为什么我的频道陷入僵局？

问题描述：

I am trying to program a simple Go script that calculates the sum of the natural numbers up to 8:

package main
import "fmt" 

func sum(nums []int, c chan int) {
    var sum int = 0
    for _, v := range nums {
        sum += v    
    }
    c <- sum
}

func main() {
    allNums := []int{1, 2, 3, 4, 5, 6, 7, 8}
    c1 := make(chan int)
    c2 := make(chan int)
    sum(allNums[:len(allNums)/2], c1)
    sum(allNums[len(allNums)/2:], c2)
    a := <- c1
    b := <- c2
    fmt.Printf("%d + %d is %d :D", a, b, a + b)
}

However, running this program produces the following output.

throw: all goroutines are asleep - deadlock!

goroutine 1 [chan send]:
main.sum(0x44213af00, 0x800000004, 0x420fbaa0, 0x2f29f, 0x7aaa8, ...)
    main.go:9 +0x6e
main.main()
    main.go:16 +0xe6

goroutine 2 [syscall]:
created by runtime.main
    /usr/local/go/src/pkg/runtime/proc.c:221

exit status 2

Why is my code deadlocking? I am confused because I am using 2 separate channels to calculate the sub-sums. How are the two channels dependent at all?

答

Yes, you need to add go like

go sum(allNums[:len(allNums)/2], c1)

go sum(allNums[len(allNums)/2:], c2)

c1 := make(chan int,1)
c2 := make(chan int,1)

add channel cache.

答

I haven't used Go in a while, so this may not be the case, but from what I remember you need go to get another goroutine started, so:

go sum(allNums[:len(allNums)/2], c1)
go sum(allNums[len(allNums)/2:], c2)

If sum isn't running on another goroutine, it tries to execute:

c <- sum

But nothing's reading c; the code reading c has not been reached yet because it's waiting for sum to finish, and sum won't finish because it needs to give it to that code first!

答

Your channels are unbuffered, so the c <- sum line in sum() will block until some other routine reads from the other end.

One option would be to add buffers to the channels, so you can write a value to the channel without it blocking:

c1 := make(chan int, 1)
c2 := make(chan int, 1)

Alternatively, if you run the sum() function as a separate goroutine, then it can block while your main() function continues to the point where it reads from the channels.

为什么我的频道陷入僵局？

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