Clojure 中的快速随机字符串生成器

Question

我想知道是否有一种方法可以在 Clojure 中生成固定长度的随机字符串。

快速搜索结果：

https://gist.github.com/rboyd/5053955

(defn rand-str [len]
  (apply str (take len (repeatedly #(char (+ (rand 26) 65))))))

在我查看了 VisualVM CPU 配置文件数据后，我意识到它消耗了大量的 CPU:

我决定将其重写为类似于我曾经使用的 Java 函数：

(defn rand-str2-slow
  ^String [^Long len]
  (let [leftLimit 97
        rightLimit 122
        random (Random.)
        stringBuilder (StringBuilder. len)
        diff (- rightLimit leftLimit)]
    (dotimes [_ len]
      (let [ch (char (.intValue (+ leftLimit (* (.nextFloat random) (+ diff 1)))))]
        (.append stringBuilder ch)))
        (.toString stringBuilder)))

这导致代码更慢，但堆栈跟踪的深度要小得多：

我注意到它做了很多 Reflector.getMethods()。有没有办法键入提示函数来避免这种情况？

更新 1：

相关微基准：

rand-str

(with-progress-reporting (quick-bench (rand-str 5000) :verbose))

      Execution time sample mean : 1.483232 ms
             Execution time mean : 1.483547 ms
Execution time sample std-deviation : 31.161960 µs
    Execution time std-deviation : 31.651732 µs
   Execution time lower quantile : 1.441678 ms ( 2.5%)
   Execution time upper quantile : 1.531289 ms (97.5%)
                   Overhead used : 14.598226 ns

rand-str2-慢

(with-progress-reporting (quick-bench (rand-str2-slow 5000) :verbose))

      Execution time sample mean : 17.637256 ms
             Execution time mean : 17.647974 ms
Execution time sample std-deviation : 523.527242 µs
    Execution time std-deviation : 528.559280 µs
   Execution time lower quantile : 17.322583 ms ( 2.5%)
   Execution time upper quantile : 18.522246 ms (97.5%)
                   Overhead used : 14.598226 ns

rand-str2（快速）

(with-progress-reporting (quick-bench (rand-str2 5000) :verbose))

      Execution time sample mean : 84.362974 µs
             Execution time mean : 84.355379 µs
Execution time sample std-deviation : 3.496944 µs
    Execution time std-deviation : 3.674542 µs
   Execution time lower quantile : 80.911920 µs ( 2.5%)
   Execution time upper quantile : 89.264431 µs (97.5%)
                   Overhead used : 14.598226 ns

Answer 1

让我回答我自己的问题：

(defn rand-str2
  ^String [^Long len]
  (let [leftLimit 97
        rightLimit 122
        random (Random.)
        stringBuilder (StringBuilder. len)
        diff (- rightLimit leftLimit)]
    (dotimes [_ len]
      (let [ch (char (.intValue ^Double (+ leftLimit (* (.nextFloat ^Random random) (+ diff 1)))))]
        (.append ^StringBuilder stringBuilder ch)))
        (.toString ^StringBuilder stringBuilder)))

Clojure 中的快速随机字符串生成器

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