Move MainThreadTaskRunner off Oilpan heap to simplify posting.

third_party/WebKit/Source/core/dom/MainThreadTaskRunner.cpp

 /*
  * Copyright (C) 2013 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 21 matching lines @@
 #include "platform/ThreadSafeFunctional.h"
 #include "public/platform/Platform.h"
 #include "wtf/Assertions.h"
 
 namespace blink {
 
 MainThreadTaskRunner::MainThreadTaskRunner(ExecutionContext* context)
     : m_context(context)
     , m_pendingTasksTimer(this, &MainThreadTaskRunner::pendingTasksTimerFired)
     , m_suspended(false)
+    , m_weakFactory(this)
 {
 }
 
 MainThreadTaskRunner::~MainThreadTaskRunner()
 {
 }
 
-DEFINE_TRACE(MainThreadTaskRunner)
-{
-    visitor->trace(m_context);
-}
-
 void MainThreadTaskRunner::postTaskInternal(const WebTraceLocation& location, PassOwnPtr<ExecutionContextTask> task, bool isInspectorTask)
 {
     Platform::current()->mainThread()->getWebTaskRunner()->postTask(location, threadSafeBind(
         &MainThreadTaskRunner::perform,
-        CrossThreadWeakPersistentThisPointer<MainThreadTaskRunner>(this),
+        AllowCrossThreadAccess(m_weakFactory.createWeakPtr()),
         passed(std::move(task)),
         isInspectorTask));
 }
 
 void MainThreadTaskRunner::postTask(const WebTraceLocation& location, PassOwnPtr<ExecutionContextTask> task)
 {
     if (!task->taskNameForInstrumentation().isEmpty())
         InspectorInstrumentation::asyncTaskScheduled(m_context, task->taskNameForInstrumentation(), task.get());
     postTaskInternal(location, std::move(task), false);
 }
 
 void MainThreadTaskRunner::postInspectorTask(const WebTraceLocation& location, PassOwnPtr<ExecutionContextTask> task)
 {
     postTaskInternal(location, std::move(task), true);
 }
 
 void MainThreadTaskRunner::perform(PassOwnPtr<ExecutionContextTask> task, bool isInspectorTask)
 {
+    // If the owner m_context is about to be swept then it
+    // is no longer safe to access.
+    if (ThreadHeap::willObjectBeLazilySwept(m_context.get()))

[haraken, 2016/05/04 03:21:33]

Why was this check not needed before this CL?

[sof, 2016/05/04 05:17:39]

The closure is constructed using
CrossThreadWeakPersistentThisPointer<MainThreadTaskRunner>(this) and
MainThreadTaskRunner & Document die at the same time, so no need to separately
check the liveness of m_context here.

+        return;
+
     if (!isInspectorTask && (m_context->tasksNeedSuspension() || !m_pendingTasks.isEmpty())) {
         m_pendingTasks.append(std::move(task));
         return;
     }
 
     InspectorInstrumentation::AsyncTask asyncTask(m_context, task.get(), !isInspectorTask);
     task->performTask(m_context);
 }
 
 void MainThreadTaskRunner::suspend()
 {
     DCHECK(!m_suspended);
     m_pendingTasksTimer.stop();
     m_suspended = true;
 }
 
 void MainThreadTaskRunner::resume()
 {
     DCHECK(m_suspended);
     if (!m_pendingTasks.isEmpty())
         m_pendingTasksTimer.startOneShot(0, BLINK_FROM_HERE);
 
     m_suspended = false;
 }
 
 void MainThreadTaskRunner::pendingTasksTimerFired(Timer<MainThreadTaskRunner>*)
 {
+    // If the owner m_context is about to be swept then it
+    // is no longer safe to access.
+    if (ThreadHeap::willObjectBeLazilySwept(m_context.get()))
+        return;
+
     while (!m_pendingTasks.isEmpty()) {
         OwnPtr<ExecutionContextTask> task = m_pendingTasks[0].release();
         m_pendingTasks.remove(0);
         const bool instrumenting = !task->taskNameForInstrumentation().isEmpty();
         InspectorInstrumentation::AsyncTask asyncTask(m_context, task.get(), instrumenting);
         task->performTask(m_context);
     }
 }
 
 } // namespace blink