X-Git-Url: http://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=compat_futex.c;h=6ec0b3912b34afbda58c873371f83aec55d35f68;hp=e7342fe38ccda2330b45e157cd0c1d7cb02cd3ef;hb=f4fe930941ad7e73ca2064c8be1abc31626ec50b;hpb=5c02e37d09b7b89f68429751344d2af00c89f4fd

diff --git a/compat_futex.c b/compat_futex.c
index e7342fe..6ec0b39 100644
--- a/compat_futex.c
+++ b/compat_futex.c
@@ -30,6 +30,7 @@
 
 #include <urcu/arch.h>
 #include <urcu/futex.h>
+#include <urcu/system.h>
 
 /*
  * Using attribute "weak" for __urcu_compat_futex_lock and
@@ -72,17 +73,26 @@ int compat_futex_noasync(int32_t *uaddr, int op, int32_t val,
 	assert(!ret);
 	switch (op) {
 	case FUTEX_WAIT:
-		if (*uaddr != val)
-			goto end;
-		pthread_cond_wait(&__urcu_compat_futex_cond, &__urcu_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:
+		/*
+		 * 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(&__urcu_compat_futex_lock);
 	assert(!ret);
 	return gret;
@@ -112,7 +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: