From 3fab00b46aad44e0375988fd61e13e900fa114a4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Sebastian=20Dr=C3=B6ge?= <sebastian@centricular.com>
Date: Tue, 13 Dec 2016 20:51:17 +0200
Subject: [PATCH] queue/queue2: Protect against spurious condition variable
 wakeups

Make sure that we only wake up when we have to flush, or when this
specific query was handled.

https://bugzilla.gnome.org/show_bug.cgi?id=776039
---
 plugins/elements/gstqueue.c  | 6 +++++-
 plugins/elements/gstqueue.h  | 1 +
 plugins/elements/gstqueue2.c | 6 +++++-
 plugins/elements/gstqueue2.h | 1 +
 4 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/plugins/elements/gstqueue.c b/plugins/elements/gstqueue.c
index 1f0c09cf15..c6d66ebf27 100644
--- a/plugins/elements/gstqueue.c
+++ b/plugins/elements/gstqueue.c
@@ -1045,7 +1045,10 @@ gst_queue_handle_sink_query (GstPad * pad, GstObject * parent, GstQuery * query)
         qitem.size = 0;
         gst_queue_array_push_tail_struct (queue->queue, &qitem);
         GST_QUEUE_SIGNAL_ADD (queue);
-        g_cond_wait (&queue->query_handled, &queue->qlock);
+        while (queue->srcresult == GST_FLOW_OK &&
+            queue->last_handled_query != query)
+          g_cond_wait (&queue->query_handled, &queue->qlock);
+        queue->last_handled_query = NULL;
         if (queue->srcresult != GST_FLOW_OK)
           goto out_flushing;
         res = queue->last_query;
@@ -1443,6 +1446,7 @@ next:
     ret = gst_pad_peer_query (queue->srcpad, query);
     GST_QUEUE_MUTEX_LOCK_CHECK (queue, out_flushing_query);
     queue->last_query = ret;
+    queue->last_handled_query = query;
     g_cond_signal (&queue->query_handled);
     GST_CAT_LOG_OBJECT (queue_dataflow, queue,
         "did query %p, return %d", query, queue->last_query);
diff --git a/plugins/elements/gstqueue.h b/plugins/elements/gstqueue.h
index 4c7491c33e..2a9cb3612a 100644
--- a/plugins/elements/gstqueue.h
+++ b/plugins/elements/gstqueue.h
@@ -135,6 +135,7 @@ struct _GstQueue {
 
   GCond query_handled;
   gboolean last_query;
+  GstQuery *last_handled_query;
 
   gboolean flush_on_eos; /* flush on EOS */
 };
diff --git a/plugins/elements/gstqueue2.c b/plugins/elements/gstqueue2.c
index 4c670a024b..3a878e0d1f 100644
--- a/plugins/elements/gstqueue2.c
+++ b/plugins/elements/gstqueue2.c
@@ -2642,7 +2642,10 @@ gst_queue2_handle_sink_query (GstPad * pad, GstObject * parent,
                 GST_QUEUE2_ITEM_TYPE_QUERY);
 
             STATUS (queue, queue->sinkpad, "wait for QUERY");
-            g_cond_wait (&queue->query_handled, &queue->qlock);
+            while (queue->sinkresult == GST_FLOW_OK &&
+                queue->last_handled_query != query)
+              g_cond_wait (&queue->query_handled, &queue->qlock);
+            queue->last_handled_query = NULL;
             if (queue->sinkresult != GST_FLOW_OK)
               goto out_flushing;
             res = queue->last_query;
@@ -2970,6 +2973,7 @@ next:
     GstQuery *query = GST_QUERY_CAST (data);
 
     GST_LOG_OBJECT (queue->srcpad, "Peering query %p", query);
+    queue->last_handled_query = query;
     queue->last_query = gst_pad_peer_query (queue->srcpad, query);
     GST_LOG_OBJECT (queue->srcpad, "Peered query");
     GST_CAT_LOG_OBJECT (queue_dataflow, queue,
diff --git a/plugins/elements/gstqueue2.h b/plugins/elements/gstqueue2.h
index a1b94a7865..34e3abaf6a 100644
--- a/plugins/elements/gstqueue2.h
+++ b/plugins/elements/gstqueue2.h
@@ -102,6 +102,7 @@ struct _GstQueue2
 
   GCond query_handled;
   gboolean last_query; /* result of last serialized query */
+  GstQuery *last_handled_query;
 
   GstQueue2Size cur_level;       /* currently in the queue */
   GstQueue2Size max_level;       /* max. amount of data allowed in the queue */