sndio: emulate flush

This is really crappy, but it's as good as I can make it with such a
dumb interface.

modules/audio_output/sndio.c

@@ -46,6 +46,7 @@ vlc_module_end ()
 static int TimeGet (audio_output, mtime_t *);
 static void Play (audio_output_t *, block_t *);
 static void Pause (audio_output_t *, bool, mtime_t);
+static void Flush (audio_output_t *, bool);
 static int VolumeSet (audio_output_t *, float);
 static int MuteSet (audio_output_t *, bool);
 static void VolumeChanged (void *, unsigned);
@@ -59,6 +60,7 @@ struct aout_sys_t
     unsigned rate;
     unsigned volume;
     bool mute;
+    bool paused;
 };
 
 /** Initializes an sndio playback stream */
@@ -158,7 +160,7 @@ static int Start (audio_output_t *aout, audio_sample_format_t *restrict fmt)
     aout->time_get = TimeGet;
     aout->play = Play;
     aout->pause = Pause;
-    aout->flush  = NULL; /* sndio sucks! */
+    aout->flush = Flush;
     if (sio_onvol(sys->hdl, VolumeChanged, aout))
     {
         aout->volume_set = VolumeSet;
@@ -172,6 +174,7 @@ static int Start (audio_output_t *aout, audio_sample_format_t *restrict fmt)
 
     sys->read_offset = 0;
     sys->write_offset = 0;
+    sys->paused = false;
     sio_onmove (sys->hdl, PositionChanged, aout);
     sio_start (sys->hdl);
     return VLC_SUCCESS;
@@ -238,9 +241,33 @@ static void Pause (audio_output_t *aout, bool pause, mtime_t date)
         sys->write_offset = 0;
         sio_start (sys->hdl);
     }
+    sys->paused = pause;
     (void) date;
 }
 
+static void Drain (audio_output_t *aout)
+{
+    long long frames = sys->write_offset - sys->read_offset;
+
+    if (frames > 0)
+        msleep (frames * CLOCK_FREQ / sys->rate);
+}
+
+static void Flush (audio_output_t *aout, bool wait)
+{
+    if (wait)
+    {
+        Drain (aout);
+    }
+    else
+    {
+        if (sys->paused)
+            return;
+        Pause (aout, true);
+        Pause (aout, false);
+    }
+}
+
 static void VolumeChanged (void *arg, unsigned volume)
 {
     audio_output_t *aout = arg;