Implement suspend() and resume() for OfflineAudioContext

Source/modules/webaudio/OfflineAudioDestinationNode.cpp

Index: Source/modules/webaudio/OfflineAudioDestinationNode.cpp
diff --git a/Source/modules/webaudio/OfflineAudioDestinationNode.cpp b/Source/modules/webaudio/OfflineAudioDestinationNode.cpp
index dc3e752110b98e4fd2a3f986548af82da6767041..beb8623f26dbd005c6e11c0d38d2ae7c915a45d3 100644
--- a/Source/modules/webaudio/OfflineAudioDestinationNode.cpp
+++ b/Source/modules/webaudio/OfflineAudioDestinationNode.cpp
@@ -28,6 +28,7 @@
 
 #include "core/dom/CrossThreadTask.h"
 #include "modules/webaudio/AbstractAudioContext.h"
+#include "modules/webaudio/OfflineAudioContext.h"
 #include "platform/Task.h"
 #include "platform/audio/AudioBus.h"
 #include "platform/audio/HRTFDatabaseLoader.h"
@@ -41,7 +42,10 @@ const size_t renderQuantumSize = 128;
 OfflineAudioDestinationHandler::OfflineAudioDestinationHandler(AudioNode& node, AudioBuffer* renderTarget)
     : AudioDestinationHandler(node, renderTarget->sampleRate())
     , m_renderTarget(renderTarget)
-    , m_startedRendering(false)
+    , m_renderThread(adoptPtr(Platform::current()->createThread("offline audio renderer")))
+    , m_framesProcessed(0)
+    , m_framesToProcess(0)
+    , m_isRenderingStarted(false)
 {
     m_renderBus = AudioBus::create(renderTarget->numberOfChannels(), renderQuantumSize);
 }
@@ -81,18 +85,30 @@ void OfflineAudioDestinationHandler::uninitialize()
     AudioHandler::uninitialize();
 }
 
+OfflineAudioContext* OfflineAudioDestinationHandler::context() const
+{
+    return static_cast<OfflineAudioContext*>(m_context);
+}
+
 void OfflineAudioDestinationHandler::startRendering()
 {
     ASSERT(isMainThread());
     ASSERT(m_renderTarget);
+    ASSERT(m_renderThread);
+
     if (!m_renderTarget)
         return;
 
-    if (!m_startedRendering) {
-        m_startedRendering = true;
-        m_renderThread = adoptPtr(Platform::current()->createThread("Offline Audio Renderer"));
-        m_renderThread->postTask(FROM_HERE, new Task(threadSafeBind(&OfflineAudioDestinationHandler::offlineRender, PassRefPtr<OfflineAudioDestinationHandler>(this))));
+    // Rendering was not started. Starting now.
+    if (!m_isRenderingStarted) {
+        m_renderThread->postTask(FROM_HERE, new Task(threadSafeBind(&OfflineAudioDestinationHandler::startOfflineRendering, this)));
+        m_isRenderingStarted = true;
+        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()
@@ -100,15 +116,25 @@ void OfflineAudioDestinationHandler::stopRendering()
     ASSERT_NOT_REACHED();
 }
 
-void OfflineAudioDestinationHandler::offlineRender()
+size_t OfflineAudioDestinationHandler::quantizeTimeToRenderQuantum(double when) const
+{
+    ASSERT(when >= 0);
+
+    size_t whenAsFrame = when * sampleRate();
+    return whenAsFrame - (whenAsFrame % renderQuantumSize);
+}
+
+WebThread* OfflineAudioDestinationHandler::offlineRenderThread()
 {
-    offlineRenderInternal();
-    context()->handlePostRenderTasks();
+    ASSERT(m_renderThread);
+
+    return m_renderThread.get();
 }
 
-void OfflineAudioDestinationHandler::offlineRenderInternal()
+void OfflineAudioDestinationHandler::startOfflineRendering()
 {
     ASSERT(!isMainThread());
+
     ASSERT(m_renderBus);
     if (!m_renderBus)
         return;
@@ -128,31 +154,59 @@ void OfflineAudioDestinationHandler::offlineRenderInternal()
     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) {
+        ASSERT(m_framesToProcess == 0);
+        finishOfflineRendering();
+        return;
+    }
+
+    // Otherwise resolve pending suspend promises.
+    context()->resolvePendingSuspendPromises();
+}
+
+void OfflineAudioDestinationHandler::finishOfflineRendering()
+{
+    ASSERT(!isMainThread());
+
     // Our work is done. Let the AbstractAudioContext 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()