Hi all, while implementing a 0MQ architecture which needs to dynamically create and destroy sockets during operation I ran into the current behaviour of zmq_close() being semantically different from the standard close() system call.
Consider a scenario where we wish to send a bunch of messages, then close the socket: zmq_send (s, ...) zmq_send (s, ...) zmq_send (s, ...) zmq_close (s) The current behaviour is that zmq_close() will discard any messages which have been queued ("sent") with zmq_send() but have not yet been pushed out to the network. Contrast this with the behaviour of the close() system call on a standard socket where the call means "please make this socket go away, but finish sending any outstanding data on it asynchronously if you can"[1]. In my opinion the proper solution is to use the same semantics as the close() system call, in other words, zmq_close() shall invalidate the socket from the caller's point of view so no further operations may be performed on it, but 0MQ shall send any outstanding messages in the background *as long as a endpoint for those messages still exists* before destroying the socket "for real". This would mean a second change to the API which would make zmq_term() a blocking call, since it would need to wait until all outstanding messages are sent. The analogous functionality for the close() system call is handled by the OS kernel -- obviously if the OS shuts down then data will be lost. The downside is that zmq_term() could freeze for an arbitrary amount of time if the remote end is "stuck". For applications where this is undesirable it would mean adding a "KILL" flag or separate zmq_term_kill() function which means "we don't care, really go away now". Please let me know your opinions on this change; ultimately I think it's the right way to go especially if OS integration of 0MQ sockets is (a long way) down the road. -mato [1] This behaviour can be changed using the SO_LINGER option, we'd probably want to implement a similar option for 0MQ sockets. _______________________________________________ zeromq-dev mailing list zeromq-dev@lists.zeromq.org http://lists.zeromq.org/mailman/listinfo/zeromq-dev