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< ol class = "chapter" > < li class = "chapter-item expanded affix " > < a href = "../index.html" > Go语言圣经< / a > < / li > < li class = "chapter-item expanded affix " > < a href = "../preface.html" > 前言< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1.html" > < strong aria-hidden = "true" > 1.< / strong > 入门< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-01.html" > < strong aria-hidden = "true" > 1.1.< / strong > Hello, World< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-02.html" > < strong aria-hidden = "true" > 1.2.< / strong > 命令行参数< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-03.html" > < strong aria-hidden = "true" > 1.3.< / strong > 查找重复的行< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-04.html" > < strong aria-hidden = "true" > 1.4.< / strong > GIF动画< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-05.html" > < strong aria-hidden = "true" > 1.5.< / strong > 获取URL< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-06.html" > < strong aria-hidden = "true" > 1.6.< / strong > 并发获取多个URL< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-07.html" > < strong aria-hidden = "true" > 1.7.< / strong > Web服务< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-08.html" > < strong aria-hidden = "true" > 1.8.< / strong > 本章要点< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2.html" > < strong aria-hidden = "true" > 2.< / strong > 程序结构< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-01.html" > < strong aria-hidden = "true" > 2.1.< / strong > 命名< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-02.html" > < strong aria-hidden = "true" > 2.2.< / strong > 声明< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-03.html" > < strong aria-hidden = "true" > 2.3.< / strong > 变量< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-04.html" > < strong aria-hidden = "true" > 2.4.< / strong > 赋值< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-05.html" > < strong aria-hidden = "true" > 2.5.< / strong > 类型< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-06.html" > < strong aria-hidden = "true" > 2.6.< / strong > 包和文件< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-07.html" > < strong aria-hidden = "true" > 2.7.< / strong > 作用域< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3.html" > < strong aria-hidden = "true" > 3.< / strong > 基础数据类型< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-01.html" > < strong aria-hidden = "true" > 3.1.< / strong > 整型< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-02.html" > < strong aria-hidden = "true" > 3.2.< / strong > 浮点数< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-03.html" > < strong aria-hidden = "true" > 3.3.< / strong > 复数< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-04.html" > < strong aria-hidden = "true" > 3.4.< / strong > 布尔型< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-05.html" > < strong aria-hidden = "true" > 3.5.< / strong > 字符串< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-06.html" > < strong aria-hidden = "true" > 3.6.< / strong > 常量< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4.html" > < strong aria-hidden = "true" > 4.< / strong > 复合数据类型< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-01.html" > < strong aria-hidden = "true" > 4.1.< / strong > 数组< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-02.html" > < strong aria-hidden = "true" > 4.2.< / strong > Slice< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-03.html" > < strong aria-hidden = "true" > 4.3.< / strong > Map< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-04.html" > < strong aria-hidden = "true" > 4.4.< / strong > 结构体< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-05.html" > < strong aria-hidden = "true" > 4.5.< / strong > JSON< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-06.html" > < strong aria-hidd
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< li > < em > KusonStack一站式可编程配置技术栈(Go): < a href = "https://github.com/KusionStack/kusion" > https://github.com/KusionStack/kusion< / a > < / em > < / li >
< li > < em > KCL 配置编程语言(Rust): < a href = "https://github.com/KusionStack/KCLVM" > https://github.com/KusionStack/KCLVM< / a > < / em > < / li >
< li > < em > 凹语言™: < a href = "https://github.com/wa-lang/wa" > https://github.com/wa-lang/wa< / a > < / em > < / li >
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< h2 id = "87-基于select的多路复用" > < a class = "header" href = "#87-基于select的多路复用" > 8.7. 基于select的多路复用< / a > < / h2 >
< p > 下面的程序会进行火箭发射的倒计时。time.Tick函数返回一个channel， ， < / p >
< p > < u > < i > gopl.io/ch8/countdown1< / i > < / u > < / p >
< pre > < code class = "language-go" > func main() {
fmt.Println(" Commencing countdown." )
tick := time.Tick(1 * time.Second)
for countdown := 10; countdown > 0; countdown-- {
fmt.Println(countdown)
< -tick
}
launch()
}
< / code > < / pre >
< p > 现在我们让这个程序支持在倒计时中， ， ， ， ， < / p >
< p > < u > < i > gopl.io/ch8/countdown2< / i > < / u > < / p >
< pre > < code class = "language-go" > abort := make(chan struct{})
go func() {
os.Stdin.Read(make([]byte, 1)) // read a single byte
abort < - struct{}{}
}()
< / code > < / pre >
< p > 现在每一次计数循环的迭代都需要等待两个channel中的其中一个返回事件了： （ " nominal" ， ： ） ， ， ， （ ） ， ， < / p >
< pre > < code class = "language-go" > select {
case < -ch1:
// ...
case x := < -ch2:
// ...use x...
case ch3 < - y:
// ...
default:
// ...
}
< / code > < / pre >
< p > 上面是select语句的一般形式。和switch语句稍微有点相似， （ ） ， （ ： ） ， ， ， ； < / p >
< p > select会等待case中有能够执行的case时去执行。当条件满足时， ； < / p >
< p > 让我们回到我们的火箭发射程序。time.After函数会立即返回一个channel， ， ， < / p >
< pre > < code class = "language-go" > func main() {
// ...create abort channel...
fmt.Println(" Commencing countdown. Press return to abort." )
select {
case < -time.After(10 * time.Second):
// Do nothing.
case < -abort:
fmt.Println(" Launch aborted!" )
return
}
launch()
}
< / code > < / pre >
< p > 下面这个例子更微妙。ch这个channel的buffer大小是1， ， ， ， < / p >
< pre > < code class = "language-go" > ch := make(chan int, 1)
for i := 0; i < 10; i++ {
select {
case x := < -ch:
fmt.Println(x) // " 0" " 2" " 4" " 6" " 8"
case ch < - i:
}
}
< / code > < / pre >
< p > 如果多个case同时就绪时， ， ， ， < / p >
< p > 下面让我们的发射程序打印倒计时。这里的select语句会使每次循环迭代等待一秒来执行退出操作。< / p >
< p > < u > < i > gopl.io/ch8/countdown3< / i > < / u > < / p >
< pre > < code class = "language-go" > func main() {
// ...create abort channel...
fmt.Println(" Commencing countdown. Press return to abort." )
tick := time.Tick(1 * time.Second)
for countdown := 10; countdown > 0; countdown-- {
fmt.Println(countdown)
select {
case < -tick:
// Do nothing.
case < -abort:
fmt.Println(" Launch aborted!" )
return
}
}
launch()
}
< / code > < / pre >
< p > time.Tick函数表现得好像它创建了一个在循环中调用time.Sleep的goroutine， ， ， ， ， （ < / p >
< p > Tick函数挺方便， ， ： < / p >
< pre > < code class = "language-go" > ticker := time.NewTicker(1 * time.Second)
< -ticker.C // receive from the ticker's channel
ticker.Stop() // cause the ticker's goroutine to terminate
< / code > < / pre >
< p > 有时候我们希望能够从channel中发送或者接收值， ， < / p >
< p > 下面的select语句会在abort channel中有值时， ； ； < / p >
< pre > < code class = "language-go" > select {
case < -abort:
fmt.Printf(" Launch aborted!\n" )
return
default:
// do nothing
}
< / code > < / pre >
< p > channel的零值是nil。也许会让你觉得比较奇怪， ， < / p >
< p > 这使得我们可以用nil来激活或者禁用case， < / p >
< p > < strong > 练习 8.8： < / strong > 使用select来改造8.3节中的echo服务器， ， < / p >
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