[mythtv-commits] Ticket #11410: backend hang: mpeg recordings with vbi sometimes hang at finish

MythTV noreply at mythtv.org
Tue Feb 19 06:01:43 UTC 2013


#11410: backend hang: mpeg recordings with vbi sometimes hang at finish
----------------------------------------+----------------------------
 Reporter:  rd.mora@…                   |          Owner:  danielk
     Type:  Bug Report - Hang/Deadlock  |         Status:  new
 Priority:  minor                       |      Milestone:  unknown
Component:  MythTV - Recording          |        Version:  0.26-fixes
 Severity:  medium                      |     Resolution:
 Keywords:  mpegrecorder vbi hang       |  Ticket locked:  0
----------------------------------------+----------------------------
Changes (by wagnerrp):

 * priority:  major => minor
 * severity:  high => medium


Old description:

> Witnessed mpeg recordings with vbi occasionally hanging at finish
> (causing the backend in general to hang) and under gdb saw:
>
> Thread 3 (Thread 0x7fbd69ffb700 (LWP 8322)):
> #0  0x00007fbd8bf7a61c in pthread_cond_wait@@GLIBC_2.3.2 () from
> /lib64/libpthread.so.0
> #1  0x00007fbd8c207699 in QWaitCondition::wait(QMutex*, unsigned long) ()
> from /usr/lib64/libQtCore.so.4
> #2  0x00007fbd8c206824 in QThread::wait(unsigned long) () from
> /usr/lib64/libQtCore.so.4
> #3  0x00007fbd9293f9bc in MpegRecorder::run (this=0x7fbd6c224d00) at
> mpegrecorder.cpp:1124
> #4  0x00007fbd91b9ec07 in MThread::run (this=0x7fbd6c9f35a0) at
> mthread.cpp:319
> #5  0x00007fbd8c206775 in ?? () from /usr/lib64/libQtCore.so.4
> #6  0x00007fbd8bf767b6 in start_thread () from /lib64/libpthread.so.0
> #7  0x00007fbd8b5399cd in clone () from /lib64/libc.so.6
> #8  0x0000000000000000 in ?? ()
>
> Thread 2 (Thread 0x7fbd697fa700 (LWP 8323)):
> #0  0x00007fbd8bf7d76d in read () from /lib64/libpthread.so.0
> #1  0x00007fbd9292263c in V4LRecorder::RunVBIDevice (this=0x7fbd6c224d00)
> at v4lrecorder.cpp:308
> #2  0x00007fbd9291aeb2 in VBIThread::run (this=0x1111d40) at
> v4lrecorder.h:82
> #3  0x00007fbd8c206775 in ?? () from /usr/lib64/libQtCore.so.4
> #4  0x00007fbd8bf767b6 in start_thread () from /lib64/libpthread.so.0
> #5  0x00007fbd8b5399cd in clone () from /lib64/libc.so.6
> #6  0x0000000000000000 in ?? ()
>
> Looking at mpegrecorder.cpp:
>
> 1113        LOG(VB_RECORD, LOG_INFO, LOC + "run finishing up");
> 1114
> 1115        StopEncoding();
> 1116
> 1117        {
> 1118            QMutexLocker locker(&pauseLock);
> 1119            request_helper = false;
> 1120        }
> 1121
> 1122        if (vbi_thread)
> 1123        {
> 1124            vbi_thread->wait();
> 1125            delete vbi_thread;
> 1126            vbi_thread = NULL;
> 1127            CloseVBIDevice();
> 1128        }
> 1129
> 1130        FinishRecording();
>
> Line 1119 signals the vbi thread to stop reading and exit, however, the
> encoder is signaled to stop *before* this on line 1115.  Thus it is
> possible for the vbi thread to return from select, try to read data from
> the vbi fd and then block on the read because the vbi fd is no longer
> returning data (has been stopped).
>
> Simple solution seems to be to swap the order, i.e. signal vbi thread to
> stop reading before stopping the encoder.  I have no idea if there are
> any unforeseen consequences to this though..... comments?
>
> diff --git a/mythtv/libs/libmythtv/mpegrecorder.cpp
> b/mythtv/libs/libmythtv/mpegrecorder.cpp
> index b158513..35644af 100644
> --- a/mythtv/libs/libmythtv/mpegrecorder.cpp
> +++ b/mythtv/libs/libmythtv/mpegrecorder.cpp
> @@ -1112,13 +1112,13 @@ void MpegRecorder::run(void)
>
>      LOG(VB_RECORD, LOG_INFO, LOC + "run finishing up");
>
> -    StopEncoding();
> -
>      {
>          QMutexLocker locker(&pauseLock);
>          request_helper = false;
>      }
>
> +    StopEncoding();
> +
>      if (vbi_thread)
>      {
>          vbi_thread->wait();
> lines 1-20/20 (END)

New description:

 Witnessed mpeg recordings with vbi occasionally hanging at finish (causing
 the backend in general to hang) and under gdb saw:

 {{{
 Thread 3 (Thread 0x7fbd69ffb700 (LWP 8322)):
 #0  0x00007fbd8bf7a61c in pthread_cond_wait@@GLIBC_2.3.2 () from
 /lib64/libpthread.so.0
 #1  0x00007fbd8c207699 in QWaitCondition::wait(QMutex*, unsigned long) ()
 from /usr/lib64/libQtCore.so.4
 #2  0x00007fbd8c206824 in QThread::wait(unsigned long) () from
 /usr/lib64/libQtCore.so.4
 #3  0x00007fbd9293f9bc in MpegRecorder::run (this=0x7fbd6c224d00) at
 mpegrecorder.cpp:1124
 #4  0x00007fbd91b9ec07 in MThread::run (this=0x7fbd6c9f35a0) at
 mthread.cpp:319
 #5  0x00007fbd8c206775 in ?? () from /usr/lib64/libQtCore.so.4
 #6  0x00007fbd8bf767b6 in start_thread () from /lib64/libpthread.so.0
 #7  0x00007fbd8b5399cd in clone () from /lib64/libc.so.6
 #8  0x0000000000000000 in ?? ()

 Thread 2 (Thread 0x7fbd697fa700 (LWP 8323)):
 #0  0x00007fbd8bf7d76d in read () from /lib64/libpthread.so.0
 #1  0x00007fbd9292263c in V4LRecorder::RunVBIDevice (this=0x7fbd6c224d00)
 at v4lrecorder.cpp:308
 #2  0x00007fbd9291aeb2 in VBIThread::run (this=0x1111d40) at
 v4lrecorder.h:82
 #3  0x00007fbd8c206775 in ?? () from /usr/lib64/libQtCore.so.4
 #4  0x00007fbd8bf767b6 in start_thread () from /lib64/libpthread.so.0
 #5  0x00007fbd8b5399cd in clone () from /lib64/libc.so.6
 #6  0x0000000000000000 in ?? ()
 }}}

 Looking at mpegrecorder.cpp:

 {{{
 1113        LOG(VB_RECORD, LOG_INFO, LOC + "run finishing up");
 1114
 1115        StopEncoding();
 1116
 1117        {
 1118            QMutexLocker locker(&pauseLock);
 1119            request_helper = false;
 1120        }
 1121
 1122        if (vbi_thread)
 1123        {
 1124            vbi_thread->wait();
 1125            delete vbi_thread;
 1126            vbi_thread = NULL;
 1127            CloseVBIDevice();
 1128        }
 1129
 1130        FinishRecording();
 }}}

 Line 1119 signals the vbi thread to stop reading and exit, however, the
 encoder is signaled to stop *before* this on line 1115.  Thus it is
 possible for the vbi thread to return from select, try to read data from
 the vbi fd and then block on the read because the vbi fd is no longer
 returning data (has been stopped).

 Simple solution seems to be to swap the order, i.e. signal vbi thread to
 stop reading before stopping the encoder.  I have no idea if there are any
 unforeseen consequences to this though..... comments?

 {{{
 diff --git a/mythtv/libs/libmythtv/mpegrecorder.cpp
 b/mythtv/libs/libmythtv/mpegrecorder.cpp
 index b158513..35644af 100644
 --- a/mythtv/libs/libmythtv/mpegrecorder.cpp
 +++ b/mythtv/libs/libmythtv/mpegrecorder.cpp
 @@ -1112,13 +1112,13 @@ void MpegRecorder::run(void)

      LOG(VB_RECORD, LOG_INFO, LOC + "run finishing up");

 -    StopEncoding();
 -
      {
          QMutexLocker locker(&pauseLock);
          request_helper = false;
      }

 +    StopEncoding();
 +
      if (vbi_thread)
      {
          vbi_thread->wait();
 lines 1-20/20 (END)
 }}}

--

-- 
Ticket URL: <http://code.mythtv.org/trac/ticket/11410#comment:1>
MythTV <http://code.mythtv.org/trac>
MythTV Media Center


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