go语言的选择(select)可等待多个通道操作。将goroutine和channel与select结合是go语言的一个强大功能。

对于这个示例，将选择两个通道。
每个通道将在一段时间后开始接收值，以模拟阻塞在并发goroutines中执行的rpc操作。我们将使用select同时等待这两个值，在每个值到达时打印它们。

执行实例程序得到的值是“one”，然后是“two”。注意，总执行时间只有1〜2秒，因为1-2秒sleeps同时执行。

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.h3.com/go/go_environment.html

select.go的完整代码如下所示 -

package main

import "time"
import "fmt"

func main() {

    // for our example we'll select across two channels.
    c1 := make(chan string)
    c2 := make(chan string)

    // each channel will receive a value after some amount
    // of time, to simulate e.g. blocking rpc operations
    // executing in concurrent goroutines.
    go func() {
        time.sleep(time.second * 1)
        c1 <- "one"
    }()
    go func() {
        time.sleep(time.second * 2)
        c2 <- "two"
    }()

    // we'll use `select` to await both of these values
    // simultaneously, printing each one as it arrives.
    for i := 0; i < 2; i++ {
        select {
        case msg1 := <-c1:
            fmt.println("received", msg1)
        case msg2 := <-c2:
            fmt.println("received", msg2)
        }
    }
}

执行上面代码，将得到以下输出结果 -

f:\worksp\golang>go run select.go
received one
received two