[FFmpeg-trac] #773(avcodec:new): Decoding H.264 gets stuck with Win XP, w32threads, and custom AVCodecContext.get_buffer

[FFmpeg]

#773: Decoding H.264 gets stuck with Win XP, w32threads, and custom
AVCodecContext.get_buffer
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             Reporter:  andreasg  |                    Owner:
                 Type:  defect    |                   Status:  new
             Priority:  normal    |                Component:  avcodec
              Version:  0.9       |               Resolution:
             Keywords:            |               Blocked By:
             Blocking:            |  Reproduced by developer:  0
Analyzed by developer:  0         |
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Comment (by reimar):

 I don't know who implemented that code and based on what, but it is just
 broken.
 There are gems like this I can't see what purpose they would serve:
     pthread_mutex_lock(&win32_cond->mtx_broadcast);
     pthread_mutex_unlock(&win32_cond->mtx_broadcast);
 However more serious the waiter_count is decremented at the wrong place.
 If you look at pthread_cond_wait the WaitForSingleObject is outside of all
 locks.
 This means if somehow all threads leaving that function would be delayed
 for some time, you could use pthread_cond_signal to arbitrarily increase
 the value of the semaphore, even though there was never more than one
 thread waiting.
 As a consequence pthread_cond_wait would never be waiting anymore after
 that and from there it is only downhill.
 I can't really (easily at least) explain a hang with that though, there
 should at least some other things go wrong first.
 The method presented here:
 http://research.microsoft.com/pubs/64242/implementingcvs.pdf looks like it
 might at least work, even if performance is not exactly good.
 Seems their hope of people not repeating mistakes was not exactly
 justified though.

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Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/773#comment:1>
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