Hi, I'm trying to implement the following message pattern, I call it "directory" (have a better name?). Directory pattern has two socket types: ASK and ANSWER. They are mostly analogous to REQ and REP types respectively. The difference is that ANSWER socket can choose what requests it serves. This works by setting SUBSCRIBE option on the socket, which sends the subscription to ASK socket, similarly to how it's done for PUB/SUB sockets in crossroads IO (with subscription forwarding). ASK socket keeps a trie of prefixes and for each node of the trie a list of pipes (ANSWER endpoints) is kept to load-balance between them. So each message matches against trie to find a subset of pipes that can be used to serve a request. Illustration attached. At the picture there is a single node A which serves requests for "cars" and two nodes (B and C) which serve requests for "computers" This way we get a request-reply pattern with stateful routing, while keeping important properties of other patterns (scalability, uniformity and interjection) In the future it's intended to use same infrastructure that will be implemented for PUB/SUB subscriptions (i.e. plugins for subscription matching) I currently have the following questions: 1. Does AF_SP_RAW intended for asynchronous socket handling, similarly to how X* sockets worked in zeromq? It matters because xask and xanswer going to operate on subscriptions with messages, and asynchronous sockets should subscribe by socket option. However, non-raw answer socket can only process one request at a time, which is unviable for asynchronous applications. 2. When pipe is added to answer socket, all subscriptions should be resent. Is there a way to put all the subscriptions into a pipe without any limits? Otherwise, I need either build a complex state machine to track which subscriptions are already resent, or bundle all subscriptions to a single message (inventing some ad-hoc message format). BTW, similar problem with just adding a subscription, when some output pipes are full. What crossroads does in this case? 3. I'm going to use NN_RESEND_IVL and NN_SUBSCRIBE options, but they have same integer value. So I either need to reinvent names, or we need to set unique numbers for built-in socket options. I think the latter is preferable, as it also less error prone (can't setsockopt(NN_RESEND_IVL) for SUB socket) 4. Martin, could you describe a bit, how chunks work? I need to mark messages for being either subscriptions or request/reply, as well as keep a chain of routing data like for req-rep. Any suggestions? 5. The POLLOUT will always be signaled. It's useless to check if at least one pipe is not full, as the subset of pipes can be used for each message. The end to end resending mechanism will be used to fix the problem. Is the tradeoff ok? Of course, overall comments on pattern design are appreciated. -- Paul
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