Fix crashes and deadlocks with previewing preset

[PhysSong]

While investigating #3897, I found another bug.
Steps to reproduce:

1. Click any preset on sidebar and hold it.
2. Close LMMS with Alt+F4 or Ctrl+Q(while previewing).
3. LMMS will crash.

Edit: clarified steps to reproduce.

Here's a part of a backtrace:

Thread 1 (Thread 0x7ffff7ee1900 (LWP 11830)):
#0  0x000000000053c74a in PresetPreviewPlayHandle::isFromTrack(Track const*) const ()
#1  0x0000000000526e8c in Mixer::removePlayHandlesOfTypes(Track*, unsigned char) ()
#2  0x00000000006275a7 in InstrumentTrack::silenceAllNotes(bool) ()
#3  0x000000000062c86d in InstrumentTrack::~InstrumentTrack() ()
#4  0x000000000062ca59 in InstrumentTrack::~InstrumentTrack() ()
#5  0x00000000005c54ba in TrackContainerView::clearAllTracks() ()
#6  0x0000000000552a5c in Song::clearProject() ()
#7  0x00000000004fc74f in LmmsCore::destroy() ()

So I added PlayHandle::TypePresetPreviewHandle in InstrumentTrack::silenceAllNotes(). I also add simple safety check code in PresetPreviewPlayHandle::isFromTrack().

Note: PresetPreviewPlayHandle::play() does nothing since #2586, so the code below is no longer needed. However, leaving it as-is looks fine for me.

lmms/src/gui/FileBrowser.cpp

Lines 448 to 455 in fbfcb43

	if( m_previewPlayHandle != NULL )
	{
	if( !Engine::mixer()->addPlayHandle(
	m_previewPlayHandle ) )
	{
	m_previewPlayHandle = NULL;
	}
	}

Edit: I added a commit which fixes #3456, per #3905 (comment).

[gi0e5b06]

Bug confirmed and proposed fix working. Approved
(and applied to my branch)

[zonkmachine]

I can't reproduce the bug on my machine. Linuxmint 17.3 at fbfcb43

[PhysSong]

@zonkmachine I clarified the "steps to reproduce" section. I can confirm the issue with the same revision. Could you please test that again?

[zonkmachine]

Ah, got it!

Bug verified. Testing the fix but it doesn't appear to shut down completely. Alt + F4.

Program received signal SIGINT, Interrupt.
syscall () at ../sysdeps/unix/sysv/linux/x86_64/syscall.S:38
38	../sysdeps/unix/sysv/linux/x86_64/syscall.S: No such file or directory.
(gdb) bt full
#0  syscall () at ../sysdeps/unix/sysv/linux/x86_64/syscall.S:38
No locals.
#1  0x00007ffff6858dd3 in _q_futex (val2=0, addr2=0x0, timeout=0x0, val=2, op=0, addr=0xef6da0) at thread/qmutex_unix.cpp:99
No locals.
#2  QMutexPrivate::wait (this=this@entry=0xef6da0, timeout=timeout@entry=-1) at thread/qmutex_unix.cpp:113
        ts = {tv_sec = 140737488343808, tv_nsec = 1}
        pts = 0x0
        timer = {t1 = 140737488343808, t2 = 27866800}
#3  0x00007ffff6855275 in QMutex::lockInternal (this=<optimized out>) at thread/qmutex.cpp:450
        maximumSpinTime = <optimized out>
        averageWaitTime = <optimized out>
        actualWaitTime = <optimized out>
        spinTime = 1000326
        d = 0xef6da0
        elapsedTimer = {t1 = 6344, t2 = 617602127}
        maximumSpinTime = <optimized out>
        spinTime = <optimized out>
#4  0x000000000054b43a in PreviewTrackContainer::lockData (this=0xef6d20) at /home/zonkmachine/builds/lmms/lmms/src/core/PresetPreviewPlayHandle.cpp:79
No locals.
#5  0x000000000054ad64 in PresetPreviewPlayHandle::~PresetPreviewPlayHandle (this=0x201c1a0, __in_chrg=<optimized out>)
    at /home/zonkmachine/builds/lmms/lmms/src/core/PresetPreviewPlayHandle.cpp:198
No locals.
#6  0x000000000054adf4 in PresetPreviewPlayHandle::~PresetPreviewPlayHandle (this=0x201c1a0, __in_chrg=<optimized out>)
    at /home/zonkmachine/builds/lmms/lmms/src/core/PresetPreviewPlayHandle.cpp:207
No locals.

[PhysSong]

Okay. There is a releated bug #3456. I'll add a fix for that. It would help fixing new issue.

[gi0e5b06]

@PhysSong Also double-click in the file browser. The second click happens outside the previewing and so add the controller. I fixed that too.

[PhysSong]

The second commit fixes #3456.
Note: lock***()-style functions should be replaced with safer QMutexLocker later anywhere available.

Edit: done by bdf4884.

[zonkmachine]

The second commit fixes #3456.

Both bugs and their fixes confirmed.

[PhysSong]

This PR seems to work good. However, I will add some commits to remove potential chances to generate errors because I've changed some lock-related parts. I think using atomic pointers can be a solution.

[PhysSong]

Note: lock***()-style functions should be replaced with safer QMutexLocker later anywhere available.

I will add some commits to remove potential chances to generate errors because I've changed some lock-related parts.

Done by bdf4884.

[zonkmachine]

I've retested this PR and it still works like a charm. I also retested the bug in question and it seem the crash on exit doesn't happen if the project is playing, only when previewing and the song is stopped.

[PhysSong]

Merge?

[zonkmachine]

Totally...

[PhysSong]

Okay. I'll merge it soon. 😄