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Eliminate branch and insert an explicit reader memory barrier to ensure

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that waiter bit is set before reading semaphore count.
This commit is contained in:
davidxu 2012-01-16 04:39:10 +00:00
parent c3eb99c02f
commit 0483748480
1 changed files with 2 additions and 3 deletions
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5
sys/kern/kern_umtx.c
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@ -2804,9 +2804,8 @@ do_sem_wait(struct thread *td, struct _usem *sem, struct timespec *timeout)
umtxq_insert(uq);
umtxq_unlock(&uq->uq_key);
if (fuword32(__DEVOLATILE(uint32_t *, &sem->_has_waiters)) == 0)
casuword32(__DEVOLATILE(uint32_t *, &sem->_has_waiters), 0, 1);
casuword32(__DEVOLATILE(uint32_t *, &sem->_has_waiters), 0, 1);
rmb();
count = fuword32(__DEVOLATILE(uint32_t *, &sem->_count));
if (count != 0) {
umtxq_lock(&uq->uq_key);