fix comments from 2/24/16

Author: frankeh

src/semaphore.c

@@ -891,11 +891,6 @@ _dispatch_thread_semaphore_wait(_dispatch_thread_semaphore_t sema)
 }
 
 #if USE_FUTEX_SEM
-#define DISPATCH_FUTEX_NUM_SPINS 100
-#define DISPATCH_FUTEX_VALUE_MAX INT_MAX
-#define DISPATCH_FUTEX_NWAITERS_SHIFT 32
-#define DISPATCH_FUTEX_VALUE_MASK ((1ull << DISPATCH_FUTEX_NWAITERS_SHIFT) - 1)
-
 static bool _dispatch_futex_wait_slow(dispatch_futex_t dfx,
 		const struct timespec* timeout);
 
@@ -918,8 +913,8 @@ DISPATCH_INLINE
 bool
 _dispatch_futex_trywait(dispatch_futex_t dfx)
 {
-	uint64_t orig;
-	while ((orig = dfx->dfx_data) & DISPATCH_FUTEX_VALUE_MASK) {
+    uint64_t orig = dispatch_atomic_load2o(dfx, dfx_data, relaxed);
+    while (orig & DISPATCH_FUTEX_VALUE_MASK) {
 		if (dispatch_atomic_cmpxchg2o(dfx, dfx_data, orig, orig - 1, acquire)) {
 			return true;
 		}
@@ -933,9 +928,8 @@ DISPATCH_INLINE
 bool
 _dispatch_futex_signal(dispatch_futex_t dfx)
 {
-	uint64_t orig;
-	do {
-		orig = dfx->dfx_data;
+    uint64_t orig = dispatch_atomic_load2o(dfx, dfx_data, relaxed);
+    do {
 		if (slowpath((orig & DISPATCH_FUTEX_VALUE_MASK) ==
 					 DISPATCH_FUTEX_VALUE_MAX)) {
 			DISPATCH_CRASH("semaphore overflow");
@@ -965,15 +959,16 @@ _dispatch_futex_wait_slow(dispatch_futex_t dfx, const struct timespec *timeout)
 {
 	int spins = DISPATCH_FUTEX_NUM_SPINS;
 	// Spin for a short time (if there are no waiters).
-	while (spins-- && !dfx->dfx_data) {
+	while (spins-- && !dispatch_atomic_load2o(dfx, dfx_data, relaxed)) {
 		dispatch_hardware_pause();
 	}
 	while (!_dispatch_futex_trywait(dfx)) {
 		dispatch_atomic_add2o(dfx, dfx_data,
-							  1ull << DISPATCH_FUTEX_NWAITERS_SHIFT, relaxed);
-		int ret = _dispatch_futex_syscall(&dfx->dfx_futex, FUTEX_WAIT, 0, timeout);
+				1ull << DISPATCH_FUTEX_NWAITERS_SHIFT, relaxed);
+		int ret = _dispatch_futex_syscall(&dfx->dfx_futex, FUTEX_WAIT, 
+							0, timeout);
 		dispatch_atomic_sub2o(dfx, dfx_data,
-							  1ull << DISPATCH_FUTEX_NWAITERS_SHIFT, acquire);
+				1ull << DISPATCH_FUTEX_NWAITERS_SHIFT, acquire);
 		switch (ret == -1 ? errno : 0) {
 		case EWOULDBLOCK:
 			if (!timeout) {

src/semaphore_internal.h

@@ -45,6 +45,11 @@ typedef union {
 } dispatch_futex_s;
 #define DISPATCH_FUTEX_INIT  ((dispatch_futex_s){ 0 })
 typedef dispatch_futex_s *dispatch_futex_t;
+
+#define DISPATCH_FUTEX_NUM_SPINS 100
+#define DISPATCH_FUTEX_VALUE_MAX INT_MAX
+#define DISPATCH_FUTEX_NWAITERS_SHIFT 32
+#define DISPATCH_FUTEX_VALUE_MASK ((1ull << DISPATCH_FUTEX_NWAITERS_SHIFT) - 1)
 #endif  /* USE_FUTEX_SEM */
 
 DISPATCH_CLASS_DECL(semaphore);
@@ -85,6 +90,10 @@ void _dispatch_thread_semaphore_dispose(_dispatch_thread_semaphore_t);
 void _dispatch_thread_semaphore_wait(_dispatch_thread_semaphore_t);
 void _dispatch_thread_semaphore_signal(_dispatch_thread_semaphore_t);
 
+#if USE_FUTEX_SEM
+#define _dispatch_get_thread_semaphore() _dispatch_thread_semaphore_create()
+#define _dispatch_put_thread_semaphore(s) _dispatch_thread_semaphore_dispose(s)
+#else
 DISPATCH_ALWAYS_INLINE
 static inline _dispatch_thread_semaphore_t
 _dispatch_get_thread_semaphore(void)
@@ -109,5 +118,6 @@ _dispatch_put_thread_semaphore(_dispatch_thread_semaphore_t sema)
 		return _dispatch_thread_semaphore_dispose(old_sema);
 	}
 }
+#endif
 
 #endif