[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：

打开文件，写入内容，关闭文件。如此重复多次
打开文件，写入内容，defer 关闭文件。如此重复多次
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 mainimport ("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 timesfor 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 timesfor 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 filefile, 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, 1000d := [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)=38.719386mstime of way(1)=31.428677mstime of way(2)=17.930829msway 0 cost time is    2.2 times of way 2way 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)=170.003521ms1 1021 open file failed. open benchmarkFile.txt: too many open filestime of way(1)=32.388994mstime of way(2)=77.777936msway 0 cost time is    2.2 times of way 2way 1 cost time is    0.4 times of way 2