当向 go 例程之外的 channel 发送值时，go 例程会死锁

Question

在 Golang 之旅中学习 Go select 语句时，我尝试对代码进行了一些更改:https://tour.golang.org/concurrency/5 .但是，我遇到了问题:

fatal error: all goroutines are asleep - deadlock!

goroutine 1 [chan send]:
main.main()
        concurrency.go:26 +0xa3

goroutine 33 [chan receive]:
main.main.func1(0xc000088000)
        concurrency.go:24 +0x42
created by main.main
        concurrency.go:23 +0x89
exit status 2

这是我试过并得到问题的代码

func fibonacci(c, quit chan int) {
    x, y := 0, 1
    for {
        select {
            case c <- x:  //sending value x into channel c
                x, y = y, x+y
            case <-quit:    //receive value from quit
                fmt.Println("quit")
        return
        }
    }
}

func main() {
    //create two channels
    c := make(chan int)
    quit := make(chan int)
    go func() { //spin off the second function in order to let consume from c , so fibonaci can continue to work
        fmt.Println(<-c)    //read value from channel c
    }()
    //Try moving the statement that send value to channel quit in order to 
    //return function fibonacci
    quit <- 0   
    fibonacci(c, quit)
}

起初，我认为结果与下面代码的结果相同

//function fibonacci is same with the first one
func fibonacci(c, quit chan int) {
    x, y := 0, 1
    for {
        select {
            case c <- x:  //sending value x into channel c
                x, y = y, x+y
            case <-quit:    //receive value from quit
                fmt.Println("quit")
        return
        }
    }
}

func main() {
    //create two channels
    c := make(chan int)
    quit := make(chan int)
    go func() { //spin off the second function in order to let consume from c , so fibonaci can continue to work
        fmt.Println(<-c)    //read value from channel c
        quit <- 0 //CHANGE: move the statement inside the closure function 
    }()

    fibonacci(c, quit)
}

输出是

0
quit

您能否解释一下执行第一个示例时出现死锁的根本原因是什么？在 go 例程中将值发送到退出 channel 与在主线程中将值发送到退出 channel 有什么区别。

谢谢你们。

Answer 1

quit channel 是一个无缓冲的 channel 。在发送和接收 goroutine 都准备好之前，无缓冲 channel 上的通信不会继续。声明quit <- 0在应用程序执行接收值的函数之前阻塞。接收 goroutine 永远不会就绪

通过关闭 channel 修复:

c := make(chan int)
quit := make(chan int)
go func() {
    fmt.Println(<-c)
}()
close(quit)
fibonacci(c, quit)

...或者通过缓冲 channel

c := make(chan int, 1) // <- note size 1
quit := make(chan int)
go func() { 
    fmt.Println(<-c) 
}()
quit <- 0   
fibonacci(c, quit)

在这种情况下，fibonacci将在产生值之前退出。