Remove the concept of a cleanup task

Source/core/workers/WorkerThread.cpp

Index: Source/core/workers/WorkerThread.cpp
diff --git a/Source/core/workers/WorkerThread.cpp b/Source/core/workers/WorkerThread.cpp
index d8f75cc105c1285c6f3df3d80327ff396782a07a..55202cc58b653b6ea4b768c2e212a8088183daec 100644
--- a/Source/core/workers/WorkerThread.cpp
+++ b/Source/core/workers/WorkerThread.cpp
@@ -58,20 +58,32 @@ namespace {
 const int64_t kShortIdleHandlerDelayMs = 1000;
 const int64_t kLongIdleHandlerDelayMs = 10*1000;
 
-class MicrotaskRunner : public WebThread::TaskObserver {
+} // namespace
+
+class WorkerMicrotaskRunner : public WebThread::TaskObserver {
 public:
-    explicit MicrotaskRunner(WorkerThread* workerThread)
+    explicit WorkerMicrotaskRunner(WorkerThread* workerThread)
         : m_workerThread(workerThread)
     {
     }
 
-    virtual void willProcessTask() override { }
+    virtual void willProcessTask() override
+    {
+        // No tasks should get executed after we have closed.
+        if (WorkerGlobalScope* globalScope = m_workerThread->workerGlobalScope())
+            ASSERT_UNUSED(globalScope, !globalScope->isClosing());
+    }
+
     virtual void didProcessTask() override
     {
         Microtask::performCheckpoint();
         if (WorkerGlobalScope* globalScope = m_workerThread->workerGlobalScope()) {
             if (WorkerScriptController* scriptController = globalScope->script())
                 scriptController->rejectedPromises()->processQueue();
+            if (globalScope->isClosing()) {
+                m_workerThread->workerReportingProxy().workerGlobalScopeClosed();
+                m_workerThread->cleanup();
+            }
         }
     }
 
@@ -81,8 +93,6 @@ private:
     WorkerThread* m_workerThread;
 };
 
-} // namespace
-
 static Mutex& threadSetMutex()
 {
     AtomicallyInitializedStaticReference(Mutex, mutex, new Mutex);
@@ -208,15 +218,11 @@ public:
     virtual void run() override
     {
         WorkerGlobalScope* workerGlobalScope = m_workerThread.workerGlobalScope();
-        // Tasks could be put on the message loop after the cleanup task,
-        // ensure none of those are ran.
-        if (!workerGlobalScope)
-            return;
+        ASSERT(workerGlobalScope);
 
         if (m_isInstrumented)
             InspectorInstrumentation::willPerformExecutionContextTask(workerGlobalScope, m_task.get());
-        if ((!workerGlobalScope->isClosing() && !m_workerThread.terminated()) || m_task->isCleanupTask())
-            m_task->performTask(workerGlobalScope);
+        m_task->performTask(workerGlobalScope);
         if (m_isInstrumented)
             InspectorInstrumentation::didPerformExecutionContextTask(workerGlobalScope);
     }
@@ -319,9 +325,9 @@ void WorkerThread::initialize()
             return;
         }
 
-        m_microtaskRunner = adoptPtr(new MicrotaskRunner(this));
+        m_microtaskRunner = adoptPtr(new WorkerMicrotaskRunner(this));
         backingThread().addTaskObserver(m_microtaskRunner.get());
-        backingThread().attachGC();
+        backingThread().initialize();
 
         m_isolate = initializeIsolate();
         m_workerGlobalScope = createWorkerGlobalScope(m_startupData.release());
@@ -354,6 +360,13 @@ void WorkerThread::initialize()
 
 void WorkerThread::cleanup()

[haraken, 2015/05/09 15:54:36]

Nit: We're mixing cleanup, destroy, dispose and shutdown. We might want to unify
the names. We can do this in a follow-up CL.

[Sami, 2015/05/11 10:35:32]

Agreed, I'm open to suggestions. I think renaming cleanup to shutdown might be a
good first step -- which I've now taken.

 {
+    MutexLocker lock(m_threadCreationMutex);

[kinuko, 2015/05/09 10:20:10]

I don't think we need this? This lock's mainly used to protect things against
initialize() which runs on the worker thread, while cleanup also runs on the
worker thread.

[Sami, 2015/05/11 10:35:32]

I added it because Kinuko pointed out that WorkerThread::stopInternal() can run
on the main thread and that function accesses members which are also written
here (e.g., m_workerGlobalScope).

[Sami, 2015/05/11 10:37:34]

Oops, somehow I read this comment being written by Kentaro and not you :) The
point still stands I think :)

[kinuko, 2015/05/11 13:26:40]

;)

If I'm reading correctly stopInternal() is the only one that posts a task to
call this method on the worker thread, is that right?  If so I think there's a
happens-before relationship, therefore nullifying m_workerGlobalScope here
should be safe.

[Sami, 2015/05/11 14:02:36]

I think this sequence of events could result in racy access to
m_workerGlobalScope:

1. On the worker thread:

   self.close() (in Javascript)
   => WorkerMicroTaskRunner::didProcessTask
   => WorkerThread::shutdown()
   => writes to m_workerGlobalScope

2. On the main thread:

   WorkerThread::terminateAndWait()
   => WorkerThread::stop()
   => WorkerThread::stopInternal()
   => reads from m_workerGlobalScope

+    ASSERT(isCurrentThread());
+
+    PlatformThreadData::current().threadTimers().setSharedTimer(nullptr);
+    workerGlobalScope()->dispose();
+    willDestroyIsolate();
+
     // This should be called before we start the shutdown procedure.
     workerReportingProxy().willDestroyWorkerGlobalScope();
 
@@ -366,10 +379,10 @@ void WorkerThread::cleanup()
     m_workerGlobalScope->notifyContextDestroyed();
     m_workerGlobalScope = nullptr;
 
-    backingThread().detachGC();
+    backingThread().removeTaskObserver(m_microtaskRunner.get());
+    backingThread().shutdown();
     destroyIsolate();
 
-    backingThread().removeTaskObserver(m_microtaskRunner.get());
     m_microtaskRunner = nullptr;
 
     // Notify the proxy that the WorkerGlobalScope has been disposed of.
@@ -382,50 +395,6 @@ void WorkerThread::cleanup()
     PlatformThreadData::current().destroy();
 }
 
-class WorkerThreadShutdownFinishTask : public ExecutionContextTask {
-public:
-    static PassOwnPtr<WorkerThreadShutdownFinishTask> create()
-    {
-        return adoptPtr(new WorkerThreadShutdownFinishTask());
-    }
-
-    virtual void performTask(ExecutionContext *context)
-    {
-        WorkerGlobalScope* workerGlobalScope = toWorkerGlobalScope(context);
-        workerGlobalScope->dispose();
-
-        WorkerThread* workerThread = workerGlobalScope->thread();
-        workerThread->willDestroyIsolate();
-        workerThread->backingThread().postTask(FROM_HERE, new Task(WTF::bind(&WorkerThread::cleanup, workerThread)));
-    }
-
-    virtual bool isCleanupTask() const { return true; }
-};
-
-class WorkerThreadShutdownStartTask : public ExecutionContextTask {
-public:
-    static PassOwnPtr<WorkerThreadShutdownStartTask> create()
-    {
-        return adoptPtr(new WorkerThreadShutdownStartTask());
-    }
-
-    virtual void performTask(ExecutionContext *context)
-    {
-        WorkerGlobalScope* workerGlobalScope = toWorkerGlobalScope(context);
-        workerGlobalScope->stopActiveDOMObjects();
-        PlatformThreadData::current().threadTimers().setSharedTimer(nullptr);
-
-        // Event listeners would keep DOMWrapperWorld objects alive for too long. Also, they have references to JS objects,
-        // which become dangling once Heap is destroyed.
-        workerGlobalScope->removeAllEventListeners();
-
-        // Stick a shutdown command at the end of the queue, so that we deal
-        // with all the cleanup tasks the databases post first.
-        workerGlobalScope->postTask(FROM_HERE, WorkerThreadShutdownFinishTask::create());
-    }
-
-    virtual bool isCleanupTask() const { return true; }
-};
 
 void WorkerThread::stop()
 {
@@ -473,7 +442,7 @@ void WorkerThread::stopInternal()
 
     InspectorInstrumentation::didKillAllExecutionContextTasks(m_workerGlobalScope.get());
     m_debuggerMessageQueue.kill();
-    postTask(FROM_HERE, WorkerThreadShutdownStartTask::create());
+    backingThread().postTask(FROM_HERE, new Task(threadSafeBind(&WorkerThread::cleanup, AllowCrossThreadAccess(this))));
 }
 
 void WorkerThread::didStartRunLoop()