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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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<hr>
<h2 id="82-示例-并发的clock服务"><a class="header" href="#82-示例-并发的clock服务">8.2. 示例: 并发的Clock服务</a></h2>
<p>网络编程是并发大显身手的一个领域由于服务器是最典型的需要同时处理很多连接的程序这些连接一般来自于彼此独立的客户端。在本小节中我们会讲解go语言的net包这个包提供编写一个网络客户端或者服务器程序的基本组件无论两者间通信是使用TCP、UDP或者Unix domain sockets。在第一章中我们使用过的net/http包里的方法也算是net包的一部分。</p>
<p>我们的第一个例子是一个顺序执行的时钟服务器,它会每隔一秒钟将当前时间写到客户端:</p>
<p><u><i>gopl.io/ch8/clock1</i></u></p>
<pre><code class="language-go">// Clock1 is a TCP server that periodically writes the time.
package main
import (
&quot;io&quot;
&quot;log&quot;
&quot;net&quot;
&quot;time&quot;
)
func main() {
listener, err := net.Listen(&quot;tcp&quot;, &quot;localhost:8000&quot;)
if err != nil {
log.Fatal(err)
}
for {
conn, err := listener.Accept()
if err != nil {
log.Print(err) // e.g., connection aborted
continue
}
handleConn(conn) // handle one connection at a time
}
}
func handleConn(c net.Conn) {
defer c.Close()
for {
_, err := io.WriteString(c, time.Now().Format(&quot;15:04:05\n&quot;))
if err != nil {
return // e.g., client disconnected
}
time.Sleep(1 * time.Second)
}
}
</code></pre>
<p>Listen函数创建了一个net.Listener的对象这个对象会监听一个网络端口上到来的连接在这个例子里我们用的是TCP的localhost:8000端口。listener对象的Accept方法会直接阻塞直到一个新的连接被创建然后会返回一个net.Conn对象来表示这个连接。</p>
<p>handleConn函数会处理一个完整的客户端连接。在一个for死循环中用time.Now()获取当前时刻然后写到客户端。由于net.Conn实现了io.Writer接口我们可以直接向其写入内容。这个死循环会一直执行直到写入失败。最可能的原因是客户端主动断开连接。这种情况下handleConn函数会用defer调用关闭服务器侧的连接然后返回到主函数继续等待下一个连接请求。</p>
<p>time.Time.Format方法提供了一种格式化日期和时间信息的方式。它的参数是一个格式化模板标识如何来格式化时间而这个格式化模板限定为Mon Jan 2 03:04:05PM 2006 UTC-0700。有8个部分周几、月份、一个月的第几天……。可以以任意的形式来组合前面这个模板出现在模板中的部分会作为参考来对时间格式进行输出。在上面的例子中我们只用到了小时、分钟和秒。time包里定义了很多标准时间格式比如time.RFC1123。在进行格式化的逆向操作time.Parse时也会用到同样的策略。译注这是go语言和其它语言相比比较奇葩的一个地方。你需要记住格式化字符串是1月2日下午3点4分5秒零六年UTC-0700而不像其它语言那样Y-m-d H:i:s一样当然了这里可以用1234567的方式来记忆倒是也不麻烦。</p>
<p>为了连接例子里的服务器我们需要一个客户端程序比如netcat这个工具nc命令这个工具可以用来执行网络连接操作。</p>
<pre><code>$ go build gopl.io/ch8/clock1
$ ./clock1 &amp;
$ nc localhost 8000
13:58:54
13:58:55
13:58:56
13:58:57
^C
</code></pre>
<p>客户端将服务器发来的时间显示了出来我们用Control+C来中断客户端的执行在Unix系统上你会看到^C这样的响应。如果你的系统没有装nc这个工具你可以用telnet来实现同样的效果或者也可以用我们下面的这个用go写的简单的telnet程序用net.Dial就可以简单地创建一个TCP连接</p>
<p><u><i>gopl.io/ch8/netcat1</i></u></p>
<pre><code class="language-go">// Netcat1 is a read-only TCP client.
package main
import (
&quot;io&quot;
&quot;log&quot;
&quot;net&quot;
&quot;os&quot;
)
func main() {
conn, err := net.Dial(&quot;tcp&quot;, &quot;localhost:8000&quot;)
if err != nil {
log.Fatal(err)
}
defer conn.Close()
mustCopy(os.Stdout, conn)
}
func mustCopy(dst io.Writer, src io.Reader) {
if _, err := io.Copy(dst, src); err != nil {
log.Fatal(err)
}
}
</code></pre>
<p>这个程序会从连接中读取数据并将读到的内容写到标准输出中直到遇到end of file的条件或者发生错误。mustCopy这个函数我们在本节的几个例子中都会用到。让我们同时运行两个客户端来进行一个测试这里可以开两个终端窗口下面左边的是其中的一个的输出右边的是另一个的输出</p>
<pre><code>$ go build gopl.io/ch8/netcat1
$ ./netcat1
13:58:54 $ ./netcat1
13:58:55
13:58:56
^C
13:58:57
13:58:58
13:58:59
^C
$ killall clock1
</code></pre>
<p>killall命令是一个Unix命令行工具可以用给定的进程名来杀掉所有名字匹配的进程。</p>
<p>第二个客户端必须等待第一个客户端完成工作这样服务端才能继续向后执行因为我们这里的服务器程序同一时间只能处理一个客户端连接。我们这里对服务端程序做一点小改动使其支持并发在handleConn函数调用的地方增加go关键字让每一次handleConn的调用都进入一个独立的goroutine。</p>
<p><u><i>gopl.io/ch8/clock2</i></u></p>
<pre><code class="language-go">for {
conn, err := listener.Accept()
if err != nil {
log.Print(err) // e.g., connection aborted
continue
}
go handleConn(conn) // handle connections concurrently
}
</code></pre>
<p>现在多个客户端可以同时接收到时间了:</p>
<pre><code>$ go build gopl.io/ch8/clock2
$ ./clock2 &amp;
$ go build gopl.io/ch8/netcat1
$ ./netcat1
14:02:54 $ ./netcat1
14:02:55 14:02:55
14:02:56 14:02:56
14:02:57 ^C
14:02:58
14:02:59 $ ./netcat1
14:03:00 14:03:00
14:03:01 14:03:01
^C 14:03:02
^C
$ killall clock2
</code></pre>
<p><strong>练习 8.1</strong> 修改clock2来支持传入参数作为端口号然后写一个clockwall的程序这个程序可以同时与多个clock服务器通信从多个服务器中读取时间并且在一个表格中一次显示所有服务器传回的结果类似于你在某些办公室里看到的时钟墙。如果你有地理学上分布式的服务器可以用的话让这些服务器跑在不同的机器上面或者在同一台机器上跑多个不同的实例这些实例监听不同的端口假装自己在不同的时区。像下面这样</p>
<pre><code>$ TZ=US/Eastern ./clock2 -port 8010 &amp;
$ TZ=Asia/Tokyo ./clock2 -port 8020 &amp;
$ TZ=Europe/London ./clock2 -port 8030 &amp;
$ clockwall NewYork=localhost:8010 Tokyo=localhost:8020 London=localhost:8030
</code></pre>
<p><strong>练习 8.2</strong> 实现一个并发FTP服务器。服务器应该解析客户端发来的一些命令比如cd命令来切换目录ls来列出目录内文件get和send来传输文件close来关闭连接。你可以用标准的ftp命令来作为客户端或者也可以自己实现一个。</p>
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