discoverer: Drop new stream tags once preroll is done

This makes sure we do not touch the stream taglist once the pipeline has
been prerolled. Adding of stream tags happens in the pad event probe
which runs in a different thread from discoverer stream processing, so
modifying the tag list while discoverer might be processing it can
sometimes cause a crash.

https://bugzilla.gnome.org/show_bug.cgi?id=639778

diff --git a/gst-libs/gst/pbutils/gstdiscoverer.c b/gst-libs/gst/pbutils/gstdiscoverer.c
index 46e2cfb..8422d8f 100644 (file)
--- a/gst-libs/gst/pbutils/gstdiscoverer.c
+++ b/gst-libs/gst/pbutils/gstdiscoverer.c
@@ -393,10 +393,15 @@ _event_probe (GstPad * pad, GstEvent * event, PrivateStream * ps)
     gst_event_parse_tag (event, &tl);
     GST_DEBUG_OBJECT (pad, "tags %" GST_PTR_FORMAT, tl);
     DISCO_LOCK (ps->dc);
-    tmp = gst_tag_list_merge (ps->tags, tl, GST_TAG_MERGE_APPEND);
-    if (ps->tags)
-      gst_tag_list_free (ps->tags);
-    ps->tags = tmp;
+    /* If preroll is complete, drop these tags - the collected information is
+     * possibly already being processed and adding more tags would be racy */
+    if (G_LIKELY (ps->dc->priv->processing)) {
+      tmp = gst_tag_list_merge (ps->tags, tl, GST_TAG_MERGE_APPEND);
+      if (ps->tags)
+        gst_tag_list_free (ps->tags);
+      ps->tags = tmp;
+    } else
+      GST_DEBUG_OBJECT (ps->dc, "Dropping tags since preroll is done");
     DISCO_UNLOCK (ps->dc);
   }
 
@@ -1143,7 +1148,10 @@ discoverer_bus_cb (GstBus * bus, GstMessage * msg, GstDiscoverer * dc)
   if (dc->priv->processing) {
     if (handle_message (dc, msg)) {
       GST_DEBUG ("Stopping asynchronously");
+      /* Serialise with _event_probe() */
+      DISCO_LOCK (dc);
       dc->priv->processing = FALSE;
+      DISCO_UNLOCK (dc);
       discoverer_collect (dc);
       discoverer_cleanup (dc);
     }