[mythtv-commits] Ticket #1716: Decoder locking in NuppelVideoPlayer

[MythTV]

#1716: Decoder locking in NuppelVideoPlayer
--------------------------------+-------------------------------------------
 Reporter:  dm at prolingua.co.uk  |       Owner:  ijr
     Type:  defect              |      Status:  new
 Priority:  minor               |   Milestone:     
Component:  mythtv              |     Version:     
 Severity:  medium              |  
--------------------------------+-------------------------------------------
 I have noticed a number of crashes in the frontend when changing channels
 but hadn't been able to pin it down to anything until it happened last
 week when I was running under gdb.  I managed to get a backtrace
 (attached) but I've since investigated it a bit further.  The crash
 happened in a function called from NuppelVideoPlayer::SetWatchingRecording
 and it appeared that the decoder object had changed under the feet of the
 function.

 {{{
 (gdb) up
 #5  0x00b25d04 in NuppelVideoPlayer::SetWatchingRecording (this=0x8e986b8,
     mode=false) at NuppelVideoPlayer.cpp:338
 338             GetDecoder()->setWatchingRecording(mode);
 (gdb) print decoder
 $22 = (class DecoderBase *) 0xa96028f0
 (gdb) down
 #4  0x00b5e94e in DecoderBase::setWatchingRecording (this=0xaa31a4d8,
     mode=false) at decoderbase.cpp:95
 95              SyncPositionMap();
 (gdb) print this
 $23 = (DecoderBase * const) 0xaa31a4d8
 }}}

 It seems that NVP creates a new thread that at some point calls SetDecoder
 to update the decoder but there is no locking to ensure that another
 thread is not using the decoder object.  I wanted to confirm that there
 really was a problem so the attached patch contains calls to sleep and
 printf to demonstrate the problem.  There's also the beginnings of a fix
 although someone who knows the code better may well come up with something
 better.  There may be other functions that need to lock the decoder
 object.

 David.

-- 
Ticket URL: <http://cvs.mythtv.org/trac/ticket/1716>
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