golang中上下文很重要，傳遞時特別需要注意

package main

import (
	"fmt"
	"sync"
)

type httpPkg struct{}

func (httpPkg) Get(url string) {
	fmt.Println("to get url=", url)
}

var http httpPkg

func main()  {
	var wg sync.WaitGroup
	var urls = []string {
		"http://www.baodu.com",
		"http://goproxy.cn",
	}
	//
	fmt.Printf("%p\n", &wg)
	//
	for index, url := range urls {
		fmt.Printf("for-> %p\n", &wg)
		wg.Add(1)
		fmt.Println(index, url)

		//獨立函數方式
		go doActionImp(&wg, index, url)

		//lambda方式
		//go func(index int, url string) {
		//	//
		//	fmt.Printf("%p\n", &wg)
		//	defer wg.Done()
		//	//
		//	fmt.Println(index, url)
		//	http.Get(url)
		//}(index, url)
	}
	//
	fmt.Println("waiting....")
	wg.Wait()
	fmt.Println("done")
}

func doActionImp(wg *sync.WaitGroup, index int, url string)  {
	fmt.Printf("%p\n", wg)
	defer wg.Done()

	fmt.Println(index, url)
	http.Get(url)
}

參考上面的例子：

採用lambda方式寫協程時，wg的上下文是同一個，其實可以理解在func main中的都是同一個；如果，實現放到了外面，則上下文就全變了，需要傳引用（指針）纔可以：

#gosetup
C:\Users\houwenbin\AppData\Local\Temp\___go_build_gonet_test__2_.exe #gosetup
0xc000062090
for-> 0xc000062090
0 http://www.baodu.com
for-> 0xc000062090
1 http://goproxy.cn
waiting....
0xc000062090
1 http://goproxy.cn
to get url= http://goproxy.cn
0xc000062090
0 http://www.baodu.com
to get url= http://www.baodu.com
done

Process finished with exit code 0

參考：https://www.jianshu.com/p/4c2c80076094