Closing Channels {.en}

关闭通道 {.zh}

::: {.en} Closing a channel indicates that no more values will be sent on it. This can be useful to communicate completion to the channel’s receivers. :::

::: {.zh}

关闭 一个通道意味着不能再向这个通道发送值了。这个特性可以 用来给这个通道的接收方传达工作已经完成的信息。

:::

  1. package main
  2. import "fmt"

::: {.en} 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. :::

::: {.zh}

在这个例子中，我们将使用一个 jobs 通道来传递 main() 中 Go 协程任务执行的结束信息到一个工作 Go 协程中。当我们没有多余的 任务给这个工作 Go 协程时，我们将 close 这个 jobs 通道。

:::

  1. func main() {
  2.     jobs := make(chan int, 5)
  3.     done := make(chan bool)

::: {.en} 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 closed and all values in the channel have already been received. We use this to notify on done when we’ve worked all our jobs. :::

::: {.zh}

这是工作 Go 协程。使用 j, more := <- jobs 循环的从 jobs 接收数据。在接收的这个特殊的二值形式的值中， 如果 jobs 已经关闭了，并且通道中所有的值都已经接收 完毕，那么 more 的值将是 false。当我们完成所有 的任务时，将使用这个特性通过 done 通道去进行通知。

:::

  1.     go func() {
  2.         for {
  3.             j, more := <-jobs
  4.             if more {
  5.                 fmt.Println("received job", j)
  6.             } else {
  7.                 fmt.Println("received all jobs")
  8.                 done <- true
  9.                 return
  10.             }
  11.         }
  12.     }()

::: {.en} This sends 3 jobs to the worker over the jobs channel, then closes it. :::

::: {.zh}

这里使用 jobs 发送 3 个任务到工作函数中，然后 关闭 jobs。

:::

  1.     for j := 1; j <= 3; j++ {
  2.         jobs <- j
  3.         fmt.Println("sent job", j)
  4.     }
  5.     close(jobs)
  6.     fmt.Println("sent all jobs")

::: {.en} We await the worker using the synchronization approach we saw earlier. :::

::: {.zh}

我们使用前面学到的通道同步 方法等待任务结束。

:::

  1.     <-done
  2. }
  1. $ go run closing-channels.go 
  2. sent job 1
  3. received job 1
  4. sent job 2
  5. received job 2
  6. sent job 3
  7. received job 3
  8. sent all jobs
  9. received all jobs

::: {.en} The idea of closed channels leads naturally to our next example: range over channels. :::

::: {.zh}

通过关闭通道的学习，也让下面学习通道遍历水到渠成。

:::