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.
diff --git a/src/thread/pthread_cond_broadcast.c b/src/thread/pthread_cond_broadcast.c
index 4fab999..7e5ea91 100644
--- a/src/thread/pthread_cond_broadcast.c
+++ b/src/thread/pthread_cond_broadcast.c
@@ -30,8 +30,12 @@
}
/* 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. */
