libdispatch-501.40.12.tar.gz

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

/*
 * Copyright (c) 2008-2013 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@
 */

// Contains exported global data and initialization & other routines that must
// only exist once in the shared library even when resolvers are used.

#include "internal.h"

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

#pragma mark -
#pragma mark dispatch_init

#if USE_LIBDISPATCH_INIT_CONSTRUCTOR
DISPATCH_NOTHROW __attribute__((constructor))
void
_libdispatch_init(void);

DISPATCH_EXPORT DISPATCH_NOTHROW
void
_libdispatch_init(void)
{
        libdispatch_init();
}
#endif

DISPATCH_EXPORT DISPATCH_NOTHROW
void
dispatch_atfork_prepare(void)
{
}

DISPATCH_EXPORT DISPATCH_NOTHROW
void
dispatch_atfork_parent(void)
{
}

#pragma mark -
#pragma mark dispatch_globals

#if DISPATCH_COCOA_COMPAT
void (*dispatch_begin_thread_4GC)(void);
void (*dispatch_end_thread_4GC)(void);
void *(*_dispatch_begin_NSAutoReleasePool)(void);
void (*_dispatch_end_NSAutoReleasePool)(void *);
#endif

#if !DISPATCH_USE_DIRECT_TSD
pthread_key_t dispatch_queue_key;
pthread_key_t dispatch_sema4_key;
pthread_key_t dispatch_cache_key;
pthread_key_t dispatch_io_key;
pthread_key_t dispatch_apply_key;
pthread_key_t dispatch_defaultpriority_key;
#if DISPATCH_INTROSPECTION
pthread_key_t dispatch_introspection_key;
#elif DISPATCH_PERF_MON
pthread_key_t dispatch_bcounter_key;
#endif
#endif // !DISPATCH_USE_DIRECT_TSD

#if VOUCHER_USE_MACH_VOUCHER
dispatch_once_t _voucher_task_mach_voucher_pred;
mach_voucher_t _voucher_task_mach_voucher;
_voucher_atm_t _voucher_task_atm;
_voucher_activity_t _voucher_activity_default;
#endif
voucher_activity_mode_t _voucher_activity_mode;
int _dispatch_set_qos_class_enabled;


DISPATCH_NOINLINE
voucher_activity_mode_t
voucher_activity_get_mode(void)
{
        return _voucher_activity_mode;
}

void
voucher_activity_set_mode_4libtrace(voucher_activity_mode_t mode)
{
        if (_voucher_activity_disabled()) return;
        _voucher_activity_mode = mode;
}

DISPATCH_HW_CONFIG();
bool _dispatch_safe_fork = true, _dispatch_child_of_unsafe_fork;

DISPATCH_NOINLINE
bool
_dispatch_is_multithreaded(void)
{
        return !_dispatch_safe_fork;
}

DISPATCH_NOINLINE
bool
_dispatch_is_fork_of_multithreaded_parent(void)
{
        return _dispatch_child_of_unsafe_fork;
}

const struct dispatch_queue_offsets_s dispatch_queue_offsets = {
        .dqo_version = 5,
        .dqo_label = offsetof(struct dispatch_queue_s, dq_label),
        .dqo_label_size = sizeof(((dispatch_queue_t)NULL)->dq_label),
        .dqo_flags = 0,
        .dqo_flags_size = 0,
        .dqo_serialnum = offsetof(struct dispatch_queue_s, dq_serialnum),
        .dqo_serialnum_size = sizeof(((dispatch_queue_t)NULL)->dq_serialnum),
        .dqo_width = offsetof(struct dispatch_queue_s, dq_width),
        .dqo_width_size = sizeof(((dispatch_queue_t)NULL)->dq_width),
        .dqo_running = offsetof(struct dispatch_queue_s, dq_running),
        .dqo_running_size = sizeof(((dispatch_queue_t)NULL)->dq_running),
        .dqo_suspend_cnt = offsetof(struct dispatch_queue_s, do_suspend_cnt),
        .dqo_suspend_cnt_size = sizeof(((dispatch_queue_t)NULL)->do_suspend_cnt),
        .dqo_target_queue = offsetof(struct dispatch_queue_s, do_targetq),
        .dqo_target_queue_size = sizeof(((dispatch_queue_t)NULL)->do_targetq),
        .dqo_priority = offsetof(struct dispatch_queue_s, dq_priority),
        .dqo_priority_size = sizeof(((dispatch_queue_t)NULL)->dq_priority),
};

#if VOUCHER_USE_MACH_VOUCHER
const struct voucher_offsets_s voucher_offsets = {
        .vo_version = 1,
        .vo_activity_ids_count = offsetof(struct voucher_s, v_activities),
        .vo_activity_ids_count_size = sizeof(((voucher_t)NULL)->v_activities),
        .vo_activity_ids_array = (uint16_t)_voucher_activity_ids((voucher_t)(NULL)),
        .vo_activity_ids_array_entry_size = sizeof(voucher_activity_id_t),
};
#else // VOUCHER_USE_MACH_VOUCHER
const struct voucher_offsets_s voucher_offsets = {
        .vo_version = 0,
};
#endif // VOUCHER_USE_MACH_VOUCHER

#if DISPATCH_USE_DIRECT_TSD
const struct dispatch_tsd_indexes_s dispatch_tsd_indexes = {
        .dti_version = 2,
        .dti_queue_index = dispatch_queue_key,
        .dti_voucher_index = dispatch_voucher_key,
        .dti_qos_class_index = dispatch_priority_key,
};
#else // DISPATCH_USE_DIRECT_TSD
#error Not implemented on this platform
#endif // DISPATCH_USE_DIRECT_TSD

// 6618342 Contact the team that owns the Instrument DTrace probe before
//         renaming this symbol
DISPATCH_CACHELINE_ALIGN
struct dispatch_queue_s _dispatch_main_q = {
        .do_vtable = DISPATCH_VTABLE(queue),
#if !DISPATCH_USE_RESOLVERS
        .do_targetq = &_dispatch_root_queues[
                        DISPATCH_ROOT_QUEUE_IDX_DEFAULT_QOS_OVERCOMMIT],
#endif
        .do_ref_cnt = DISPATCH_OBJECT_GLOBAL_REFCNT,
        .do_xref_cnt = DISPATCH_OBJECT_GLOBAL_REFCNT,
        .do_suspend_cnt = DISPATCH_OBJECT_SUSPEND_LOCK,
        .dq_label = "com.apple.main-thread",
        .dq_running = 1,
        .dq_width = 1,
        .dq_is_thread_bound = 1,
        .dq_override_voucher = DISPATCH_NO_VOUCHER,
        .dq_serialnum = 1,
};

#pragma mark -
#pragma mark dispatch_queue_attr_t

#define DISPATCH_QUEUE_ATTR_INITIALIZER(qos, prio, overcommit, concurrent) \
                { \
                        .do_vtable = DISPATCH_VTABLE(queue_attr), \
                        .do_ref_cnt = DISPATCH_OBJECT_GLOBAL_REFCNT, \
                        .do_xref_cnt = DISPATCH_OBJECT_GLOBAL_REFCNT, \
                        .do_next = DISPATCH_OBJECT_LISTLESS, \
                        .dqa_qos_class = (qos), \
                        .dqa_relative_priority = (qos) ? (prio) : 0, \
                        .dqa_overcommit = _dispatch_queue_attr_overcommit_##overcommit, \
                        .dqa_concurrent = (concurrent), \
                }

#define DISPATCH_QUEUE_ATTR_KIND_INIT(qos, prio) \
                { \
                        [DQA_INDEX_NON_OVERCOMMIT][DQA_INDEX_CONCURRENT] = \
                                        DISPATCH_QUEUE_ATTR_INITIALIZER(qos, prio, disabled, 1), \
                        [DQA_INDEX_NON_OVERCOMMIT][DQA_INDEX_SERIAL] = \
                                        DISPATCH_QUEUE_ATTR_INITIALIZER(qos, prio, disabled, 0), \
                        [DQA_INDEX_OVERCOMMIT][DQA_INDEX_CONCURRENT] = \
                                        DISPATCH_QUEUE_ATTR_INITIALIZER(qos, prio, enabled, 1), \
                        [DQA_INDEX_OVERCOMMIT][DQA_INDEX_SERIAL] = \
                                        DISPATCH_QUEUE_ATTR_INITIALIZER(qos, prio, enabled, 0), \
                        [DQA_INDEX_UNSPECIFIED_OVERCOMMIT][DQA_INDEX_CONCURRENT] = \
                                        DISPATCH_QUEUE_ATTR_INITIALIZER(qos, prio, unspecified, 1),\
                        [DQA_INDEX_UNSPECIFIED_OVERCOMMIT][DQA_INDEX_SERIAL] = \
                                        DISPATCH_QUEUE_ATTR_INITIALIZER(qos, prio, unspecified, 0),\
                }

#define DISPATCH_QUEUE_ATTR_PRIO_INITIALIZER(qos, prio) \
                [prio] = DISPATCH_QUEUE_ATTR_KIND_INIT(qos, -(prio))

#define DISPATCH_QUEUE_ATTR_PRIO_INIT(qos) \
                { \
                        DISPATCH_QUEUE_ATTR_PRIO_INITIALIZER(qos, 0), \
                        DISPATCH_QUEUE_ATTR_PRIO_INITIALIZER(qos, 1), \
                        DISPATCH_QUEUE_ATTR_PRIO_INITIALIZER(qos, 2), \
                        DISPATCH_QUEUE_ATTR_PRIO_INITIALIZER(qos, 3), \
                        DISPATCH_QUEUE_ATTR_PRIO_INITIALIZER(qos, 4), \
                        DISPATCH_QUEUE_ATTR_PRIO_INITIALIZER(qos, 5), \
                        DISPATCH_QUEUE_ATTR_PRIO_INITIALIZER(qos, 6), \
                        DISPATCH_QUEUE_ATTR_PRIO_INITIALIZER(qos, 7), \
                        DISPATCH_QUEUE_ATTR_PRIO_INITIALIZER(qos, 8), \
                        DISPATCH_QUEUE_ATTR_PRIO_INITIALIZER(qos, 9), \
                        DISPATCH_QUEUE_ATTR_PRIO_INITIALIZER(qos, 10), \
                        DISPATCH_QUEUE_ATTR_PRIO_INITIALIZER(qos, 11), \
                        DISPATCH_QUEUE_ATTR_PRIO_INITIALIZER(qos, 12), \
                        DISPATCH_QUEUE_ATTR_PRIO_INITIALIZER(qos, 13), \
                        DISPATCH_QUEUE_ATTR_PRIO_INITIALIZER(qos, 14), \
                        DISPATCH_QUEUE_ATTR_PRIO_INITIALIZER(qos, 15), \
                }

#define DISPATCH_QUEUE_ATTR_QOS_INITIALIZER(qos) \
                [DQA_INDEX_QOS_CLASS_##qos] = \
                                DISPATCH_QUEUE_ATTR_PRIO_INIT(_DISPATCH_QOS_CLASS_##qos)

// DISPATCH_QUEUE_CONCURRENT resp. _dispatch_queue_attr_concurrent is aliased
// to array member [0][0][0][0] and their properties must match!
const struct dispatch_queue_attr_s _dispatch_queue_attrs[]
                [DISPATCH_QUEUE_ATTR_PRIO_COUNT]
                [DISPATCH_QUEUE_ATTR_OVERCOMMIT_COUNT]
                [DISPATCH_QUEUE_ATTR_CONCURRENCY_COUNT] = {
        DISPATCH_QUEUE_ATTR_QOS_INITIALIZER(UNSPECIFIED),
        DISPATCH_QUEUE_ATTR_QOS_INITIALIZER(MAINTENANCE),
        DISPATCH_QUEUE_ATTR_QOS_INITIALIZER(BACKGROUND),
        DISPATCH_QUEUE_ATTR_QOS_INITIALIZER(UTILITY),
        DISPATCH_QUEUE_ATTR_QOS_INITIALIZER(DEFAULT),
        DISPATCH_QUEUE_ATTR_QOS_INITIALIZER(USER_INITIATED),
        DISPATCH_QUEUE_ATTR_QOS_INITIALIZER(USER_INTERACTIVE),
};


#pragma mark -
#pragma mark dispatch_vtables

DISPATCH_VTABLE_INSTANCE(semaphore,
        .do_type = DISPATCH_SEMAPHORE_TYPE,
        .do_kind = "semaphore",
        .do_dispose = _dispatch_semaphore_dispose,
        .do_debug = _dispatch_semaphore_debug,
);

DISPATCH_VTABLE_INSTANCE(group,
        .do_type = DISPATCH_GROUP_TYPE,
        .do_kind = "group",
        .do_dispose = _dispatch_semaphore_dispose,
        .do_debug = _dispatch_semaphore_debug,
);

DISPATCH_VTABLE_INSTANCE(queue,
        .do_type = DISPATCH_QUEUE_TYPE,
        .do_kind = "queue",
        .do_dispose = _dispatch_queue_dispose,
        .do_invoke = _dispatch_queue_invoke,
        .do_probe = _dispatch_queue_probe,
        .do_debug = dispatch_queue_debug,
);

DISPATCH_VTABLE_SUBCLASS_INSTANCE(queue_root, queue,
        .do_type = DISPATCH_QUEUE_ROOT_TYPE,
        .do_kind = "global-queue",
        .do_dispose = _dispatch_pthread_root_queue_dispose,
        .do_probe = _dispatch_root_queue_probe,
        .do_debug = dispatch_queue_debug,
);

DISPATCH_VTABLE_SUBCLASS_INSTANCE(queue_runloop, queue,
        .do_type = DISPATCH_QUEUE_ROOT_TYPE,
        .do_kind = "runloop-queue",
        .do_dispose = _dispatch_runloop_queue_dispose,
        .do_invoke = _dispatch_queue_invoke,
        .do_probe = _dispatch_runloop_queue_probe,
        .do_debug = dispatch_queue_debug,
);

DISPATCH_VTABLE_SUBCLASS_INSTANCE(queue_mgr, queue,
        .do_type = DISPATCH_QUEUE_MGR_TYPE,
        .do_kind = "mgr-queue",
        .do_invoke = _dispatch_mgr_thread,
        .do_probe = _dispatch_mgr_queue_probe,
        .do_debug = dispatch_queue_debug,
);

DISPATCH_VTABLE_INSTANCE(queue_specific_queue,
        .do_type = DISPATCH_QUEUE_SPECIFIC_TYPE,
        .do_kind = "queue-context",
        .do_dispose = _dispatch_queue_specific_queue_dispose,
        .do_invoke = (void*)_dispatch_queue_invoke,
        .do_probe = (void *)_dispatch_queue_probe,
        .do_debug = (void *)dispatch_queue_debug,
);

DISPATCH_VTABLE_INSTANCE(queue_attr,
        .do_type = DISPATCH_QUEUE_ATTR_TYPE,
        .do_kind = "queue-attr",
);

DISPATCH_VTABLE_INSTANCE(source,
        .do_type = DISPATCH_SOURCE_KEVENT_TYPE,
        .do_kind = "kevent-source",
        .do_dispose = _dispatch_source_dispose,
        .do_invoke = _dispatch_source_invoke,
        .do_probe = _dispatch_source_probe,
        .do_debug = _dispatch_source_debug,
);

DISPATCH_VTABLE_INSTANCE(mach,
        .do_type = DISPATCH_MACH_CHANNEL_TYPE,
        .do_kind = "mach-channel",
        .do_dispose = _dispatch_mach_dispose,
        .do_invoke = _dispatch_mach_invoke,
        .do_probe = _dispatch_mach_probe,
        .do_debug = _dispatch_mach_debug,
);

DISPATCH_VTABLE_INSTANCE(mach_msg,
        .do_type = DISPATCH_MACH_MSG_TYPE,
        .do_kind = "mach-msg",
        .do_dispose = _dispatch_mach_msg_dispose,
        .do_invoke = _dispatch_mach_msg_invoke,
        .do_debug = _dispatch_mach_msg_debug,
);

#if !USE_OBJC
DISPATCH_VTABLE_INSTANCE(data,
        .do_type = DISPATCH_DATA_TYPE,
        .do_kind = "data",
        .do_dispose = _dispatch_data_dispose,
        .do_debug = _dispatch_data_debug,
);
#endif

DISPATCH_VTABLE_INSTANCE(io,
        .do_type = DISPATCH_IO_TYPE,
        .do_kind = "channel",
        .do_dispose = _dispatch_io_dispose,
        .do_debug = _dispatch_io_debug,
);

DISPATCH_VTABLE_INSTANCE(operation,
        .do_type = DISPATCH_OPERATION_TYPE,
        .do_kind = "operation",
        .do_dispose = _dispatch_operation_dispose,
        .do_debug = _dispatch_operation_debug,
);

DISPATCH_VTABLE_INSTANCE(disk,
        .do_type = DISPATCH_DISK_TYPE,
        .do_kind = "disk",
        .do_dispose = _dispatch_disk_dispose,
);

void
_dispatch_vtable_init(void)
{
#if USE_OBJC
        // ObjC classes and dispatch vtables are co-located via linker order and
        // alias files, verify correct layout during initialization rdar://10640168
        DISPATCH_OBJC_CLASS_DECL(semaphore);
        dispatch_assert((char*)DISPATCH_VTABLE(semaphore) -
                        (char*)DISPATCH_OBJC_CLASS(semaphore) == 0);
        dispatch_assert((char*)&DISPATCH_CONCAT(_,DISPATCH_CLASS(semaphore_vtable))
                        - (char*)DISPATCH_OBJC_CLASS(semaphore) ==
                        sizeof(_os_object_class_s));
#endif // USE_OBJC
}

#pragma mark -
#pragma mark dispatch_bug

static char _dispatch_build[16];

static void
_dispatch_build_init(void *context DISPATCH_UNUSED)
{
#ifdef __APPLE__
        int mib[] = { CTL_KERN, KERN_OSVERSION };
        size_t bufsz = sizeof(_dispatch_build);

        sysctl(mib, 2, _dispatch_build, &bufsz, NULL, 0);
#else
        /*
         * XXXRW: What to do here for !Mac OS X?
         */
        memset(_dispatch_build, 0, sizeof(_dispatch_build));
#endif
}

static dispatch_once_t _dispatch_build_pred;

char*
_dispatch_get_build(void)
{
        dispatch_once_f(&_dispatch_build_pred, NULL, _dispatch_build_init);
        return _dispatch_build;
}

#define _dispatch_bug_log(msg, ...) do { \
        static void *last_seen; \
        void *ra = __builtin_return_address(0); \
        if (last_seen != ra) { \
                last_seen = ra; \
                _dispatch_log(msg, ##__VA_ARGS__); \
        } \
} while(0)

void
_dispatch_bug(size_t line, long val)
{
        dispatch_once_f(&_dispatch_build_pred, NULL, _dispatch_build_init);
        _dispatch_bug_log("BUG in libdispatch: %s - %lu - 0x%lx",
                        _dispatch_build, (unsigned long)line, val);
}

void
_dispatch_bug_client(const char* msg)
{
        _dispatch_bug_log("BUG in libdispatch client: %s", msg);
}

void
_dispatch_bug_mach_client(const char* msg, mach_msg_return_t kr)
{
        _dispatch_bug_log("BUG in libdispatch client: %s %s - 0x%x", msg,
                        mach_error_string(kr), kr);
}

void
_dispatch_bug_kevent_client(const char* msg, const char* filter,
                const char *operation, int err)
{
        _dispatch_bug_log("BUG in libdispatch client: %s[%s] %s: \"%s\" - 0x%x",
                        msg, filter, operation, strerror(err), err);
}

void
_dispatch_abort(size_t line, long val)
{
        _dispatch_bug(line, val);
        abort();
}

#if !DISPATCH_USE_OS_DEBUG_LOG

#pragma mark -
#pragma mark dispatch_log

static int dispatch_logfile = -1;
static bool dispatch_log_disabled;
#if DISPATCH_DEBUG
static uint64_t dispatch_log_basetime;
#endif
static dispatch_once_t _dispatch_logv_pred;

static void
_dispatch_logv_init(void *context DISPATCH_UNUSED)
{
#if DISPATCH_DEBUG
        bool log_to_file = true;
#else
        bool log_to_file = false;
#endif
        char *e = getenv("LIBDISPATCH_LOG");
        if (e) {
                if (strcmp(e, "YES") == 0) {
                        // default
                } else if (strcmp(e, "NO") == 0) {
                        dispatch_log_disabled = true;
                } else if (strcmp(e, "syslog") == 0) {
                        log_to_file = false;
                } else if (strcmp(e, "file") == 0) {
                        log_to_file = true;
                } else if (strcmp(e, "stderr") == 0) {
                        log_to_file = true;
                        dispatch_logfile = STDERR_FILENO;
                }
        }
        if (!dispatch_log_disabled) {
                if (log_to_file && dispatch_logfile == -1) {
                        char path[PATH_MAX];
                        snprintf(path, sizeof(path), "/var/tmp/libdispatch.%d.log",
                                        getpid());
                        dispatch_logfile = open(path, O_WRONLY | O_APPEND | O_CREAT |
                                        O_NOFOLLOW | O_CLOEXEC, 0666);
                }
                if (dispatch_logfile != -1) {
                        struct timeval tv;
                        gettimeofday(&tv, NULL);
#if DISPATCH_DEBUG
                        dispatch_log_basetime = mach_absolute_time();
#endif
                        dprintf(dispatch_logfile, "=== log file opened for %s[%u] at "
                                        "%ld.%06u ===\n", getprogname() ?: "", getpid(),
                                        tv.tv_sec, tv.tv_usec);
                }
        }
}

static inline void
_dispatch_log_file(char *buf, size_t len)
{
        ssize_t r;

        buf[len++] = '\n';
retry:
        r = write(dispatch_logfile, buf, len);
        if (slowpath(r == -1) && errno == EINTR) {
                goto retry;
        }
}

DISPATCH_NOINLINE
static void
_dispatch_logv_file(const char *msg, va_list ap)
{
        char buf[2048];
        size_t bufsiz = sizeof(buf), offset = 0;
        int r;

#if DISPATCH_DEBUG
        offset += dsnprintf(&buf[offset], bufsiz - offset, "%llu\t",
                        mach_absolute_time() - dispatch_log_basetime);
#endif
        r = vsnprintf(&buf[offset], bufsiz - offset, msg, ap);
        if (r < 0) return;
        offset += (size_t)r;
        if (offset > bufsiz - 1) {
                offset = bufsiz - 1;
        }
        _dispatch_log_file(buf, offset);
}

#if DISPATCH_USE_SIMPLE_ASL
static inline void
_dispatch_syslog(const char *msg)
{
        _simple_asl_log(ASL_LEVEL_NOTICE, "com.apple.libsystem.libdispatch", msg);
}

static inline void
_dispatch_vsyslog(const char *msg, va_list ap)
{
        char *str;
    vasprintf(&str, msg, ap);
        if (str) {
                _dispatch_syslog(str);
                free(str);
        }
}
#else // DISPATCH_USE_SIMPLE_ASL
static inline void
_dispatch_syslog(const char *msg)
{
        syslog(LOG_NOTICE, "%s", msg);
}

static inline void
_dispatch_vsyslog(const char *msg, va_list ap)
{
        vsyslog(LOG_NOTICE, msg, *ap_ptr);
}
#endif // DISPATCH_USE_SIMPLE_ASL

DISPATCH_ALWAYS_INLINE
static inline void
_dispatch_logv(const char *msg, size_t len, va_list *ap_ptr)
{
        dispatch_once_f(&_dispatch_logv_pred, NULL, _dispatch_logv_init);
        if (slowpath(dispatch_log_disabled)) {
                return;
        }
        if (slowpath(dispatch_logfile != -1)) {
                if (!ap_ptr) {
                        return _dispatch_log_file((char*)msg, len);
                }
                return _dispatch_logv_file(msg, *ap_ptr);
        }
        if (!ap_ptr) {
                return _dispatch_syslog(msg);
        }
        return _dispatch_vsyslog(msg, *ap_ptr);
}

DISPATCH_NOINLINE
void
_dispatch_log(const char *msg, ...)
{
        va_list ap;

        va_start(ap, msg);
        _dispatch_logv(msg, 0, &ap);
        va_end(ap);
}

#endif // DISPATCH_USE_OS_DEBUG_LOG

#pragma mark -
#pragma mark dispatch_debug

static size_t
_dispatch_object_debug2(dispatch_object_t dou, char* buf, size_t bufsiz)
{
        DISPATCH_OBJECT_TFB(_dispatch_objc_debug, dou, buf, bufsiz);
        if (dou._do->do_vtable->do_debug) {
                return dx_debug(dou._do, buf, bufsiz);
        }
        return strlcpy(buf, "NULL vtable slot: ", bufsiz);
}

DISPATCH_NOINLINE
static void
_dispatch_debugv(dispatch_object_t dou, const char *msg, va_list ap)
{
        char buf[2048];
        size_t bufsiz = sizeof(buf), offset = 0;
        int r;
#if DISPATCH_DEBUG && !DISPATCH_USE_OS_DEBUG_LOG
        offset += dsnprintf(&buf[offset], bufsiz - offset, "%llu\t\t%p\t",
                        mach_absolute_time() - dispatch_log_basetime,
                        (void *)_dispatch_thread_self());
#endif
        if (dou._do) {
                offset += _dispatch_object_debug2(dou, &buf[offset], bufsiz - offset);
                dispatch_assert(offset + 2 < bufsiz);
                buf[offset++] = ':';
                buf[offset++] = ' ';
                buf[offset]   = '\0';
        } else {
                offset += strlcpy(&buf[offset], "NULL: ", bufsiz - offset);
        }
        r = vsnprintf(&buf[offset], bufsiz - offset, msg, ap);
#if !DISPATCH_USE_OS_DEBUG_LOG
        size_t len = offset + (r < 0 ? 0 : (size_t)r);
        if (len > bufsiz - 1) {
                len = bufsiz - 1;
        }
        _dispatch_logv(buf, len, NULL);
#else
        _dispatch_log("%s", buf);
#endif
}

DISPATCH_NOINLINE
void
dispatch_debugv(dispatch_object_t dou, const char *msg, va_list ap)
{
        _dispatch_debugv(dou, msg, ap);
}

DISPATCH_NOINLINE
void
dispatch_debug(dispatch_object_t dou, const char *msg, ...)
{
        va_list ap;

        va_start(ap, msg);
        _dispatch_debugv(dou, msg, ap);
        va_end(ap);
}

#if DISPATCH_DEBUG
DISPATCH_NOINLINE
void
_dispatch_object_debug(dispatch_object_t dou, const char *msg, ...)
{
        va_list ap;

        va_start(ap, msg);
        _dispatch_debugv(dou._do, msg, ap);
        va_end(ap);
}
#endif

#pragma mark -
#pragma mark dispatch_calloc

DISPATCH_NOINLINE
void
_dispatch_temporary_resource_shortage(void)
{
        sleep(1);
}

void *
_dispatch_calloc(size_t num_items, size_t size)
{
        void *buf;
        while (!fastpath(buf = calloc(num_items, size))) {
                _dispatch_temporary_resource_shortage();
        }
        return buf;
}

#pragma mark -
#pragma mark dispatch_block_t

#ifdef __BLOCKS__

#undef _dispatch_Block_copy
dispatch_block_t
_dispatch_Block_copy(dispatch_block_t db)
{
        dispatch_block_t rval;

        if (fastpath(db)) {
                while (!fastpath(rval = Block_copy(db))) {
                        _dispatch_temporary_resource_shortage();
                }
                return rval;
        }
        DISPATCH_CLIENT_CRASH("NULL was passed where a block should have been");
}

void
_dispatch_call_block_and_release(void *block)
{
        void (^b)(void) = block;
        b();
        Block_release(b);
}

#endif // __BLOCKS__

#pragma mark -
#pragma mark dispatch_client_callout

// Abort on uncaught exceptions thrown from client callouts rdar://8577499
#if DISPATCH_USE_CLIENT_CALLOUT && (__USING_SJLJ_EXCEPTIONS__ || !USE_OBJC)
// On platforms with SjLj exceptions, avoid the SjLj overhead on every callout
// by clearing the unwinder's TSD pointer to the handler stack around callouts

#define _dispatch_get_tsd_base()
#define _dispatch_get_unwind_tsd() (NULL)
#define _dispatch_set_unwind_tsd(u) do {(void)(u);} while (0)
#define _dispatch_free_unwind_tsd()

#undef _dispatch_client_callout
DISPATCH_NOINLINE
void
_dispatch_client_callout(void *ctxt, dispatch_function_t f)
{
        _dispatch_get_tsd_base();
        void *u = _dispatch_get_unwind_tsd();
        if (fastpath(!u)) return f(ctxt);
        _dispatch_set_unwind_tsd(NULL);
        f(ctxt);
        _dispatch_free_unwind_tsd();
        _dispatch_set_unwind_tsd(u);
}

#undef _dispatch_client_callout2
DISPATCH_NOINLINE
void
_dispatch_client_callout2(void *ctxt, size_t i, void (*f)(void *, size_t))
{
        _dispatch_get_tsd_base();
        void *u = _dispatch_get_unwind_tsd();
        if (fastpath(!u)) return f(ctxt, i);
        _dispatch_set_unwind_tsd(NULL);
        f(ctxt, i);
        _dispatch_free_unwind_tsd();
        _dispatch_set_unwind_tsd(u);
}

#undef _dispatch_client_callout4
void
_dispatch_client_callout4(void *ctxt, dispatch_mach_reason_t reason,
                dispatch_mach_msg_t dmsg, mach_error_t error,
                dispatch_mach_handler_function_t f)
{
        _dispatch_get_tsd_base();
        void *u = _dispatch_get_unwind_tsd();
        if (fastpath(!u)) return f(ctxt, reason, dmsg, error);
        _dispatch_set_unwind_tsd(NULL);
        f(ctxt, reason, dmsg, error);
        _dispatch_free_unwind_tsd();
        _dispatch_set_unwind_tsd(u);
}

#endif // DISPATCH_USE_CLIENT_CALLOUT

#pragma mark -
#pragma mark _os_object_t no_objc

#if !USE_OBJC

static const _os_object_class_s _os_object_class;

void
_os_object_init(void)
{
        return;
}

inline _os_object_t
_os_object_alloc_realized(const void *cls, size_t size)
{
        _os_object_t obj;
        dispatch_assert(size >= sizeof(struct _os_object_s));
        while (!fastpath(obj = calloc(1u, size))) {
                _dispatch_temporary_resource_shortage();
        }
        obj->os_obj_isa = cls;
        return obj;
}

_os_object_t
_os_object_alloc(const void *cls, size_t size)
{
        if (!cls) cls = &_os_object_class;
        return _os_object_alloc_realized(cls, size);
}

void
_os_object_dealloc(_os_object_t obj)
{
        *((void *volatile*)&obj->os_obj_isa) = (void *)0x200;
        return free(obj);
}

void
_os_object_xref_dispose(_os_object_t obj)
{
        _os_object_xrefcnt_dispose_barrier(obj);
        if (fastpath(obj->os_obj_isa->_os_obj_xref_dispose)) {
                return obj->os_obj_isa->_os_obj_xref_dispose(obj);
        }
        return _os_object_release_internal(obj);
}

void
_os_object_dispose(_os_object_t obj)
{
        _os_object_refcnt_dispose_barrier(obj);
        if (fastpath(obj->os_obj_isa->_os_obj_dispose)) {
                return obj->os_obj_isa->_os_obj_dispose(obj);
        }
        return _os_object_dealloc(obj);
}

void*
os_retain(void *obj)
{
        if (fastpath(obj)) {
                return _os_object_retain(obj);
        }
        return obj;
}

#undef os_release
void
os_release(void *obj)
{
        if (fastpath(obj)) {
                return _os_object_release(obj);
        }
}

#pragma mark -
#pragma mark dispatch_autorelease_pool no_objc

#if DISPATCH_COCOA_COMPAT

void *_dispatch_autorelease_pool_push(void) {
        void *pool = NULL;
        if (_dispatch_begin_NSAutoReleasePool) {
                pool = _dispatch_begin_NSAutoReleasePool();
        }
        return pool;
}

void _dispatch_autorelease_pool_pop(void *pool) {
        if (_dispatch_end_NSAutoReleasePool) {
                _dispatch_end_NSAutoReleasePool(pool);
        }
}

#endif // DISPATCH_COCOA_COMPAT
#endif // !USE_OBJC

#pragma mark -
#pragma mark dispatch_source_types

static void
dispatch_source_type_timer_init(dispatch_source_t ds,
        dispatch_source_type_t type DISPATCH_UNUSED,
        uintptr_t handle DISPATCH_UNUSED,
        unsigned long mask,
        dispatch_queue_t q)
{
        if (fastpath(!ds->ds_refs)) {
                ds->ds_refs = _dispatch_calloc(1ul,
                                sizeof(struct dispatch_timer_source_refs_s));
        }
        ds->ds_needs_rearm = true;
        ds->ds_is_timer = true;
        if (q == dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0)
                        || q == dispatch_get_global_queue(
                        DISPATCH_QUEUE_PRIORITY_BACKGROUND, DISPATCH_QUEUE_OVERCOMMIT)){
                mask |= DISPATCH_TIMER_BACKGROUND; // <rdar://problem/12200216>
        }
        ds_timer(ds->ds_refs).flags = mask;
}

const struct dispatch_source_type_s _dispatch_source_type_timer = {
        .ke = {
                .filter = DISPATCH_EVFILT_TIMER,
        },
        .mask = DISPATCH_TIMER_STRICT|DISPATCH_TIMER_BACKGROUND|
                        DISPATCH_TIMER_WALL_CLOCK,
        .init = dispatch_source_type_timer_init,
};

static void
dispatch_source_type_timer_with_aggregate_init(dispatch_source_t ds,
        dispatch_source_type_t type, uintptr_t handle, unsigned long mask,
        dispatch_queue_t q)
{
        ds->ds_refs = _dispatch_calloc(1ul,
                        sizeof(struct dispatch_timer_source_aggregate_refs_s));
        dispatch_source_type_timer_init(ds, type, handle, mask, q);
        ds_timer(ds->ds_refs).flags |= DISPATCH_TIMER_WITH_AGGREGATE;
        ds->dq_specific_q = (void*)handle;
        _dispatch_retain(ds->dq_specific_q);
}

const struct dispatch_source_type_s _dispatch_source_type_timer_with_aggregate={
        .ke = {
                .filter = DISPATCH_EVFILT_TIMER,
                .ident = ~0ull,
        },
        .mask = DISPATCH_TIMER_STRICT|DISPATCH_TIMER_BACKGROUND,
        .init = dispatch_source_type_timer_with_aggregate_init,
};

static void
dispatch_source_type_interval_init(dispatch_source_t ds,
        dispatch_source_type_t type, uintptr_t handle, unsigned long mask,
        dispatch_queue_t q)
{
        dispatch_source_type_timer_init(ds, type, handle, mask, q);
        ds_timer(ds->ds_refs).flags |= DISPATCH_TIMER_INTERVAL;
        unsigned long ident = _dispatch_source_timer_idx(ds->ds_refs);
        ds->ds_dkev->dk_kevent.ident = ds->ds_ident_hack = ident;
        _dispatch_source_set_interval(ds, handle);
}

const struct dispatch_source_type_s _dispatch_source_type_interval = {
        .ke = {
                .filter = DISPATCH_EVFILT_TIMER,
                .ident = ~0ull,
        },
        .mask = DISPATCH_TIMER_STRICT|DISPATCH_TIMER_BACKGROUND|
                        DISPATCH_INTERVAL_UI_ANIMATION,
        .init = dispatch_source_type_interval_init,
};

#if !DISPATCH_USE_SELECT_FALLBACK || DISPATCH_DYNAMIC_SELECT_FALLBACK
static void
dispatch_source_type_readwrite_init(dispatch_source_t ds,
        dispatch_source_type_t type DISPATCH_UNUSED,
        uintptr_t handle DISPATCH_UNUSED,
        unsigned long mask DISPATCH_UNUSED,
        dispatch_queue_t q DISPATCH_UNUSED)
{
        ds->ds_dkev->dk_kevent.flags |= EV_UDATA_SPECIFIC;
        ds->ds_is_direct_kevent = true;
        // bypass kernel check for device kqueue support rdar://19004921
        ds->ds_dkev->dk_kevent.fflags = NOTE_LOWAT;
        ds->ds_dkev->dk_kevent.data = 1;
}
#else
#define dispatch_source_type_readwrite_init NULL
#endif

const struct dispatch_source_type_s _dispatch_source_type_read = {
        .ke = {
                .filter = EVFILT_READ,
                .flags = EV_DISPATCH,
        },
        .init = dispatch_source_type_readwrite_init,
};

const struct dispatch_source_type_s _dispatch_source_type_write = {
        .ke = {
                .filter = EVFILT_WRITE,
                .flags = EV_DISPATCH,
        },
        .init = dispatch_source_type_readwrite_init,
};

#if DISPATCH_USE_MEMORYSTATUS

#if TARGET_IPHONE_SIMULATOR // rdar://problem/9219483
static int _dispatch_ios_simulator_memory_warnings_fd = -1;
static void
_dispatch_ios_simulator_memorypressure_init(void *context DISPATCH_UNUSED)
{
        char *e = getenv("SIMULATOR_MEMORY_WARNINGS");
        if (!e) return;
        _dispatch_ios_simulator_memory_warnings_fd = open(e, O_EVTONLY);
        if (_dispatch_ios_simulator_memory_warnings_fd == -1) {
                (void)dispatch_assume_zero(errno);
        }
}
#endif

static void
dispatch_source_type_memorystatus_init(dispatch_source_t ds,
        dispatch_source_type_t type DISPATCH_UNUSED,
        uintptr_t handle DISPATCH_UNUSED,
        unsigned long mask DISPATCH_UNUSED,
        dispatch_queue_t q DISPATCH_UNUSED)
{
#if TARGET_IPHONE_SIMULATOR
        static dispatch_once_t pred;
        dispatch_once_f(&pred, NULL, _dispatch_ios_simulator_memorypressure_init);
        handle = (uintptr_t)_dispatch_ios_simulator_memory_warnings_fd;
        mask = NOTE_ATTRIB;
        ds->ds_dkev->dk_kevent.filter = EVFILT_VNODE;
        ds->ds_dkev->dk_kevent.ident = handle;
        ds->ds_dkev->dk_kevent.flags |= EV_CLEAR;
        ds->ds_dkev->dk_kevent.fflags = (uint32_t)mask;
        ds->ds_ident_hack = handle;
        ds->ds_pending_data_mask = mask;
        ds->ds_memorystatus_override = 1;
#endif
        ds->ds_is_level = false;
}

#ifndef NOTE_MEMORYSTATUS_LOW_SWAP
#define NOTE_MEMORYSTATUS_LOW_SWAP 0x8
#endif

const struct dispatch_source_type_s _dispatch_source_type_memorystatus = {
        .ke = {
                .filter = EVFILT_MEMORYSTATUS,
                .flags = EV_DISPATCH|EV_UDATA_SPECIFIC,
        },
        .mask = NOTE_MEMORYSTATUS_PRESSURE_NORMAL|NOTE_MEMORYSTATUS_PRESSURE_WARN
                        |NOTE_MEMORYSTATUS_PRESSURE_CRITICAL|NOTE_MEMORYSTATUS_LOW_SWAP,
        .init = dispatch_source_type_memorystatus_init,
};

static void
dispatch_source_type_vm_init(dispatch_source_t ds,
        dispatch_source_type_t type,
        uintptr_t handle,
        unsigned long mask,
        dispatch_queue_t q)
{
        // Map legacy vm pressure to memorystatus warning rdar://problem/15907505
        mask = NOTE_MEMORYSTATUS_PRESSURE_WARN;
        ds->ds_dkev->dk_kevent.fflags = (uint32_t)mask;
        ds->ds_pending_data_mask = mask;
        ds->ds_vmpressure_override = 1;
        dispatch_source_type_memorystatus_init(ds, type, handle, mask, q);
}

const struct dispatch_source_type_s _dispatch_source_type_vm = {
        .ke = {
                .filter = EVFILT_MEMORYSTATUS,
                .flags = EV_DISPATCH|EV_UDATA_SPECIFIC,
        },
        .mask = NOTE_VM_PRESSURE,
        .init = dispatch_source_type_vm_init,
};

#elif DISPATCH_USE_VM_PRESSURE

static void
dispatch_source_type_vm_init(dispatch_source_t ds,
        dispatch_source_type_t type DISPATCH_UNUSED,
        uintptr_t handle DISPATCH_UNUSED,
        unsigned long mask DISPATCH_UNUSED,
        dispatch_queue_t q DISPATCH_UNUSED)
{
        ds->ds_is_level = false;
}

const struct dispatch_source_type_s _dispatch_source_type_vm = {
        .ke = {
                .filter = EVFILT_VM,
                .flags = EV_DISPATCH|EV_UDATA_SPECIFIC,
        },
        .mask = NOTE_VM_PRESSURE,
        .init = dispatch_source_type_vm_init,
};

#endif // DISPATCH_USE_VM_PRESSURE

static void
dispatch_source_type_proc_init(dispatch_source_t ds,
        dispatch_source_type_t type DISPATCH_UNUSED,
        uintptr_t handle DISPATCH_UNUSED,
        unsigned long mask DISPATCH_UNUSED,
        dispatch_queue_t q DISPATCH_UNUSED)
{
        ds->ds_dkev->dk_kevent.fflags |= NOTE_EXIT; // rdar://16655831
}

const struct dispatch_source_type_s _dispatch_source_type_proc = {
        .ke = {
                .filter = EVFILT_PROC,
                .flags = EV_CLEAR|EV_UDATA_SPECIFIC,
        },
        .mask = NOTE_EXIT|NOTE_FORK|NOTE_EXEC
#if HAVE_DECL_NOTE_SIGNAL
                        |NOTE_SIGNAL
#endif
#if HAVE_DECL_NOTE_REAP
                        |NOTE_REAP
#endif
                        ,
        .init = dispatch_source_type_proc_init,
};

const struct dispatch_source_type_s _dispatch_source_type_signal = {
        .ke = {
                .filter = EVFILT_SIGNAL,
                .flags = EV_UDATA_SPECIFIC,
        },
};

const struct dispatch_source_type_s _dispatch_source_type_vnode = {
        .ke = {
                .filter = EVFILT_VNODE,
                .flags = EV_CLEAR|EV_UDATA_SPECIFIC,
        },
        .mask = NOTE_DELETE|NOTE_WRITE|NOTE_EXTEND|NOTE_ATTRIB|NOTE_LINK|
                        NOTE_RENAME|NOTE_REVOKE
#if HAVE_DECL_NOTE_NONE
                        |NOTE_NONE
#endif
                        ,
};

const struct dispatch_source_type_s _dispatch_source_type_vfs = {
        .ke = {
                .filter = EVFILT_FS,
                .flags = EV_CLEAR|EV_UDATA_SPECIFIC,
        },
        .mask = VQ_NOTRESP|VQ_NEEDAUTH|VQ_LOWDISK|VQ_MOUNT|VQ_UNMOUNT|VQ_DEAD|
                        VQ_ASSIST|VQ_NOTRESPLOCK
#if HAVE_DECL_VQ_UPDATE
                        |VQ_UPDATE
#endif
#if HAVE_DECL_VQ_VERYLOWDISK
                        |VQ_VERYLOWDISK
#endif
#if HAVE_DECL_VQ_QUOTA
                        |VQ_QUOTA
#endif
                        ,
};

const struct dispatch_source_type_s _dispatch_source_type_sock = {
#ifdef EVFILT_SOCK
        .ke = {
                .filter = EVFILT_SOCK,
                .flags = EV_CLEAR|EV_UDATA_SPECIFIC,
        },
        .mask = NOTE_CONNRESET |  NOTE_READCLOSED | NOTE_WRITECLOSED |
                NOTE_TIMEOUT | NOTE_NOSRCADDR |  NOTE_IFDENIED | NOTE_SUSPEND |
                NOTE_RESUME | NOTE_KEEPALIVE
#ifdef NOTE_ADAPTIVE_WTIMO
                | NOTE_ADAPTIVE_WTIMO | NOTE_ADAPTIVE_RTIMO
#endif
#ifdef NOTE_CONNECTED
                | NOTE_CONNECTED | NOTE_DISCONNECTED | NOTE_CONNINFO_UPDATED
#endif
                ,
#endif // EVFILT_SOCK
};

#if DISPATCH_USE_EV_UDATA_SPECIFIC
static void
dispatch_source_type_data_init(dispatch_source_t ds,
        dispatch_source_type_t type DISPATCH_UNUSED,
        uintptr_t handle DISPATCH_UNUSED,
        unsigned long mask DISPATCH_UNUSED,
        dispatch_queue_t q DISPATCH_UNUSED)
{
        ds->ds_needs_rearm = false; // not registered with kevent
}
#else
#define dispatch_source_type_data_init NULL
#endif

const struct dispatch_source_type_s _dispatch_source_type_data_add = {
        .ke = {
                .filter = DISPATCH_EVFILT_CUSTOM_ADD,
                .flags = EV_UDATA_SPECIFIC,
        },
        .init = dispatch_source_type_data_init,
};

const struct dispatch_source_type_s _dispatch_source_type_data_or = {
        .ke = {
                .filter = DISPATCH_EVFILT_CUSTOM_OR,
                .flags = EV_CLEAR|EV_UDATA_SPECIFIC,
                .fflags = ~0u,
        },
        .init = dispatch_source_type_data_init,
};

#if HAVE_MACH

static void
dispatch_source_type_mach_send_init(dispatch_source_t ds,
        dispatch_source_type_t type DISPATCH_UNUSED,
        uintptr_t handle DISPATCH_UNUSED, unsigned long mask,
        dispatch_queue_t q DISPATCH_UNUSED)
{
        if (!mask) {
                // Preserve legacy behavior that (mask == 0) => DISPATCH_MACH_SEND_DEAD
                ds->ds_dkev->dk_kevent.fflags = DISPATCH_MACH_SEND_DEAD;
                ds->ds_pending_data_mask = DISPATCH_MACH_SEND_DEAD;
        }
}

const struct dispatch_source_type_s _dispatch_source_type_mach_send = {
        .ke = {
                .filter = DISPATCH_EVFILT_MACH_NOTIFICATION,
                .flags = EV_CLEAR,
        },
        .mask = DISPATCH_MACH_SEND_DEAD|DISPATCH_MACH_SEND_POSSIBLE,
        .init = dispatch_source_type_mach_send_init,
};

static void
dispatch_source_type_mach_recv_init(dispatch_source_t ds,
        dispatch_source_type_t type DISPATCH_UNUSED,
        uintptr_t handle DISPATCH_UNUSED,
        unsigned long mask DISPATCH_UNUSED,
        dispatch_queue_t q DISPATCH_UNUSED)
{
        ds->ds_is_level = false;
}

const struct dispatch_source_type_s _dispatch_source_type_mach_recv = {
        .ke = {
                .filter = EVFILT_MACHPORT,
                .flags = EV_DISPATCH,
                .fflags = DISPATCH_MACH_RECV_MESSAGE,
        },
        .init = dispatch_source_type_mach_recv_init,
};

#pragma mark -
#pragma mark dispatch_mig

void *
dispatch_mach_msg_get_context(mach_msg_header_t *msg)
{
        mach_msg_context_trailer_t *tp;
        void *context = NULL;

        tp = (mach_msg_context_trailer_t *)((uint8_t *)msg +
                        round_msg(msg->msgh_size));
        if (tp->msgh_trailer_size >=
                        (mach_msg_size_t)sizeof(mach_msg_context_trailer_t)) {
                context = (void *)(uintptr_t)tp->msgh_context;
        }
        return context;
}

kern_return_t
_dispatch_wakeup_runloop_thread(mach_port_t mp DISPATCH_UNUSED)
{
        // dummy function just to pop a runloop thread out of mach_msg()
        return 0;
}

kern_return_t
_dispatch_consume_send_once_right(mach_port_t mp DISPATCH_UNUSED)
{
        // dummy function to consume a send-once right
        return 0;
}

kern_return_t
_dispatch_mach_notify_port_destroyed(mach_port_t notify DISPATCH_UNUSED,
                mach_port_t name)
{
        kern_return_t kr;
        // this function should never be called
        (void)dispatch_assume_zero(name);
        kr = mach_port_mod_refs(mach_task_self(), name, MACH_PORT_RIGHT_RECEIVE,-1);
        DISPATCH_VERIFY_MIG(kr);
        (void)dispatch_assume_zero(kr);
        return KERN_SUCCESS;
}

kern_return_t
_dispatch_mach_notify_no_senders(mach_port_t notify,
                mach_port_mscount_t mscnt DISPATCH_UNUSED)
{
        // this function should never be called
        (void)dispatch_assume_zero(notify);
        return KERN_SUCCESS;
}

kern_return_t
_dispatch_mach_notify_send_once(mach_port_t notify DISPATCH_UNUSED)
{
        // we only register for dead-name notifications
        // some code deallocated our send-once right without consuming it
#if DISPATCH_DEBUG
        _dispatch_log("Corruption: An app/library deleted a libdispatch "
                        "dead-name notification");
#endif
        return KERN_SUCCESS;
}

#endif // HAVE_MACH