@nfyig #91

贴一个今早老大发的文章.

https://i.imgur.com/faxK88j.png

用 js 实现上图中需求, 可能需要 `redux-saga` 中的 `race/take` 等 effects.

下面是 clj 的实现, 用 core.async 来解决异步通讯问题

```clj/cljs
(require-macros '[clojure.core.async.macros :refer [go go-loop]])
(require '[cljs.core.async :refer [promise-chan chan timeout mult <! >!]])

;; 模拟关灯, 读取不成功时执行关灯操作
(defn- mock-light-off []
(print "关灯!!!"))

;; 模拟读取情况, 随机 2000 毫秒返回模拟消息
(defn- mock-read [c]
(go (do
(<! (timeout (rand-int 2000)))
(>! c "[msg head....]"))))

;; 模拟生成消息, 60ms 之内,随机时间, 消息内容为 '-'
(defn- mock-msg [c]
(go (do
(<! (timeout (rand-int 55)))
(>! c "-"))))

;; 后续消息读取, 50ms 读不到就结束,读到就增加到消息尾部, 然后继续读, 直到超时
(defn- mock-read-proceed [c v]
(go (>! c v))
(go-loop [msg ""]
(mock-msg c)
(let [[v q] (alts! [c (timeout 50)])]
(if (= c q)
(do (println "读到消息:" v)
(recur (str msg v)))
(println "读取结束, 最终结果为:" msg)))))

;; 读取函数, 模拟 1000 秒超时
(defn scan-with-time-out [c]
(mock-read c)
(go
(let [[v q] (alts! [c (timeout 1000)])]
(if (= c q)
(do (println "读到消息头:" v)
(mock-read-proceed c v))
(do (println "首次读取超时,操作结束")
(mock-light-off))))))

(let [c (chan)]
(scan-with-time-out c))
```