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 030586f4d409064f9104460129d823414c9ac71f..cf32cc77ac25cbb0983825d1f6f1c2decaa6ca98 100644
--- a/Source/modules/webaudio/OfflineAudioContext.h
+++ b/Source/modules/webaudio/OfflineAudioContext.h
@@ -28,9 +28,20 @@
 #include "modules/ModulesExport.h"
 #include "modules/webaudio/AbstractAudioContext.h"
 
+#include "wtf/HashMap.h"
+#include "wtf/HashSet.h"
+
 namespace blink {
 
 class ExceptionState;
+class ScheduledSuspendContainer;
+class OfflineAudioDestinationHandler;
+
+// The HashMap with 'zero' key is needed because |currentSampleFrame| can be
+// zero. Also ScheduledSuspendContainer is a raw pointer (rather than RefPtr)
+// because it must be guaranteed that the main thread keeps it alive while the
+// render thread uses it.
+using SuspendContainerMap = HashMap<size_t, ScheduledSuspendContainer*, DefaultHash<size_t>::Hash, WTF::UnsignedWithZeroKeyHashTraits<size_t>>;
 
 class MODULES_EXPORT OfflineAudioContext final : public AbstractAudioContext {
     DEFINE_WRAPPERTYPEINFO();
@@ -39,16 +50,90 @@ public:
 
     ~OfflineAudioContext() override;
 
+    DECLARE_VIRTUAL_TRACE();
+
+    DEFINE_ATTRIBUTE_EVENT_LISTENER(complete);
+
+    // 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();
+
+    // Clear suspensions marked as 'resolved' in the list.
+    void resolvePendingSuspendPromises();
+
+    // Fire completion event when the rendering is finished.
+    void fireCompletionEvent();
+
     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.
+    ScriptPromise suspendContext(ScriptState*) final;
+
     bool hasRealtimeConstraint() final { return false; }
 
 private:
     OfflineAudioContext(Document*, unsigned numberOfChannels, size_t numberOfFrames, float sampleRate);
+
+    // Fetch directly the destination handler.
+    OfflineAudioDestinationHandler& destinationHandler();
+
+    // Check a suspend container if it has a duplicate scheduled frame or
+    // is behind the current frame. If the validation fails, post a task to the
+    // main thread to reject the promise.
+    void validateSuspendContainerOnRenderThread(ScheduledSuspendContainer*, double, size_t);
+
+    // Reject a suspend container on the main thread when the validation fails.
+    void rejectSuspendContainerOnMainThread(ScheduledSuspendContainer*, const String&);
+
+    // Resolve a pending suspend container.
+    void resolveSuspendContainerOnMainThread(ScheduledSuspendContainer*);
+
+    // This set is for maintaining the ownership of SchduledSuspendContainer
+    // raw pointers. It is accessed only on the main thread and its elements
+    // (ScheduledSuspendContainer*) are constructed/destructed on the main
+    // thread.
+    HashSet<ScheduledSuspendContainer*> m_suspendContainers;
+
+    // This map is to check the timing of scheduled suspends. This is accessed
+    // only by the offline render thread and its value
+    // (ScheduledSuspendContainer*) must not be dereferenced in the render
+    // thread.
+    SuspendContainerMap m_scheduledSuspendContainers;
+
+    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;
+};
+
+// A container class for a pair of time information and the suspend promise
+// resolver. This class does not need to be |ThreadSafeRefCounted| because it
+// needs to be created and destructed in the main thread.
+class ScheduledSuspendContainer {
+public:
+    static ScheduledSuspendContainer* create(PassRefPtrWillBeRawPtr<ScriptPromiseResolver>);
+    ~ScheduledSuspendContainer();
+
+    // {Resolve, Reject} the promise resolver on the main thread.
+    void resolvePromise();
+    void rejectPromise(ExceptionCode, const String&);
+
+private:
+    ScheduledSuspendContainer(PassRefPtrWillBeRawPtr<ScriptPromiseResolver>);
+
+    // Associated promise resolver.
+    RefPtrWillBePersistent<ScriptPromiseResolver> m_resolver;
 };
 
 } // namespace blink