From ae58f7d771998539087a975b2b8a3942f9b7d516 Mon Sep 17 00:00:00 2001
From: Ludvig Rappe <ludvigr@axis.com>
Date: Tue, 26 May 2020 15:31:22 +0200
Subject: [PATCH] rtsp-media: wait for all GstRTSPStreamBlocking messages

Make sure rtsp-media have received a GstRTSPStreamBlocking message from
each active stream when checking if all streams are blocked.

Without this change there will be a race condition when using two or
more streams and rtsp-media receives a GstRTSPStreamBlocking message
from one of the streams. This is because rtsp-media then checks if all
streams are blocked by calling gst_rtsp_stream_is_blocking() for each
stream. This function call returns TRUE if the stream has sent a
GstRTSPStreamBlocking message, however, rtsp-media may have yet to
receive this message. This would then result in that rtsp-media
erroneously thinks it is blocking all streams which could result in
rtsp-media changing state, from PREPARING to PREPARED. In the case of a
preroll, this could result in that rtsp-media thinks that the pipeline
is prerolled even though that might not be the case.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-rtsp-server/-/merge_requests/124>
---
 gst/rtsp-server/rtsp-media.c | 32 +++++++++++++++++++++++++++++++-
 1 file changed, 31 insertions(+), 1 deletion(-)

diff --git a/gst/rtsp-server/rtsp-media.c b/gst/rtsp-server/rtsp-media.c
index 1493ecc67d..b17ced155f 100644
--- a/gst/rtsp-server/rtsp-media.c
+++ b/gst/rtsp-server/rtsp-media.c
@@ -114,6 +114,7 @@ struct _GstRTSPMediaPrivate
   gboolean blocked;
   GstRTSPTransportMode transport_mode;
   gboolean stop_on_disconnect;
+  guint blocking_msg_received;
 
   GstElement *element;
   GRecMutex state_lock;         /* locking order: state lock, lock */
@@ -493,6 +494,7 @@ gst_rtsp_media_init (GstRTSPMedia * media)
   priv->do_rate_control = DEFAULT_DO_RATE_CONTROL;
   priv->dscp_qos = DEFAULT_DSCP_QOS;
   priv->expected_async_done = FALSE;
+  priv->blocking_msg_received = 0;
 }
 
 static void
@@ -2739,6 +2741,9 @@ media_streams_set_blocked (GstRTSPMedia * media, gboolean blocked)
   GST_DEBUG ("media %p set blocked %d", media, blocked);
   priv->blocked = blocked;
   g_ptr_array_foreach (priv->streams, (GFunc) stream_update_blocked, media);
+
+  if (!blocked)
+    priv->blocking_msg_received = 0;
 }
 
 static void
@@ -2757,6 +2762,7 @@ media_unblock (GstRTSPMedia * media)
    * streams that are complete */
   priv->blocked = FALSE;
   g_ptr_array_foreach (priv->streams, (GFunc) stream_unblock, media);
+  priv->blocking_msg_received = 0;
 }
 
 static void
@@ -3140,6 +3146,25 @@ set_target_state (GstRTSPMedia * media, GstState state, gboolean do_state)
   return ret;
 }
 
+static void
+stream_collect_active (GstRTSPStream * stream, guint * active_streams)
+{
+  if (gst_rtsp_stream_is_complete (stream))
+    (*active_streams)++;
+}
+
+static guint
+nbr_active_streams (GstRTSPMedia * media)
+{
+  guint ret = 0;
+
+  g_ptr_array_foreach (media->priv->streams, (GFunc) stream_collect_active,
+      &ret);
+
+  return ret;
+}
+
+ /* called with state-lock */
 /* called with state-lock */
 static gboolean
 default_handle_message (GstRTSPMedia * media, GstMessage * message)
@@ -3247,8 +3272,11 @@ default_handle_message (GstRTSPMedia * media, GstMessage * message)
       s = gst_message_get_structure (message);
       if (gst_structure_has_name (s, "GstRTSPStreamBlocking")) {
         GST_DEBUG ("media received blocking message");
+        priv->blocking_msg_received++;
         if (priv->blocked && media_streams_blocking (media) &&
-            priv->no_more_pads_pending == 0) {
+            priv->no_more_pads_pending == 0 &&
+            (priv->blocking_msg_received == nbr_active_streams (media) ||
+                priv->blocking_msg_received == priv->streams->len)) {
           GST_DEBUG_OBJECT (GST_MESSAGE_SRC (message), "media is blocking");
           g_mutex_lock (&priv->lock);
           collect_media_stats (media);
@@ -3256,6 +3284,8 @@ default_handle_message (GstRTSPMedia * media, GstMessage * message)
 
           if (priv->status == GST_RTSP_MEDIA_STATUS_PREPARING)
             gst_rtsp_media_set_status (media, GST_RTSP_MEDIA_STATUS_PREPARED);
+
+          priv->blocking_msg_received = 0;
         }
       }
       break;