pool.clj

(ns question.pool
  (:refer-clojure :exclude [take])
  (:require
    [clojure.tools.logging :as log]))

(def pool (ref []))

(defn take
  [pool]
  (dosync
    (let [[h & t] @pool]
      (ref-set pool (vec t))
      h)))

(defn put
  [pool value]
  (dosync
    (alter pool conj value)
    nil))

(defn init-with-size
  [size init-fn & args]
  (do
    (log/infof "creating pool with size %s" size)
    (dotimes [n size]
      (put pool (apply init-fn args)))
    pool))


(defmacro with-resource-from-pool
  [current-pool object-name & body]
   `(let [~object-name (take ~current-pool)]
      (try
        (let [res# ~@body]
          (put ~current-pool ~object-name)
          res#)
        (catch Exception e#
          (put ~current-pool ~object-name)
          (log/errorf "Pool exception: %s" e#)
          (throw e#)))))