golang range for循環中如何正確的給goroutine傳參

1.code example

 公共方法

func testDomain(ii string) {
	time.Sleep(time.Second * 4)
	fmt.Printf("pid: %d___point addr: %d___%s \n", GoID(), &ii, ii)
}

func GoID() int {
	var buf [64]byte
	n := runtime.Stack(buf[:], false)
	idField := strings.Fields(strings.TrimPrefix(string(buf[:n]), "goroutine "))[0]
	id, err := strconv.Atoi(idField)
	if err != nil {
		panic(fmt.Sprintf("cannot get goroutine id: %v", err))
	}
	return id
}

　　

2. 錯誤示範

var a []string
for i := 1; i < 5; i++ {
   a = append(a, fmt.Sprintf("%d", i))
}

	for _, i := range a {
		fmt.Printf("-----%s---\n", i)

		go func() {
			time.Sleep(time.Second * 4)
			testDomain(i)
		}()
	
	}

　打印發現i每次地址都是同一個

    協助每次先阻塞4秒

　 4秒後 i的值是4， 這是協程中的方法testDomain開始工做，將i的值傳給本身的形參

3. 正確示範

	for _, i := range a {
		fmt.Printf("-----%s---\n", i)
		go func(a string) {
			//time.Sleep(time.Second * 4)
			testDomain(a)
		}(i)
	}

　這種操做會先將i的值傳遞給形參a，i的變化不會對testDomain方法的執行產生影響

 

4. 完整代碼

package main

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

func main() {
	var a []string
	for i := 1; i < 5; i++ {
		a = append(a, fmt.Sprintf("%d", i))
	}
	for _, i := range a {
		fmt.Printf("-----%s---\n", i)
		go func(a string) {
			//time.Sleep(time.Second * 4)
			testDomain(a)
		}(i)

		go func() {
			time.Sleep(time.Second * 4)
			testDomain(i)
		}()
		fmt.Println(&i)
		time.Sleep(time.Second * 1)
	}

	time.Sleep(100 * time.Second)
}

func testDomain(ii string) {
	time.Sleep(time.Second * 4)
	fmt.Printf("pid: %d___point addr: %d___%s \n", GoID(), &ii, ii)
}

func GoID() int {
	var buf [64]byte
	n := runtime.Stack(buf[:], false)
	idField := strings.Fields(strings.TrimPrefix(string(buf[:n]), "goroutine "))[0]
	id, err := strconv.Atoi(idField)
	if err != nil {
		panic(fmt.Sprintf("cannot get goroutine id: %v", err))
	}
	return id
}