
}

#pragma mark -
#pragma mark dispatch_mig_server

mach_msg_return_t
dispatch_mig_server(dispatch_source_t ds, size_t maxmsgsz,
                dispatch_mig_callback_t callback)
{
        mach_msg_options_t options = MACH_RCV_MSG | MACH_RCV_TIMEOUT
                | MACH_RCV_TRAILER_ELEMENTS(MACH_RCV_TRAILER_CTX)
                | MACH_RCV_TRAILER_TYPE(MACH_MSG_TRAILER_FORMAT_0) | MACH_RCV_VOUCHER;
        mach_msg_options_t tmp_options;
        mig_reply_error_t *bufTemp, *bufRequest, *bufReply;
        mach_msg_return_t kr = 0;
        uint64_t assertion_token = 0;
        unsigned int cnt = 1000; // do not stall out serial queues
        boolean_t demux_success;
        bool received = false;
        size_t rcv_size = maxmsgsz + MAX_TRAILER_SIZE;

        bufRequest = alloca(rcv_size);
        bufRequest->RetCode = 0;
        for (mach_vm_address_t p = mach_vm_trunc_page(bufRequest + vm_page_size);
                        p < (mach_vm_address_t)bufRequest + rcv_size; p += vm_page_size) {
                *(char*)p = 0; // ensure alloca buffer doesn't overlap with stack guard
        }

        bufReply = alloca(rcv_size);
        bufReply->Head.msgh_size = 0;
        for (mach_vm_address_t p = mach_vm_trunc_page(bufReply + vm_page_size);
                        p < (mach_vm_address_t)bufReply + rcv_size; p += vm_page_size) {
                *(char*)p = 0; // ensure alloca buffer doesn't overlap with stack guard
        }

#if DISPATCH_DEBUG
        options |= MACH_RCV_LARGE; // rdar://problem/8422992
#endif
        tmp_options = options;
        // XXX FIXME -- change this to not starve out the target queue
        for (;;) {
                if (DISPATCH_QUEUE_IS_SUSPENDED(ds) || (--cnt == 0)) {
                        options &= ~MACH_RCV_MSG;
                        tmp_options &= ~MACH_RCV_MSG;

                        if (!(tmp_options & MACH_SEND_MSG)) {
                                goto out;
                        }
                }
                kr = mach_msg(&bufReply->Head, tmp_options, bufReply->Head.msgh_size,
                                (mach_msg_size_t)rcv_size, (mach_port_t)ds->ds_ident_hack, 0,0);

                tmp_options = options;

                if (slowpath(kr)) {
                        switch (kr) {
                        case MACH_SEND_INVALID_DEST:
                        case MACH_SEND_TIMED_OUT:
                                if (bufReply->Head.msgh_bits & MACH_MSGH_BITS_COMPLEX) {
                                        mach_msg_destroy(&bufReply->Head);
                                }
                                break;
                        case MACH_RCV_TIMED_OUT:
                                // Don't return an error if a message was sent this time or
                                // a message was successfully received previously
                                // rdar://problems/7363620&7791738
                                if(bufReply->Head.msgh_remote_port || received) {
                                        kr = MACH_MSG_SUCCESS;
                                }
                                break;
                        case MACH_RCV_INVALID_NAME:
                                break;
#if DISPATCH_DEBUG
                        case MACH_RCV_TOO_LARGE:
                                // receive messages that are too large and log their id and size
                                // rdar://problem/8422992
                                tmp_options &= ~MACH_RCV_LARGE;
                                size_t large_size = bufReply->Head.msgh_size + MAX_TRAILER_SIZE;
                                void *large_buf = malloc(large_size);
                                if (large_buf) {
                                        rcv_size = large_size;
                                        bufReply = large_buf;
                                }
                                if (!mach_msg(&bufReply->Head, tmp_options, 0,
                                                (mach_msg_size_t)rcv_size,
                                                (mach_port_t)ds->ds_ident_hack, 0, 0)) {
                                        _dispatch_log("BUG in libdispatch client: "
                                                        "dispatch_mig_server received message larger than "
                                                        "requested size %zd: id = 0x%x, size = %d",
                                                        maxmsgsz, bufReply->Head.msgh_id,
                                                        bufReply->Head.msgh_size);
                                }
                                if (large_buf) {
                                        free(large_buf);
                                }
                                // fall through
#endif
                        default:
                                _dispatch_bug_mach_client(
                                                "dispatch_mig_server: mach_msg() failed", kr);
                                break;
                        }
                        goto out;
                }

                if (!(tmp_options & MACH_RCV_MSG)) {
                        goto out;
                }

                if (assertion_token) {
#if DISPATCH_USE_IMPORTANCE_ASSERTION
                        int r = proc_importance_assertion_complete(assertion_token);
                        (void)dispatch_assume_zero(r);
#endif
                        assertion_token = 0;
                }
                received = true;

                bufTemp = bufRequest;
                bufRequest = bufReply;
                bufReply = bufTemp;

#if DISPATCH_USE_IMPORTANCE_ASSERTION
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wdeprecated-declarations"
                int r = proc_importance_assertion_begin_with_msg(&bufRequest->Head,
                                NULL, &assertion_token);
                if (r && slowpath(r != EIO)) {
                        (void)dispatch_assume_zero(r);
                }
#pragma clang diagnostic pop
#endif
                _voucher_replace(voucher_create_with_mach_msg(&bufRequest->Head));
                demux_success = callback(&bufRequest->Head, &bufReply->Head);

                if (!demux_success) {
                        // destroy the request - but not the reply port
                        bufRequest->Head.msgh_remote_port = 0;
                        mach_msg_destroy(&bufRequest->Head);
                } else if (!(bufReply->Head.msgh_bits & MACH_MSGH_BITS_COMPLEX)) {
                        // if MACH_MSGH_BITS_COMPLEX is _not_ set, then bufReply->RetCode
                        // is present
                        if (slowpath(bufReply->RetCode)) {
                                if (bufReply->RetCode == MIG_NO_REPLY) {
                                        continue;
                                }

                                // destroy the request - but not the reply port
                                bufRequest->Head.msgh_remote_port = 0;
                                mach_msg_destroy(&bufRequest->Head);
                        }
                }

                if (bufReply->Head.msgh_remote_port) {
                        tmp_options |= MACH_SEND_MSG;
                        if (MACH_MSGH_BITS_REMOTE(bufReply->Head.msgh_bits) !=
                                        MACH_MSG_TYPE_MOVE_SEND_ONCE) {
                                tmp_options |= MACH_SEND_TIMEOUT;
                        }
                }
        }

out:
        if (assertion_token) {
#if DISPATCH_USE_IMPORTANCE_ASSERTION
                int r = proc_importance_assertion_complete(assertion_token);
                (void)dispatch_assume_zero(r);
#endif
        }

        return kr;
}

#endif /* HAVE_MACH */

#pragma mark -
#pragma mark dispatch_source_debug

DISPATCH_NOINLINE
static const char *
_evfiltstr(short filt)
{
        switch (filt) {
#define _evfilt2(f) case (f): return #f
        _evfilt2(EVFILT_READ);
        _evfilt2(EVFILT_WRITE);
        _evfilt2(EVFILT_AIO);
        _evfilt2(EVFILT_VNODE);
        _evfilt2(EVFILT_PROC);
        _evfilt2(EVFILT_SIGNAL);
        _evfilt2(EVFILT_TIMER);
#if HAVE_MACH
        _evfilt2(EVFILT_MACHPORT);
        _evfilt2(DISPATCH_EVFILT_MACH_NOTIFICATION);
#endif
        _evfilt2(EVFILT_FS);
        _evfilt2(EVFILT_USER);
#ifdef EVFILT_SOCK
        _evfilt2(EVFILT_SOCK);
#endif
#ifdef EVFILT_MEMORYSTATUS
        _evfilt2(EVFILT_MEMORYSTATUS);
#endif

        _evfilt2(DISPATCH_EVFILT_TIMER);
        _evfilt2(DISPATCH_EVFILT_CUSTOM_ADD);
        _evfilt2(DISPATCH_EVFILT_CUSTOM_OR);
        default:
                return "EVFILT_missing";
        }
}

#if DISPATCH_DEBUG
static const char *
_evflagstr2(uint16_t *flagsp)
{
#define _evflag2(f) \
        if ((*flagsp & (f)) == (f) && (f)) { \
                *flagsp &= ~(f); \
                return #f "|"; \
        }
        _evflag2(EV_ADD);
        _evflag2(EV_DELETE);
        _evflag2(EV_ENABLE);
        _evflag2(EV_DISABLE);
        _evflag2(EV_ONESHOT);
        _evflag2(EV_CLEAR);
        _evflag2(EV_RECEIPT);
        _evflag2(EV_DISPATCH);
        _evflag2(EV_UDATA_SPECIFIC);
#ifdef EV_POLL
        _evflag2(EV_POLL);
#endif
#ifdef EV_OOBAND
        _evflag2(EV_OOBAND);
#endif
        _evflag2(EV_ERROR);
        _evflag2(EV_EOF);
        _evflag2(EV_VANISHED);
        *flagsp = 0;
        return "EV_UNKNOWN ";
}

DISPATCH_NOINLINE
static const char *
_evflagstr(uint16_t flags, char *str, size_t strsize)
{
        str[0] = 0;
        while (flags) {
                strlcat(str, _evflagstr2(&flags), strsize);
        }
        size_t sz = strlen(str);
        if (sz) str[sz-1] = 0;
        return str;
}
#endif

static size_t
_dispatch_source_debug_attr(dispatch_source_t ds, char* buf, size_t bufsiz)
{
        dispatch_queue_t target = ds->do_targetq;
        return dsnprintf(buf, bufsiz, "target = %s[%p], ident = 0x%lx, "
                        "mask = 0x%lx, pending_data = 0x%lx, registered = %d, "
                        "armed = %d, deleted = %d%s, canceled = %d, ",
                        target && target->dq_label ? target->dq_label : "", target,
                        ds->ds_ident_hack, ds->ds_pending_data_mask, ds->ds_pending_data,
                        ds->ds_is_installed, (bool)(ds->dq_atomic_flags & DSF_ARMED),
                        (bool)(ds->dq_atomic_flags & DSF_DELETED),
                        (ds->dq_atomic_flags & DSF_DEFERRED_DELETE) ? " (pending)" : "",
                        (bool)(ds->dq_atomic_flags & DSF_CANCELED));
}

static size_t
_dispatch_timer_debug_attr(dispatch_source_t ds, char* buf, size_t bufsiz)
{
        dispatch_source_refs_t dr = ds->ds_refs;
        return dsnprintf(buf, bufsiz, "timer = { target = 0x%llx, deadline = 0x%llx"
                        ", last_fire = 0x%llx, interval = 0x%llx, flags = 0x%lx }, ",
                        (unsigned long long)ds_timer(dr).target,
                        (unsigned long long)ds_timer(dr).deadline,
                        (unsigned long long)ds_timer(dr).last_fire,
                        (unsigned long long)ds_timer(dr).interval, ds_timer(dr).flags);
}

size_t
_dispatch_source_debug(dispatch_source_t ds, char* buf, size_t bufsiz)
{
        size_t offset = 0;
        offset += dsnprintf(&buf[offset], bufsiz - offset, "%s[%p] = { ",
                        dx_kind(ds), ds);
        offset += _dispatch_object_debug_attr(ds, &buf[offset], bufsiz - offset);
        offset += _dispatch_source_debug_attr(ds, &buf[offset], bufsiz - offset);
        if (ds->ds_is_timer) {
                offset += _dispatch_timer_debug_attr(ds, &buf[offset], bufsiz - offset);
        }
        const char *filter;
        if (!ds->ds_dkev) {
                filter = "????";
        } else if (ds->ds_is_custom_source) {
                filter = _evfiltstr((int16_t)(uintptr_t)ds->ds_dkev);
        } else {
                filter = _evfiltstr(ds->ds_dkev->dk_kevent.filter);
        }
        offset += dsnprintf(&buf[offset], bufsiz - offset, "kevent = %p%s, "
                        "filter = %s }", ds->ds_dkev,  ds->ds_is_direct_kevent ? " (direct)"
                        : "", filter);
        return offset;
}

#if HAVE_MACH
static size_t
_dispatch_mach_debug_attr(dispatch_mach_t dm, char* buf, size_t bufsiz)
{
        dispatch_queue_t target = dm->do_targetq;
        return dsnprintf(buf, bufsiz, "target = %s[%p], receive = 0x%x, "
                        "send = 0x%x, send-possible = 0x%x%s, checkin = 0x%x%s, "
                        "send state = %016llx, disconnected = %d, canceled = %d ",
                        target && target->dq_label ? target->dq_label : "", target,
                        dm->ds_dkev ?(mach_port_t)dm->ds_dkev->dk_kevent.ident:0,
                        dm->dm_refs->dm_send,
                        dm->dm_dkev ?(mach_port_t)dm->dm_dkev->dk_kevent.ident:0,
                        dm->dm_dkev && DISPATCH_MACH_NOTIFICATION_ARMED(dm->dm_dkev) ?
                        " (armed)" : "", dm->dm_refs->dm_checkin_port,
                        dm->dm_refs->dm_checkin ? " (pending)" : "",
                        dm->dm_refs->dm_state, dm->dm_refs->dm_disconnect_cnt,
                        (bool)(dm->dq_atomic_flags & DSF_CANCELED));
}

size_t
_dispatch_mach_debug(dispatch_mach_t dm, char* buf, size_t bufsiz)
{
        size_t offset = 0;
        offset += dsnprintf(&buf[offset], bufsiz - offset, "%s[%p] = { ",
                        dm->dq_label && !dm->dm_cancel_handler_called ? dm->dq_label :
                        dx_kind(dm), dm);
        offset += _dispatch_object_debug_attr(dm, &buf[offset], bufsiz - offset);
        offset += _dispatch_mach_debug_attr(dm, &buf[offset], bufsiz - offset);
        offset += dsnprintf(&buf[offset], bufsiz - offset, "}");
        return offset;
}
#endif // HAVE_MACH

#if DISPATCH_DEBUG
DISPATCH_NOINLINE
static void
dispatch_kevent_debug(const char *verb, const _dispatch_kevent_qos_s *kev,
                int i, int n, const char *function, unsigned int line)
{
        char flagstr[256];
        char i_n[31];

        if (n > 1) {
                snprintf(i_n, sizeof(i_n), "%d/%d ", i + 1, n);
        } else {
                i_n[0] = '\0';
        }
#if DISPATCH_USE_KEVENT_QOS
        _dispatch_debug("%s kevent[%p] %s= { ident = 0x%llx, filter = %s, "
                        "flags = %s (0x%x), fflags = 0x%x, data = 0x%llx, udata = 0x%llx, "
                        "qos = 0x%x, ext[0] = 0x%llx, ext[1] = 0x%llx, ext[2] = 0x%llx, "
                        "ext[3] = 0x%llx }: %s #%u", verb, kev, i_n, kev->ident,
                        _evfiltstr(kev->filter), _evflagstr(kev->flags, flagstr,
                        sizeof(flagstr)), kev->flags, kev->fflags, kev->data, kev->udata,
                        kev->qos, kev->ext[0], kev->ext[1], kev->ext[2], kev->ext[3],
                        function, line);
#else
        _dispatch_debug("%s kevent[%p] %s= { ident = 0x%llx, filter = %s, "
                        "flags = %s (0x%x), fflags = 0x%x, data = 0x%llx, udata = 0x%llx, "
                        "ext[0] = 0x%llx, ext[1] = 0x%llx }: %s #%u", verb, kev, i_n,
                        kev->ident, _evfiltstr(kev->filter), _evflagstr(kev->flags, flagstr,
                        sizeof(flagstr)), kev->flags, kev->fflags, kev->data, kev->udata,
#ifndef IGNORE_KEVENT64_EXT
                        kev->ext[0], kev->ext[1],
#else
                        0ull, 0ull,
#endif
                        function, line);
#endif
}

#if HAVE_MACH

#ifndef MACH_PORT_TYPE_SPREQUEST
#define MACH_PORT_TYPE_SPREQUEST 0x40000000
#endif

DISPATCH_NOINLINE
void
dispatch_debug_machport(mach_port_t name, const char* str)
{
        mach_port_type_t type;
        mach_msg_bits_t ns = 0, nr = 0, nso = 0, nd = 0;
        unsigned int dnreqs = 0, dnrsiz;
        kern_return_t kr = mach_port_type(mach_task_self(), name, &type);
        if (kr) {
                _dispatch_log("machport[0x%08x] = { error(0x%x) \"%s\" }: %s", name,
                                kr, mach_error_string(kr), str);
                return;
        }
        if (type & MACH_PORT_TYPE_SEND) {
                (void)dispatch_assume_zero(mach_port_get_refs(mach_task_self(), name,
                                MACH_PORT_RIGHT_SEND, &ns));
        }
        if (type & MACH_PORT_TYPE_SEND_ONCE) {
                (void)dispatch_assume_zero(mach_port_get_refs(mach_task_self(), name,
                                MACH_PORT_RIGHT_SEND_ONCE, &nso));
        }
        if (type & MACH_PORT_TYPE_DEAD_NAME) {
                (void)dispatch_assume_zero(mach_port_get_refs(mach_task_self(), name,
                                MACH_PORT_RIGHT_DEAD_NAME, &nd));
        }
        if (type & (MACH_PORT_TYPE_RECEIVE|MACH_PORT_TYPE_SEND)) {
                kr = mach_port_dnrequest_info(mach_task_self(), name, &dnrsiz, &dnreqs);
                if (kr != KERN_INVALID_RIGHT) (void)dispatch_assume_zero(kr);
        }
        if (type & MACH_PORT_TYPE_RECEIVE) {
                mach_port_status_t status = { .mps_pset = 0, };
                mach_msg_type_number_t cnt = MACH_PORT_RECEIVE_STATUS_COUNT;
                (void)dispatch_assume_zero(mach_port_get_refs(mach_task_self(), name,
                                MACH_PORT_RIGHT_RECEIVE, &nr));
                (void)dispatch_assume_zero(mach_port_get_attributes(mach_task_self(),
                                name, MACH_PORT_RECEIVE_STATUS, (void*)&status, &cnt));
                _dispatch_log("machport[0x%08x] = { R(%03u) S(%03u) SO(%03u) D(%03u) "
                                "dnreqs(%03u) spreq(%s) nsreq(%s) pdreq(%s) srights(%s) "
                                "sorights(%03u) qlim(%03u) msgcount(%03u) mkscount(%03u) "
                                "seqno(%03u) }: %s", name, nr, ns, nso, nd, dnreqs,
                                type & MACH_PORT_TYPE_SPREQUEST ? "Y":"N",
                                status.mps_nsrequest ? "Y":"N", status.mps_pdrequest ? "Y":"N",
                                status.mps_srights ? "Y":"N", status.mps_sorights,
                                status.mps_qlimit, status.mps_msgcount, status.mps_mscount,
                                status.mps_seqno, str);
        } else if (type & (MACH_PORT_TYPE_SEND|MACH_PORT_TYPE_SEND_ONCE|
                        MACH_PORT_TYPE_DEAD_NAME)) {
                _dispatch_log("machport[0x%08x] = { R(%03u) S(%03u) SO(%03u) D(%03u) "
                                "dnreqs(%03u) spreq(%s) }: %s", name, nr, ns, nso, nd, dnreqs,
                                type & MACH_PORT_TYPE_SPREQUEST ? "Y":"N", str);
        } else {
                _dispatch_log("machport[0x%08x] = { type(0x%08x) }: %s", name, type,
                                str);
        }
}

#endif // HAVE_MACH

#endif // DISPATCH_DEBUG