From c149f4ca16db6ae9538490041f3145d50585e65b Mon Sep 17 00:00:00 2001 From: David Young Date: Thu, 27 Feb 2020 11:27:45 -0600 Subject: The first implementation seemed to allow for the possibility that a thread could block at the barrier, wake and exit the barrier, re-acquire the barrier lock and increase `nentered` before the other blocked threads woke and checked `nentered % count == 0`. Then the other blocked threads would check `nentered % count == 0` and, finding it false, go back to sleep in the barrier. This new implementation waits for a looser condition to obtain so that threads don't go back to sleep in the barrier. --- test/thread_id.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/test/thread_id.c b/test/thread_id.c index 49e3710..e3cf42e 100644 --- a/test/thread_id.c +++ b/test/thread_id.c @@ -143,6 +143,7 @@ int pthread_barrier_wait(pthread_barrier_t *barrier) { int rc; + uint64_t threshold; if (barrier == NULL) return EINVAL; @@ -152,8 +153,14 @@ pthread_barrier_wait(pthread_barrier_t *barrier) rc = EINVAL; goto out; } + /* Compute the release `threshold`. All threads entering with count = 5 + * and `nentered` in [0, 4] should be released once `nentered` reaches 5: + * call 5 the release `threshold`. All threads entering with count = 5 + * and `nentered` in [5, 9] should be released once `nentered` reaches 10. + */ + threshold = (barrier->nentered / barrier->count + 1) * barrier->count; barrier->nentered++; - while (barrier->nentered % barrier->count != 0) { + while (barrier->nentered < threshold) { if ((rc = pthread_cond_wait(&barrier->cv, &barrier->mtx)) != 0) goto out; } -- cgit v0.12