Re-opening an ALSA connection

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Hello,

the C++ app I am working on uses ALSA and usually works. However, when I s2ram 
my computer while an ALSA connection is active, and the computer starts again, 
the connection is broken (snd_pcm_writei returns < 0). In that case, I'd like 
to reopen the connection. This raises up questions:

  * Do the calls of snd_pcm_... have to match per thread? I.e. can you call 
    snd_pcm_open() with one thread and then call snd_pcm_close() with another 
    one? Is there a portable answer, i.e. one that's true for all systems?

  * Do you need to init the hardware parameters again? In my case, must the 
    code from [1] be re-executed? Actually, if you've saved the params object 
    from the previous connection, I'd have said "no", However, the audio 
    handle was always involved in the snd_pcm_hw_params() calls, which makes 
    me unsure whether they could really be left out for a "reopen". In the 
    code from [1], I'd have simply done this:

reopenAudio();
{
    // token from stopAudio()
    snd_pcm_t *handle = audio.handle;
    audio.handle = NULL;
    snd_pcm_drain(handle);
    if(snd_pcm_close(handle)) { /* error handling ... */ }
    
    // token from openAudio(), but without lines 291-320: 
    int rc = 0;
    /* Open PCM device for playback. */
    audio.handle = NULL;

    const char *device = getenv("ALSA_DEVICE");
    if(device == 0)
        device = "hw:0";

    rc = snd_pcm_open(&audio.handle, device,
                      SND_PCM_STREAM_PLAYBACK, 0);
    if(rc < 0) { /* error handling... */ }

    /* ??? no need to re-init audio params here ??? */

    /* Write the parameters to the driver */
    rc = snd_pcm_hw_params(audio.handle, audio.params);
    if(rc < 0) { /* error handling... */ }
}


Thanks + regards,
Johannes


[1] 
https://github.com/zynaddsubfx/zynaddsubfx/blob/master/src/Nio/AlsaEngine.cpp#L291-L320





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