为什么此Scala代码运行缓慢? [英] Why is this Scala code slow?

问题描述

我正在运行以下Scala代码:

I'm running the following Scala code:

import scala.util.parsing.json._
import scala.io._

object Main {
        def jsonStringMap(str: String) =
                JSON.parseFull(str) match {
                        case Some(m: Map[_,_]) => m collect {
                                        // If this doesn't match, we'll just ignore the value
                                        case (k: String, v: String) => (k,v)
                                } toMap
                        case _ => Map[String,String]()
                }

        def main(args: Array[String]) {
                val fh = Source.fromFile("listings.txt")
                try {
                        fh.getLines map(jsonStringMap) foreach { v => println(v) }
                } finally {
                        fh.close
                }
        }
}

在我的计算机上，从 http://sortable.com/blog/coding-challenge/获取的文件大约需要3分钟.我编写的等效Haskell和Ruby程序用时不到4秒.我在做什么错了?

On my machine it takes ~3 minutes on the file from http://sortable.com/blog/coding-challenge/. Equivalent Haskell and Ruby programs I wrote take under 4 seconds. What am I doing wrong?

我在没有map(jsonStringMap)的情况下尝试了相同的代码，而且速度非常快，所以JSON解析器真的很慢吗?

I tried the same code without the map(jsonStringMap) and it was plenty fast, so is the JSON parser just really slow?

默认JSON解析器似乎确实很慢，但是我尝试了 https://github.com/stevej/scala-json ，虽然将其缩短到35秒，但仍然比Ruby慢得多.

It does seem likely that the default JSON parser is just really slow, however I tried https://github.com/stevej/scala-json and while that gets it down to 35 seconds, that's still much slower than Ruby.

我现在正在使用 https://github.com/codahale/jerkson ，它甚至更快[em] ！现在，我的程序仅对数据运行6秒钟，仅比Ruby慢3秒钟，而Ruby可能只是JVM的启动.

I am now using https://github.com/codahale/jerkson which is even faster! My program now runs in only 6 seconds on my data, only 3 seconds slower than Ruby, which is probably just the JVM starting up.

推荐答案

快速浏览scala用户档案似乎表明没有人对scala标准库中的JSON解析器进行过认真的工作.

A quick look at the scala-user archive seems to indicate that nobody is doing serious work with the JSON parser in the scala standard library.

请参见 http://groups.google.com/group/scala-user /msg/fba208f2d3c08936

似乎解析器最终出现在标准库中，而此时scala并不是人们关注的焦点，并且没有今天的期望.

It seems the parser ended up in the standard library at a time when scala was less in the spotlight and didn't have the expectations it has today.

这篇关于为什么此Scala代码运行缓慢?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！