[gstreamer-bugs] [Bug 547352] New: race condition with GstPadBufferAllocFunction

[GStreamer (bugzilla.gnome.org)]

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  GStreamer | gstreamer (core) | Ver: HEAD CVS
           Summary: race condition with GstPadBufferAllocFunction
           Product: GStreamer
           Version: HEAD CVS
          Platform: Other
        OS/Version: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: Normal
         Component: gstreamer (core)
        AssignedTo: gstreamer-bugs at lists.sourceforge.net
        ReportedBy: ivanohe at abacom.com
         QAContact: gstreamer-bugs at lists.sourceforge.net
     GNOME version: Unspecified
   GNOME milestone: Unspecified


There is a race condition when gstreamer call an element
GstPadBufferAllocFunction. There is a possibility that the element is doing a
state change from paused to ready at the same time.

I got the problem in my older version of gstreamer, but I see the problem is
still there in head.

I can see this with this pipeline and some modif in the code

gst-launch videotestsrc num-buffers=2000 !  videoscale ! "video/x-raw-yuv,
format=(fourcc)YUY2, width=(int)320, height=(int)240, framerate=(fraction)30/1"
!  fakesink

And doing ctrl-c.

The modif I made to see the problem occur are in gstbasetransform. I just set
flags and some g_usleep to make the problem occur more often. I can see that 
gst_base_transform_activate is called (and code after the STREAM_LOCK/UNLOCK
run while at the same time, some code is running on the same element in
gst_base_transform_buffer_alloc.

(on my older gstreamer, this cause a problem with the variable
trans->have_same_caps being changed and causing a gwarning since I run my app
with --gst-fatal-warnings).

The fix is simple and consist of putting a stream lock in gstpad.c

GST_PAD_STREAM_LOCK (pad);
   ret = bufferallocfunc (pad, offset, size, caps, buf);
GST_PAD_STREAM_UNLOCK (pad);

This seems to work correct with my application (and my not up to date
gstreamer). However, I am wondering if this can cause some problem.


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