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multiqueue: only block serialized query when it's safe

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We must be certain that we don't cause a deadlock when blocking the serialized
queries. One such deadlock can happen when we are buffering and downstream is
blocked in preroll and a serialized query arrives. Downstream will not unblock
(and allow our query to execute) until we complete buffering and buffering will
not complete until we can answer the query..

https://bugzilla.gnome.org/show_bug.cgi?id=702840
This commit is contained in:
Sebastian Dröge 2013-07-16 11:36:50 +02:00
parent c279bdb663
commit 0dc232e114
1 changed files with 22 additions and 9 deletions
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31
plugins/elements/gstmultiqueue.c
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@ -1614,17 +1614,30 @@ gst_multi_queue_sink_query (GstPad * pad, GstObject * parent, GstQuery * query)
if (sq->srcresult != GST_FLOW_OK)
goto out_flushing;
/* Get an unique incrementing id. */
curid = g_atomic_int_add ((gint *) & mq->counter, 1);
/* serialized events go in the queue. We need to be certain that we
* don't cause deadlocks waiting for the query return value. We check if
* the queue is empty (nothing is blocking downstream and the query can
* be pushed for sure) or we are not buffering. If we are buffering,
* the pipeline waits to unblock downstream until our queue fills up
* completely, which can not happen if we block on the query..
* Therefore we only potentially block when we are not buffering. */
if (!mq->use_buffering || gst_data_queue_is_empty (sq->queue)) {
/* Get an unique incrementing id. */
curid = g_atomic_int_add ((gint *) & mq->counter, 1);
item = gst_multi_queue_mo_item_new ((GstMiniObject *) query, curid);
item = gst_multi_queue_mo_item_new ((GstMiniObject *) query, curid);
GST_DEBUG_OBJECT (mq,
"SingleQueue %d : Enqueuing query %p of type %s with id %d",
sq->id, query, GST_QUERY_TYPE_NAME (query), curid);
res = gst_data_queue_push (sq->queue, (GstDataQueueItem *) item);
g_cond_wait (&sq->query_handled, &mq->qlock);
res = sq->last_query;
GST_DEBUG_OBJECT (mq,
"SingleQueue %d : Enqueuing query %p of type %s with id %d",
sq->id, query, GST_QUERY_TYPE_NAME (query), curid);
res = gst_data_queue_push (sq->queue, (GstDataQueueItem *) item);
g_cond_wait (&sq->query_handled, &mq->qlock);
res = sq->last_query;
} else {
GST_DEBUG_OBJECT (mq, "refusing query, we are buffering and the "
"queue is not empty");
res = FALSE;
}
GST_MULTI_QUEUE_MUTEX_UNLOCK (mq);
} else {
/* default handling */