The Pipewire audio output driver does not cleanly destroy when FluidSynth exits

[KynikossDragonn]

FluidSynth version

FluidSynth executable version 2.3.4
Sample type=double

Describe the bug

Various PipeWire functions related to destroying the context produce numerous errors when FluidSynth exits or otherwise wants to destroy the audio context.

*** pw_stream_destroy called from wrong context, check thread and locking: Operation not permitted
*** impl_ext_end_proxy called from wrong context, check thread and locking: Operation not permitted
*** impl_ext_end_proxy called from wrong context, check thread and locking: Operation not permitted

Occasionally, this can result in a segfault or abort.

Expected behavior

The PipeWire context should be cleanly removed, and not produce these error messages.

Steps to reproduce

Launch FluidSynth in a interactable shell with the PipeWire audio driver $ fluidsynth -a pipewire
Type quit into the shell

Additional context

The Mumble project ran into similiar pitfalls; more information here: mumble-voip/mumble#6103
https://gitlab.freedesktop.org/pipewire/pipewire/-/issues/3150#note_1862593

[derselbst]

I found some time to look into this. However, I must admit that I never got pipewire working on my system and this time wasn't any different (error: PipeWire stream connection failed).

Unfortunately, I don't see what causes this error either. The audio driver is created here:

fluidsynth/src/fluidsynth.c

Line 1135 in eabae3b

adriver = new_fluid_audio_driver(settings, synth);

and destroyed here:

fluidsynth/src/fluidsynth.c

Line 1198 in eabae3b

delete_fluid_audio_driver(adriver);

Both is done by the main-thread. I'd welcome a PR for this.

[mawe42]

I can reproduce this on my machine with pipewire 1.0.3 and FluidSynth 2.3.4. No errors when playing a MIDI file and exiting via CTRL-C, but when I type in "quit" into the interactive shell the above mentioned errors are shown.

[mawe42]

When I add code to stop the thread loop before destroying the stream, I don't see any errors from pipewire anymore.

[mawe42]

Actually, the correct fix seems to be to grab the thread lock before destroying the stream. The error message even hints at that: "check thread and locking". I've updated the PR accordingly.