package main

import (

    "sync"

)

type httpPkg struct{}

func (httpPkg) Get(url string) {}

var http httpPkg

func main() {

    var wg sync.WaitGroup

    var urls = []string{

        "http://www.golang.org/",

        "http://www.google.com/",

        "http://www.somestupidname.com/",

    }

    for _, url := range urls {

        // Increment the WaitGroup counter.

        wg.Add(1)

        // Launch a goroutine to fetch the URL.

        go func(url string) {

            // Decrement the counter when the goroutine completes.

            defer wg.Done()

            // Fetch the URL.

            http.Get(url)

        }(url)

    }

    // Wait for all HTTP fetches to complete.

    wg.Wait()

}

func main() {

    var wg sync.WaitGroup

    ch := make(chan int, 1000)

    for i := 0; i < 1000; i++ {

        wg.Add(1)

        go doSomething(i, wg, ch)

    }

    wg.Wait()

    fmt.Println("all done")

    for i := 0; i < 1000; i++ {

        dd := <-ch

        fmt.Println("from ch:"+strconv.Itoa(dd))

    }

}

func doSomething(index int, wg  sync.WaitGroup, ch chan int) {

    defer wg.Done()

    fmt.Println("start done:" + strconv.Itoa(index))

    //time.Sleep(20 * time.Millisecond)

    ch <- index

}

fatal error: all goroutines are asleep - deadlock!

goroutine 1 [semacquire]:

sync.runtime_Semacquire(0xc42001608c)

    /usr/local/Cellar/go/1.10.3/libexec/src/runtime/sema.go:56 +0x39

sync.(*WaitGroup).Wait(0xc420016080)

    /usr/local/Cellar/go/1.10.3/libexec/src/sync/waitgroup.go:129 +0x72

main.main()

    /Users/taoli/go/src/github.com/c60/cai/tx_gorutine.go:16 +0xea

go doSomething(i, &wg, ch)

func doSomething(index int, wg *sync.WaitGroup, ch chan int) {