91 lines
1.7 KiB
Plaintext
91 lines
1.7 KiB
Plaintext
Conditional Variable pseudocode.
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================================
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int pthread_cond_timedwait (pthread_cond_t *cv, pthread_mutex_t *mutex);
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int pthread_cond_signal (pthread_cond_t *cv);
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int pthread_cond_broadcast (pthread_cond_t *cv);
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struct pthread_cond_t {
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unsigned int lock:
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internal mutex
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unsigned int nr_wakers:
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number of threads signalled to be woken up.
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unsigned int nr_sleepers:
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number of threads waiting for the cv.
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}
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#define ALL_THREADS (1 << (BITS_PER_LONG-1))
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cond_wait_timeout(cv, mutex, timeout):
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{
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lll_lock(cv->lock);
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mutex_unlock(mutex);
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cv->nr_sleepers++;
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for (;;) {
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if (cv->nr_wakers) {
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cv->nr_wakers--;
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break;
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}
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val = cv->nr_wakers;
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lll_unlock(cv->lock);
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ret = FUTEX WAIT (cv->nr_wakers, val, timeout)
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lll_lock(cv->lock);
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if (ret == TIMEOUT)
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break;
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ret = 0;
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}
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if (!--cv->nr_sleepers)
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cv->nr_wakers = 0; /* no memory of wakeups */
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lll_unlock(cv->lock);
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mutex_lock(mutex);
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return ret;
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}
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cond_signal(cv)
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{
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int do_wakeup = 0;
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lll_lock(cv->lock);
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if (cv->nr_sleepers) {
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if (!++cv->nr_wakers) /* overflow detection for the nutcase */
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cv->nr_wakers = ALL_THREADS;
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do_wakeup = 1;
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}
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lll_unlock(cv->lock);
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if (do_wakeup)
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FUTEX WAKE (cv->nr_wakers, 1)
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}
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cond_broadcast(cv)
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{
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int do_wakeup = 0;
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lll_lock(cv->lock);
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if (cv->nr_sleepers) {
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cv->nr_wakers |= ALL_THREADS;
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do_wakeup = 1;
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}
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lll_unlock(cv->lock);
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if (do_wakeup)
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FUTEX WAKE (cv->nr_wakers, ALL_THREADS);
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}
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weaknesses of the implementation:
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it might generate spurious wakeups in the broadcast case, but those are
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allowed by POSIX.
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