conquerant

async/await for Clojure

A lightweight Clojure wrapper around ForkJoinPool and CompletableFuture for concurrency that is simple and easy.

Why

core.async is very powerful, but quite low-level by design

• it allows for a very flexible style of writing concurrent code
• but has a huge surface area, and can be daunting to learn
• we don't always want this kind of power
• doesn't allow using custom threadpools
• breaks emacs

Usage

[conquerant "0.1.5"]

;; Async HTTP Exaxmple
;; ===================
(refer-clojure :exclude '[await promise])
(require '[clj-http.client :as client]
         '[conquerant.core :refer [async await promise]])

(def url "https://gist.githubusercontent.com/divs1210/2ce84f3707b785a76d225d23f18c4904/raw/2dedab13201a8a8a2c91c3800040c84b70fef2e2/data.edn")

(defn fetch [url]
  (promise [resolve]
    (client/get url
                {:async? true}
                #(resolve [% nil])
                #(resolve [nil %]))))

(async
  (let [[response err] (await (fetch url))]
    (if err
      (println "Error:" (.getMessage err))
      (println "Response Body:" (:body response)))))

(println "fetching asynchronously...")
;; => fetching asynchronously...
;; => Response Body: {:result 1}

• promise

  • gets value/error out of callback
  • returns a CompletableFuture

• async

  • can wrap
    • defn and fn forms - supports variadic versions: (async (defn [a] (inc a)))
    • any other expression, returning a CompletableFuture: @(async [1 2])
  • all let blocks inside async run asynchronously and return CompletableFutures.
  • conquerant.internals/*executor* is bound to the common ForkJoinPool pool by default

• await

  • can only be used in async let blocks
    • normal let block anywhere inside an async block
    • works across function boundaries, unlike core.async

License

Copyright © 2018 Divyansh Prakash

Distributed under the Eclipse Public License either version 1.0.