Poll(2) blocking test of PCM dmix plugin.

timer-and-dmix-plugin-test.c

#include <stdio.h>
#include <stdlib.h>

#include <string.h>
#include <errno.h>

#include <pthread.h>
#include <stdbool.h>

#include <alsa/asoundlib.h>

#define CHANNELS	2
#define RATE		48000
#define FRAMES		480

/* Equal to 32bit sample * 2 ch * 480 frames. */
static unsigned char buffer[4 * CHANNELS * FRAMES];

static pthread_t thread;
static bool thread_running;

static void *listener_run(void *arg)
{
	snd_pcm_t *handle = arg;
	snd_pcm_status_t *status;
	int err;

	snd_pcm_status_alloca(&status);

	thread_running = true;
	while (thread_running) {
		err = snd_pcm_status(handle, status);
		if (err < 0) {
			printf("snd_pcm_status(): %s\n", strerror(-err));
			break;
		}
	}

	printf("listener exit.\n");
	return NULL;
}

int main(int argc, const char *const argv[])
{
	snd_pcm_t *handle;
	snd_pcm_sframes_t frames;
	unsigned int i;
	int err;

	/* Open PCM character device with dmix plugin. */
	err = snd_pcm_open(&handle, "pcm.dmix:0,0", SND_PCM_STREAM_PLAYBACK, 0);
	if (err < 0) {
		printf("snd_pcm_open(2): %s\n", strerror(-errno));
		return EXIT_FAILURE;
	}

	/*
	 * Set parameters for PCM substream. Keep 500 msec buffer so that dmix
	 * plugin can work well.
	 */
	err = snd_pcm_set_params(handle, SND_PCM_FORMAT_S32,
				 SND_PCM_ACCESS_RW_INTERLEAVED, CHANNELS, RATE,
				 1, 500 * 1000);
	if (err < 0) {
		printf("snd_pcm_set_params(): %s\n", strerror(-err));
		snd_pcm_close(handle);
		return EXIT_FAILURE;
	}

	/* Start listener for the PCM substream. */
	err = pthread_create(&thread, NULL, listener_run, (void *)handle);
	if (err < 0) {
		printf("pthread_create(2): %s\n", strerror(err));
		snd_pcm_close(handle);
		return EXIT_FAILURE;
	}

	/* Write as much frames as 1 sec. */
	for (i = 0; i < RATE / FRAMES; ++i) {
		frames = snd_pcm_writei(handle, buffer, FRAMES);
		if (frames < 0) {
			printf("snd_pcm_writei(): %s\n", strerror(-frames));
			snd_pcm_close(handle);
			return EXIT_FAILURE;
		}

		if (frames != FRAMES) {
			printf("Blocking mode actually works against our "
			       "expectation: %ld\n",
			       frames);
			break;
		}
	}

	/*
	 * Let's drain frames in the PCM substream. In this thread, execution
	 * is sometimes blocked at poll(2). In this case, this program will not
	 * finish unless receiving any signal.
	 */
	snd_pcm_drain(handle);

	/* Finish a thread for listener. */
	thread_running = false;

	snd_pcm_close(handle);

	return EXIT_SUCCESS;
}