Support for AudioContextOptions latencyHint.

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

 /*
  * Copyright (C) 2010, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1.  Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 62 matching lines @@
 class OscillatorNode;
 class PannerNode;
 class PeriodicWave;
 class PeriodicWaveConstraints;
 class ScriptProcessorNode;
 class ScriptPromiseResolver;
 class ScriptState;
 class SecurityOrigin;
 class StereoPannerNode;
 class WaveShaperNode;
+class WebAudioLatencyHint;
 
 // BaseAudioContext is the cornerstone of the web audio API and all AudioNodes
 // are created from it.  For thread safety between the audio thread and the main
 // thread, it has a rendering graph locking mechanism.
 
 class MODULES_EXPORT BaseAudioContext : public EventTargetWithInlineData,
                                         public ActiveScriptWrappable,
                                         public ActiveDOMObject {
   USING_GARBAGE_COLLECTED_MIXIN(BaseAudioContext);
   DEFINE_WRAPPERTYPEINFO();
 
  public:
   // The state of an audio context.  On creation, the state is Suspended. The
   // state is Running if audio is being processed (audio graph is being pulled
   // for data). The state is Closed if the audio context has been closed.  The
   // valid transitions are from Suspended to either Running or Closed; Running
   // to Suspended or Closed. Once Closed, there are no valid transitions.
   enum AudioContextState { Suspended, Running, Closed };
 
   // Create an AudioContext for rendering to the audio hardware.
-  static BaseAudioContext* create(Document&, ExceptionState&);
+  static BaseAudioContext* create(Document&,
+                                  const WebAudioLatencyHint&,
+                                  ExceptionState&);
 
   ~BaseAudioContext() override;
 
   DECLARE_VIRTUAL_TRACE();
 
   // Is the destination node initialized and ready to handle audio?
   bool isDestinationInitialized() const {
     AudioDestinationNode* dest = destination();
     return dest ? dest->audioDestinationHandler().isInitialized() : false;
   }
 
   // Document notification
   void contextDestroyed() final;
   bool hasPendingActivity() const final;
 
   // Cannnot be called from the audio thread.
   AudioDestinationNode* destination() const;
 
   size_t currentSampleFrame() const {
     // TODO: What is the correct value for the current frame if the destination
     // node has gone away?  0 is a valid frame.
     return m_destinationNode

[o1ka, 2016/11/30 11:46:26]

It does not look like having null m_destinationNode is normal. If so, we should
not check it anywhere - just DCHECK in the constructor.

[Andrew MacPherson, 2016/12/01 12:11:56]

I believe an OfflineAudioContext does not have an m_destinationNode so it would
be null in that case.

[Raymond Toy, 2016/12/01 16:26:51]

It should.  OfflineAudioContext is a subclass of BaseAudioContext, which defines
m_destinationNode.

[Andrew MacPherson, 2016/12/02 09:42:55]

Sorry, I see it now, the value is being set directly in OfflineAudioContext
rather than in the Base. It looks like it's possible to have a NULL
m_destinationNode though by doing AudioContext.close() from JS so without these
checks calling ctx.sampleRate for example after that would cause a crash. WDYT?

[Raymond Toy, 2016/12/02 16:57:45]

Yes, as currently implemented closed contexts have a null m_destinationNode. 
But see also crbug.com/670065.

                ? m_destinationNode->audioDestinationHandler()
                      .currentSampleFrame()
                : 0;
   }
 
   double currentTime() const {
     // TODO: What is the correct value for the current time if the destination
     // node has gone away? 0 is a valid time.
     return m_destinationNode
                ? m_destinationNode->audioDestinationHandler().currentTime()
                : 0;
   }
 
   float sampleRate() const {
-    return m_destinationNode ? m_destinationNode->handler().sampleRate() : 0;
+    return m_destinationNode
+               ? m_destinationNode->audioDestinationHandler().sampleRate()
+               : 0;
+  }
+
+  float framesPerBuffer() const {
+    return m_destinationNode
+               ? m_destinationNode->audioDestinationHandler().framesPerBuffer()
+               : 0;
   }
 
   String state() const;
+  double baseLatency() const;
   AudioContextState contextState() const { return m_contextState; }
   void throwExceptionForClosedState(ExceptionState&);
 
   AudioBuffer* createBuffer(unsigned numberOfChannels,
                             size_t numberOfFrames,
                             float sampleRate,
                             ExceptionState&);
 
   // Asynchronous audio file data decoding.
   ScriptPromise decodeAudioData(ScriptState*,
@@ skipping 144 matching lines @@
   // Get the PeriodicWave for the specified oscillator type.  The table is
   // initialized internally if necessary.
   PeriodicWave* periodicWave(int type);
 
   // For metrics purpose, records when start() is called on a
   // AudioScheduledSourceHandler or a AudioBufferSourceHandler without a user
   // gesture while the AudioContext requires a user gesture.
   void maybeRecordStartAttempt();
 
  protected:
-  explicit BaseAudioContext(Document*);
+  explicit BaseAudioContext(Document*, const WebAudioLatencyHint&);
   BaseAudioContext(Document*,
                    unsigned numberOfChannels,
                    size_t numberOfFrames,
                    float sampleRate);
 
   void initialize();
   void uninitialize();
 
   void setContextState(AudioContextState);
 
@@ skipping 128 matching lines @@
   // This is considering 32 is large enough for multiple channels audio.
   // It is somewhat arbitrary and could be increased if necessary.
   enum { MaxNumberOfChannels = 32 };
 
   Optional<AutoplayStatus> m_autoplayStatus;
 };
 
 }  // namespace blink
 
 #endif  // BaseAudioContext_h