gistfile1.clj

(defn calculate-deposit* [ch]
  (let [control (chan 256)
        users   (udb/get-users)
        total   (count users)]
    (doseq [g (partition-all (quot total 50) users)]
      (future
        (doseq [user g]
          (let [data (calculate-user-deposit-row user)]
            (if data (put! ch (str data "\n")))
            (put! control 1)))))
    (go
      (<!
        (go-loop [i 1]
          (if (and (<! control) (< i total)) (recur (inc i)))))
      (close! ch))))


(defn calculate-deposit [req]
  (let [headers {"Content-Type" "text/csv"
                 "Content-Disposition" "attachment; filename=\"deposit.csv\""}
        res-ch  (chan 256)]
    (with-channel req channel
      (send! channel {:headers headers :status 200} false)
      (calculate-deposit* res-ch)
      (go
        (<! (go-loop []
              (when-let [e (<! res-ch)]
                (send! channel e false)
                (recur))))
        (close channel)))))