compositor-worker: Keep worker backing thread alive for the lifetime of the compositor thread.

third_party/WebKit/Source/modules/ModulesInitializer.cpp

 // Copyright (c) 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ModulesInitializer.h"
 
 #include "bindings/modules/v8/ModuleBindingsInitializer.h"
 #include "core/EventTypeNames.h"
 #include "core/css/CSSPaintImageGenerator.h"
 #include "core/dom/Document.h"
 #include "core/html/HTMLCanvasElement.h"
 #include "core/offscreencanvas/OffscreenCanvas.h"
 #include "modules/EventModulesFactory.h"
 #include "modules/EventModulesNames.h"
 #include "modules/EventTargetModulesNames.h"
 #include "modules/IndexedDBNames.h"
 #include "modules/accessibility/AXObjectCacheImpl.h"
 #include "modules/canvas2d/CanvasRenderingContext2D.h"
+#include "modules/compositorworker/CompositorWorkerThread.h"
 #include "modules/csspaint/CSSPaintImageGeneratorImpl.h"
 #include "modules/filesystem/DraggedIsolatedFileSystemImpl.h"
 #include "modules/imagebitmap/ImageBitmapRenderingContext.h"
 #include "modules/offscreencanvas2d/OffscreenCanvasRenderingContext2D.h"
 #include "modules/webdatabase/DatabaseManager.h"
 #include "modules/webgl/WebGL2RenderingContext.h"
 #include "modules/webgl/WebGLRenderingContext.h"
 
 namespace blink {
 
@@ skipping 27 matching lines @@
     // OffscreenCanvas context types must be registered with the OffscreenCanvas.
     OffscreenCanvas::registerRenderingContextFactory(adoptPtr(new OffscreenCanvasRenderingContext2D::Factory()));
     OffscreenCanvas::registerRenderingContextFactory(adoptPtr(new WebGLRenderingContext::Factory()));
 
     ASSERT(isInitialized());
 }
 
 void ModulesInitializer::shutdown()
 {
     ASSERT(isInitialized());
+    CompositorWorkerThread::clearSharedBackingThread();

[haraken, 2016/05/09 02:00:53]

Backing threads of other workers are shut down in
WorkerThread::terminateAndWaitForAllWorkers(). Can we shut down the backing
thread of the compositor worker there as well?

[flackr, 2016/05/10 18:07:39]

This does make sense, however core/ is not allowed to include modules so we
aren't allowed to get the CompositorWorkerThread's BackingThreadHolder instance
to clear the thread pointer. This does suggest though that maybe we should clear
the shared backing thread after calling CoreInitializer::shutdown call.

[haraken, 2016/05/11 00:18:31]

Can we add some virtual method on WorkerThread and override it on
CompositorWorkerThread? That way you can call CompositorWorkerThread's method
from CoreInitializer::shutdown.

[flackr, 2016/05/18 05:26:49]

No, the problem is that the backing thread is a singleton shared by all
CompositorWorkerThreads and required even after they all go away (because the
LayerTreeHostImpl will still be holding onto an oilpan CompositorMutatorImpl).
We may not have any CompositorWorkerThreads but still have a backing thread.

     DatabaseManager::terminateDatabaseThread();
     CoreInitializer::shutdown();
 }
 
 } // namespace blink