- status changed from new to accepted
- owner set to dsteffen@…
GCC has apparently changed the __sync intrinsics to no longer be compiler barriers (nonsensical IMO since they are defined to generate memory barrier instructions). The cleanest fix for the Lion branch is to change the default barrier defines in atomic.h
diff --git i/src/shims/atomic.h w/src/shims/atomic.h
index fbc1171..5dfe71b 100644
--- i/src/shims/atomic.h
+++ w/src/shims/atomic.h
@@ -42,11 +42,14 @@
// see comment in dispatch_once.c
#define dispatch_atomic_maximally_synchronizing_barrier() \
_dispatch_atomic_barrier()
-// assume atomic builtins provide barriers
-#define dispatch_atomic_barrier()
-#define dispatch_atomic_acquire_barrier()
-#define dispatch_atomic_release_barrier()
-#define dispatch_atomic_store_barrier()
+// assume atomic builtins provide memory barriers, but ensure compiler does not
+// reorder across them (workaround bugs in recent GCC)
+// http://libdispatch.macosforge.org/trac/ticket/35
+#define dispatch_atomic_barrier() \
+ __asm__ __volatile__("" : : : "memory")
+#define dispatch_atomic_acquire_barrier() dispatch_atomic_barrier()
+#define dispatch_atomic_release_barrier() dispatch_atomic_barrier()
+#define dispatch_atomic_store_barrier() dispatch_atomic_barrier()
#define _dispatch_hardware_pause() asm("")
#define _dispatch_debugger() asm("trap")