void
_dispatch_semaphore_dispose(dispatch_object_t dou)
{
dispatch_semaphore_t dsema = dou._dsema;
if (dsema->dsema_value < dsema->dsema_orig) {
DISPATCH_CLIENT_CRASH(
"Semaphore/group object deallocated while in use");
}
#if USE_MACH_SEM
kern_return_t kr;
if (dsema->dsema_port) {
kr = semaphore_destroy(mach_task_self(), dsema->dsema_port);
DISPATCH_SEMAPHORE_VERIFY_KR(kr);
}
if (dsema->dsema_waiter_port) {
kr = semaphore_destroy(mach_task_self(), dsema->dsema_waiter_port);
DISPATCH_SEMAPHORE_VERIFY_KR(kr);
}
#elif USE_POSIX_SEM
int ret = sem_destroy(&dsema->dsema_sem);
DISPATCH_SEMAPHORE_VERIFY_RET(ret);
#endif
}
DISPATCH_NOINLINE
long
_dispatch_semaphore_signal_slow(dispatch_semaphore_t dsema)
{
// Before dsema_sent_ksignals is incremented we can rely on the reference
// held by the waiter. However, once this value is incremented the waiter
// may return between the atomic increment and the semaphore_signal(),
// therefore an explicit reference must be held in order to safely access
// dsema after the atomic increment.
_dispatch_retain(dsema);
(void)dispatch_atomic_inc2o(dsema, dsema_sent_ksignals);
#if USE_MACH_SEM
_dispatch_semaphore_create_port(&dsema->dsema_port);
kern_return_t kr = semaphore_signal(dsema->dsema_port);
DISPATCH_SEMAPHORE_VERIFY_KR(kr);
#elif USE_POSIX_SEM
int ret = sem_post(&dsema->dsema_sem);
DISPATCH_SEMAPHORE_VERIFY_RET(ret);
#endif
_dispatch_release(dsema);
return 1;
}
void
_dispatch_sema4_signal(_dispatch_sema4_t *sema, long count)
{
do {
int ret = sem_post(sema);
DISPATCH_SEMAPHORE_VERIFY_RET(ret);
} while (--count);
}
void
_dispatch_thread_semaphore_signal(_dispatch_thread_semaphore_t sema)
{
#if USE_MACH_SEM
semaphore_t s4 = (semaphore_t)sema;
kern_return_t kr = semaphore_signal(s4);
DISPATCH_SEMAPHORE_VERIFY_KR(kr);
#elif USE_POSIX_SEM
int ret = sem_post((sem_t *)sema);
DISPATCH_SEMAPHORE_VERIFY_RET(ret);
#endif
}
DISPATCH_NOINLINE
void
_dispatch_thread_semaphore_dispose(_dispatch_thread_semaphore_t sema)
{
#if USE_MACH_SEM
semaphore_t s4 = (semaphore_t)sema;
kern_return_t kr = semaphore_destroy(mach_task_self(), s4);
DISPATCH_SEMAPHORE_VERIFY_KR(kr);
#elif USE_POSIX_SEM
int ret = sem_destroy((sem_t *)sema);
free((sem_t *) sema);
DISPATCH_SEMAPHORE_VERIFY_RET(ret);
#endif
}
static void
_dispatch_semaphore_init(long value, dispatch_object_t dou)
{
dispatch_semaphore_t dsema = dou._dsema;
dsema->do_next = DISPATCH_OBJECT_LISTLESS;
dsema->do_targetq = dispatch_get_global_queue(
DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dsema->dsema_value = value;
dsema->dsema_orig = value;
#if USE_POSIX_SEM
int ret = sem_init(&dsema->dsema_sem, 0, 0);
DISPATCH_SEMAPHORE_VERIFY_RET(ret);
#endif
}
DISPATCH_NOINLINE
static long
_dispatch_group_wake(dispatch_semaphore_t dsema)
{
struct dispatch_sema_notify_s *next, *head, *tail = NULL;
long rval;
head = dispatch_atomic_xchg2o(dsema, dsema_notify_head, NULL);
if (head) {
// snapshot before anything is notified/woken <rdar://problem/8554546>
tail = dispatch_atomic_xchg2o(dsema, dsema_notify_tail, NULL);
}
rval = dispatch_atomic_xchg2o(dsema, dsema_group_waiters, 0);
if (rval) {
// wake group waiters
#if USE_MACH_SEM
_dispatch_semaphore_create_port(&dsema->dsema_waiter_port);
do {
kern_return_t kr = semaphore_signal(dsema->dsema_waiter_port);
DISPATCH_SEMAPHORE_VERIFY_KR(kr);
} while (--rval);
#elif USE_POSIX_SEM
do {
int ret = sem_post(&dsema->dsema_sem);
DISPATCH_SEMAPHORE_VERIFY_RET(ret);
} while (--rval);
#endif
}
if (head) {
// async group notify blocks
do {
dispatch_async_f(head->dsn_queue, head->dsn_ctxt, head->dsn_func);
_dispatch_release(head->dsn_queue);
next = fastpath(head->dsn_next);
if (!next && head != tail) {
while (!(next = fastpath(head->dsn_next))) {
_dispatch_hardware_pause();
}
}
free(head);
} while ((head = next));
_dispatch_release(dsema);
}
return 0;
}
void
_dispatch_thread_semaphore_wait(_dispatch_thread_semaphore_t sema)
{
#if USE_MACH_SEM
semaphore_t s4 = (semaphore_t)sema;
kern_return_t kr;
do {
kr = semaphore_wait(s4);
} while (slowpath(kr == KERN_ABORTED));
DISPATCH_SEMAPHORE_VERIFY_KR(kr);
#elif USE_POSIX_SEM
int ret;
do {
ret = sem_wait((sem_t *) sema);
} while (slowpath(ret != 0));
DISPATCH_SEMAPHORE_VERIFY_RET(ret);
#endif
}
bool
_dispatch_sema4_timedwait(_dispatch_sema4_t *sema, dispatch_time_t timeout)
{
struct timespec _timeout;
int ret;
do {
uint64_t nsec = _dispatch_time_nanoseconds_since_epoch(timeout);
_timeout.tv_sec = (typeof(_timeout.tv_sec))(nsec / NSEC_PER_SEC);
_timeout.tv_nsec = (typeof(_timeout.tv_nsec))(nsec % NSEC_PER_SEC);
ret = slowpath(sem_timedwait(sema, &_timeout));
} while (ret == -1 && errno == EINTR);
if (ret == -1 && errno == ETIMEDOUT) {
return true;
}
DISPATCH_SEMAPHORE_VERIFY_RET(ret);
return false;
}
DISPATCH_NOINLINE
static _dispatch_thread_semaphore_t
_dispatch_thread_semaphore_create(void)
{
_dispatch_safe_fork = false;
#if USE_MACH_SEM
semaphore_t s4;
kern_return_t kr;
while (slowpath(kr = semaphore_create(mach_task_self(), &s4,
SYNC_POLICY_FIFO, 0))) {
DISPATCH_VERIFY_MIG(kr);
sleep(1);
}
return s4;
#elif USE_POSIX_SEM
sem_t *s4 = malloc(sizeof(*s4));
int ret = sem_init(s4, 0, 0);
DISPATCH_SEMAPHORE_VERIFY_RET(ret);
return (_dispatch_thread_semaphore_t) s4;
#endif
}
DISPATCH_NOINLINE
static long
_dispatch_group_wait_slow(dispatch_semaphore_t dsema, dispatch_time_t timeout)
{
long orig;
again:
// check before we cause another signal to be sent by incrementing
// dsema->dsema_group_waiters
if (dsema->dsema_value == dsema->dsema_orig) {
return _dispatch_group_wake(dsema);
}
// Mach semaphores appear to sometimes spuriously wake up. Therefore,
// we keep a parallel count of the number of times a Mach semaphore is
// signaled (6880961).
(void)dispatch_atomic_inc2o(dsema, dsema_group_waiters);
// check the values again in case we need to wake any threads
if (dsema->dsema_value == dsema->dsema_orig) {
return _dispatch_group_wake(dsema);
}
#if USE_MACH_SEM
mach_timespec_t _timeout;
kern_return_t kr;
_dispatch_semaphore_create_port(&dsema->dsema_waiter_port);
// From xnu/osfmk/kern/sync_sema.c:
// wait_semaphore->count = -1; /* we don't keep an actual count */
//
// The code above does not match the documentation, and that fact is
// not surprising. The documented semantics are clumsy to use in any
// practical way. The above hack effectively tricks the rest of the
// Mach semaphore logic to behave like the libdispatch algorithm.
switch (timeout) {
default:
do {
uint64_t nsec = _dispatch_timeout(timeout);
_timeout.tv_sec = (typeof(_timeout.tv_sec))(nsec / NSEC_PER_SEC);
_timeout.tv_nsec = (typeof(_timeout.tv_nsec))(nsec % NSEC_PER_SEC);
kr = slowpath(semaphore_timedwait(dsema->dsema_waiter_port,
_timeout));
} while (kr == KERN_ABORTED);
if (kr != KERN_OPERATION_TIMED_OUT) {
DISPATCH_SEMAPHORE_VERIFY_KR(kr);
break;
}
// Fall through and try to undo the earlier change to
// dsema->dsema_group_waiters
case DISPATCH_TIME_NOW:
while ((orig = dsema->dsema_group_waiters)) {
if (dispatch_atomic_cmpxchg2o(dsema, dsema_group_waiters, orig,
orig - 1)) {
return KERN_OPERATION_TIMED_OUT;
}
}
// Another thread called semaphore_signal().
// Fall through and drain the wakeup.
case DISPATCH_TIME_FOREVER:
do {
kr = semaphore_wait(dsema->dsema_waiter_port);
} while (kr == KERN_ABORTED);
DISPATCH_SEMAPHORE_VERIFY_KR(kr);
break;
}
#elif USE_POSIX_SEM
struct timespec _timeout;
int ret;
switch (timeout) {
default:
do {
_timeout = _dispatch_timeout_ts(timeout);
ret = slowpath(sem_timedwait(&dsema->dsema_sem, &_timeout));
} while (ret == -1 && errno == EINTR);
if (!(ret == -1 && errno == ETIMEDOUT)) {
DISPATCH_SEMAPHORE_VERIFY_RET(ret);
break;
}
// Fall through and try to undo the earlier change to
// dsema->dsema_group_waiters
case DISPATCH_TIME_NOW:
while ((orig = dsema->dsema_group_waiters)) {
if (dispatch_atomic_cmpxchg2o(dsema, dsema_group_waiters, orig,
orig - 1)) {
errno = ETIMEDOUT;
return -1;
}
}
// Another thread called semaphore_signal().
// Fall through and drain the wakeup.
case DISPATCH_TIME_FOREVER:
do {
ret = sem_wait(&dsema->dsema_sem);
} while (ret == -1 && errno == EINTR);
DISPATCH_SEMAPHORE_VERIFY_RET(ret);
break;
}
#endif
goto again;
}
void
_dispatch_sema4_wait(_dispatch_sema4_t *sema)
{
int ret = sem_wait(sema);
DISPATCH_SEMAPHORE_VERIFY_RET(ret);
}
void
_dispatch_sema4_dispose_slow(_dispatch_sema4_t *sema, int policy DISPATCH_UNUSED)
{
int rc = sem_destroy(sema);
DISPATCH_SEMAPHORE_VERIFY_RET(rc);
}
void
_dispatch_sema4_init(_dispatch_sema4_t *sema, int policy DISPATCH_UNUSED)
{
int rc = sem_init(sema, 0, 0);
DISPATCH_SEMAPHORE_VERIFY_RET(rc);
}
