X-Git-Url: http://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=compat_futex.c;h=6ec0b3912b34afbda58c873371f83aec55d35f68;hp=e8d1e70f23d247437c83345ff3443be3f01cec36;hb=f4fe930941ad7e73ca2064c8be1abc31626ec50b;hpb=2f3dd0a582f21370ed852cec76a0f97ed33416a5

diff --git a/compat_futex.c b/compat_futex.c
index e8d1e70..6ec0b39 100644
--- a/compat_futex.c
+++ b/compat_futex.c
@@ -30,9 +30,20 @@
 
 #include <urcu/arch.h>
 #include <urcu/futex.h>
+#include <urcu/system.h>
 
-static pthread_mutex_t compat_futex_lock = PTHREAD_MUTEX_INITIALIZER;
-static pthread_cond_t compat_futex_cond = PTHREAD_COND_INITIALIZER;
+/*
+ * Using attribute "weak" for __urcu_compat_futex_lock and
+ * __urcu_compat_futex_cond. Those are globally visible by the entire
+ * program, even though many shared objects may have their own version.
+ * The first version that gets loaded will be used by the entire program
+ * (executable and all shared objects).
+ */
+
+__attribute__((weak))
+pthread_mutex_t __urcu_compat_futex_lock = PTHREAD_MUTEX_INITIALIZER;
+__attribute__((weak))
+pthread_cond_t __urcu_compat_futex_cond = PTHREAD_COND_INITIALIZER;
 
 /*
  * _NOT SIGNAL-SAFE_. pthread_cond is not signal-safe anyway. Though.
@@ -43,7 +54,7 @@ static pthread_cond_t compat_futex_cond = PTHREAD_COND_INITIALIZER;
 int compat_futex_noasync(int32_t *uaddr, int op, int32_t val,
 	const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
 {
-	int ret, i, gret = 0;
+	int ret, gret = 0;
 
 	/*
 	 * Check if NULL. Don't let users expect that they are taken into
@@ -58,23 +69,31 @@ int compat_futex_noasync(int32_t *uaddr, int op, int32_t val,
 	 */
 	cmm_smp_mb();
 
-	ret = pthread_mutex_lock(&compat_futex_lock);
+	ret = pthread_mutex_lock(&__urcu_compat_futex_lock);
 	assert(!ret);
 	switch (op) {
 	case FUTEX_WAIT:
-		if (*uaddr != val)
-			goto end;
-		pthread_cond_wait(&compat_futex_cond, &compat_futex_lock);
+		/*
+		 * Wait until *uaddr is changed to something else than "val".
+		 * Comparing *uaddr content against val figures out which
+		 * thread has been awakened.
+		 */
+		while (CMM_LOAD_SHARED(*uaddr) == val)
+			pthread_cond_wait(&__urcu_compat_futex_cond,
+				&__urcu_compat_futex_lock);
 		break;
 	case FUTEX_WAKE:
-		for (i = 0; i < val; i++)
-			pthread_cond_signal(&compat_futex_cond);
+		/*
+		 * Each wake is sending a broadcast, thus attempting wakeup of
+		 * all awaiting threads, independently of their respective
+		 * uaddr.
+		 */
+		pthread_cond_broadcast(&__urcu_compat_futex_cond);
 		break;
 	default:
 		gret = -EINVAL;
 	}
-end:
-	ret = pthread_mutex_unlock(&compat_futex_lock);
+	ret = pthread_mutex_unlock(&__urcu_compat_futex_lock);
 	assert(!ret);
 	return gret;
 }
@@ -103,7 +122,7 @@ int compat_futex_async(int32_t *uaddr, int op, int32_t val,
 
 	switch (op) {
 	case FUTEX_WAIT:
-		while (*uaddr == val)
+		while (CMM_LOAD_SHARED(*uaddr) == val)
 			poll(NULL, 0, 10);
 		break;
 	case FUTEX_WAKE:
@@ -111,4 +130,5 @@ int compat_futex_async(int32_t *uaddr, int op, int32_t val,
 	default:
 		return -EINVAL;
 	}
+	return 0;
 }