Problems with export of project with Sample Track

[zonkmachine]

As discussed in PR #3341 there is some issues with exporting projects containing a Sample Track. I've only seen this when using SDL. ALSA works fine and other sound engines I haven't tried.

The renderer process will simply hang and never return to main(). If you do a --rendertracks export it will stop on the first Sample Track it tries tor render.

I'm not done bisecting this but it may have happened around these commits 8497d39 e55ec80

[zonkmachine]

(gdb)   thread apply all bt full

Thread 2 (Thread 0x7fffdffc5700 (LWP 21314)):
#0  pthread_cond_wait@@GLIBC_2.3.2 () at ../nptl/sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
No locals.
#1  0x00007ffff685a816 in wait (time=18446744073709551615, this=0xb84070) at thread/qwaitcondition_unix.cpp:86
        code = <optimized out>
#2  QWaitCondition::wait (this=<optimized out>, mutex=0x7fffdffc4e40, time=18446744073709551615) at thread/qwaitcondition_unix.cpp:158
No locals.
#3  0x0000000000535596 in MixerWorkerThread::run (this=0xa01840) at /home/zonkmachine/builds/lmms/lmms/src/core/MixerWorkerThread.cpp:162
        m = {d = 0x7fffd80013d0}
#4  0x00007ffff685a32f in QThreadPrivate::start (arg=0xa01840) at thread/qthread_unix.cpp:349
        __clframe = {__cancel_routine = 0x7ffff6859300 <QThreadPrivate::finish(void*)>, __cancel_arg = 0xa01840, __do_it = 1, 
          __cancel_type = <optimized out>}
        thr = 0xa01840
        data = <optimized out>
        objectName = {static null = {<No data fields>}, static shared_null = {ref = {_q_value = 1743}, alloc = 0, size = 0, 
            data = 0x7ffff6cc293a <QString::shared_null+26>, clean = 0, simpletext = 0, righttoleft = 0, asciiCache = 0, capacity = 0, reserved = 0, 
            array = {0}}, static shared_empty = {ref = {_q_value = 2}, alloc = 0, size = 0, data = 0x7ffff6cc291a <QString::shared_empty+26>, clean = 0, 
            simpletext = 0, righttoleft = 0, asciiCache = 0, capacity = 0, reserved = 0, array = {0}}, d = 0x7ffff6cc2920 <QString::shared_null>, 
          static codecForCStrings = 0x0}
#5  0x00007ffff7bc4184 in start_thread (arg=0x7fffdffc5700) at pthread_create.c:312
        __res = <optimized out>
        pd = 0x7fffdffc5700
        now = <optimized out>
        unwind_buf = {cancel_jmp_buf = {{jmp_buf = {140736951244544, -2079227267844162622, 1, 0, 140736951245248, 140736951244544, 2079156870619577282, 
                2079245381250431938}, mask_was_saved = 0}}, priv = {pad = {0x0, 0x0, 0x0, 0x0}, data = {prev = 0x0, cleanup = 0x0, canceltype = 0}}}
        not_first_call = <optimized out>
        pagesize_m1 = <optimized out>
        sp = <optimized out>
        freesize = <optimized out>
        __PRETTY_FUNCTION__ = "start_thread"
#6  0x00007ffff3f35ffd in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:111
No locals.

Thread 1 (Thread 0x7ffff7fab7c0 (LWP 21310)):
#0  pthread_cond_wait@@GLIBC_2.3.2 () at ../nptl/sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
No locals.
#1  0x00007ffff685a816 in wait (time=18446744073709551615, this=0xa01e60) at thread/qwaitcondition_unix.cpp:86
        code = <optimized out>
#2  QWaitCondition::wait (this=<optimized out>, mutex=0xb7bff8, time=18446744073709551615) at thread/qwaitcondition_unix.cpp:158
No locals.
#3  0x0000000000530ce0 in Mixer::requestChangeInModel (this=0xb7bec0) at /home/zonkmachine/builds/lmms/lmms/src/core/Mixer.cpp:773
No locals.
#4  0x0000000000530a58 in Mixer::removePlayHandlesOfTypes (this=0xb7bec0, _track=0x7fffeac2a420, types=4 '\004')
    at /home/zonkmachine/builds/lmms/lmms/src/core/Mixer.cpp:734
        it = {i = 0x1}
#5  0x000000000062f0e3 in SampleTCO::playbackPositionChanged (this=0x7fffeac2a820) at /home/zonkmachine/builds/lmms/lmms/src/tracks/SampleTrack.cpp:168
        st = 0x7ffff6962e09 <QMetaObject::cast(QObject*) const+25>
#6  0x00000000006402af in SampleTCO::qt_static_metacall (_o=0x7fffeac2a820, _c=QMetaObject::InvokeMetaMethod, _id=5, _a=0x7fffa4003270)
    at /home/zonkmachine/builds/lmms/lmms/build/src/moc_SampleTrack.cpp:65
        _t = 0x7fffeac2a820
#7  0x00007ffff6974c1e in QObject::event (this=0x7fffeac2a820, e=<optimized out>) at kernel/qobject.cpp:1194
---Type <return> to continue, or q <return> to quit---
        mce = <optimized out>
        currentSender = {sender = 0xb80160, signal = 9, ref = 1}
        previousSender = 0x0

[PhysSong]

Reproduced with ALSA.

[musikBear]

@PhysSong can you elaborate
How long was the sample?
Where in the project was it placed?
Was there other tracks in the project (upload project on lsp
Was it a cmd-line export, and how did it go if the export was internal from menu?
Ogg or wave or both?

[PhysSong]

@musikBear I can reproduce it for various samples. I used gui, and the exported file has .wav extension.
However, It seems to be a bug of LMMS core. I think it is from thread synchronization.

[PhysSong]

I think 5606a04 may be related. @jasp00 may know what goes wrong.

[musikBear]

I used gui, : a bug of LMMS core. I think it is from thread synchronization.

Then its a critical :/

[PhysSong]

• Revert 8497d39: still stops.
• Revert e55ec80: still stops.
• Revert 5606a04: haven't tested yet.

[PhysSong]

After the exporting ends, ProjectRenderer::run() calls Song::stopExport(), it calls Song::stop(), and it emits playbackStateChanged(), so SampleTCO::playbackPositionChanged() receives the signal.

requestChangeInModel() waits for runChangesInModel(), which is called by AudioDevice::getNextBuffer() while exporting, or Mixer::fifoWriter::run() otherwise.
So, runChangesInModel() is never called between the end of export and the calling of restoreAudioDevice() in ~ProjectRenderer().

However, ~ProjectRenderer() isn't called until finished() signal is emitted by renderer. To be emitted finished(), event handling must be finished, but SampleTCO::playbackPositionChanged() is still waiting. Now there's a deadlock!

[zonkmachine]

Easy to fix?

[PhysSong]

I'm testing a simple fix: postpone the emitting of playbackStateChanged(). It looks fine, but I need more testings.

[musikBear]

but I need more testings.

I will install a test binary if you have any @PhysSong

[PhysSong]

Actually I have some choices.
@musikBear I'll post the binary after I choose one of them.