所有的 goroutine 都在休眠 - 死锁！与等待组

Question

这是我的代码，我哪里出错了？

func main() {
  intChan := make(chan int)
  wg := sync.WaitGroup{}

  for i := 0;i<5;i++{
    wg.Add(1)
    go send(intChan,i,&wg)
  }

  wg.Add(1)
  go get(intChan,&wg)
  wg.Wait()
  time.Sleep(5*time.Second)
  close(intChan)
}

func send(c chan int,index int,wg *sync.WaitGroup){
  defer func() {
    wg.Done()
  }()

  c <- index
}

func get(c chan int,wg *sync.WaitGroup){
  defer func() {
    wg.Done()
  }()

  for i := range c{
    fmt.Printf("%d\n",i)
  }
}

当我运行它时，我收到错误fatal error: all goroutines are asleep - deadlock!

这是错误信息：

goroutine 1 [semacquire]:
sync.runtime_Semacquire(0xc0000120d8)
    C:/Go/src/runtime/sema.go:56 +0x40
sync.(*WaitGroup).Wait(0xc0000120d0)
    C:/Go/src/sync/waitgroup.go:130 +0x6b
main.main()
    F:/go/src/demo/channel.go:94 +0xf9

goroutine 10 [chan receive]:
main.get(0xc00001c120, 0xc0000120d0)
    F:/go/src/demo/channel.go:112 +0xe0
created by main.main
    F:/go/src/demo/channel.go:92 +0xeb

谢谢大家，这是我的第一个问题。

Answer 1

正如 Andy 在 cmets 中所说，只有在收到所有输入并关闭通道时，您才会退出 get 函数。如您所知，有五样东西要接收，您可以在发送中使用类似的for 循环：

func main() {
    intChan := make(chan int)
    wg := sync.WaitGroup{}

    for i := 0; i < 5; i++ {
        wg.Add(1)
        go send(intChan, i, &wg)
    }

    wg.Add(1)
    go get(intChan, &wg)
    wg.Wait()
    close(intChan)
}

func send(c chan int, index int, wg *sync.WaitGroup) {
    defer func() {
        wg.Done()
    }()

    c <- index
}

func get(c chan int, wg *sync.WaitGroup) {
    defer func() {
        wg.Done()
    }()

    for i := 0; i < 5; i++ {
        input := <- c
        fmt.Printf("%d\n", input)
    }
}

https://play.golang.org/p/CB8HUKPBu2I

如果您想坚持在频道上进行测距，那么您必须在发送完所有消息后关闭它，我会通过添加第二个等待组来做到这一点：

func main() {
    intChan := make(chan int)
    allSent := sync.WaitGroup{}

    for i := 0; i < 5; i++ {
        allSent.Add(1)
        go send(intChan, i, &allSent)
    }

    allReceived := sync.WaitGroup{}
    allReceived.Add(1)
    go get(intChan, &allReceived)

    allSent.Wait()
    close(intChan)
    allReceived.Wait()
}

func send(c chan int, index int, wg *sync.WaitGroup) {
    defer func() {
        wg.Done()
    }()

    c <- index
}

func get(c chan int, wg *sync.WaitGroup) {
    defer func() {
        wg.Done()
    }()

    for i := range c {
        fmt.Printf("%d\n", i)
    }
}

https://play.golang.org/p/svFVrBdwmAc

Answer 2

这可以工作！

func main() {
    intChan := make(chan int)
    wg := sync.WaitGroup{}

    for i := 0;i<5;i++{
        wg.Add(1)
        go send(intChan,i,&wg)
    }

    wg.Add(1)
    go get(intChan,&wg)

    wg.Wait()
    close(intChan)
}

func send(c chan int,index int,wg *sync.WaitGroup){
    defer func() {
        wg.Done()
    }()

    c <- index
}

func get(c chan int,wg *sync.WaitGroup){
    defer func() {
        wg.Done()
    }()

    for {
        select {
            case i := <-c:
                fmt.Printf("%d\n",i)
            default:
                return
        }
    }
}