On Mon, Mar 6, 2017, at 01:26 AM, Francesco wrote: > Hi Justin, > > >> > My advice > >> > is to publish at a fixed rate, for example by sleeping between publishes. > >> > >> Unfortunately this is not a solution in my case, as the events I > >> publish are generated by other incoming events that I cannot control > >> and in general I will not know at which rate they arrive. > > > > Ah, but even if your writes automatically slowed down to the fastest > > subscriber, you'd still face this problem. What will you do with > > incoming events while you're waiting for the fastest subscriber to > > become writable again? > > In such a case I just need to drop input events.
If you want to drop events to subscribers that can't read, including events to the fastest subscriber, then you simply use PUB. ;) I think this moves us into the realm of diagnostics. You want to know if the publisher is dropping messages. It might be handy if there were an alternative to ZMQ_XPUB_NODROP (say ZMQ_XPUB_ATLEASTONE) that required at least one subscriber to be writable, but not all of them. Then you could send with ZMQ_DONTWAIT, and an EAGAIN error would indicate that not even the fastest subscriber was writable (you could then discard the message yourself and not retry sending it). To solve your problem without changing ZeroMQ, you might make a subscriber feedback system. For example, add a sequence ID to the published payloads, and if a subscriber sees an ID out of sequence then it can keep a running count of missed messages. Periodically, each subscriber should submit the number of messages it has missed (or zero if none missed) to the publisher (via a separate socket, like PUSH) and then zero out its counter. As long as the publisher regularly receives messages saying zero missed, then you know there's at least one subscriber out there keeping up. If nobody is saying zero missed, then you've gone over. _______________________________________________ zeromq-dev mailing list zeromq-dev@lists.zeromq.org https://lists.zeromq.org/mailman/listinfo/zeromq-dev
