Worker: Protect a running debugger task from forcible worker termination (2)

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 c862eb2915d0f5aec5188a86ed7df6ea9eb4089b..4c9fd41c6bf49d98dd87d6148515aaf77e919bc4 100644
--- a/third_party/WebKit/Source/core/workers/WorkerThread.cpp
+++ b/third_party/WebKit/Source/core/workers/WorkerThread.cpp
@@ -351,6 +351,14 @@ void WorkerThread::terminateInternal(TerminationMode mode)
 
     // If terminate has already been called.
     if (m_terminated) {
+        if (m_runningDebuggerTask) {
+            // Any debugger task is guaranteed to finish, so we can wait for the
+            // completion even if the synchronous forcible termination is
+            // requested. Shutdown sequence will start after the task.
+            DCHECK(!m_scheduledForceTerminationTask);
+            return;
+        }
+
         // The synchronous forcible termination request should overtake the
         // scheduled termination task because the request will block the main
         // thread and the scheduled termination task never runs.
@@ -385,7 +393,7 @@ void WorkerThread::terminateInternal(TerminationMode mode)
     // loop. If script execution weren't forbidden, a while(1) loop in JS could
     // keep the thread alive forever.
     //
-    // (1) |m_readyToShutdown|: It this is set, the worker thread has already
+    // (1) |m_readyToShutdown|: If this is set, the worker thread has already
     // noticed that the thread is about to be terminated and the worker global
     // scope is already disposed, so we don't have to explicitly terminate the
     // worker execution.
@@ -581,11 +589,13 @@ void WorkerThread::performDebuggerTaskOnWorkerThread(std::unique_ptr<CrossThread
     ThreadDebugger::idleStarted(isolate());
     {
         MutexLocker lock(m_threadStateMutex);
-        m_runningDebuggerTask = false;
-
-        if (!m_terminated)
+        if (!m_terminated) {
+            m_runningDebuggerTask = false;
             return;
+        }
         // terminate() was called. Shutdown sequence will start soon.
+        // Keep |m_runningDebuggerTask| to prevent forcible termination from the
+        // main thread before shutdown preparation.
     }
     // Stop further worker tasks to run after this point.
     prepareForShutdownOnWorkerThread();