[mythtv-commits] Ticket #9780: Network Remote Control Interface breaks DVD playback

[MythTV]

#9780: Network Remote Control Interface breaks DVD playback
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 Reporter:  dave@…                      |          Owner:  markk
     Type:  Bug Report - Hang/Deadlock  |         Status:  infoneeded_new
 Priority:  major                       |      Milestone:  unknown
Component:  MythTV - DVD Playback       |        Version:  0.24-fixes
 Severity:  medium                      |     Resolution:
 Keywords:                              |  Ticket locked:  0
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Comment (by Github):

 DVDRingBuffer: Unlock the ring buffer when waiting on state changes.

 The DVD ringbuffer does not use the read ahead thread and hence holding
 the writelock during safe_read is not strictly necessary (see
 RingBuffer::ReadPriv). DVDRingBuffer::safe_read can also hold that lock
 for tens of seconds when, for example, displaying a still frame (the dvd
 device simply returns specific events, but not data, until it is told to
 skip the still frame).

 Under normal operation this is not a problem but events received from
 external sources (such as network control) can trigger code that tries
 to lock the ringbuffer from the main UI thread (e.g.
 RingBuffer::GetFilename). The lock is not obtained, event processing in
 the main thread is blocked and the wait state in the ringbuffer thread
 is not cleared - and the frontend deadlocks as a result.

 The solution is to release the lock while sleeping within
 DVDRingBuffer::safe_read to allow other threads to obtain the lock
 temporarily. I've also added a warning message should the read ahead
 thread be running in the DVD ringbuffer.

 Refs #9780
  Branch:    master
  Changeset: fd5e33a69b630aa9c0b94a8c2dd7693f02726316

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Ticket URL: <http://code.mythtv.org/trac/ticket/9780#comment:5>
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