[gstreamer-bugs] [Bug 593983] New: dead lock in rtp session

[GStreamer (bugzilla.gnome.org)]

http://bugzilla.gnome.org/show_bug.cgi?id=593983

           Summary: dead lock in rtp session
    Classification: Desktop
           Product: GStreamer
           Version: git
        OS/Version: Linux
            Status: UNCONFIRMED
          Severity: critical
          Priority: Normal
         Component: gst-plugins-bad
        AssignedTo: gstreamer-bugs at lists.sourceforge.net
        ReportedBy: csxnju at sogou.com
         QAContact: gstreamer-bugs at lists.sourceforge.net
      GNOME target: ---
     GNOME version: ---


--- Comment #0 from ric <csxnju at sogou.com> 2009-09-03 02:50:05 UTC ---
There is dead lock in gstrtpsession.c and rtpsession.c.
This will influence five thread, two rtcp receiving threads, two rtcp sending
threads and one control thread.

The dead lock will occur under this situation,
rtcp_thread() --> GST_RTP_SESSION_LOCK (rtpsession) -->
rtp_session_next_timeout (rtpsession->priv->session, current_time) -->
RTP_SESSION_LOCK (sess)

or 
rtcp_thread() --> GST_RTP_SESSION_LOCK (rtpsession) --> rtp_session_on_timeout
(rtpsession->priv->session, current_time, ntpnstime) --> RTP_SESSION_LOCK
(sess)

But the receiving sender's rtcp thread do something like this,
rtp_session_process_rtcp() --> RTP_SESSION_LOCK (sess) -->
rtp_session_process_bye (sess, &packet, &arrival) -->
sess->callbacks.reconsider (sess, sess->reconsider_user_data)
[gst_rtp_session_reconsider (RTPSession * sess, gpointer user_data) ] -->
GST_RTP_SESSION_LOCK (rtpsession)

see, one thread lock GST_RTP_SESSION_LOCK (rtpsession) first, then try to lock
RTP_SESSION_LOCK (sess); but another thread lock RTP_SESSION_LOCK (sess) first,
then try to lock GST_RTP_SESSION_LOCK (rtpsession); this will causes dead lock
sooner or later. And I have encountered such a situation.

The solutions,
1. This is a simple one. Add another lock in "struct _RTPSession" called
inter_lock. Above five thread can't acquire their desired lock unless they
acquire this inter_lock first. This will change the following function,
rtcp_thread(), stop_rtcp_thread(), rtp_session_init(), rtp_session_finalize(),
rtp_session_process_rtcp()

2. This is a theoretic one. Change the calling logic of this five threads. This
is a big change and it needs more careful thinkings. I have not done this.

Tks.

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