Worker: Initiate worker thread shutdown always on the main thread

third_party/WebKit/Source/core/workers/WorkerThread.cpp

Index: third_party/WebKit/Source/core/workers/WorkerThread.cpp
diff --git a/third_party/WebKit/Source/core/workers/WorkerThread.cpp b/third_party/WebKit/Source/core/workers/WorkerThread.cpp
index 8d6889c9357640bc1b0b48c1f7d5cd2ac8a998f7..ac0b1c3172931c475a2cb7fdfedabfb87b659835 100644
--- a/third_party/WebKit/Source/core/workers/WorkerThread.cpp
+++ b/third_party/WebKit/Source/core/workers/WorkerThread.cpp
@@ -72,8 +72,11 @@ public:
             if (WorkerOrWorkletScriptController* scriptController = globalScope->scriptController())
                 scriptController->getRejectedPromises()->processQueue();
             if (globalScope->isClosing()) {
+                // |m_workerThread| will eventually be requested to terminate.
                 m_workerThread->workerReportingProxy().workerGlobalScopeClosed();
-                m_workerThread->terminateFromWorkerThread();
+
+                // Dispose WorkerGlobalScope to avoid processing the next task.
+                m_workerThread->prepareForShutdown();
             }
         }
     }
@@ -129,16 +132,9 @@ std::unique_ptr<CrossThreadClosure> WorkerThread::createWorkerThreadTask(std::un
 }
 
 WorkerThread::WorkerThread(PassRefPtr<WorkerLoaderProxy> workerLoaderProxy, WorkerReportingProxy& workerReportingProxy)
-    : m_started(false)
-    , m_terminated(false)
-    , m_shutdown(false)
-    , m_pausedInDebugger(false)
-    , m_runningDebuggerTask(false)
-    , m_shouldTerminateV8Execution(false)
-    , m_inspectorTaskRunner(adoptPtr(new InspectorTaskRunner()))
+    : m_inspectorTaskRunner(adoptPtr(new InspectorTaskRunner()))
     , m_workerLoaderProxy(workerLoaderProxy)
     , m_workerReportingProxy(workerReportingProxy)
-    , m_webScheduler(nullptr)
     , m_terminationEvent(adoptPtr(new WaitableEvent(
         WaitableEvent::ResetPolicy::Manual,
         WaitableEvent::InitialState::NonSignaled)))
@@ -240,19 +236,7 @@ void WorkerThread::initialize(PassOwnPtr<WorkerThreadStartupData> startupData)
 void WorkerThread::shutdown()
 {
     DCHECK(isCurrentThread());
-    {
-        MutexLocker lock(m_threadStateMutex);
-        if (m_shutdown)
-            return;
-        m_shutdown = true;
-    }
-
-    // This should be called before we start the shutdown procedure.
-    workerReportingProxy().willDestroyWorkerGlobalScope();
-
-    workerGlobalScope()->dispose();
-
-    workerBackingThread().backingThread().removeTaskObserver(m_microtaskRunner.get());
+    prepareForShutdown();
     postTask(BLINK_FROM_HERE, createSameThreadTask(&WorkerThread::performShutdownTask, this));
 }
 
@@ -310,10 +294,19 @@ void WorkerThread::terminateAndWaitForAllWorkers()
         thread->m_shutdownEvent->wait();
 }
 
-void WorkerThread::terminateFromWorkerThread()
+void WorkerThread::prepareForShutdown()
 {
     DCHECK(isCurrentThread());
-    shutdown();
+    {
+        MutexLocker lock(m_threadStateMutex);
+        if (m_readyToShutdown)
+            return;
+        m_readyToShutdown = true;
+    }
+
+    workerReportingProxy().willDestroyWorkerGlobalScope();
+    workerGlobalScope()->dispose();
+    workerBackingThread().backingThread().removeTaskObserver(m_microtaskRunner.get());
 }
 
 WorkerGlobalScope* WorkerThread::workerGlobalScope()
@@ -345,20 +338,21 @@ void WorkerThread::terminateInternal()
     if (m_terminationEvent)
         m_terminationEvent->signal();
 
-    // If the thread has already initiated shutdown, just return.
-    if (m_shutdown)
-        return;
-
     // If the worker thread was never initialized, don't start another
     // shutdown, but still wait for the thread to signal when shutdown has
     // completed on initialize().
     if (!m_workerGlobalScope)
         return;
 
-    // Ensure that tasks are being handled by thread event loop. If script
-    // execution weren't forbidden, a while(1) loop in JS could keep the thread
-    // alive forever.
-    m_workerGlobalScope->scriptController()->willScheduleExecutionTermination();
+    // If |m_readyToShutdown| is set, scriptController() is already disposed.
+    if (!m_readyToShutdown) {
+        DCHECK(m_workerGlobalScope->scriptController());
+
+        // Ensure that tasks are being handled by thread event loop. If script
+        // execution weren't forbidden, a while(1) loop in JS could keep the thread
+        // alive forever.
+        m_workerGlobalScope->scriptController()->willScheduleExecutionTermination();
+    }
 
     if (workerBackingThread().workerScriptCount() == 1) {
         // This condition is not entirely correct because other scripts
@@ -412,7 +406,7 @@ void WorkerThread::appendDebuggerTask(std::unique_ptr<CrossThreadClosure> task)
 {
     {
         MutexLocker lock(m_threadStateMutex);
-        if (m_shutdown)
+        if (m_readyToShutdown)
             return;
     }
     m_inspectorTaskRunner->appendTask(threadSafeBind(&WorkerThread::runDebuggerTask, AllowCrossThreadAccess(this), passed(std::move(task))));