[apple/libpthread.git] / src / pthread_mutex.c

/*
 * Copyright (c) 2000-2003, 2007, 2008 Apple Inc. All rights reserved.
 *
 * @APPLE_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. 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_LICENSE_HEADER_END@
 */
/*
 * Copyright 1996 1995 by Open Software Foundation, Inc. 1997 1996 1995 1994 1993 1992 1991
 *              All Rights Reserved
 *
 * Permission to use, copy, modify, and distribute this software and
 * its documentation for any purpose and without fee is hereby granted,
 * provided that the above copyright notice appears in all copies and
 * that both the copyright notice and this permission notice appear in
 * supporting documentation.
 *
 * OSF DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE
 * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE.
 *
 * IN NO EVENT SHALL OSF BE LIABLE FOR ANY SPECIAL, INDIRECT, OR
 * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
 * LOSS OF USE, DATA OR PROFITS, WHETHER IN ACTION OF CONTRACT,
 * NEGLIGENCE, OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION
 * WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 *
 */
/*
 * MkLinux
 */

/*
 * POSIX Pthread Library
 * -- Mutex variable support
 */

#include "resolver.h"
#include "internal.h"
#include "kern/kern_trace.h"

#ifndef BUILDING_VARIANT /* [ */

#ifdef PLOCKSTAT
#include "plockstat.h"
/* This function is never called and exists to provide never-fired dtrace
 * probes so that user d scripts don't get errors.
 */
PTHREAD_NOEXPORT PTHREAD_USED
void
_plockstat_never_fired(void)
{
        PLOCKSTAT_MUTEX_SPIN(NULL);
        PLOCKSTAT_MUTEX_SPUN(NULL, 0, 0);
}
#else /* !PLOCKSTAT */
#define PLOCKSTAT_MUTEX_SPIN(x)
#define PLOCKSTAT_MUTEX_SPUN(x, y, z)
#define PLOCKSTAT_MUTEX_ERROR(x, y)
#define PLOCKSTAT_MUTEX_BLOCK(x)
#define PLOCKSTAT_MUTEX_BLOCKED(x, y)
#define PLOCKSTAT_MUTEX_ACQUIRE(x, y, z)
#define PLOCKSTAT_MUTEX_RELEASE(x, y)
#endif /* PLOCKSTAT */

#define BLOCK_FAIL_PLOCKSTAT    0
#define BLOCK_SUCCESS_PLOCKSTAT 1

#define PTHREAD_MUTEX_INIT_UNUSED 1

PTHREAD_NOEXPORT PTHREAD_WEAK
int _pthread_mutex_lock_init_slow(_pthread_mutex *mutex, bool trylock);

PTHREAD_NOEXPORT PTHREAD_WEAK // prevent inlining of return value into callers
int _pthread_mutex_fairshare_lock_slow(_pthread_mutex *mutex, bool trylock);

PTHREAD_NOEXPORT PTHREAD_WEAK // prevent inlining of return value into callers
int _pthread_mutex_firstfit_lock_slow(_pthread_mutex *mutex, bool trylock);

PTHREAD_NOEXPORT PTHREAD_WEAK // prevent inlining of return value into callers
int _pthread_mutex_fairshare_unlock_slow(_pthread_mutex *mutex);

PTHREAD_NOEXPORT PTHREAD_WEAK // prevent inlining of return value into callers
int _pthread_mutex_firstfit_unlock_slow(_pthread_mutex *mutex);

PTHREAD_NOEXPORT PTHREAD_WEAK // prevent inlining of return value into callers
int _pthread_mutex_corruption_abort(_pthread_mutex *mutex);

extern int __pthread_mutex_default_opt_policy PTHREAD_NOEXPORT;


int __pthread_mutex_default_opt_policy PTHREAD_NOEXPORT =
                _PTHREAD_MTX_OPT_POLICY_DEFAULT;

static inline bool
_pthread_mutex_policy_validate(int policy)
{
        return (policy >= 0 && policy < _PTHREAD_MUTEX_POLICY_LAST);
}

static inline int
_pthread_mutex_policy_to_opt(int policy)
{
        switch (policy) {
        case PTHREAD_MUTEX_POLICY_FAIRSHARE_NP:
                return _PTHREAD_MTX_OPT_POLICY_FAIRSHARE;
        case PTHREAD_MUTEX_POLICY_FIRSTFIT_NP:
                return _PTHREAD_MTX_OPT_POLICY_FIRSTFIT;
        default:
                __builtin_unreachable();
        }
}

PTHREAD_NOEXPORT
void
_pthread_mutex_global_init(const char *envp[],
                struct _pthread_registration_data *registration_data)
{

        int opt = _PTHREAD_MTX_OPT_POLICY_DEFAULT;
        if (registration_data->mutex_default_policy) {
                int policy = registration_data->mutex_default_policy;
                if (_pthread_mutex_policy_validate(policy)) {
                        opt = _pthread_mutex_policy_to_opt(policy);
                }
        }

        const char *envvar = _simple_getenv(envp, "PTHREAD_MUTEX_DEFAULT_POLICY");
        if (envvar) {
                int policy = envvar[0] - '0';
                if (_pthread_mutex_policy_validate(policy)) {
                        opt = _pthread_mutex_policy_to_opt(policy);
                }
        }

        if (opt != __pthread_mutex_default_opt_policy) {
                __pthread_mutex_default_opt_policy = opt;
        }
}



PTHREAD_ALWAYS_INLINE
static inline int _pthread_mutex_init(_pthread_mutex *mutex,
                const pthread_mutexattr_t *attr, uint32_t static_type);

typedef union mutex_seq {
        uint32_t seq[2];
        struct { uint32_t lgenval; uint32_t ugenval; };
        struct { uint32_t mgen; uint32_t ugen; };
        uint64_t seq_LU;
        uint64_t _Atomic atomic_seq_LU;
} mutex_seq;

_Static_assert(sizeof(mutex_seq) == 2 * sizeof(uint32_t),
                "Incorrect mutex_seq size");

#if !__LITTLE_ENDIAN__
#error MUTEX_GETSEQ_ADDR assumes little endian layout of 2 32-bit sequence words
#endif

PTHREAD_ALWAYS_INLINE
static inline void
MUTEX_GETSEQ_ADDR(_pthread_mutex *mutex, mutex_seq **seqaddr)
{
        // 64-bit aligned address inside m_seq array (&m_seq[0] for aligned mutex)
        // We don't require more than byte alignment on OS X. rdar://22278325
        *seqaddr = (void *)(((uintptr_t)mutex->m_seq + 0x7ul) & ~0x7ul);
}

PTHREAD_ALWAYS_INLINE
static inline void
MUTEX_GETTID_ADDR(_pthread_mutex *mutex, uint64_t **tidaddr)
{
        // 64-bit aligned address inside m_tid array (&m_tid[0] for aligned mutex)
        // We don't require more than byte alignment on OS X. rdar://22278325
        *tidaddr = (void*)(((uintptr_t)mutex->m_tid + 0x7ul) & ~0x7ul);
}

PTHREAD_ALWAYS_INLINE
static inline void
mutex_seq_load(mutex_seq *seqaddr, mutex_seq *oldseqval)
{
        oldseqval->seq_LU = seqaddr->seq_LU;
}

#define mutex_seq_atomic_load(seqaddr, oldseqval, m) \
                mutex_seq_atomic_load_##m(seqaddr, oldseqval)

PTHREAD_ALWAYS_INLINE PTHREAD_USED
static inline bool
mutex_seq_atomic_cmpxchgv_relaxed(mutex_seq *seqaddr, mutex_seq *oldseqval,
                mutex_seq *newseqval)
{
        return os_atomic_cmpxchgv(&seqaddr->atomic_seq_LU, oldseqval->seq_LU,
                        newseqval->seq_LU, &oldseqval->seq_LU, relaxed);
}

PTHREAD_ALWAYS_INLINE PTHREAD_USED
static inline bool
mutex_seq_atomic_cmpxchgv_acquire(mutex_seq *seqaddr, mutex_seq *oldseqval,
                mutex_seq *newseqval)
{
        return os_atomic_cmpxchgv(&seqaddr->atomic_seq_LU, oldseqval->seq_LU,
                        newseqval->seq_LU, &oldseqval->seq_LU, acquire);
}

PTHREAD_ALWAYS_INLINE PTHREAD_USED
static inline bool
mutex_seq_atomic_cmpxchgv_release(mutex_seq *seqaddr, mutex_seq *oldseqval,
                mutex_seq *newseqval)
{
        return os_atomic_cmpxchgv(&seqaddr->atomic_seq_LU, oldseqval->seq_LU,
                        newseqval->seq_LU, &oldseqval->seq_LU, release);
}

#define mutex_seq_atomic_cmpxchgv(seqaddr, oldseqval, newseqval, m)\
                mutex_seq_atomic_cmpxchgv_##m(seqaddr, oldseqval, newseqval)

/*
 * Initialize a mutex variable, possibly with additional attributes.
 * Public interface - so don't trust the lock - initialize it first.
 */
PTHREAD_NOEXPORT_VARIANT
int
pthread_mutex_init(pthread_mutex_t *omutex, const pthread_mutexattr_t *attr)
{
#if 0
        /* conformance tests depend on not having this behavior */
        /* The test for this behavior is optional */
        if (_pthread_mutex_check_signature(mutex))
                return EBUSY;
#endif
        _pthread_mutex *mutex = (_pthread_mutex *)omutex;
        _PTHREAD_LOCK_INIT(mutex->lock);
        return (_pthread_mutex_init(mutex, attr, 0x7));
}

PTHREAD_NOEXPORT_VARIANT
int
pthread_mutex_getprioceiling(const pthread_mutex_t *omutex, int *prioceiling)
{
        int res = EINVAL;
        _pthread_mutex *mutex = (_pthread_mutex *)omutex;
        if (_pthread_mutex_check_signature(mutex)) {
                _PTHREAD_LOCK(mutex->lock);
                *prioceiling = mutex->prioceiling;
                res = 0;
                _PTHREAD_UNLOCK(mutex->lock);
        }
        return res;
}

PTHREAD_NOEXPORT_VARIANT
int
pthread_mutex_setprioceiling(pthread_mutex_t *omutex, int prioceiling,
                int *old_prioceiling)
{
        int res = EINVAL;
        _pthread_mutex *mutex = (_pthread_mutex *)omutex;
        if (_pthread_mutex_check_signature(mutex)) {
                _PTHREAD_LOCK(mutex->lock);
                if (prioceiling >= -999 && prioceiling <= 999) {
                        *old_prioceiling = mutex->prioceiling;
                        mutex->prioceiling = (int16_t)prioceiling;
                        res = 0;
                }
                _PTHREAD_UNLOCK(mutex->lock);
        }
        return res;
}


int
pthread_mutexattr_getprioceiling(const pthread_mutexattr_t *attr,
                int *prioceiling)
{
        int res = EINVAL;
        if (attr->sig == _PTHREAD_MUTEX_ATTR_SIG) {
                *prioceiling = attr->prioceiling;
                res = 0;
        }
        return res;
}

int
pthread_mutexattr_getprotocol(const pthread_mutexattr_t *attr, int *protocol)
{
        int res = EINVAL;
        if (attr->sig == _PTHREAD_MUTEX_ATTR_SIG) {
                *protocol = attr->protocol;
                res = 0;
        }
        return res;
}

int
pthread_mutexattr_getpolicy_np(const pthread_mutexattr_t *attr, int *policy)
{
        int res = EINVAL;
        if (attr->sig == _PTHREAD_MUTEX_ATTR_SIG) {
                switch (attr->opt) {
                case _PTHREAD_MTX_OPT_POLICY_FAIRSHARE:
                        *policy = PTHREAD_MUTEX_POLICY_FAIRSHARE_NP;
                        res = 0;
                        break;
                case _PTHREAD_MTX_OPT_POLICY_FIRSTFIT:
                        *policy = PTHREAD_MUTEX_POLICY_FIRSTFIT_NP;
                        res = 0;
                        break;
                }
        }
        return res;
}

int
pthread_mutexattr_gettype(const pthread_mutexattr_t *attr, int *type)
{
        int res = EINVAL;
        if (attr->sig == _PTHREAD_MUTEX_ATTR_SIG) {
                *type = attr->type;
                res = 0;
        }
        return res;
}

int
pthread_mutexattr_getpshared(const pthread_mutexattr_t *attr, int *pshared)
{
        int res = EINVAL;
        if (attr->sig == _PTHREAD_MUTEX_ATTR_SIG) {
                *pshared = (int)attr->pshared;
                res = 0;
        }
        return res;
}

int
pthread_mutexattr_init(pthread_mutexattr_t *attr)
{
        attr->prioceiling = _PTHREAD_DEFAULT_PRIOCEILING;
        attr->protocol = _PTHREAD_DEFAULT_PROTOCOL;
        attr->opt = __pthread_mutex_default_opt_policy;
        attr->type = PTHREAD_MUTEX_DEFAULT;
        attr->sig = _PTHREAD_MUTEX_ATTR_SIG;
        attr->pshared = _PTHREAD_DEFAULT_PSHARED;
        return 0;
}

int
pthread_mutexattr_setprioceiling(pthread_mutexattr_t *attr, int prioceiling)
{
        int res = EINVAL;
        if (attr->sig == _PTHREAD_MUTEX_ATTR_SIG) {
                if (prioceiling >= -999 && prioceiling <= 999) {
                        attr->prioceiling = prioceiling;
                        res = 0;
                }
        }
        return res;
}

int
pthread_mutexattr_setprotocol(pthread_mutexattr_t *attr, int protocol)
{
        int res = EINVAL;
        if (attr->sig == _PTHREAD_MUTEX_ATTR_SIG) {
                switch (protocol) {
                        case PTHREAD_PRIO_NONE:
                        case PTHREAD_PRIO_INHERIT:
                        case PTHREAD_PRIO_PROTECT:
                                attr->protocol = protocol;
                                res = 0;
                                break;
                }
        }
        return res;
}

int
pthread_mutexattr_setpolicy_np(pthread_mutexattr_t *attr, int policy)
{
        int res = EINVAL;
        if (attr->sig == _PTHREAD_MUTEX_ATTR_SIG) {
                // <rdar://problem/35844519> the first-fit implementation was broken
                // pre-Liberty so this mapping exists to ensure that the old first-fit
                // define (2) is no longer valid when used on older systems.
                switch (policy) {
                case PTHREAD_MUTEX_POLICY_FAIRSHARE_NP:
                        attr->opt = _PTHREAD_MTX_OPT_POLICY_FAIRSHARE;
                        res = 0;
                        break;
                case PTHREAD_MUTEX_POLICY_FIRSTFIT_NP:
                        attr->opt = _PTHREAD_MTX_OPT_POLICY_FIRSTFIT;
                        res = 0;
                        break;
                }
        }
        return res;
}

int
pthread_mutexattr_settype(pthread_mutexattr_t *attr, int type)
{
        int res = EINVAL;
        if (attr->sig == _PTHREAD_MUTEX_ATTR_SIG) {
                switch (type) {
                        case PTHREAD_MUTEX_NORMAL:
                        case PTHREAD_MUTEX_ERRORCHECK:
                        case PTHREAD_MUTEX_RECURSIVE:
                        //case PTHREAD_MUTEX_DEFAULT:
                                attr->type = type;
                                res = 0;
                                break;
                }
        }
        return res;
}

int
pthread_mutexattr_setpshared(pthread_mutexattr_t *attr, int pshared)
{
        int res = EINVAL;
#if __DARWIN_UNIX03
        if (__unix_conforming == 0) {
                __unix_conforming = 1;
        }
#endif /* __DARWIN_UNIX03 */

        if (attr->sig == _PTHREAD_MUTEX_ATTR_SIG) {
#if __DARWIN_UNIX03
                if (( pshared == PTHREAD_PROCESS_PRIVATE) ||
                                (pshared == PTHREAD_PROCESS_SHARED))
#else /* __DARWIN_UNIX03 */
                if ( pshared == PTHREAD_PROCESS_PRIVATE)
#endif /* __DARWIN_UNIX03 */
                {
                        attr->pshared = pshared;
                        res = 0;
                }
        }
        return res;
}

PTHREAD_NOEXPORT PTHREAD_NOINLINE PTHREAD_NORETURN
int
_pthread_mutex_corruption_abort(_pthread_mutex *mutex)
{
        PTHREAD_ABORT("pthread_mutex corruption: mutex owner changed in the "
                        "middle of lock/unlock");
}


PTHREAD_NOINLINE
static int
_pthread_mutex_check_init_slow(_pthread_mutex *mutex)
{
        int res = EINVAL;

        if (_pthread_mutex_check_signature_init(mutex)) {
                _PTHREAD_LOCK(mutex->lock);
                if (_pthread_mutex_check_signature_init(mutex)) {
                        // initialize a statically initialized mutex to provide
                        // compatibility for misbehaving applications.
                        // (unlock should not be the first operation on a mutex)
                        res = _pthread_mutex_init(mutex, NULL, (mutex->sig & 0xf));
                } else if (_pthread_mutex_check_signature(mutex)) {
                        res = 0;
                }
                _PTHREAD_UNLOCK(mutex->lock);
        } else if (_pthread_mutex_check_signature(mutex)) {
                res = 0;
        }
        if (res != 0) {
                PLOCKSTAT_MUTEX_ERROR((pthread_mutex_t *)mutex, res);
        }
        return res;
}

PTHREAD_ALWAYS_INLINE
static inline int
_pthread_mutex_check_init(_pthread_mutex *mutex)
{
        int res = 0;
        if (!_pthread_mutex_check_signature(mutex)) {
                return _pthread_mutex_check_init_slow(mutex);
        }
        return res;
}

PTHREAD_ALWAYS_INLINE
static inline bool
_pthread_mutex_is_fairshare(_pthread_mutex *mutex)
{
        return (mutex->mtxopts.options.policy == _PTHREAD_MTX_OPT_POLICY_FAIRSHARE);
}

PTHREAD_ALWAYS_INLINE
static inline bool
_pthread_mutex_is_firstfit(_pthread_mutex *mutex)
{
        return (mutex->mtxopts.options.policy == _PTHREAD_MTX_OPT_POLICY_FIRSTFIT);
}

PTHREAD_ALWAYS_INLINE
static inline bool
_pthread_mutex_is_recursive(_pthread_mutex *mutex)
{
        return (mutex->mtxopts.options.type == PTHREAD_MUTEX_RECURSIVE);
}

PTHREAD_ALWAYS_INLINE
static int
_pthread_mutex_lock_handle_options(_pthread_mutex *mutex, bool trylock,
                uint64_t *tidaddr)
{
        if (mutex->mtxopts.options.type == PTHREAD_MUTEX_NORMAL) {
                // NORMAL does not do EDEADLK checking
                return 0;
        }

        uint64_t selfid = _pthread_selfid_direct();
        if (os_atomic_load(tidaddr, relaxed) == selfid) {
                if (_pthread_mutex_is_recursive(mutex)) {
                        if (mutex->mtxopts.options.lock_count < USHRT_MAX) {
                                mutex->mtxopts.options.lock_count += 1;
                                return mutex->mtxopts.options.lock_count;
                        } else {
                                return -EAGAIN;
                        }
                } else if (trylock) { /* PTHREAD_MUTEX_ERRORCHECK */
                        // <rdar://problem/16261552> as per OpenGroup, trylock cannot
                        // return EDEADLK on a deadlock, it should return EBUSY.
                        return -EBUSY;
                } else { /* PTHREAD_MUTEX_ERRORCHECK */
                        return -EDEADLK;
                }
        }

        // Not recursive, or recursive but first lock.
        return 0;
}

PTHREAD_ALWAYS_INLINE
static int
_pthread_mutex_unlock_handle_options(_pthread_mutex *mutex, uint64_t *tidaddr)
{
        if (mutex->mtxopts.options.type == PTHREAD_MUTEX_NORMAL) {
                // NORMAL does not do EDEADLK checking
                return 0;
        }

        uint64_t selfid = _pthread_selfid_direct();
        if (os_atomic_load(tidaddr, relaxed) != selfid) {
                return -EPERM;
        } else if (_pthread_mutex_is_recursive(mutex) &&
                        --mutex->mtxopts.options.lock_count) {
                return 1;
        }
        return 0;
}

/*
 * Sequence numbers and TID:
 *
 * In steady (and uncontended) state, an unlocked mutex will
 * look like A=[L4 U4 TID0]. When it is being locked, it transitions
 * to B=[L5+KE U4 TID0] and then C=[L5+KE U4 TID940]. For an uncontended mutex,
 * the unlock path will then transition to D=[L5 U4 TID0] and then finally
 * E=[L5 U5 TID0].
 *
 * If a contender comes in after B, the mutex will instead transition to
 * E=[L6+KE U4 TID0] and then F=[L6+KE U4 TID940]. If a contender comes in after
 * C, it will transition to F=[L6+KE U4 TID940] directly. In both cases, the
 * contender will enter the kernel with either mutexwait(U4, TID0) or
 * mutexwait(U4, TID940). The first owner will unlock the mutex by first
 * updating the owner to G=[L6+KE U4 TID-1] and then doing the actual unlock to
 * H=[L6+KE U5 TID=-1] before entering the kernel with mutexdrop(U5, -1) to
 * signal the next waiter (potentially as a prepost). When the waiter comes out
 * of the kernel, it will update the owner to I=[L6+KE U5 TID941]. An unlock at
 * this point is simply J=[L6 U5 TID0] and then K=[L6 U6 TID0].
 *
 * At various points along these timelines, since the sequence words and TID are
 * written independently, a thread may get preempted and another thread might
 * see inconsistent data. In the worst case, another thread may see the TID in
 * the SWITCHING (-1) state or unlocked (0) state for longer because the owning
 * thread was preempted.
 */

/*
 * Drop the mutex unlock references from cond_wait or mutex_unlock.
 */
PTHREAD_ALWAYS_INLINE
static inline int
_pthread_mutex_fairshare_unlock_updatebits(_pthread_mutex *mutex,
                uint32_t *flagsp, uint32_t **pmtxp, uint32_t *mgenp, uint32_t *ugenp)
{
        uint32_t flags = mutex->mtxopts.value;
        flags &= ~_PTHREAD_MTX_OPT_NOTIFY; // no notification by default

        mutex_seq *seqaddr;
        MUTEX_GETSEQ_ADDR(mutex, &seqaddr);

        mutex_seq oldseq, newseq;
        mutex_seq_load(seqaddr, &oldseq);

        uint64_t *tidaddr;
        MUTEX_GETTID_ADDR(mutex, &tidaddr);
        uint64_t oldtid, newtid;

        int res = _pthread_mutex_unlock_handle_options(mutex, tidaddr);
        if (res > 0) {
                // Valid recursive unlock
                if (flagsp) {
                        *flagsp = flags;
                }
                PLOCKSTAT_MUTEX_RELEASE((pthread_mutex_t *)mutex, 1);
                return 0;
        } else if (res < 0) {
                PLOCKSTAT_MUTEX_ERROR((pthread_mutex_t *)mutex, -res);
                return -res;
        }

        bool clearnotify, spurious;
        do {
                newseq = oldseq;
                oldtid = os_atomic_load(tidaddr, relaxed);

                clearnotify = false;
                spurious = false;

                // pending waiters
                int numwaiters = diff_genseq(oldseq.lgenval, oldseq.ugenval);
                if (numwaiters == 0) {
                        // spurious unlock (unlock of unlocked lock)
                        spurious = true;
                } else {
                        newseq.ugenval += PTHRW_INC;

                        if ((oldseq.lgenval & PTHRW_COUNT_MASK) ==
                                        (newseq.ugenval & PTHRW_COUNT_MASK)) {
                                // our unlock sequence matches to lock sequence, so if the
                                // CAS is successful, the mutex is unlocked

                                /* do not reset Ibit, just K&E */
                                newseq.lgenval &= ~(PTH_RWL_KBIT | PTH_RWL_EBIT);
                                clearnotify = true;
                                newtid = 0; // clear owner
                        } else {
                                newtid = PTHREAD_MTX_TID_SWITCHING;
                                // need to signal others waiting for mutex
                                flags |= _PTHREAD_MTX_OPT_NOTIFY;
                        }

                        if (newtid != oldtid) {
                                // We're giving up the mutex one way or the other, so go ahead
                                // and update the owner to 0 so that once the CAS below
                                // succeeds, there is no stale ownership information. If the
                                // CAS of the seqaddr fails, we may loop, but it's still valid
                                // for the owner to be SWITCHING/0
                                if (!os_atomic_cmpxchg(tidaddr, oldtid, newtid, relaxed)) {
                                        // we own this mutex, nobody should be updating it except us
                                        return _pthread_mutex_corruption_abort(mutex);
                                }
                        }
                }

                if (clearnotify || spurious) {
                        flags &= ~_PTHREAD_MTX_OPT_NOTIFY;
                }
        } while (!mutex_seq_atomic_cmpxchgv(seqaddr, &oldseq, &newseq, release));

        PTHREAD_TRACE(psynch_mutex_unlock_updatebits, mutex, oldseq.lgenval,
                        newseq.lgenval, oldtid);

        if (mgenp != NULL) {
                *mgenp = newseq.lgenval;
        }
        if (ugenp != NULL) {
                *ugenp = newseq.ugenval;
        }
        if (pmtxp != NULL) {
                *pmtxp = (uint32_t *)mutex;
        }
        if (flagsp != NULL) {
                *flagsp = flags;
        }

        return 0;
}

PTHREAD_ALWAYS_INLINE
static inline int
_pthread_mutex_fairshare_lock_updatebits(_pthread_mutex *mutex, uint64_t selfid)
{
        bool firstfit = _pthread_mutex_is_firstfit(mutex);
        bool gotlock = true;

        mutex_seq *seqaddr;
        MUTEX_GETSEQ_ADDR(mutex, &seqaddr);

        mutex_seq oldseq, newseq;
        mutex_seq_load(seqaddr, &oldseq);

        uint64_t *tidaddr;
        MUTEX_GETTID_ADDR(mutex, &tidaddr);

        do {
                newseq = oldseq;

                if (firstfit) {
                        // firstfit locks can have the lock stolen out from under a locker
                        // between the unlock from the kernel and this lock path. When this
                        // happens, we still want to set the K bit before leaving the loop
                        // (or notice if the lock unlocks while we try to update).
                        gotlock = !is_rwl_ebit_set(oldseq.lgenval);
                } else if ((oldseq.lgenval & (PTH_RWL_KBIT | PTH_RWL_EBIT)) == 
                                (PTH_RWL_KBIT | PTH_RWL_EBIT)) {
                        // bit are already set, just update the owner tidaddr
                        break;
                }

                newseq.lgenval |= PTH_RWL_KBIT | PTH_RWL_EBIT;
        } while (!mutex_seq_atomic_cmpxchgv(seqaddr, &oldseq, &newseq,
                        acquire));

        if (gotlock) {
                os_atomic_store(tidaddr, selfid, relaxed);
        }

        PTHREAD_TRACE(psynch_mutex_lock_updatebits, mutex, oldseq.lgenval,
                        newseq.lgenval, 0);

        // failing to take the lock in firstfit returns 1 to force the caller
        // to wait in the kernel
        return gotlock ? 0 : 1;
}

PTHREAD_NOINLINE
static int
_pthread_mutex_fairshare_lock_wait(_pthread_mutex *mutex, mutex_seq newseq,
                uint64_t oldtid)
{
        uint64_t *tidaddr;
        MUTEX_GETTID_ADDR(mutex, &tidaddr);
        uint64_t selfid = _pthread_selfid_direct();

        PLOCKSTAT_MUTEX_BLOCK((pthread_mutex_t *)mutex);
        do {
                uint32_t updateval;
                do {
                        updateval = __psynch_mutexwait(mutex, newseq.lgenval,
                                        newseq.ugenval, oldtid, mutex->mtxopts.value);
                        oldtid = os_atomic_load(tidaddr, relaxed);
                } while (updateval == (uint32_t)-1);

                // returns 0 on succesful update; in firstfit it may fail with 1
        } while (_pthread_mutex_fairshare_lock_updatebits(mutex, selfid) == 1);
        PLOCKSTAT_MUTEX_BLOCKED((pthread_mutex_t *)mutex, BLOCK_SUCCESS_PLOCKSTAT);

        return 0;
}

PTHREAD_NOEXPORT PTHREAD_NOINLINE
int
_pthread_mutex_fairshare_lock_slow(_pthread_mutex *omutex, bool trylock)
{
        int res, recursive = 0;
        _pthread_mutex *mutex = (_pthread_mutex *)omutex;

        mutex_seq *seqaddr;
        MUTEX_GETSEQ_ADDR(mutex, &seqaddr);

        mutex_seq oldseq, newseq;
        mutex_seq_load(seqaddr, &oldseq);

        uint64_t *tidaddr;
        MUTEX_GETTID_ADDR(mutex, &tidaddr);
        uint64_t oldtid, selfid = _pthread_selfid_direct();

        res = _pthread_mutex_lock_handle_options(mutex, trylock, tidaddr);
        if (res > 0) {
                recursive = 1;
                res = 0;
                goto out;
        } else if (res < 0) {
                res = -res;
                goto out;
        }

        bool gotlock;
        do {
                newseq = oldseq;
                oldtid = os_atomic_load(tidaddr, relaxed);

                gotlock = ((oldseq.lgenval & PTH_RWL_EBIT) == 0);

                if (trylock && !gotlock) {
                        // A trylock on a held lock will fail immediately. But since
                        // we did not load the sequence words atomically, perform a
                        // no-op CAS64 to ensure that nobody has unlocked concurrently.
                } else {
                        // Increment the lock sequence number and force the lock into E+K
                        // mode, whether "gotlock" is true or not.
                        newseq.lgenval += PTHRW_INC;
                        newseq.lgenval |= PTH_RWL_EBIT | PTH_RWL_KBIT;
                }
        } while (!mutex_seq_atomic_cmpxchgv(seqaddr, &oldseq, &newseq, acquire));

        PTHREAD_TRACE(psynch_mutex_lock_updatebits, omutex, oldseq.lgenval,
                        newseq.lgenval, 0);

        if (gotlock) {
                os_atomic_store(tidaddr, selfid, relaxed);
                res = 0;
                PTHREAD_TRACE(psynch_mutex_ulock, omutex, newseq.lgenval,
                                newseq.ugenval, selfid);
        } else if (trylock) {
                res = EBUSY;
                PTHREAD_TRACE(psynch_mutex_utrylock_failed, omutex, newseq.lgenval,
                                newseq.ugenval, oldtid);
        } else {
                PTHREAD_TRACE(psynch_mutex_ulock | DBG_FUNC_START, omutex,
                                newseq.lgenval, newseq.ugenval, oldtid);
                res = _pthread_mutex_fairshare_lock_wait(mutex, newseq, oldtid);
                PTHREAD_TRACE(psynch_mutex_ulock | DBG_FUNC_END, omutex,
                                newseq.lgenval, newseq.ugenval, oldtid);
        }

        if (res == 0 && _pthread_mutex_is_recursive(mutex)) {
                mutex->mtxopts.options.lock_count = 1;
        }

out:
#if PLOCKSTAT
        if (res == 0) {
                PLOCKSTAT_MUTEX_ACQUIRE((pthread_mutex_t *)mutex, recursive, 0);
        } else {
                PLOCKSTAT_MUTEX_ERROR((pthread_mutex_t *)mutex, res);
        }
#endif

        return res;
}

PTHREAD_NOINLINE
static inline int
_pthread_mutex_fairshare_lock(_pthread_mutex *mutex, bool trylock)
{
#if ENABLE_USERSPACE_TRACE
        return _pthread_mutex_fairshare_lock_slow(mutex, trylock);
#elif PLOCKSTAT
        if (PLOCKSTAT_MUTEX_ACQUIRE_ENABLED() || PLOCKSTAT_MUTEX_ERROR_ENABLED()) {
                return _pthread_mutex_fairshare_lock_slow(mutex, trylock);
        }
#endif

        uint64_t *tidaddr;
        MUTEX_GETTID_ADDR(mutex, &tidaddr);
        uint64_t selfid = _pthread_selfid_direct();

        mutex_seq *seqaddr;
        MUTEX_GETSEQ_ADDR(mutex, &seqaddr);

        mutex_seq oldseq, newseq;
        mutex_seq_load(seqaddr, &oldseq);

        if (os_unlikely(oldseq.lgenval & PTH_RWL_EBIT)) {
                return _pthread_mutex_fairshare_lock_slow(mutex, trylock);
        }

        bool gotlock;
        do {
                newseq = oldseq;

                gotlock = ((oldseq.lgenval & PTH_RWL_EBIT) == 0);

                if (trylock && !gotlock) {
                        // A trylock on a held lock will fail immediately. But since
                        // we did not load the sequence words atomically, perform a
                        // no-op CAS64 to ensure that nobody has unlocked concurrently.
                } else if (os_likely(gotlock)) {
                        // Increment the lock sequence number and force the lock into E+K
                        // mode, whether "gotlock" is true or not.
                        newseq.lgenval += PTHRW_INC;
                        newseq.lgenval |= PTH_RWL_EBIT | PTH_RWL_KBIT;
                } else {
                        return _pthread_mutex_fairshare_lock_slow(mutex, trylock);
                }
        } while (os_unlikely(!mutex_seq_atomic_cmpxchgv(seqaddr, &oldseq, &newseq,
                        acquire)));

        if (os_likely(gotlock)) {
                os_atomic_store(tidaddr, selfid, relaxed);
                return 0;
        } else if (trylock) {
                return EBUSY;
        } else {
                __builtin_trap();
        }
}

PTHREAD_NOINLINE
static int
_pthread_mutex_fairshare_unlock_drop(_pthread_mutex *mutex, mutex_seq newseq,
                uint32_t flags)
{
        int res;
        uint32_t updateval;

        uint64_t *tidaddr;
        MUTEX_GETTID_ADDR(mutex, &tidaddr);

        PTHREAD_TRACE(psynch_mutex_uunlock | DBG_FUNC_START, mutex, newseq.lgenval,
                        newseq.ugenval, os_atomic_load(tidaddr, relaxed));

        updateval = __psynch_mutexdrop(mutex, newseq.lgenval, newseq.ugenval,
                        os_atomic_load(tidaddr, relaxed), flags);

        PTHREAD_TRACE(psynch_mutex_uunlock | DBG_FUNC_END, mutex, updateval, 0, 0);

        if (updateval == (uint32_t)-1) {
                res = errno;

                if (res == EINTR) {
                        res = 0;
                }
                if (res != 0) {
                        PTHREAD_ABORT("__psynch_mutexdrop failed with error %d", res);
                }
                return res;
        }

        return 0;
}

PTHREAD_NOEXPORT PTHREAD_NOINLINE
int
_pthread_mutex_fairshare_unlock_slow(_pthread_mutex *mutex)
{
        int res;
        mutex_seq newseq;
        uint32_t flags;

        res = _pthread_mutex_fairshare_unlock_updatebits(mutex, &flags, NULL,
                        &newseq.lgenval, &newseq.ugenval);
        if (res != 0) return res;

        if ((flags & _PTHREAD_MTX_OPT_NOTIFY) != 0) {
                return _pthread_mutex_fairshare_unlock_drop(mutex, newseq, flags);
        } else {
                uint64_t *tidaddr;
                MUTEX_GETTID_ADDR(mutex, &tidaddr);
                PTHREAD_TRACE(psynch_mutex_uunlock, mutex, newseq.lgenval,
                                newseq.ugenval, os_atomic_load(tidaddr, relaxed));
        }

        return 0;
}

PTHREAD_NOINLINE
static int
_pthread_mutex_fairshare_unlock(_pthread_mutex *mutex)
{
#if ENABLE_USERSPACE_TRACE
        return _pthread_mutex_fairshare_unlock_slow(mutex);
#elif PLOCKSTAT
        if (PLOCKSTAT_MUTEX_RELEASE_ENABLED() || PLOCKSTAT_MUTEX_ERROR_ENABLED()) {
                return _pthread_mutex_fairshare_unlock_slow(mutex);
        }
#endif

        uint64_t *tidaddr;
        MUTEX_GETTID_ADDR(mutex, &tidaddr);

        mutex_seq *seqaddr;
        MUTEX_GETSEQ_ADDR(mutex, &seqaddr);

        mutex_seq oldseq, newseq;
        mutex_seq_load(seqaddr, &oldseq);

        int numwaiters = diff_genseq(oldseq.lgenval, oldseq.ugenval);
        if (os_unlikely(numwaiters == 0)) {
                // spurious unlock (unlock of unlocked lock)
                return 0;
        }

        // We're giving up the mutex one way or the other, so go ahead and
        // update the owner to 0 so that once the CAS below succeeds, there
        // is no stale ownership information. If the CAS of the seqaddr
        // fails, we may loop, but it's still valid for the owner to be
        // SWITCHING/0
        os_atomic_store(tidaddr, 0, relaxed);

        do {
                newseq = oldseq;
                newseq.ugenval += PTHRW_INC;

                if (os_likely((oldseq.lgenval & PTHRW_COUNT_MASK) ==
                                (newseq.ugenval & PTHRW_COUNT_MASK))) {
                        // if we succeed in performing the CAS we can be sure of a fast
                        // path (only needing the CAS) unlock, if:
                        //   a. our lock and unlock sequence are equal
                        //   b. we don't need to clear an unlock prepost from the kernel

                        // do not reset Ibit, just K&E
                        newseq.lgenval &= ~(PTH_RWL_KBIT | PTH_RWL_EBIT);
                } else {
                        return _pthread_mutex_fairshare_unlock_slow(mutex);
                }
        } while (os_unlikely(!mutex_seq_atomic_cmpxchgv(seqaddr, &oldseq, &newseq,
                        release)));

        return 0;
}

#pragma mark firstfit

PTHREAD_ALWAYS_INLINE
static inline int
_pthread_mutex_firstfit_unlock_updatebits(_pthread_mutex *mutex,
                uint32_t *flagsp, uint32_t **mutexp, uint32_t *lvalp, uint32_t *uvalp)
{
        uint32_t flags = mutex->mtxopts.value & ~_PTHREAD_MTX_OPT_NOTIFY;
        bool kernel_wake;

        mutex_seq *seqaddr;
        MUTEX_GETSEQ_ADDR(mutex, &seqaddr);

        mutex_seq oldseq, newseq;
        mutex_seq_load(seqaddr, &oldseq);

        uint64_t *tidaddr;
        MUTEX_GETTID_ADDR(mutex, &tidaddr);
        uint64_t oldtid;

        int res = _pthread_mutex_unlock_handle_options(mutex, tidaddr);
        if (res > 0) {
                // Valid recursive unlock
                if (flagsp) {
                        *flagsp = flags;
                }
                PLOCKSTAT_MUTEX_RELEASE((pthread_mutex_t *)mutex, 1);
                return 0;
        } else if (res < 0) {
                PLOCKSTAT_MUTEX_ERROR((pthread_mutex_t *)mutex, -res);
                return -res;
        }

        do {
                newseq = oldseq;
                oldtid = os_atomic_load(tidaddr, relaxed);
                // More than one kernel waiter means we need to do a wake.
                kernel_wake = diff_genseq(oldseq.lgenval, oldseq.ugenval) > 0;
                newseq.lgenval &= ~PTH_RWL_EBIT;

                if (kernel_wake) {
                        // Going to the kernel post-unlock removes a single waiter unlock
                        // from the mutex counts.
                        newseq.ugenval += PTHRW_INC;
                }

                if (oldtid != 0) {
                        if (!os_atomic_cmpxchg(tidaddr, oldtid, 0, relaxed)) {
                                return _pthread_mutex_corruption_abort(mutex);
                        }
                }
        } while (!mutex_seq_atomic_cmpxchgv(seqaddr, &oldseq, &newseq, release));

        PTHREAD_TRACE(psynch_ffmutex_unlock_updatebits, mutex, oldseq.lgenval,
                        newseq.lgenval, newseq.ugenval);

        if (kernel_wake) {
                // We choose to return this out via flags because the condition
                // variable also uses this to determine whether to do a kernel wake
                // when beginning a cvwait.
                flags |= _PTHREAD_MTX_OPT_NOTIFY;
        }
        if (lvalp) {
                *lvalp = newseq.lgenval;
        }
        if (uvalp) {
                *uvalp = newseq.ugenval;
        }
        if (mutexp) {
                *mutexp = (uint32_t *)mutex;
        }
        if (flagsp) {
                *flagsp = flags;
        }
        return 0;
}

PTHREAD_NOEXPORT PTHREAD_NOINLINE
static int
_pthread_mutex_firstfit_wake(_pthread_mutex *mutex, mutex_seq newseq,
                uint32_t flags)
{
        PTHREAD_TRACE(psynch_ffmutex_wake, mutex, newseq.lgenval, newseq.ugenval,
                        0);
        int res = __psynch_mutexdrop(mutex, newseq.lgenval, newseq.ugenval, 0,
                        flags);

        if (res == -1) {
                res = errno;
                if (res == EINTR) {
                        res = 0;
                }
                if (res != 0) {
                        PTHREAD_ABORT("__psynch_mutexdrop failed with error %d", res);
                }
                return res;
        }
        return 0;
}

PTHREAD_NOEXPORT PTHREAD_NOINLINE
int
_pthread_mutex_firstfit_unlock_slow(_pthread_mutex *mutex)
{
        mutex_seq newseq;
        uint32_t flags;
        int res;

        res = _pthread_mutex_firstfit_unlock_updatebits(mutex, &flags, NULL,
                        &newseq.lgenval, &newseq.ugenval);
        if (res != 0) return res;

        if (flags & _PTHREAD_MTX_OPT_NOTIFY) {
                return _pthread_mutex_firstfit_wake(mutex, newseq, flags);
        }
        return 0;
}

PTHREAD_ALWAYS_INLINE
static bool
_pthread_mutex_firstfit_lock_updatebits(_pthread_mutex *mutex, uint64_t selfid,
                mutex_seq *newseqp)
{
        bool gotlock;

        mutex_seq *seqaddr;
        MUTEX_GETSEQ_ADDR(mutex, &seqaddr);

        mutex_seq oldseq, newseq;
        mutex_seq_load(seqaddr, &oldseq);

        uint64_t *tidaddr;
        MUTEX_GETTID_ADDR(mutex, &tidaddr);

        PTHREAD_TRACE(psynch_ffmutex_lock_updatebits | DBG_FUNC_START, mutex,
                        oldseq.lgenval, oldseq.ugenval, 0);

        do {
                newseq = oldseq;
                gotlock = is_rwl_ebit_clear(oldseq.lgenval);

                if (gotlock) {
                        // If we see the E-bit cleared, we should just attempt to take it.
                        newseq.lgenval |= PTH_RWL_EBIT;
                } else {
                        // If we failed to get the lock then we need to put ourselves back
                        // in the queue of waiters. The previous unlocker that woke us out
                        // of the kernel consumed the S-count for our previous wake. So
                        // take another ticket on L and go back in the kernel to sleep.
                        newseq.lgenval += PTHRW_INC;
                }
        } while (!mutex_seq_atomic_cmpxchgv(seqaddr, &oldseq, &newseq, acquire));

        if (gotlock) {
                os_atomic_store(tidaddr, selfid, relaxed);
        }

        PTHREAD_TRACE(psynch_ffmutex_lock_updatebits | DBG_FUNC_END, mutex,
                        newseq.lgenval, newseq.ugenval, 0);

        if (newseqp) {
                *newseqp = newseq;
        }
        return gotlock;
}

PTHREAD_NOINLINE
static int
_pthread_mutex_firstfit_lock_wait(_pthread_mutex *mutex, mutex_seq newseq,
                uint64_t oldtid)
{
        uint64_t *tidaddr;
        MUTEX_GETTID_ADDR(mutex, &tidaddr);
        uint64_t selfid = _pthread_selfid_direct();

        PLOCKSTAT_MUTEX_BLOCK((pthread_mutex_t *)mutex);
        do {
                uint32_t uval;
                do {
                        PTHREAD_TRACE(psynch_ffmutex_wait | DBG_FUNC_START, mutex,
                                        newseq.lgenval, newseq.ugenval, mutex->mtxopts.value);
                        uval = __psynch_mutexwait(mutex, newseq.lgenval, newseq.ugenval,
                                        oldtid, mutex->mtxopts.value);
                        PTHREAD_TRACE(psynch_ffmutex_wait | DBG_FUNC_END, mutex,
                                        uval, 0, 0);
                        oldtid = os_atomic_load(tidaddr, relaxed);
                } while (uval == (uint32_t)-1);
        } while (!_pthread_mutex_firstfit_lock_updatebits(mutex, selfid, &newseq));
        PLOCKSTAT_MUTEX_BLOCKED((pthread_mutex_t *)mutex, BLOCK_SUCCESS_PLOCKSTAT);

        return 0;
}

PTHREAD_NOEXPORT PTHREAD_NOINLINE
int
_pthread_mutex_firstfit_lock_slow(_pthread_mutex *mutex, bool trylock)
{
        int res, recursive = 0;

        mutex_seq *seqaddr;
        MUTEX_GETSEQ_ADDR(mutex, &seqaddr);

        mutex_seq oldseq, newseq;
        mutex_seq_load(seqaddr, &oldseq);

        uint64_t *tidaddr;
        MUTEX_GETTID_ADDR(mutex, &tidaddr);
        uint64_t oldtid, selfid = _pthread_selfid_direct();

        res = _pthread_mutex_lock_handle_options(mutex, trylock, tidaddr);
        if (res > 0) {
                recursive = 1;
                res = 0;
                goto out;
        } else if (res < 0) {
                res = -res;
                goto out;
        }

        PTHREAD_TRACE(psynch_ffmutex_lock_updatebits | DBG_FUNC_START, mutex,
                        oldseq.lgenval, oldseq.ugenval, 0);

        bool gotlock;
        do {
                newseq = oldseq;
                oldtid = os_atomic_load(tidaddr, relaxed);

                gotlock = is_rwl_ebit_clear(oldseq.lgenval);
                if (trylock && !gotlock) {
                        // We still want to perform the CAS here, even though it won't
                        // do anything so that it fails if someone unlocked while we were
                        // in the loop
                } else if (gotlock) {
                        // In first-fit, getting the lock simply adds the E-bit
                        newseq.lgenval |= PTH_RWL_EBIT;
                } else {
                        // Failed to get the lock, increment the L-val and go to
                        // the kernel to sleep
                        newseq.lgenval += PTHRW_INC;
                }
        } while (!mutex_seq_atomic_cmpxchgv(seqaddr, &oldseq, &newseq, acquire));

        PTHREAD_TRACE(psynch_ffmutex_lock_updatebits | DBG_FUNC_END, mutex,
                        newseq.lgenval, newseq.ugenval, 0);

        if (gotlock) {
                os_atomic_store(tidaddr, selfid, relaxed);
                res = 0;
                PTHREAD_TRACE(psynch_mutex_ulock, mutex, newseq.lgenval,
                                newseq.ugenval, selfid);
        } else if (trylock) {
                res = EBUSY;
                PTHREAD_TRACE(psynch_mutex_utrylock_failed, mutex, newseq.lgenval,
                                newseq.ugenval, oldtid);
        } else {
                PTHREAD_TRACE(psynch_mutex_ulock | DBG_FUNC_START, mutex,
                                newseq.lgenval, newseq.ugenval, oldtid);
                res = _pthread_mutex_firstfit_lock_wait(mutex, newseq, oldtid);
                PTHREAD_TRACE(psynch_mutex_ulock | DBG_FUNC_END, mutex,
                                newseq.lgenval, newseq.ugenval, oldtid);
        }

        if (res == 0 && _pthread_mutex_is_recursive(mutex)) {
                mutex->mtxopts.options.lock_count = 1;
        }

out:
#if PLOCKSTAT
        if (res == 0) {
                PLOCKSTAT_MUTEX_ACQUIRE((pthread_mutex_t *)mutex, recursive, 0);
        } else {
                PLOCKSTAT_MUTEX_ERROR((pthread_mutex_t *)mutex, res);
        }
#endif
        return res;
}

#pragma mark fast path

PTHREAD_NOEXPORT PTHREAD_NOINLINE
int
_pthread_mutex_droplock(_pthread_mutex *mutex, uint32_t *flagsp,
                uint32_t **pmtxp, uint32_t *mgenp, uint32_t *ugenp)
{
        if (_pthread_mutex_is_fairshare(mutex)) {
                return _pthread_mutex_fairshare_unlock_updatebits(mutex, flagsp,
                                pmtxp, mgenp, ugenp);
        }
        return _pthread_mutex_firstfit_unlock_updatebits(mutex, flagsp, pmtxp,
                        mgenp, ugenp);
}

PTHREAD_NOEXPORT PTHREAD_NOINLINE
int
_pthread_mutex_lock_init_slow(_pthread_mutex *mutex, bool trylock)
{
        int res;

        res = _pthread_mutex_check_init(mutex);
        if (res != 0) return res;

        if (os_unlikely(_pthread_mutex_is_fairshare(mutex))) {
                return _pthread_mutex_fairshare_lock_slow(mutex, trylock);
        }
        return _pthread_mutex_firstfit_lock_slow(mutex, trylock);
}

PTHREAD_NOEXPORT PTHREAD_NOINLINE
static int
_pthread_mutex_unlock_init_slow(_pthread_mutex *mutex)
{
        int res;

        // Initialize static mutexes for compatibility with misbehaving
        // applications (unlock should not be the first operation on a mutex).
        res = _pthread_mutex_check_init(mutex);
        if (res != 0) return res;

        if (os_unlikely(_pthread_mutex_is_fairshare(mutex))) {
                return _pthread_mutex_fairshare_unlock_slow(mutex);
        }
        return _pthread_mutex_firstfit_unlock_slow(mutex);
}

PTHREAD_NOEXPORT_VARIANT
int
pthread_mutex_unlock(pthread_mutex_t *omutex)
{
        _pthread_mutex *mutex = (_pthread_mutex *)omutex;
        if (os_unlikely(!_pthread_mutex_check_signature_fast(mutex))) {
                return _pthread_mutex_unlock_init_slow(mutex);
        }

        if (os_unlikely(_pthread_mutex_is_fairshare(mutex))) {
                return _pthread_mutex_fairshare_unlock(mutex);
        }

#if ENABLE_USERSPACE_TRACE
        return _pthread_mutex_firstfit_unlock_slow(mutex);
#elif PLOCKSTAT
        if (PLOCKSTAT_MUTEX_RELEASE_ENABLED() || PLOCKSTAT_MUTEX_ERROR_ENABLED()) {
                return _pthread_mutex_firstfit_unlock_slow(mutex);
        }
#endif

        /*
         * This is the first-fit fast path. The fairshare fast-ish path is in
         * _pthread_mutex_firstfit_unlock()
         */
        uint64_t *tidaddr;
        MUTEX_GETTID_ADDR(mutex, &tidaddr);

        mutex_seq *seqaddr;
        MUTEX_GETSEQ_ADDR(mutex, &seqaddr);

        mutex_seq oldseq, newseq;
        mutex_seq_load(seqaddr, &oldseq);

        // We're giving up the mutex one way or the other, so go ahead and
        // update the owner to 0 so that once the CAS below succeeds, there
        // is no stale ownership information. If the CAS of the seqaddr
        // fails, we may loop, but it's still valid for the owner to be
        // SWITCHING/0
        os_atomic_store(tidaddr, 0, relaxed);

        do {
                newseq = oldseq;

                if (diff_genseq(oldseq.lgenval, oldseq.ugenval) == 0) {
                        // No outstanding waiters in kernel, we can simply drop the E-bit
                        // and return.
                        newseq.lgenval &= ~PTH_RWL_EBIT;
                } else {
                        return _pthread_mutex_firstfit_unlock_slow(mutex);
                }
        } while (os_unlikely(!mutex_seq_atomic_cmpxchgv(seqaddr, &oldseq, &newseq,
                        release)));

        return 0;
}

PTHREAD_ALWAYS_INLINE
static inline int
_pthread_mutex_firstfit_lock(pthread_mutex_t *omutex, bool trylock)
{
        _pthread_mutex *mutex = (_pthread_mutex *)omutex;
        if (os_unlikely(!_pthread_mutex_check_signature_fast(mutex))) {
                return _pthread_mutex_lock_init_slow(mutex, trylock);
        }

        if (os_unlikely(_pthread_mutex_is_fairshare(mutex))) {
                return _pthread_mutex_fairshare_lock(mutex, trylock);
        }

#if ENABLE_USERSPACE_TRACE
        return _pthread_mutex_firstfit_lock_slow(mutex, trylock);
#elif PLOCKSTAT
        if (PLOCKSTAT_MUTEX_ACQUIRE_ENABLED() || PLOCKSTAT_MUTEX_ERROR_ENABLED()) {
                return _pthread_mutex_firstfit_lock_slow(mutex, trylock);
        }
#endif

        /*
         * This is the first-fit fast path. The fairshare fast-ish path is in
         * _pthread_mutex_firstfit_lock()
         */
        uint64_t *tidaddr;
        MUTEX_GETTID_ADDR(mutex, &tidaddr);
        uint64_t selfid = _pthread_selfid_direct();

        mutex_seq *seqaddr;
        MUTEX_GETSEQ_ADDR(mutex, &seqaddr);

        mutex_seq oldseq, newseq;
        mutex_seq_load(seqaddr, &oldseq);

        if (os_unlikely(oldseq.lgenval & PTH_RWL_EBIT)) {
                return _pthread_mutex_firstfit_lock_slow(mutex, trylock);
        }

        bool gotlock;
        do {
                newseq = oldseq;
                gotlock = is_rwl_ebit_clear(oldseq.lgenval);

                if (trylock && !gotlock) {
                        // A trylock on a held lock will fail immediately. But since
                        // we did not load the sequence words atomically, perform a
                        // no-op CAS64 to ensure that nobody has unlocked concurrently.
                } else if (os_likely(gotlock)) {
                        // In first-fit, getting the lock simply adds the E-bit
                        newseq.lgenval |= PTH_RWL_EBIT;
                } else {
                        return _pthread_mutex_firstfit_lock_slow(mutex, trylock);
                }
        } while (os_unlikely(!mutex_seq_atomic_cmpxchgv(seqaddr, &oldseq, &newseq,
                        acquire)));

        if (os_likely(gotlock)) {
                os_atomic_store(tidaddr, selfid, relaxed);
                return 0;
        } else if (trylock) {
                return EBUSY;
        } else {
                __builtin_trap();
        }
}

PTHREAD_NOEXPORT_VARIANT
int
pthread_mutex_lock(pthread_mutex_t *mutex)
{
        return _pthread_mutex_firstfit_lock(mutex, false);
}

PTHREAD_NOEXPORT_VARIANT
int
pthread_mutex_trylock(pthread_mutex_t *mutex)
{
        return _pthread_mutex_firstfit_lock(mutex, true);
}


PTHREAD_ALWAYS_INLINE
static inline int
_pthread_mutex_init(_pthread_mutex *mutex, const pthread_mutexattr_t *attr,
                uint32_t static_type)
{
        mutex->mtxopts.value = 0;
        mutex->mtxopts.options.mutex = 1;
        if (attr) {
                if (attr->sig != _PTHREAD_MUTEX_ATTR_SIG) {
                        return EINVAL;
                }
                mutex->prioceiling = (int16_t)attr->prioceiling;
                mutex->mtxopts.options.protocol = attr->protocol;
                mutex->mtxopts.options.policy = attr->opt;
                mutex->mtxopts.options.type = attr->type;
                mutex->mtxopts.options.pshared = attr->pshared;
        } else {
                switch (static_type) {
                        case 1:
                                mutex->mtxopts.options.type = PTHREAD_MUTEX_ERRORCHECK;
                                break;
                        case 2:
                                mutex->mtxopts.options.type = PTHREAD_MUTEX_RECURSIVE;
                                break;
                        case 3:
                                /* firstfit fall thru */
                        case 7:
                                mutex->mtxopts.options.type = PTHREAD_MUTEX_DEFAULT;
                                break;
                        default:
                                return EINVAL;
                }

                mutex->prioceiling = _PTHREAD_DEFAULT_PRIOCEILING;
                mutex->mtxopts.options.protocol = _PTHREAD_DEFAULT_PROTOCOL;
                if (static_type != 3) {
                        mutex->mtxopts.options.policy = __pthread_mutex_default_opt_policy;
                } else {
                        mutex->mtxopts.options.policy = _PTHREAD_MTX_OPT_POLICY_FIRSTFIT;
                }
                mutex->mtxopts.options.pshared = _PTHREAD_DEFAULT_PSHARED;
        }
        mutex->priority = 0;

        mutex_seq *seqaddr;
        MUTEX_GETSEQ_ADDR(mutex, &seqaddr);

        uint64_t *tidaddr;
        MUTEX_GETTID_ADDR(mutex, &tidaddr);

#if PTHREAD_MUTEX_INIT_UNUSED
        if ((uint32_t*)tidaddr != mutex->m_tid) {
                mutex->mtxopts.options.misalign = 1;
                __builtin_memset(mutex->m_tid, 0xff, sizeof(mutex->m_tid));
        }
        __builtin_memset(mutex->m_mis, 0xff, sizeof(mutex->m_mis));
#endif // PTHREAD_MUTEX_INIT_UNUSED
        *tidaddr = 0;
        *seqaddr = (mutex_seq){ };

        long sig = _PTHREAD_MUTEX_SIG;
        if (mutex->mtxopts.options.type == PTHREAD_MUTEX_NORMAL &&
                        (_pthread_mutex_is_fairshare(mutex) ||
                         _pthread_mutex_is_firstfit(mutex))) {
                // rdar://18148854 _pthread_mutex_lock & pthread_mutex_unlock fastpath
                sig = _PTHREAD_MUTEX_SIG_fast;
        }

#if PTHREAD_MUTEX_INIT_UNUSED
        // For detecting copied mutexes and smashes during debugging
        uint32_t sig32 = (uint32_t)sig;
#if defined(__LP64__)
        uintptr_t guard = ~(uintptr_t)mutex; // use ~ to hide from leaks
        __builtin_memcpy(mutex->_reserved, &guard, sizeof(guard));
        mutex->_reserved[2] = sig32;
        mutex->_reserved[3] = sig32;
        mutex->_pad = sig32;
#else
        mutex->_reserved[0] = sig32;
#endif
#endif // PTHREAD_MUTEX_INIT_UNUSED

        // Ensure all contents are properly set before setting signature.
#if defined(__LP64__)
        // For binary compatibility reasons we cannot require natural alignment of
        // the 64bit 'sig' long value in the struct. rdar://problem/21610439
        uint32_t *sig32_ptr = (uint32_t*)&mutex->sig;
        uint32_t *sig32_val = (uint32_t*)&sig;
        *(sig32_ptr + 1) = *(sig32_val + 1);
        os_atomic_store(sig32_ptr, *sig32_val, release);
#else
        os_atomic_store2o(mutex, sig, sig, release);
#endif

        return 0;
}

PTHREAD_NOEXPORT_VARIANT
int
pthread_mutex_destroy(pthread_mutex_t *omutex)
{
        _pthread_mutex *mutex = (_pthread_mutex *)omutex;

        int res = EINVAL;

        _PTHREAD_LOCK(mutex->lock);
        if (_pthread_mutex_check_signature(mutex)) {
                mutex_seq *seqaddr;
                MUTEX_GETSEQ_ADDR(mutex, &seqaddr);

                mutex_seq seq;
                mutex_seq_load(seqaddr, &seq);

                uint64_t *tidaddr;
                MUTEX_GETTID_ADDR(mutex, &tidaddr);

                if ((os_atomic_load(tidaddr, relaxed) == 0) &&
                                (seq.lgenval & PTHRW_COUNT_MASK) ==
                                (seq.ugenval & PTHRW_COUNT_MASK)) {
                        mutex->sig = _PTHREAD_NO_SIG;
                        res = 0;
                } else {
                        res = EBUSY;
                }
        } else if (_pthread_mutex_check_signature_init(mutex)) {
                mutex->sig = _PTHREAD_NO_SIG;
                res = 0;
        }
        _PTHREAD_UNLOCK(mutex->lock);

        return res;
}

#endif /* !BUILDING_VARIANT ] */

/*
 * Destroy a mutex attribute structure.
 */
int
pthread_mutexattr_destroy(pthread_mutexattr_t *attr)
{
#if __DARWIN_UNIX03
        if (__unix_conforming == 0) {
                __unix_conforming = 1;
        }
        if (attr->sig != _PTHREAD_MUTEX_ATTR_SIG) {
                return EINVAL;
        }
#endif /* __DARWIN_UNIX03 */

        attr->sig = _PTHREAD_NO_SIG;
        return 0;
}