Audio buffer, mixer and sink improvements

Signed-off-by: Andrew Opalach <andrew@akon.city>

2 files changed, 21 insertions, 5 deletions

diff --git a/src/mixer/mixer.c b/src/mixer/mixer.c
index 5a21b19..1360934 100644
--- a/src/mixer/mixer.c
+++ b/src/mixer/mixer.c
@@ -13,10 +13,12 @@ static s32 data_callback(void *userdata, u8 *data, s32 frame_count, bool *silenc
 {
     struct camu_mixer *mixer = (struct camu_mixer *)userdata;
     size_t req = camu_audio_format_samples_to_bytes(&mixer->fmt.req, (size_t)frame_count);
+#ifdef CAMU_MIXER_THREADED_START_STOP
     if (UNLIKELY(mixer->paused)) {
         al_memset(data, 0, req);
         *silence = MIXER_WANT_INITIAL_SILENCE;
     } else {
+#endif
 #ifdef CAMU_MIXER_THREADED
         if (al_atomic_load(u8)(&mixer->queued, AL_ATOMIC_RELAXED)) {
             camu_mixer_run_queue(mixer);
@@ -58,7 +60,9 @@ static s32 data_callback(void *userdata, u8 *data, s32 frame_count, bool *silenc
             }
             break;
         }
+#ifdef CAMU_MIXER_THREADED_START_STOP
     }
+#endif
     return frame_count;
 }
 
@@ -260,7 +264,7 @@ void camu_mixer_clear(struct camu_mixer *mixer)
 
 void camu_mixer_pause(struct camu_mixer *mixer)
 {
-#ifdef CAMU_MIXER_THREADED
+#ifdef CAMU_MIXER_THREADED_START_STOP
     nn_mutex_lock(&mixer->mutex);
 #endif
     if (!mixer->paused) {
@@ -268,25 +272,29 @@ void camu_mixer_pause(struct camu_mixer *mixer)
         mixer->paused = true;
     }
 #ifdef CAMU_MIXER_THREADED
+    // This assumes stop() blocks until the output actually stops.
+    // That may not be the behavior we want to require.
     run_queue_internal(mixer);
+#endif
+#ifdef CAMU_MIXER_THREADED_START_STOP
     nn_mutex_unlock(&mixer->mutex);
 #endif
 }
 
 void camu_mixer_resume(struct camu_mixer *mixer)
 {
-#ifdef CAMU_MIXER_THREADED
+#ifdef CAMU_MIXER_THREADED_START_STOP
     nn_mutex_lock(&mixer->mutex);
 #endif
     if (mixer->paused) {
         // start() can internally call data_callback once before returning.
-        // In that call mixer->paused will still be true. So, we have a special case to
-        // immediately return silence and avoid any possible locking.
+        // In that call mixer->paused will still be true. So, if MIXER_THREADED_START_STOP
+        // is defined, we have a special case to immediately return silence to avoid a deadlock.
         // Outputs can treat that silence as part of the stream with MIXER_WANT_INITIAL_SILENCE.
         mixer->audio->start(mixer->audio);
         mixer->paused = false;
     }
-#ifdef CAMU_MIXER_THREADED
+#ifdef CAMU_MIXER_THREADED_START_STOP
     nn_mutex_unlock(&mixer->mutex);
 #endif
 }
diff --git a/src/mixer/mixer.h b/src/mixer/mixer.h
index 16ec924..802d1b5 100644
--- a/src/mixer/mixer.h
+++ b/src/mixer/mixer.h
@@ -9,6 +9,14 @@
 
 #include "../codec/codec.h"
 
+#ifdef CAMU_MIXER_THREADED
+// Do we need to lock in order to synchronize the mixers paused state.
+// Disabling this is a very specific optimization to allow the audio device to
+// buffer data during start(). It requires pause(), resume(), and remove_buffer()
+// to all come from the same thread.
+//#define CAMU_MIXER_THREADED_START_STOP
+#endif
+
 enum {
     CAMU_MIXER_EMPTY = 0
 };