queue: Fix handling of min-threshold and serialized queries

Only consider the queue empty if the minimum thresholds
are not reached and data is at the queue head. Otherwise
we would block forever on serialized queries.

This also makes sending of serialized events, like caps, happen
faster and potentially improves negotiation performance.

Fixes bug #679458.

diff --git a/plugins/elements/gstqueue.c b/plugins/elements/gstqueue.c
index e116aa2..52475f9 100644 (file)
--- a/plugins/elements/gstqueue.c
+++ b/plugins/elements/gstqueue.c
@@ -821,9 +821,19 @@ out_flushing:
 static gboolean
 gst_queue_is_empty (GstQueue * queue)
 {
+  GstMiniObject *head;
+
   if (queue->queue->length == 0)
     return TRUE;
 
+  /* Only consider the queue empty if the minimum thresholds
+   * are not reached and data is at the queue head. Otherwise
+   * we would block forever on serialized queries.
+   */
+  head = queue->queue->array[queue->queue->head];
+  if (!GST_IS_BUFFER (head) && !GST_IS_BUFFER_LIST (head))
+    return FALSE;
+
   /* It is possible that a max size is reached before all min thresholds are.
    * Therefore, only consider it empty if it is not filled. */
   return ((queue->min_threshold.buffers > 0 &&