一个博文引起代码优化的思路

Posted 2021-05-07 Myuniverse

• 参考博文：一步步提升Go语言生成随机字符串的效率

• 根据自己的理解写出来的性能测试函数：

package generateString

import(
    "time"
    "testing"
    "math/rand"
)

var letterRunes = []rune("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ")
const letterBtyes = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
const letterIdxBits = 6
const letterIdxMask = 1 << letterIdxBits -1
const letterIdxMax = 63 /letterIdxBits
var src = rand.NewSource(time.Now().UnixNano())

func init(){
    rand.Seed(time.Now().UnixNano())
}

// 常见做法
func RandStringRunes(n int) string {
    b := make([]rune,n)
    for i:= range b{
        b[i] = letterRunes[rand.Intn(len(letterRunes))]
    }
    return string(b)
}

// bytes改进
func RandStringByte(n int) string{
    b := make([]byte,n)
    for i := range b{
        b[i] = letterBtyes[rand.Intn(len(letterBtyes))]
    }
    return string(b)
}

// 余数改进
func RandStringByteRmndr(n int)string{
    b := make([]byte,n)
    for i:= range b{
        b[i] = letterBtyes[rand.Int63()%int64(len(letterBtyes))]
    }
    return string(b)
}

// 掩码
func RandStringByteMask(n int)string{
    b := make([]byte,n)
    for i:=0;i<n;{
        // & 按位与
        if idx := int(rand.Int63()&letterIdxMask);idx < len(letterBtyes){
            b[i] = letterBtyes[idx]
            i++
        }
    }
    return string(b)
}

// 掩码改进，保证公平性的利用资源
func RandStringByteMaskImpr(n int)string{
    b := make([]byte,n)
    for i,cache,remain := n-1,src.Int63(),letterIdxMax;i>=0;{
        if remain==0{
            cache,remain = src.Int63(),letterIdxMax
        }
        if idx := int(cache & letterIdxMask);idx < len(letterBtyes) {
            b[i] = letterBtyes[idx]
            i--
        }
        cache >>= letterIdxBits  //可以移动十次
        remain--  //修改十次
    }
    return string(b)
}

func BenchmarkRandStringRunes(b *testing.B){
    for i:=0;i<b.N;i++{
        RandStringRunes(5)
    }
}

func BenchmarkRandStringBytes(b *testing.B){
    for i:=0;i<b.N;i++{
        RandStringByte(5)
    }
}

func BenchmarkRandStringByteRmndr(b *testing.B){
    for i:=0;i<b.N;i++{
        RandStringByteRmndr(5)
    }
}

func BenchmarkRandStringByteMask(b *testing.B){
    for i:=0;i<b.N;i++{
        RandStringByteMask(5)
    }
}

// 这部分缩短的时间太多了吧
func BenchmarkRandStringByteMaskTmpr(b *testing.B){
    for i:=0;i<b.N;i++{
        RandStringByteMaskImpr(5)
    }
}

• 输出结果

goos: windows
goarch: amd64
BenchmarkRandStringRunes-8               5756960               219 ns/op              40 B/op          2 allocs/op
BenchmarkRandStringBytes-8               8533357               146 ns/op              10 B/op          2 allocs/op
BenchmarkRandStringByteRmndr-8           9865086               125 ns/op              10 B/op          2 allocs/op
BenchmarkRandStringByteMask-8            8979186               141 ns/op              10 B/op          2 allocs/op
BenchmarkRandStringByteMaskTmpr-8       20043025                61.9 ns/op            10 B/op          2 allocs/op
PASS
ok      command-line-arguments  7.266s

• 优化代码的思路
  • 要拥有的工具：学会使用go test中性能测试
  • 通过使用性能测试工具，找到耗时的地方
  • 内存资源尽可能多的利用