gst-discoverer: use state changes instead of ASYNC_DONE.

And monitor no_more_pads.

With live sources such as rtsp, uridecodebin only creates its
child decodebins between PAUSED and PLAYING.

This means that the ASYNC_DONE it posts when getting NO_PREROLL
in its change_state method gets immediately propagated by the
GstBin parent class, as opposed to a situation where a
decodebin has been added to it already, and has posted ASYNC_START.

The proposed solution, instead of simply waiting for ASYNC_DONE,
and finishing prematurely in that case, waits for three conditions
to be true:

* the uridecodebin needs to have emitted no_more_pads
* its current state must be PAUSED if not live, PLAYING otherwise
* There must be no "pending subtitle pads", ie pads where we haven't
  received tags yet.

All these conditions are checked in the message handler, as we
post custom messages on it when we get subtitle tags or no_more_pads.

https://bugzilla.gnome.org/show_bug.cgi?id=783257

gst-libs/gst/pbutils/gstdiscoverer.c

@@ -95,9 +95,6 @@ struct _GstDiscovererPrivate
   /* TRUE if discoverer has been started */
   gboolean running;
 
-  /* TRUE if ASYNC_DONE has been received (need to check for subtitle tags) */
-  gboolean async_done;
-
   /* current items */
   GstDiscovererInfo *current_info;
   GError *current_error;
@@ -109,6 +106,12 @@ struct _GstDiscovererPrivate
   /* List of these sinks and their handler IDs (to remove the probe) */
   guint pending_subtitle_pads;
 
+  /* Whether we received no_more_pads */
+  gboolean no_more_pads;
+
+  GstState target_state;
+  GstState current_state;
+
   /* Global elements */
   GstBin *pipeline;
   GstElement *uridecodebin;
@@ -127,6 +130,7 @@ struct _GstDiscovererPrivate
   /* Handler ids for various callbacks */
   gulong pad_added_id;
   gulong pad_remove_id;
+  gulong no_more_pads_id;
   gulong source_chg_id;
   gulong element_added_id;
   gulong bus_cb_id;
@@ -182,6 +186,8 @@ static void uridecodebin_pad_added_cb (GstElement * uridecodebin, GstPad * pad,
     GstDiscoverer * dc);
 static void uridecodebin_pad_removed_cb (GstElement * uridecodebin,
     GstPad * pad, GstDiscoverer * dc);
+static void uridecodebin_no_more_pads_cb (GstElement * uridecodebin,
+    GstDiscoverer * dc);
 static void uridecodebin_source_changed_cb (GstElement * uridecodebin,
     GParamSpec * pspec, GstDiscoverer * dc);
 
@@ -307,12 +313,15 @@ gst_discoverer_init (GstDiscoverer * dc)
 
   dc->priv->timeout = DEFAULT_PROP_TIMEOUT;
   dc->priv->async = FALSE;
-  dc->priv->async_done = FALSE;
 
   g_mutex_init (&dc->priv->lock);
 
   dc->priv->pending_subtitle_pads = 0;
 
+  dc->priv->current_state = GST_STATE_NULL;
+  dc->priv->target_state = GST_STATE_NULL;
+  dc->priv->no_more_pads = FALSE;
+
   GST_LOG ("Creating pipeline");
   dc->priv->pipeline = (GstBin *) gst_pipeline_new ("Discoverer");
   GST_LOG_OBJECT (dc, "Creating uridecodebin");
@@ -331,6 +340,9 @@ gst_discoverer_init (GstDiscoverer * dc)
   dc->priv->pad_remove_id =
       g_signal_connect_object (dc->priv->uridecodebin, "pad-removed",
       G_CALLBACK (uridecodebin_pad_removed_cb), dc, 0);
+  dc->priv->no_more_pads_id =
+      g_signal_connect_object (dc->priv->uridecodebin, "no-more-pads",
+      G_CALLBACK (uridecodebin_no_more_pads_cb), dc, 0);
   dc->priv->source_chg_id =
       g_signal_connect_object (dc->priv->uridecodebin, "notify::source",
       G_CALLBACK (uridecodebin_source_changed_cb), dc, 0);
@@ -392,6 +404,7 @@ gst_discoverer_dispose (GObject * obj)
     /* Workaround for bug #118536 */
     DISCONNECT_SIGNAL (dc->priv->uridecodebin, dc->priv->pad_added_id);
     DISCONNECT_SIGNAL (dc->priv->uridecodebin, dc->priv->pad_remove_id);
+    DISCONNECT_SIGNAL (dc->priv->uridecodebin, dc->priv->no_more_pads_id);
     DISCONNECT_SIGNAL (dc->priv->uridecodebin, dc->priv->source_chg_id);
     DISCONNECT_SIGNAL (dc->priv->uridecodebin, dc->priv->element_added_id);
     DISCONNECT_SIGNAL (dc->priv->bus, dc->priv->bus_cb_id);
@@ -551,6 +564,7 @@ is_subtitle_caps (const GstCaps * caps)
 static GstPadProbeReturn
 got_subtitle_data (GstPad * pad, GstPadProbeInfo * info, GstDiscoverer * dc)
 {
+  GstMessage *msg;
 
   if (!(GST_IS_BUFFER (info->data) || (GST_IS_EVENT (info->data)
               && (GST_EVENT_TYPE ((GstEvent *) info->data) == GST_EVENT_GAP
@@ -563,11 +577,10 @@ got_subtitle_data (GstPad * pad, GstPadProbeInfo * info, GstDiscoverer * dc)
 
   dc->priv->pending_subtitle_pads--;
 
-  if (dc->priv->pending_subtitle_pads == 0) {
+  msg = gst_message_new_application (NULL,
-    GstMessage *msg = gst_message_new_application (NULL,
       gst_structure_new_empty ("DiscovererDone"));
   gst_element_post_message ((GstElement *) dc->priv->pipeline, msg);
-  }
+
   DISCO_UNLOCK (dc);
 
   return GST_PAD_PROBE_REMOVE;
@@ -669,6 +682,18 @@ error:
   return;
 }
 
+static void
+uridecodebin_no_more_pads_cb (GstElement * uridecodebin, GstDiscoverer * dc)
+{
+  GstMessage *msg = gst_message_new_application (NULL,
+      gst_structure_new_empty ("DiscovererDone"));
+
+  DISCO_LOCK (dc);
+  dc->priv->no_more_pads = TRUE;
+  gst_element_post_message ((GstElement *) dc->priv->pipeline, msg);
+  DISCO_UNLOCK (dc);
+}
+
 static void
 uridecodebin_pad_removed_cb (GstElement * uridecodebin, GstPad * pad,
     GstDiscoverer * dc)
@@ -1439,33 +1464,44 @@ handle_message (GstDiscoverer * dc, GstMessage * msg)
       break;
 
     case GST_MESSAGE_APPLICATION:{
-      const gchar *name;
+      const gchar *name =
-      gboolean async_done;
+          gst_structure_get_name (gst_message_get_structure (msg));
-      name = gst_structure_get_name (gst_message_get_structure (msg));
+
-      /* Maybe ASYNC_DONE is received & we're just waiting for subtitle tags */
+      if (g_strcmp0 (name, "DiscovererDone"))
+        break;
+
+      /* Maybe we already reached the target state, and all we're waiting for
+       * is either the subtitle tags or no_more_pads
+       */
       DISCO_LOCK (dc);
-      async_done = dc->priv->async_done;
+      if (dc->priv->pending_subtitle_pads == 0)
+        done = dc->priv->no_more_pads
+            && dc->priv->target_state == dc->priv->current_state;
       DISCO_UNLOCK (dc);
-      if (g_str_equal (name, "DiscovererDone") && async_done) {
+
-        done = TRUE;
+      if (done)
-        dump_name = "gst-discoverer-async-done-subtitle";
+        dump_name = "gst-discoverer-application-message";
     }
       break;
-    }
 
-    case GST_MESSAGE_ASYNC_DONE:
+    case GST_MESSAGE_STATE_CHANGED:{
+      GstState old, new, pending;
+
+      gst_message_parse_state_changed (msg, &old, &new, &pending);
       if (GST_MESSAGE_SRC (msg) == (GstObject *) dc->priv->pipeline) {
-        GST_DEBUG ("Finished changing state asynchronously");
         DISCO_LOCK (dc);
-        if (dc->priv->pending_subtitle_pads == 0) {
+        dc->priv->current_state = new;
-          done = TRUE;
-          dump_name = "gst-discoverer-async-done";
-        } else {
-          /* Remember that ASYNC_DONE has been received, wait for subtitles */
-          dc->priv->async_done = TRUE;
-        }
-        DISCO_UNLOCK (dc);
 
+        if (dc->priv->pending_subtitle_pads == 0)
+          done = dc->priv->no_more_pads
+              && dc->priv->target_state == dc->priv->current_state;
+        /* Else we should get unblocked in GST_MESSAGE_APPLICATION */
+
+        DISCO_UNLOCK (dc);
+      }
+
+      if (done)
+        dump_name = "gst-discoverer-target-state";
     }
       break;
 
@@ -1602,20 +1638,25 @@ _setup_locked (GstDiscoverer * dc)
 
   dc->priv->processing = TRUE;
 
+  dc->priv->target_state = GST_STATE_PAUSED;
+
   /* set pipeline to PAUSED */
   DISCO_UNLOCK (dc);
   GST_DEBUG ("Setting pipeline to PAUSED");
   ret =
       gst_element_set_state ((GstElement *) dc->priv->pipeline,
-      GST_STATE_PAUSED);
+      dc->priv->target_state);
+
   if (ret == GST_STATE_CHANGE_NO_PREROLL) {
     GST_DEBUG ("Source is live, switching to PLAYING");
+    dc->priv->target_state = GST_STATE_PLAYING;
     ret =
         gst_element_set_state ((GstElement *) dc->priv->pipeline,
-        GST_STATE_PLAYING);
+        dc->priv->target_state);
   }
   DISCO_LOCK (dc);
 
+
   GST_DEBUG_OBJECT (dc, "Pipeline going to PAUSED : %s",
       gst_element_state_change_return_get_name (ret));
 }
@@ -1649,7 +1690,10 @@ discoverer_cleanup (GstDiscoverer * dc)
   dc->priv->current_info = NULL;
 
   dc->priv->pending_subtitle_pads = 0;
-  dc->priv->async_done = FALSE;
+
+  dc->priv->current_state = GST_STATE_NULL;
+  dc->priv->target_state = GST_STATE_NULL;
+  dc->priv->no_more_pads = FALSE;
 
   /* Try popping the next uri */
   if (dc->priv->async) {