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 87374edd52f409f7dedee7624efbcd28db28c724..e8458511cda0b75e8caa0acdd0a73ac551168414 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/AudioContext.h"
+#include "modules/webaudio/OfflineAudioContext.h"
 #include "platform/Task.h"
 #include "platform/audio/AudioBus.h"
 #include "platform/audio/HRTFDatabaseLoader.h"
@@ -36,14 +37,16 @@
 
 namespace blink {
 
-const size_t renderQuantumSize = 128;
+const size_t kRenderQuantumSize = 128;

[Raymond Toy, 2015/05/13 17:16:08]

Don't rename.

[hongchan, 2015/05/13 17:30:53]

renderQuantumSize does look like a local variable. Adding 'k' at the head seems
to be reasonable and helpful. Is there any other way to express this variable is
a constant for this class?

[Raymond Toy, 2015/05/19 21:46:40]

Blink style guide doesn't seem to say, but I think the chromium style is start
with k.

This isn't really relevant to this CL.

[hongchan, 2015/05/20 22:09:40]

Acknowledged. Will change in PS4.

 
 OfflineAudioDestinationHandler::OfflineAudioDestinationHandler(AudioNode& node, AudioBuffer* renderTarget)
     : AudioDestinationHandler(node, renderTarget->sampleRate())
     , m_renderTarget(renderTarget)
-    , m_startedRendering(false)
+    , m_isRenderingStarted(false)
+    , m_framesProcessed(0)
+    , m_framesToProcess(0)
 {
-    m_renderBus = AudioBus::create(renderTarget->numberOfChannels(), renderQuantumSize);
+    m_renderBus = AudioBus::create(renderTarget->numberOfChannels(), kRenderQuantumSize);
 }
 
 PassRefPtr<OfflineAudioDestinationHandler> OfflineAudioDestinationHandler::create(AudioNode& node, AudioBuffer* renderTarget)
@@ -88,11 +91,23 @@ void OfflineAudioDestinationHandler::startRendering()
     if (!m_renderTarget)
         return;
 
-    if (!m_startedRendering) {
-        m_startedRendering = true;
+    // fprintf(stderr, "startRendering() called\n");
+
+    // Rendering was not started. Starting now.
+    if (!m_isRenderingStarted) {
+        m_isRenderingStarted = true;
         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::initiateOfflineRendering, this)));
+        return;
     }
+
+    // Rendering was already started, which implicitly means we resume the
+    // rendering by calling |renderNextQuantum| on m_renderThread.
+    // TO FIX: is there any corner case for this?
+    m_renderThread->postTask(FROM_HERE,
+        threadSafeBind(&OfflineAudioDestinationHandler::renderNextQuantum, this));
+    return;
 }
 
 void OfflineAudioDestinationHandler::stopRendering()
@@ -100,15 +115,10 @@ void OfflineAudioDestinationHandler::stopRendering()
     ASSERT_NOT_REACHED();
 }
 
-void OfflineAudioDestinationHandler::offlineRender()
-{
-    offlineRenderInternal();
-    context()->handlePostRenderTasks();
-}
-
-void OfflineAudioDestinationHandler::offlineRenderInternal()
+void OfflineAudioDestinationHandler::initiateOfflineRendering()
 {
     ASSERT(!isMainThread());
+
     ASSERT(m_renderBus);
     if (!m_renderBus)
         return;
@@ -123,36 +133,66 @@ void OfflineAudioDestinationHandler::offlineRenderInternal()
     if (!channelsMatch)
         return;
 
-    bool isRenderBusAllocated = m_renderBus->length() >= renderQuantumSize;
+    bool isRenderBusAllocated = m_renderBus->length() >= kRenderQuantumSize;
     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();
-    unsigned numberOfChannels = m_renderTarget->numberOfChannels();
+    m_framesToProcess = m_renderTarget->length();
 
-    unsigned n = 0;
-    while (framesToProcess > 0) {
-        // Render one render quantum.
-        render(0, m_renderBus.get(), renderQuantumSize);
+    // Initiate rendering.
+    renderNextQuantum();
+}
 
-        size_t framesAvailableToCopy = std::min(framesToProcess, renderQuantumSize);
+void OfflineAudioDestinationHandler::renderNextQuantum()
+{
+    ASSERT(!isMainThread());
 
-        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);
+    if (context()->suspendIfNecessary()) {
+        if (context()->executionContext()) {
+            context()->executionContext()->postTask(FROM_HERE,
+                createCrossThreadTask(&OfflineAudioDestinationHandler::notifySuspend, this));
         }
+        return;
+    }
+
+    // Render one render quantum. Note that this includes pre/post render tasks.
+    render(0, m_renderBus.get(), kRenderQuantumSize);
 
-        n += framesAvailableToCopy;
-        framesToProcess -= framesAvailableToCopy;
+    unsigned numberOfChannels = m_renderTarget->numberOfChannels();
+    size_t framesAvailableToCopy = std::min(m_framesToProcess, kRenderQuantumSize);
+
+    for (unsigned channelIndex = 0; channelIndex < numberOfChannels; ++channelIndex) {
+        const float* source = m_renderBus->channel(channelIndex)->data();
+        float* destination = m_renderTarget->getChannelData(channelIndex)->data();
+        memcpy(destination + m_framesProcessed, source, sizeof(float) * framesAvailableToCopy);
     }
 
+    m_framesProcessed += framesAvailableToCopy;
+    m_framesToProcess -= framesAvailableToCopy;
+
+    if (m_framesToProcess > 0)
+        renderNextQuantum();
+    else
+        finishOfflineRendering();
+}
+
+void OfflineAudioDestinationHandler::finishOfflineRendering()
+{
+    ASSERT(!isMainThread());
+
     // Our work is done. Let the AudioContext know.
-    if (context()->executionContext())
-        context()->executionContext()->postTask(FROM_HERE, createCrossThreadTask(&OfflineAudioDestinationHandler::notifyComplete, PassRefPtr<OfflineAudioDestinationHandler>(this)));
+    if (context()->executionContext()) {
+        context()->executionContext()->postTask(FROM_HERE,
+            createCrossThreadTask(&OfflineAudioDestinationHandler::notifyComplete, this));
+    }
+}
+
+void OfflineAudioDestinationHandler::notifySuspend()
+{
+    // The AudioContext might be gone.
+    if (context())

[Raymond Toy, 2015/05/13 17:16:08]

How can the context go away?

[hongchan, 2015/05/13 17:30:53]

I simply used the code below. I should think about corner cases for this.

+        context()->fireSuspendEvent();
 }
 
 void OfflineAudioDestinationHandler::notifyComplete()