Agreed, but the bad design is not in ZMQ, but the way it is being used. A client should never just wait forever for a response to a message. Any reliable syst

Agreed, but the bad design is not in ZMQ, but the way it is being used. A client should never just wait forever for a response to a message. Any reliable system has to implement something like timeouts our immediate message acknowledgement (at which point maybe you can wait forever for a reply.) There's a comprehensive discussion of this in chapter 4 "Reliable Request Reply" of the ZMQ guide. TCP doesn't give you guaranteed response either. Just guaranteed delivery (or error.) In this case, this is exactly what the author's getting with ZMQ. The client's Request socket makes a successful delivery, then the server crashes before generating a response, and the client waits forever for the response that will not come.