alsa: add a less dirty hack to detect the PA plugin and disable the flaky underrun handling in the plugin.

1 files changed, 103 insertions, 3 deletions

diff --git a/src/cubeb_alsa.c b/src/cubeb_alsa.c
index 84475c4..924b4ae 100644
--- a/src/cubeb_alsa.c
+++ b/src/cubeb_alsa.c
@@ -20,6 +20,9 @@
 #define CUBEB_WATCHDOG_MS 10000
 #define UNUSED __attribute__ ((__unused__))
 
+#define CUBEB_ALSA_PCM_NAME "default"
+#define CUBEB_ALSA_PCM_NODE_NAME "pcm.default"
+
 /* ALSA is not thread-safe.  snd_pcm_t instances are individually protected
    by the owning cubeb_stream's mutex.  snd_pcm_t creation and destruction
    is not thread-safe until ALSA 1.0.24 (see alsa-lib.git commit 91c9c8f1),
@@ -50,6 +53,11 @@ struct cubeb {
   /* Track number of active streams.  This is limited to CUBEB_STREAM_MAX
      due to resource contraints. */
   unsigned int active_streams;
+
+  /* Local configuration with handle_underrun workaround set for PulseAudio
+     ALSA plugin.  Will be NULL if the PA ALSA plugin is not in use or the
+     workaround is not required. */
+  snd_config_t * local_config;
 };
 
 enum stream_state {
@@ -409,13 +417,99 @@ cubeb_run_thread(void * context)
   return NULL;
 }
 
+/* Work around PulseAudio ALSA plugin bug where the PA server forces a
+   higher than requested latency, but the plugin does not update its (and
+   ALSA's) internal state to reflect that, leading to an immediate underrun
+   situation.  Inspired by WINE's make_handle_underrun_config.
+   Reference: http://mailman.alsa-project.org/pipermail/alsa-devel/2012-July/053391.html
+ */
+static snd_config_t *
+init_local_config_with_workaround(char const * pcm_node_name)
+{
+  int r;
+  snd_config_t * lconf;
+  snd_config_t * device_node;
+  snd_config_t * type_node;
+  snd_config_t * node;
+  char const * type_string;
+
+  lconf = NULL;
+
+  pthread_mutex_lock(&cubeb_alsa_mutex);
+
+  if (snd_config == NULL) {
+    snd_config_update();
+  }
+
+  r = snd_config_copy(&lconf, snd_config);
+  assert(r >= 0);
+
+  r = snd_config_search(lconf, pcm_node_name, &device_node);
+  if (r != 0) {
+    snd_config_delete(lconf);
+    pthread_mutex_unlock(&cubeb_alsa_mutex);
+    return NULL;
+  }
+
+  /* Fetch the PCM node's type, and bail out if it's not the PulseAudio plugin. */
+  r = snd_config_search(device_node, "type", &type_node);
+  if (r != 0) {
+    snd_config_delete(lconf);
+    pthread_mutex_unlock(&cubeb_alsa_mutex);
+    return NULL;
+  }
+
+  r = snd_config_get_string(type_node, &type_string);
+  if (r != 0) {
+    snd_config_delete(lconf);
+    pthread_mutex_unlock(&cubeb_alsa_mutex);
+    return NULL;
+  }
+
+  if (strcmp(type_string, "pulse") != 0) {
+    snd_config_delete(lconf);
+    pthread_mutex_unlock(&cubeb_alsa_mutex);
+    return NULL;
+  }
+
+  /* Don't clobber an explicit existing handle_underrun value, set it only
+     if it doesn't already exist. */
+  r = snd_config_search(device_node, "handle_underrun", &node);
+  if (r != -ENOENT) {
+    snd_config_delete(lconf);
+    pthread_mutex_unlock(&cubeb_alsa_mutex);
+    return NULL;
+  }
+
+  r = snd_config_imake_integer(&node, "handle_underrun", 0);
+  if (r != 0) {
+    snd_config_delete(lconf);
+    pthread_mutex_unlock(&cubeb_alsa_mutex);
+    return NULL;
+  }
+
+  r = snd_config_add(device_node, node);
+  if (r != 0) {
+    snd_config_delete(lconf);
+    pthread_mutex_unlock(&cubeb_alsa_mutex);
+    return NULL;
+  }
+
+  pthread_mutex_unlock(&cubeb_alsa_mutex);
+  return lconf;
+}
+
 static int
-cubeb_locked_pcm_open(snd_pcm_t ** pcm, snd_pcm_stream_t stream)
+cubeb_locked_pcm_open(snd_pcm_t ** pcm, snd_pcm_stream_t stream, snd_config_t * local_config)
 {
   int r;
 
   pthread_mutex_lock(&cubeb_alsa_mutex);
-  r = snd_pcm_open(pcm, "default", stream, SND_PCM_NONBLOCK);
+  if (local_config) {
+    r = snd_pcm_open_lconf(pcm, CUBEB_ALSA_PCM_NAME, stream, SND_PCM_NONBLOCK, local_config);
+  } else {
+    r = snd_pcm_open(pcm, CUBEB_ALSA_PCM_NAME, stream, SND_PCM_NONBLOCK);
+  }
   pthread_mutex_unlock(&cubeb_alsa_mutex);
 
   return r;
@@ -526,6 +620,8 @@ cubeb_init(cubeb ** context, char const * context_name UNUSED)
   r = pthread_attr_destroy(&attr);
   assert(r == 0);
 
+  ctx->local_config = init_local_config_with_workaround(CUBEB_ALSA_PCM_NODE_NAME);
+
   *context = ctx;
 
   return CUBEB_OK;
@@ -557,6 +653,10 @@ cubeb_destroy(cubeb * ctx)
   pthread_mutex_destroy(&ctx->mutex);
   free(ctx->fds);
 
+  if (ctx->local_config) {
+    snd_config_delete(ctx->local_config);
+  }
+
   free(ctx);
 }
 
@@ -618,7 +718,7 @@ cubeb_stream_init(cubeb * ctx, cubeb_stream ** stream, char const * stream_name
   r = pthread_mutex_init(&stm->mutex, NULL);
   assert(r == 0);
 
-  r = cubeb_locked_pcm_open(&stm->pcm, SND_PCM_STREAM_PLAYBACK);
+  r = cubeb_locked_pcm_open(&stm->pcm, SND_PCM_STREAM_PLAYBACK, ctx->local_config);
   if (r < 0) {
     cubeb_stream_destroy(stm);
     return CUBEB_ERROR;