Revision: 156 http://trac.macosforge.org/projects/libdispatch/changeset/156 Author: kvv@apple.com Date: 2009-11-14 15:58:57 -0800 (Sat, 14 Nov 2009) Log Message: ----------- 10.6.2: Always run dispatch_sync blocks on the current thread to better support the thread-local garbage collector. <rdar://problem/7181849> Modified Paths: -------------- trunk/src/queue.c Modified: trunk/src/queue.c =================================================================== --- trunk/src/queue.c 2009-11-14 23:53:59 UTC (rev 155) +++ trunk/src/queue.c 2009-11-14 23:58:57 UTC (rev 156) @@ -716,8 +716,9 @@ } struct dispatch_barrier_sync_slow2_s { + dispatch_queue_t dbss2_dq; dispatch_function_t dbss2_func; - dispatch_function_t dbss2_ctxt; + dispatch_function_t dbss2_ctxt; dispatch_semaphore_t dbss2_sema; }; @@ -726,7 +727,13 @@ { struct dispatch_barrier_sync_slow2_s *dbss2 = ctxt; - dbss2->dbss2_func(dbss2->dbss2_ctxt); + dispatch_assert(dbss2->dbss2_dq == dispatch_get_current_queue()); + // ALL blocks on the main queue, must be run on the main thread + if (dbss2->dbss2_dq == dispatch_get_main_queue()) { + dbss2->dbss2_func(dbss2->dbss2_ctxt); + } else { + dispatch_suspend(dbss2->dbss2_dq); + } dispatch_semaphore_signal(dbss2->dbss2_sema); } @@ -734,9 +741,15 @@ static void _dispatch_barrier_sync_f_slow(dispatch_queue_t dq, void *ctxt, dispatch_function_t func) { + + // It's preferred to execute synchronous blocks on the current thread + // due to thread-local side effects, garbage collection, etc. However, + // blocks submitted to the main thread MUST be run on the main thread + struct dispatch_barrier_sync_slow2_s dbss2 = { + .dbss2_dq = dq, .dbss2_func = func, - .dbss2_ctxt = ctxt, + .dbss2_ctxt = ctxt, .dbss2_sema = _dispatch_get_thread_semaphore(), }; struct dispatch_barrier_sync_slow_s { @@ -746,17 +759,17 @@ .dc_func = _dispatch_barrier_sync_f_slow_invoke, .dc_ctxt = &dbss2, }; - + + dispatch_queue_t old_dq = _dispatch_thread_getspecific(dispatch_queue_key); _dispatch_queue_push(dq, (void *)&dbss); + dispatch_semaphore_wait(dbss2.dbss2_sema, DISPATCH_TIME_FOREVER); - while (dispatch_semaphore_wait(dbss2.dbss2_sema, dispatch_time(0, 3ull * NSEC_PER_SEC))) { - if (DISPATCH_OBJECT_SUSPENDED(dq)) { - continue; - } - if (_dispatch_queue_trylock(dq)) { - _dispatch_queue_drain(dq); - _dispatch_queue_unlock(dq); - } + if (dq != dispatch_get_main_queue()) { + _dispatch_thread_setspecific(dispatch_queue_key, dq); + func(ctxt); + _dispatch_workitem_inc(); + _dispatch_thread_setspecific(dispatch_queue_key, old_dq); + dispatch_resume(dq); } _dispatch_put_thread_semaphore(dbss2.dbss2_sema); } @@ -765,6 +778,13 @@ void dispatch_barrier_sync(dispatch_queue_t dq, void (^work)(void)) { + // Blocks submitted to the main queue MUST be run on the main thread, + // therefore we must Block_copy in order to notify the thread-local + // garbage collector that the objects are transferring to the main thread + if (dq == dispatch_get_main_queue()) { + dispatch_block_t block = Block_copy(work); + return dispatch_barrier_sync_f(dq, block, _dispatch_call_block_and_release); + } struct Block_basic *bb = (void *)work; dispatch_barrier_sync_f(dq, work, (dispatch_function_t)bb->Block_invoke);