Web Animations: Timeline should not advance during task execution

Source/web/WebKit.cpp

 /*
  * Copyright (C) 2009 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 17 matching lines @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #include "config.h"
 #include "public/web/WebKit.h"
 
 #include "RuntimeEnabledFeatures.h"
 #include "bindings/v8/V8Binding.h"
 #include "bindings/v8/V8Initializer.h"
 #include "core/Init.h"
+#include "core/animation/AnimationClock.h"
 #include "core/dom/Microtask.h"
 #include "core/frame/Settings.h"
 #include "core/page/Page.h"
 #include "core/workers/WorkerGlobalScopeProxy.h"
 #include "gin/public/v8_platform.h"
 #include "platform/LayoutTestSupport.h"
 #include "platform/Logging.h"
 #include "platform/graphics/ImageDecodingStore.h"
 #include "platform/graphics/media/MediaPlayer.h"
 #include "platform/heap/Heap.h"
 #include "platform/heap/glue/MessageLoopInterruptor.h"
 #include "platform/heap/glue/PendingGCRunner.h"
 #include "public/platform/Platform.h"
 #include "public/platform/WebPrerenderingSupport.h"
 #include "public/platform/WebThread.h"
 #include "web/IndexedDBClientImpl.h"
 #include "web/WebMediaPlayerClientImpl.h"
 #include "wtf/Assertions.h"
 #include "wtf/CryptographicallyRandomNumber.h"
 #include "wtf/MainThread.h"
 #include "wtf/WTF.h"
 #include "wtf/text/AtomicString.h"
 #include "wtf/text/TextEncoding.h"
 #include <v8.h>
 
 namespace blink {
 
 namespace {
 
 class EndOfTaskRunner : public WebThread::TaskObserver {

[dstockwell, 2014/04/30 12:07:22]

We probably want to rename this, or create a separate observer. Suggestions?

 public:
-    virtual void willProcessTask() { }
+    virtual void willProcessTask()
+    {
+        WebCore::AnimationClock::notifyTaskStartTime(monotonicallyIncreasingTime());

[esprehn, 2014/04/30 22:43:50]

How expensive is monotonicallyIncreasingTime? Can we freeze the animation clock
at frame boundaries and unfreeze always at end of microtask only if it's already
frozen?

[dstockwell, 2014/04/30 22:59:51]

I will investigate.
I don't think this helps. For any task which is not a frame task we still need
an up to date time value. A significant amount of time might pass before the
next frame.

+    }

[abarth-chromium, 2014/04/30 22:39:16]

Doesn't this make the entire engine slower?  We execute many, many tasks...

[dstockwell, 2014/05/01 00:22:21]

I'm going to try a new approach which should reduce this to an increment before
the task, or require a micro task.

     virtual void didProcessTask()
     {
         WebCore::Microtask::performCheckpoint();
     }
 };
 
 } // namespace
 
 static WebThread::TaskObserver* s_endOfTaskRunner = 0;
 static WebThread::TaskObserver* s_pendingGCRunner = 0;
@@ skipping 179 matching lines @@
         channel->state = WTFLogChannelOn;
 #endif // !LOG_DISABLED
 }
 
 void resetPluginCache(bool reloadPages)
 {
     WebCore::Page::refreshPlugins(reloadPages);
 }
 
 } // namespace blink