For Jan

singpool.clj

;;; First we'll define a new kind of (degenerate) connection pool to encapsulate the behavior you want:
(defrecord SingletonPool [conn] ; Keeps a single connection atom
  IConnectionPool
  (get-conn [_ spec]
    (or (when-let [c @conn] (when (conn-alive? c) c)) ; Aliveness check may not be necessary
        (println "making a new conn!")
        (reset! conn (make-new-connection spec))))
 
  (release-conn [_ _]      nil)
  (release-conn [this _ _] nil)
 
  java.io.Closeable
  (close [this] (when-let [c @conn] (reset! conn (close-conn c)))))
 
;;; And a helper:
(defmacro with-singleton-pool
  [conn-name spec & body]
  `(with-open [singleton-pool# (->SingletonPool (atom nil))]
     (let [~conn-name {:pool singleton-pool# :spec ~spec}]
       ~@body)))
 
;;; Now we can code to [almost] the same API as if we had a real pool:
(with-singleton-pool c1 {}
  (let [reply1 (wcar c1 (echo "foo"))
        reply2 (wcar c1 (echo "bar"))]
    (wcar c1 (set "my-key" (str reply1 reply2)))))