Go lang 多路复用所有 goroutines 都睡着了 - 死锁

Question

我想使用多个 go 例程返回 channel 创建一个扇入函数，这是我的代码。

package main

import (
    "fmt"
    "math/rand"
    "sync"
    "time"
)

var wg, wg2 sync.WaitGroup

func main() {
    final := talk(boring("Joe"), boring("Ann"))
    for i := 0; i < 10; i++ {
        fmt.Println(<-final)
    }
    fmt.Println("You are both boring I'm leaving")
}

func talk(input1, input2 <-chan string) <-chan string {
    out := make(chan string)
    go func() {
        wg.Add(1)
        for {
            out <- <-input1
        }
    }()
    go func() {
        wg.Add(1)
        for {
            out <- <-input2
        }
    }()
    wg.Done()
    close(out)
    return out
}

func boring(msg string) <-chan string {
    c := make(chan string)
    for i := 0; i < 5; i++ {
        c <- fmt.Sprintf("%s%d\n", msg, i)
        time.Sleep(time.Duration(rand.Intn(1e3)) * time.Millisecond)
    }
    return c
}

但是我运行上面的代码后出现错误

all goroutines are asleep - deadlock

我已经尝试关闭 channel ，但它仍然给我错误。我曾尝试将无聊的返回 channel 分配给 Joe 和 Ann，然后将这些 channel 传递给多路复用的通话功能，但仍然没有成功。我是新来学习 channel 的，对这个概念不是很清楚。

Answer 1

代替 WaitGroup ，您可以使用select:https://tour.golang.org/concurrency/5

The select statement lets a goroutine wait on multiple communication operations.

A select blocks until one of its cases can run, then it executes that case. It chooses one at random if multiple are ready.

package main

import (
    "fmt"
    "math/rand"
    "time"
)

func main() {
    final := talk(boring("Joe"), boring("Ann"))
    for i := 0; i < 10; i++ {
        fmt.Println(<-final)
    }
    fmt.Println("You are both boring I'm leaving")
}

func talk(input1, input2 <-chan string) <-chan string {
    c := make(chan string)
    go func() {
        for {
            select {
            case s := <-input1:
                c <- s
            case s := <-input2:
                c <- s
            }
        }
    }()
    return c
}

func boring(msg string) <-chan string {
    c := make(chan string)
    go func() {
        for i := 0; i < 5; i++ {
            c <- fmt.Sprintf("%s: %d", msg, i)
            time.Sleep(time.Duration(rand.Intn(1e3)) * time.Millisecond)
        }
    }()
    return c
}

Try it on Playground

编辑:

在您给出的示例中，boring 函数不使用 goroutine 重复发送 channel ，这将永远阻塞，因为: https://tour.golang.org/concurrency/2

By default, sends and receives block until the other side is ready. This allows goroutines to synchronize without explicit locks or condition variables.

此外，wg.Done() 需要成为 goroutine 的一部分。

我通过进行上述更改使其正常工作:https://play.golang.org/p/YN0kfBO6iT