src/semaphore.c

/*
 * Copyright (c) 2008-2013 Apple Inc. All rights reserved.
 *
 * @APPLE_APACHE_LICENSE_HEADER_START@
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * @APPLE_APACHE_LICENSE_HEADER_END@
 */

#include "internal.h"

// semaphores are too fundamental to use the dispatch_assume*() macros
#if USE_WIN32_SEM
// rdar://problem/8428132
static DWORD best_resolution = 1; // 1ms

DWORD
_push_timer_resolution(DWORD ms)
{
	MMRESULT res;
	static dispatch_once_t once;

	if (ms > 16) {
		// only update timer resolution if smaller than default 15.6ms
		// zero means not updated
		return 0;
	}

	// aim for the best resolution we can accomplish
	dispatch_once(&once, ^{
		TIMECAPS tc;
		MMRESULT res;
		res = timeGetDevCaps(&tc, sizeof(tc));
		if (res == MMSYSERR_NOERROR) {
			best_resolution = min(max(tc.wPeriodMin, best_resolution),
					tc.wPeriodMax);
		}
	});

	res = timeBeginPeriod(best_resolution);
	if (res == TIMERR_NOERROR) {
		return best_resolution;
	}
	// zero means not updated
	return 0;
}

// match ms parameter to result from _push_timer_resolution
void
_pop_timer_resolution(DWORD ms)
{
	if (ms) {
		timeEndPeriod(ms);
	}
}
#endif	/* USE_WIN32_SEM */


DISPATCH_WEAK // rdar://problem/8503746
long _dispatch_semaphore_signal_slow(dispatch_semaphore_t dsema);

#pragma mark -
#pragma mark dispatch_semaphore_class_t

static void
_dispatch_semaphore_class_init(long value, dispatch_semaphore_class_t dsemau)
{
	struct dispatch_semaphore_header_s *dsema = dsemau._dsema_hdr;

	dsema->do_next = DISPATCH_OBJECT_LISTLESS;
	dsema->do_targetq = _dispatch_get_root_queue(_DISPATCH_QOS_CLASS_DEFAULT,
			false);
	dsema->dsema_value = value;
#if USE_POSIX_SEM
	int ret = sem_init(&dsema->dsema_sem, 0, 0);
	DISPATCH_SEMAPHORE_VERIFY_RET(ret);
#endif
}

static void
_dispatch_semaphore_class_dispose(dispatch_semaphore_class_t dsemau)
{
	struct dispatch_semaphore_header_s *dsema = dsemau._dsema_hdr;

#if USE_MACH_SEM
	kern_return_t kr;
	if (dsema->dsema_port) {
		kr = semaphore_destroy(mach_task_self(), dsema->dsema_port);
		DISPATCH_VERIFY_MIG(kr);
		DISPATCH_SEMAPHORE_VERIFY_KR(kr);
	}
	dsema->dsema_port = MACH_PORT_DEAD;
#elif USE_POSIX_SEM
	int ret = sem_destroy(&dsema->dsema_sem);
	DISPATCH_SEMAPHORE_VERIFY_RET(ret);
#elif USE_WIN32_SEM
	if (dsema->dsema_handle) {
		CloseHandle(dsema->dsema_handle);
	}
#endif
}

#pragma mark -
#pragma mark dispatch_semaphore_t

dispatch_semaphore_t
dispatch_semaphore_create(long value)
{
	dispatch_semaphore_t dsema;

	// If the internal value is negative, then the absolute of the value is
	// equal to the number of waiting threads. Therefore it is bogus to
	// initialize the semaphore with a negative value.
	if (value < 0) {
		return DISPATCH_BAD_INPUT;
	}

	dsema = (dispatch_semaphore_t)_dispatch_alloc(DISPATCH_VTABLE(semaphore),
			sizeof(struct dispatch_semaphore_s));
	_dispatch_semaphore_class_init(value, dsema);
	dsema->dsema_orig = value;
	return dsema;
}

#if USE_MACH_SEM
static void
_dispatch_semaphore_create_port(semaphore_t *s4)
{
	kern_return_t kr;
	semaphore_t tmp;

	if (*s4) {
		return;
	}
	_dispatch_fork_becomes_unsafe();

	// lazily allocate the semaphore port

	// Someday:
	// 1) Switch to a doubly-linked FIFO in user-space.
	// 2) User-space timers for the timeout.
	// 3) Use the per-thread semaphore port.

	while ((kr = semaphore_create(mach_task_self(), &tmp,
			SYNC_POLICY_FIFO, 0))) {
		DISPATCH_VERIFY_MIG(kr);
		_dispatch_temporary_resource_shortage();
	}

	if (!os_atomic_cmpxchg(s4, 0, tmp, relaxed)) {
		kr = semaphore_destroy(mach_task_self(), tmp);
		DISPATCH_VERIFY_MIG(kr);
		DISPATCH_SEMAPHORE_VERIFY_KR(kr);
	}
}
#elif USE_WIN32_SEM
static void
_dispatch_semaphore_create_handle(HANDLE *s4)
{
	HANDLE tmp;

	if (*s4) {
		return;
	}

	// lazily allocate the semaphore port

	while (!dispatch_assume(tmp = CreateSemaphore(NULL, 0, LONG_MAX, NULL))) {
		_dispatch_temporary_resource_shortage();
	}

	if (!os_atomic_cmpxchg(s4, 0, tmp)) {
		CloseHandle(tmp);
	}
}
#endif

void
_dispatch_semaphore_dispose(dispatch_object_t dou)
{
	dispatch_semaphore_t dsema = dou._dsema;

	if (dsema->dsema_value < dsema->dsema_orig) {
		DISPATCH_CLIENT_CRASH(dsema->dsema_orig - dsema->dsema_value,
				"Semaphore object deallocated while in use");
	}

	_dispatch_semaphore_class_dispose(dsema);
}

size_t
_dispatch_semaphore_debug(dispatch_object_t dou, char *buf, size_t bufsiz)
{
	dispatch_semaphore_t dsema = dou._dsema;

	size_t offset = 0;
	offset += dsnprintf(&buf[offset], bufsiz - offset, "%s[%p] = { ",
			dx_kind(dsema), dsema);
	offset += _dispatch_object_debug_attr(dsema, &buf[offset], bufsiz - offset);
#if USE_MACH_SEM
	offset += dsnprintf(&buf[offset], bufsiz - offset, "port = 0x%u, ",
			dsema->dsema_port);
#endif
	offset += dsnprintf(&buf[offset], bufsiz - offset,
			"value = %ld, orig = %ld }", dsema->dsema_value, dsema->dsema_orig);
	return offset;
}

DISPATCH_NOINLINE
long
_dispatch_semaphore_signal_slow(dispatch_semaphore_t dsema)
{
#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);
#elif USE_WIN32_SEM
	_dispatch_semaphore_create_handle(&dsema->dsema_handle);
	int ret = ReleaseSemaphore(dsema->dsema_handle, 1, NULL);
	dispatch_assume(ret);
#endif
	return 1;
}

long
dispatch_semaphore_signal(dispatch_semaphore_t dsema)
{
	long value = os_atomic_inc2o(dsema, dsema_value, release);
	if (fastpath(value > 0)) {
		return 0;
	}
	if (slowpath(value == LONG_MIN)) {
		DISPATCH_CLIENT_CRASH(value,
				"Unbalanced call to dispatch_semaphore_signal()");
	}
	return _dispatch_semaphore_signal_slow(dsema);
}

DISPATCH_NOINLINE
static long
_dispatch_semaphore_wait_slow(dispatch_semaphore_t dsema,
		dispatch_time_t timeout)
{
	long orig;

#if USE_MACH_SEM
	mach_timespec_t _timeout;
	kern_return_t kr;
#elif USE_POSIX_SEM
	struct timespec _timeout;
	int ret;
#elif USE_WIN32_SEM
	uint64_t nsec;
	DWORD msec;
	DWORD resolution;
	DWORD wait_result;
#endif

#if USE_MACH_SEM
	_dispatch_semaphore_create_port(&dsema->dsema_port);
#elif USE_WIN32_SEM
	_dispatch_semaphore_create_handle(&dsema->dsema_handle);
#endif

	switch (timeout) {
	default:
#if USE_MACH_SEM
		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_port, _timeout));
		} while (kr == KERN_ABORTED);

		if (kr != KERN_OPERATION_TIMED_OUT) {
			DISPATCH_SEMAPHORE_VERIFY_KR(kr);
			break;
		}
#elif USE_POSIX_SEM
		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(&dsema->dsema_sem, &_timeout));
		} while (ret == -1 && errno == EINTR);

		if (!(ret == -1 && errno == ETIMEDOUT)) {
			DISPATCH_SEMAPHORE_VERIFY_RET(ret);
			break;
		}
#elif USE_WIN32_SEM
		nsec = _dispatch_timeout(timeout);
		msec = (DWORD)(nsec / (uint64_t)1000000);
		resolution = _push_timer_resolution(msec);
		wait_result = WaitForSingleObject(dsema->dsema_handle, msec);
		_pop_timer_resolution(resolution);
		if (wait_result != WAIT_TIMEOUT) {
			break;
		}
#endif
		// Fall through and try to undo what the fast path did to
		// dsema->dsema_value
	case DISPATCH_TIME_NOW:
		orig = dsema->dsema_value;
		while (orig < 0) {
			if (os_atomic_cmpxchgvw2o(dsema, dsema_value, orig, orig + 1,
					&orig, relaxed)) {
#if USE_MACH_SEM
				return KERN_OPERATION_TIMED_OUT;
#elif USE_POSIX_SEM || USE_WIN32_SEM
				errno = ETIMEDOUT;
				return -1;
#endif
			}
		}
		// Another thread called semaphore_signal().
		// Fall through and drain the wakeup.
	case DISPATCH_TIME_FOREVER:
#if USE_MACH_SEM
		do {
			kr = semaphore_wait(dsema->dsema_port);
		} while (kr == KERN_ABORTED);
		DISPATCH_SEMAPHORE_VERIFY_KR(kr);
#elif USE_POSIX_SEM
		do {
			ret = sem_wait(&dsema->dsema_sem);
		} while (ret != 0);
		DISPATCH_SEMAPHORE_VERIFY_RET(ret);
#elif USE_WIN32_SEM
		WaitForSingleObject(dsema->dsema_handle, INFINITE);
#endif
		break;
	}
	return 0;
}

long
dispatch_semaphore_wait(dispatch_semaphore_t dsema, dispatch_time_t timeout)
{
	long value = os_atomic_dec2o(dsema, dsema_value, acquire);
	if (fastpath(value >= 0)) {
		return 0;
	}
	return _dispatch_semaphore_wait_slow(dsema, timeout);
}

#pragma mark -
#pragma mark dispatch_group_t

DISPATCH_ALWAYS_INLINE
static inline dispatch_group_t
_dispatch_group_create_with_count(long count)
{
	dispatch_group_t dg = (dispatch_group_t)_dispatch_alloc(
			DISPATCH_VTABLE(group), sizeof(struct dispatch_group_s));
	_dispatch_semaphore_class_init(count, dg);
	if (count) {
		os_atomic_store2o(dg, do_ref_cnt, 1, relaxed); // <rdar://problem/22318411>
	}
	return dg;
}

dispatch_group_t
dispatch_group_create(void)
{
	return _dispatch_group_create_with_count(0);
}

dispatch_group_t
_dispatch_group_create_and_enter(void)
{
	return _dispatch_group_create_with_count(1);
}

void
dispatch_group_enter(dispatch_group_t dg)
{
	long value = os_atomic_inc_orig2o(dg, dg_value, acquire);
	if (slowpath((unsigned long)value >= (unsigned long)LONG_MAX)) {
		DISPATCH_CLIENT_CRASH(value,
				"Too many nested calls to dispatch_group_enter()");
	}
	if (value == 0) {
		_dispatch_retain(dg); // <rdar://problem/22318411>
	}
}

DISPATCH_NOINLINE
static long
_dispatch_group_wake(dispatch_group_t dg, bool needs_release)
{
	dispatch_continuation_t next, head, tail = NULL;
	long rval;

	// cannot use os_mpsc_capture_snapshot() because we can have concurrent
	// _dispatch_group_wake() calls
	head = os_atomic_xchg2o(dg, dg_notify_head, NULL, relaxed);
	if (head) {
		// snapshot before anything is notified/woken <rdar://problem/8554546>
		tail = os_atomic_xchg2o(dg, dg_notify_tail, NULL, release);
	}
	rval = (long)os_atomic_xchg2o(dg, dg_waiters, 0, relaxed);
	if (rval) {
		// wake group waiters
#if USE_MACH_SEM
		_dispatch_semaphore_create_port(&dg->dg_port);
		do {
			kern_return_t kr = semaphore_signal(dg->dg_port);
			DISPATCH_GROUP_VERIFY_KR(kr);
		} while (--rval);
#elif USE_POSIX_SEM
		do {
			int ret = sem_post(&dg->dg_sem);
			DISPATCH_SEMAPHORE_VERIFY_RET(ret);
		} while (--rval);
#elif USE_WIN32_SEM
		_dispatch_semaphore_create_handle(&dg->dg_handle);
		int ret;
		ret = ReleaseSemaphore(dg->dg_handle, rval, NULL);
		dispatch_assume(ret);
#else
#error "No supported semaphore type"
#endif
	}
	if (head) {
		// async group notify blocks
		do {
			next = os_mpsc_pop_snapshot_head(head, tail, do_next);
			dispatch_queue_t dsn_queue = (dispatch_queue_t)head->dc_data;
			_dispatch_continuation_async(dsn_queue, head);
			_dispatch_release(dsn_queue);
		} while ((head = next));
		_dispatch_release(dg);
	}
	if (needs_release) {
		_dispatch_release(dg); // <rdar://problem/22318411>
	}
	return 0;
}

void
dispatch_group_leave(dispatch_group_t dg)
{
	long value = os_atomic_dec2o(dg, dg_value, release);
	if (slowpath(value == 0)) {
		return (void)_dispatch_group_wake(dg, true);
	}
	if (slowpath(value < 0)) {
		DISPATCH_CLIENT_CRASH(value,
				"Unbalanced call to dispatch_group_leave()");
	}
}

void
_dispatch_group_dispose(dispatch_object_t dou)
{
	dispatch_group_t dg = dou._dg;

	if (dg->dg_value) {
		DISPATCH_CLIENT_CRASH(dg->dg_value,
				"Group object deallocated while in use");
	}

	_dispatch_semaphore_class_dispose(dg);
}

size_t
_dispatch_group_debug(dispatch_object_t dou, char *buf, size_t bufsiz)
{
	dispatch_group_t dg = dou._dg;

	size_t offset = 0;
	offset += dsnprintf(&buf[offset], bufsiz - offset, "%s[%p] = { ",
			dx_kind(dg), dg);
	offset += _dispatch_object_debug_attr(dg, &buf[offset], bufsiz - offset);
#if USE_MACH_SEM
	offset += dsnprintf(&buf[offset], bufsiz - offset, "port = 0x%u, ",
			dg->dg_port);
#endif
	offset += dsnprintf(&buf[offset], bufsiz - offset,
			"count = %ld, waiters = %d }", dg->dg_value, dg->dg_waiters);
	return offset;
}

DISPATCH_NOINLINE
static long
_dispatch_group_wait_slow(dispatch_group_t dg, dispatch_time_t timeout)
{
	long value;
	int orig_waiters;

#if USE_MACH_SEM
	mach_timespec_t _timeout;
	kern_return_t kr;
#elif USE_POSIX_SEM // KVV
	struct timespec _timeout;
	int ret;
#elif USE_WIN32_SEM // KVV
	uint64_t nsec;
	DWORD msec;
	DWORD resolution;
	DWORD wait_result;
#endif

	// check before we cause another signal to be sent by incrementing
	// dg->dg_waiters
	value = os_atomic_load2o(dg, dg_value, ordered); // 19296565
	if (value == 0) {
		return _dispatch_group_wake(dg, false);
	}

	(void)os_atomic_inc2o(dg, dg_waiters, relaxed);
	// check the values again in case we need to wake any threads
	value = os_atomic_load2o(dg, dg_value, ordered); // 19296565
	if (value == 0) {
		_dispatch_group_wake(dg, false);
		// Fall through to consume the extra signal, forcing timeout to avoid
		// useless setups as it won't block
		timeout = DISPATCH_TIME_FOREVER;
	}

#if USE_MACH_SEM
	_dispatch_semaphore_create_port(&dg->dg_port);
#elif USE_WIN32_SEM
	_dispatch_semaphore_create_handle(&dg->dg_handle);
#endif

	switch (timeout) {
	default:
#if USE_MACH_SEM
		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(dg->dg_port, _timeout));
		} while (kr == KERN_ABORTED);

		if (kr != KERN_OPERATION_TIMED_OUT) {
			DISPATCH_GROUP_VERIFY_KR(kr);
			break;
		}
#elif USE_POSIX_SEM
		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(&dg->dg_sem, &_timeout));
		} while (ret == -1 && errno == EINTR);

		if (!(ret == -1 && errno == ETIMEDOUT)) {
			DISPATCH_SEMAPHORE_VERIFY_RET(ret);
			break;
		}
#elif USE_WIN32_SEM
		nsec = _dispatch_timeout(timeout);
		msec = (DWORD)(nsec / (uint64_t)1000000);
		resolution = _push_timer_resolution(msec);
		wait_result = WaitForSingleObject(dg->dg_handle, msec);
		_pop_timer_resolution(resolution);
		if (wait_result != WAIT_TIMEOUT) {
			break;
		}
#endif
		// Fall through and try to undo the earlier change to
		// dg->dg_waiters
	case DISPATCH_TIME_NOW:
		orig_waiters = dg->dg_waiters;
		while (orig_waiters) {
			if (os_atomic_cmpxchgvw2o(dg, dg_waiters, orig_waiters,
					orig_waiters - 1, &orig_waiters, relaxed)) {
#if USE_MACH_SEM
				return KERN_OPERATION_TIMED_OUT;
#elif USE_POSIX_SEM || USE_WIN32_SEM
				errno = ETIMEDOUT;
				return -1;
#endif
			}
		}
		// Another thread called semaphore_signal().
		// Fall through and drain the wakeup.
	case DISPATCH_TIME_FOREVER:
#if USE_MACH_SEM
		do {
			kr = semaphore_wait(dg->dg_port);
		} while (kr == KERN_ABORTED);
		DISPATCH_GROUP_VERIFY_KR(kr);
#elif USE_POSIX_SEM
		do {
			ret = sem_wait(&dg->dg_sem);
		} while (ret == -1 && errno == EINTR);
		DISPATCH_SEMAPHORE_VERIFY_RET(ret);
#elif USE_WIN32_SEM
		WaitForSingleObject(dg->dg_handle, INFINITE);
#endif
		break;
	}
	return 0;
}

long
dispatch_group_wait(dispatch_group_t dg, dispatch_time_t timeout)
{
	if (dg->dg_value == 0) {
		return 0;
	}
	if (timeout == 0) {
#if USE_MACH_SEM
		return KERN_OPERATION_TIMED_OUT;
#elif USE_POSIX_SEM || USE_WIN32_SEM
		errno = ETIMEDOUT;
		return (-1);
#endif
	}
	return _dispatch_group_wait_slow(dg, timeout);
}

DISPATCH_ALWAYS_INLINE
static inline void
_dispatch_group_notify(dispatch_group_t dg, dispatch_queue_t dq,
		dispatch_continuation_t dsn)
{
	dsn->dc_data = dq;
	dsn->do_next = NULL;
	_dispatch_retain(dq);
	if (os_mpsc_push_update_tail(dg, dg_notify, dsn, do_next)) {
		_dispatch_retain(dg);
		os_atomic_store2o(dg, dg_notify_head, dsn, ordered);
		// seq_cst with atomic store to notify_head <rdar://problem/11750916>
		if (os_atomic_load2o(dg, dg_value, ordered) == 0) {
			_dispatch_group_wake(dg, false);
		}
	}
}

DISPATCH_NOINLINE
void
dispatch_group_notify_f(dispatch_group_t dg, dispatch_queue_t dq, void *ctxt,
		dispatch_function_t func)
{
	dispatch_continuation_t dsn = _dispatch_continuation_alloc();
	_dispatch_continuation_init_f(dsn, dq, ctxt, func, 0, 0,
			DISPATCH_OBJ_CONSUME_BIT);
	_dispatch_group_notify(dg, dq, dsn);
}

#ifdef __BLOCKS__
void
dispatch_group_notify(dispatch_group_t dg, dispatch_queue_t dq,
		dispatch_block_t db)
{
	dispatch_continuation_t dsn = _dispatch_continuation_alloc();
	_dispatch_continuation_init(dsn, dq, db, 0, 0, DISPATCH_OBJ_CONSUME_BIT);
	_dispatch_group_notify(dg, dq, dsn);
}
#endif