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revert previous change in cond var waiter move

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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.
This commit is contained in:
Rich Felker
2011-09-25 21:14:40 -04:00
parent cf940165d4
commit c11d1e6967
1 changed files with 6 additions and 2 deletions
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6
src/thread/pthread_cond_broadcast.c
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@ -30,8 +30,12 @@ int pthread_cond_broadcast(pthread_cond_t *c)
} }
/* Move waiter count to the mutex */ /* Move waiter count to the mutex */
w = a_swap(&c->_c_waiters, 0); for (;;) {
w = c->_c_waiters;
a_fetch_add(&m->_m_waiters, w); 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 /* Perform the futex requeue, waking one waiter unless we know
* that the calling thread holds the mutex. */ * that the calling thread holds the mutex. */