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 on function boundaries
• breaks emacs

Usage

;; 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}
                (fn [response]
                  (resolve [response nil]))
                (fn [error]
                  (resolve [nil error])))))

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

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

• promise

  • gets value out of callback
  • returns a CompletableFuture
  • can be resolved from outside via complete
  • can be derefed: @(promise [resolve] (resolve :hi))

• async

  • can wrap
    • defn and fn forms - supports variadic versions

    (async (defn f
             ([a]
               (inc a))
             ([a b]
               (* a b))))
    

    • any other expression, returning a CompletableFuture (promise)

    @(async [1 2]) ;; => [1 2]
    

  • can run on a custom ExecutorService using with-async-executor

• await

  • can only be used in async let bindings
    • normal let block anywhere inside an async block
    • every let block with a call to await returns a CompletableFuture
  • works across function boundaries
  • can timeout like deref: (await p 1000 :timeout)

• channels

  • supports core.async-like channel operations!

Walkthrough

Clone this repo, fire up a REPL, and walk through the conquerant walkthrough.

License

Copyright © 2018 Divyansh Prakash

Distributed under the Eclipse Public License either version 1.0.