A parallel sum of numbers from a core.async channel.

async-num-summer.clj

(ns test1.numbers
  (:require [clojure.core.async :as a]))

(defn number-generator [n]
  (let [c (a/chan 1024)]
    (a/go
      (dotimes [x n]
        (a/>! c x))
      (a/close! c))
    c))
 
(defn sum-channel [ch]
  (a/go-loop [s 0]
    (if-some [x (a/<! ch)]
      (recur (+ x s))
      s)))

(defn parallel-sum [ch pnum]
  (let [sums (for [_ (range pnum)]
               (sum-channel ch))]
    (a/reduce + 0 (a/merge sums))))
        
(time (a/<!! (sum-channel (number-generator 1000000)))) ; 409 ms
(time (a/<!! (parallel-sum (number-generator 1000000) 1))) ; 551 ms
(time (a/<!! (parallel-sum (number-generator 1000000) 4))) ; 1244 ms