crash / GUI freeze when loading track into deck with passthrough enabled

[ronso0]

* configure outputs and VC input for deckN
* load track <-- !
* enable passthrough
* load another song
* deck overview shows "Analyzing..." string then GUI freezes instantly
* GUI updates every 30 seconds or so, one Mixxx thread uses 100% of CPU
* click passthrough button
* on next GUI update it 'unfreezes'

I could reproduce this with I/O both on integrated card of TerminalMix 2/4, as well as with loopback device and no controller attached.
Only happenes when a track is loaded when enabling passthrough. Enabling passthrough and then loading a track as well as ejecting works flawlessly.

reproducible with
2.3 352f75428b --> crashes with std::bad_alloc, see backtrace
sometimes also prints
Warning [Main]: CachingReader - Loading a new track while loading a track may lead to inconsistent states
^ up to 3 times
Critical [Engine]: DEBUG ASSERT: "atomicLoadRelaxed(m_state) == STATE_TRACK_LOADING" in function void CachingReader::process() at /src/engine/cachingreader/cachingreader.cpp:285
terminate called after throwing an instance of 'std::bad_alloc'
  what(): std::bad_alloc

main c126267767 --> freezes until passtrhough is disabled

EDIT
vc type doesn't matter

[ronso0 (ronso0)]

The crash seems to be caused by the waveform renderer. Choosing 'Empty' or the vsync test prevents the crash.
Crash occurs with any overview.

Side effect:
With any (main) waveform renderer, when loading a track to a passthrough deck the overview playposition would get stuck at the center.
With no renderer, the playposition is reset to the beginning.
In both cases, disabling passthrough makes the playpos seek to the desired place.

[ronso0 (ronso0)]

Okay, as the backtrace shows the culprit is
https://github.com/mixxxdj/mixxx/blob/352f75428b5c8e0ab014206939c085c49b1ccc4b/src/waveform/renderers/waveformrenderbeat.cpp#L90-L92
though I just don't get (yet) how this is related to passthrough...

[Uwe Klotz (uklotzde-deactivatedaccount)]

Non-terminating iterator, unlimited growth of memory, crash when calling m_beats.resize().

Also reported here:
https://bugs.launchpad.net/mixxx/+bug/1959489

[ronso0 (ronso0)]

Yes, this is the symptom.

The root cause seems to be the engine playposition:
if passthrough is enabled, loading a track queues the new position. only after disabling passthrough the engineDeck will process the buffer and processSeek() is called.
Thus, with passthrough kInitialPlayPosition persists (std::numeric_limits<double>::lowest()) which leads to confusion down the line.

I could add a workaround, probably considered a hack, but it definitely solves the GUI freeze / crash.
https://github.com/mixxxdj/mixxx/pull/4787

[Uwe Klotz (uklotzde-deactivatedaccount)]

Final fix: https://github.com/mixxxdj/mixxx/pull/4789

[Swiftb0y (swiftb0y)]

Mixxx now uses GitHub for bug tracking. This bug has been migrated to:
https://github.com/mixxxdj/mixxx/issues/10743