@staticmethod    def instance():        """Returns a global `IOLoop` instance.        Most applications have a single, global `IOLoop` running on the        main thread.  Use this method to get this instance from        another thread.  To get the current thread‘s `IOLoop`, use `current()`.        """        if not hasattr(IOLoop, "_instance"):            with IOLoop._instance_lock:                if not hasattr(IOLoop, "_instance"):                    # New instance after double check                    IOLoop._instance = IOLoop()        return IOLoop._instance