通道的基本发送和接收都阻塞。但是，可以使用select和default子句来实现非阻塞发送，接收，甚至非阻塞多路选择(select)。

这里是一个非阻塞接收。如果消息上有可用的值，则选择将使用该值的<-message大小写。如果不是，它会立即采用默认情况。
非阻塞发送工作类似。

可以使用多个上面的默认子句来实现多路非阻塞选择(select)。这里尝试对消息(message)和信号(signals)的非阻塞接收。

所有的示例代码，都放在 F:\worksp\golang 目录下。安装Go编程环境请参考：http://www.yiibai.com/go/go_environment.html

non-blocking-channel-operations.go的完整代码如下所示 -

package main

import "fmt"

func main() {
    messages := make(chan string)
    signals := make(chan bool)

    // Here's a non-blocking receive. If a value is
    // available on `messages` then `select` will take
    // the `<-messages` `case` with that value. If not
    // it will immediately take the `default` case.
    select {
    case msg := <-messages:
        fmt.Println("received message", msg)
    default:
        fmt.Println("no message received")
    }

    // A non-blocking send works similarly.
    msg := "hi"
    select {
    case messages <- msg:
        fmt.Println("sent message", msg)
    default:
        fmt.Println("no message sent")
    }

    // We can use multiple `case`s above the `default`
    // clause to implement a multi-way non-blocking
    // select. Here we attempt non-blocking receives
    // on both `messages` and `signals`.
    select {
    case msg := <-messages:
        fmt.Println("received message", msg)
    case sig := <-signals:
        fmt.Println("received signal", sig)
    default:
        fmt.Println("no activity")
    }
}

执行上面代码，将得到以下输出结果 -

F:\worksp\golang>go run non-blocking-channel-operations.go
no message received
no message sent
no activity

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