Pub Sub not working without interim sleep

[kul]

The following sample doesnt work without the sleep statement, i have excluded jzmq and using jeromq. moreover i dont see any error.

(ns exp.distributed
  (:use [clojure.tools.logging :only (warn info error)])
  (:require [zeromq.zmq :as zmq]
            [clojure.core.async :as async :refer :all]))

(defn start-subs []
  (future
    (let [ctx (zmq/context 1)]
      (with-open [sub (doto (zmq/socket ctx :sub)
                        (zmq/connect "tcp://127.0.0.1:5556")
                        (zmq/subscribe "topic"))]
        (dotimes [i 10]
          (info (zmq/receive-str sub)))))
    (info "listeners quits.")))

(defn start-pubs []
  (future
    (let [ctx (zmq/context 1)]
      (with-open [pub (doto (zmq/socket ctx :pub)
                        (zmq/bind "tcp://*:5556"))]
        (Thread/sleep 1000);removing this doesnt works
        (dotimes [i 10]
          (zmq/send-str pub (format "topic %d" i)))))
    (info "publisher quits.")))

(do
    (start-subs)
    (start-pubs))

[jjcomer]

This is the "slow joiner" problem. If you search in The Guide (http://zguide.zeromq.org) they have a detailed explanation of what causes this issue. The TL;DR is that subscribing is not a 0 time operation and the subscriber will miss any messages sent by the publisher until this process is finished. Adding the sleep is a good quick work around when testing but shouldn't be used in production. In terms of a real solution the guide suggests you view the pub-sub message stream as infinite thus having no beginning or end. This way you will never be expecting specific sequences of messages.

[kul]

This issue represent the new face of "slow joiner".

Thanks!