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authorRich Felker <dalias@aerifal.cx>2011-09-25 21:14:40 -0400
committerRich Felker <dalias@aerifal.cx>2011-09-25 21:14:40 -0400
commitc11d1e696723f41d7873332e51fb6858b417fa5f (patch)
tree4109f54cb4bd53b6e21086bf905d53aa19fe7a28 /src/thread/pthread_cond_broadcast.c
parentcf940165d4caf132405a3fe3df58b57eb735ac04 (diff)
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revert previous change in cond var waiter move
using swap has a race condition: the waiters must be added to the
mutex waiter count *before* they are taken off the cond var waiter
count, or wake events can be lost.
Diffstat (limited to 'src/thread/pthread_cond_broadcast.c')
-rw-r--r--src/thread/pthread_cond_broadcast.c8
1 files changed, 6 insertions, 2 deletions
diff --git a/src/thread/pthread_cond_broadcast.c b/src/thread/pthread_cond_broadcast.c
index 4fab9994..7e5ea91c 100644
--- a/src/thread/pthread_cond_broadcast.c
+++ b/src/thread/pthread_cond_broadcast.c
@@ -30,8 +30,12 @@ int pthread_cond_broadcast(pthread_cond_t *c)
 	}
 
 	/* Move waiter count to the mutex */
-	w = a_swap(&c->_c_waiters, 0);
-	a_fetch_add(&m->_m_waiters, w);
+	for (;;) {
+		w = c->_c_waiters;
+		a_fetch_add(&m->_m_waiters, w);
+		if (a_cas(&c->_c_waiters, w, 0) == w) break;
+		a_fetch_add(&m->_m_waiters, -w);
+	}
 
 	/* Perform the futex requeue, waking one waiter unless we know
 	 * that the calling thread holds the mutex. */