snd_pcm_drain stucked.

alsa-project/alsa-lib issue #457 was opened from yangyagami:

When snd_pcm_drain is called, if snd_pcm_drop is called in another thread, snd_pcm_drain will get stuck. ```cpp #include <iostream> #include <cmath> #include <thread>

#include <alsa/asoundlib.h>

#define SAMPLE_RATE 44100 #define FREQUENCY 440.0 // A4 note #define DURATION 5.0 // seconds

using namespace std::chrono_literals;

int main() { snd_pcm_t *handle; snd_pcm_hw_params_t *params; unsigned int rate = SAMPLE_RATE; int dir; int pcm;

pcm = snd_pcm_open(&handle, "default", SND_PCM_STREAM_PLAYBACK, 0); if (pcm < 0) { std::cerr << "Unable to open PCM device: " << snd_strerror(pcm) << std::endl; return 1; }

snd_pcm_hw_params_alloca(&params); snd_pcm_hw_params_any(handle, params);

snd_pcm_hw_params_set_access(handle, params, SND_PCM_ACCESS_RW_INTERLEAVED); snd_pcm_hw_params_set_format(handle, params, SND_PCM_FORMAT_S16_LE); snd_pcm_hw_params_set_rate_near(handle, params, &rate, &dir); snd_pcm_hw_params_set_channels(handle, params, 1);

pcm = snd_pcm_hw_params(handle, params); if (pcm < 0) { std::cerr << "Unable to set HW parameters: " << snd_strerror(pcm) << std::endl; return 1; }

int samples = static_cast<int>(DURATION * SAMPLE_RATE); int16_t *buffer = new int16_t[samples];

for (int i = 0; i < samples; ++i) { buffer[i] = static_cast<int16_t>(32767 * sin(2 * M_PI * FREQUENCY * i / SAMPLE_RATE)); }

pcm = snd_pcm_writei(handle, buffer, samples); if (pcm < 0) { std::cerr << "Playback error: " << snd_strerror(pcm) << std::endl; }

std::thread t([handle](){ std::this_thread::sleep_for(500ms); snd_pcm_drop(handle); });

snd_pcm_drain(handle);

t.join();

delete[] buffer; snd_pcm_close(handle);

return 0; } ```

gdb output ```shell Thread 1 "main" received signal SIGINT, Interrupt. 0x00007ffff71b5e22 in ?? () from /usr/lib/libc.so.6 (gdb) bt #0 0x00007ffff71b5e22 in ?? () from /usr/lib/libc.so.6 #1 0x00007ffff71a9fda in ?? () from /usr/lib/libc.so.6 #2 0x00007ffff71aa64c in ?? () from /usr/lib/libc.so.6 #3 0x00007ffff71acd1e in pthread_cond_wait () from /usr/lib/libc.so.6 #4 0x00007ffff6b9e2b9 in pw_thread_loop_wait () from /usr/lib/libpipewire-0.3.so.0 #5 0x00007ffff7f2ec8f in ?? () from /usr/lib/alsa-lib/libasound_module_pcm_pipewire.so #6 0x00007ffff777c2b8 in ?? () from /usr/lib/libasound.so.2 #7 0x0000555555558d6f in main () at main.cc:116 (gdb) ```

Issue URL : https://github.com/alsa-project/alsa-lib/issues/457 Repository URL: https://github.com/alsa-project/alsa-lib