golang 基础（22）WaitGroup

square-gopher.png

waitGroup 从字面上来看是等待组，好处是主线程的退出或执行需要其之前所有 goroutine 执行完毕才回到主线程执行，这是保证所有的 goroutine 都会被执行到

···

import (
    "fmt"
    "time"
    "sync"
)

func doSomething(millisecs time.Duration, wg *sync.WaitGroup){
    duration := millisecs * time.Millisecond
    time.Sleep(duration)
    fmt.Println("Function in background, duration:", duration)
    wg.Done()
}

func main(){
    var wg sync.WaitGroup
    wg.Add(4)
    go doSomething(200, &wg)
    go doSomething(400, &wg)
    go doSomething(150, &wg)
    go doSomething(600, &wg)

    wg.Wait()
    fmt.Println("Done")
}

为发生我们添加多余 wg 造成 deadlock 好的的喜欢写一个 goroutine 就 Add 一次。

func main(){
    var wg sync.WaitGroup
    wg.Add(1)
    go dosomething(200, &wg)
    wg.Add(1)
    go dosomething(400, &wg)
    wg.Add(1)
    go dosomething(150, &wg)
    wg.Add(1)
    go dosomething(600, &wg)

    wg.Wait()
    fmt.Println("Done")
}

Function in background, duration: 150ms
Function in background, duration: 200ms
Function in background, duration: 400ms
Function in background, duration: 600ms
Done

如果我们 wg.Add 数量超出了现有 goroutine 个数就会发生 deadlock! 错误

wg.Add(5)

fatal error: all goroutines are asleep - deadlock!

gophercloud.png