core.clj

(ns async-example.core
  (:gen-class)
  (:require [clojure.core.async
                 :as a
                 :refer [>! <! >!! <!! go chan buffer close! thread
                         alts! alts!! timeout]]))

(def write-to-file-channel (chan 10000))

(defn get-contents [name]
  (Thread/sleep (+ 40 (rand 30))) ;waiting for a service
  (str (java.util.UUID/randomUUID)))

(defn write-to-file [name]
  (clojure.core/spit (clojure.java.io/file "/tmp/async-example/" name) ; /tmp/async-example/ must exist
                     (get-contents name)))

(defn -main [number-of-workers]
  (dotimes [n 10000]
    (go (>! write-to-file-channel (str n ".txt"))))
  (dotimes [n (read-string number-of-workers)]
    (thread
      (while true
        (write-to-file (<!! write-to-file-channel)))))
  (println "Done in main. Taking a nap.")
  (Thread/sleep 50000) ; The program continues doing other things
)