jack: Make the running state tracing code more robust to multi-thread access.

Fixes: https://github.com/alsa-project/alsa-plugins/issues/11
Fixes: 2352e4e ("jack: trace the running state")
Signed-off-by: "Jerome M. Berger" <jeberger@free.fr>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>

diff --git a/jack/pcm_jack.c b/jack/pcm_jack.c
index 324da714abbdff7b7ff15e0d0cf3c4bfbfad7371..436aefe255dc51c94843a512bd74aef79c00874f 100644 (file)
--- a/jack/pcm_jack.c
+++ b/jack/pcm_jack.c
@@ -28,6 +28,7 @@
 #include <jack/jack.h>
 #include <alsa/asoundlib.h>
 #include <alsa/pcm_external.h>
+#include <pthread.h>
 
 #define MAX_PERIODS_MULTIPLE 64
 
@@ -44,6 +45,7 @@ typedef struct {
 
        int fd;
        int activated;          /* jack is activated? */
+       pthread_mutex_t running_mutex;
        int running;            /* jack is running? */
 
        snd_pcm_jack_port_list_t **port_names;
@@ -160,6 +162,7 @@ static void snd_pcm_jack_free(snd_pcm_jack_t *jack)
                free(jack->port_names);
                jack->port_names = NULL;
        }
+       pthread_mutex_destroy (&jack->running_mutex);
        if (jack->fd >= 0)
                close(jack->fd);
        if (jack->io.poll_fd >= 0)
@@ -209,8 +212,17 @@ snd_pcm_jack_process_cb(jack_nframes_t nframes, snd_pcm_ioplug_t *io)
        snd_pcm_uframes_t xfer = 0;
        unsigned int channel;
 
-       if (!jack->running)
+       if (pthread_mutex_trylock (&jack->running_mutex) == EBUSY) {
+               /* Note that locking should only ever fail if
+                * snd_pcm_jack_start or snd_pcm_jack_stop is called at the
+                * same time, in which case dropping the current buffer is not
+                * an issue. */
                return 0;
+       }
+       if (!jack->running) {
+               pthread_mutex_unlock (&jack->running_mutex);
+               return 0;
+       }
        
        for (channel = 0; channel < io->channels; channel++) {
                jack->areas[channel].addr = 
@@ -272,6 +284,8 @@ snd_pcm_jack_process_cb(jack_nframes_t nframes, snd_pcm_ioplug_t *io)
 
        pcm_poll_unblock_check(io); /* unblock socket for polling if needed */
 
+       pthread_mutex_unlock (&jack->running_mutex);
+
        return 0;
 }
 
@@ -370,8 +384,9 @@ static int snd_pcm_jack_prepare(snd_pcm_ioplug_t *io)
 static int snd_pcm_jack_start(snd_pcm_ioplug_t *io)
 {
        snd_pcm_jack_t *jack = io->private_data;
-
-       jack->running = jack->activated;
+       pthread_mutex_lock (&jack->running_mutex);
+       jack->running = 1;
+       pthread_mutex_unlock (&jack->running_mutex);
        /*
         * Since the processing of jack_activate() and jack_connect() take a
         * while longer, snd_pcm_jack_start() was blocked.
@@ -389,8 +404,9 @@ static int snd_pcm_jack_start(snd_pcm_ioplug_t *io)
 static int snd_pcm_jack_stop(snd_pcm_ioplug_t *io)
 {
        snd_pcm_jack_t *jack = io->private_data;
-
+       pthread_mutex_lock (&jack->running_mutex);
        jack->running = 0;
+       pthread_mutex_unlock (&jack->running_mutex);
        return 0;
 }
 
@@ -402,7 +418,6 @@ static int snd_pcm_jack_hw_free(snd_pcm_ioplug_t *io)
                jack_deactivate(jack->client);
                jack->activated = 0;
        }
-       jack->running = 0;
 #if 0
        unsigned i;
        for (i = 0; i < io->channels; i++) {
@@ -557,6 +572,8 @@ static int snd_pcm_jack_open(snd_pcm_t **pcmp, const char *name,
        if (!jack)
                return -ENOMEM;
 
+       pthread_mutex_init (&jack->running_mutex, NULL);
+
        jack->fd = -1;
        jack->io.poll_fd = -1;
        jack->use_period_alignment = use_period_alignment;