《Go语言圣经》关闭一个channel-优快云博客

《Go语言圣经》关闭一个channel

func main() {
    naturals := make(chan int)
    squares := make(chan int)

    // Counter
    go func() {
        for x := 0; x < 100; x++ {
            naturals <- x
        }
        close(naturals)
    }()

    // Squarer
    go func() {
        for x := range naturals {
            squares <- x * x
        }
        close(squares)
    }()

    // Printer (in main goroutine)
    for x := range squares {
        fmt.Println(x)
    }
}

在Go语言中，当一个channel被关闭后，已经发送到该channel中的数据仍然可以被正常接收，直到所有数据都被处理完毕。
试图重复关闭一个channel将导致panic异常，试图关闭一个nil值的channel也将导致panic异常。关闭一个channels还会触发一个广播机制，

详细解释

在你的代码中：

Counter协程向naturals channel发送0到99的整数，然后关闭该channel
Squarer协程使用for x := range naturals循环从naturals接收数据
当naturals被关闭时：
- 已经发送到naturals中的数据（0到99）仍然会被Squarer协程正常接收
- for ... range循环会继续处理这些数据，直到所有数据都被处理完毕
- 只有当所有数据都被接收后，for ... range循环才会退出

关键点

关闭channel不会影响已发送的数据：关闭操作只是阻止后续的数据发送，不会影响已经在channel中的数据
for ... range循环会处理所有已发送的数据：无论channel是否关闭，循环都会继续执行，直到所有数据被接收
关闭是一种信号：关闭channel是向接收方发送一个信号，表示"不会再有新数据了"，但已有的数据仍然有效

验证代码

以下代码可以帮助你验证这个过程：

package main

import "fmt"

func main() {
    naturals := make(chan int)
    squares := make(chan int)

    // Counter
    go func() {
        for x := 0; x < 5; x++ {
            naturals <- x
            fmt.Println("Counter sent:", x)
            // 添加延迟以便观察执行顺序
            if x == 2 {
                close(naturals)
                fmt.Println("Counter closed naturals")
            }
        }
    }()

    // Squarer
    go func() {
        for x := range naturals {
            squares <- x * x
            fmt.Println("Squarer received:", x, "sending:", x*x)
        }
        close(squares)
        fmt.Println("Squarer closed squares")
    }()

    // Printer
    for x := range squares {
        fmt.Println("Printer received:", x)
    }
    fmt.Println("Done")
}

输出示例

Counter sent: 0
Squarer received: 0 sending: 0
Printer received: 0
Counter sent: 1
Squarer received: 1 sending: 1
Printer received: 1
Counter sent: 2
Squarer received: 2 sending: 4
Printer received: 4
Counter closed naturals
Counter sent: 3
Squarer received: 3 sending: 9
Printer received: 9
Counter sent: 4
Squarer received: 4 sending: 16
Printer received: 16
Squarer closed squares
Done