If there is a single waiting thread, pthread_cond_signal is the
same as pthread_cond_broadcast and no extra synchronization is
necessary.
Signed-off-by: Paolo Bonzini <bonzini@xxxxxxx>
---
compat/win32/pthread.c | 19 ++++++++++---------
1 files changed, 10 insertions(+), 9 deletions(-)
diff --git a/compat/win32/pthread.c b/compat/win32/pthread.c
index 1a38981..d46a51c 100644
--- a/compat/win32/pthread.c
+++ b/compat/win32/pthread.c
@@ -172,9 +172,10 @@ int pthread_cond_broadcast(pthread_cond_t *cond)
* As in pthread_cond_signal, access to cond->waiters and
* cond->was_broadcast is locked via the external mutex.
*/
-
- if ((cond->was_broadcast = cond->waiters > 0)) {
+ if (cond->waiters > 0) {
BOOLEAN result;
+ cond->was_broadcast = cond->waiters > 1;
+
/* wake up all waiters */
result = ReleaseSemaphore(cond->sema, cond->waiters, NULL);
if (!result)
@@ -187,14 +188,14 @@ int pthread_cond_broadcast(pthread_cond_t *cond)
* yet. For this reason, we can be sure that no thread gets
* a chance to eat *more* than one slice. OTOH, it means
* that the last waiter must send us a wake-up.
+ *
+ * As an optimization, when there was exactly one waiter
+ * broadcast is the same as signal and we can skip this step.
*/
- WaitForSingleObject(cond->continue_broadcast, INFINITE);
- /*
- * Since the external mutex is held, no thread can enter
- * cond_wait, and, hence, it is safe to reset this flag
- * without cond->waiters_lock held.
- */
- cond->was_broadcast = 0;
+ if (cond->was_broadcast) {
+ WaitForSingleObject(cond->continue_broadcast, INFINITE);
+ cond->was_broadcast = 0;
+ }
}
return 0;
}
--
1.7.0.1
--
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