search_fastest.clj

(use 'clojure.core.async)

(defn req [server query]
  (go
   (<! (timeout (rand-int 100)))
   (str query " from " server)))

(defn fastest [query & servers]
  (let [c (chan)]
    (doseq [server servers]
      (go
       (>! c (<! (req server query)))
       (close! c)))
    c))


;; go returns channel with return value
(defn search [query t]
  (let [c (chan)
        t (timeout t)]
    (go (>! c (<! (fastest query "web1" "web2" "web3"))))
    (go (>! c (<! (fastest query "img1" "img2"))))
    (go (>! c (<! (fastest query "video1" "video2"))))
    (go-loop [ret []]
          (if (>= (count ret) 3)
            ret
            (recur
             (conj ret (alt! [c t] ([v] v))))))))

(<!! (search "abc" 90))