Merge pull request #20 from dgrove-oss/sem_timedwait_fix_v2

posix sem_timedwait requires epoch-based timeout

Author: MadCoder

src/internal.h

@@ -528,6 +528,7 @@ void _dispatch_vtable_init(void);
 char *_dispatch_get_build(void);
 
 uint64_t _dispatch_timeout(dispatch_time_t when);
+uint64_t _dispatch_time_to_nanoseconds(dispatch_time_t when);
 
 extern bool _dispatch_safe_fork, _dispatch_child_of_unsafe_fork;
 

src/semaphore.c

@@ -342,7 +342,7 @@ _dispatch_semaphore_wait_slow(dispatch_semaphore_t dsema,
 		}
 #elif USE_POSIX_SEM
 		do {
-			uint64_t nsec = _dispatch_timeout(timeout);
+			uint64_t nsec = _dispatch_time_to_nanoseconds(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));
@@ -582,7 +582,7 @@ _dispatch_group_wait_slow(dispatch_semaphore_t dsema, dispatch_time_t timeout)
 		}
 #elif USE_POSIX_SEM
 		do {
-			uint64_t nsec = _dispatch_timeout(timeout);
+			uint64_t nsec = _dispatch_time_to_nanoseconds(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));

src/time.c

@@ -145,3 +145,16 @@ _dispatch_timeout(dispatch_time_t when)
 	now = _dispatch_absolute_time();
 	return now >= when ? 0 : _dispatch_time_mach2nano(when - now);
 }
+
+uint64_t
+_dispatch_time_to_nanoseconds(dispatch_time_t when)
+{
+	if (when == DISPATCH_TIME_FOREVER) {
+		return DISPATCH_TIME_FOREVER;
+	}
+	if ((int64_t)when < 0) {
+		// time in nanoseconds since the POSIX epoch already
+		return -(int64_t)when;
+	}
+	return _dispatch_get_nanoseconds() + _dispatch_timeout(when);
+}