Implement suspend() and resume() for OfflineAudioContext

Source/modules/webaudio/OfflineAudioDestinationNode.cpp

 /*
  * Copyright (C) 2011, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1.  Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 10 matching lines @@
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #include "config.h"
 #if ENABLE(WEB_AUDIO)
 #include "modules/webaudio/OfflineAudioDestinationNode.h"
 
 #include "core/dom/CrossThreadTask.h"
 #include "modules/webaudio/AudioContext.h"
+#include "modules/webaudio/OfflineAudioContext.h"
 #include "platform/Task.h"
 #include "platform/audio/AudioBus.h"
 #include "platform/audio/HRTFDatabaseLoader.h"
 #include "public/platform/Platform.h"
 #include <algorithm>
 
 namespace blink {
 
 const size_t renderQuantumSize = 128;
 
 OfflineAudioDestinationHandler::OfflineAudioDestinationHandler(AudioNode& node, AudioBuffer* renderTarget)
     : AudioDestinationHandler(node, renderTarget->sampleRate())
     , m_renderTarget(renderTarget)
-    , m_startedRendering(false)
+    , m_framesProcessed(0)
+    , m_framesToProcess(0)
 {
     m_renderBus = AudioBus::create(renderTarget->numberOfChannels(), renderQuantumSize);
 }
 
 PassRefPtr<OfflineAudioDestinationHandler> OfflineAudioDestinationHandler::create(AudioNode& node, AudioBuffer* renderTarget)
 {
     return adoptRef(new OfflineAudioDestinationHandler(node, renderTarget));
 }
 
 OfflineAudioDestinationHandler::~OfflineAudioDestinationHandler()
@@ skipping 26 matching lines @@
     AudioHandler::uninitialize();
 }
 
 void OfflineAudioDestinationHandler::startRendering()
 {
     ASSERT(isMainThread());
     ASSERT(m_renderTarget);
     if (!m_renderTarget)
         return;
 
-    if (!m_startedRendering) {
-        m_startedRendering = true;
+    // Rendering was not started. Starting now.
+    if (!m_renderThread) {
         m_renderThread = adoptPtr(Platform::current()->createThread("Offline Audio Renderer"));
-        m_renderThread->postTask(FROM_HERE, new Task(threadSafeBind(&OfflineAudioDestinationHandler::offlineRender, PassRefPtr<OfflineAudioDestinationHandler>(this))));
+        m_renderThread->postTask(FROM_HERE, new Task(threadSafeBind(&OfflineAudioDestinationHandler::startOfflineRendering, this)));
+        return;
     }
+
+    // Rendering is already started, which implicitly means we resume the
+    // rendering by calling |runOfflineRendering| on m_renderThread.
+    m_renderThread->postTask(FROM_HERE, threadSafeBind(&OfflineAudioDestinationHandler::runOfflineRendering, this));
 }
 
 void OfflineAudioDestinationHandler::stopRendering()
 {
     ASSERT_NOT_REACHED();
 }
 
-void OfflineAudioDestinationHandler::offlineRender()
+size_t OfflineAudioDestinationHandler::quantizeTimeToRenderQuantum(double when) const
 {
-    offlineRenderInternal();
-    context()->handlePostRenderTasks();
+    ASSERT(when >= 0);
+
+    size_t whenAsFrame = when * sampleRate();
+    return whenAsFrame - (whenAsFrame % renderQuantumSize);
 }
 
-void OfflineAudioDestinationHandler::offlineRenderInternal()
+void OfflineAudioDestinationHandler::startOfflineRendering()
 {
     ASSERT(!isMainThread());
+
     ASSERT(m_renderBus);
     if (!m_renderBus)
         return;
 
     bool isAudioContextInitialized = context()->isInitialized();
     ASSERT(isAudioContextInitialized);
     if (!isAudioContextInitialized)
         return;
 
     bool channelsMatch = m_renderBus->numberOfChannels() == m_renderTarget->numberOfChannels();
     ASSERT(channelsMatch);
     if (!channelsMatch)
         return;
 
     bool isRenderBusAllocated = m_renderBus->length() >= renderQuantumSize;
     ASSERT(isRenderBusAllocated);
     if (!isRenderBusAllocated)
         return;
 
-    // Break up the render target into smaller "render quantize" sized pieces.
-    // Render until we're finished.
-    size_t framesToProcess = m_renderTarget->length();
+    m_framesToProcess = m_renderTarget->length();
+
+    // Start rendering.
+    runOfflineRendering();
+}
+
+void OfflineAudioDestinationHandler::runOfflineRendering()
+{
+    ASSERT(!isMainThread());
+
     unsigned numberOfChannels = m_renderTarget->numberOfChannels();
 
-    unsigned n = 0;
-    while (framesToProcess > 0) {
-        // Render one render quantum.
+    // If there is more to process and there is no suspension at the moment,
+    // do continue to render quanta. If there is a suspend scheduled at the
+    // current sample frame, stop the render loop and put the context into the
+    // suspended state. Then calling OfflineAudioContext.resume() will pick up
+    // the render loop again from where it was suspended.
+    while (m_framesToProcess > 0 && !context()->shouldSuspendNow()) {
+
+        // Render one render quantum. Note that this includes pre/post render
+        // tasks from the online audio context.
         render(0, m_renderBus.get(), renderQuantumSize);
 
-        size_t framesAvailableToCopy = std::min(framesToProcess, renderQuantumSize);
+        size_t framesAvailableToCopy = std::min(m_framesToProcess, renderQuantumSize);
 
         for (unsigned channelIndex = 0; channelIndex < numberOfChannels; ++channelIndex) {
             const float* source = m_renderBus->channel(channelIndex)->data();
             float* destination = m_renderTarget->getChannelData(channelIndex)->data();
-            memcpy(destination + n, source, sizeof(float) * framesAvailableToCopy);
+            memcpy(destination + m_framesProcessed, source, sizeof(float) * framesAvailableToCopy);
         }
 
-        n += framesAvailableToCopy;
-        framesToProcess -= framesAvailableToCopy;
+        m_framesProcessed += framesAvailableToCopy;
+        m_framesToProcess -= framesAvailableToCopy;
     }
 
+    // Finish up the rendering loop if there is no more to process.
+    if (m_framesToProcess <= 0) {
+        finishOfflineRendering();
+        return;
+    }
+
+    // Otherwise resolve pending suspend promises.
+    context()->resolvePendingSuspendPromises();
+}
+
+void OfflineAudioDestinationHandler::finishOfflineRendering()
+{
+    ASSERT(!isMainThread());
+
+    // Perform post-render tasks once more.
+    context()->handlePostRenderTasks();

[Raymond Toy, 2015/06/16 17:57:09]

Is this necessary?  Is there something that could have happened between the last
call to render() and this that needs cleanup? It probably doesn't matter, but
I'm curious to know if you see some case where something still needs to be
handled.

[hongchan, 2015/06/16 21:31:21]

I've thought about it and I think we should remove this. In the previous
implementation, handling post render task depended on the tryLock() mechanism.
It means there was a possibility of missing the chance to run the task. However,
now we forced the OAC to execute the post render task and thus we don't need
this anymore.

+
     // Our work is done. Let the AudioContext know.
     if (context()->executionContext())
-        context()->executionContext()->postTask(FROM_HERE, createCrossThreadTask(&OfflineAudioDestinationHandler::notifyComplete, PassRefPtr<OfflineAudioDestinationHandler>(this)));
+        context()->executionContext()->postTask(FROM_HERE, createCrossThreadTask(&OfflineAudioDestinationHandler::notifyComplete, this));
 }
 
 void OfflineAudioDestinationHandler::notifyComplete()
 {
-    // The AudioContext might be gone.
+    // The OfflineAudioContext might be gone.
     if (context())
         context()->fireCompletionEvent();
 }
 
 // ----------------------------------------------------------------
 
 OfflineAudioDestinationNode::OfflineAudioDestinationNode(AudioContext& context, AudioBuffer* renderTarget)
     : AudioDestinationNode(context)
 {
     setHandler(OfflineAudioDestinationHandler::create(*this, renderTarget));
 }
 
 OfflineAudioDestinationNode* OfflineAudioDestinationNode::create(AudioContext* context, AudioBuffer* renderTarget)
 {
     return new OfflineAudioDestinationNode(*context, renderTarget);
 }
 
 } // namespace blink
 
 #endif // ENABLE(WEB_AUDIO)