Lazy initialization of the rendering thread in OfflineAudioContext

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

 /*
  * Copyright (C) 2011, 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 28 matching lines @@
 #include "platform/wtf/PtrUtil.h"
 #include "public/platform/Platform.h"
 
 namespace blink {
 
 OfflineAudioDestinationHandler::OfflineAudioDestinationHandler(
     AudioNode& node,
     AudioBuffer* render_target)
     : AudioDestinationHandler(node),
       render_target_(render_target),
-      render_thread_(
-          Platform::Current()->CreateThread("offline audio renderer")),
       frames_processed_(0),
       frames_to_process_(0),
       is_rendering_started_(false),
       should_suspend_(false) {
   render_bus_ = AudioBus::Create(render_target->numberOfChannels(),
                                  AudioUtilities::kRenderQuantumFrames);
   frames_to_process_ = render_target_->length();
 
   // Node-specific defaults.
   channel_count_ = render_target_->numberOfChannels();
@@ skipping 36 matching lines @@
 OfflineAudioContext* OfflineAudioDestinationHandler::Context() const {
   return static_cast<OfflineAudioContext*>(AudioDestinationHandler::Context());
 }
 
 unsigned long OfflineAudioDestinationHandler::MaxChannelCount() const {
   return channel_count_;
 }
 
 void OfflineAudioDestinationHandler::StartRendering() {
   DCHECK(IsMainThread());
-  DCHECK(render_thread_);
   DCHECK(render_target_);
 
   if (!render_target_)
     return;
 
+  render_thread_ = Platform::Current()->CreateThread("offline audio renderer");

[Raymond Toy, 2017/05/19 19:37:54]

Maybe if we fail to create the thread we can reject the promise?  Can't see
anything in the spec about this, but it makes sense since promise always have a
resolve and a reject.

+  DCHECK(render_thread_);
+
   // Rendering was not started. Starting now.
   if (!is_rendering_started_) {
     is_rendering_started_ = true;
     render_thread_->GetWebTaskRunner()->PostTask(
         BLINK_FROM_HERE,
         CrossThreadBind(&OfflineAudioDestinationHandler::StartOfflineRendering,
                         WrapPassRefPtr(this)));
     return;
   }
 
@@ skipping 218 matching lines @@
   SetHandler(OfflineAudioDestinationHandler::Create(*this, render_target));
 }
 
 OfflineAudioDestinationNode* OfflineAudioDestinationNode::Create(
     BaseAudioContext* context,
     AudioBuffer* render_target) {
   return new OfflineAudioDestinationNode(*context, render_target);
 }
 
 }  // namespace blink