Might Help with Audio Latency Issues

src/apulse-stream.c

@@ -58,6 +58,7 @@ deh_stream_first_readwrite_callback(pa_mainloop_api *api, pa_defer_event *de, vo
     pa_stream_unref(s);
 }
 
+static int xruns=0;
 static
 void
 data_available_for_stream(pa_mainloop_api *a, pa_io_event *ioe, int fd, pa_io_event_flags_t events,
@@ -167,17 +168,20 @@ data_available_for_stream(pa_mainloop_api *a, pa_io_event *ioe, int fd, pa_io_ev
     }
 
     if (events & PA_IO_EVENT_OUTPUT) {
+      int r;
+
         if (paused) {
             // client stream is corked. Pass silence to ALSA
             size_t bytecnt = MIN(buf_size, frame_count * frame_size);
             memset(buf, 0, bytecnt);
-            snd_pcm_writei(s->ph, buf, bytecnt / frame_size);
+            r= snd_pcm_writei(s->ph, buf, bytecnt / frame_size);
         } else {
             size_t writable_size = pa_stream_writable_size(s);
 
             // Ask client for data, but only if we are ready for at least |minreq| bytes.
-            if (s->write_cb && writable_size >= s->buffer_attr.minreq)
-                s->write_cb(s, s->buffer_attr.minreq, s->write_cb_userdata);
+            if (s->write_cb && writable_size >= s->buffer_attr.minreq) {
+                s->write_cb(s, writable_size, s->write_cb_userdata);
+	    }
 
             size_t bytecnt = MIN(buf_size, frame_count * frame_size);
             bytecnt = ringbuffer_read(s->rb, buf, bytecnt);
@@ -188,9 +192,29 @@ data_available_for_stream(pa_mainloop_api *a, pa_io_event *ioe, int fd, pa_io_ev
                 // application is not ready yet, play silence
                 bytecnt = MIN(buf_size, frame_count * frame_size);
                 memset(buf, 0, bytecnt);
+		trace_warning("application not ready\n");
             }
-            snd_pcm_writei(s->ph, buf, bytecnt / frame_size);
+            r = snd_pcm_writei(s->ph, buf, bytecnt / frame_size);
         }
+
+        if (r < 0) {
+	  switch (r) {
+	    case -EAGAIN:  // non-blocking I/O, no need to do anything
+	      break;
+	    case -EBADFD:  // FD in wrong state
+	      trace_warning("ALSA badfd: rv=%d\n", r);
+	      snd_pcm_prepare(s->ph);
+	      break;
+	    case -EPIPE:  // XRUN
+	      xruns++;
+	      trace_warning("ALSA xrun: rv=%d, xruns=%d\n", r, xruns);
+	      snd_pcm_recover(s->ph, r, 1);
+	      break;
+	    default:
+	      trace_warning("ALSA error: rv=%d\n", r);
+	      snd_pcm_recover(s->ph, r, 1);
+	  }
+	}
     }
 
     if (events & PA_IO_EVENT_INPUT) {

src/apulse-threaded-mainloop.c

@@ -129,15 +129,30 @@ pa_threaded_mainloop_signal(pa_threaded_mainloop *m, int wait_for_accept)
     pthread_cond_signal(&m->cond);
 }
 
+#define AUDIO_THREAD_RT_PRIORITY 60
+
 APULSE_EXPORT
 int
 pa_threaded_mainloop_start(pa_threaded_mainloop *m)
 {
+    struct sched_param rtparam;
+    int err;
     trace_info_f("F %s m=%p\n", __func__, m);
 
     if (m->running)
         return 1;
     pthread_create(&m->t, NULL, mainloop_thread, m);
+
+    memset(&rtparam, 0, sizeof(rtparam));
+    rtparam.sched_priority = AUDIO_THREAD_RT_PRIORITY;
+
+    if ((err = pthread_setschedparam(m->t, SCHED_FIFO, &rtparam)) != 0) {
+      trace_warning(
+          "cannot use real-time scheduling (FIFO at priority %d) "
+          "for audio thread (%d: %s)",
+          rtparam.sched_priority, err, strerror(err));
+    }
+
     m->running = 1;
     return 0;
 }