为什么这个Clojure程序这么慢？如何使它运行快？ [英] Why is this Clojure program so slow? How to make it run fast?

问题描述

这里清楚地解释了如何优化Clojure程序处理原始值：使用类型注释和未检查的数学，它会运行快速：

Here it is clearly explained how to optimize a Clojure program dealing with primitive values: use type annotations and unchecked math, and it will run fast:

(set! *unchecked-math* true)

(defn add-up ^long [^long n]
  (loop [n n i 0 sum 0]
    (if (< n i)
      sum
      (recur n (inc i) (+ i sum)))))

好奇心，我试过在 lein repl ，令我惊讶的是，发现这个代码运行慢约20倍的预期（Clojure 1.6.0在Oracle JDK 1.8.0_11 x64）：

So, just out of curiosity, I've tried it in lein repl and, to my surprise, found this code running ~20 times slower that expected (Clojure 1.6.0 on Oracle JDK 1.8.0_11 x64):

user=> (time (add-up 1e8))
"Elapsed time: 2719.188432 msecs"
5000000050000000

$ b b

Scala 2.10.4（相同JVM）中的等效代码在〜90ms内运行：

Equivalent code in Scala 2.10.4 (same JVM) runs in ~90ms:

def addup(n: Long) = { 
  @annotation.tailrec def sum(s: Long, i: Long): Long = 
    if (i == 0) s else sum(s + i, i - 1)
  sum(0, n)
}

Clojure代码示例？为什么它这么慢（理论上应该大致相同的速度）？

So, what am I missing in the Clojure code sample? Why is it so slow (should theoretically be roughly the same speed)?

推荐答案

用 通常是一个坏主意，因为它专门设置非服务器JVM设置。直接使用Clojure JAR我在一个3.5GHz的i7 iMac上看到〜40ms，在OS X 10.9下运行JDK 8.

Benchmarking with lein repl is generally a bad idea as it specifically sets non-server JVM settings. Using the Clojure JAR directly I see ~40ms on a 3.5ghz i7 iMac running JDK 8 under OS X 10.9.

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