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2023-06-26 17:30:52 +00:00
< 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-zh.html" > 译者序< / 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< /
2022-08-04 06:59:33 +00:00
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2023-06-26 17:46:27 +00:00
< li > < em > 凹语言(专为 WebAssembly 设计): < a href = "https://github.com/wa-lang/wa" > https://github.com/wa-lang/wa< / a > < / em > < / li >
< li > < em > KCL 配置语言(Rust): < a href = "https://github.com/kcl-lang/kcl" > https://github.com/kcl-lang/kcl< / a > < / em > < / li >
< / ul >
2022-08-04 06:59:33 +00:00
< hr >
< h2 id = "89-并发的退出" > < a class = "header" href = "#89-并发的退出" > 8.9. 并发的退出< / a > < / h2 >
< p > 有时候我们需要通知goroutine停止它正在干的事情， ， < / p >
< p > Go语言并没有提供在一个goroutine中终止另一个goroutine的方法， ， ， ？ < / p >
< p > 一种可能的手段是向abort的channel里发送和goroutine数目一样多的事件来退出它们。如果这些goroutine中已经有一些自己退出了， ， ， ， ， ， ， ， ， ， ， ， ， < / p >
< p > 回忆一下我们关闭了一个channel并且被消费掉了所有已发送的值， ， ， ： ， < / p >
< p > 只要一些小修改， ， ， ， ， ， < / p >
< p > < u > < i > gopl.io/ch8/du4< / i > < / u > < / p >
< pre > < code class = "language-go" > var done = make(chan struct{})
func cancelled() bool {
select {
case < -done:
return true
default:
return false
}
}
< / code > < / pre >
< p > 下面我们创建一个从标准输入流中读取内容的goroutine， （ ） ， < / p >
< pre > < code class = "language-go" > // Cancel traversal when input is detected.
go func() {
os.Stdin.Read(make([]byte, 1)) // read a single byte
close(done)
}()
< / code > < / pre >
< p > 现在我们需要使我们的goroutine来对取消进行响应。在main goroutine中， ， ， ， ， ， ， < / p >
< pre > < code class = "language-go" > for {
select {
case < -done:
// Drain fileSizes to allow existing goroutines to finish.
for range fileSizes {
// Do nothing.
}
return
case size, ok := < -fileSizes:
// ...
}
}
< / code > < / pre >
< p > walkDir这个goroutine一启动就会轮询取消状态， ， < / p >
< pre > < code class = "language-go" > func walkDir(dir string, n *sync.WaitGroup, fileSizes chan< - int64) {
defer n.Done()
if cancelled() {
return
}
for _, entry := range dirents(dir) {
// ...
}
}
< / code > < / pre >
< p > 在walkDir函数的循环中我们对取消状态进行轮询可以带来明显的益处， ； ， < / p >
< p > 对这个程序的一个简单的性能分析可以揭示瓶颈在dirents函数中获取一个信号量。下面的select可以让这种操作可以被取消， < / p >
< pre > < code class = "language-go" > func dirents(dir string) []os.FileInfo {
select {
case sema < - struct{}{}: // acquire token
case < -done:
return nil // cancelled
}
defer func() { < -sema }() // release token
// ...read directory...
}
< / code > < / pre >
< p > 现在当取消发生时， ， ， ， （ ： ， ） ： ， ， ， ， ， ； ， < / p >
< p > < strong > 练习 8.10： < / strong > HTTP请求可能会因http.Request结构体中Cancel channel的关闭而取消。修改8.6节中的web crawler来支持取消http请求。（ ： ， ， ） < / p >
< p > < strong > 练习 8.11： < / strong > 紧接着8.4.4中的mirroredQuery流程， ， < / p >
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