clojure - 计算 Clojure channel 中的事件发生率

Question

我想计算事件的发生率，例如按键事件，并显示它。我也想仅在第一个事件发生后才开始速率计算。另一个要求是速率计算应在一定数量的按键事件后停止。我目前的做法是

(defn keypress-chan
  "Returns a channel that receives keys"
  []
  (let [out (chan) handler (fn [e] (put! out (.-key e)))]
    (js/document.addEventListener "keypress" handler false)
    out))

(defn tick
  "Pushes to `out` 1000 ms later"
  [out]
  (go
    (<! (timeout 1000))
    (>! out 1)))

(defn get-rate
  "Calculates keypress per minute rate"
  [ticks pressed]
  (quot (* pressed 60) ticks))

(defn complete?
  [count]
  (>= count 100))

(defn main-loop []
  (let [key-chan (keypress-chan) ticker-chan (chan)]
    (go-loop [pressed 0 ticks 0]
      (let [[value ch] (alts! [key-chan ticker-chan])]
        (if (= ch key-chan)
          (do
            ;; Start timer to calculate keypress rate
            (if (zero? pressed)
              (tick ticker-chan))

            ;; Do something with `value`, i. e. the key being pressed

            (when-not (complete?)
              (recur (inc pressed) ticks)))

          (let [speed (get-rate ticks pressed)]
            (swap! app-state assoc :rate rate)
            (tick ticker-chan)
            (recur pressed (inc ticks))))))))

所以，这是有效的，但是 main-loop 中的代码对我来说似乎很丑。我一直在想有一个“触发器”，只有当第一个值出现在 key-chan 中时才会触发。并启动计时器。然后另一个触发器在必要时停止计时器。但我是 Clojure 的新手，不知道如何使用 async ，所以我无法创建比上面的代码更好的东西。

如何改进这个循环？
我可以将计时器移动到函数并通过 key-chan 中的第一个值启动计时器吗？ ?
我以后如何停止该计时器？

Answer 1

我想出了以下解决方案。

(ns ratecalc.core
  (:require [cljs.core.async :refer [chan <! go-loop]])
  (:import [goog.date DateTime]))

(defn calc-rate [input-chan do-fun max-count]
  (go-loop [count 0
            start-time nil]
    (<! input-chan)
    (let [inc-count (inc count)
          now (.getTime (DateTime.))
          start-time* (if-not start-time now start-time)
          rate-per-ms (/ inc-count (- now start-time*))]
      (do-fun rate-per-ms)
      (if (= count max-count)
        rate-per-ms
        (recur inc-count start-time*)))))

calc-rate函数计算每毫秒 channel 上的消息数。你可以传递一个函数来做一些副作用，比如打印当前的平均值。最后一个参数将其计算限制为最大消息数。以下是如何使用它的示例:

(calc-rate (keypress-chan) println 10)