Go协程代码触发Deadlock，请求协助定位问题原因

问题代码 #

package main

import "fmt"

func main() {
    // create & consume channel
    counter := make(chan int)
    even := make(chan int)
    odd := make(chan int)
    square := make(chan int)
    merge := make(chan int)
    out := make(chan struct{})

    //GoRoutines
    go counterFn(counter)
    go squarerFn(counter, square)
    go counterSplit(counter, even, odd)
    go merger(square, odd, merge) // 此处参数传递错误
    go printOut(merge, out)
    <-out
}

func counterFn(counter chan int) {
    for i := 0; i < 5; i++ {
        counter <- i
    }
    close(counter)
}

func squarerFn(counter chan int, square chan int) {
    for i := range counter {
        square <- i * i
    }
    close(square)
}

func counterSplit(counter chan int, even chan int, odd chan int) {
    for i := range counter {
        if i%2 == 0 {
            even <- i
        } else {
            odd <- i
        }
    }
    close(even)
    close(odd)
}

func merger(even chan int, odd chan int, merge chan int) {
    i := 0
    for {
        fmt.Printf("%d \n", i)
        a, ok := <-even
        if !ok {
            i++
        } else {
            merge <- a
        }
        a, ok = <-odd
        if !ok {
            i++
        } else {
            merge <- a
        }
        if i == 2 {
            break
        }
    }
    close(merge)
}

func printOut(merge chan int, out chan struct{}) {
    for i := range merge {
        fmt.Print(i)
    }
    close(out)
}

错误输出 #

go run channel_pipelineAdv.go
0 
0 , 0
1
0 , 9
fatal error: all goroutines are asleep - deadlock!

goroutine 1 [chan receive]:
main.main()
        D:/channel_pipelineAdv.go:20 +0x233

goroutine 7 [chan send]:
main.squarerFn(0x0?, 0x0?)
        D:/channel_pipelineAdv.go:32 +0x45
created by main.main in goroutine 1
        D:/channel_pipelineAdv.go:16 +0x114

goroutine 8 [chan send]:
main.counterSplit(0x0?, 0x0?, 0x0?)
        D:/channel_pipelineAdv.go:40 +0x5e
created by main.main in goroutine 1
        D:/channel_pipelineAdv.go:17 +0x179

goroutine 9 [chan receive]:
main.merger(0x0?, 0x0?, 0x0?)
        D:/channel_pipelineAdv.go:59 +0xca
created by main.main in goroutine 1
        D:/channel_pipelineAdv.go:18 +0x1d9

goroutine 10 [chan receive]:
main.printOut(0x0?, 0x0?)
        D:/channel_pipelineAdv.go:73 +0x77
created by main.main in goroutine 1
        D:/channel_pipelineAdv.go:19 +0x227
exit status 2

问题定位 #

1. 参数传递错误：main中调用merger时，错误地将square通道作为第一个参数传入，而merger函数定义的第一个参数是even通道。这导致：

   • even通道的数据没有任何goroutine接收，counterSplit在向even发送偶数时会永久阻塞
   • merger一直在读取square和odd通道，但counterSplit阻塞后无法向odd发送更多数据，merger读取odd时会阻塞

2. 无缓冲通道阻塞连锁反应：所有通道都是无缓冲的，发送操作必须等待接收操作完成。当counterSplit阻塞在even发送时，无法继续接收counter通道的数据，导致counterFn后续的发送操作也阻塞；同时squarerFn在向square发送数据时，因merger阻塞在odd读取，无法接收square的数据，也会进入阻塞状态。最终所有goroutine都陷入等待，触发死锁。

3. merger循环逻辑缺陷：merger的循环采用顺序读取even和odd的方式，若其中一个通道无数据且未关闭，会直接阻塞。这种方式无法正确处理两个通道的异步数据。

修复方案 #

1. 修正参数传递：将merger的第一个参数改为even通道，确保counterSplit发送的偶数能被正常接收。
2. 优化merger循环逻辑：使用select语句同时监听两个通道，配合通道关闭状态判断，确保所有数据被读取完成后再退出循环。

修正后的完整代码 #

package main

import "fmt"

func main() {
    counter := make(chan int)
    even := make(chan int)
    odd := make(chan int)
    square := make(chan int)
    merge := make(chan int)
    out := make(chan struct{})

    go counterFn(counter)
    go squarerFn(counter, square)
    go counterSplit(counter, even, odd)
    go merger(even, odd, merge) // 修正参数：传入even而非square
    go printOut(merge, out)
    <-out
}

func counterFn(counter chan int) {
    for i := 0; i < 5; i++ {
        counter <- i
    }
    close(counter)
}

func squarerFn(counter chan int, square chan int) {
    for i := range counter {
        square <- i * i
    }
    close(square)
}

func counterSplit(counter chan int, even chan int, odd chan int) {
    for i := range counter {
        if i%2 == 0 {
            even <- i
        } else {
            odd <- i
        }
    }
    close(even)
    close(odd)
}

func merger(even chan int, odd chan int, merge chan int) {
    evenClosed := false
    oddClosed := false

    for !evenClosed || !oddClosed {
        select {
        case val, ok := <-even:
            if ok {
                merge <- val
            } else {
                evenClosed = true
            }
        case val, ok := <-odd:
            if ok {
                merge <- val
            } else {
                oddClosed = true
            }
        }
    }
    close(merge)
}

func printOut(merge chan int, out chan struct{}) {
    for i := range merge {
        fmt.Printf("%d ", i)
    }
    close(out)
}

说明 #

修正后，counterSplit发送的偶数能被merger正常接收，merger通过select异步处理两个通道的数据，所有goroutine都能正常执行完毕，不会触发死锁。

内容的提问来源于stack exchange，提问作者Monicka Akilan