WASAPI: better pause/unpause and clear buffer behavior

See libuv#3

example/sio_sine.c

@@ -186,6 +186,11 @@ int main(int argc, char **argv) {
         return 1;
     }
 
+    fprintf(stderr,
+            "'p\\n' - pause\n"
+            "'u\\n' - unpause\n"
+            "'c\\n' - clear buffer\n"
+            "'q\\n' - quit\n");
     fprintf(stderr, "Output device: %s\n", device->name);
 
     if (device->probe_error) {

soundio/soundio.h

@@ -973,12 +973,17 @@ SOUNDIO_EXPORT int soundio_outstream_end_write(struct SoundIoOutStream *outstrea
 
 /// Clears the output stream buffer.
 /// This function can be called from any thread.
+/// This function can be called regardless of whether the outstream is paused
+/// or not.
 /// Some backends do not support clearing the buffer. On these backends this
 /// function will return SoundIoErrorIncompatibleBackend.
+/// Some devices do not support clearing the buffer. On these devices this
+/// function might return SoundIoErrorIncompatibleDevice.
 /// Possible errors:
 ///
 /// * #SoundIoErrorStreaming
 /// * #SoundIoErrorIncompatibleBackend
+/// * #SoundIoErrorIncompatibleDevice
 SOUNDIO_EXPORT int soundio_outstream_clear_buffer(struct SoundIoOutStream *outstream);
 
 /// If the underlying device supports pausing, this pauses the stream.

src/alsa.cpp

@@ -1138,6 +1138,7 @@ static void instream_thread_run(void *arg) {
                 }
                 continue;
             case SND_PCM_STATE_RUNNING:
+            case SND_PCM_STATE_PAUSED:
             {
                 if ((err = instream_wait_for_poll(is)) < 0) {
                     if (!isa->thread_exit_flag.test_and_set())
@@ -1176,7 +1177,6 @@ static void instream_thread_run(void *arg) {
                 continue;
             case SND_PCM_STATE_OPEN:
             case SND_PCM_STATE_DRAINING:
-            case SND_PCM_STATE_PAUSED:
             case SND_PCM_STATE_DISCONNECTED:
                 instream->error_callback(instream, SoundIoErrorStreaming);
                 return;

src/wasapi.cpp

@@ -1246,14 +1246,46 @@ void outstream_shared_run(SoundIoOutStreamPrivate *os) {
             return;
         }
         soundio_os_mutex_unlock(osw->mutex);
+        bool reset_buffer = false;
+        if (!osw->clear_buffer_flag.test_and_set()) {
+            if (!osw->is_paused) {
+                if (FAILED(hr = IAudioClient_Stop(osw->audio_client))) {
+                    outstream->error_callback(outstream, SoundIoErrorStreaming);
+                    return;
+                }
+                osw->is_paused = true;
+            }
+            if (FAILED(hr = IAudioClient_Reset(osw->audio_client))) {
+                outstream->error_callback(outstream, SoundIoErrorStreaming);
+                return;
+            }
+            osw->pause_resume_flag.clear();
+            reset_buffer = true;
+        }
+        if (!osw->pause_resume_flag.test_and_set()) {
+            bool pause = osw->desired_pause_state.load();
+            if (pause && !osw->is_paused) {
+                if (FAILED(hr = IAudioClient_Stop(osw->audio_client))) {
+                    outstream->error_callback(outstream, SoundIoErrorStreaming);
+                    return;
+                }
+                osw->is_paused = true;
+            } else if (!pause && osw->is_paused) {
+                if (FAILED(hr = IAudioClient_Start(osw->audio_client))) {
+                    outstream->error_callback(outstream, SoundIoErrorStreaming);
+                    return;
+                }
+                osw->is_paused = false;
+            }
+        }
 
         if (FAILED(hr = IAudioClient_GetCurrentPadding(osw->audio_client, &frames_used))) {
             outstream->error_callback(outstream, SoundIoErrorStreaming);
             return;
         }
         osw->writable_frame_count = osw->buffer_frame_count - frames_used;
         if (osw->writable_frame_count > 0) {
-            if (frames_used == 0)
+            if (frames_used == 0 && !reset_buffer)
                 outstream->underflow_callback(outstream);
             outstream->write_callback(outstream, 0, osw->writable_frame_count);
         }
@@ -1277,6 +1309,22 @@ void outstream_raw_run(SoundIoOutStreamPrivate *os) {
         WaitForSingleObject(osw->h_event, INFINITE);
         if (!osw->thread_exit_flag.test_and_set())
             return;
+        if (!osw->pause_resume_flag.test_and_set()) {
+            bool pause = osw->desired_pause_state.load();
+            if (pause && !osw->is_paused) {
+                if (FAILED(hr = IAudioClient_Stop(osw->audio_client))) {
+                    outstream->error_callback(outstream, SoundIoErrorStreaming);
+                    return;
+                }
+                osw->is_paused = true;
+            } else if (!pause && osw->is_paused) {
+                if (FAILED(hr = IAudioClient_Start(osw->audio_client))) {
+                    outstream->error_callback(outstream, SoundIoErrorStreaming);
+                    return;
+                }
+                osw->is_paused = false;
+            }
+        }
 
         outstream->write_callback(outstream, osw->buffer_frame_count, osw->buffer_frame_count);
     }
@@ -1331,6 +1379,10 @@ static int outstream_open_wasapi(struct SoundIoPrivate *si, struct SoundIoOutStr
     SoundIoDevice *device = outstream->device;
     SoundIo *soundio = &si->pub;
 
+    osw->pause_resume_flag.test_and_set();
+    osw->clear_buffer_flag.test_and_set();
+    osw->desired_pause_state.store(false);
+
     // All the COM functions are supposed to be called from the same thread. libsoundio API does not
     // restrict the calling thread context in this way. Furthermore, the user might have called
     // CoInitializeEx with a different threading model than Single Threaded Apartment.
@@ -1385,19 +1437,19 @@ static int outstream_open_wasapi(struct SoundIoPrivate *si, struct SoundIoOutStr
     return 0;
 }
 
-
 static int outstream_pause_wasapi(struct SoundIoPrivate *si, struct SoundIoOutStreamPrivate *os, bool pause) {
     SoundIoOutStreamWasapi *osw = &os->backend_data.wasapi;
-    HRESULT hr;
-    if (pause && !osw->is_paused) {
-        if (FAILED(hr = IAudioClient_Stop(osw->audio_client)))
-            return SoundIoErrorStreaming;
-        osw->is_paused = true;
-    } else if (!pause && osw->is_paused) {
-        if (FAILED(hr = IAudioClient_Start(osw->audio_client)))
-            return SoundIoErrorStreaming;
-        osw->is_paused = false;
+
+    osw->desired_pause_state.store(pause);
+    osw->pause_resume_flag.clear();
+    if (osw->h_event) {
+        SetEvent(osw->h_event);
+    } else {
+        soundio_os_mutex_lock(osw->mutex);
+        soundio_os_cond_signal(osw->cond, osw->mutex);
+        soundio_os_mutex_unlock(osw->mutex);
     }
+
     return 0;
 }
 
@@ -1450,9 +1502,15 @@ static int outstream_end_write_wasapi(struct SoundIoPrivate *si, struct SoundIoO
 
 static int outstream_clear_buffer_wasapi(struct SoundIoPrivate *si, struct SoundIoOutStreamPrivate *os) {
     SoundIoOutStreamWasapi *osw = &os->backend_data.wasapi;
-    HRESULT hr;
-    if (FAILED(hr = IAudioClient_Reset(osw->audio_client)))
-        return SoundIoErrorStreaming;
+
+    if (osw->h_event) {
+        return SoundIoErrorIncompatibleDevice;
+    } else {
+        osw->clear_buffer_flag.clear();
+        soundio_os_mutex_lock(osw->mutex);
+        soundio_os_cond_signal(osw->cond, osw->mutex);
+        soundio_os_mutex_unlock(osw->mutex);
+    }
 
     return 0;
 }

src/wasapi.hpp

@@ -67,6 +67,9 @@ struct SoundIoOutStreamWasapi {
     UINT32 buffer_frame_count;
     int write_frame_count;
     HANDLE h_event;
+    atomic_bool desired_pause_state;
+    atomic_flag pause_resume_flag;
+    atomic_flag clear_buffer_flag;
     bool is_paused;
     bool open_complete;
     int open_err;