Revision: 84 http://trac.macosforge.org/projects/libdispatch/changeset/84 Author: robert@fledge.watson.org Date: 2009-11-02 03:38:43 -0800 (Mon, 02 Nov 2009) Log Message: ----------- Unconditionally initialize the POSIX semaphore supporting a dispatch semaphore, as the type sem_t may not be a scalar on all platforms. Even if it were, the current code was racey as it failed to do an atomic test-and-set to make sure that two threads hadn't triggered on-demand initialization of the dispatch semaphore at the same time. In practice, this should remain fairly efficient as non-pshared POSIX semaphores will generally be implemented entirely with libpthread, and likely not require kernel involvement during allocation (as is required for Mach semaphores, hence lazy allocation optimizations). Spotted by: Kevin Van Vechten <kvv@apple.com> Modified Paths: -------------- trunk/src/semaphore.c Modified: trunk/src/semaphore.c =================================================================== --- trunk/src/semaphore.c 2009-11-02 11:27:33 UTC (rev 83) +++ trunk/src/semaphore.c 2009-11-02 11:38:43 UTC (rev 84) @@ -86,6 +86,9 @@ dispatch_semaphore_create(long value) { dispatch_semaphore_t dsema; +#if USE_POSIX_SEM + int ret; +#endif // 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 @@ -104,6 +107,10 @@ dsema->do_targetq = dispatch_get_global_queue(0, 0); dsema->dsema_value = value; dsema->dsema_orig = value; +#if USE_POSIX_SEM + ret = sem_init(&dsema->dsema_sem, 0, 0); + dispatch_assume_zero(ret); +#endif } return dsema; @@ -140,21 +147,7 @@ _dispatch_safe_fork = false; } #endif -#if USE_POSIX_SEM -static void -_dispatch_posix_semaphore_create(sem_t *s4) -{ - int ret; - if (*s4) { - return; - } - - ret = sem_init(s4, 0, 0); - dispatch_assume_zero(ret); -} -#endif - DISPATCH_NOINLINE static long _dispatch_semaphore_wait_slow(dispatch_semaphore_t dsema, dispatch_time_t timeout) @@ -183,9 +176,6 @@ #if USE_MACH_SEM _dispatch_semaphore_create_port(&dsema->dsema_port); #endif -#if USE_POSIX_SEM - _dispatch_posix_semaphore_create(&dsema->dsema_sem); -#endif // From xnu/osfmk/kern/sync_sema.c: // wait_semaphore->count = -1; /* we don't keep an actual count */