Using LockService to guarantee leader with Clojure and JGroups

core.clj

(ns leader-guarantee.core
        (:import (org.jgroups.blocks.locking LockService)
                                         (org.jgroups.protocols CENTRAL_LOCK)
                                         (org.jgroups JChannel)
                                         (java.util.concurrent.locks Lock)))

(defn- get-lock
        [lock-service with-lock-fn]
        (fn []
          (let [lock (.getLock lock-service "leader")]
            (do
              (.lock lock) ;; <<< Lock is acquired here - will block until Leader
              (with-lock-fn)))))

(defn when-leader*
        "Executes with-lock-fn when the local application container becomes leader of the cluster-name cluster."
        [cluster-name with-lock-fn]
        (let [channel (doto (JChannel.) ;; Uses udp by default
                        (.. getProtocolStack (addProtocol (doto (CENTRAL_LOCK.) (.init))))
                        (.connect cluster-name))
              lock-service (LockService. channel)]
          ;; Create a thread to get us the Leader Lock
          (doto (Thread. (get-lock lock-service with-lock-fn) "LeaderAppointmentThread")
              (.setDaemon true)
              (.start))))