[笔记]Go语言写文件几种方式性能对比？

Go语言中写文件有多种方式，这里进行如下几种方式的速度对比：

1. 打开文件，写入内容，关闭文件。如此重复多次
2. 打开文件，写入内容，defer 关闭文件。如此重复多次
3. 打开文件，重复多次写入内容，defer 关闭文件

在VMWare下的Ubuntu 14.04下运行的结果表明：

• 方式1速度最慢，但是慢的很稳定
• 方式2比方式1略快，但是重复次数多了后会报错，应该是defer被压栈太多导致系统撑不了太多打开的文件
• 方式3速度约是前两者的2倍，因为减少了很多打开关闭文件的操作

测试代码如下：

package main

import (
    "fmt"
    "os"
    "time"
)

func benchmarkFileWrite(filename string, n int, index int) (d time.Duration) {
    v := "ni shuo wo shi bu shi tai wu liao le a?"

    os.Remove(filename)

    t0 := time.Now()
    switch index {

    case 0: // open file and write, then close, repeat n times
        for i := 0; i < n; i++ {
            file, err := os.OpenFile(filename, os.O_WRONLY|os.O_APPEND|os.O_CREATE, 0666)
            if err != nil {
                fmt.Println(index, i, "open file failed.", err.Error())
                break
            }

            file.WriteString(v)
            file.WriteString("\n")
            file.Close()
        }
    case 1: // open file and write, defer close, repeat n times
        for i := 0; i < n; i++ {
            file, err := os.OpenFile(filename, os.O_WRONLY|os.O_APPEND|os.O_CREATE, 0666)
            if err != nil {
                fmt.Println(index, i, "open file failed.", err.Error())
                break
            }
            defer file.Close()

            file.WriteString(v)
            file.WriteString("\n")
        }
    case 2: // open file and write n times, then close file
        file, err := os.OpenFile(filename, os.O_WRONLY|os.O_APPEND|os.O_CREATE, 0666)
        if err != nil {
            fmt.Println(index, "open file failed.", err.Error())
            break
        }
        defer file.Close()

        for i := 0; i < n; i++ {
            file.WriteString(v)
            file.WriteString("\n")
        }
    }

    t1 := time.Now()
    d = t1.Sub(t0)
    fmt.Printf("time of way(%d)=%v\n", index, d)
    return d
}

func main() {
    const k, n int = 3, 1000
    d := [k]time.Duration{}
    for i := 0; i < k; i++ {
        d[i] = benchmarkFileWrite("benchmarkFile.txt", n, i)
    }

    for i := 0; i < k-1; i++ {
        fmt.Printf("way %d cost time is %6.1f times of way %d\n", i, float32(d[i])/float32(d[k-1]), k-1)
    }
}

当n=1000时，测试结果如下

  time of way(0)=38.719386ms
  time of way(1)=31.428677ms
  time of way(2)=17.930829ms
  way 0 cost time is    2.2 times of way 2
  way 1 cost time is    1.8 times of way 2

当n=5000时，测试结果如下（因为方式1报错，所以它的时间是错的）

  time of way(0)=170.003521ms
  1 1021 open file failed. open benchmarkFile.txt: too many open files
  time of way(1)=32.388994ms
  time of way(2)=77.777936ms
  way 0 cost time is    2.2 times of way 2
  way 1 cost time is    0.4 times of way 2