[alsa-devel] 1.1.3 bug report: dmix reports inconsistent status

[Cheng Sun]

On 24 May 2017 at 20:18, Cheng Sun <chengsun9 at gmail.com> wrote:
> Hi all,
>
> The following commit (released in v1.1.3) introduced an issue where
> dmix reports its state differently when snd_pcm_state is queried,
> compared to snd_pcm_status.
>
>     38a2d2eda880fda9ed5a4a219db498d9c0856d71
>
> (I suspect faf53c197cabeb1eb0fd1f66cd001d1469ebac09 affects dshare
> similarly, but this is not tested)
>
> The sample program attached at the bottom of this email demonstrates
> this behaviour by printing the following on underrun:
>
> try 1: status_state=3, state=4
> try 2: status_state=3, state=4
> ALSA lib pcm.c:8306:(snd_pcm_recover) underrun occurred
>
> Cheers,
> Cheng

Just realised that my original sample program had a slight flaw
(snd_pcm_status only called once). Here's the corrected version, which
still exhibits the erroneous behaviour.

(Also to clarify, this problem is still present in v1.1.4 and master.)

Cheers,
Cheng

---

#include <assert.h>
#include <alsa/asoundlib.h>
#include <stdint.h>
#define FRAMES 100
int32_t buffer[FRAMES][2];
int main(int argc, char *argv[]) {
    const char *pcmname = argc == 2 ? argv[1] : "default";
    snd_pcm_t *pcm;
    assert( snd_pcm_open(&pcm, pcmname, SND_PCM_STREAM_PLAYBACK, 0) == 0 );
    assert( snd_pcm_set_params(pcm, SND_PCM_FORMAT_S32_LE,
SND_PCM_ACCESS_RW_INTERLEAVED, 2, 48000, 1, 250) == 0 );
    for (;;) {
        snd_pcm_sframes_t written = snd_pcm_writei(pcm, buffer, FRAMES);
        if (written <= 0) {
            snd_pcm_status_t *status;
            snd_pcm_status_alloca(&status);

            int status_state, state;

            assert( snd_pcm_status(pcm, status) == 0 );
            status_state = snd_pcm_status_get_state(status);
            state = snd_pcm_state(pcm);
            printf("try 1: status_state=%d, state=%d\n", status_state, state);

            assert( snd_pcm_status(pcm, status) == 0 );
            status_state = snd_pcm_status_get_state(status);
            state = snd_pcm_state(pcm);
            printf("try 2: status_state=%d, state=%d\n", status_state, state);

            assert( snd_pcm_recover(pcm,written,0) == 0 );
        }
    }
}