if you bind async_server::run to a thread and then immediately call stop on that server instance, you can end up with a sync issue where calling cancel or similar on the acceptor will throw because it may not be open and listening yet.

a possible fix would be to check if async_server is in listening mode yet or not, and then only attempt to cancel the acceptor if so.

further, checking if async_server is stopping before attempting to start_listening would be useful too.