/*
* Copyright (C) 2008 The Android Open Source Project
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#include <pthread.h>
#include <errno.h>
#include <limits.h>
#include <stdatomic.h>
#include <string.h>
#include <sys/cdefs.h>
#include <sys/mman.h>
#include <unistd.h>
#include "pthread_internal.h"
#include "private/bionic_constants.h"
#include "private/bionic_futex.h"
#include "private/bionic_systrace.h"
#include "private/bionic_time_conversions.h"
#include "private/bionic_tls.h"
/* a mutex attribute holds the following fields
*
* bits: name description
* 0-3 type type of mutex
* 4 shared process-shared flag
*/
#define MUTEXATTR_TYPE_MASK 0x000f
#define MUTEXATTR_SHARED_MASK 0x0010
int pthread_mutexattr_init(pthread_mutexattr_t *attr)
{
*attr = PTHREAD_MUTEX_DEFAULT;
return 0;
}
int pthread_mutexattr_destroy(pthread_mutexattr_t *attr)
{
*attr = -1;
return 0;
}
int pthread_mutexattr_gettype(const pthread_mutexattr_t *attr, int *type_p)
{
int type = (*attr & MUTEXATTR_TYPE_MASK);
if (type < PTHREAD_MUTEX_NORMAL || type > PTHREAD_MUTEX_ERRORCHECK) {
return EINVAL;
}
*type_p = type;
return 0;
}
int pthread_mutexattr_settype(pthread_mutexattr_t *attr, int type)
{
if (type < PTHREAD_MUTEX_NORMAL || type > PTHREAD_MUTEX_ERRORCHECK ) {
return EINVAL;
}
*attr = (*attr & ~MUTEXATTR_TYPE_MASK) | type;
return 0;
}
/* process-shared mutexes are not supported at the moment */
int pthread_mutexattr_setpshared(pthread_mutexattr_t *attr, int pshared)
{
switch (pshared) {
case PTHREAD_PROCESS_PRIVATE:
*attr &= ~MUTEXATTR_SHARED_MASK;
return 0;
case PTHREAD_PROCESS_SHARED:
/* our current implementation of pthread actually supports shared
* mutexes but won't cleanup if a process dies with the mutex held.
* Nevertheless, it's better than nothing. Shared mutexes are used
* by surfaceflinger and audioflinger.
*/
*attr |= MUTEXATTR_SHARED_MASK;
return 0;
}
return EINVAL;
}
int pthread_mutexattr_getpshared(const pthread_mutexattr_t* attr, int* pshared) {
*pshared = (*attr & MUTEXATTR_SHARED_MASK) ? PTHREAD_PROCESS_SHARED : PTHREAD_PROCESS_PRIVATE;
return 0;
}
/* a mutex contains a state value and a owner_tid.
* The value is implemented as a 16-bit integer holding the following fields:
*
* bits: name description
* 15-14 type mutex type
* 13 shared process-shared flag
* 12-2 counter counter of recursive mutexes
* 1-0 state lock state (0, 1 or 2)
*
* The owner_tid is used only in recursive and errorcheck mutex to hold the mutex owner thread tid.
*/
/* Convenience macro, creates a mask of 'bits' bits that starts from
* the 'shift'-th least significant bit in a 32-bit word.
*
* Examples: FIELD_MASK(0,4) -> 0xf
* FIELD_MASK(16,9) -> 0x1ff0000
*/
#define FIELD_MASK(shift,bits) (((1 << (bits))-1) << (shift))
/* This one is used to create a bit pattern from a given field value */
#define FIELD_TO_BITS(val,shift,bits) (((val) & ((1 << (bits))-1)) << (shift))
/* And this one does the opposite, i.e. extract a field's value from a bit pattern */
#define FIELD_FROM_BITS(val,shift,bits) (((val) >> (shift)) & ((1 << (bits))-1))
/* Convenience macros.
*
* These are used to form or modify the bit pattern of a given mutex value
*/
/* Mutex state:
*
* 0 for unlocked
* 1 for locked, no waiters
* 2 for locked, maybe waiters
*/
#define MUTEX_STATE_SHIFT 0
#define MUTEX_STATE_LEN 2
#define MUTEX_STATE_MASK FIELD_MASK(MUTEX_STATE_SHIFT, MUTEX_STATE_LEN)
#define MUTEX_STATE_FROM_BITS(v) FIELD_FROM_BITS(v, MUTEX_STATE_SHIFT, MUTEX_STATE_LEN)
#define MUTEX_STATE_TO_BITS(v) FIELD_TO_BITS(v, MUTEX_STATE_SHIFT, MUTEX_STATE_LEN)
#define MUTEX_STATE_UNLOCKED 0 /* must be 0 to match PTHREAD_MUTEX_INITIALIZER */
#define MUTEX_STATE_LOCKED_UNCONTENDED 1 /* must be 1 due to atomic dec in unlock operation */
#define MUTEX_STATE_LOCKED_CONTENDED 2 /* must be 1 + LOCKED_UNCONTENDED due to atomic dec */
#define MUTEX_STATE_BITS_UNLOCKED MUTEX_STATE_TO_BITS(MUTEX_STATE_UNLOCKED)
#define MUTEX_STATE_BITS_LOCKED_UNCONTENDED MUTEX_STATE_TO_BITS(MUTEX_STATE_LOCKED_UNCONTENDED)
#define MUTEX_STATE_BITS_LOCKED_CONTENDED MUTEX_STATE_TO_BITS(MUTEX_STATE_LOCKED_CONTENDED)
/* return true iff the mutex if locked with no waiters */
#define MUTEX_STATE_BITS_IS_LOCKED_UNCONTENDED(v) (((v) & MUTEX_STATE_MASK) == MUTEX_STATE_BITS_LOCKED_UNCONTENDED)
/* return true iff the mutex if locked with maybe waiters */
#define MUTEX_STATE_BITS_IS_LOCKED_CONTENDED(v) (((v) & MUTEX_STATE_MASK) == MUTEX_STATE_BITS_LOCKED_CONTENDED)
/* used to flip from LOCKED_UNCONTENDED to LOCKED_CONTENDED */
#define MUTEX_STATE_BITS_FLIP_CONTENTION(v) ((v) ^ (MUTEX_STATE_BITS_LOCKED_CONTENDED ^ MUTEX_STATE_BITS_LOCKED_UNCONTENDED))
/* Mutex counter:
*
* We need to check for overflow before incrementing, and we also need to
* detect when the counter is 0
*/
#define MUTEX_COUNTER_SHIFT 2
#define MUTEX_COUNTER_LEN 11
#define MUTEX_COUNTER_MASK FIELD_MASK(MUTEX_COUNTER_SHIFT, MUTEX_COUNTER_LEN)
#define MUTEX_COUNTER_BITS_WILL_OVERFLOW(v) (((v) & MUTEX_COUNTER_MASK) == MUTEX_COUNTER_MASK)
#define MUTEX_COUNTER_BITS_IS_ZERO(v) (((v) & MUTEX_COUNTER_MASK) == 0)
/* Used to increment the counter directly after overflow has been checked */
#define MUTEX_COUNTER_BITS_ONE FIELD_TO_BITS(1, MUTEX_COUNTER_SHIFT,MUTEX_COUNTER_LEN)
/* Mutex shared bit flag
*
* This flag is set to indicate that the mutex is shared among processes.
* This changes the futex opcode we use for futex wait/wake operations
* (non-shared operations are much faster).
*/
#define MUTEX_SHARED_SHIFT 13
#define MUTEX_SHARED_MASK FIELD_MASK(MUTEX_SHARED_SHIFT,1)
/* Mutex type:
* We support normal, recursive and errorcheck mutexes.
*/
#define MUTEX_TYPE_SHIFT 14
#define MUTEX_TYPE_LEN 2
#define MUTEX_TYPE_MASK FIELD_MASK(MUTEX_TYPE_SHIFT,MUTEX_TYPE_LEN)
#define MUTEX_TYPE_TO_BITS(t) FIELD_TO_BITS(t, MUTEX_TYPE_SHIFT, MUTEX_TYPE_LEN)
#define MUTEX_TYPE_BITS_NORMAL MUTEX_TYPE_TO_BITS(PTHREAD_MUTEX_NORMAL)
#define MUTEX_TYPE_BITS_RECURSIVE MUTEX_TYPE_TO_BITS(PTHREAD_MUTEX_RECURSIVE)
#define MUTEX_TYPE_BITS_ERRORCHECK MUTEX_TYPE_TO_BITS(PTHREAD_MUTEX_ERRORCHECK)
struct pthread_mutex_internal_t {
_Atomic(uint16_t) state;
#if defined(__LP64__)
uint16_t __pad;
atomic_int owner_tid;
char __reserved[32];
#else
_Atomic(uint16_t) owner_tid;
#endif
} __attribute__((aligned(4)));
static_assert(sizeof(pthread_mutex_t) == sizeof(pthread_mutex_internal_t),
"pthread_mutex_t should actually be pthread_mutex_internal_t in implementation.");
// For binary compatibility with old version of pthread_mutex_t, we can't use more strict alignment
// than 4-byte alignment.
static_assert(alignof(pthread_mutex_t) == 4,
"pthread_mutex_t should fulfill the alignment of pthread_mutex_internal_t.");
static inline pthread_mutex_internal_t* __get_internal_mutex(pthread_mutex_t* mutex_interface) {
return reinterpret_cast<pthread_mutex_internal_t*>(mutex_interface);
}
int pthread_mutex_init(pthread_mutex_t* mutex_interface, const pthread_mutexattr_t* attr) {
pthread_mutex_internal_t* mutex = __get_internal_mutex(mutex_interface);
memset(mutex, 0, sizeof(pthread_mutex_internal_t));
if (__predict_true(attr == NULL)) {
atomic_init(&mutex->state, MUTEX_TYPE_BITS_NORMAL);
return 0;
}
uint16_t state = 0;
if ((*attr & MUTEXATTR_SHARED_MASK) != 0) {
state |= MUTEX_SHARED_MASK;
}
switch (*attr & MUTEXATTR_TYPE_MASK) {
case PTHREAD_MUTEX_NORMAL:
state |= MUTEX_TYPE_BITS_NORMAL;
break;
case PTHREAD_MUTEX_RECURSIVE:
state |= MUTEX_TYPE_BITS_RECURSIVE;
break;
case PTHREAD_MUTEX_ERRORCHECK:
state |= MUTEX_TYPE_BITS_ERRORCHECK;
break;
default:
return EINVAL;
}
atomic_init(&mutex->state, state);
atomic_init(&mutex->owner_tid, 0);
return 0;
}
static inline __always_inline int __pthread_normal_mutex_trylock(pthread_mutex_internal_t* mutex,
uint16_t shared) {
const uint16_t unlocked = shared | MUTEX_STATE_BITS_UNLOCKED;
const uint16_t locked_uncontended = shared | MUTEX_STATE_BITS_LOCKED_UNCONTENDED;
uint16_t old_state = unlocked;
if (__predict_true(atomic_compare_exchange_strong_explicit(&mutex->state, &old_state,
locked_uncontended, memory_order_acquire, memory_order_relaxed))) {
return 0;
}
return EBUSY;
}
/*
* Lock a mutex of type NORMAL.
*
* As noted above, there are three states:
* 0 (unlocked, no contention)
* 1 (locked, no contention)
* 2 (locked, contention)
*
* Non-recursive mutexes don't use the thread-id or counter fields, and the
* "type" value is zero, so the only bits that will be set are the ones in
* the lock state field.
*/
static inline __always_inline int __pthread_normal_mutex_lock(pthread_mutex_internal_t* mutex,
uint16_t shared,
const timespec* abs_timeout_or_null,
clockid_t clock) {
if (__predict_true(__pthread_normal_mutex_trylock(mutex, shared) == 0)) {
return 0;
}
ScopedTrace trace("Contending for pthread mutex");
const uint16_t unlocked = shared | MUTEX_STATE_BITS_UNLOCKED;
const uint16_t locked_contended = shared | MUTEX_STATE_BITS_LOCKED_CONTENDED;
// We want to go to sleep until the mutex is available, which requires
// promoting it to locked_contended. We need to swap in the new state
// and then wait until somebody wakes us up.
// An atomic_exchange is used to compete with other threads for the lock.
// If it returns unlocked, we have acquired the lock, otherwise another
// thread still holds the lock and we should wait again.
// If lock is acquired, an acquire fence is needed to make all memory accesses
// made by other threads visible to the current CPU.
while (atomic_exchange_explicit(&mutex->state, locked_contended,
memory_order_acquire) != unlocked) {
timespec ts;
timespec* rel_timeout = NULL;
if (abs_timeout_or_null != NULL) {
rel_timeout = &ts;
if (!timespec_from_absolute_timespec(*rel_timeout, *abs_timeout_or_null, clock)) {
return ETIMEDOUT;
}
}
if (__futex_wait_ex(&mutex->state, shared, locked_contended, rel_timeout) == -ETIMEDOUT) {
return ETIMEDOUT;
}
}
return 0;
}
/*
* Release a normal mutex. The caller is responsible for determining
* that we are in fact the owner of this lock.
*/
static inline __always_inline void __pthread_normal_mutex_unlock(pthread_mutex_internal_t* mutex,
uint16_t shared) {
const uint16_t unlocked = shared | MUTEX_STATE_BITS_UNLOCKED;
const uint16_t locked_contended = shared | MUTEX_STATE_BITS_LOCKED_CONTENDED;
// We use an atomic_exchange to release the lock. If locked_contended state
// is returned, some threads is waiting for the lock and we need to wake up
// one of them.
// A release fence is required to make previous stores visible to next
// lock owner threads.
if (atomic_exchange_explicit(&mutex->state, unlocked,
memory_order_release) == locked_contended) {
// Wake up one waiting thread. We don't know which thread will be
// woken or when it'll start executing -- futexes make no guarantees
// here. There may not even be a thread waiting.
//
// The newly-woken thread will replace the unlocked state we just set above
// with locked_contended state, which means that when it eventually releases
// the mutex it will also call FUTEX_WAKE. This results in one extra wake
// call whenever a lock is contended, but let us avoid forgetting anyone
// without requiring us to track the number of sleepers.
//
// It's possible for another thread to sneak in and grab the lock between
// the exchange above and the wake call below. If the new thread is "slow"
// and holds the lock for a while, we'll wake up a sleeper, which will swap
// in locked_uncontended state and then go back to sleep since the lock is
// still held. If the new thread is "fast", running to completion before
// we call wake, the thread we eventually wake will find an unlocked mutex
// and will execute. Either way we have correct behavior and nobody is
// orphaned on the wait queue.
__futex_wake_ex(&mutex->state, shared, 1);
}
}
/* This common inlined function is used to increment the counter of a recursive mutex.
*
* If the counter overflows, it will return EAGAIN.
* Otherwise, it atomically increments the counter and returns 0.
*
*/
static inline __always_inline int __recursive_increment(pthread_mutex_internal_t* mutex,
uint16_t old_state) {
// Detect recursive lock overflow and return EAGAIN.
// This is safe because only the owner thread can modify the
// counter bits in the mutex value.
if (MUTEX_COUNTER_BITS_WILL_OVERFLOW(old_state)) {
return EAGAIN;
}
// Other threads are able to change the lower bits (e.g. promoting it to "contended"),
// but the mutex counter will not overflow. So we use atomic_fetch_add operation here.
// The mutex is still locked by current thread, so we don't need a release fence.
atomic_fetch_add_explicit(&mutex->state, MUTEX_COUNTER_BITS_ONE, memory_order_relaxed);
return 0;
}
static inline __always_inline int __recursive_or_errorcheck_mutex_wait(
pthread_mutex_internal_t* mutex,
uint16_t shared,
uint16_t old_state,
const timespec* rel_timeout) {
// __futex_wait always waits on a 32-bit value. But state is 16-bit. For a normal mutex, the owner_tid
// field in mutex is not used. On 64-bit devices, the __pad field in mutex is not used.
// But when a recursive or errorcheck mutex is used on 32-bit devices, we need to add the
// owner_tid value in the value argument for __futex_wait, otherwise we may always get EAGAIN error.
#if defined(__LP64__)
return __futex_wait_ex(&mutex->state, shared, old_state, rel_timeout);
#else
// This implementation works only when the layout of pthread_mutex_internal_t matches below expectation.
// And it is based on the assumption that Android is always in little-endian devices.
static_assert(offsetof(pthread_mutex_internal_t, state) == 0, "");
static_assert(offsetof(pthread_mutex_internal_t, owner_tid) == 2, "");
uint32_t owner_tid = atomic_load_explicit(&mutex->owner_tid, memory_order_relaxed);
return __futex_wait_ex(&mutex->state, shared, (owner_tid << 16) | old_state, rel_timeout);
#endif
}
static int __pthread_mutex_lock_with_timeout(pthread_mutex_internal_t* mutex,
const timespec* abs_timeout_or_null, clockid_t clock) {
uint16_t old_state = atomic_load_explicit(&mutex->state, memory_order_relaxed);
uint16_t mtype = (old_state & MUTEX_TYPE_MASK);
uint16_t shared = (old_state & MUTEX_SHARED_MASK);
// Handle common case first.
if ( __predict_true(mtype == MUTEX_TYPE_BITS_NORMAL) ) {
return __pthread_normal_mutex_lock(mutex, shared, abs_timeout_or_null, clock);
}
// Do we already own this recursive or error-check mutex?
pid_t tid = __get_thread()->tid;
if (tid == atomic_load_explicit(&mutex->owner_tid, memory_order_relaxed)) {
if (mtype == MUTEX_TYPE_BITS_ERRORCHECK) {
return EDEADLK;
}
return __recursive_increment(mutex, old_state);
}
const uint16_t unlocked = mtype | shared | MUTEX_STATE_BITS_UNLOCKED;
const uint16_t locked_uncontended = mtype | shared | MUTEX_STATE_BITS_LOCKED_UNCONTENDED;
const uint16_t locked_contended = mtype | shared | MUTEX_STATE_BITS_LOCKED_CONTENDED;
// First, if the mutex is unlocked, try to quickly acquire it.
// In the optimistic case where this works, set the state to locked_uncontended.
if (old_state == unlocked) {
// If exchanged successfully, an acquire fence is required to make
// all memory accesses made by other threads visible to the current CPU.
if (__predict_true(atomic_compare_exchange_strong_explicit(&mutex->state, &old_state,
locked_uncontended, memory_order_acquire, memory_order_relaxed))) {
atomic_store_explicit(&mutex->owner_tid, tid, memory_order_relaxed);
return 0;
}
}
ScopedTrace trace("Contending for pthread mutex");
while (true) {
if (old_state == unlocked) {
// NOTE: We put the state to locked_contended since we _know_ there
// is contention when we are in this loop. This ensures all waiters
// will be unlocked.
// If exchanged successfully, an acquire fence is required to make
// all memory accesses made by other threads visible to the current CPU.
if (__predict_true(atomic_compare_exchange_weak_explicit(&mutex->state,
&old_state, locked_contended,
memory_order_acquire,
memory_order_relaxed))) {
atomic_store_explicit(&mutex->owner_tid, tid, memory_order_relaxed);
return 0;
}
continue;
} else if (MUTEX_STATE_BITS_IS_LOCKED_UNCONTENDED(old_state)) {
// We should set it to locked_contended beforing going to sleep. This can make
// sure waiters will be woken up eventually.
int new_state = MUTEX_STATE_BITS_FLIP_CONTENTION(old_state);
if (__predict_false(!atomic_compare_exchange_weak_explicit(&mutex->state,
&old_state, new_state,
memory_order_relaxed,
memory_order_relaxed))) {
continue;
}
old_state = new_state;
}
// We are in locked_contended state, sleep until someone wakes us up.
timespec ts;
timespec* rel_timeout = NULL;
if (abs_timeout_or_null != NULL) {
rel_timeout = &ts;
if (!timespec_from_absolute_timespec(*rel_timeout, *abs_timeout_or_null, clock)) {
return ETIMEDOUT;
}
}
if (__recursive_or_errorcheck_mutex_wait(mutex, shared, old_state, rel_timeout) == -ETIMEDOUT) {
return ETIMEDOUT;
}
old_state = atomic_load_explicit(&mutex->state, memory_order_relaxed);
}
}
int pthread_mutex_lock(pthread_mutex_t* mutex_interface) {
#if !defined(__LP64__)
if (mutex_interface == NULL) {
return EINVAL;
}
#endif
pthread_mutex_internal_t* mutex = __get_internal_mutex(mutex_interface);
uint16_t old_state = atomic_load_explicit(&mutex->state, memory_order_relaxed);
uint16_t mtype = (old_state & MUTEX_TYPE_MASK);
uint16_t shared = (old_state & MUTEX_SHARED_MASK);
// Avoid slowing down fast path of normal mutex lock operation.
if (__predict_true(mtype == MUTEX_TYPE_BITS_NORMAL)) {
if (__predict_true(__pthread_normal_mutex_trylock(mutex, shared) == 0)) {
return 0;
}
}
return __pthread_mutex_lock_with_timeout(mutex, NULL, 0);
}
int pthread_mutex_unlock(pthread_mutex_t* mutex_interface) {
#if !defined(__LP64__)
if (mutex_interface == NULL) {
return EINVAL;
}
#endif
pthread_mutex_internal_t* mutex = __get_internal_mutex(mutex_interface);
uint16_t old_state = atomic_load_explicit(&mutex->state, memory_order_relaxed);
uint16_t mtype = (old_state & MUTEX_TYPE_MASK);
uint16_t shared = (old_state & MUTEX_SHARED_MASK);
// Handle common case first.
if (__predict_true(mtype == MUTEX_TYPE_BITS_NORMAL)) {
__pthread_normal_mutex_unlock(mutex, shared);
return 0;
}
// Do we already own this recursive or error-check mutex?
pid_t tid = __get_thread()->tid;
if ( tid != atomic_load_explicit(&mutex->owner_tid, memory_order_relaxed) ) {
return EPERM;
}
// If the counter is > 0, we can simply decrement it atomically.
// Since other threads can mutate the lower state bits (and only the
// lower state bits), use a compare_exchange loop to do it.
if (!MUTEX_COUNTER_BITS_IS_ZERO(old_state)) {
// We still own the mutex, so a release fence is not needed.
atomic_fetch_sub_explicit(&mutex->state, MUTEX_COUNTER_BITS_ONE, memory_order_relaxed);
return 0;
}
// The counter is 0, so we'are going to unlock the mutex by resetting its
// state to unlocked, we need to perform a atomic_exchange inorder to read
// the current state, which will be locked_contended if there may have waiters
// to awake.
// A release fence is required to make previous stores visible to next
// lock owner threads.
atomic_store_explicit(&mutex->owner_tid, 0, memory_order_relaxed);
const uint16_t unlocked = mtype | shared | MUTEX_STATE_BITS_UNLOCKED;
old_state = atomic_exchange_explicit(&mutex->state, unlocked, memory_order_release);
if (MUTEX_STATE_BITS_IS_LOCKED_CONTENDED(old_state)) {
__futex_wake_ex(&mutex->state, shared, 1);
}
return 0;
}
int pthread_mutex_trylock(pthread_mutex_t* mutex_interface) {
pthread_mutex_internal_t* mutex = __get_internal_mutex(mutex_interface);
uint16_t old_state = atomic_load_explicit(&mutex->state, memory_order_relaxed);
uint16_t mtype = (old_state & MUTEX_TYPE_MASK);
uint16_t shared = (old_state & MUTEX_SHARED_MASK);
const uint16_t unlocked = mtype | shared | MUTEX_STATE_BITS_UNLOCKED;
const uint16_t locked_uncontended = mtype | shared | MUTEX_STATE_BITS_LOCKED_UNCONTENDED;
// Handle common case first.
if (__predict_true(mtype == MUTEX_TYPE_BITS_NORMAL)) {
return __pthread_normal_mutex_trylock(mutex, shared);
}
// Do we already own this recursive or error-check mutex?
pid_t tid = __get_thread()->tid;
if (tid == atomic_load_explicit(&mutex->owner_tid, memory_order_relaxed)) {
if (mtype == MUTEX_TYPE_BITS_ERRORCHECK) {
return EBUSY;
}
return __recursive_increment(mutex, old_state);
}
// Same as pthread_mutex_lock, except that we don't want to wait, and
// the only operation that can succeed is a single compare_exchange to acquire the
// lock if it is released / not owned by anyone. No need for a complex loop.
// If exchanged successfully, an acquire fence is required to make
// all memory accesses made by other threads visible to the current CPU.
old_state = unlocked;
if (__predict_true(atomic_compare_exchange_strong_explicit(&mutex->state, &old_state,
locked_uncontended,
memory_order_acquire,
memory_order_relaxed))) {
atomic_store_explicit(&mutex->owner_tid, tid, memory_order_relaxed);
return 0;
}
return EBUSY;
}
#if !defined(__LP64__)
extern "C" int pthread_mutex_lock_timeout_np(pthread_mutex_t* mutex_interface, unsigned ms) {
timespec abs_timeout;
clock_gettime(CLOCK_MONOTONIC, &abs_timeout);
abs_timeout.tv_sec += ms / 1000;
abs_timeout.tv_nsec += (ms % 1000) * 1000000;
if (abs_timeout.tv_nsec >= NS_PER_S) {
abs_timeout.tv_sec++;
abs_timeout.tv_nsec -= NS_PER_S;
}
int error = __pthread_mutex_lock_with_timeout(__get_internal_mutex(mutex_interface),
&abs_timeout, CLOCK_MONOTONIC);
if (error == ETIMEDOUT) {
error = EBUSY;
}
return error;
}
#endif
int pthread_mutex_timedlock(pthread_mutex_t* mutex_interface, const timespec* abs_timeout) {
return __pthread_mutex_lock_with_timeout(__get_internal_mutex(mutex_interface),
abs_timeout, CLOCK_REALTIME);
}
int pthread_mutex_destroy(pthread_mutex_t* mutex_interface) {
// Use trylock to ensure that the mutex is valid and not already locked.
int error = pthread_mutex_trylock(mutex_interface);
if (error != 0) {
return error;
}
return 0;
}