[gstreamer-bugs] [Bug 580716] New: race condition in gst_element_lost_state
bugzilla-daemon at bugzilla.gnome.org
Wed Apr 29 02:39:47 PDT 2009
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GStreamer | gstreamer (core) | Ver: git
Summary: race condition in gst_element_lost_state
Component: gstreamer (core)
AssignedTo: gstreamer-bugs at lists.sourceforge.net
ReportedBy: wingo at pobox.com
QAContact: gstreamer-bugs at lists.sourceforge.net
GNOME version: Unspecified
GNOME milestone: Unspecified
gst_element_lost_state has a race condition. Here's my understanding of how it
can happen, but Wim understands it better.
1. Have a pipeline in PLAYING
2. Set it to PAUSED
3. Send a flushing seek
After (2) the pipeline is asynchronously changing to paused. If the transition
completes successfully before the seek happens, there's no race; but if we seek
while the element has a GST_STATE_PENDING, the sink's call to
gst_element_lost_state will fail to post an async-start message.
The async-start message is needed to tell the pipeline to reset the base time
when the element goes PLAYING again. Loss of this message means that the
pipeline won't get a base_time reset.
We haven't seen this problem very much until now because most of our pipelines
run with the audio clock, which does not run in PAUSED, hence no need to
distribute a new base time. But if the clock does run in PAUSED, this problem
is fairly easy to hit.
The solution is to post async-start (though not state-changed) in
gst_element_lost_state if lost_state is called during an async state change.
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