BLI_threads Queue: add `BLI_thread_queue_is_empty()`.

Avoids counting the whole queue when we only want to check whether it is empty or not!

source/blender/blenlib/BLI_threads.h

@@ -175,6 +175,7 @@ void BLI_thread_queue_push(ThreadQueue *queue, void *work);
 void *BLI_thread_queue_pop(ThreadQueue *queue);
 void *BLI_thread_queue_pop_timeout(ThreadQueue *queue, int ms);
 int BLI_thread_queue_size(ThreadQueue *queue);
+bool BLI_thread_queue_is_empty(ThreadQueue *queue);
 
 void BLI_thread_queue_wait_finish(ThreadQueue *queue);
 void BLI_thread_queue_nowait(ThreadQueue *queue);

source/blender/blenlib/intern/threads.c

@@ -777,6 +777,17 @@ int BLI_thread_queue_size(ThreadQueue *queue)
 	return size;
 }
 
+bool BLI_thread_queue_is_empty(ThreadQueue *queue)
+{
+	bool is_empty;
+
+	pthread_mutex_lock(&queue->mutex);
+	is_empty = BLI_gsqueue_is_empty(queue->queue);
+	pthread_mutex_unlock(&queue->mutex);
+
+	return is_empty;
+}
+
 void BLI_thread_queue_nowait(ThreadQueue *queue)
 {
 	pthread_mutex_lock(&queue->mutex);