DISPATCH_ALWAYS_INLINE
static inline void
_dispatch_apply_invoke(void *ctxt)
{
dispatch_apply_t da = (dispatch_apply_t)ctxt;
size_t const iter = da->da_iterations;
typeof(da->da_func) const func = da->da_func;
void *const da_ctxt = da->da_ctxt;
size_t idx, done = 0;
_dispatch_workitem_dec(); // this unit executes many items
// Make nested dispatch_apply fall into serial case rdar://problem/9294578
_dispatch_thread_setspecific(dispatch_apply_key, (void*)~0ul);
// Striding is the responsibility of the caller.
while (fastpath((idx = dispatch_atomic_inc2o(da, da_index) - 1) < iter)) {
_dispatch_client_callout2(da_ctxt, idx, func);
_dispatch_workitem_inc();
done++;
}
_dispatch_thread_setspecific(dispatch_apply_key, NULL);
dispatch_atomic_release_barrier();
// The thread that finished the last workitem wakes up the (possibly waiting)
// thread that called dispatch_apply. They could be one and the same.
if (done && (dispatch_atomic_add2o(da, da_done, done) == iter)) {
_dispatch_thread_semaphore_signal(da->da_sema);
}
if (dispatch_atomic_dec2o(da, da_thr_cnt) == 0) {
_dispatch_continuation_free((dispatch_continuation_t)da);
}
}
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_group_leave(dispatch_group_t dg)
{
dispatch_semaphore_t dsema = (dispatch_semaphore_t)dg;
dispatch_atomic_release_barrier();
long value = dispatch_atomic_inc2o(dsema, dsema_value);
if (slowpath(value == LONG_MIN)) {
DISPATCH_CLIENT_CRASH("Unbalanced call to dispatch_group_leave()");
}
if (slowpath(value == dsema->dsema_orig)) {
(void)_dispatch_group_wake(dsema);
}
}
long
dispatch_semaphore_signal(dispatch_semaphore_t dsema)
{
dispatch_atomic_release_barrier();
long value = dispatch_atomic_inc2o(dsema, dsema_value);
if (fastpath(value > 0)) {
return 0;
}
if (slowpath(value == LONG_MIN)) {
DISPATCH_CLIENT_CRASH("Unbalanced call to dispatch_semaphore_signal()");
}
return _dispatch_semaphore_signal_slow(dsema);
}
DISPATCH_NOINLINE
_os_object_t
_os_object_retain(_os_object_t obj)
{
int xref_cnt = obj->os_obj_xref_cnt;
if (slowpath(xref_cnt == _OS_OBJECT_GLOBAL_REFCNT)) {
return obj; // global object
}
xref_cnt = dispatch_atomic_inc2o(obj, os_obj_xref_cnt, relaxed);
if (slowpath(xref_cnt <= 0)) {
_OS_OBJECT_CLIENT_CRASH("Resurrection of an object");
}
return obj;
}
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;
}
