Go 程序陷入僵局

Question

这是我正在玩的 Golang 程序，只是为了让我的概念正确。当我运行程序时它死锁我不明白为什么？请任何人指出出了什么问题？package mainimport (    "fmt"    "sync")var wg sync.WaitGroupfunc main() {    numOfGoRoutines := 10    wg.Add(numOfGoRoutines)    ch := make(chan int, numOfGoRoutines)    for i := 0; i < numOfGoRoutines; i++ {        a := i        go sqr(ch, a, wg)    }    wg.Wait()    fmt.Println("After WAIT")    close(ch)    var res int    for i := range ch {        res += i    }    ch = nil    fmt.Println("result = ", res)}func sqr(ch chan int, val int, wg sync.WaitGroup) {    fmt.Println("go - ", val)    s := val * val    ch <- s    wg.Done()}输出是：warning: GOPATH set to GOROOT (C:\\Go) has no effectgo -  9go -  0go -  1go -  2go -  3go -  4go -  5go -  6go -  7go -  8fatal error: all goroutines are asleep - deadlock!goroutine 1 [semacquire]:sync.runtime_Semacquire(0x5bcabc)        C:/Go/src/runtime/sema.go:47 +0x2dsync.(*WaitGroup).Wait(0x5bcab0)        C:/Go/src/sync/waitgroup.go:127 +0xbbmain.main()        C:/demo/go-work/main.go:20 +0xdfexit status 2

Answer 1

问题是您将副本传递sync.WaitGroup给 goroutine，而不是引用（即指针）：

package main

import (

    "fmt"

    "sync"

)

var wg sync.WaitGroup

func main() {

    numOfGoRoutines := 10

    wg.Add(numOfGoRoutines)

    ch := make(chan int, numOfGoRoutines)

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

        a := i

        go sqr(ch, a, &wg)

    }

    wg.Wait()

    fmt.Println("After WAIT")

    close(ch)

    var res int

    for i := range ch {

        res += i

    }

    ch = nil

    fmt.Println("result = ", res)

}

func sqr(ch chan int, val int, wg *sync.WaitGroup) {

    fmt.Println("go - ", val)

    s := val * val

    ch <- s

    wg.Done()

}

此外，由于wg是一个全局变量，您可以完全删除该参数：

package main

import (

    "fmt"

    "sync"

)

var wg sync.WaitGroup

func main() {

    numOfGoRoutines := 10

    wg.Add(numOfGoRoutines)

    ch := make(chan int, numOfGoRoutines)

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

        a := i

        go sqr(ch, a)

    }

    wg.Wait()

    fmt.Println("After WAIT")

    close(ch)

    var res int

    for i := range ch {

        res += i

    }

    ch = nil

    fmt.Println("result = ", res)

}

func sqr(ch chan int, val int) {

    fmt.Println("go - ", val)

    s := val * val

    ch <- s

    wg.Done()

}