[m1kor]

When a duplex stream is opened with the PulseAudio API and the input half fails to open, openStream never returns.

Cause

RtApi::openStream calls probeDeviceOpen for OUTPUT, then for INPUT. The OUTPUT call starts the callback thread, which waits in callbackEvent on pah->runnable_cv because the stream is stopped. If the INPUT call then fails, the error: path in RtApiPulse::probeDeviceOpen calls pthread_cond_destroy( &pah->runnable_cv ) while that thread is still waiting on it. glibc's pthread_cond_destroy waits for existing waiters to leave, so the caller blocks forever. On other implementations it's undefined behaviour: the thread later touches a destroyed condition variable and a deleted handle.

Stacks of the hung process:

caller:           __pthread_cond_destroy
                  RtApiPulse::probeDeviceOpen (mode=INPUT, channels=8)
                  RtApi::openStream
callback thread:  __pthread_cond_wait
                  RtApiPulse::callbackEvent
                  pulseaudio_callback

Fix

In the error path, stop the callback thread the same way closeStream does before destroying the condition variable: clear isRunning, set runnable and signal under the stream mutex, then join. The pa_simple streams that were already opened are freed too; previously they leaked.

Reproduction

Seen on PipeWire (pipewire-pulse) with a Focusrite Clarett 4Pre USB. Its source has 10 channels; a record stream asking for 8 fails in pa_simple_new, and one asking for 4 succeeds.

RtAudio rt(RtAudio::LINUX_PULSE);
RtAudio::StreamParameters out{clarett, 2, 0}, in{clarett, 8, 0};
unsigned frames = 256;
rt.openStream(&out, &in, RTAUDIO_FLOAT32, 48000, &frames, callback);  // hangs

Tested on current master (ea2c88c), built with the PulseAudio API only:

• Before: the call above hangs.
• After: it returns RTAUDIO_SYSTEM_ERROR ("error connecting input to PulseAudio server."), and the same RtAudio object then opens and runs a duplex stream with 4 input channels.

Output-only and input-only streams, and duplex streams whose halves both open, don't go through this path.