Stopping a synchronous Server stalls

[AiyionPrime]

Currently I'm short of a minimal example; but when I'm starting a synchronous server, handle some methods and want to stop it eventually via an OPC UA endpoint I'm running into troubles closing a ThreadPool, which simply never stops.

my_server.stop()
calls _tloop.post(self.aiostop()),
which successfuly halts its bserver but hangs upon stopping iserver,
which tries to call method_service.stop().

The latter is a call to shutdown() on a ThreadPoolExecutor instance.
shutdown() does gracefully wait for all futures to finish and aborts None.

Is there a step I'm missing prior to my_server.stop(), which would clear this ThreadPoolExecutor, so that stopping the server actually works?

[AiyionPrime]

Nevermind. Rereading it beat me to it.
The method I'm waiting for is my stop method which should not handle stopping the server synchronously.
It can't evaluate the result anyway, so calling the stop of my server async does the trick;
another approach would be setting a flag which an observer pattern watches and reacts on (and shuts down the server eventually)