code: def instance():
          
          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
docs: 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()`.