golang []byte和string的高性能转换

golang []byte和string的高性能转换

在fasthttp的最佳实践中有这么一句话：

[]bytestring[]bytestring[]bytestring

[]bytestring[]bytestring

// b2s converts byte slice to a string without memory allocation.
// See https://groups.google.com/forum/#!msg/Golang-Nuts/ENgbUzYvCuU/90yGx7GUAgAJ .
//
// Note it may break if string and/or slice header will change
// in the future go versions.
func b2s(b []byte) string {
	/* #nosec G103 */
	return *(*string)(unsafe.Pointer(&b))
}

// s2b converts string to a byte slice without memory allocation.
//
// Note it may break if string and/or slice header will change
// in the future go versions.
func s2b(s string) (b []byte) {
	/* #nosec G103 */
	bh := (*reflect.SliceHeader)(unsafe.Pointer(&b))
	/* #nosec G103 */
	sh := (*reflect.StringHeader)(unsafe.Pointer(&s))
	bh.Data = sh.Data
	bh.Cap = sh.Len
	bh.Len = sh.Len
	return b
}

[]bytestring

var s = "adsfasdfadsfadsfasdfadfadfasdfasdfadsfasdfasdfasdfsadfas"
func BenchmarkB2sFast(b *testing.B) {
    for i := 0; i < b.N; i++ {
       _ = s2b(s)
    }
}

func BenchmarkB2sStd(b *testing.B) {
    var _ []byte
    for i := 0; i < b.N; i++ {
        _ = []byte(s)
    }
}

var bt = []byte("adsfasdfadsfadsfasdfadfadfasdfasdfadsfasdfasdfasdfsadfas")
func BenchmarkS2BFast(b *testing.B) {
    for i := 0; i < b.N; i++ {
        _ = b2s(bt)
    }
}

func BenchmarkS2BStd(b *testing.B) {
    var _ []byte
    for i := 0; i < b.N; i++ {
        _ = string(bt)
    }
}

测试结果如下：

goos: windows
goarch: amd64
pkg: awesomeProject5/lib
cpu: Intel(R) Core(TM) i7-10510U CPU @ 1.80GHz
BenchmarkB2sFast
BenchmarkB2sFast-8   	1000000000	         0.2383 ns/op
BenchmarkB2sStd
BenchmarkB2sStd-8    	41089557	        27.65 ns/op
BenchmarkS2BFast
BenchmarkS2BFast-8   	1000000000	         0.2378 ns/op
BenchmarkS2BStd
BenchmarkS2BStd-8    	54249056	        22.51 ns/op
PASS

可以看到在相同测试条件下，其性能差异竟然达到了100倍！

[]bytestring

需要注意的是这种方式也有弊端，在代码注释中可以看到它依赖golang中的string或slice的首部定义。如果后续golang版本对此有修改，则有可能导致代码无法运行。