access/alsa.c: capture audio in a seperate thread

On some systems the latency for audio capture when used with input-slave
is too big, resulting in poll timeouts and no audio. Running the audio
capture in a separate thread solves this latency issue.

modules/access/alsa.c

@@ -118,6 +118,19 @@ static int OpenAudioDev( demux_t *, const char * );
 static bool ProbeAudioDevAlsa( demux_t *, const char * );
 static char *ListAvailableDevices( demux_t *, bool b_probe );
 
+/* --- AudioGrab Thread --- */
+typedef struct audio_grab_s
+{
+    VLC_COMMON_MEMBERS
+
+    demux_t      *p_demux;
+    block_fifo_t *p_fifo;
+
+} audio_grab_t;
+
+static void *AudioThread( vlc_object_t * );
+/* --- AudioGrab Thread --- */
+
 struct demux_sys_t
 {
     /* Audio */
@@ -134,6 +147,8 @@ struct demux_sys_t
     int i_alsa_chunk_size;
 
     int64_t i_next_demux_date; /* Used to handle alsa:// as input-slave properly */
+
+    audio_grab_t *p_grab;
 };
 
 static int FindMainDevice( demux_t *p_demux, const char *psz_device )
@@ -268,6 +283,30 @@ static int DemuxOpen( vlc_object_t *p_this )
         return VLC_EGENERIC;
     }
 
+    p_sys->p_grab = vlc_object_create( p_demux, sizeof(audio_grab_t) );
+    if( !p_sys->p_grab )
+    {
+        DemuxClose( p_this );
+        return VLC_ENOMEM;
+    }
+
+    p_sys->p_grab->p_demux = p_demux;
+    p_sys->p_grab->p_fifo = block_FifoNew();
+    if( !p_sys->p_grab->p_fifo )
+    {
+        vlc_object_release( p_sys->p_grab );
+        p_sys->p_grab = NULL;
+        DemuxClose( p_this );
+        return VLC_ENOMEM;
+    }
+
+    if( vlc_thread_create( p_sys->p_grab, "AudioGrab Thread",
+                       AudioThread, VLC_THREAD_PRIORITY_INPUT) < 0 )
+    {
+        msg_Err( p_this, "Failed to create Audio Capture Thread" );
+        DemuxClose( p_this );
+        return VLC_EGENERIC;
+    }
     return VLC_SUCCESS;
 }
 
@@ -279,6 +318,15 @@ static void DemuxClose( vlc_object_t *p_this )
     demux_t     *p_demux = (demux_t *)p_this;
     demux_sys_t *p_sys   = p_demux->p_sys;
 
+    if( p_sys->p_grab )
+    {
+        vlc_object_kill( p_sys->p_grab );
+        vlc_thread_join( p_sys->p_grab );
+        if( p_sys->p_grab->p_fifo )
+            block_FifoRelease( p_sys->p_grab->p_fifo );
+        vlc_object_release( p_sys->p_grab );
+    }
+
     if( p_sys->p_alsa_pcm )
     {
         snd_pcm_close( p_sys->p_alsa_pcm );
@@ -332,34 +380,65 @@ static int DemuxControl( demux_t *p_demux, int i_query, va_list args )
 static int Demux( demux_t *p_demux )
 {
     demux_sys_t *p_sys = p_demux->p_sys;
-
-    block_t *p_block = NULL;
+    block_t *p_block;
 
     do
     {
-        if( p_block )
-        {
+        if( block_FifoCount( p_sys->p_grab->p_fifo ) <= 0 )
+            break;
+
+        p_block = block_FifoGet( p_sys->p_grab->p_fifo );
+        if( !p_block ) break;
+
+        mtime_t i_pts = p_block->i_pts;
+        es_out_Control( p_demux->out, ES_OUT_SET_PCR, p_block->i_pts );
         es_out_Send( p_demux->out, p_sys->p_es, p_block );
         p_block = NULL;
-        }
 
+        if( p_sys->i_next_demux_date <= 0 &&
+            i_pts >= p_sys->i_next_demux_date )
+            break;
+
+    } while( vlc_object_alive(p_demux) );
+    return 1;
+}
+
+static void *AudioThread( vlc_object_t *p_this )
+{
+    audio_grab_t *p_grab = (audio_grab_t *) p_this;
+    demux_t *p_demux = (demux_t *) p_grab->p_demux;
+    demux_sys_t *p_sys = (demux_sys_t *) p_demux->p_sys;
+
+    block_t *p_block = NULL;
+
+    do
+    {
         /* Wait for data */
         int i_wait = snd_pcm_wait( p_sys->p_alsa_pcm, 10 ); /* See poll() comment in oss.c */
+#if 0
+        msg_Info( p_demux, "ALSA snd_pcm_wait returned (%d): %s %"PRId64,
+                  i_wait, snd_strerror(i_wait), mdate() );
+#endif
         switch( i_wait )
         {
             case 1:
             {
                 p_block = GrabAudio( p_demux );
                 if( p_block )
-                    es_out_Control( p_demux->out, ES_OUT_SET_PCR, p_block->i_pts );
+                {
+                    block_FifoPut( p_sys->p_grab->p_fifo, p_block );
+                    p_block = NULL;
+                }
             }
 
             /* FIXME: this is a copy paste from below. Shouldn't be needed
              * twice. */
             case -EPIPE:
+            {
                 /* xrun */
                 snd_pcm_prepare( p_sys->p_alsa_pcm );
                 break;
+            }
             case -ESTRPIPE:
             {
                 /* suspend */
@@ -368,14 +447,23 @@ static int Demux( demux_t *p_demux )
                 break;
             }
             /* </FIXME> */
+            default:
+            {
+                if (i_wait == 0)
+                {
+                   snd_pcm_prepare( p_sys->p_alsa_pcm );
+                }
+                else
+                    msg_Err(p_demux, "returned: %d (%s)", i_wait, snd_strerror(i_wait));
+                break;
+            }
         }
-    } while( p_block && p_sys->i_next_demux_date > 0 &&
-             p_block->i_pts < p_sys->i_next_demux_date );
+    } while( vlc_object_alive( p_grab ) );
 
     if( p_block )
-        es_out_Send( p_demux->out, p_sys->p_es, p_block );
+        block_Release( p_block );
 
-    return 1;
+    return NULL;
 }
 
 
@@ -409,9 +497,14 @@ static block_t* GrabAudio( demux_t *p_demux )
             case -EAGAIN:
                 break;
             case -EPIPE:
+            {
                 /* xrun */
-                snd_pcm_prepare( p_sys->p_alsa_pcm );
+                int err = 0;
+                if ((err = snd_pcm_prepare( p_sys->p_alsa_pcm )) < 0 )
+                    msg_Info( p_demux, "GrabAudio ALSA snd_pcm_prepare returned (%s)",
+                              snd_strerror(err) );
                 break;
+            }
             case -ESTRPIPE:
                 /* suspend */
                 i_resume = snd_pcm_resume( p_sys->p_alsa_pcm );
@@ -462,7 +555,9 @@ static block_t* GrabAudio( demux_t *p_demux )
     p_block->i_pts = p_block->i_dts =
         mdate() - INT64_C(1000000) * (mtime_t)i_correct /
         2 / ( p_sys->b_stereo ? 2 : 1) / p_sys->i_sample_rate;
-
+#if 0
+    msg_Info( p_demux, "ALSA snd_pcm_read returned (%d bytes)", i_read );
+#endif
     return p_block;
 }