Lazy initialization of the rendering thread in OfflineAudioContext

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

 /*
  * Copyright (C) 2012, 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
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  * 2.  Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 194 matching lines @@
                              "cannot call startRendering more than once"));
   }
 
   DCHECK(!is_rendering_started_);
 
   complete_resolver_ = ScriptPromiseResolver::Create(script_state);
 
   // Start rendering and return the promise.
   is_rendering_started_ = true;
   SetContextState(kRunning);
+  DestinationHandler().InitializeOfflineRenderThread();
   DestinationHandler().StartRendering();
 
   return complete_resolver_->Promise();
 }
 
 ScriptPromise OfflineAudioContext::suspendContext(ScriptState* script_state) {
   LOG(FATAL) << "This CANNOT be called on OfflineAudioContext; this is only to "
                 "implement the pure virtual interface from BaseAudioContext.";
   return ScriptPromise();
 }
 
 ScriptPromise OfflineAudioContext::suspendContext(ScriptState* script_state,
                                                   double when) {
   DCHECK(IsMainThread());
 
   ScriptPromiseResolver* resolver = ScriptPromiseResolver::Create(script_state);
   ScriptPromise promise = resolver->Promise();
 
-  // The render thread does not exist; reject the promise.
-  if (!DestinationHandler().OfflineRenderThread()) {

[Raymond Toy, 2017/05/23 17:05:01]

What happened before if I try to suspend a context that has already finished
rendering?  What happens with this CL?

[hongchan, 2017/05/23 18:10:38]

A good catch. My mistake. I forgot to revert this back.

[Raymond Toy, 2017/05/23 18:14:41]

In that case, we want to include a test for this with this CL.

-    resolver->Reject(DOMException::Create(kInvalidStateError,
-                                          "the rendering is already finished"));
-    return promise;
-  }
-
   // The specified suspend time is negative; reject the promise.
   if (when < 0) {
     resolver->Reject(DOMException::Create(
         kInvalidStateError,
         "negative suspend time (" + String::Number(when) + ") is not allowed"));
     return promise;
   }
 
   // Quantize (to the lower boundary) the suspend time by the render quantum.
   size_t frame = when * sampleRate();
@@ skipping 202 matching lines @@
 
   // Note that the GraphLock is required before this check. Since this needs
   // to run on the audio thread, OfflineGraphAutoLocker must be used.
   if (scheduled_suspends_.Contains(CurrentSampleFrame()))
     return true;
 
   return false;
 }
 
 }  // namespace blink