Go關閉通道實例

關閉通道表示不會再發送更多值。這對於將完成通信到通道的接收器是很有用的。

在這個例子中，我們將使用一個作業通道來完成從main()goroutine到worker goroutine的工作。當沒有更多的工作時，則將關閉工作通道。

這裏是工作程序goroutine。 它反覆從j的工作接收more := <-jobs。在這種特殊的2值形式的接收中，如果作業已關閉並且已經接收到通道中的所有值，則 more 的值將爲 false。當已經完成了所有的工作時，使用這個通知。

這會通過作業通道向工作線程發送3個作業，然後關閉它。

等待工作程序，可使用前面看到的同步方法。

所有的示例代碼，都放在 F:\worksp\golang 目錄下。安裝Go編程環境請參考：http://www.yiibai.com/go/go\_environment.html

closing-channels.go的完整代碼如下所示 -

package main

import "fmt"

// In this example we'll use a `jobs` channel to
// communicate work to be done from the `main()` goroutine
// to a worker goroutine. When we have no more jobs for
// the worker we'll `close` the `jobs` channel.
func main() {
    jobs := make(chan int, 5)
    done := make(chan bool)

    // Here's the worker goroutine. It repeatedly receives
    // from `jobs` with `j, more := <-jobs`. In this
    // special 2-value form of receive, the `more` value
    // will be `false` if `jobs` has been `close`d and all
    // values in the channel have already been received.
    // We use this to notify on `done` when we've worked
    // all our jobs.
    go func() {
        for {
            j, more := <-jobs
            if more {
                fmt.Println("received job", j)
            } else {
                fmt.Println("received all jobs")
                done <- true
                return
            }
        }
    }()

    // This sends 3 jobs to the worker over the `jobs`
    // channel, then closes it.
    for j := 1; j <= 3; j++ {
        jobs <- j
        fmt.Println("sent job", j)
    }
    close(jobs)
    fmt.Println("sent all jobs")

    // We await the worker using the
    // [synchronization](channel-synchronization) approach
    // we saw earlier.
    <-done
}

執行上面代碼，將得到以下輸出結果 -

F:\worksp\golang>go run closing-channels.go
sent job 1
sent job 2
sent job 3
sent all jobs
received job 1
received job 2
received job 3
received all jobs