I have to say that I can't find another obvious deadlock that would lead to an issue in this particular scenario - the interface is such though that it is pretty easy to deadlock if the thread processing the subscription does anything else involving subscriptions, such as try to subscribe to another prefix. Maybe it would be best just to never block on the sending side and just use try_send? That or simply use a concurrent map as the registry so those locks don't have to be taken while sending is going on.