[apple/libpthread.git] / kern / kern_support.c

/*
 * Copyright (c) 2000-2012 Apple Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 *
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 *
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 *
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
 */
/* Copyright (c) 1995-2005 Apple Computer, Inc. All Rights Reserved */
/*
 *      pthread_synch.c
 */

#pragma mark - Front Matter

#define  _PTHREAD_CONDATTR_T
#define  _PTHREAD_COND_T
#define _PTHREAD_MUTEXATTR_T
#define _PTHREAD_MUTEX_T
#define _PTHREAD_RWLOCKATTR_T
#define _PTHREAD_RWLOCK_T

#undef pthread_mutexattr_t
#undef pthread_mutex_t
#undef pthread_condattr_t
#undef pthread_cond_t
#undef pthread_rwlockattr_t
#undef pthread_rwlock_t

#include <sys/cdefs.h>
#include <os/log.h>

// <rdar://problem/26158937> panic() should be marked noreturn
extern void panic(const char *string, ...) __printflike(1,2) __dead2;

#include <sys/param.h>
#include <sys/queue.h>
#include <sys/resourcevar.h>
//#include <sys/proc_internal.h>
#include <sys/kauth.h>
#include <sys/systm.h>
#include <sys/timeb.h>
#include <sys/times.h>
#include <sys/acct.h>
#include <sys/kernel.h>
#include <sys/wait.h>
#include <sys/signalvar.h>
#include <sys/sysctl.h>
#include <sys/syslog.h>
#include <sys/stat.h>
#include <sys/lock.h>
#include <sys/kdebug.h>
//#include <sys/sysproto.h>
#include <sys/vm.h>
#include <sys/user.h>           /* for coredump */
#include <sys/proc_info.h>      /* for fill_procworkqueue */

#include <mach/mach_port.h>
#include <mach/mach_types.h>
#include <mach/semaphore.h>
#include <mach/sync_policy.h>
#include <mach/task.h>
#include <mach/vm_prot.h>
#include <kern/kern_types.h>
#include <kern/task.h>
#include <kern/clock.h>
#include <mach/kern_return.h>
#include <kern/thread.h>
#include <kern/zalloc.h>
#include <kern/sched_prim.h>    /* for thread_exception_return */
#include <kern/processor.h>
#include <kern/assert.h>
#include <mach/mach_vm.h>
#include <mach/mach_param.h>
#include <mach/thread_status.h>
#include <mach/thread_policy.h>
#include <mach/message.h>
#include <mach/port.h>
//#include <vm/vm_protos.h>
#include <vm/vm_fault.h>
#include <vm/vm_map.h>
#include <mach/thread_act.h> /* for thread_resume */
#include <machine/machine_routines.h>
#include <mach/shared_region.h>

#include <libkern/OSAtomic.h>
#include <libkern/libkern.h>

#include <sys/pthread_shims.h>
#include "kern_internal.h"

// XXX: Dirty import for sys/signarvar.h that's wrapped in BSD_KERNEL_PRIVATE
#define sigcantmask (sigmask(SIGKILL) | sigmask(SIGSTOP))

// XXX: Ditto for thread tags from kern/thread.h
#define THREAD_TAG_MAINTHREAD 0x1
#define THREAD_TAG_PTHREAD 0x10
#define THREAD_TAG_WORKQUEUE 0x20

lck_grp_attr_t   *pthread_lck_grp_attr;
lck_grp_t    *pthread_lck_grp;
lck_attr_t   *pthread_lck_attr;

zone_t pthread_zone_workqueue;
zone_t pthread_zone_threadlist;
zone_t pthread_zone_threadreq;

extern void thread_set_cthreadself(thread_t thread, uint64_t pself, int isLP64);
extern void workqueue_thread_yielded(void);

#define WQ_SETUP_FIRST_USE  1
#define WQ_SETUP_CLEAR_VOUCHER  2
static void _setup_wqthread(proc_t p, thread_t th, struct workqueue *wq,
                struct threadlist *tl, int flags);

static void reset_priority(struct threadlist *tl, pthread_priority_t pri);
static pthread_priority_t pthread_priority_from_wq_class_index(struct workqueue *wq, int index);

static void wq_unpark_continue(void* ptr, wait_result_t wait_result) __dead2;

static bool workqueue_addnewthread(proc_t p, struct workqueue *wq);
static void workqueue_removethread(struct threadlist *tl, bool fromexit, bool first_use);
static void workqueue_lock_spin(struct workqueue *);
static void workqueue_unlock(struct workqueue *);

#define WQ_RUN_TR_THROTTLED 0
#define WQ_RUN_TR_THREAD_NEEDED 1
#define WQ_RUN_TR_THREAD_STARTED 2
#define WQ_RUN_TR_EXITING 3
static int workqueue_run_threadreq_and_unlock(proc_t p, struct workqueue *wq,
                struct threadlist *tl, struct threadreq *req, bool may_add_new_thread);

static bool may_start_constrained_thread(struct workqueue *wq,
                uint32_t at_priclass, struct threadlist *tl, bool may_start_timer);

static mach_vm_offset_t stack_addr_hint(proc_t p, vm_map_t vmap);
static boolean_t wq_thread_is_busy(uint64_t cur_ts,
                _Atomic uint64_t *lastblocked_tsp);

int proc_settargetconc(pid_t pid, int queuenum, int32_t targetconc);
int proc_setalltargetconc(pid_t pid, int32_t * targetconcp);

#define WQ_MAXPRI_MIN   0       /* low prio queue num */
#define WQ_MAXPRI_MAX   2       /* max  prio queuenum */
#define WQ_PRI_NUM      3       /* number of prio work queues */

#define C_32_STK_ALIGN          16
#define C_64_STK_ALIGN          16
#define C_64_REDZONE_LEN        128

#define PTHREAD_T_OFFSET 0

/*
 * Flags filed passed to bsdthread_create and back in pthread_start
31  <---------------------------------> 0
_________________________________________
| flags(8) | policy(8) | importance(16) |
-----------------------------------------
*/

#define PTHREAD_START_CUSTOM            0x01000000
#define PTHREAD_START_SETSCHED          0x02000000
#define PTHREAD_START_DETACHED          0x04000000
#define PTHREAD_START_QOSCLASS          0x08000000
#define PTHREAD_START_TSD_BASE_SET      0x10000000
#define PTHREAD_START_QOSCLASS_MASK     0x00ffffff
#define PTHREAD_START_POLICY_BITSHIFT 16
#define PTHREAD_START_POLICY_MASK 0xff
#define PTHREAD_START_IMPORTANCE_MASK 0xffff

#define SCHED_OTHER      POLICY_TIMESHARE
#define SCHED_FIFO       POLICY_FIFO
#define SCHED_RR         POLICY_RR

#define BASEPRI_DEFAULT 31

#pragma mark sysctls

static uint32_t wq_stalled_window_usecs = WQ_STALLED_WINDOW_USECS;
static uint32_t wq_reduce_pool_window_usecs     = WQ_REDUCE_POOL_WINDOW_USECS;
static uint32_t wq_max_timer_interval_usecs     = WQ_MAX_TIMER_INTERVAL_USECS;
static uint32_t wq_max_threads                  = WORKQUEUE_MAXTHREADS;
static uint32_t wq_max_constrained_threads      = WORKQUEUE_MAXTHREADS / 8;
static uint32_t wq_max_concurrency[WORKQUEUE_NUM_BUCKETS + 1]; // set to ncpus on load

SYSCTL_INT(_kern, OID_AUTO, wq_stalled_window_usecs, CTLFLAG_RW | CTLFLAG_LOCKED,
           &wq_stalled_window_usecs, 0, "");

SYSCTL_INT(_kern, OID_AUTO, wq_reduce_pool_window_usecs, CTLFLAG_RW | CTLFLAG_LOCKED,
           &wq_reduce_pool_window_usecs, 0, "");

SYSCTL_INT(_kern, OID_AUTO, wq_max_timer_interval_usecs, CTLFLAG_RW | CTLFLAG_LOCKED,
           &wq_max_timer_interval_usecs, 0, "");

SYSCTL_INT(_kern, OID_AUTO, wq_max_threads, CTLFLAG_RW | CTLFLAG_LOCKED,
           &wq_max_threads, 0, "");

SYSCTL_INT(_kern, OID_AUTO, wq_max_constrained_threads, CTLFLAG_RW | CTLFLAG_LOCKED,
           &wq_max_constrained_threads, 0, "");

#ifdef DEBUG
static int wq_kevent_test SYSCTL_HANDLER_ARGS;
SYSCTL_PROC(_debug, OID_AUTO, wq_kevent_test, CTLFLAG_MASKED | CTLFLAG_RW | CTLFLAG_LOCKED | CTLFLAG_ANYBODY | CTLTYPE_OPAQUE, NULL, 0, wq_kevent_test, 0, "-");
#endif

static uint32_t wq_init_constrained_limit = 1;

uint32_t pthread_debug_tracing = 1;

SYSCTL_INT(_kern, OID_AUTO, pthread_debug_tracing, CTLFLAG_RW | CTLFLAG_LOCKED,
                   &pthread_debug_tracing, 0, "")

static uint32_t pthread_mutex_default_policy;

SYSCTL_INT(_kern, OID_AUTO, pthread_mutex_default_policy, CTLFLAG_RW | CTLFLAG_LOCKED,
           &pthread_mutex_default_policy, 0, "");

/*
 *       +-----+-----+-----+-----+-----+-----+-----+
 *       | MT  | BG  | UT  | DE  | IN  | UN  | mgr |
 * +-----+-----+-----+-----+-----+-----+-----+-----+
 * | pri |  5  |  4  |  3  |  2  |  1  |  0  |  6  |
 * | qos |  1  |  2  |  3  |  4  |  5  |  6  |  7  |
 * +-----+-----+-----+-----+-----+-----+-----+-----+
 */
static inline uint32_t
_wq_bucket_to_thread_qos(int pri)
{
        if (pri == WORKQUEUE_EVENT_MANAGER_BUCKET) {
                return WORKQUEUE_EVENT_MANAGER_BUCKET + 1;
        }
        return WORKQUEUE_EVENT_MANAGER_BUCKET - pri;
}

#pragma mark wq_thactive

#if defined(__LP64__)
// Layout is:
//   7 * 16 bits for each QoS bucket request count (including manager)
//   3 bits of best QoS among all pending constrained requests
//   13 bits of zeroes
#define WQ_THACTIVE_BUCKET_WIDTH 16
#define WQ_THACTIVE_QOS_SHIFT    (7 * WQ_THACTIVE_BUCKET_WIDTH)
#else
// Layout is:
//   6 * 10 bits for each QoS bucket request count (except manager)
//   1 bit for the manager bucket
//   3 bits of best QoS among all pending constrained requests
#define WQ_THACTIVE_BUCKET_WIDTH 10
#define WQ_THACTIVE_QOS_SHIFT    (6 * WQ_THACTIVE_BUCKET_WIDTH + 1)
#endif
#define WQ_THACTIVE_BUCKET_MASK  ((1U << WQ_THACTIVE_BUCKET_WIDTH) - 1)
#define WQ_THACTIVE_BUCKET_HALF  (1U << (WQ_THACTIVE_BUCKET_WIDTH - 1))
#define WQ_THACTIVE_NO_PENDING_REQUEST 6

_Static_assert(sizeof(wq_thactive_t) * CHAR_BIT - WQ_THACTIVE_QOS_SHIFT >= 3,
                "Make sure we have space to encode a QoS");

static inline wq_thactive_t
_wq_thactive_fetch_and_add(struct workqueue *wq, wq_thactive_t offset)
{
#if PTHREAD_INLINE_RMW_ATOMICS || !defined(__LP64__)
        return atomic_fetch_add_explicit(&wq->wq_thactive, offset,
                        memory_order_relaxed);
#else
        return pthread_kern->atomic_fetch_add_128_relaxed(&wq->wq_thactive, offset);
#endif
}

static inline wq_thactive_t
_wq_thactive(struct workqueue *wq)
{
#if PTHREAD_INLINE_RMW_ATOMICS || !defined(__LP64__)
        return atomic_load_explicit(&wq->wq_thactive, memory_order_relaxed);
#else
        return pthread_kern->atomic_load_128_relaxed(&wq->wq_thactive);
#endif
}

#define WQ_THACTIVE_BEST_CONSTRAINED_REQ_QOS(tha) \
                ((tha) >> WQ_THACTIVE_QOS_SHIFT)

static inline uint32_t
_wq_thactive_best_constrained_req_qos(struct workqueue *wq)
{
        // Avoid expensive atomic operations: the three bits we're loading are in
        // a single byte, and always updated under the workqueue lock
        wq_thactive_t v = *(wq_thactive_t *)&wq->wq_thactive;
        return WQ_THACTIVE_BEST_CONSTRAINED_REQ_QOS(v);
}

static inline wq_thactive_t
_wq_thactive_set_best_constrained_req_qos(struct workqueue *wq,
                uint32_t orig_qos, uint32_t new_qos)
{
        wq_thactive_t v;
        v = (wq_thactive_t)(new_qos - orig_qos) << WQ_THACTIVE_QOS_SHIFT;
        /*
         * We can do an atomic add relative to the initial load because updates
         * to this qos are always serialized under the workqueue lock.
         */
        return _wq_thactive_fetch_and_add(wq, v) + v;
}

static inline wq_thactive_t
_wq_thactive_offset_for_qos(int qos)
{
        return (wq_thactive_t)1 << (qos * WQ_THACTIVE_BUCKET_WIDTH);
}

static inline wq_thactive_t
_wq_thactive_inc(struct workqueue *wq, int qos)
{
        return _wq_thactive_fetch_and_add(wq, _wq_thactive_offset_for_qos(qos));
}

static inline wq_thactive_t
_wq_thactive_dec(struct workqueue *wq, int qos)
{
        return _wq_thactive_fetch_and_add(wq, -_wq_thactive_offset_for_qos(qos));
}

static inline wq_thactive_t
_wq_thactive_move(struct workqueue *wq, int oldqos, int newqos)
{
        return _wq_thactive_fetch_and_add(wq, _wq_thactive_offset_for_qos(newqos) -
                        _wq_thactive_offset_for_qos(oldqos));
}

static inline uint32_t
_wq_thactive_aggregate_downto_qos(struct workqueue *wq, wq_thactive_t v,
                int qos, uint32_t *busycount, uint32_t *max_busycount)
{
        uint32_t count = 0, active;
        uint64_t curtime;

#ifndef __LP64__
        /*
         * on 32bits the manager bucket is a single bit and the best constrained
         * request QoS 3 bits are where the 10 bits of a regular QoS bucket count
         * would be. Mask them out.
         */
        v &= ~(~0ull << WQ_THACTIVE_QOS_SHIFT);
#endif
        if (busycount) {
                curtime = mach_absolute_time();
                *busycount = 0;
        }
        if (max_busycount) {
                *max_busycount = qos + 1;
        }
        for (int i = 0; i <= qos; i++, v >>= WQ_THACTIVE_BUCKET_WIDTH) {
                active = v & WQ_THACTIVE_BUCKET_MASK;
                count += active;
                if (busycount && wq->wq_thscheduled_count[i] > active) {
                        if (wq_thread_is_busy(curtime, &wq->wq_lastblocked_ts[i])) {
                                /*
                                 * We only consider the last blocked thread for a given bucket
                                 * as busy because we don't want to take the list lock in each
                                 * sched callback. However this is an approximation that could
                                 * contribute to thread creation storms.
                                 */
                                (*busycount)++;
                        }
                }
        }
        return count;
}

#pragma mark - Process/Thread Setup/Teardown syscalls

static mach_vm_offset_t
stack_addr_hint(proc_t p, vm_map_t vmap)
{
        mach_vm_offset_t stackaddr;
        mach_vm_offset_t aslr_offset;
        bool proc64bit = proc_is64bit(p);

        // We can't safely take random values % something unless its a power-of-two
        _Static_assert(powerof2(PTH_DEFAULT_STACKSIZE), "PTH_DEFAULT_STACKSIZE is a power-of-two");

#if defined(__i386__) || defined(__x86_64__)
        if (proc64bit) {
                // Matches vm_map_get_max_aslr_slide_pages's image shift in xnu
                aslr_offset = random() % (1 << 28); // about 512 stacks
        } else {
                // Actually bigger than the image shift, we've got ~256MB to work with
                aslr_offset = random() % (16 * PTH_DEFAULT_STACKSIZE);
        }
        aslr_offset = vm_map_trunc_page_mask(aslr_offset, vm_map_page_mask(vmap));
        if (proc64bit) {
                // Above nanomalloc range (see NANOZONE_SIGNATURE)
                stackaddr = 0x700000000000 + aslr_offset;
        } else {
                stackaddr = SHARED_REGION_BASE_I386 + SHARED_REGION_SIZE_I386 + aslr_offset;
        }
#elif defined(__arm__) || defined(__arm64__)
        user_addr_t main_thread_stack_top = 0;
        if (pthread_kern->proc_get_user_stack) {
                main_thread_stack_top = pthread_kern->proc_get_user_stack(p);
        }
        if (proc64bit && main_thread_stack_top) {
                // The main thread stack position is randomly slid by xnu (c.f.
                // load_main() in mach_loader.c), so basing pthread stack allocations
                // where the main thread stack ends is already ASLRd and doing so
                // avoids creating a gap in the process address space that may cause
                // extra PTE memory usage. rdar://problem/33328206
                stackaddr = vm_map_trunc_page_mask((vm_map_offset_t)main_thread_stack_top,
                                vm_map_page_mask(vmap));
        } else {
                // vm_map_get_max_aslr_slide_pages ensures 1MB of slide, we do better
                aslr_offset = random() % ((proc64bit ? 4 : 2) * PTH_DEFAULT_STACKSIZE);
                aslr_offset = vm_map_trunc_page_mask((vm_map_offset_t)aslr_offset,
                                vm_map_page_mask(vmap));
                if (proc64bit) {
                        // 64 stacks below shared region
                        stackaddr = SHARED_REGION_BASE_ARM64 - 64 * PTH_DEFAULT_STACKSIZE - aslr_offset;
                } else {
                        // If you try to slide down from this point, you risk ending up in memory consumed by malloc
                        stackaddr = SHARED_REGION_BASE_ARM - 32 * PTH_DEFAULT_STACKSIZE + aslr_offset;
                }
        }
#else
#error Need to define a stack address hint for this architecture
#endif
        return stackaddr;
}

/**
 * bsdthread_create system call.  Used by pthread_create.
 */
int
_bsdthread_create(struct proc *p, user_addr_t user_func, user_addr_t user_funcarg, user_addr_t user_stack, user_addr_t user_pthread, uint32_t flags, user_addr_t *retval)
{
        kern_return_t kret;
        void * sright;
        int error = 0;
        int allocated = 0;
        mach_vm_offset_t stackaddr;
        mach_vm_size_t th_allocsize = 0;
        mach_vm_size_t th_guardsize;
        mach_vm_offset_t th_stack;
        mach_vm_offset_t th_pthread;
        mach_vm_offset_t th_tsd_base;
        mach_port_name_t th_thport;
        thread_t th;
        vm_map_t vmap = pthread_kern->current_map();
        task_t ctask = current_task();
        unsigned int policy, importance;
        uint32_t tsd_offset;

        int isLP64 = 0;

        if (pthread_kern->proc_get_register(p) == 0) {
                return EINVAL;
        }

        PTHREAD_TRACE(TRACE_pthread_thread_create | DBG_FUNC_START, flags, 0, 0, 0, 0);

        isLP64 = proc_is64bit(p);
        th_guardsize = vm_map_page_size(vmap);

        stackaddr = pthread_kern->proc_get_stack_addr_hint(p);
        kret = pthread_kern->thread_create(ctask, &th);
        if (kret != KERN_SUCCESS)
                return(ENOMEM);
        thread_reference(th);

        pthread_kern->thread_set_tag(th, THREAD_TAG_PTHREAD);

        sright = (void *)pthread_kern->convert_thread_to_port(th);
        th_thport = pthread_kern->ipc_port_copyout_send(sright, pthread_kern->task_get_ipcspace(ctask));
        if (!MACH_PORT_VALID(th_thport)) {
                error = EMFILE; // userland will convert this into a crash
                goto out;
        }

        if ((flags & PTHREAD_START_CUSTOM) == 0) {
                mach_vm_size_t pthread_size =
                        vm_map_round_page_mask(pthread_kern->proc_get_pthsize(p) + PTHREAD_T_OFFSET, vm_map_page_mask(vmap));
                th_allocsize = th_guardsize + user_stack + pthread_size;
                user_stack += PTHREAD_T_OFFSET;

                kret = mach_vm_map(vmap, &stackaddr,
                                th_allocsize,
                                page_size-1,
                                VM_MAKE_TAG(VM_MEMORY_STACK)| VM_FLAGS_ANYWHERE , NULL,
                                0, FALSE, VM_PROT_DEFAULT, VM_PROT_ALL,
                                VM_INHERIT_DEFAULT);
                if (kret != KERN_SUCCESS){
                        kret = mach_vm_allocate(vmap,
                                        &stackaddr, th_allocsize,
                                        VM_MAKE_TAG(VM_MEMORY_STACK)| VM_FLAGS_ANYWHERE);
                }
                if (kret != KERN_SUCCESS) {
                        error = ENOMEM;
                        goto out;
                }

                PTHREAD_TRACE(TRACE_pthread_thread_create|DBG_FUNC_NONE, th_allocsize, stackaddr, 0, 2, 0);

                allocated = 1;
                /*
                 * The guard page is at the lowest address
                 * The stack base is the highest address
                 */
                kret = mach_vm_protect(vmap,  stackaddr, th_guardsize, FALSE, VM_PROT_NONE);

                if (kret != KERN_SUCCESS) {
                        error = ENOMEM;
                        goto out1;
                }

                th_pthread = stackaddr + th_guardsize + user_stack;
                th_stack = th_pthread;

                /*
                * Pre-fault the first page of the new thread's stack and the page that will
                * contain the pthread_t structure.
                */
                if (vm_map_trunc_page_mask((vm_map_offset_t)(th_stack - C_64_REDZONE_LEN), vm_map_page_mask(vmap)) !=
                                vm_map_trunc_page_mask((vm_map_offset_t)th_pthread, vm_map_page_mask(vmap))){
                        vm_fault( vmap,
                                        vm_map_trunc_page_mask((vm_map_offset_t)(th_stack - C_64_REDZONE_LEN), vm_map_page_mask(vmap)),
                                        VM_PROT_READ | VM_PROT_WRITE,
                                        FALSE,
                                        THREAD_UNINT, NULL, 0);
                }

                vm_fault( vmap,
                                vm_map_trunc_page_mask((vm_map_offset_t)th_pthread, vm_map_page_mask(vmap)),
                                VM_PROT_READ | VM_PROT_WRITE,
                                FALSE,
                                THREAD_UNINT, NULL, 0);

        } else {
                th_stack = user_stack;
                th_pthread = user_pthread;

                PTHREAD_TRACE(TRACE_pthread_thread_create|DBG_FUNC_NONE, 0, 0, 0, 3, 0);
        }

        tsd_offset = pthread_kern->proc_get_pthread_tsd_offset(p);
        if (tsd_offset) {
                th_tsd_base = th_pthread + tsd_offset;
                kret = pthread_kern->thread_set_tsd_base(th, th_tsd_base);
                if (kret == KERN_SUCCESS) {
                        flags |= PTHREAD_START_TSD_BASE_SET;
                }
        }

#if defined(__i386__) || defined(__x86_64__)
        /*
         * Set up i386 registers & function call.
         */
        if (isLP64 == 0) {
                x86_thread_state32_t state = {
                        .eip = (unsigned int)pthread_kern->proc_get_threadstart(p),
                        .eax = (unsigned int)th_pthread,
                        .ebx = (unsigned int)th_thport,
                        .ecx = (unsigned int)user_func,
                        .edx = (unsigned int)user_funcarg,
                        .edi = (unsigned int)user_stack,
                        .esi = (unsigned int)flags,
                        /*
                         * set stack pointer
                         */
                        .esp = (int)((vm_offset_t)(th_stack-C_32_STK_ALIGN))
                };

                error = pthread_kern->thread_set_wq_state32(th, (thread_state_t)&state);
                if (error != KERN_SUCCESS) {
                        error = EINVAL;
                        goto out;
                }
        } else {
                x86_thread_state64_t state64 = {
                        .rip = (uint64_t)pthread_kern->proc_get_threadstart(p),
                        .rdi = (uint64_t)th_pthread,
                        .rsi = (uint64_t)(th_thport),
                        .rdx = (uint64_t)user_func,
                        .rcx = (uint64_t)user_funcarg,
                        .r8 = (uint64_t)user_stack,
                        .r9 = (uint64_t)flags,
                        /*
                         * set stack pointer aligned to 16 byte boundary
                         */
                        .rsp = (uint64_t)(th_stack - C_64_REDZONE_LEN)
                };

                error = pthread_kern->thread_set_wq_state64(th, (thread_state_t)&state64);
                if (error != KERN_SUCCESS) {
                        error = EINVAL;
                        goto out;
                }

        }
#elif defined(__arm__)
        arm_thread_state_t state = {
                .pc = (int)pthread_kern->proc_get_threadstart(p),
                .r[0] = (unsigned int)th_pthread,
                .r[1] = (unsigned int)th_thport,
                .r[2] = (unsigned int)user_func,
                .r[3] = (unsigned int)user_funcarg,
                .r[4] = (unsigned int)user_stack,
                .r[5] = (unsigned int)flags,

                /* Set r7 & lr to 0 for better back tracing */
                .r[7] = 0,
                .lr = 0,

                /*
                 * set stack pointer
                 */
                .sp = (int)((vm_offset_t)(th_stack-C_32_STK_ALIGN))
        };

        (void) pthread_kern->thread_set_wq_state32(th, (thread_state_t)&state);

#else
#error bsdthread_create  not defined for this architecture
#endif

        if ((flags & PTHREAD_START_SETSCHED) != 0) {
                /* Set scheduling parameters if needed */
                thread_extended_policy_data_t    extinfo;
                thread_precedence_policy_data_t   precedinfo;

                importance = (flags & PTHREAD_START_IMPORTANCE_MASK);
                policy = (flags >> PTHREAD_START_POLICY_BITSHIFT) & PTHREAD_START_POLICY_MASK;

                if (policy == SCHED_OTHER) {
                        extinfo.timeshare = 1;
                } else {
                        extinfo.timeshare = 0;
                }

                thread_policy_set(th, THREAD_EXTENDED_POLICY, (thread_policy_t)&extinfo, THREAD_EXTENDED_POLICY_COUNT);

                precedinfo.importance = (importance - BASEPRI_DEFAULT);
                thread_policy_set(th, THREAD_PRECEDENCE_POLICY, (thread_policy_t)&precedinfo, THREAD_PRECEDENCE_POLICY_COUNT);
        } else if ((flags & PTHREAD_START_QOSCLASS) != 0) {
                /* Set thread QoS class if requested. */
                pthread_priority_t priority = (pthread_priority_t)(flags & PTHREAD_START_QOSCLASS_MASK);

                thread_qos_policy_data_t qos;
                qos.qos_tier = pthread_priority_get_thread_qos(priority);
                qos.tier_importance = (qos.qos_tier == QOS_CLASS_UNSPECIFIED) ? 0 :
                                _pthread_priority_get_relpri(priority);

                pthread_kern->thread_policy_set_internal(th, THREAD_QOS_POLICY, (thread_policy_t)&qos, THREAD_QOS_POLICY_COUNT);
        }

        if (pthread_kern->proc_get_mach_thread_self_tsd_offset) {
                uint64_t mach_thread_self_offset =
                                pthread_kern->proc_get_mach_thread_self_tsd_offset(p);
                if (mach_thread_self_offset && tsd_offset) {
                        bool proc64bit = proc_is64bit(p);
                        if (proc64bit) {
                                uint64_t th_thport_tsd = (uint64_t)th_thport;
                                error = copyout(&th_thport_tsd, th_pthread + tsd_offset +
                                                mach_thread_self_offset, sizeof(th_thport_tsd));
                        } else {
                                uint32_t th_thport_tsd = (uint32_t)th_thport;
                                error = copyout(&th_thport_tsd, th_pthread + tsd_offset +
                                                mach_thread_self_offset, sizeof(th_thport_tsd));
                        }
                        if (error) {
                                goto out1;
                        }
                }
        }

        kret = pthread_kern->thread_resume(th);
        if (kret != KERN_SUCCESS) {
                error = EINVAL;
                goto out1;
        }
        thread_deallocate(th);  /* drop the creator reference */

        PTHREAD_TRACE(TRACE_pthread_thread_create|DBG_FUNC_END, error, th_pthread, 0, 0, 0);

        // cast required as mach_vm_offset_t is always 64 bits even on 32-bit platforms
        *retval = (user_addr_t)th_pthread;

        return(0);

out1:
        if (allocated != 0) {
                (void)mach_vm_deallocate(vmap, stackaddr, th_allocsize);
        }
out:
        (void)pthread_kern->mach_port_deallocate(pthread_kern->task_get_ipcspace(ctask), th_thport);
        if (pthread_kern->thread_will_park_or_terminate) {
                pthread_kern->thread_will_park_or_terminate(th);
        }
        (void)thread_terminate(th);
        (void)thread_deallocate(th);
        return(error);
}

/**
 * bsdthread_terminate system call.  Used by pthread_terminate
 */
int
_bsdthread_terminate(__unused struct proc *p,
                     user_addr_t stackaddr,
                     size_t size,
                     uint32_t kthport,
                     uint32_t sem,
                     __unused int32_t *retval)
{
        mach_vm_offset_t freeaddr;
        mach_vm_size_t freesize;
        kern_return_t kret;
        thread_t th = current_thread();

        freeaddr = (mach_vm_offset_t)stackaddr;
        freesize = size;

        PTHREAD_TRACE(TRACE_pthread_thread_terminate|DBG_FUNC_START, freeaddr, freesize, kthport, 0xff, 0);

        if ((freesize != (mach_vm_size_t)0) && (freeaddr != (mach_vm_offset_t)0)) {
                if (pthread_kern->thread_get_tag(th) & THREAD_TAG_MAINTHREAD){
                        vm_map_t user_map = pthread_kern->current_map();
                        freesize = vm_map_trunc_page_mask((vm_map_offset_t)freesize - 1, vm_map_page_mask(user_map));
                        kret = mach_vm_behavior_set(user_map, freeaddr, freesize, VM_BEHAVIOR_REUSABLE);
                        assert(kret == KERN_SUCCESS || kret == KERN_INVALID_ADDRESS);
                        kret = kret ? kret : mach_vm_protect(user_map, freeaddr, freesize, FALSE, VM_PROT_NONE);
                        assert(kret == KERN_SUCCESS || kret == KERN_INVALID_ADDRESS);
                } else {
                        kret = mach_vm_deallocate(pthread_kern->current_map(), freeaddr, freesize);
                        if (kret != KERN_SUCCESS) {
                                PTHREAD_TRACE(TRACE_pthread_thread_terminate|DBG_FUNC_END, kret, 0, 0, 0, 0);
                                return(EINVAL);
                        }
                }
        }

        if (pthread_kern->thread_will_park_or_terminate) {
                pthread_kern->thread_will_park_or_terminate(th);
        }
        (void)thread_terminate(th);
        if (sem != MACH_PORT_NULL) {
                 kret = pthread_kern->semaphore_signal_internal_trap(sem);
                if (kret != KERN_SUCCESS) {
                        PTHREAD_TRACE(TRACE_pthread_thread_terminate|DBG_FUNC_END, kret, 0, 0, 0, 0);
                        return(EINVAL);
                }
        }

        if (kthport != MACH_PORT_NULL) {
                pthread_kern->mach_port_deallocate(pthread_kern->task_get_ipcspace(current_task()), kthport);
        }

        PTHREAD_TRACE(TRACE_pthread_thread_terminate|DBG_FUNC_END, 0, 0, 0, 0, 0);

        pthread_kern->thread_exception_return();
        panic("bsdthread_terminate: still running\n");

        PTHREAD_TRACE(TRACE_pthread_thread_terminate|DBG_FUNC_END, 0, 0xff, 0, 0, 0);

        return(0);
}

/**
 * bsdthread_register system call.  Performs per-process setup.  Responsible for
 * returning capabilitiy bits to userspace and receiving userspace function addresses.
 */
int
_bsdthread_register(struct proc *p,
                    user_addr_t threadstart,
                    user_addr_t wqthread,
                    int pthsize,
                    user_addr_t pthread_init_data,
                    user_addr_t pthread_init_data_size,
                    uint64_t dispatchqueue_offset,
                    int32_t *retval)
{
        struct _pthread_registration_data data = {};
        uint32_t max_tsd_offset;
        kern_return_t kr;
        size_t pthread_init_sz = 0;

        /* syscall randomizer test can pass bogus values */
        if (pthsize < 0 || pthsize > MAX_PTHREAD_SIZE) {
                return(EINVAL);
        }
        /*
         * if we have pthread_init_data, then we use that and target_concptr
         * (which is an offset) get data.
         */
        if (pthread_init_data != 0) {
                if (pthread_init_data_size < sizeof(data.version)) {
                        return EINVAL;
                }
                pthread_init_sz = MIN(sizeof(data), (size_t)pthread_init_data_size);
                int ret = copyin(pthread_init_data, &data, pthread_init_sz);
                if (ret) {
                        return ret;
                }
                if (data.version != (size_t)pthread_init_data_size) {
                        return EINVAL;
                }
        } else {
                data.dispatch_queue_offset = dispatchqueue_offset;
        }

        /* We have to do this before proc_get_register so that it resets after fork */
        mach_vm_offset_t stackaddr = stack_addr_hint(p, pthread_kern->current_map());
        pthread_kern->proc_set_stack_addr_hint(p, (user_addr_t)stackaddr);

        /* prevent multiple registrations */
        if (pthread_kern->proc_get_register(p) != 0) {
                return(EINVAL);
        }

        pthread_kern->proc_set_threadstart(p, threadstart);
        pthread_kern->proc_set_wqthread(p, wqthread);
        pthread_kern->proc_set_pthsize(p, pthsize);
        pthread_kern->proc_set_register(p);

        uint32_t tsd_slot_sz = proc_is64bit(p) ? sizeof(uint64_t) : sizeof(uint32_t);
        if ((uint32_t)pthsize >= tsd_slot_sz &&
                        data.tsd_offset <= (uint32_t)(pthsize - tsd_slot_sz)) {
                max_tsd_offset = ((uint32_t)pthsize - data.tsd_offset - tsd_slot_sz);
        } else {
                data.tsd_offset = 0;
                max_tsd_offset = 0;
        }
        pthread_kern->proc_set_pthread_tsd_offset(p, data.tsd_offset);

        if (data.dispatch_queue_offset > max_tsd_offset) {
                data.dispatch_queue_offset = 0;
        }
        pthread_kern->proc_set_dispatchqueue_offset(p, data.dispatch_queue_offset);

        if (pthread_kern->proc_set_return_to_kernel_offset) {
                if (data.return_to_kernel_offset > max_tsd_offset) {
                        data.return_to_kernel_offset = 0;
                }
                pthread_kern->proc_set_return_to_kernel_offset(p,
                                data.return_to_kernel_offset);
        }

        if (pthread_kern->proc_set_mach_thread_self_tsd_offset) {
                if (data.mach_thread_self_offset > max_tsd_offset) {
                        data.mach_thread_self_offset = 0;
                }
                pthread_kern->proc_set_mach_thread_self_tsd_offset(p,
                                data.mach_thread_self_offset);
        }

        if (pthread_init_data != 0) {
                /* Outgoing data that userspace expects as a reply */
                data.version = sizeof(struct _pthread_registration_data);
                if (pthread_kern->qos_main_thread_active()) {
                        mach_msg_type_number_t nqos = THREAD_QOS_POLICY_COUNT;
                        thread_qos_policy_data_t qos;
                        boolean_t gd = FALSE;

                        kr = pthread_kern->thread_policy_get(current_thread(), THREAD_QOS_POLICY, (thread_policy_t)&qos, &nqos, &gd);
                        if (kr != KERN_SUCCESS || qos.qos_tier == THREAD_QOS_UNSPECIFIED) {
                                /* Unspecified threads means the kernel wants us to impose legacy upon the thread. */
                                qos.qos_tier = THREAD_QOS_LEGACY;
                                qos.tier_importance = 0;

                                kr = pthread_kern->thread_policy_set_internal(current_thread(), THREAD_QOS_POLICY, (thread_policy_t)&qos, THREAD_QOS_POLICY_COUNT);
                        }

                        if (kr == KERN_SUCCESS) {
                                data.main_qos = thread_qos_get_pthread_priority(qos.qos_tier);
                        } else {
                                data.main_qos = _pthread_priority_make_newest(QOS_CLASS_UNSPECIFIED, 0, 0);
                        }
                } else {
                        data.main_qos = _pthread_priority_make_newest(QOS_CLASS_UNSPECIFIED, 0, 0);
                }

                data.mutex_default_policy = pthread_mutex_default_policy;

                kr = copyout(&data, pthread_init_data, pthread_init_sz);
                if (kr != KERN_SUCCESS) {
                        return EINVAL;
                }
        }

        /* return the supported feature set as the return value. */
        *retval = PTHREAD_FEATURE_SUPPORTED;

        return(0);
}

#pragma mark - QoS Manipulation

int
_bsdthread_ctl_set_qos(struct proc *p, user_addr_t __unused cmd, mach_port_name_t kport, user_addr_t tsd_priority_addr, user_addr_t arg3, int *retval)
{
        int rv;
        thread_t th;

        pthread_priority_t priority;

        /* Unused parameters must be zero. */
        if (arg3 != 0) {
                return EINVAL;
        }

        /* QoS is stored in a given slot in the pthread TSD. We need to copy that in and set our QoS based on it. */
        if (proc_is64bit(p)) {
                uint64_t v;
                rv = copyin(tsd_priority_addr, &v, sizeof(v));
                if (rv) goto out;
                priority = (int)(v & 0xffffffff);
        } else {
                uint32_t v;
                rv = copyin(tsd_priority_addr, &v, sizeof(v));
                if (rv) goto out;
                priority = v;
        }

        if ((th = port_name_to_thread(kport)) == THREAD_NULL) {
                return ESRCH;
        }

        /* <rdar://problem/16211829> Disable pthread_set_qos_class_np() on threads other than pthread_self */
        if (th != current_thread()) {
                thread_deallocate(th);
                return EPERM;
        }

        rv = _bsdthread_ctl_set_self(p, 0, priority, 0, _PTHREAD_SET_SELF_QOS_FLAG, retval);

        /* Static param the thread, we just set QoS on it, so its stuck in QoS land now. */
        /* pthread_kern->thread_static_param(th, TRUE); */ // see <rdar://problem/16433744>, for details

        thread_deallocate(th);

out:
        return rv;
}

static inline struct threadlist *
util_get_thread_threadlist_entry(thread_t th)
{
        struct uthread *uth = pthread_kern->get_bsdthread_info(th);
        if (uth) {
                struct threadlist *tl = pthread_kern->uthread_get_threadlist(uth);
                return tl;
        }
        return NULL;
}

boolean_t
_workq_thread_has_been_unbound(thread_t th, int qos_class)
{
        struct threadlist *tl = util_get_thread_threadlist_entry(th);
        if (!tl) {
                return FALSE;
        }

        struct workqueue *wq = tl->th_workq;
        workqueue_lock_spin(wq);

        if (tl->th_priority == WORKQUEUE_EVENT_MANAGER_BUCKET) {
                goto failure;
        } else if (qos_class != class_index_get_thread_qos(tl->th_priority)) {
                goto failure;
        }

        if ((tl->th_flags & TH_LIST_KEVENT_BOUND)){
                goto failure;
        }
        tl->th_flags &= ~TH_LIST_KEVENT_BOUND;

        workqueue_unlock(wq);
        return TRUE;

failure:
        workqueue_unlock(wq);
        return FALSE;
}

int
_bsdthread_ctl_set_self(struct proc *p, user_addr_t __unused cmd, pthread_priority_t priority, mach_port_name_t voucher, _pthread_set_flags_t flags, int __unused *retval)
{
        thread_qos_policy_data_t qos;
        mach_msg_type_number_t nqos = THREAD_QOS_POLICY_COUNT;
        boolean_t gd = FALSE;
        thread_t th = current_thread();
        struct workqueue *wq = NULL;
        struct threadlist *tl = NULL;

        kern_return_t kr;
        int qos_rv = 0, voucher_rv = 0, fixedpri_rv = 0;

        if ((flags & _PTHREAD_SET_SELF_WQ_KEVENT_UNBIND) != 0) {
                tl = util_get_thread_threadlist_entry(th);
                if (tl) {
                        wq = tl->th_workq;
                } else {
                        goto qos;
                }

                workqueue_lock_spin(wq);
                if (tl->th_flags & TH_LIST_KEVENT_BOUND) {
                        tl->th_flags &= ~TH_LIST_KEVENT_BOUND;
                        unsigned int kevent_flags = KEVENT_FLAG_WORKQ | KEVENT_FLAG_UNBIND_CHECK_FLAGS;
                        if (tl->th_priority == WORKQUEUE_EVENT_MANAGER_BUCKET) {
                                kevent_flags |= KEVENT_FLAG_WORKQ_MANAGER;
                        }

                        workqueue_unlock(wq);
                        __assert_only int ret = kevent_qos_internal_unbind(p, class_index_get_thread_qos(tl->th_priority), th, kevent_flags);
                        assert(ret == 0);
                } else {
                        workqueue_unlock(wq);
                }
        }

qos:
        if ((flags & _PTHREAD_SET_SELF_QOS_FLAG) != 0) {
                kr = pthread_kern->thread_policy_get(th, THREAD_QOS_POLICY, (thread_policy_t)&qos, &nqos, &gd);
                if (kr != KERN_SUCCESS) {
                        qos_rv = EINVAL;
                        goto voucher;
                }

                /*
                 * If we have main-thread QoS then we don't allow a thread to come out
                 * of QOS_CLASS_UNSPECIFIED.
                 */
                if (pthread_kern->qos_main_thread_active() && qos.qos_tier ==
                                THREAD_QOS_UNSPECIFIED) {
                        qos_rv = EPERM;
                        goto voucher;
                }

                if (!tl) {
                        tl = util_get_thread_threadlist_entry(th);
                        if (tl) wq = tl->th_workq;
                }

                PTHREAD_TRACE_WQ(TRACE_pthread_set_qos_self | DBG_FUNC_START, wq, qos.qos_tier, qos.tier_importance, 0, 0);

                qos.qos_tier = pthread_priority_get_thread_qos(priority);
                qos.tier_importance = (qos.qos_tier == QOS_CLASS_UNSPECIFIED) ? 0 : _pthread_priority_get_relpri(priority);

                if (qos.qos_tier == QOS_CLASS_UNSPECIFIED ||
                                qos.tier_importance > 0 || qos.tier_importance < THREAD_QOS_MIN_TIER_IMPORTANCE) {
                        qos_rv = EINVAL;
                        goto voucher;
                }

                /*
                 * If we're a workqueue, the threadlist item priority needs adjusting,
                 * along with the bucket we were running in.
                 */
                if (tl) {
                        bool try_run_threadreq = false;

                        workqueue_lock_spin(wq);
                        kr = pthread_kern->thread_set_workq_qos(th, qos.qos_tier, qos.tier_importance);
                        assert(kr == KERN_SUCCESS || kr == KERN_TERMINATED);

                        /* Fix up counters. */
                        uint8_t old_bucket = tl->th_priority;
                        uint8_t new_bucket = pthread_priority_get_class_index(priority);

                        if (old_bucket != new_bucket) {
                                _wq_thactive_move(wq, old_bucket, new_bucket);
                                wq->wq_thscheduled_count[old_bucket]--;
                                wq->wq_thscheduled_count[new_bucket]++;
                                if (old_bucket == WORKQUEUE_EVENT_MANAGER_BUCKET ||
                                                old_bucket < new_bucket) {
                                        /*
                                         * if the QoS of the thread was lowered, then this could
                                         * allow for a higher QoS thread request to run, so we need
                                         * to reevaluate.
                                         */
                                        try_run_threadreq = true;
                                }
                                tl->th_priority = new_bucket;
                        }

                        bool old_overcommit = !(tl->th_flags & TH_LIST_CONSTRAINED);
                        bool new_overcommit = priority & _PTHREAD_PRIORITY_OVERCOMMIT_FLAG;
                        if (!old_overcommit && new_overcommit) {
                                if (wq->wq_constrained_threads_scheduled-- ==
                                                wq_max_constrained_threads) {
                                        try_run_threadreq = true;
                                }
                                tl->th_flags &= ~TH_LIST_CONSTRAINED;
                        } else if (old_overcommit && !new_overcommit) {
                                wq->wq_constrained_threads_scheduled++;
                                tl->th_flags |= TH_LIST_CONSTRAINED;
                        }

                        if (try_run_threadreq) {
                                workqueue_run_threadreq_and_unlock(p, wq, NULL, NULL, true);
                        } else {
                                workqueue_unlock(wq);
                        }
                } else {
                        kr = pthread_kern->thread_policy_set_internal(th, THREAD_QOS_POLICY, (thread_policy_t)&qos, THREAD_QOS_POLICY_COUNT);
                        if (kr != KERN_SUCCESS) {
                                qos_rv = EINVAL;
                        }
                }

                PTHREAD_TRACE_WQ(TRACE_pthread_set_qos_self | DBG_FUNC_END, wq, qos.qos_tier, qos.tier_importance, 0, 0);
        }

voucher:
        if ((flags & _PTHREAD_SET_SELF_VOUCHER_FLAG) != 0) {
                kr = pthread_kern->thread_set_voucher_name(voucher);
                if (kr != KERN_SUCCESS) {
                        voucher_rv = ENOENT;
                        goto fixedpri;
                }
        }

fixedpri:
        if (qos_rv) goto done;
        if ((flags & _PTHREAD_SET_SELF_FIXEDPRIORITY_FLAG) != 0) {
                thread_extended_policy_data_t extpol = {.timeshare = 0};

                if (!tl) tl  = util_get_thread_threadlist_entry(th);
                if (tl) {
                        /* Not allowed on workqueue threads */
                        fixedpri_rv = ENOTSUP;
                        goto done;
                }

                kr = pthread_kern->thread_policy_set_internal(th, THREAD_EXTENDED_POLICY, (thread_policy_t)&extpol, THREAD_EXTENDED_POLICY_COUNT);
                if (kr != KERN_SUCCESS) {
                        fixedpri_rv = EINVAL;
                        goto done;
                }
        } else if ((flags & _PTHREAD_SET_SELF_TIMESHARE_FLAG) != 0) {
                thread_extended_policy_data_t extpol = {.timeshare = 1};

                if (!tl) tl = util_get_thread_threadlist_entry(th);
                if (tl) {
                        /* Not allowed on workqueue threads */
                        fixedpri_rv = ENOTSUP;
                        goto done;
                }

                kr = pthread_kern->thread_policy_set_internal(th, THREAD_EXTENDED_POLICY, (thread_policy_t)&extpol, THREAD_EXTENDED_POLICY_COUNT);
                if (kr != KERN_SUCCESS) {
                        fixedpri_rv = EINVAL;
                        goto done;
                }
        }

done:
        if (qos_rv && voucher_rv) {
                /* Both failed, give that a unique error. */
                return EBADMSG;
        }

        if (qos_rv) {
                return qos_rv;
        }

        if (voucher_rv) {
                return voucher_rv;
        }

        if (fixedpri_rv) {
                return fixedpri_rv;
        }

        return 0;
}

int
_bsdthread_ctl_qos_override_start(struct proc __unused *p, user_addr_t __unused cmd, mach_port_name_t kport, pthread_priority_t priority, user_addr_t resource, int __unused *retval)
{
        thread_t th;
        int rv = 0;

        if ((th = port_name_to_thread(kport)) == THREAD_NULL) {
                return ESRCH;
        }

        int override_qos = pthread_priority_get_thread_qos(priority);

        struct threadlist *tl = util_get_thread_threadlist_entry(th);
        if (tl) {
                PTHREAD_TRACE_WQ(TRACE_wq_override_start | DBG_FUNC_NONE, tl->th_workq, thread_tid(th), 1, priority, 0);
        }

        /* The only failure case here is if we pass a tid and have it lookup the thread, we pass the uthread, so this all always succeeds. */
        pthread_kern->proc_usynch_thread_qos_add_override_for_resource_check_owner(th, override_qos, TRUE,
                        resource, THREAD_QOS_OVERRIDE_TYPE_PTHREAD_EXPLICIT_OVERRIDE, USER_ADDR_NULL, MACH_PORT_NULL);
        thread_deallocate(th);
        return rv;
}

int
_bsdthread_ctl_qos_override_end(struct proc __unused *p, user_addr_t __unused cmd, mach_port_name_t kport, user_addr_t resource, user_addr_t arg3, int __unused *retval)
{
        thread_t th;
        int rv = 0;

        if (arg3 != 0) {
                return EINVAL;
        }

        if ((th = port_name_to_thread(kport)) == THREAD_NULL) {
                return ESRCH;
        }

        struct uthread *uth = pthread_kern->get_bsdthread_info(th);

        struct threadlist *tl = util_get_thread_threadlist_entry(th);
        if (tl) {
                PTHREAD_TRACE_WQ(TRACE_wq_override_end | DBG_FUNC_NONE, tl->th_workq, thread_tid(th), 0, 0, 0);
        }

        pthread_kern->proc_usynch_thread_qos_remove_override_for_resource(current_task(), uth, 0, resource, THREAD_QOS_OVERRIDE_TYPE_PTHREAD_EXPLICIT_OVERRIDE);

        thread_deallocate(th);
        return rv;
}

static int
_bsdthread_ctl_qos_dispatch_asynchronous_override_add_internal(mach_port_name_t kport, pthread_priority_t priority, user_addr_t resource, user_addr_t ulock_addr)
{
        thread_t th;
        int rv = 0;

        if ((th = port_name_to_thread(kport)) == THREAD_NULL) {
                return ESRCH;
        }

        int override_qos = pthread_priority_get_thread_qos(priority);

        struct threadlist *tl = util_get_thread_threadlist_entry(th);
        if (!tl) {
                thread_deallocate(th);
                return EPERM;
        }

        PTHREAD_TRACE_WQ(TRACE_wq_override_dispatch | DBG_FUNC_NONE, tl->th_workq, thread_tid(th), 1, priority, 0);

        rv = pthread_kern->proc_usynch_thread_qos_add_override_for_resource_check_owner(th, override_qos, TRUE,
                        resource, THREAD_QOS_OVERRIDE_TYPE_DISPATCH_ASYNCHRONOUS_OVERRIDE, ulock_addr, kport);

        thread_deallocate(th);
        return rv;
}

int _bsdthread_ctl_qos_dispatch_asynchronous_override_add(struct proc __unused *p, user_addr_t __unused cmd,
                mach_port_name_t kport, pthread_priority_t priority, user_addr_t resource, int __unused *retval)
{
        return _bsdthread_ctl_qos_dispatch_asynchronous_override_add_internal(kport, priority, resource, USER_ADDR_NULL);
}

int
_bsdthread_ctl_qos_override_dispatch(struct proc *p __unused, user_addr_t cmd __unused, mach_port_name_t kport, pthread_priority_t priority, user_addr_t ulock_addr, int __unused *retval)
{
        return _bsdthread_ctl_qos_dispatch_asynchronous_override_add_internal(kport, priority, USER_ADDR_NULL, ulock_addr);
}

int
_bsdthread_ctl_qos_override_reset(struct proc *p, user_addr_t cmd, user_addr_t arg1, user_addr_t arg2, user_addr_t arg3, int *retval)
{
        if (arg1 != 0 || arg2 != 0 || arg3 != 0) {
                return EINVAL;
        }

        return _bsdthread_ctl_qos_dispatch_asynchronous_override_reset(p, cmd, 1 /* reset_all */, 0, 0, retval);
}

int
_bsdthread_ctl_qos_dispatch_asynchronous_override_reset(struct proc __unused *p, user_addr_t __unused cmd, int reset_all, user_addr_t resource, user_addr_t arg3, int __unused *retval)
{
        if ((reset_all && (resource != 0)) || arg3 != 0) {
                return EINVAL;
        }

        thread_t th = current_thread();
        struct uthread *uth = pthread_kern->get_bsdthread_info(th);
        struct threadlist *tl = pthread_kern->uthread_get_threadlist(uth);

        if (!tl) {
                return EPERM;
        }

        PTHREAD_TRACE_WQ(TRACE_wq_override_reset | DBG_FUNC_NONE, tl->th_workq, 0, 0, 0, 0);

        resource = reset_all ? THREAD_QOS_OVERRIDE_RESOURCE_WILDCARD : resource;
        pthread_kern->proc_usynch_thread_qos_reset_override_for_resource(current_task(), uth, 0, resource, THREAD_QOS_OVERRIDE_TYPE_DISPATCH_ASYNCHRONOUS_OVERRIDE);

        return 0;
}

static int
_bsdthread_ctl_max_parallelism(struct proc __unused *p, user_addr_t __unused cmd,
                int qos, unsigned long flags, int *retval)
{
        _Static_assert(QOS_PARALLELISM_COUNT_LOGICAL ==
                        _PTHREAD_QOS_PARALLELISM_COUNT_LOGICAL, "logical");
        _Static_assert(QOS_PARALLELISM_REALTIME ==
                        _PTHREAD_QOS_PARALLELISM_REALTIME, "realtime");

        if (flags & ~(QOS_PARALLELISM_REALTIME | QOS_PARALLELISM_COUNT_LOGICAL)) {
                return EINVAL;
        }

        if (flags & QOS_PARALLELISM_REALTIME) {
                if (qos) {
                        return EINVAL;
                }
        } else if (qos == THREAD_QOS_UNSPECIFIED || qos >= THREAD_QOS_LAST) {
                return EINVAL;
        }

        *retval = pthread_kern->qos_max_parallelism(qos, flags);
        return 0;
}

int
_bsdthread_ctl(struct proc *p, user_addr_t cmd, user_addr_t arg1, user_addr_t arg2, user_addr_t arg3, int *retval)
{
        switch (cmd) {
        case BSDTHREAD_CTL_SET_QOS:
                return _bsdthread_ctl_set_qos(p, cmd, (mach_port_name_t)arg1, arg2, arg3, retval);
        case BSDTHREAD_CTL_QOS_OVERRIDE_START:
                return _bsdthread_ctl_qos_override_start(p, cmd, (mach_port_name_t)arg1, (pthread_priority_t)arg2, arg3, retval);
        case BSDTHREAD_CTL_QOS_OVERRIDE_END:
                return _bsdthread_ctl_qos_override_end(p, cmd, (mach_port_name_t)arg1, arg2, arg3, retval);
        case BSDTHREAD_CTL_QOS_OVERRIDE_RESET:
                return _bsdthread_ctl_qos_override_reset(p, cmd, arg1, arg2, arg3, retval);
        case BSDTHREAD_CTL_QOS_OVERRIDE_DISPATCH:
                return _bsdthread_ctl_qos_override_dispatch(p, cmd, (mach_port_name_t)arg1, (pthread_priority_t)arg2, arg3, retval);
        case BSDTHREAD_CTL_QOS_DISPATCH_ASYNCHRONOUS_OVERRIDE_ADD:
                return _bsdthread_ctl_qos_dispatch_asynchronous_override_add(p, cmd, (mach_port_name_t)arg1, (pthread_priority_t)arg2, arg3, retval);
        case BSDTHREAD_CTL_QOS_DISPATCH_ASYNCHRONOUS_OVERRIDE_RESET:
                return _bsdthread_ctl_qos_dispatch_asynchronous_override_reset(p, cmd, (int)arg1, arg2, arg3, retval);
        case BSDTHREAD_CTL_SET_SELF:
                return _bsdthread_ctl_set_self(p, cmd, (pthread_priority_t)arg1, (mach_port_name_t)arg2, (_pthread_set_flags_t)arg3, retval);
        case BSDTHREAD_CTL_QOS_MAX_PARALLELISM:
                return _bsdthread_ctl_max_parallelism(p, cmd, (int)arg1, (unsigned long)arg2, retval);
        default:
                return EINVAL;
        }
}

#pragma mark - Workqueue Implementation

#pragma mark wq_flags

static inline uint32_t
_wq_flags(struct workqueue *wq)
{
        return atomic_load_explicit(&wq->wq_flags, memory_order_relaxed);
}

static inline bool
_wq_exiting(struct workqueue *wq)
{
        return _wq_flags(wq) & WQ_EXITING;
}

static inline uint32_t
_wq_flags_or_orig(struct workqueue *wq, uint32_t v)
{
#if PTHREAD_INLINE_RMW_ATOMICS
        uint32_t state;
        do {
                state = _wq_flags(wq);
        } while (!OSCompareAndSwap(state, state | v, &wq->wq_flags));
        return state;
#else
        return atomic_fetch_or_explicit(&wq->wq_flags, v, memory_order_relaxed);
#endif
}

static inline uint32_t
_wq_flags_and_orig(struct workqueue *wq, uint32_t v)
{
#if PTHREAD_INLINE_RMW_ATOMICS
        uint32_t state;
        do {
                state = _wq_flags(wq);
        } while (!OSCompareAndSwap(state, state & v, &wq->wq_flags));
        return state;
#else
        return atomic_fetch_and_explicit(&wq->wq_flags, v, memory_order_relaxed);
#endif
}

static inline bool
WQ_TIMER_DELAYED_NEEDED(struct workqueue *wq)
{
        uint32_t oldflags, newflags;
        do {
                oldflags = _wq_flags(wq);
                if (oldflags & (WQ_EXITING | WQ_ATIMER_DELAYED_RUNNING)) {
                        return false;
                }
                newflags = oldflags | WQ_ATIMER_DELAYED_RUNNING;
        } while (!OSCompareAndSwap(oldflags, newflags, &wq->wq_flags));
        return true;
}

static inline bool
WQ_TIMER_IMMEDIATE_NEEDED(struct workqueue *wq)
{
        uint32_t oldflags, newflags;
        do {
                oldflags = _wq_flags(wq);
                if (oldflags & (WQ_EXITING | WQ_ATIMER_IMMEDIATE_RUNNING)) {
                        return false;
                }
                newflags = oldflags | WQ_ATIMER_IMMEDIATE_RUNNING;
        } while (!OSCompareAndSwap(oldflags, newflags, &wq->wq_flags));
        return true;
}

#pragma mark thread requests pacing

static inline uint32_t
_wq_pacing_shift_for_pri(int pri)
{
        return _wq_bucket_to_thread_qos(pri) - 1;
}

static inline int
_wq_highest_paced_priority(struct workqueue *wq)
{
        uint8_t paced = wq->wq_paced;
        int msb = paced ? 32 - __builtin_clz(paced) : 0; // fls(paced) == bit + 1
        return WORKQUEUE_EVENT_MANAGER_BUCKET - msb;
}

static inline uint8_t
_wq_pacing_bit_for_pri(int pri)
{
        return 1u << _wq_pacing_shift_for_pri(pri);
}

static inline bool
_wq_should_pace_priority(struct workqueue *wq, int pri)
{
        return wq->wq_paced >= _wq_pacing_bit_for_pri(pri);
}

static inline void
_wq_pacing_start(struct workqueue *wq, struct threadlist *tl)
{
        uint8_t bit = _wq_pacing_bit_for_pri(tl->th_priority);
        assert((tl->th_flags & TH_LIST_PACING) == 0);
        assert((wq->wq_paced & bit) == 0);
        wq->wq_paced |= bit;
        tl->th_flags |= TH_LIST_PACING;
}

static inline bool
_wq_pacing_end(struct workqueue *wq, struct threadlist *tl)
{
        if (tl->th_flags & TH_LIST_PACING) {
                uint8_t bit = _wq_pacing_bit_for_pri(tl->th_priority);
                assert((wq->wq_paced & bit) != 0);
                wq->wq_paced ^= bit;
                tl->th_flags &= ~TH_LIST_PACING;
                return wq->wq_paced < bit; // !_wq_should_pace_priority
        }
        return false;
}

#pragma mark thread requests

static void
_threadreq_init_alloced(struct threadreq *req, int priority, int flags)
{
        assert((flags & TR_FLAG_ONSTACK) == 0);
        req->tr_state = TR_STATE_NEW;
        req->tr_priority = priority;
        req->tr_flags = flags;
}

static void
_threadreq_init_stack(struct threadreq *req, int priority, int flags)
{
        req->tr_state = TR_STATE_NEW;
        req->tr_priority = priority;
        req->tr_flags = flags | TR_FLAG_ONSTACK;
}

static void
_threadreq_copy_prepare(struct workqueue *wq)
{
again:
        if (wq->wq_cached_threadreq) {
                return;
        }

        workqueue_unlock(wq);
        struct threadreq *req = zalloc(pthread_zone_threadreq);
        workqueue_lock_spin(wq);

        if (wq->wq_cached_threadreq) {
                /*
                 * We lost the race and someone left behind an extra threadreq for us
                 * to use.  Throw away our request and retry.
                 */
                workqueue_unlock(wq);
                zfree(pthread_zone_threadreq, req);
                workqueue_lock_spin(wq);
                goto again;
        } else {
                wq->wq_cached_threadreq = req;
        }

        assert(wq->wq_cached_threadreq);
}

static bool
_threadreq_copy_prepare_noblock(struct workqueue *wq)
{
        if (wq->wq_cached_threadreq) {
                return true;
        }

        wq->wq_cached_threadreq = zalloc_noblock(pthread_zone_threadreq);

        return wq->wq_cached_threadreq != NULL;
}

static inline struct threadreq_head *
_threadreq_list_for_req(struct workqueue *wq, const struct threadreq *req)
{
        if (req->tr_flags & TR_FLAG_OVERCOMMIT) {
                return &wq->wq_overcommit_reqlist[req->tr_priority];
        } else {
                return &wq->wq_reqlist[req->tr_priority];
        }
}

static void
_threadreq_enqueue(struct workqueue *wq, struct threadreq *req)
{
        assert(req && req->tr_state == TR_STATE_NEW);
        if (req->tr_priority == WORKQUEUE_EVENT_MANAGER_BUCKET) {
                assert(wq->wq_event_manager_threadreq.tr_state != TR_STATE_WAITING);
                memcpy(&wq->wq_event_manager_threadreq, req, sizeof(struct threadreq));
                req = &wq->wq_event_manager_threadreq;
                req->tr_flags &= ~(TR_FLAG_ONSTACK | TR_FLAG_NO_PACING);
        } else {
                if (req->tr_flags & TR_FLAG_ONSTACK) {
                        assert(wq->wq_cached_threadreq);
                        struct threadreq *newreq = wq->wq_cached_threadreq;
                        wq->wq_cached_threadreq = NULL;

                        memcpy(newreq, req, sizeof(struct threadreq));
                        newreq->tr_flags &= ~(TR_FLAG_ONSTACK | TR_FLAG_NO_PACING);
                        req->tr_state = TR_STATE_DEAD;
                        req = newreq;
                }
                TAILQ_INSERT_TAIL(_threadreq_list_for_req(wq, req), req, tr_entry);
        }
        req->tr_state = TR_STATE_WAITING;
        wq->wq_reqcount++;
}

static void
_threadreq_dequeue(struct workqueue *wq, struct threadreq *req)
{
        if (req->tr_priority != WORKQUEUE_EVENT_MANAGER_BUCKET) {
                struct threadreq_head *req_list = _threadreq_list_for_req(wq, req);
#if DEBUG
                struct threadreq *cursor = NULL;
                TAILQ_FOREACH(cursor, req_list, tr_entry) {
                        if (cursor == req) break;
                }
                assert(cursor == req);
#endif
                TAILQ_REMOVE(req_list, req, tr_entry);
        }
        wq->wq_reqcount--;
}

/*
 * Mark a thread request as complete.  At this point, it is treated as owned by
 * the submitting subsystem and you should assume it could be freed.
 *
 * Called with the workqueue lock held.
 */
static int
_threadreq_complete_and_unlock(proc_t p, struct workqueue *wq,
                struct threadreq *req, struct threadlist *tl)
{
        struct threadreq *req_tofree = NULL;
        bool sync = (req->tr_state == TR_STATE_NEW);
        bool workloop = req->tr_flags & TR_FLAG_WORKLOOP;
        bool onstack = req->tr_flags & TR_FLAG_ONSTACK;
        bool kevent = req->tr_flags & TR_FLAG_KEVENT;
        bool unbinding = tl->th_flags & TH_LIST_UNBINDING;
        bool locked = true;
        bool waking_parked_thread = (tl->th_flags & TH_LIST_BUSY);
        int ret;

        req->tr_state = TR_STATE_COMPLETE;

        if (!workloop && !onstack && req != &wq->wq_event_manager_threadreq) {
                if (wq->wq_cached_threadreq) {
                        req_tofree = req;
                } else {
                        wq->wq_cached_threadreq = req;
                }
        }

        if (tl->th_flags & TH_LIST_UNBINDING) {
                tl->th_flags &= ~TH_LIST_UNBINDING;
                assert((tl->th_flags & TH_LIST_KEVENT_BOUND));
        } else if (workloop || kevent) {
                assert((tl->th_flags & TH_LIST_KEVENT_BOUND) == 0);
                tl->th_flags |= TH_LIST_KEVENT_BOUND;
        }

        if (workloop) {
                workqueue_unlock(wq);
                ret = pthread_kern->workloop_fulfill_threadreq(wq->wq_proc, (void*)req,
                                tl->th_thread, sync ? WORKLOOP_FULFILL_THREADREQ_SYNC : 0);
                assert(ret == 0);
                locked = false;
        } else if (kevent) {
                unsigned int kevent_flags = KEVENT_FLAG_WORKQ;
                if (sync) {
                        kevent_flags |= KEVENT_FLAG_SYNCHRONOUS_BIND;
                }
                if (tl->th_priority == WORKQUEUE_EVENT_MANAGER_BUCKET) {
                        kevent_flags |= KEVENT_FLAG_WORKQ_MANAGER;
                }
                workqueue_unlock(wq);
                ret = kevent_qos_internal_bind(wq->wq_proc,
                                class_index_get_thread_qos(tl->th_priority), tl->th_thread,
                                kevent_flags);
                if (ret != 0) {
                        workqueue_lock_spin(wq);
                        tl->th_flags &= ~TH_LIST_KEVENT_BOUND;
                        locked = true;
                } else {
                        locked = false;
                }
        }

        /*
         * Run Thread, Run!
         */
        PTHREAD_TRACE_WQ(TRACE_wq_run_threadreq | DBG_FUNC_END, wq, 0, 0, 0, 0);
        PTHREAD_TRACE_WQ_REQ(TRACE_wq_runitem | DBG_FUNC_START, wq, req, tl->th_priority,
                        thread_tid(current_thread()), thread_tid(tl->th_thread));

        if (waking_parked_thread) {
                if (!locked) {
                        workqueue_lock_spin(wq);
                }
                tl->th_flags &= ~(TH_LIST_BUSY);
                if ((tl->th_flags & TH_LIST_REMOVING_VOUCHER) == 0) {
                        /*
                         * If the thread is in the process of removing its voucher, then it
                         * isn't actually in the wait event yet and we don't need to wake
                         * it up.  Save the trouble (and potential lock-ordering issues
                         * (see 30617015)).
                         */
                        thread_wakeup_thread(tl, tl->th_thread);
                }
                workqueue_unlock(wq);

                if (req_tofree) zfree(pthread_zone_threadreq, req_tofree);
                return WQ_RUN_TR_THREAD_STARTED;
        }

        assert ((tl->th_flags & TH_LIST_PACING) == 0);
        if (locked) {
                workqueue_unlock(wq);
        }
        if (req_tofree) zfree(pthread_zone_threadreq, req_tofree);
        if (unbinding) {
                return WQ_RUN_TR_THREAD_STARTED;
        }
        _setup_wqthread(p, tl->th_thread, wq, tl, WQ_SETUP_CLEAR_VOUCHER);
        pthread_kern->unix_syscall_return(EJUSTRETURN);
        __builtin_unreachable();
}

/*
 * Mark a thread request as cancelled.  Has similar ownership semantics to the
 * complete call above.
 */
static void
_threadreq_cancel(struct workqueue *wq, struct threadreq *req)
{
        assert(req->tr_state == TR_STATE_WAITING);
        req->tr_state = TR_STATE_DEAD;

        assert((req->tr_flags & TR_FLAG_ONSTACK) == 0);
        if (req->tr_flags & TR_FLAG_WORKLOOP) {
                __assert_only int ret;
                ret = pthread_kern->workloop_fulfill_threadreq(wq->wq_proc, (void*)req,
                                THREAD_NULL, WORKLOOP_FULFILL_THREADREQ_CANCEL);
                assert(ret == 0 || ret == ECANCELED);
        } else if (req != &wq->wq_event_manager_threadreq) {
                zfree(pthread_zone_threadreq, req);
        }
}

#pragma mark workqueue lock

static boolean_t workqueue_lock_spin_is_acquired_kdp(struct workqueue *wq) {
  return kdp_lck_spin_is_acquired(&wq->wq_lock);
}

static void
workqueue_lock_spin(struct workqueue *wq)
{
        assert(ml_get_interrupts_enabled() == TRUE);
        lck_spin_lock(&wq->wq_lock);
}

static bool
workqueue_lock_try(struct workqueue *wq)
{
        return lck_spin_try_lock(&wq->wq_lock);
}

static void
workqueue_unlock(struct workqueue *wq)
{
        lck_spin_unlock(&wq->wq_lock);
}

#pragma mark workqueue add timer

/**
 * Sets up the timer which will call out to workqueue_add_timer
 */
static void
workqueue_interval_timer_start(struct workqueue *wq)
{
        uint64_t deadline;

        /* n.b. wq_timer_interval is reset to 0 in workqueue_add_timer if the
         ATIMER_RUNNING flag is not present.  The net effect here is that if a
         sequence of threads is required, we'll double the time before we give out
         the next one. */
        if (wq->wq_timer_interval == 0) {
                wq->wq_timer_interval = wq_stalled_window_usecs;

        } else {
                wq->wq_timer_interval = wq->wq_timer_interval * 2;

                if (wq->wq_timer_interval > wq_max_timer_interval_usecs) {
                        wq->wq_timer_interval = wq_max_timer_interval_usecs;
                }
        }
        clock_interval_to_deadline(wq->wq_timer_interval, 1000, &deadline);

        PTHREAD_TRACE_WQ(TRACE_wq_start_add_timer, wq, wq->wq_reqcount,
                        _wq_flags(wq), wq->wq_timer_interval, 0);

        thread_call_t call = wq->wq_atimer_delayed_call;
        if (thread_call_enter1_delayed(call, call, deadline)) {
                panic("delayed_call was already enqueued");
        }
}

/**
 * Immediately trigger the workqueue_add_timer
 */
static void
workqueue_interval_timer_trigger(struct workqueue *wq)
{
        PTHREAD_TRACE_WQ(TRACE_wq_start_add_timer, wq, wq->wq_reqcount,
                        _wq_flags(wq), 0, 0);

        thread_call_t call = wq->wq_atimer_immediate_call;
        if (thread_call_enter1(call, call)) {
                panic("immediate_call was already enqueued");
        }
}

/**
 * returns whether lastblocked_tsp is within wq_stalled_window_usecs of cur_ts
 */
static boolean_t
wq_thread_is_busy(uint64_t cur_ts, _Atomic uint64_t *lastblocked_tsp)
{
        clock_sec_t     secs;
        clock_usec_t    usecs;
        uint64_t lastblocked_ts;
        uint64_t elapsed;

        lastblocked_ts = atomic_load_explicit(lastblocked_tsp, memory_order_relaxed);
        if (lastblocked_ts >= cur_ts) {
                /*
                 * because the update of the timestamp when a thread blocks isn't
                 * serialized against us looking at it (i.e. we don't hold the workq lock)
                 * it's possible to have a timestamp that matches the current time or
                 * that even looks to be in the future relative to when we grabbed the current
                 * time... just treat this as a busy thread since it must have just blocked.
                 */
                return (TRUE);
        }
        elapsed = cur_ts - lastblocked_ts;

        pthread_kern->absolutetime_to_microtime(elapsed, &secs, &usecs);

        return (secs == 0 && usecs < wq_stalled_window_usecs);
}

/**
 * handler function for the timer
 */
static void
workqueue_add_timer(struct workqueue *wq, thread_call_t thread_call_self)
{
        proc_t p = wq->wq_proc;

        workqueue_lock_spin(wq);

        PTHREAD_TRACE_WQ(TRACE_wq_add_timer | DBG_FUNC_START, wq,
                        _wq_flags(wq), wq->wq_nthreads, wq->wq_thidlecount, 0);

        /*
         * There's two tricky issues here.
         *
         * First issue: we start the thread_call's that invoke this routine without
         * the workqueue lock held.  The scheduler callback needs to trigger
         * reevaluation of the number of running threads but shouldn't take that
         * lock, so we can't use it to synchronize state around the thread_call.
         * As a result, it might re-enter the thread_call while this routine is
         * already running.  This could cause it to fire a second time and we'll
         * have two add_timers running at once.  Obviously, we don't want that to
         * keep stacking, so we need to keep it at two timers.
         *
         * Solution: use wq_flags (accessed via atomic CAS) to synchronize the
         * enqueue of the thread_call itself.  When a thread needs to trigger the
         * add_timer, it checks for ATIMER_DELAYED_RUNNING and, when not set, sets
         * the flag then does a thread_call_enter.  We'll then remove that flag
         * only once we've got the lock and it's safe for the thread_call to be
         * entered again.
         *
         * Second issue: we need to make sure that the two timers don't execute this
         * routine concurrently.  We can't use the workqueue lock for this because
         * we'll need to drop it during our execution.
         *
         * Solution: use WQL_ATIMER_BUSY as a condition variable to indicate that
         * we are currently executing the routine and the next thread should wait.
         *
         * After all that, we arrive at the following four possible states:
         * !WQ_ATIMER_DELAYED_RUNNING && !WQL_ATIMER_BUSY       no pending timer, no active timer
         * !WQ_ATIMER_DELAYED_RUNNING &&  WQL_ATIMER_BUSY       no pending timer,  1 active timer
         *  WQ_ATIMER_DELAYED_RUNNING && !WQL_ATIMER_BUSY        1 pending timer, no active timer
         *  WQ_ATIMER_DELAYED_RUNNING &&  WQL_ATIMER_BUSY        1 pending timer,  1 active timer
         *
         * Further complication sometimes we need to trigger this function to run
         * without delay.  Because we aren't under a lock between setting
         * WQ_ATIMER_DELAYED_RUNNING and calling thread_call_enter, we can't simply
         * re-enter the thread call: if thread_call_enter() returned false, we
         * wouldn't be able to distinguish the case where the thread_call had
         * already fired from the case where it hadn't been entered yet from the
         * other thread.  So, we use a separate thread_call for immediate
         * invocations, and a separate RUNNING flag, WQ_ATIMER_IMMEDIATE_RUNNING.
         */

        while (wq->wq_lflags & WQL_ATIMER_BUSY) {
                wq->wq_lflags |= WQL_ATIMER_WAITING;

                assert_wait((caddr_t)wq, (THREAD_UNINT));
                workqueue_unlock(wq);

                thread_block(THREAD_CONTINUE_NULL);

                workqueue_lock_spin(wq);
        }
        /*
         * Prevent _workqueue_mark_exiting() from going away
         */
        wq->wq_lflags |= WQL_ATIMER_BUSY;

        /*
         * Decide which timer we are and remove the RUNNING flag.
         */
        if (thread_call_self == wq->wq_atimer_delayed_call) {
                uint64_t wq_flags = _wq_flags_and_orig(wq, ~WQ_ATIMER_DELAYED_RUNNING);
                if ((wq_flags & WQ_ATIMER_DELAYED_RUNNING) == 0) {
                        panic("workqueue_add_timer(delayed) w/o WQ_ATIMER_DELAYED_RUNNING");
                }
        } else if (thread_call_self == wq->wq_atimer_immediate_call) {
                uint64_t wq_flags = _wq_flags_and_orig(wq, ~WQ_ATIMER_IMMEDIATE_RUNNING);
                if ((wq_flags & WQ_ATIMER_IMMEDIATE_RUNNING) == 0) {
                        panic("workqueue_add_timer(immediate) w/o WQ_ATIMER_IMMEDIATE_RUNNING");
                }
        } else {
                panic("workqueue_add_timer can't figure out which timer it is");
        }

        int ret = WQ_RUN_TR_THREAD_STARTED;
        while (ret == WQ_RUN_TR_THREAD_STARTED && wq->wq_reqcount) {
                ret = workqueue_run_threadreq_and_unlock(p, wq, NULL, NULL, true);

                workqueue_lock_spin(wq);
        }
        _threadreq_copy_prepare(wq);

        /*
         * If we called WQ_TIMER_NEEDED above, then this flag will be set if that
         * call marked the timer running.  If so, we let the timer interval grow.
         * Otherwise, we reset it back to 0.
         */
        uint32_t wq_flags = _wq_flags(wq);
        if (!(wq_flags & WQ_ATIMER_DELAYED_RUNNING)) {
                wq->wq_timer_interval = 0;
        }

        wq->wq_lflags &= ~WQL_ATIMER_BUSY;

        if ((wq_flags & WQ_EXITING) || (wq->wq_lflags & WQL_ATIMER_WAITING)) {
                /*
                 * wakeup the thread hung up in _workqueue_mark_exiting or
                 * workqueue_add_timer waiting for this timer to finish getting out of
                 * the way
                 */
                wq->wq_lflags &= ~WQL_ATIMER_WAITING;
                wakeup(wq);
        }

        PTHREAD_TRACE_WQ(TRACE_wq_add_timer | DBG_FUNC_END, wq, 0, wq->wq_nthreads, wq->wq_thidlecount, 0);

        workqueue_unlock(wq);
}

#pragma mark thread state tracking

// called by spinlock code when trying to yield to lock owner
void
_workqueue_thread_yielded(void)
{
}

static void
workqueue_callback(int type, thread_t thread)
{
        struct uthread *uth = pthread_kern->get_bsdthread_info(thread);
        struct threadlist *tl = pthread_kern->uthread_get_threadlist(uth);
        struct workqueue *wq = tl->th_workq;
        uint32_t old_count, req_qos, qos = tl->th_priority;
        wq_thactive_t old_thactive;

        switch (type) {
        case SCHED_CALL_BLOCK: {
                bool start_timer = false;

                old_thactive = _wq_thactive_dec(wq, tl->th_priority);
                req_qos = WQ_THACTIVE_BEST_CONSTRAINED_REQ_QOS(old_thactive);
                old_count = _wq_thactive_aggregate_downto_qos(wq, old_thactive,
                                qos, NULL, NULL);

                if (old_count == wq_max_concurrency[tl->th_priority]) {
                        /*
                         * The number of active threads at this priority has fallen below
                         * the maximum number of concurrent threads that are allowed to run
                         *
                         * if we collide with another thread trying to update the
                         * last_blocked (really unlikely since another thread would have to
                         * get scheduled and then block after we start down this path), it's
                         * not a problem.  Either timestamp is adequate, so no need to retry
                         */
                        atomic_store_explicit(&wq->wq_lastblocked_ts[qos],
                                        mach_absolute_time(), memory_order_relaxed);
                }

                if (req_qos == WORKQUEUE_EVENT_MANAGER_BUCKET || qos > req_qos) {
                        /*
                         * The blocking thread is at a lower QoS than the highest currently
                         * pending constrained request, nothing has to be redriven
                         */
                } else {
                        uint32_t max_busycount, old_req_count;
                        old_req_count = _wq_thactive_aggregate_downto_qos(wq, old_thactive,
                                        req_qos, NULL, &max_busycount);
                        /*
                         * If it is possible that may_start_constrained_thread had refused
                         * admission due to being over the max concurrency, we may need to
                         * spin up a new thread.
                         *
                         * We take into account the maximum number of busy threads
                         * that can affect may_start_constrained_thread as looking at the
                         * actual number may_start_constrained_thread will see is racy.
                         *
                         * IOW at NCPU = 4, for IN (req_qos = 1), if the old req count is
                         * between NCPU (4) and NCPU - 2 (2) we need to redrive.
                         */
                        if (wq_max_concurrency[req_qos] <= old_req_count + max_busycount &&
                                        old_req_count <= wq_max_concurrency[req_qos]) {
                                if (WQ_TIMER_DELAYED_NEEDED(wq)) {
                                        start_timer = true;
                                        workqueue_interval_timer_start(wq);
                                }
                        }
                }

                PTHREAD_TRACE_WQ(TRACE_wq_thread_block | DBG_FUNC_START, wq,
                                old_count - 1, qos | (req_qos << 8),
                                wq->wq_reqcount << 1 | start_timer, 0);
                break;
        }
        case SCHED_CALL_UNBLOCK: {
                /*
                 * we cannot take the workqueue_lock here...
                 * an UNBLOCK can occur from a timer event which
                 * is run from an interrupt context... if the workqueue_lock
                 * is already held by this processor, we'll deadlock...
                 * the thread lock for the thread being UNBLOCKED
                 * is also held
                 */
                old_thactive = _wq_thactive_inc(wq, qos);
                if (pthread_debug_tracing) {
                        req_qos = WQ_THACTIVE_BEST_CONSTRAINED_REQ_QOS(old_thactive);
                        old_count = _wq_thactive_aggregate_downto_qos(wq, old_thactive,
                                        qos, NULL, NULL);
                        PTHREAD_TRACE_WQ(TRACE_wq_thread_block | DBG_FUNC_END, wq,
                                        old_count + 1, qos | (req_qos << 8),
                                        wq->wq_threads_scheduled, 0);
                }
                break;
        }
        }
}

sched_call_t
_workqueue_get_sched_callback(void)
{
        return workqueue_callback;
}

#pragma mark thread addition/removal

static mach_vm_size_t
_workqueue_allocsize(struct workqueue *wq)
{
        proc_t p = wq->wq_proc;
        mach_vm_size_t guardsize = vm_map_page_size(wq->wq_map);
        mach_vm_size_t pthread_size =
                vm_map_round_page_mask(pthread_kern->proc_get_pthsize(p) + PTHREAD_T_OFFSET, vm_map_page_mask(wq->wq_map));
        return guardsize + PTH_DEFAULT_STACKSIZE + pthread_size;
}

/**
 * pop goes the thread
 *
 * If fromexit is set, the call is from workqueue_exit(,
 * so some cleanups are to be avoided.
 */
static void
workqueue_removethread(struct threadlist *tl, bool fromexit, bool first_use)
{
        struct uthread * uth;
        struct workqueue * wq = tl->th_workq;

        if (tl->th_priority == WORKQUEUE_EVENT_MANAGER_BUCKET){
                TAILQ_REMOVE(&wq->wq_thidlemgrlist, tl, th_entry);
        } else {
                TAILQ_REMOVE(&wq->wq_thidlelist, tl, th_entry);
        }

        if (fromexit == 0) {
                assert(wq->wq_nthreads && wq->wq_thidlecount);
                wq->wq_nthreads--;
                wq->wq_thidlecount--;
        }

        /*
         * Clear the threadlist pointer in uthread so
         * blocked thread on wakeup for termination will
         * not access the thread list as it is going to be
         * freed.
         */
        pthread_kern->thread_sched_call(tl->th_thread, NULL);

        uth = pthread_kern->get_bsdthread_info(tl->th_thread);
        if (uth != (struct uthread *)0) {
                pthread_kern->uthread_set_threadlist(uth, NULL);
        }
        if (fromexit == 0) {
                /* during exit the lock is not held */
                workqueue_unlock(wq);
        }

        if ( (tl->th_flags & TH_LIST_NEW) || first_use ) {
                /*
                 * thread was created, but never used...
                 * need to clean up the stack and port ourselves
                 * since we're not going to spin up through the
                 * normal exit path triggered from Libc
                 */
                if (fromexit == 0) {
                        /* vm map is already deallocated when this is called from exit */
                        (void)mach_vm_deallocate(wq->wq_map, tl->th_stackaddr, _workqueue_allocsize(wq));
                }
                (void)pthread_kern->mach_port_deallocate(pthread_kern->task_get_ipcspace(wq->wq_task), tl->th_thport);
        }
        /*
         * drop our ref on the thread
         */
        thread_deallocate(tl->th_thread);

        zfree(pthread_zone_threadlist, tl);
}


/**
 * Try to add a new workqueue thread.
 *
 * - called with workq lock held
 * - dropped and retaken around thread creation
 * - return with workq lock held
 */
static bool
workqueue_addnewthread(proc_t p, struct workqueue *wq)
{
        kern_return_t kret;

        wq->wq_nthreads++;

        workqueue_unlock(wq);

        struct threadlist *tl = zalloc(pthread_zone_threadlist);
        bzero(tl, sizeof(struct threadlist));

        thread_t th;
        kret = pthread_kern->thread_create_workq_waiting(wq->wq_task, wq_unpark_continue, tl, &th);
        if (kret != KERN_SUCCESS) {
                PTHREAD_TRACE_WQ(TRACE_wq_thread_create_failed | DBG_FUNC_NONE, wq, kret, 0, 0, 0);
                goto fail_free;
        }

        mach_vm_offset_t stackaddr = pthread_kern->proc_get_stack_addr_hint(p);

        mach_vm_size_t guardsize = vm_map_page_size(wq->wq_map);
        mach_vm_size_t pthread_size =
                vm_map_round_page_mask(pthread_kern->proc_get_pthsize(p) + PTHREAD_T_OFFSET, vm_map_page_mask(wq->wq_map));
        mach_vm_size_t th_allocsize = guardsize + PTH_DEFAULT_STACKSIZE + pthread_size;

        kret = mach_vm_map(wq->wq_map, &stackaddr,
                        th_allocsize, page_size-1,
                        VM_MAKE_TAG(VM_MEMORY_STACK)| VM_FLAGS_ANYWHERE, NULL,
                        0, FALSE, VM_PROT_DEFAULT, VM_PROT_ALL,
                        VM_INHERIT_DEFAULT);

        if (kret != KERN_SUCCESS) {
                kret = mach_vm_allocate(wq->wq_map,
                                &stackaddr, th_allocsize,
                                VM_MAKE_TAG(VM_MEMORY_STACK) | VM_FLAGS_ANYWHERE);
        }

        if (kret != KERN_SUCCESS) {
                PTHREAD_TRACE_WQ(TRACE_wq_thread_create_failed | DBG_FUNC_NONE, wq, kret, 1, 0, 0);
                goto fail_terminate;
        }

        /*
         * The guard page is at the lowest address
         * The stack base is the highest address
         */
        kret = mach_vm_protect(wq->wq_map, stackaddr, guardsize, FALSE, VM_PROT_NONE);
        if (kret != KERN_SUCCESS) {
                PTHREAD_TRACE_WQ(TRACE_wq_thread_create_failed | DBG_FUNC_NONE, wq, kret, 2, 0, 0);
                goto fail_vm_deallocate;
        }


        pthread_kern->thread_set_tag(th, THREAD_TAG_PTHREAD | THREAD_TAG_WORKQUEUE);
        pthread_kern->thread_static_param(th, TRUE);

        /*
         * convert_thread_to_port() consumes a reference
         */
        thread_reference(th);
        void *sright = (void *)pthread_kern->convert_thread_to_port(th);
        tl->th_thport = pthread_kern->ipc_port_copyout_send(sright,
                        pthread_kern->task_get_ipcspace(wq->wq_task));

        tl->th_flags = TH_LIST_INITED | TH_LIST_NEW;
        tl->th_thread = th;
        tl->th_workq = wq;
        tl->th_stackaddr = stackaddr;
        tl->th_priority = WORKQUEUE_NUM_BUCKETS;

        struct uthread *uth;
        uth = pthread_kern->get_bsdthread_info(tl->th_thread);

        workqueue_lock_spin(wq);

        void *current_tl = pthread_kern->uthread_get_threadlist(uth);
        if (current_tl == NULL) {
                pthread_kern->uthread_set_threadlist(uth, tl);
                TAILQ_INSERT_TAIL(&wq->wq_thidlelist, tl, th_entry);
                wq->wq_thidlecount++;
        } else if (current_tl == WQ_THREADLIST_EXITING_POISON) {
                /*
                 * Failed thread creation race: The thread already woke up and has exited.
                 */
                PTHREAD_TRACE_WQ(TRACE_wq_thread_create_failed | DBG_FUNC_NONE, wq, kret, 3, 0, 0);
                goto fail_unlock;
        } else {
                panic("Unexpected initial threadlist value");
        }

        PTHREAD_TRACE_WQ(TRACE_wq_thread_create | DBG_FUNC_NONE, wq, 0, 0, 0, 0);

        return (TRUE);

fail_unlock:
        workqueue_unlock(wq);
        (void)pthread_kern->mach_port_deallocate(pthread_kern->task_get_ipcspace(wq->wq_task),
                        tl->th_thport);

fail_vm_deallocate:
        (void) mach_vm_deallocate(wq->wq_map, stackaddr, th_allocsize);

fail_terminate:
        if (pthread_kern->thread_will_park_or_terminate) {
                pthread_kern->thread_will_park_or_terminate(th);
        }
        (void)thread_terminate(th);
        thread_deallocate(th);

fail_free:
        zfree(pthread_zone_threadlist, tl);

        workqueue_lock_spin(wq);
        wq->wq_nthreads--;

        return (FALSE);
}

/**
 * Setup per-process state for the workqueue.
 */
int
_workq_open(struct proc *p, __unused int32_t *retval)
{
        struct workqueue * wq;
        char * ptr;
        uint32_t num_cpus;
        int error = 0;

        if (pthread_kern->proc_get_register(p) == 0) {
                return EINVAL;
        }

        num_cpus = pthread_kern->ml_get_max_cpus();

        if (wq_init_constrained_limit) {
                uint32_t limit;
                /*
                 * set up the limit for the constrained pool
                 * this is a virtual pool in that we don't
                 * maintain it on a separate idle and run list
                 */
                limit = num_cpus * WORKQUEUE_CONSTRAINED_FACTOR;

                if (limit > wq_max_constrained_threads)
                        wq_max_constrained_threads = limit;

                wq_init_constrained_limit = 0;

                if (wq_max_threads > WQ_THACTIVE_BUCKET_HALF) {
                        wq_max_threads = WQ_THACTIVE_BUCKET_HALF;
                }
                if (wq_max_threads > pthread_kern->config_thread_max - 20) {
                        wq_max_threads = pthread_kern->config_thread_max - 20;
                }
        }

        if (pthread_kern->proc_get_wqptr(p) == NULL) {
                if (pthread_kern->proc_init_wqptr_or_wait(p) == FALSE) {
                        assert(pthread_kern->proc_get_wqptr(p) != NULL);
                        goto out;
                }

                ptr = (char *)zalloc(pthread_zone_workqueue);
                bzero(ptr, sizeof(struct workqueue));

                wq = (struct workqueue *)ptr;
                wq->wq_proc = p;
                wq->wq_task = current_task();
                wq->wq_map  = pthread_kern->current_map();

                // Start the event manager at the priority hinted at by the policy engine
                int mgr_priority_hint = pthread_kern->task_get_default_manager_qos(current_task());
                wq->wq_event_manager_priority = (uint32_t)thread_qos_get_pthread_priority(mgr_priority_hint) | _PTHREAD_PRIORITY_EVENT_MANAGER_FLAG;

                TAILQ_INIT(&wq->wq_thrunlist);
                TAILQ_INIT(&wq->wq_thidlelist);
                for (int i = 0; i < WORKQUEUE_EVENT_MANAGER_BUCKET; i++) {
                        TAILQ_INIT(&wq->wq_overcommit_reqlist[i]);
                        TAILQ_INIT(&wq->wq_reqlist[i]);
                }

                wq->wq_atimer_delayed_call =
                                thread_call_allocate_with_priority((thread_call_func_t)workqueue_add_timer,
                                                (thread_call_param_t)wq, THREAD_CALL_PRIORITY_KERNEL);
                wq->wq_atimer_immediate_call =
                                thread_call_allocate_with_priority((thread_call_func_t)workqueue_add_timer,
                                                (thread_call_param_t)wq, THREAD_CALL_PRIORITY_KERNEL);

                lck_spin_init(&wq->wq_lock, pthread_lck_grp, pthread_lck_attr);

                wq->wq_cached_threadreq = zalloc(pthread_zone_threadreq);
                *(wq_thactive_t *)&wq->wq_thactive =
                                (wq_thactive_t)WQ_THACTIVE_NO_PENDING_REQUEST <<
                                WQ_THACTIVE_QOS_SHIFT;

                pthread_kern->proc_set_wqptr(p, wq);

        }
out:

        return(error);
}

/*
 * Routine:     workqueue_mark_exiting
 *
 * Function:    Mark the work queue such that new threads will not be added to the
 *              work queue after we return.
 *
 * Conditions:  Called against the current process.
 */
void
_workqueue_mark_exiting(struct proc *p)
{
        struct workqueue *wq = pthread_kern->proc_get_wqptr(p);
        if (!wq) return;

        PTHREAD_TRACE_WQ(TRACE_wq_pthread_exit|DBG_FUNC_START, wq, 0, 0, 0, 0);

        workqueue_lock_spin(wq);

        /*
         * We arm the add timer without holding the workqueue lock so we need
         * to synchronize with any running or soon to be running timers.
         *
         * Threads that intend to arm the timer atomically OR
         * WQ_ATIMER_{DELAYED,IMMEDIATE}_RUNNING into the wq_flags, only if
         * WQ_EXITING is not present.  So, once we have set WQ_EXITING, we can
         * be sure that no new RUNNING flags will be set, but still need to
         * wait for the already running timers to complete.
         *
         * We always hold the workq lock when dropping WQ_ATIMER_RUNNING, so
         * the check for and sleep until clear is protected.
         */
        uint64_t wq_flags = _wq_flags_or_orig(wq, WQ_EXITING);

        if (wq_flags & WQ_ATIMER_DELAYED_RUNNING) {
                if (thread_call_cancel(wq->wq_atimer_delayed_call) == TRUE) {
                        wq_flags = _wq_flags_and_orig(wq, ~WQ_ATIMER_DELAYED_RUNNING);
                }
        }
        if (wq_flags & WQ_ATIMER_IMMEDIATE_RUNNING) {
                if (thread_call_cancel(wq->wq_atimer_immediate_call) == TRUE) {
                        wq_flags = _wq_flags_and_orig(wq, ~WQ_ATIMER_IMMEDIATE_RUNNING);
                }
        }
        while ((_wq_flags(wq) & (WQ_ATIMER_DELAYED_RUNNING | WQ_ATIMER_IMMEDIATE_RUNNING)) ||
                        (wq->wq_lflags & WQL_ATIMER_BUSY)) {
                assert_wait((caddr_t)wq, (THREAD_UNINT));
                workqueue_unlock(wq);

                thread_block(THREAD_CONTINUE_NULL);

                workqueue_lock_spin(wq);
        }

        /*
         * Save off pending requests, will complete/free them below after unlocking
         */
        TAILQ_HEAD(, threadreq) local_list = TAILQ_HEAD_INITIALIZER(local_list);

        for (int i = 0; i < WORKQUEUE_EVENT_MANAGER_BUCKET; i++) {
                TAILQ_CONCAT(&local_list, &wq->wq_overcommit_reqlist[i], tr_entry);
                TAILQ_CONCAT(&local_list, &wq->wq_reqlist[i], tr_entry);
        }

        /*
         * XXX: Can't deferred cancel the event manager request, so just smash it.
         */
        assert((wq->wq_event_manager_threadreq.tr_flags & TR_FLAG_WORKLOOP) == 0);
        wq->wq_event_manager_threadreq.tr_state = TR_STATE_DEAD;

        workqueue_unlock(wq);

        struct threadreq *tr, *tr_temp;
        TAILQ_FOREACH_SAFE(tr, &local_list, tr_entry, tr_temp) {
                _threadreq_cancel(wq, tr);
        }
        PTHREAD_TRACE(TRACE_wq_pthread_exit|DBG_FUNC_END, 0, 0, 0, 0, 0);
}

/*
 * Routine:     workqueue_exit
 *
 * Function:    clean up the work queue structure(s) now that there are no threads
 *              left running inside the work queue (except possibly current_thread).
 *
 * Conditions:  Called by the last thread in the process.
 *              Called against current process.
 */
void
_workqueue_exit(struct proc *p)
{
        struct workqueue  * wq;
        struct threadlist  * tl, *tlist;
        struct uthread  *uth;

        wq = pthread_kern->proc_get_wqptr(p);
        if (wq != NULL) {

                PTHREAD_TRACE_WQ(TRACE_wq_workqueue_exit|DBG_FUNC_START, wq, 0, 0, 0, 0);

                pthread_kern->proc_set_wqptr(p, NULL);

                /*
                 * Clean up workqueue data structures for threads that exited and
                 * didn't get a chance to clean up after themselves.
                 */
                TAILQ_FOREACH_SAFE(tl, &wq->wq_thrunlist, th_entry, tlist) {
                        assert((tl->th_flags & TH_LIST_RUNNING) != 0);

                        pthread_kern->thread_sched_call(tl->th_thread, NULL);

                        uth = pthread_kern->get_bsdthread_info(tl->th_thread);
                        if (uth != (struct uthread *)0) {
                                pthread_kern->uthread_set_threadlist(uth, NULL);
                        }
                        TAILQ_REMOVE(&wq->wq_thrunlist, tl, th_entry);

                        /*
                         * drop our last ref on the thread
                         */
                        thread_deallocate(tl->th_thread);

                        zfree(pthread_zone_threadlist, tl);
                }
                TAILQ_FOREACH_SAFE(tl, &wq->wq_thidlelist, th_entry, tlist) {
                        assert((tl->th_flags & TH_LIST_RUNNING) == 0);
                        assert(tl->th_priority != WORKQUEUE_EVENT_MANAGER_BUCKET);
                        workqueue_removethread(tl, true, false);
                }
                TAILQ_FOREACH_SAFE(tl, &wq->wq_thidlemgrlist, th_entry, tlist) {
                        assert((tl->th_flags & TH_LIST_RUNNING) == 0);
                        assert(tl->th_priority == WORKQUEUE_EVENT_MANAGER_BUCKET);
                        workqueue_removethread(tl, true, false);
                }
                if (wq->wq_cached_threadreq) {
                        zfree(pthread_zone_threadreq, wq->wq_cached_threadreq);
                }
                thread_call_free(wq->wq_atimer_delayed_call);
                thread_call_free(wq->wq_atimer_immediate_call);
                lck_spin_destroy(&wq->wq_lock, pthread_lck_grp);

                for (int i = 0; i < WORKQUEUE_EVENT_MANAGER_BUCKET; i++) {
                        assert(TAILQ_EMPTY(&wq->wq_overcommit_reqlist[i]));
                        assert(TAILQ_EMPTY(&wq->wq_reqlist[i]));
                }

                zfree(pthread_zone_workqueue, wq);

                PTHREAD_TRACE(TRACE_wq_workqueue_exit|DBG_FUNC_END, 0, 0, 0, 0, 0);
        }
}


#pragma mark workqueue thread manipulation


/**
 * Entry point for libdispatch to ask for threads
 */
static int
wqops_queue_reqthreads(struct proc *p, int reqcount,
                pthread_priority_t priority)
{
        bool overcommit = _pthread_priority_get_flags(priority) & _PTHREAD_PRIORITY_OVERCOMMIT_FLAG;
        bool event_manager = _pthread_priority_get_flags(priority) & _PTHREAD_PRIORITY_EVENT_MANAGER_FLAG;
        int class = event_manager ? WORKQUEUE_EVENT_MANAGER_BUCKET :
                        pthread_priority_get_class_index(priority);

        if ((reqcount <= 0) || (class < 0) || (class >= WORKQUEUE_NUM_BUCKETS) ||
                        (overcommit && event_manager)) {
                return EINVAL;
        }

        struct workqueue *wq;
        if ((wq = (struct workqueue *)pthread_kern->proc_get_wqptr(p)) == NULL) {
                return EINVAL;
        }

        workqueue_lock_spin(wq);
        _threadreq_copy_prepare(wq);

        PTHREAD_TRACE_WQ(TRACE_wq_wqops_reqthreads | DBG_FUNC_NONE, wq, reqcount, priority, 0, 0);

        int tr_flags = 0;
        if (overcommit) tr_flags |= TR_FLAG_OVERCOMMIT;
        if (reqcount > 1) {
                /*
                 * when libdispatch asks for more than one thread, it wants to achieve
                 * parallelism. Pacing would be detrimental to this ask, so treat
                 * these specially to not do the pacing admission check
                 */
                tr_flags |= TR_FLAG_NO_PACING;
        }

        while (reqcount-- && !_wq_exiting(wq)) {
                struct threadreq req;
                _threadreq_init_stack(&req, class, tr_flags);

                workqueue_run_threadreq_and_unlock(p, wq, NULL, &req, true);

                workqueue_lock_spin(wq); /* reacquire */
                _threadreq_copy_prepare(wq);
        }

        workqueue_unlock(wq);

        return 0;
}

/*
 * Used by the kevent system to request threads.
 *
 * Currently count is ignored and we always return one thread per invocation.
 */
static thread_t
_workq_kevent_reqthreads(struct proc *p, pthread_priority_t priority,
                bool no_emergency)
{
        int wq_run_tr = WQ_RUN_TR_THROTTLED;
        bool emergency_thread = false;
        struct threadreq req;


        struct workqueue *wq;
        if ((wq = (struct workqueue *)pthread_kern->proc_get_wqptr(p)) == NULL) {
                return THREAD_NULL;
        }

        int class = pthread_priority_get_class_index(priority);

        workqueue_lock_spin(wq);
        bool has_threadreq = _threadreq_copy_prepare_noblock(wq);

        PTHREAD_TRACE_WQ_REQ(TRACE_wq_kevent_reqthreads | DBG_FUNC_NONE, wq, NULL, priority, 0, 0);

        /*
         * Skip straight to event manager if that's what was requested
         */
        if ((_pthread_priority_get_qos_newest(priority) == QOS_CLASS_UNSPECIFIED) ||
                        (_pthread_priority_get_flags(priority) & _PTHREAD_PRIORITY_EVENT_MANAGER_FLAG)){
                goto event_manager;
        }

        bool will_pace = _wq_should_pace_priority(wq, class);
        if ((wq->wq_thidlecount == 0 || will_pace) && has_threadreq == false) {
                /*
                 * We'll need to persist the request and can't, so return the emergency
                 * thread instead, which has a persistent request object.
                 */
                emergency_thread = true;
                goto event_manager;
        }

        /*
         * Handle overcommit requests
         */
        if ((_pthread_priority_get_flags(priority) & _PTHREAD_PRIORITY_OVERCOMMIT_FLAG) != 0){
                _threadreq_init_stack(&req, class, TR_FLAG_KEVENT | TR_FLAG_OVERCOMMIT);
                wq_run_tr = workqueue_run_threadreq_and_unlock(p, wq, NULL, &req, false);
                goto done;
        }

        /*
         * Handle constrained requests
         */
        boolean_t may_start = may_start_constrained_thread(wq, class, NULL, false);
        if (may_start || no_emergency) {
                _threadreq_init_stack(&req, class, TR_FLAG_KEVENT);
                wq_run_tr = workqueue_run_threadreq_and_unlock(p, wq, NULL, &req, false);
                goto done;
        } else {
                emergency_thread = true;
        }


event_manager:
        _threadreq_init_stack(&req, WORKQUEUE_EVENT_MANAGER_BUCKET, TR_FLAG_KEVENT);
        wq_run_tr = workqueue_run_threadreq_and_unlock(p, wq, NULL, &req, false);

done:
        if (wq_run_tr == WQ_RUN_TR_THREAD_NEEDED && WQ_TIMER_IMMEDIATE_NEEDED(wq)) {
                workqueue_interval_timer_trigger(wq);
        }
        return emergency_thread ? (void*)-1 : 0;
}

thread_t
_workq_reqthreads(struct proc *p, __assert_only int requests_count,
                workq_reqthreads_req_t request)
{
        assert(requests_count == 1);

        pthread_priority_t priority = request->priority;
        bool no_emergency = request->count & WORKQ_REQTHREADS_NOEMERGENCY;

        return _workq_kevent_reqthreads(p, priority, no_emergency);
}


int
workq_kern_threadreq(struct proc *p, workq_threadreq_t _req,
                enum workq_threadreq_type type, unsigned long priority, int flags)
{
        struct workqueue *wq;
        int ret;

        if ((wq = (struct workqueue *)pthread_kern->proc_get_wqptr(p)) == NULL) {
                return EINVAL;
        }

        switch (type) {
        case WORKQ_THREADREQ_KEVENT: {
                bool no_emergency = flags & WORKQ_THREADREQ_FLAG_NOEMERGENCY;
                (void)_workq_kevent_reqthreads(p, priority, no_emergency);
                return 0;
        }
        case WORKQ_THREADREQ_WORKLOOP:
        case WORKQ_THREADREQ_WORKLOOP_NO_THREAD_CALL: {
                struct threadreq *req = (struct threadreq *)_req;
                int req_class = pthread_priority_get_class_index(priority);
                int req_flags = TR_FLAG_WORKLOOP;
                if ((_pthread_priority_get_flags(priority) &
                                _PTHREAD_PRIORITY_OVERCOMMIT_FLAG) != 0){
                        req_flags |= TR_FLAG_OVERCOMMIT;
                }

                thread_t thread = current_thread();
                struct threadlist *tl = util_get_thread_threadlist_entry(thread);

                if (tl && tl != WQ_THREADLIST_EXITING_POISON &&
                                (tl->th_flags & TH_LIST_UNBINDING)) {
                        /*
                         * we're called back synchronously from the context of
                         * kevent_qos_internal_unbind from within wqops_thread_return()
                         * we can try to match up this thread with this request !
                         */
                } else {
                        tl = NULL;
                }

                _threadreq_init_alloced(req, req_class, req_flags);
                workqueue_lock_spin(wq);
                PTHREAD_TRACE_WQ_REQ(TRACE_wq_kevent_reqthreads | DBG_FUNC_NONE, wq, req, priority, 1, 0);
                ret = workqueue_run_threadreq_and_unlock(p, wq, tl, req, false);
                if (ret == WQ_RUN_TR_EXITING) {
                        return ECANCELED;
                }
                if (ret == WQ_RUN_TR_THREAD_NEEDED) {
                        if (type == WORKQ_THREADREQ_WORKLOOP_NO_THREAD_CALL) {
                                return EAGAIN;
                        }
                        if (WQ_TIMER_IMMEDIATE_NEEDED(wq)) {
                                workqueue_interval_timer_trigger(wq);
                        }
                }
                return 0;
        }
        case WORKQ_THREADREQ_REDRIVE:
                PTHREAD_TRACE_WQ_REQ(TRACE_wq_kevent_reqthreads | DBG_FUNC_NONE, wq, 0, 0, 4, 0);
                workqueue_lock_spin(wq);
                ret = workqueue_run_threadreq_and_unlock(p, wq, NULL, NULL, true);
                if (ret == WQ_RUN_TR_EXITING) {
                        return ECANCELED;
                }
                return 0;
        default:
                return ENOTSUP;
        }
}

int
workq_kern_threadreq_modify(struct proc *p, workq_threadreq_t _req,
                enum workq_threadreq_op operation, unsigned long arg1,
                unsigned long __unused arg2)
{
        struct threadreq *req = (struct threadreq *)_req;
        struct workqueue *wq;
        int priclass, ret = 0, wq_tr_rc = WQ_RUN_TR_THROTTLED;

        if (req == NULL || (wq = pthread_kern->proc_get_wqptr(p)) == NULL) {
                return EINVAL;
        }

        workqueue_lock_spin(wq);

        if (_wq_exiting(wq)) {
                ret = ECANCELED;
                goto out_unlock;
        }

        /*
         * Find/validate the referenced request structure
         */
        if (req->tr_state != TR_STATE_WAITING) {
                ret = EINVAL;
                goto out_unlock;
        }
        assert(req->tr_priority < WORKQUEUE_EVENT_MANAGER_BUCKET);
        assert(req->tr_flags & TR_FLAG_WORKLOOP);

        switch (operation) {
        case WORKQ_THREADREQ_CHANGE_PRI:
        case WORKQ_THREADREQ_CHANGE_PRI_NO_THREAD_CALL:
                priclass = pthread_priority_get_class_index(arg1);
                PTHREAD_TRACE_WQ_REQ(TRACE_wq_kevent_reqthreads | DBG_FUNC_NONE, wq, req, arg1, 2, 0);
                if (req->tr_priority == priclass) {
                        goto out_unlock;
                }
                _threadreq_dequeue(wq, req);
                req->tr_priority = priclass;
                req->tr_state = TR_STATE_NEW; // what was old is new again
                wq_tr_rc = workqueue_run_threadreq_and_unlock(p, wq, NULL, req, false);
                goto out;

        case WORKQ_THREADREQ_CANCEL:
                PTHREAD_TRACE_WQ_REQ(TRACE_wq_kevent_reqthreads | DBG_FUNC_NONE, wq, req, 0, 3, 0);
                _threadreq_dequeue(wq, req);
                req->tr_state = TR_STATE_DEAD;
                break;

        default:
                ret = ENOTSUP;
                break;
        }

out_unlock:
        workqueue_unlock(wq);
out:
        if (wq_tr_rc == WQ_RUN_TR_THREAD_NEEDED) {
                if (operation == WORKQ_THREADREQ_CHANGE_PRI_NO_THREAD_CALL) {
                        ret = EAGAIN;
                } else if (WQ_TIMER_IMMEDIATE_NEEDED(wq)) {
                        workqueue_interval_timer_trigger(wq);
                }
        }
        return ret;
}


static int
wqops_thread_return(struct proc *p, struct workqueue *wq)
{
        thread_t th = current_thread();
        struct uthread *uth = pthread_kern->get_bsdthread_info(th);
        struct threadlist *tl = pthread_kern->uthread_get_threadlist(uth);

        /* reset signal mask on the workqueue thread to default state */
        if (pthread_kern->uthread_get_sigmask(uth) != (sigset_t)(~workq_threadmask)) {
                pthread_kern->proc_lock(p);
                pthread_kern->uthread_set_sigmask(uth, ~workq_threadmask);
                pthread_kern->proc_unlock(p);
        }

        if (wq == NULL || !tl) {
                return EINVAL;
        }

        PTHREAD_TRACE_WQ(TRACE_wq_override_reset | DBG_FUNC_START, tl->th_workq, 0, 0, 0, 0);

        /*
         * This squash call has neat semantics: it removes the specified overrides,
         * replacing the current requested QoS with the previous effective QoS from
         * those overrides.  This means we won't be preempted due to having our QoS
         * lowered.  Of course, now our understanding of the thread's QoS is wrong,
         * so we'll adjust below.
         */
        bool was_manager = (tl->th_priority == WORKQUEUE_EVENT_MANAGER_BUCKET);
        int new_qos;

        if (!was_manager) {
                new_qos = pthread_kern->proc_usynch_thread_qos_squash_override_for_resource(th,
                                THREAD_QOS_OVERRIDE_RESOURCE_WILDCARD,
                                THREAD_QOS_OVERRIDE_TYPE_DISPATCH_ASYNCHRONOUS_OVERRIDE);
        }

        PTHREAD_TRACE_WQ(TRACE_wq_runitem | DBG_FUNC_END, wq, tl->th_priority, 0, 0, 0);

        workqueue_lock_spin(wq);

        if (tl->th_flags & TH_LIST_KEVENT_BOUND) {
                unsigned int flags = KEVENT_FLAG_WORKQ;
                if (was_manager) {
                        flags |= KEVENT_FLAG_WORKQ_MANAGER;
                }

                tl->th_flags |= TH_LIST_UNBINDING;
                workqueue_unlock(wq);
                kevent_qos_internal_unbind(p, class_index_get_thread_qos(tl->th_priority), th, flags);
                if (!(tl->th_flags & TH_LIST_UNBINDING)) {
                        _setup_wqthread(p, th, wq, tl, WQ_SETUP_CLEAR_VOUCHER);
                        pthread_kern->unix_syscall_return(EJUSTRETURN);
                        __builtin_unreachable();
                }
                workqueue_lock_spin(wq);
                tl->th_flags &= ~(TH_LIST_KEVENT_BOUND | TH_LIST_UNBINDING);
        }

        if (!was_manager) {
                /* Fix up counters from the squash operation. */
                uint8_t old_bucket = tl->th_priority;
                uint8_t new_bucket = thread_qos_get_class_index(new_qos);

                if (old_bucket != new_bucket) {
                        _wq_thactive_move(wq, old_bucket, new_bucket);
                        wq->wq_thscheduled_count[old_bucket]--;
                        wq->wq_thscheduled_count[new_bucket]++;

                        PTHREAD_TRACE_WQ(TRACE_wq_thread_squash | DBG_FUNC_NONE, wq, tl->th_priority, new_bucket, 0, 0);
                        tl->th_priority = new_bucket;
                        PTHREAD_TRACE_WQ(TRACE_wq_override_reset | DBG_FUNC_END, tl->th_workq, new_qos, 0, 0, 0);
                }
        }

        workqueue_run_threadreq_and_unlock(p, wq, tl, NULL, false);
        return 0;
}

/**
 * Multiplexed call to interact with the workqueue mechanism
 */
int
_workq_kernreturn(struct proc *p,
                  int options,
                  user_addr_t item,
                  int arg2,
                  int arg3,
                  int32_t *retval)
{
        struct workqueue *wq;
        int error = 0;

        if (pthread_kern->proc_get_register(p) == 0) {
                return EINVAL;
        }

        switch (options) {
        case WQOPS_QUEUE_NEWSPISUPP: {
                /*
                 * arg2 = offset of serialno into dispatch queue
                 * arg3 = kevent support
                 */
                int offset = arg2;
                if (arg3 & 0x01){
                        // If we get here, then userspace has indicated support for kevent delivery.
                }

                pthread_kern->proc_set_dispatchqueue_serialno_offset(p, (uint64_t)offset);
                break;
        }
        case WQOPS_QUEUE_REQTHREADS: {
                /*
                 * arg2 = number of threads to start
                 * arg3 = priority
                 */
                error = wqops_queue_reqthreads(p, arg2, arg3);
                break;
        }
        case WQOPS_SET_EVENT_MANAGER_PRIORITY: {
                /*
                 * arg2 = priority for the manager thread
                 *
                 * if _PTHREAD_PRIORITY_EVENT_MANAGER_FLAG is set, the
                 * ~_PTHREAD_PRIORITY_FLAGS_MASK contains a scheduling priority instead
                 * of a QOS value
                 */
                pthread_priority_t pri = arg2;

                wq = (struct workqueue *)pthread_kern->proc_get_wqptr(p);
                if (wq == NULL) {
                        error = EINVAL;
                        break;
                }
                workqueue_lock_spin(wq);
                if (pri & _PTHREAD_PRIORITY_SCHED_PRI_FLAG){
                        /*
                         * If userspace passes a scheduling priority, that takes precidence
                         * over any QoS.  (So, userspace should take care not to accidenatally
                         * lower the priority this way.)
                         */
                        uint32_t sched_pri = pri & _PTHREAD_PRIORITY_SCHED_PRI_MASK;
                        if (wq->wq_event_manager_priority & _PTHREAD_PRIORITY_SCHED_PRI_FLAG){
                                wq->wq_event_manager_priority = MAX(sched_pri, wq->wq_event_manager_priority & _PTHREAD_PRIORITY_SCHED_PRI_MASK)
                                                | _PTHREAD_PRIORITY_SCHED_PRI_FLAG | _PTHREAD_PRIORITY_EVENT_MANAGER_FLAG;
                        } else {
                                wq->wq_event_manager_priority = sched_pri
                                                | _PTHREAD_PRIORITY_SCHED_PRI_FLAG | _PTHREAD_PRIORITY_EVENT_MANAGER_FLAG;
                        }
                } else if ((wq->wq_event_manager_priority & _PTHREAD_PRIORITY_SCHED_PRI_FLAG) == 0){
                        int cur_qos = pthread_priority_get_thread_qos(wq->wq_event_manager_priority);
                        int new_qos = pthread_priority_get_thread_qos(pri);
                        wq->wq_event_manager_priority = (uint32_t)thread_qos_get_pthread_priority(MAX(cur_qos, new_qos)) | _PTHREAD_PRIORITY_EVENT_MANAGER_FLAG;
                }
                workqueue_unlock(wq);
                break;
        }
        case WQOPS_THREAD_KEVENT_RETURN:
        case WQOPS_THREAD_WORKLOOP_RETURN:
                wq = (struct workqueue *)pthread_kern->proc_get_wqptr(p);
                PTHREAD_TRACE_WQ(TRACE_wq_runthread | DBG_FUNC_END, wq, options, 0, 0, 0);
                if (item != 0 && arg2 != 0) {
                        int32_t kevent_retval;
                        int ret;
                        if (options == WQOPS_THREAD_KEVENT_RETURN) {
                                ret = kevent_qos_internal(p, -1, item, arg2, item, arg2, NULL, NULL,
                                                KEVENT_FLAG_WORKQ | KEVENT_FLAG_IMMEDIATE | KEVENT_FLAG_ERROR_EVENTS,
                                                &kevent_retval);
                        } else /* options == WQOPS_THREAD_WORKLOOP_RETURN */ {
                                kqueue_id_t kevent_id = -1;
                                ret = kevent_id_internal(p, &kevent_id, item, arg2, item, arg2,
                                                NULL, NULL,
                                                KEVENT_FLAG_WORKLOOP | KEVENT_FLAG_IMMEDIATE | KEVENT_FLAG_ERROR_EVENTS,
                                                &kevent_retval);
                        }
                        /*
                         * We shouldn't be getting more errors out than events we put in, so
                         * reusing the input buffer should always provide enough space.  But,
                         * the assert is commented out since we get errors in edge cases in the
                         * process lifecycle.
                         */
                        //assert(ret == KERN_SUCCESS && kevent_retval >= 0);
                        if (ret != KERN_SUCCESS){
                                error = ret;
                                break;
                        } else if (kevent_retval > 0){
                                assert(kevent_retval <= arg2);
                                *retval = kevent_retval;
                                error = 0;
                                break;
                        }
                }
                goto thread_return;

        case WQOPS_THREAD_RETURN:
                wq = (struct workqueue *)pthread_kern->proc_get_wqptr(p);
                PTHREAD_TRACE_WQ(TRACE_wq_runthread | DBG_FUNC_END, wq, options, 0, 0, 0);
        thread_return:
                error = wqops_thread_return(p, wq);
                // NOT REACHED except in case of error
                assert(error);
                break;

        case WQOPS_SHOULD_NARROW: {
                /*
                 * arg2 = priority to test
                 * arg3 = unused
                 */
                pthread_priority_t priority = arg2;
                thread_t th = current_thread();
                struct threadlist *tl = util_get_thread_threadlist_entry(th);

                if (tl == NULL || (tl->th_flags & TH_LIST_CONSTRAINED) == 0) {
                        error = EINVAL;
                        break;
                }

                int class = pthread_priority_get_class_index(priority);
                wq = tl->th_workq;
                workqueue_lock_spin(wq);
                bool should_narrow = !may_start_constrained_thread(wq, class, tl, false);
                workqueue_unlock(wq);

                *retval = should_narrow;
                break;
        }
        default:
                error = EINVAL;
                break;
        }

        switch (options) {
        case WQOPS_THREAD_KEVENT_RETURN:
        case WQOPS_THREAD_WORKLOOP_RETURN:
        case WQOPS_THREAD_RETURN:
                PTHREAD_TRACE_WQ(TRACE_wq_runthread | DBG_FUNC_START, wq, options, 0, 0, 0);
                break;
        }
        return (error);
}

/*
 * We have no work to do, park ourselves on the idle list.
 *
 * Consumes the workqueue lock and does not return.
 */
static void __dead2
parkit(struct workqueue *wq, struct threadlist *tl, thread_t thread)
{
        assert(thread == tl->th_thread);
        assert(thread == current_thread());

        PTHREAD_TRACE_WQ(TRACE_wq_thread_park | DBG_FUNC_START, wq, 0, 0, 0, 0);

        uint32_t us_to_wait = 0;

        TAILQ_REMOVE(&wq->wq_thrunlist, tl, th_entry);

        tl->th_flags &= ~TH_LIST_RUNNING;
        tl->th_flags &= ~TH_LIST_KEVENT;
        assert((tl->th_flags & TH_LIST_KEVENT_BOUND) == 0);

        if (tl->th_flags & TH_LIST_CONSTRAINED) {
                wq->wq_constrained_threads_scheduled--;
                tl->th_flags &= ~TH_LIST_CONSTRAINED;
        }

        _wq_thactive_dec(wq, tl->th_priority);
        wq->wq_thscheduled_count[tl->th_priority]--;
        wq->wq_threads_scheduled--;
        uint32_t thidlecount = ++wq->wq_thidlecount;

        pthread_kern->thread_sched_call(thread, NULL);

        /*
         * We'd like to always have one manager thread parked so that we can have
         * low latency when we need to bring a manager thread up.  If that idle
         * thread list is empty, make this thread a manager thread.
         *
         * XXX: This doesn't check that there's not a manager thread outstanding,
         * so it's based on the assumption that most manager callouts will change
         * their QoS before parking.  If that stops being true, this may end up
         * costing us more than we gain.
         */
        if (TAILQ_EMPTY(&wq->wq_thidlemgrlist) &&
                        tl->th_priority != WORKQUEUE_EVENT_MANAGER_BUCKET){
                PTHREAD_TRACE_WQ(TRACE_wq_thread_reset_priority | DBG_FUNC_NONE,
                                        wq, thread_tid(thread),
                                        (tl->th_priority << 16) | WORKQUEUE_EVENT_MANAGER_BUCKET, 2, 0);
                reset_priority(tl, pthread_priority_from_wq_class_index(wq, WORKQUEUE_EVENT_MANAGER_BUCKET));
                tl->th_priority = WORKQUEUE_EVENT_MANAGER_BUCKET;
        }

        if (tl->th_priority == WORKQUEUE_EVENT_MANAGER_BUCKET){
                TAILQ_INSERT_HEAD(&wq->wq_thidlemgrlist, tl, th_entry);
        } else {
                TAILQ_INSERT_HEAD(&wq->wq_thidlelist, tl, th_entry);
        }

        /*
         * When we remove the voucher from the thread, we may lose our importance
         * causing us to get preempted, so we do this after putting the thread on
         * the idle list.  That when, when we get our importance back we'll be able
         * to use this thread from e.g. the kevent call out to deliver a boosting
         * message.
         */
        tl->th_flags |= TH_LIST_REMOVING_VOUCHER;
        workqueue_unlock(wq);
        if (pthread_kern->thread_will_park_or_terminate) {
                pthread_kern->thread_will_park_or_terminate(tl->th_thread);
        }
        __assert_only kern_return_t kr;
        kr = pthread_kern->thread_set_voucher_name(MACH_PORT_NULL);
        assert(kr == KERN_SUCCESS);
        workqueue_lock_spin(wq);
        tl->th_flags &= ~(TH_LIST_REMOVING_VOUCHER);

        if ((tl->th_flags & TH_LIST_RUNNING) == 0) {
                if (thidlecount < 101) {
                        us_to_wait = wq_reduce_pool_window_usecs - ((thidlecount-2) * (wq_reduce_pool_window_usecs / 100));
                } else {
                        us_to_wait = wq_reduce_pool_window_usecs / 100;
                }

                thread_set_pending_block_hint(thread, kThreadWaitParkedWorkQueue);
                assert_wait_timeout_with_leeway((caddr_t)tl, (THREAD_INTERRUPTIBLE),
                                TIMEOUT_URGENCY_SYS_BACKGROUND|TIMEOUT_URGENCY_LEEWAY, us_to_wait,
                                wq_reduce_pool_window_usecs/10, NSEC_PER_USEC);

                workqueue_unlock(wq);

                thread_block(wq_unpark_continue);
                panic("thread_block(wq_unpark_continue) returned!");
        } else {
                workqueue_unlock(wq);

                /*
                 * While we'd dropped the lock to unset our voucher, someone came
                 * around and made us runnable.  But because we weren't waiting on the
                 * event their wakeup() was ineffectual.  To correct for that, we just
                 * run the continuation ourselves.
                 */
                wq_unpark_continue(NULL, THREAD_AWAKENED);
        }
}

static bool
may_start_constrained_thread(struct workqueue *wq, uint32_t at_priclass,
                struct threadlist *tl, bool may_start_timer)
{
        uint32_t req_qos = _wq_thactive_best_constrained_req_qos(wq);
        wq_thactive_t thactive;

        if (may_start_timer && at_priclass < req_qos) {
                /*
                 * When called from workqueue_run_threadreq_and_unlock() pre-post newest
                 * higher priorities into the thactive state so that
                 * workqueue_callback() takes the right decision.
                 *
                 * If the admission check passes, workqueue_run_threadreq_and_unlock
                 * will reset this value before running the request.
                 */
                thactive = _wq_thactive_set_best_constrained_req_qos(wq, req_qos,
                                at_priclass);
#ifdef __LP64__
                PTHREAD_TRACE_WQ(TRACE_wq_thactive_update, 1, (uint64_t)thactive,
                                (uint64_t)(thactive >> 64), 0, 0);
#endif
        } else {
                thactive = _wq_thactive(wq);
        }

        uint32_t constrained_threads = wq->wq_constrained_threads_scheduled;
        if (tl && (tl->th_flags & TH_LIST_CONSTRAINED)) {
                /*
                 * don't count the current thread as scheduled
                 */
                constrained_threads--;
        }
        if (constrained_threads >= wq_max_constrained_threads) {
                PTHREAD_TRACE_WQ(TRACE_wq_constrained_admission | DBG_FUNC_NONE, wq, 1,
                                wq->wq_constrained_threads_scheduled,
                                wq_max_constrained_threads, 0);
                /*
                 * we need 1 or more constrained threads to return to the kernel before
                 * we can dispatch additional work
                 */
                return false;
        }

        /*
         * Compute a metric for many how many threads are active.  We find the
         * highest priority request outstanding and then add up the number of
         * active threads in that and all higher-priority buckets.  We'll also add
         * any "busy" threads which are not active but blocked recently enough that
         * we can't be sure they've gone idle yet.  We'll then compare this metric
         * to our max concurrency to decide whether to add a new thread.
         */

        uint32_t busycount, thactive_count;

        thactive_count = _wq_thactive_aggregate_downto_qos(wq, thactive,
                        at_priclass, &busycount, NULL);

        if (tl && tl->th_priority <= at_priclass) {
                /*
                 * don't count this thread as currently active
                 */
                assert(thactive_count > 0);
                thactive_count--;
        }

        if (thactive_count + busycount < wq_max_concurrency[at_priclass]) {
                PTHREAD_TRACE_WQ(TRACE_wq_constrained_admission | DBG_FUNC_NONE, wq, 2,
                                thactive_count, busycount, 0);
                return true;
        } else {
                PTHREAD_TRACE_WQ(TRACE_wq_constrained_admission | DBG_FUNC_NONE, wq, 3,
                                thactive_count, busycount, 0);
        }

        if (busycount && may_start_timer) {
                /*
                 * If this is called from the add timer, we won't have another timer
                 * fire when the thread exits the "busy" state, so rearm the timer.
                 */
                if (WQ_TIMER_DELAYED_NEEDED(wq)) {
                        workqueue_interval_timer_start(wq);
                }
        }

        return false;
}

static struct threadlist *
pop_from_thidlelist(struct workqueue *wq, uint32_t priclass)
{
        assert(wq->wq_thidlecount);

        struct threadlist *tl = NULL;

        if (!TAILQ_EMPTY(&wq->wq_thidlemgrlist) &&
                        (priclass == WORKQUEUE_EVENT_MANAGER_BUCKET || TAILQ_EMPTY(&wq->wq_thidlelist))){
                tl = TAILQ_FIRST(&wq->wq_thidlemgrlist);
                TAILQ_REMOVE(&wq->wq_thidlemgrlist, tl, th_entry);
                assert(tl->th_priority == WORKQUEUE_EVENT_MANAGER_BUCKET);
        } else if (!TAILQ_EMPTY(&wq->wq_thidlelist) &&
                        (priclass != WORKQUEUE_EVENT_MANAGER_BUCKET || TAILQ_EMPTY(&wq->wq_thidlemgrlist))){
                tl = TAILQ_FIRST(&wq->wq_thidlelist);
                TAILQ_REMOVE(&wq->wq_thidlelist, tl, th_entry);
                assert(tl->th_priority != WORKQUEUE_EVENT_MANAGER_BUCKET);
        } else {
                panic("pop_from_thidlelist called with no threads available");
        }
        assert((tl->th_flags & TH_LIST_RUNNING) == 0);

        assert(wq->wq_thidlecount);
        wq->wq_thidlecount--;

        TAILQ_INSERT_TAIL(&wq->wq_thrunlist, tl, th_entry);

        tl->th_flags |= TH_LIST_RUNNING | TH_LIST_BUSY;

        wq->wq_threads_scheduled++;
        wq->wq_thscheduled_count[priclass]++;
        _wq_thactive_inc(wq, priclass);
        return tl;
}

static pthread_priority_t
pthread_priority_from_wq_class_index(struct workqueue *wq, int index)
{
        if (index == WORKQUEUE_EVENT_MANAGER_BUCKET){
                return wq->wq_event_manager_priority;
        } else {
                return class_index_get_pthread_priority(index);
        }
}

static void
reset_priority(struct threadlist *tl, pthread_priority_t pri)
{
        kern_return_t ret;
        thread_t th = tl->th_thread;

        if ((pri & _PTHREAD_PRIORITY_SCHED_PRI_FLAG) == 0){
                ret = pthread_kern->thread_set_workq_qos(th, pthread_priority_get_thread_qos(pri), 0);
                assert(ret == KERN_SUCCESS || ret == KERN_TERMINATED);

                if (tl->th_flags & TH_LIST_EVENT_MGR_SCHED_PRI) {

                        /* Reset priority to default (masked by QoS) */

                        ret = pthread_kern->thread_set_workq_pri(th, 31, POLICY_TIMESHARE);
                        assert(ret == KERN_SUCCESS || ret == KERN_TERMINATED);

                        tl->th_flags &= ~TH_LIST_EVENT_MGR_SCHED_PRI;
                }
        } else {
                ret = pthread_kern->thread_set_workq_qos(th, THREAD_QOS_UNSPECIFIED, 0);
                assert(ret == KERN_SUCCESS || ret == KERN_TERMINATED);
                ret = pthread_kern->thread_set_workq_pri(th, (pri & (~_PTHREAD_PRIORITY_FLAGS_MASK)), POLICY_TIMESHARE);
                assert(ret == KERN_SUCCESS || ret == KERN_TERMINATED);

                tl->th_flags |= TH_LIST_EVENT_MGR_SCHED_PRI;
        }
}

/*
 * Picks the best request to run, and returns the best overcommit fallback
 * if the best pick is non overcommit and risks failing its admission check.
 */
static struct threadreq *
workqueue_best_threadreqs(struct workqueue *wq, struct threadlist *tl,
                struct threadreq **fallback)
{
        struct threadreq *req, *best_req = NULL;
        int priclass, prilimit;

        if ((wq->wq_event_manager_threadreq.tr_state == TR_STATE_WAITING) &&
                        ((wq->wq_thscheduled_count[WORKQUEUE_EVENT_MANAGER_BUCKET] == 0) ||
                        (tl && tl->th_priority == WORKQUEUE_EVENT_MANAGER_BUCKET))) {
                /*
                 * There's an event manager request and either:
                 *   - no event manager currently running
                 *   - we are re-using the event manager
                 */
                req = &wq->wq_event_manager_threadreq;
                PTHREAD_TRACE_WQ_REQ(TRACE_wq_run_threadreq_req_select | DBG_FUNC_NONE, wq, req, 1, 0, 0);
                return req;
        }

        if (tl) {
                prilimit = WORKQUEUE_EVENT_MANAGER_BUCKET;
        } else {
                prilimit = _wq_highest_paced_priority(wq);
        }
        for (priclass = 0; priclass < prilimit; priclass++) {
                req = TAILQ_FIRST(&wq->wq_overcommit_reqlist[priclass]);
                if (req) {
                        PTHREAD_TRACE_WQ_REQ(TRACE_wq_run_threadreq_req_select | DBG_FUNC_NONE, wq, req, 2, 0, 0);
                        if (best_req) {
                                *fallback = req;
                        } else {
                                best_req = req;
                        }
                        break;
                }
                if (!best_req) {
                        best_req = TAILQ_FIRST(&wq->wq_reqlist[priclass]);
                        if (best_req) {
                                PTHREAD_TRACE_WQ_REQ(TRACE_wq_run_threadreq_req_select | DBG_FUNC_NONE, wq, best_req, 3, 0, 0);
                        }
                }
        }
        return best_req;
}

/**
 * Runs a thread request on a thread
 *
 * - if thread is THREAD_NULL, will find a thread and run the request there.
 *   Otherwise, the thread must be the current thread.
 *
 * - if req is NULL, will find the highest priority request and run that.  If
 *   it is not NULL, it must be a threadreq object in state NEW.  If it can not
 *   be run immediately, it will be enqueued and moved to state WAITING.
 *
 *   Either way, the thread request object serviced will be moved to state
 *   PENDING and attached to the threadlist.
 *
 *   Should be called with the workqueue lock held.  Will drop it.
 *
 *   WARNING: _workq_kevent_reqthreads needs to be able to preflight any
 *   admission checks in this function.  If you are changing this function,
 *   keep that one up-to-date.
 *
 * - if parking_tl is non NULL, then the current thread is parking. This will
 *   try to reuse this thread for a request. If no match is found, it will be
 *   parked.
 */
static int
workqueue_run_threadreq_and_unlock(proc_t p, struct workqueue *wq,
                struct threadlist *parking_tl, struct threadreq *req,
                bool may_add_new_thread)
{
        struct threadreq *incoming_req = req;

        struct threadlist *tl = parking_tl;
        int rc = WQ_RUN_TR_THROTTLED;

        assert(tl == NULL || tl->th_thread == current_thread());
        assert(req == NULL || req->tr_state == TR_STATE_NEW);
        assert(!may_add_new_thread || !tl);

        PTHREAD_TRACE_WQ_REQ(TRACE_wq_run_threadreq | DBG_FUNC_START, wq, req,
                        tl ? thread_tid(tl->th_thread) : 0,
                        req ? (req->tr_priority << 16 | req->tr_flags) : 0, 0);

        /*
         * Special cases when provided an event manager request
         */
        if (req && req->tr_priority == WORKQUEUE_EVENT_MANAGER_BUCKET) {
                // Clients must not rely on identity of event manager requests
                assert(req->tr_flags & TR_FLAG_ONSTACK);
                // You can't be both overcommit and event manager
                assert((req->tr_flags & TR_FLAG_OVERCOMMIT) == 0);

                /*
                 * We can only ever have one event manager request, so coalesce them if
                 * there's already one outstanding.
                 */
                if (wq->wq_event_manager_threadreq.tr_state == TR_STATE_WAITING) {
                        PTHREAD_TRACE_WQ_REQ(TRACE_wq_run_threadreq_mgr_merge | DBG_FUNC_NONE, wq, req, 0, 0, 0);

                        struct threadreq *existing_req = &wq->wq_event_manager_threadreq;
                        if (req->tr_flags & TR_FLAG_KEVENT) {
                                existing_req->tr_flags |= TR_FLAG_KEVENT;
                        }

                        req = existing_req;
                        incoming_req = NULL;
                }

                if (wq->wq_thscheduled_count[WORKQUEUE_EVENT_MANAGER_BUCKET] &&
                                (!tl || tl->th_priority != WORKQUEUE_EVENT_MANAGER_BUCKET)){
                        /*
                         * There can only be one event manager running at a time.
                         */
                        PTHREAD_TRACE_WQ(TRACE_wq_run_threadreq | DBG_FUNC_END, wq, 1, 0, 0, 0);
                        goto done;
                }
        }

again: // Start again after creating a thread

        if (_wq_exiting(wq)) {
                rc = WQ_RUN_TR_EXITING;
                goto exiting;
        }

        /*
         * Thread request selection and admission control
         */
        struct threadreq *fallback = NULL;
        if (req) {
                if ((req->tr_flags & TR_FLAG_NO_PACING) == 0 &&
                                _wq_should_pace_priority(wq, req->tr_priority)) {
                        /*
                         * If a request fails the pacing admission check, then thread
                         * requests are redriven when the pacing thread is finally scheduled
                         * when it calls _wq_pacing_end() in wq_unpark_continue().
                         */
                        goto done;
                }
        } else if (wq->wq_reqcount == 0) {
                PTHREAD_TRACE_WQ(TRACE_wq_run_threadreq | DBG_FUNC_END, wq, 2, 0, 0, 0);
                goto done;
        } else if ((req = workqueue_best_threadreqs(wq, tl, &fallback)) == NULL) {
                PTHREAD_TRACE_WQ(TRACE_wq_run_threadreq | DBG_FUNC_END, wq, 3, 0, 0, 0);
                goto done;
        }

        if ((req->tr_flags & TR_FLAG_OVERCOMMIT) == 0 &&
                        (req->tr_priority < WORKQUEUE_EVENT_MANAGER_BUCKET)) {
                if (!may_start_constrained_thread(wq, req->tr_priority, parking_tl, true)) {
                        if (!fallback) {
                                PTHREAD_TRACE_WQ(TRACE_wq_run_threadreq | DBG_FUNC_END, wq, 4, 0, 0, 0);
                                goto done;
                        }
                        assert(req->tr_state == TR_STATE_WAITING);
                        req = fallback;
                }
        }

        /*
         * Thread selection.
         */
        if (parking_tl) {
                if (tl->th_priority != req->tr_priority) {
                        _wq_thactive_move(wq, tl->th_priority, req->tr_priority);
                        wq->wq_thscheduled_count[tl->th_priority]--;
                        wq->wq_thscheduled_count[req->tr_priority]++;
                }
                PTHREAD_TRACE_WQ(TRACE_wq_run_threadreq_thread_select | DBG_FUNC_NONE,
                                wq, 1, thread_tid(tl->th_thread), 0, 0);
        } else if (wq->wq_thidlecount) {
                tl = pop_from_thidlelist(wq, req->tr_priority);
                /*
                 * This call will update wq_thscheduled_count and wq_thactive_count for
                 * the provided priority.  It will not set the returned thread to that
                 * priority.  This matches the behavior of the parking_tl clause above.
                 */
                PTHREAD_TRACE_WQ(TRACE_wq_run_threadreq_thread_select | DBG_FUNC_NONE,
                                wq, 2, thread_tid(tl->th_thread), 0, 0);
        } else /* no idle threads */ {
                if (!may_add_new_thread || wq->wq_nthreads >= wq_max_threads) {
                        PTHREAD_TRACE_WQ(TRACE_wq_run_threadreq | DBG_FUNC_END, wq, 5,
                                        may_add_new_thread, wq->wq_nthreads, 0);
                        if (wq->wq_nthreads < wq_max_threads) {
                                rc = WQ_RUN_TR_THREAD_NEEDED;
                        }
                        goto done;
                }

                bool added_thread = workqueue_addnewthread(p, wq);
                /*
                 * workqueue_addnewthread will drop and re-take the lock, so we
                 * need to ensure we still have a cached request.
                 *
                 * It also means we have to pick a new request, since our old pick may
                 * not be valid anymore.
                 */
                req = incoming_req;
                if (req && (req->tr_flags & TR_FLAG_ONSTACK)) {
                        _threadreq_copy_prepare(wq);
                }

                if (added_thread) {
                        PTHREAD_TRACE_WQ(TRACE_wq_run_threadreq_thread_select | DBG_FUNC_NONE,
                                        wq, 3, 0, 0, 0);
                        goto again;
                } else if (_wq_exiting(wq)) {
                        rc = WQ_RUN_TR_EXITING;
                        goto exiting;
                } else {
                        PTHREAD_TRACE_WQ(TRACE_wq_run_threadreq | DBG_FUNC_END, wq, 6, 0, 0, 0);
                        /*
                         * Something caused thread creation to fail.  Kick off the timer in
                         * the hope that it'll succeed next time.
                         */
                        if (WQ_TIMER_DELAYED_NEEDED(wq)) {
                                workqueue_interval_timer_start(wq);
                        }
                        goto done;
                }
        }

        /*
         * Setup thread, mark request as complete and run with it.
         */
        if (req->tr_state == TR_STATE_WAITING) {
                _threadreq_dequeue(wq, req);
        }
        if (tl->th_priority != req->tr_priority) {
                PTHREAD_TRACE_WQ(TRACE_wq_thread_reset_priority | DBG_FUNC_NONE,
                                        wq, thread_tid(tl->th_thread),
                                        (tl->th_priority << 16) | req->tr_priority, 1, 0);
                reset_priority(tl, pthread_priority_from_wq_class_index(wq, req->tr_priority));
                tl->th_priority = (uint8_t)req->tr_priority;
        }
        if (req->tr_flags & TR_FLAG_OVERCOMMIT) {
                if ((tl->th_flags & TH_LIST_CONSTRAINED) != 0) {
                        tl->th_flags &= ~TH_LIST_CONSTRAINED;
                        wq->wq_constrained_threads_scheduled--;
                }
        } else {
                if ((tl->th_flags & TH_LIST_CONSTRAINED) == 0) {
                        tl->th_flags |= TH_LIST_CONSTRAINED;
                        wq->wq_constrained_threads_scheduled++;
                }
        }

        if (!parking_tl && !(req->tr_flags & TR_FLAG_NO_PACING)) {
                _wq_pacing_start(wq, tl);
        }
        if ((req->tr_flags & TR_FLAG_OVERCOMMIT) == 0) {
                uint32_t old_qos, new_qos;

                /*
                 * If we are scheduling a constrained thread request, we may need to
                 * update the best constrained qos in the thactive atomic state.
                 */
                for (new_qos = 0; new_qos < WQ_THACTIVE_NO_PENDING_REQUEST; new_qos++) {
                        if (TAILQ_FIRST(&wq->wq_reqlist[new_qos]))
                                break;
                }
                old_qos = _wq_thactive_best_constrained_req_qos(wq);
                if (old_qos != new_qos) {
                        wq_thactive_t v = _wq_thactive_set_best_constrained_req_qos(wq,
                                        old_qos, new_qos);
#ifdef __LP64__
                        PTHREAD_TRACE_WQ(TRACE_wq_thactive_update, 2, (uint64_t)v,
                                        (uint64_t)(v >> 64), 0, 0);
#else
                        PTHREAD_TRACE_WQ(TRACE_wq_thactive_update, 2, v, 0, 0, 0);
#endif
                }
        }
        {
                uint32_t upcall_flags = WQ_FLAG_THREAD_NEWSPI;
                if (req->tr_flags & TR_FLAG_OVERCOMMIT)
                        upcall_flags |= WQ_FLAG_THREAD_OVERCOMMIT;
                if (req->tr_flags & TR_FLAG_KEVENT)
                        upcall_flags |= WQ_FLAG_THREAD_KEVENT;
                if (req->tr_flags & TR_FLAG_WORKLOOP)
                        upcall_flags |= WQ_FLAG_THREAD_WORKLOOP | WQ_FLAG_THREAD_KEVENT;
                if (tl->th_priority == WORKQUEUE_EVENT_MANAGER_BUCKET)
                        upcall_flags |= WQ_FLAG_THREAD_EVENT_MANAGER;
                tl->th_upcall_flags = upcall_flags >> WQ_FLAG_THREAD_PRIOSHIFT;
        }
        if (req->tr_flags & TR_FLAG_KEVENT) {
                tl->th_flags |= TH_LIST_KEVENT;
        } else {
                tl->th_flags &= ~TH_LIST_KEVENT;
        }
        return _threadreq_complete_and_unlock(p, wq, req, tl);

done:
        if (incoming_req) {
                _threadreq_enqueue(wq, incoming_req);
        }

exiting:

        if (parking_tl && !(parking_tl->th_flags & TH_LIST_UNBINDING)) {
                parkit(wq, parking_tl, parking_tl->th_thread);
                __builtin_unreachable();
        }

        workqueue_unlock(wq);

        return rc;
}

/**
 * parked thread wakes up
 */
static void __dead2
wq_unpark_continue(void* __unused ptr, wait_result_t wait_result)
{
        boolean_t first_use = false;
        thread_t th = current_thread();
        proc_t p = current_proc();

        struct uthread *uth = pthread_kern->get_bsdthread_info(th);
        if (uth == NULL) goto done;

        struct workqueue *wq = pthread_kern->proc_get_wqptr(p);
        if (wq == NULL) goto done;

        workqueue_lock_spin(wq);

        struct threadlist *tl = pthread_kern->uthread_get_threadlist(uth);
        assert(tl != WQ_THREADLIST_EXITING_POISON);
        if (tl == NULL) {
                /*
                 * We woke up before addnewthread() was finished setting us up.  Go
                 * ahead and exit, but before we do poison the threadlist variable so
                 * that addnewthread() doesn't think we are valid still.
                 */
                pthread_kern->uthread_set_threadlist(uth, WQ_THREADLIST_EXITING_POISON);
                workqueue_unlock(wq);
                goto done;
        }

        assert(tl->th_flags & TH_LIST_INITED);

        if ((tl->th_flags & TH_LIST_NEW)){
                tl->th_flags &= ~(TH_LIST_NEW);
                first_use = true;
        }

        if ((tl->th_flags & (TH_LIST_RUNNING | TH_LIST_BUSY)) == TH_LIST_RUNNING) {
                /*
                 * The normal wakeup path.
                 */
                goto return_to_user;
        }

        if ((tl->th_flags & TH_LIST_RUNNING) == 0 &&
                        wait_result == THREAD_TIMED_OUT &&
                        tl->th_priority == WORKQUEUE_EVENT_MANAGER_BUCKET &&
                        TAILQ_FIRST(&wq->wq_thidlemgrlist) == tl &&
                        TAILQ_NEXT(tl, th_entry) == NULL){
                /*
                 * If we are the only idle manager and we pop'ed for self-destruction,
                 * then don't actually exit.  Instead, free our stack to save some
                 * memory and re-park.
                 */

                workqueue_unlock(wq);

                vm_map_t vmap = wq->wq_map;

                // Keep this in sync with _setup_wqthread()
                const vm_size_t       guardsize = vm_map_page_size(vmap);
                const user_addr_t     freeaddr = (user_addr_t)tl->th_stackaddr + guardsize;
                const vm_map_offset_t freesize = vm_map_trunc_page_mask((PTH_DEFAULT_STACKSIZE + guardsize + PTHREAD_T_OFFSET) - 1, vm_map_page_mask(vmap)) - guardsize;

                __assert_only int kr = mach_vm_behavior_set(vmap, freeaddr, freesize, VM_BEHAVIOR_REUSABLE);
#if MACH_ASSERT
                if (kr != KERN_SUCCESS && kr != KERN_INVALID_ADDRESS) {
                        os_log_error(OS_LOG_DEFAULT, "unable to make thread stack reusable (kr: %d)", kr);
                }
#endif

                workqueue_lock_spin(wq);

                if ( !(tl->th_flags & TH_LIST_RUNNING)) {
                        thread_set_pending_block_hint(th, kThreadWaitParkedWorkQueue);
                        assert_wait((caddr_t)tl, (THREAD_INTERRUPTIBLE));

                        workqueue_unlock(wq);

                        thread_block(wq_unpark_continue);
                        __builtin_unreachable();
                }
        }

        if ((tl->th_flags & TH_LIST_RUNNING) == 0) {
                assert((tl->th_flags & TH_LIST_BUSY) == 0);
                if (!first_use) {
                        PTHREAD_TRACE_WQ(TRACE_wq_thread_park | DBG_FUNC_END, wq, 0, 0, 0, 0);
                }
                /*
                 * We were set running, but not for the purposes of actually running.
                 * This could be because the timer elapsed.  Or it could be because the
                 * thread aborted.  Either way, we need to return to userspace to exit.
                 *
                 * The call to workqueue_removethread will consume the lock.
                 */

                if (!first_use &&
                                (tl->th_priority < qos_class_get_class_index(WQ_THREAD_CLEANUP_QOS) ||
                                (tl->th_priority == WORKQUEUE_EVENT_MANAGER_BUCKET))) {
                        // Reset the QoS to something low for the pthread cleanup
                        PTHREAD_TRACE_WQ(TRACE_wq_thread_reset_priority | DBG_FUNC_NONE,
                                                wq, thread_tid(th),
                                                (tl->th_priority << 16) | qos_class_get_class_index(WQ_THREAD_CLEANUP_QOS), 3, 0);
                        pthread_priority_t cleanup_pri = _pthread_priority_make_newest(WQ_THREAD_CLEANUP_QOS, 0, 0);
                        reset_priority(tl, cleanup_pri);
                }

                workqueue_removethread(tl, 0, first_use);

                if (first_use){
                        pthread_kern->thread_bootstrap_return();
                } else {
                        pthread_kern->unix_syscall_return(0);
                }
                __builtin_unreachable();
        }

        /*
         * The timer woke us up or the thread was aborted.  However, we have
         * already started to make this a runnable thread.  Wait for that to
         * finish, then continue to userspace.
         */
        while ((tl->th_flags & TH_LIST_BUSY)) {
                assert_wait((caddr_t)tl, (THREAD_UNINT));

                workqueue_unlock(wq);

                thread_block(THREAD_CONTINUE_NULL);

                workqueue_lock_spin(wq);
        }

return_to_user:
        if (!first_use) {
                PTHREAD_TRACE_WQ(TRACE_wq_thread_park | DBG_FUNC_END, wq, 0, 0, 0, 0);
        }
        if (_wq_pacing_end(wq, tl) && wq->wq_reqcount) {
                workqueue_run_threadreq_and_unlock(p, wq, NULL, NULL, true);
        } else {
                workqueue_unlock(wq);
        }
        _setup_wqthread(p, th, wq, tl, first_use ? WQ_SETUP_FIRST_USE : 0);
        pthread_kern->thread_sched_call(th, workqueue_callback);
done:
        if (first_use){
                pthread_kern->thread_bootstrap_return();
        } else {
                pthread_kern->unix_syscall_return(EJUSTRETURN);
        }
        panic("Our attempt to return to userspace failed...");
}

/**
 * configures initial thread stack/registers to jump into:
 * _pthread_wqthread(pthread_t self, mach_port_t kport, void *stackaddr, void *keventlist, int upcall_flags, int nkevents);
 * to get there we jump through assembily stubs in pthread_asm.s.  Those
 * routines setup a stack frame, using the current stack pointer, and marshall
 * arguments from registers to the stack as required by the ABI.
 *
 * One odd thing we do here is to start the pthread_t 4k below what would be the
 * top of the stack otherwise.  This is because usually only the first 4k of the
 * pthread_t will be used and so we want to put it on the same 16k page as the
 * top of the stack to save memory.
 *
 * When we are done the stack will look like:
 * |-----------| th_stackaddr + th_allocsize
 * |pthread_t  | th_stackaddr + DEFAULT_STACKSIZE + guardsize + PTHREAD_STACK_OFFSET
 * |kevent list| optionally - at most WQ_KEVENT_LIST_LEN events
 * |kevent data| optionally - at most WQ_KEVENT_DATA_SIZE bytes
 * |stack gap  | bottom aligned to 16 bytes, and at least as big as stack_gap_min
 * |   STACK   |
 * |     ⇓     |
 * |           |
 * |guard page | guardsize
 * |-----------| th_stackaddr
 */
void
_setup_wqthread(proc_t p, thread_t th, struct workqueue *wq,
                struct threadlist *tl, int setup_flags)
{
        int error;
        if (setup_flags & WQ_SETUP_CLEAR_VOUCHER) {
                /*
                 * For preemption reasons, we want to reset the voucher as late as
                 * possible, so we do it in two places:
                 *   - Just before parking (i.e. in parkit())
                 *   - Prior to doing the setup for the next workitem (i.e. here)
                 *
                 * Those two places are sufficient to ensure we always reset it before
                 * it goes back out to user space, but be careful to not break that
                 * guarantee.
                 */
                __assert_only kern_return_t kr;
                kr = pthread_kern->thread_set_voucher_name(MACH_PORT_NULL);
                assert(kr == KERN_SUCCESS);
        }

        uint32_t upcall_flags = tl->th_upcall_flags << WQ_FLAG_THREAD_PRIOSHIFT;
        if (!(setup_flags & WQ_SETUP_FIRST_USE)) {
                upcall_flags |= WQ_FLAG_THREAD_REUSE;
        }

        /*
         * Put the QoS class value into the lower bits of the reuse_thread register, this is where
         * the thread priority used to be stored anyway.
         */
        pthread_priority_t priority = pthread_priority_from_wq_class_index(wq, tl->th_priority);
        upcall_flags |= (_pthread_priority_get_qos_newest(priority) & WQ_FLAG_THREAD_PRIOMASK);

        const vm_size_t guardsize = vm_map_page_size(tl->th_workq->wq_map);
        const vm_size_t stack_gap_min = (proc_is64bit(p) == 0) ? C_32_STK_ALIGN : C_64_REDZONE_LEN;
        const vm_size_t stack_align_min = (proc_is64bit(p) == 0) ? C_32_STK_ALIGN : C_64_STK_ALIGN;

        user_addr_t pthread_self_addr = (user_addr_t)(tl->th_stackaddr + PTH_DEFAULT_STACKSIZE + guardsize + PTHREAD_T_OFFSET);
        user_addr_t stack_top_addr = (user_addr_t)((pthread_self_addr - stack_gap_min) & -stack_align_min);
        user_addr_t stack_bottom_addr = (user_addr_t)(tl->th_stackaddr + guardsize);

        user_addr_t wqstart_fnptr = pthread_kern->proc_get_wqthread(p);
        if (!wqstart_fnptr) {
                panic("workqueue thread start function pointer is NULL");
        }

        if (setup_flags & WQ_SETUP_FIRST_USE) {
                uint32_t tsd_offset = pthread_kern->proc_get_pthread_tsd_offset(p);
                if (tsd_offset) {
                        mach_vm_offset_t th_tsd_base = (mach_vm_offset_t)pthread_self_addr + tsd_offset;
                        kern_return_t kret = pthread_kern->thread_set_tsd_base(th, th_tsd_base);
                        if (kret == KERN_SUCCESS) {
                                upcall_flags |= WQ_FLAG_THREAD_TSD_BASE_SET;
                        }
                }

                /*
                * Pre-fault the first page of the new thread's stack and the page that will
                * contain the pthread_t structure.
                */
                vm_map_t vmap = pthread_kern->current_map();
                if (vm_map_trunc_page_mask((vm_map_offset_t)(stack_top_addr - C_64_REDZONE_LEN), vm_map_page_mask(vmap)) !=
                                vm_map_trunc_page_mask((vm_map_offset_t)pthread_self_addr, vm_map_page_mask(vmap))){
                        vm_fault( vmap,
                                        vm_map_trunc_page_mask((vm_map_offset_t)(stack_top_addr - C_64_REDZONE_LEN), vm_map_page_mask(vmap)),
                                        VM_PROT_READ | VM_PROT_WRITE,
                                        FALSE,
                                        THREAD_UNINT, NULL, 0);
                }
                vm_fault( vmap,
                                vm_map_trunc_page_mask((vm_map_offset_t)pthread_self_addr, vm_map_page_mask(vmap)),
                                VM_PROT_READ | VM_PROT_WRITE,
                                FALSE,
                                THREAD_UNINT, NULL, 0);
        }

        user_addr_t kevent_list = NULL;
        int kevent_count = 0;
        if (upcall_flags & WQ_FLAG_THREAD_KEVENT){
                bool workloop = upcall_flags & WQ_FLAG_THREAD_WORKLOOP;

                kevent_list = pthread_self_addr - WQ_KEVENT_LIST_LEN * sizeof(struct kevent_qos_s);
                kevent_count = WQ_KEVENT_LIST_LEN;

                user_addr_t kevent_id_addr = kevent_list;
                if (workloop) {
                        /*
                         * The kevent ID goes just below the kevent list.  Sufficiently new
                         * userspace will know to look there.  Old userspace will just
                         * ignore it.
                         */
                        kevent_id_addr -= sizeof(kqueue_id_t);
                }

                user_addr_t kevent_data_buf = kevent_id_addr - WQ_KEVENT_DATA_SIZE;
                user_size_t kevent_data_available = WQ_KEVENT_DATA_SIZE;

                int32_t events_out = 0;

                assert(tl->th_flags | TH_LIST_KEVENT_BOUND);
                unsigned int flags = KEVENT_FLAG_STACK_DATA | KEVENT_FLAG_IMMEDIATE;
                if (tl->th_priority == WORKQUEUE_EVENT_MANAGER_BUCKET) {
                        flags |= KEVENT_FLAG_WORKQ_MANAGER;
                }
                int ret = 0;
                if (workloop) {
                        flags |= KEVENT_FLAG_WORKLOOP;
                        kqueue_id_t kevent_id = -1;
                        ret = kevent_id_internal(p, &kevent_id,
                                        NULL, 0, kevent_list, kevent_count,
                                        kevent_data_buf, &kevent_data_available,
                                        flags, &events_out);
                        copyout(&kevent_id, kevent_id_addr, sizeof(kevent_id));
                } else {
                        flags |= KEVENT_FLAG_WORKQ;
                        ret = kevent_qos_internal(p,
                                        class_index_get_thread_qos(tl->th_priority),
                                        NULL, 0, kevent_list, kevent_count,
                                        kevent_data_buf, &kevent_data_available,
                                        flags, &events_out);
                }

                // squash any errors into just empty output
                if (ret != KERN_SUCCESS || events_out == -1){
                        events_out = 0;
                        kevent_data_available = WQ_KEVENT_DATA_SIZE;
                }

                // We shouldn't get data out if there aren't events available
                assert(events_out != 0 || kevent_data_available == WQ_KEVENT_DATA_SIZE);

                if (events_out > 0){
                        if (kevent_data_available == WQ_KEVENT_DATA_SIZE){
                                stack_top_addr = (kevent_id_addr - stack_gap_min) & -stack_align_min;
                        } else {
                                stack_top_addr = (kevent_data_buf + kevent_data_available - stack_gap_min) & -stack_align_min;
                        }

                        kevent_count = events_out;
                } else {
                        kevent_list = NULL;
                        kevent_count = 0;
                }
        }

        PTHREAD_TRACE_WQ(TRACE_wq_runthread | DBG_FUNC_START, wq, 0, 0, 0, 0);

#if defined(__i386__) || defined(__x86_64__)
        if (proc_is64bit(p) == 0) {
                x86_thread_state32_t state = {
                        .eip = (unsigned int)wqstart_fnptr,
                        .eax = /* arg0 */ (unsigned int)pthread_self_addr,
                        .ebx = /* arg1 */ (unsigned int)tl->th_thport,
                        .ecx = /* arg2 */ (unsigned int)stack_bottom_addr,
                        .edx = /* arg3 */ (unsigned int)kevent_list,
                        .edi = /* arg4 */ (unsigned int)upcall_flags,
                        .esi = /* arg5 */ (unsigned int)kevent_count,

                        .esp = (int)((vm_offset_t)stack_top_addr),
                };

                error = pthread_kern->thread_set_wq_state32(th, (thread_state_t)&state);
                if (error != KERN_SUCCESS) {
                        panic(__func__ ": thread_set_wq_state failed: %d", error);
                }
        } else {
                x86_thread_state64_t state64 = {
                        // x86-64 already passes all the arguments in registers, so we just put them in their final place here
                        .rip = (uint64_t)wqstart_fnptr,
                        .rdi = (uint64_t)pthread_self_addr,
                        .rsi = (uint64_t)tl->th_thport,
                        .rdx = (uint64_t)stack_bottom_addr,
                        .rcx = (uint64_t)kevent_list,
                        .r8  = (uint64_t)upcall_flags,
                        .r9  = (uint64_t)kevent_count,

                        .rsp = (uint64_t)(stack_top_addr)
                };

                error = pthread_kern->thread_set_wq_state64(th, (thread_state_t)&state64);
                if (error != KERN_SUCCESS) {
                        panic(__func__ ": thread_set_wq_state failed: %d", error);
                }
        }
#else
#error setup_wqthread  not defined for this architecture
#endif
}

#if DEBUG
static int wq_kevent_test SYSCTL_HANDLER_ARGS {
        //(struct sysctl_oid *oidp, void *arg1, int arg2, struct sysctl_req *req)
#pragma unused(oidp, arg1, arg2)
        int error;
        struct workq_reqthreads_req_s requests[64] = {};

        if (req->newlen > sizeof(requests) || req->newlen < sizeof(struct workq_reqthreads_req_s))
                return EINVAL;

        error = copyin(req->newptr, requests, req->newlen);
        if (error) return error;

        _workq_reqthreads(req->p, (int)(req->newlen / sizeof(struct workq_reqthreads_req_s)), requests);

        return 0;
}
#endif // DEBUG

#pragma mark - Misc

int
_fill_procworkqueue(proc_t p, struct proc_workqueueinfo * pwqinfo)
{
        struct workqueue * wq;
        int error = 0;
        int     activecount;

        if ((wq = pthread_kern->proc_get_wqptr(p)) == NULL) {
                return EINVAL;
        }

        /*
         * This is sometimes called from interrupt context by the kperf sampler.
         * In that case, it's not safe to spin trying to take the lock since we
         * might already hold it.  So, we just try-lock it and error out if it's
         * already held.  Since this is just a debugging aid, and all our callers
         * are able to handle an error, that's fine.
         */
        bool locked = workqueue_lock_try(wq);
        if (!locked) {
                return EBUSY;
        }

        activecount = _wq_thactive_aggregate_downto_qos(wq, _wq_thactive(wq),
                        WORKQUEUE_NUM_BUCKETS - 1, NULL, NULL);
        pwqinfo->pwq_nthreads = wq->wq_nthreads;
        pwqinfo->pwq_runthreads = activecount;
        pwqinfo->pwq_blockedthreads = wq->wq_threads_scheduled - activecount;
        pwqinfo->pwq_state = 0;

        if (wq->wq_constrained_threads_scheduled >= wq_max_constrained_threads) {
                pwqinfo->pwq_state |= WQ_EXCEEDED_CONSTRAINED_THREAD_LIMIT;
        }

        if (wq->wq_nthreads >= wq_max_threads) {
                pwqinfo->pwq_state |= WQ_EXCEEDED_TOTAL_THREAD_LIMIT;
        }

        workqueue_unlock(wq);
        return(error);
}

uint32_t
_get_pwq_state_kdp(proc_t p)
{
        if (p == NULL) {
                return 0;
        }

        struct workqueue *wq = pthread_kern->proc_get_wqptr(p);

        if (wq == NULL || workqueue_lock_spin_is_acquired_kdp(wq)) {
                return 0;
        }

        uint32_t pwq_state = WQ_FLAGS_AVAILABLE;

        if (wq->wq_constrained_threads_scheduled >= wq_max_constrained_threads) {
                pwq_state |= WQ_EXCEEDED_CONSTRAINED_THREAD_LIMIT;
        }

        if (wq->wq_nthreads >= wq_max_threads) {
                pwq_state |= WQ_EXCEEDED_TOTAL_THREAD_LIMIT;
        }

        return pwq_state;
}

int
_thread_selfid(__unused struct proc *p, uint64_t *retval)
{
        thread_t thread = current_thread();
        *retval = thread_tid(thread);
        return KERN_SUCCESS;
}

void
_pthread_init(void)
{
        pthread_lck_grp_attr = lck_grp_attr_alloc_init();
        pthread_lck_grp = lck_grp_alloc_init("pthread", pthread_lck_grp_attr);

        /*
         * allocate the lock attribute for pthread synchronizers
         */
        pthread_lck_attr = lck_attr_alloc_init();

        pthread_list_mlock = lck_mtx_alloc_init(pthread_lck_grp, pthread_lck_attr);

        pth_global_hashinit();
        psynch_thcall = thread_call_allocate(psynch_wq_cleanup, NULL);
        psynch_zoneinit();

        pthread_zone_workqueue = zinit(sizeof(struct workqueue),
                        1024 * sizeof(struct workqueue), 8192, "pthread.workqueue");
        pthread_zone_threadlist = zinit(sizeof(struct threadlist),
                        1024 * sizeof(struct threadlist), 8192, "pthread.threadlist");
        pthread_zone_threadreq = zinit(sizeof(struct threadreq),
                        1024 * sizeof(struct threadreq), 8192, "pthread.threadreq");

        int policy_bootarg;
        if (PE_parse_boot_argn("pthread_mutex_default_policy", &policy_bootarg, sizeof(policy_bootarg))) {
                pthread_mutex_default_policy = policy_bootarg;
        }

        /*
         * register sysctls
         */
        sysctl_register_oid(&sysctl__kern_wq_stalled_window_usecs);
        sysctl_register_oid(&sysctl__kern_wq_reduce_pool_window_usecs);
        sysctl_register_oid(&sysctl__kern_wq_max_timer_interval_usecs);
        sysctl_register_oid(&sysctl__kern_wq_max_threads);
        sysctl_register_oid(&sysctl__kern_wq_max_constrained_threads);
        sysctl_register_oid(&sysctl__kern_pthread_debug_tracing);
        sysctl_register_oid(&sysctl__kern_pthread_mutex_default_policy);

#if DEBUG
        sysctl_register_oid(&sysctl__debug_wq_kevent_test);
#endif

        for (int i = 0; i < WORKQUEUE_NUM_BUCKETS; i++) {
                uint32_t thread_qos = _wq_bucket_to_thread_qos(i);
                wq_max_concurrency[i] = pthread_kern->qos_max_parallelism(thread_qos,
                                QOS_PARALLELISM_COUNT_LOGICAL);
        }
        wq_max_concurrency[WORKQUEUE_EVENT_MANAGER_BUCKET] = 1;
}