最佳化Go程式的簡單技巧 - stephen.sh

var bufpool = sync.Pool{
    New: func() interface{} {
        buf := make([]byte, 512)
        return &buf
    }}

// sync.Pool returns a interface{}: you must cast it to the underlying type
// before you use it.
b := *bufpool.Get().(*[]byte)
defer bufpool.Put(&b)


// Now, go do interesting things with your byte buffer.
buf := bytes.NewBuffer(b)

type AuthenticationResponse {
    Token string
    UserID string
}

rsp := authPool.Get().(*AuthenticationResponse)
defer authPool.Put(rsp)

// If we don't hit this if statement, we might return data from other users!  
if blah {
    rsp.UserID = "user-1"
    rsp.Token = "super-secret
}

return rsp

var (
    r io.Reader
    w io.Writer
)

// Obtain a buffer from the pool.
buf := *bufPool.Get().(*[]byte)
defer bufPool.Put(&buf)

// We only write to w exactly what we read from r, and no more.  
nr, er := r.Read(buf)
if nr > 0 {
    nw, ew := w.Write(buf[0:nr])
}

package main

import (
    "fmt"
    "runtime"
    "strconv"
    "time"
)

const (
    numElements = 10000000
)

var foo = map[string]int{}

func timeGC() {
    t := time.Now()
    runtime.GC()
    fmt.Printf("gc took: %s\n", time.Since(t))
}

func main() {
    for i := 0; i < numElements; i++ {
        foo[strconv.Itoa(i)] = i
    }

    for {
        timeGC()
        time.Sleep(1 * time.Second)
    }
}

inthash → go install && inthash
gc took: 98.726321ms
gc took: 105.524633ms
gc took: 102.829451ms
gc took: 102.71908ms
gc took: 103.084104ms
gc took: 104.821989ms

package main

import (
    "fmt"
    "runtime"
    "time"
)

const (
    numElements = 10000000
)

var foo = map[int]int{}

func timeGC() {
    t := time.Now()
    runtime.GC()
    fmt.Printf("gc took: %s\n", time.Since(t))
}

func main() {
    for i := 0; i < numElements; i++ {
        foo[i] = i
    }

    for {
        timeGC()
        time.Sleep(1 * time.Second)
    }
}

go install && inthash
gc took: 3.608993ms
gc took: 3.926913ms
gc took: 3.955706ms
gc took: 4.063795ms
gc took: 3.91519ms
gc took: 3.75226ms

package json

// Marshal take an object and returns its representation in JSON.
func Marshal(obj interface{}) ([]byte, error) {
    // Check if this object knows how to marshal itself to JSON
    // by satisfying the Marshaller interface.
    if m, is := obj.(json.Marshaller); is {
        return m.MarshalJSON()
    }

    // It doesn't know how to marshal itself. Do default reflection based marshallling.
    return marshal(obj)
}

// main.go
package main

import "strings"

var strs = []string{
    "here's",
    "a",
    "some",
    "long",
    "list",
    "of",
    "strings",
    "for",
    "you",
}

func buildStrNaive() string {
    var s string

    for _, v := range strs {
        s += v
    }

    return s
}

func buildStrBuilder() string {
    b := strings.Builder{}

    // Grow the buffer to a decent length, so we don't have to continually
    // re-allocate.
    b.Grow(60)

    for _, v := range strs {
        b.WriteString(v)
    }

    return b.String()
}

// main_test.go
package main

import (
    "testing"
)

var str string

func BenchmarkStringBuildNaive(b *testing.B) {
    for i := 0; i < b.N; i++ {
        str = buildStrNaive()
    }
}
func BenchmarkStringBuildBuilder(b *testing.B) {
    for i := 0; i < b.N; i++ {
        str = buildStrBuilder()
    }

go test -bench=. -benchmem
goos: darwin
goarch: amd64
pkg: github.com/sjwhitworth/perfblog/strbuild
BenchmarkStringBuildNaive-8          5000000           255 ns/op         216 B/op          8 allocs/op
BenchmarkStringBuildBuilder-8       20000000            54.9 ns/op        64 B/op          1 allocs/op

// main.go
package main

import (
    "fmt"
    "strconv"
)

func strconvFmt(a string, b int) string {
    return a + ":" + strconv.Itoa(b)
}

func fmtFmt(a string, b int) string {
    return fmt.Sprintf("%s:%d", a, b)
}

func main() {}
// main_test.go
package main

import (
    "testing"
)

var (
    a    = "boo"
    blah = 42
    box  = ""
)

func BenchmarkStrconv(b *testing.B) {
    for i := 0; i < b.N; i++ {
        box = strconvFmt(a, blah)
    }
    a = box
}

func BenchmarkFmt(b *testing.B) {
    for i := 0; i < b.N; i++ {
        box = fmtFmt(a, blah)
    }
    a = box
}

go test -bench=. -benchmem
goos: darwin
goarch: amd64
pkg: github.com/sjwhitworth/perfblog/strfmt
BenchmarkStrconv-8      30000000            39.5 ns/op        32 B/op          1 allocs/op
BenchmarkFmt-8          10000000           143 ns/op          72 B/op     

type slice struct {
    // pointer to underlying data in the slice.
    data uintptr
    // the number of elements in the slice.
    len int
    // the number of elements that the slice can 
    // grow to before a new underlying array
    // is allocated.
    cap int     
}

var userIDs []string
for _, bar := range rsp.Users {
    userIDs = append(userIDs, bar.ID)
}

userIDs := make([]string, 0, len(rsp.Users)

for _, bar := range rsp.Users {
    userIDs = append(userIDs, bar.ID)
}