'Calls the given callback on the next I/O loop iteration.
It is safe to call this method from any thread at any time,
except from a signal handler.  Note that this is the **only**
method in `IOLoop` that makes this thread-safety guarantee; all
other interaction with the `IOLoop` must be done from that
`IOLoop`\'s thread.  `add_callback()` may be used to transfer
control from other threads to the `IOLoop`\'s thread.
To add a callback from a signal handler, see
`add_callback_from_signal`.'

def add_callback(self, callback, *args, **kwargs):

    raise NotImplementedError()
