Implement suspend() and resume() for OfflineAudioContext

Source/modules/webaudio/OfflineAudioContext.h

Index: Source/modules/webaudio/OfflineAudioContext.h
diff --git a/Source/modules/webaudio/OfflineAudioContext.h b/Source/modules/webaudio/OfflineAudioContext.h
index 99276e7cbb5e19dc7edf2934b67a726f2eed8d2a..276110fe2798128a2aa3b38fc9358e2ad2df53c8 100644
--- a/Source/modules/webaudio/OfflineAudioContext.h
+++ b/Source/modules/webaudio/OfflineAudioContext.h
@@ -31,6 +31,7 @@
 namespace blink {
 
 class ExceptionState;
+class ScheduledSuspendContainer;
 
 class MODULES_EXPORT OfflineAudioContext final : public AudioContext {
     DEFINE_WRAPPERTYPEINFO();
@@ -39,9 +40,91 @@ public:
 
     virtual ~OfflineAudioContext();
 
+    DECLARE_VIRTUAL_TRACE();
+
+    // Fire completion event when the rendering is finished.
+    void fireCompletionEvent() override;
+
+    // Check all the scheduled suspends if the context should suspend at
+    // currentTime(). Then post tasks to resolve promises on the main thread
+    // if necessary.
+    bool shouldSuspendNow() override;
+
+    // Clear suspensions marked as 'resolved' in the list.
+    void resolvePendingSuspendPromises() override;
+
+    DEFINE_ATTRIBUTE_EVENT_LISTENER(complete);
+
     ScriptPromise startOfflineRendering(ScriptState*);
+    ScriptPromise suspendOfflineRendering(ScriptState*, double);
+    ScriptPromise resumeOfflineRendering(ScriptState*);
+
 private:
     OfflineAudioContext(Document*, unsigned numberOfChannels, size_t numberOfFrames, float sampleRate);
+
+    // Validate a suspend with various criteria on the render thread.
+    void checkDuplicateSuspend(ScheduledSuspendContainer*);
+
+    // TODO: Reject a suspend on the main thread after the validation fails.
+    void rejectSuspendOnMainThread(ScheduledSuspendContainer*);
+
+    // Resolve pending suspend promises and removes them from the list.
+    void resolvePendingSuspendPromisesOnMainThread();
+
+    HeapVector<Member<ScheduledSuspendContainer>> m_scheduledSuspends;
+    RefPtrWillBeMember<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.
+    bool m_isRenderingStarted;
+
+    // Total render sample length.
+    size_t m_totalRenderFrames;
+
+    // MutexLocker for m_scheduledSuspends.
+    Mutex m_suspendMutex;
+};
+
+// A container class for a pair of time information and the suspend promise
+// resolver.
+class ScheduledSuspendContainer : public GarbageCollectedFinalized<ScheduledSuspendContainer> {
+public:
+    static ScheduledSuspendContainer* create(double suspendTime, size_t suspendFrame, PassRefPtrWillBeRawPtr<ScriptPromiseResolver>);
+    ~ScheduledSuspendContainer();
+
+    DECLARE_TRACE();
+
+    PassRefPtrWillBeRawPtr<ScriptPromiseResolver> resolver() { return m_resolver; }
+
+    double suspendTime() const { return m_suspendTime; }
+
+    size_t suspendFrame() const { return m_suspendFrame; }
+
+    // Query if the rendering should be suspended at |whenFrame|.
+    bool shouldSuspendAtFrame(size_t whenFrame) const;
+
+    // Query if the suspend is pending for the promise resolution.
+    bool isPending() const;
+
+    // Mark the suspend as pending. Containers with 'pending' flag will
+    // be collectively resolved when the actual suspension happens.
+    void markAsPending();
+
+private:
+    ScheduledSuspendContainer(double suspendTime, size_t suspendFrame, PassRefPtrWillBeRawPtr<ScriptPromiseResolver>);
+
+    // Actual suspend time before the quantization by render quantum frame.
+    double m_suspendTime;
+
+    // Suspend time in samples.
+    size_t m_suspendFrame;
+
+    // Associated promise resolver.
+    RefPtrWillBeMember<ScriptPromiseResolver> m_resolver;
+
+    // A pending marker for the safe batch removal.
+    bool m_isPending;
 };
 
 } // namespace blink