clojure.core.async/chan

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Type: function Added: Clojure unknown Examples: 4 Runnable: 0

([] [buf-or-n] [buf-or-n xform] [buf-or-n xform ex-handler])

Creates a channel with an optional buffer, an optional transducer (like (map f), (filter p) etc or a composition thereof), and an optional exception-handler. If buf-or-n is a number, will create and use a fixed buffer of that size. If a transducer is supplied a buffer must be specified. ex-handler must be a fn of one argument - if an exception occurs during transformation it will be called with the Throwable as an argument, and any non-nil return value will be placed in the channel.

Examples

by runexec on 2014-10-01 . May have evaluation errors. ▶

(def c (chan)) #'user/c (def c (chan 1)) #'user/c (def c (chan (buffer 2))) #'user/c ;; Clojure 1.7 (def c (chan 1 (filter string?))) #'user/c

by ertugrulcetin on 2018-03-16 . May have evaluation errors. ▶

(let [c (chan 3 (map inc))] ;; providing transducer which increments values by one (>!! c 1) (>!! c 2) (>!! c 3) (println (<!! c)) (println (<!! c)) (println (<!! c))) ;; 2 ;; 3 ;; 4 ;;=> nil

by liuchong on 2021-01-20 . May have evaluation errors. ▶

(def c (chan (buffer 1) (fn [xf] (fn [_ data] (throw (Exception. (when (= data "hehe") "xform error"))))) (fn [e] (.getMessage e)))) (>!! c "hehe") ;;=> true ;; any non-nil return value from transducer will be placed in the channel (<!! c) ;;=> "xform error" (>!! c "haha") ;;=> true ;; nil return value from transducer will NOT be placed in the channel (<!! c) ;; will stuck here

by loeschzwerg on 2021-10-28 . May have evaluation errors. ▶

;; You can use mapcat to quickly dispatch a seq (def c (chan 3 (mapcat identity))) ;;=> #'user/c (>!! c (range 3)) ;;=> true (loop [x (<!! c)] (prn x) (recur (<!! c)) ;;0 ;;1 ;;2 ;; (stuck, because it's a vampire 🧛 sucking on an unclosed channel) ;; Use a go-loop to start a concurrent parking consumer instead. (go-loop [x (<! c)] (when x ;; abort when channel is closed (nil? (<! c)) (prn x) (recur (<! c)))) ;;=> #object[clojure.core.async.impl.channels.ManyToManyChannel... ;; When provisioning more items than the channel buffer allows, ;; mapcat will still put all items (>!! c (range 5)) ;;=> true ;;0 ;;1 ;;2 ;;3 ;;4 ;; Avoid that with a dropping/sliding buffer: (def c (chan (sliding-buffer 3) (mapcat identity))) ;;=> #'user/c (go-loop ...) ;;=> #object[clojure.core.async.impl.channels.ManyToManyChannel... (>!! c (range 5)) ;;=> true ;;2 ;;3 ;;4

See also

• clojure.core.async/buffer
• clojure.core.async/dropping-buffer
• clojure.core.async/sliding-buffer
• clojure.core.async/promise-chan

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