Go语言高性能字符串拼接

Go语言高性能字符串拼接

1. 使用strings.Builder

strings.Builder 使用 Write 方法来高效的构造字符串. 它使用内存最小,它使用零值,它不拷贝零值.
注意:不要拷贝strings.Builder的值,如果你要使用strings.Builder值请使用pointer

package main

import (
    "strings"
    "fmt"
)

func main() {
    var str strings.Builder

    for i := 0; i < 1000; i++ {
        str.WriteString("a")
    }

    fmt.Println(str.String())
}

2.使用bytes.Buffer

package main

import (
    "bytes"
    "fmt"
)

func main() {
    var buffer bytes.Buffer

    for i := 0; i < 1000; i++ {
        buffer.WriteString("a")
    }

    fmt.Println(buffer.String())
}

3.使用go语言内置函数copy

package main

import (
    "bytes"
    "fmt"
)

func main() {
    bs := make([]byte, 1000)
    bl := 0
   for n := 0; n < 1000; n++ {
        bl += copy(bs[bl:], "a")
    }
    fmt.Println(string(bs))
}

4.使用go语言内置函数append

package main

import (
    "bytes"
    "fmt"
)

func main() {
    bs := make([]byte, 1000)
   for n := 0; n < 1000; n++ {
        bs = append(bs,'a')
    }
    fmt.Println(string(bs))
}

5.使用字符串+运算

package main

import (
   "fmt"
)

func main() {
   var result string

   for i := 0; i < 1000; i++ {
           result += "a"
   }

   fmt.Println(result)
}

6. strings.Repeat

package main

import (
    "fmt"
    "strings"
)

func main()  {
    fmt.Println(strings.Repeat("x",1000))
}

strings.Repeat它的底层调用的是strings.Builder,提前分配了内存.

// Repeat returns a new string consisting of count copies of the string s.
//
// It panics if count is negative or if
// the result of (len(s) * count) overflows.
func Repeat(s string, count int) string {
    if count == 0 {
        return ""
    }

    // Since we cannot return an error on overflow,
    // we should panic if the repeat will generate
    // an overflow.
    // See Issue golang.org/issue/16237
    if count < 0 {
        panic("strings: negative Repeat count")
    } else if len(s)*count/count != len(s) {
        panic("strings: Repeat count causes overflow")
    }

    n := len(s) * count
    var b Builder
    b.Grow(n)
    b.WriteString(s)
    for b.Len() < n {
        if b.Len() <= n/2 {
            b.WriteString(b.String())
        } else {
            b.WriteString(b.String()[:n-b.Len()])
            break
        }
    }
    return b.String()
}

7.Benchmark

package main

import (
    "bytes"
    "strings"
    "testing"
)

const (
    sss = "https://mojotv.cn"
    cnt = 10000
)

var (
    bbb      = []byte(sss)
    expected = strings.Repeat(sss, cnt)
)
//使用 提前初始化  内置 copy函数
func BenchmarkCopyPreAllocate(b *testing.B) {
    var result string
    for n := 0; n < b.N; n++ {
        bs := make([]byte, cnt*len(sss))
        bl := 0
        for i := 0; i < cnt; i++ {
            bl += copy(bs[bl:], sss)
        }
        result = string(bs)
    }
    b.StopTimer()
    if result != expected {
        b.Errorf("unexpected result; got=%s, want=%s", string(result), expected)
    }
}
//使用 提前初始化  内置append 函数
func BenchmarkAppendPreAllocate(b *testing.B) {
    var result string
    for n := 0; n < b.N; n++ {
        data := make([]byte, 0, cnt*len(sss))
        for i := 0; i < cnt; i++ {
            data = append(data, sss...)
        }
        result = string(data)
    }
    b.StopTimer()
    if result != expected {
        b.Errorf("unexpected result; got=%s, want=%s", string(result), expected)
    }
}
//使用 提前初始化 bytes.Buffer
func BenchmarkBufferPreAllocate(b *testing.B) {
    var result string
    for n := 0; n < b.N; n++ {
        buf := bytes.NewBuffer(make([]byte, 0, cnt*len(sss)))
        for i := 0; i < cnt; i++ {
            buf.WriteString(sss)
        }
        result = buf.String()
    }
    b.StopTimer()
    if result != expected {
        b.Errorf("unexpected result; got=%s, want=%s", string(result), expected)
    }
}

//使用 strings.Repeat 本质是pre allocate + strings.Builder
func BenchmarkStringRepeat(b *testing.B) {
    var result string
    for n := 0; n < b.N; n++ {
        result = strings.Repeat(sss,cnt)
    }
    b.StopTimer()
    if result != expected {
        b.Errorf("unexpected result; got=%s, want=%s", string(result), expected)
    }
}
//使用 内置copy
func BenchmarkCopy(b *testing.B) {
    var result string
    for n := 0; n < b.N; n++ {
        data := make([]byte, 0, 64) // same size as bootstrap array of bytes.Buffer
        for i := 0; i < cnt; i++ {
            off := len(data)
            if off+len(sss) > cap(data) {
                temp := make([]byte, 2*cap(data)+len(sss))
                copy(temp, data)
                data = temp
            }
            data = data[0 : off+len(sss)]
            copy(data[off:], sss)
        }
        result = string(data)
    }
    b.StopTimer()
    if result != expected {
        b.Errorf("unexpected result; got=%s, want=%s", string(result), expected)
    }
}
//使用 内置append
func BenchmarkAppend(b *testing.B) {
    var result string
    for n := 0; n < b.N; n++ {
        data := make([]byte, 0, 64)
        for i := 0; i < cnt; i++ {
            data = append(data, sss...)
        }
        result = string(data)
    }
    b.StopTimer()
    if result != expected {
        b.Errorf("unexpected result; got=%s, want=%s", string(result), expected)
    }
}
//使用 bytes.Buffer
func BenchmarkBufferWriteBytes(b *testing.B) {
    var result string
    for n := 0; n < b.N; n++ {
        var buf bytes.Buffer
        for i := 0; i < cnt; i++ {
            buf.Write(bbb)
        }
        result = buf.String()
    }
    b.StopTimer()
    if result != expected {
        b.Errorf("unexpected result; got=%s, want=%s", string(result), expected)
    }
}
//使用 strings.Builder write bytes
func BenchmarkStringBuilderWriteBytes(b *testing.B) {
    var result string
    for n := 0; n < b.N; n++ {
        var buf strings.Builder
        for i := 0; i < cnt; i++ {
            buf.Write(bbb)
        }
        result = buf.String()
    }
    b.StopTimer()
    if result != expected {
        b.Errorf("unexpected result; got=%s, want=%s", string(result), expected)
    }
}
//使用 string buffer write string
func BenchmarkBufferWriteString(b *testing.B) {
    var result string
    for n := 0; n < b.N; n++ {
        var buf bytes.Buffer
        for i := 0; i < cnt; i++ {
            buf.WriteString(sss)
        }
        result = buf.String()
    }
    b.StopTimer()
    if result != expected {
        b.Errorf("unexpected result; got=%s, want=%s", string(result), expected)
    }
}


// 使用string 加号
func BenchmarkStringPlusOperator(b *testing.B) {
    var result string
    for n := 0; n < b.N; n++ {
        var str string
        for i := 0; i < cnt; i++ {
            str += sss
        }
        result = str
    }
    b.StopTimer()
    if result != expected {
        b.Errorf("unexpected result; got=%s, want=%s", string(result), expected)
    }
}

执行 go test -bench=. -benchmem 输出结果:

$ go test -bench=. -benchmem
goos: windows
goarch: amd64
BenchmarkCopyPreAllocate-8                 10000            117600 ns/op          344065 B/op          2 allocs/op
BenchmarkAppendPreAllocate-8               20000             75300 ns/op          344065 B/op          2 allocs/op
BenchmarkBufferPreAllocate-8               20000             97149 ns/op          344065 B/op          2 allocs/op
BenchmarkStringRepeat-8                   100000             18349 ns/op          172032 B/op          1 allocs/op
BenchmarkCopy-8                            10000            152417 ns/op          862307 B/op         13 allocs/op
BenchmarkAppend-8                          10000            157210 ns/op         1046405 B/op         23 allocs/op
BenchmarkBufferWriteBytes-8                10000            173207 ns/op          862374 B/op         14 allocs/op
BenchmarkStringBuilderWriteBytes-8         10000            155715 ns/op          874468 B/op         24 allocs/op
BenchmarkBufferWriteString-8               10000            165700 ns/op          862373 B/op         14 allocs/op
BenchmarkStringPlusOperator-8                 20          84450010 ns/op        885204590 B/op     10037 allocs/op
PASS
ok      _/D_/code/tech.mojotv.cn/tutorials      18.797s

下面着重解释下说出的结果,看到函数后面的-8了吗？这个表示运行时对应的GOMAXPROCS的值.
接着的10000表示运行for循环的次数,也就是调用被测试代码的次数,最后的174799 ns/op表示每次需要话费174799纳秒.
14 allocs/op表示每次执行分配了32字节内存.

参考文章