缓冲通道在达到其容量时不会阻塞写入

Question

https://play.golang.org/p/5A-dnZVy2aA

func closeChannel(stream chan int) {
    fmt.Println("closing the channel")
    close(stream)
}

func main() {
    chanOwner := func() <-chan int {
        resultStream := make(chan int, 5)
        go func() {
            defer closeChannel(resultStream)
            for i := 0; i <= 5; i++ {
                resultStream <- i
            }
        }()
        return resultStream
    }
    resultStream := chanOwner()
    for result := range resultStream { //this blocks until the channel is closed
        fmt.Printf("Received: %d\n", result)
    }
    fmt.Println("done receiving")
}

程序的输出

closing the channel
Received: 0
Received: 1
Received: 2
Received: 3
Received: 4
Received: 5
done receiving

为什么在上面的程序中，closing the channel 语句打印在任何Received 之前。由于通道以 5 的容量缓冲，并且我们正在向其中插入 6 个元素，因此我希望它在读取值并清除缓冲区中的空间之前阻塞在 resultStream <- i。

Answer 1

生成器 goroutine 将通道填充到其容量并阻塞。循环的接收器从通道接收第一项，这再次启用生成器 goroutine。生成器 goroutine 在接收器 for 循环打印 Received 消息之前运行完成，打印 closing the channel 消息。然后接收者循环接收所有剩余的消息。