--- thread.py	2014-09-06 22:02:09.000000000 +0800
+++ thread_new.py	2015-02-28 14:19:24.000000000 +0800
@@ -65,25 +65,36 @@
         else:
             self.future.set_result(result)
 
-def _worker(executor_reference, work_queue):
-    try:
-        while True:
-            work_item = work_queue.get(block=True)
-            if work_item is not None:
-                work_item.run()
-                continue
-            executor = executor_reference()
-            # Exit if:
-            #   - The interpreter is shutting down OR
-            #   - The executor that owns the worker has been collected OR
-            #   - The executor that owns the worker has been shutdown.
-            if _shutdown or executor is None or executor._shutdown:
-                # Notice other workers
-                work_queue.put(None)
-                return
-            del executor
-    except BaseException:
-        _base.LOGGER.critical('Exception in worker', exc_info=True)
+class Worker(threading.Thread):
+    def __init__(self, executor_reference, work_queue):
+        self.executor_reference = executor_reference
+        self.work_queue = work_queue
+        self.runLock = threading.Lock()
+        threading.Thread.__init__(self)
+    
+    def run(self):
+        try:
+            while True:
+                work_item = self.work_queue.get(block=True)
+                if work_item is not None:
+                    work_item.run()
+                    continue
+                
+                executor = self.executor_reference()
+                                    
+                # Never contended, but necessary for visibility
+                with self.runLock:
+                    # Exit if:
+                    #   - The interpreter is shutting down OR
+                    #   - The executor that owns the worker has been collected OR
+                    #   - The executor that owns the worker has been shutdown.
+                    if _shutdown or executor is None or executor._shutdown:
+                        # Notice other workers
+                        self.work_queue.put(None)
+                        return
+                del executor
+        except BaseException:
+            _base.LOGGER.critical('Exception in worker', exc_info=True)
 
 class ThreadPoolExecutor(_base.Executor):
     def __init__(self, max_workers):
@@ -120,9 +131,7 @@
         # TODO(bquinlan): Should avoid creating new threads if there are more
         # idle threads than items in the work queue.
         if len(self._threads) < self._max_workers:
-            t = threading.Thread(target=_worker,
-                                 args=(weakref.ref(self, weakref_cb),
-                                       self._work_queue))
+            t = Worker(weakref.ref(self, weakref_cb), self._work_queue)
             t.daemon = True
             t.start()
             self._threads.add(t)