periodic_executor.py 文件源码

def open(self):
        """Start. Multiple calls have no effect.

        Not safe to call from multiple threads at once.
        """
        self._stopped = False
        started = False
        try:
            started = self._thread and self._thread.is_alive()
        except ReferenceError:
            # Thread terminated.
            pass

        if not started:
            thread = threading.Thread(target=self._run, name=self._name)
            thread.daemon = True
            self._thread = weakref.proxy(thread)
            _register_executor(self)
            thread.start()