Hi,

  I ran into a small race condition in the queue element today. I'm using a queue with just place for one buffer that's leaky downstream. Currently the queue does the following to detect/handle that it's full:

 while (gst_queue_is_filled (queue)) {
    GST_QUEUE_MUTEX_UNLOCK (queue);
    g_signal_emit (G_OBJECT (queue), gst_queue_signals[SIGNAL_OVERRUN], 0);
    GST_QUEUE_MUTEX_LOCK_CHECK (queue, out_flushing);

While emitting the signal, the queue is not locked. So the loop task can take buffers from the queue. With a one place buffer this means that when the queue is locked again, which triggers an assertion in the downstream leak code.

I'll attach a patch that fixes this by rechecking if we have a full queue when the queue is locked again. Note that this slightly changes the semantics of the overrun signal in case of a leaky queue.. Currently it means that the queue was full and a buffer *is* dropped, with this patch it means that a buffer *might* be dropped

Probably a better fix would be to only signal overrun after dropping (or just before blocking), but that requires more changes then i had time for.

  Sjoerd