[alsa-devel] ALSA async callback re-enter and DEADLOCK.

[Павел Колодин]

Hello.

I've implemented a simple application using this example:
http://www.alsa-project.org/alsa-doc/alsa-lib/_2test_2pcm_8c-example.html (see
"async_callback()", line 390).

My problem is that sometimes (after 1 or 20 mins of playing sound
(unpredictable) everything just hangs - similarly to deadlock. I have found
that callback is called WHILE another callback function is still executed
(not returned yet). My debug code is like:

void async_callback(snd_async_handler_t *ahandler)
{
    std::cout << "?"; std::cout.flush();
    // some code with snd_async_handler_get_callback_private(),
snd_pcm_avail_update(), snd_pcm_writei() and so on //
    std::cout << "!"; std::cout.flush();
    return;
}

Everything is ok when i see "?!?!?!...", but if "??" occurs than app goes
into an eternal deadlock.

I work with ALSA literally as in that example - settings (HW and SW) are
the same. Soundcard is "Analog Devices AD1981", ALSA version is 1.0.19. I
do fill buffer until there is a place for periods and hear
44100/16/2channels sound without any clicks and noises before "??" occurs.

Sorry for poor english; from Siberia with love.
Thank you!