Initial simple implementation of Go "select" or Rack "sync" in Clojure

select.clj

(defn- choose [ready-chans]
  (.take (nth ready-chans (rand-int (count ready-chans)))))

(defn- peek-channels [channels]
  (let [ready (doall (keep #(when-not (nil? (.peek %)) %) channels))]
    (if (seq ready)
      (nth ready (rand-int (count ready)))  ;; pick at random if >1 ready
      (Thread/sleep 0 500))))

(defn- probe-til-ready [channels]
  (loop [chans channels ready-chan nil]
    (if ready-chan
      (.take ready-chan)
      (recur channels (peek-channels channels)))))

(defn select [& channels]
  (let [ready (doall (filterv #(not (nil? (.peek %))) channels))]
    (if (seq ready)
      (choose ready)
      (probe-til-ready channels))))