Implemented Ingo's suggestions to avoid the situation that condition variables

don't block when they should because the semaphore sometimes gets released too
much. One day I'll try to add some tests, though this seems like something you
can't exactly unit test.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@22279 a95241bf-73f2-0310-859d-f6bbb57e9c96

src/system/libroot/posix/pthread/pthread_cond.c

@@ -56,6 +56,7 @@ pthread_cond_init(pthread_cond_t *_cond, const pthread_condattr_t *_attr)
 
 	cond->mutex = NULL;
 	cond->waiter_count = 0;
+	cond->event_counter = 0;
 	memcpy(&cond->attr, attr, sizeof(pthread_condattr));	
 
 	*_cond = cond;
@@ -99,9 +100,18 @@ cond_wait(pthread_cond *cond, pthread_mutex_t *_mutex, bigtime_t timeout)
 
 	cond->mutex = _mutex;
 	cond->waiter_count++;
+
+	int32 event = atomic_get(&cond->event_counter);
+
 	pthread_mutex_unlock(_mutex);
-	status = acquire_sem_etc(cond->sem, 1, timeout == B_INFINITE_TIMEOUT ? 0 : B_ABSOLUTE_TIMEOUT, timeout);
+
+	do {
+		status = acquire_sem_etc(cond->sem, 1,
+			timeout == B_INFINITE_TIMEOUT ? 0 : B_ABSOLUTE_TIMEOUT, timeout);
+	} while (status == B_OK && atomic_get(&cond->event_counter) == event);
+
 	pthread_mutex_lock(_mutex);
+
 	cond->waiter_count--;
 	// If there are no more waiters, we can change mutexes
 	if (cond->waiter_count == 0)
@@ -116,6 +126,7 @@ cond_signal(pthread_cond *cond, bool broadcast)
 	if (cond == NULL)
 		return B_BAD_VALUE;
 
+	atomic_add(&cond->event_counter, 1);
 	return release_sem_etc(cond->sem, broadcast ? cond->waiter_count : 1, 0);
 }
 

src/system/libroot/posix/pthread/pthread_private.h

@@ -21,6 +21,7 @@ typedef struct _pthread_cond {
 	sem_id			sem;
 	pthread_mutex_t	*mutex;
 	int32			waiter_count;
+	int32			event_counter;
 	pthread_condattr attr;
 } pthread_cond;