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chai2010
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<meta charset="UTF-8">
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<meta http-equiv="X-UA-Compatible" content="IE=edge" />
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<title>示例: 併發的Echo服務 | Go编程语言</title>
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<title>示例: 併發的Echo服務 | Go语言圣经</title>
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<meta content="text/html; charset=utf-8" http-equiv="Content-Type">
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<meta name="description" content="">
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<meta name="generator" content="GitBook 2.5.2">
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<body>
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<div class="book" data-level="8.3" data-chapter-title="示例: 併發的Echo服務" data-filepath="ch8/ch8-03.md" data-basepath=".." data-revision="Mon Dec 28 2015 16:03:52 GMT+0800 (中国标准时间)">
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<div class="book" data-level="8.3" data-chapter-title="示例: 併發的Echo服務" data-filepath="ch8/ch8-03.md" data-basepath=".." data-revision="Thu Dec 31 2015 16:18:40 GMT+0800 (中国标准时间)">
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<div class="book-summary">
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<b>4.2.</b>
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切片
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Slice
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</a>
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<b>4.3.</b>
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字典
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Map
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</a>
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<!-- Title -->
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<h1>
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<i class="fa fa-circle-o-notch fa-spin"></i>
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<a href="../" >Go编程语言</a>
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<a href="../" >Go语言圣经</a>
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</h1>
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</div>
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<section class="normal" id="section-">
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<h2 id="83-示例-併發的echo服務">8.3. 示例: 併發的Echo服務</h2>
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<p>TODO</p>
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<p>clock服務器每一個連接都會起一個goroutine。在本節中我們會創建一個echo服務器，這個服務在每個連接中會有多個goroutine。大多數echo服務僅僅會返迴他們讀取到的內容，就像下面這個簡單的handleConn函數所做的一樣：</p>
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<pre><code class="lang-go"><span class="hljs-keyword">func</span> handleConn(c net.Conn) {
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io.Copy(c, c) <span class="hljs-comment">// <span class="hljs-doctag">NOTE:</span> ignoring errors</span>
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c.Close()
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}
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</code></pre>
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<p>一個更有意思的echo服務應該模擬一個實際的echo的“迴響”，併且一開始要用大寫HELLO來表示“聲音很大”，之後經過一小段延遲返迴一個有所緩和的Hello，然後一個全小寫字母的hello表示聲音漸漸變小直至消失，像下面這個版本的handleConn(譯註：笑看作者腦洞大開)：</p>
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<pre><code class="lang-go">gopl.io/ch8/reverb1
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<span class="hljs-keyword">func</span> echo(c net.Conn, shout <span class="hljs-typename">string</span>, delay time.Duration) {
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fmt.Fprintln(c, <span class="hljs-string">"\t"</span>, strings.ToUpper(shout))
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time.Sleep(delay)
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fmt.Fprintln(c, <span class="hljs-string">"\t"</span>, shout)
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time.Sleep(delay)
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fmt.Fprintln(c, <span class="hljs-string">"\t"</span>, strings.ToLower(shout))
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}
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<span class="hljs-keyword">func</span> handleConn(c net.Conn) {
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input := bufio.NewScanner(c)
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<span class="hljs-keyword">for</span> input.Scan() {
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echo(c, input.Text(), <span class="hljs-number">1</span>*time.Second)
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}
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<span class="hljs-comment">// <span class="hljs-doctag">NOTE:</span> ignoring potential errors from input.Err()</span>
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c.Close()
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}
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</code></pre>
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<p>我們需要陞級我們的客戶端程序，這樣它就可以發送終端的輸入到服務器，併把服務端的返迴輸出到終端上，這使我們有了使用併發的另一個好機會：</p>
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<pre><code class="lang-go">gopl.io/ch8/netcat2
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<span class="hljs-keyword">func</span> main() {
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conn, err := net.Dial(<span class="hljs-string">"tcp"</span>, <span class="hljs-string">"localhost:8000"</span>)
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<span class="hljs-keyword">if</span> err != <span class="hljs-constant">nil</span> {
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log.Fatal(err)
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}
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<span class="hljs-keyword">defer</span> conn.Close()
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<span class="hljs-keyword">go</span> mustCopy(os.Stdout, conn)
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mustCopy(conn, os.Stdin)
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}
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</code></pre>
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<p>當main goroutine從標準輸入流中讀取內容併將其發送給服務器時，另一個goroutine會讀取併打印服務端的響應。當main goroutine碰到輸入終止時，例如，用戶在終端中按了Control-D(^D)，在windows上是Control-Z，這時程序就會被終止，盡管其它goroutine中還有進行中的任務。(在8.4.1中引入了channels後我們會明白如何讓程序等待兩邊都結束)。</p>
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<p>下面這個會話中，客戶端的輸入是左對齊的，服務端的響應會用縮進來區别顯示。
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客戶端會向服務器“喊三次話”：</p>
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<pre><code>$ go build gopl.io/ch8/reverb1
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$ ./reverb1 &
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$ go build gopl.io/ch8/netcat2
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$ ./netcat2
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Hello?
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HELLO?
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Hello?
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hello?
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Is there anybody there?
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IS THERE ANYBODY THERE?
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Yooo-hooo!
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Is there anybody there?
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is there anybody there?
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YOOO-HOOO!
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Yooo-hooo!
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yooo-hooo!
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^D
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$ killall reverb1
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</code></pre><p>註意客戶端的第三次shout在前一個shout處理完成之前一直沒有被處理，這貌似看起來不是特别“現實”。眞實世界里的迴響應該是會由三次shout的迴聲組合而成的。爲了模擬眞實世界的迴響，我們需要更多的goroutine來做這件事情。這樣我們就再一次地需要go這個關鍵詞了，這次我們用它來調用echo：</p>
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<pre><code class="lang-go">gopl.io/ch8/reverb2
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<span class="hljs-keyword">func</span> handleConn(c net.Conn) {
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input := bufio.NewScanner(c)
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<span class="hljs-keyword">for</span> input.Scan() {
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<span class="hljs-keyword">go</span> echo(c, input.Text(), <span class="hljs-number">1</span>*time.Second)
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}
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<span class="hljs-comment">// <span class="hljs-doctag">NOTE:</span> ignoring potential errors from input.Err()</span>
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c.Close()
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}
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</code></pre>
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<p>go後跟的函數的參數會在go語句自身執行時被求值；因此input.Text()會在main goroutine中被求值。
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現在迴響是併發併且會按時間來覆蓋掉其它響應了：</p>
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<pre><code>$ go build gopl.io/ch8/reverb2
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$ ./reverb2 &
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$ ./netcat2
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Is there anybody there?
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IS THERE ANYBODY THERE?
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Yooo-hooo!
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Is there anybody there?
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YOOO-HOOO!
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is there anybody there?
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Yooo-hooo!
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yooo-hooo!
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^D
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$ killall reverb2
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</code></pre><p>讓服務使用併發不隻是處理多個客戶端的請求，甚至在處理單個連接時也可能會用到，就像我們上面的兩個go關鍵詞的用法。然而在我們使用go關鍵詞的同時，需要慎重地考慮net.Conn中的方法在併發地調用時是否安全，事實上對於大多數類型來説也確實不安全。我們會在下一章中詳細地探討併發安全性。</p>
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</section>
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