Implement suspend() and resume() for OfflineAudioContext

third_party/WebKit/Source/modules/webaudio/OfflineAudioContext.h

Index: third_party/WebKit/Source/modules/webaudio/OfflineAudioContext.h
diff --git a/third_party/WebKit/Source/modules/webaudio/OfflineAudioContext.h b/third_party/WebKit/Source/modules/webaudio/OfflineAudioContext.h
index 030586f4d409064f9104460129d823414c9ac71f..8e8bd4a1a3fc2c61fd41423934df07b8405fab73 100644
--- a/third_party/WebKit/Source/modules/webaudio/OfflineAudioContext.h
+++ b/third_party/WebKit/Source/modules/webaudio/OfflineAudioContext.h
@@ -28,9 +28,16 @@
 #include "modules/ModulesExport.h"
 #include "modules/webaudio/AbstractAudioContext.h"
 
+#include "wtf/HashMap.h"
+
 namespace blink {
 
 class ExceptionState;
+class OfflineAudioDestinationHandler;
+
+// The HashMap with 'zero' key is needed because |currentSampleFrame| can be
+// zero.
+using SuspendMap = HeapHashMap<size_t, Member<ScriptPromiseResolver>, DefaultHash<size_t>::Hash, WTF::UnsignedWithZeroKeyHashTraits<size_t>>;
 
 class MODULES_EXPORT OfflineAudioContext final : public AbstractAudioContext {
     DEFINE_WRAPPERTYPEINFO();
@@ -39,16 +46,62 @@ public:
 
     ~OfflineAudioContext() override;
 
+    DECLARE_VIRTUAL_TRACE();
+
     ScriptPromise startOfflineRendering(ScriptState*);
 
     ScriptPromise closeContext(ScriptState*) final;
-    ScriptPromise suspendContext(ScriptState*) final;
+    ScriptPromise suspendContext(ScriptState*, double) final;
     ScriptPromise resumeContext(ScriptState*) final;
 
+    // This is to implement the pure virtual method from AbstractAudioContext.
+    // CANNOT be called on OfflineAudioContext.

[Raymond Toy, 2015/10/16 23:32:36]

What does "called on OfflineAudioContext" mean here?  You're really saying
suspend without a time value is not valid for offline contexts?

[hongchan, 2015/10/19 20:08:12]

Yes, the IDL will raise the exception if the time argument is not provided. I
think it is a part of what we have on the spec? The time argument is not
optional or nullable.

[Raymond Toy, 2015/10/19 20:27:27]

Maybe change "called on Offline..." with "called for an ..." or "called from an
..."

[hongchan, 2015/10/20 22:03:06]

Done.

+    ScriptPromise suspendContext(ScriptState*) final;
+
     bool hasRealtimeConstraint() final { return false; }
 
+    DEFINE_ATTRIBUTE_EVENT_LISTENER(complete);
+
+    // Fire completion event when the rendering is suspended.
+    void fireSuspendedEvent();
+
+    // Fire completion event when the rendering is finished.
+    void fireCompletionEvent();
+
+    bool handlePreOfflineRenderTasks();
+    void handlePostOfflineRenderTasks();
+
+    // Resolve a suspend scheduled at the specified frame. With this specified
+    // frame as a unique key, the associated promise resolver can be retrieved
+    // from the map (m_scheduledSuspends) and resolved.
+    void resolveSuspendOnMainThread(size_t);
+
 private:
     OfflineAudioContext(Document*, unsigned numberOfChannels, size_t numberOfFrames, float sampleRate);
+
+    // Fetch directly the destination handler.
+    OfflineAudioDestinationHandler& destinationHandler();
+
+    AudioBuffer* renderTarget() const { return m_renderTarget.get(); }
+
+    // Check if the rendering needs to be suspended.
+    bool shouldSuspend();
+
+    Member<AudioBuffer> m_renderTarget;
+
+    // This map is to store the timing of scheduled suspends (frame) and the
+    // associated promise resolver.
+    SuspendMap m_scheduledSuspends;

[Raymond Toy, 2015/10/16 23:32:36]

Say something that this can only be read or written by the main thread?

[hongchan, 2015/10/19 20:08:12]

Done.

+
+    Member<ScriptPromiseResolver> m_completeResolver;
+
+    // This flag is necessary to indicate the rendering has actually started.
+    // Note that initial state of context is 'Suspended', which is the same
+    // state when the context is suspended.

[Raymond Toy, 2015/10/16 23:32:36]

Not for this CL, but maybe it would be good in the spec to allow a new state,
say, 'Initialized', for offline contexts.  I guess online context can also start
in 'Initialized' but transition right away to 'Running'.

[hongchan, 2015/10/19 20:08:12]

I agree with the idea, but I suggest a different name for the initial state.
Here the life of AC/OAC in my mind:
created > running > suspended > running > closed

+    bool m_isRenderingStarted;
+
+    // Total render sample length.
+    size_t m_totalRenderFrames;
 };
 
 } // namespace blink