Golang channel 使用总结

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以常规方式编写并发程序,需要对共享变量作正确的访问控制,处理起来很困难。而golang提出一种不同的方式,即共享变量通过channel传递,共享变量从不被各个独立运行的线程(goroutine)同时享有,在任一时刻,共享变量仅可被一个goroutine访问。所以,不会产生数据竞争。并发编程,golang鼓励以此种方式进行思考,精简为一句口号——“勿通过共享内存来进行通信,而应通过通信来进行内存共享”。 <br /> <strong>1 Unbuffered channels与Buffered channels</strong> <br /> Unbuffered channels的接收者阻塞直至收到消息,发送者阻塞直至接收者接收到消息,该机制可用于两个goroutine的状态同步。Buffered channels在缓冲区未满时,发送者仅在值拷贝到缓冲区之前是阻塞的,而在缓冲区已满时,发送者会阻塞,直至接收者取走了消息,缓冲区有了空余。 <br /> <strong>1.1 Unbuffered channels</strong> <br /> 如下代码使用Unbuffered channel作同步控制。给定一个整型数组,在主routine启动另一个goroutine将该数组排序,当其完成时,给done channel发送完成消息,主routine会一直等待直至排序完成,打印结果。 <div class="dp-highlighter"><div class="bar"></div><ol start="1" class="dp-j"><li class="alt"><span><span class="keyword">package</span><span>&nbsp;main&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span><span class="keyword">import</span><span>&nbsp;(&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;<span class="string">"fmt"</span><span>&nbsp;&nbsp;</span></span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;<span class="string">"sort"</span><span>&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;<span class="string">"time"</span><span>&nbsp;&nbsp;</span></span></li><li class="alt"><span>)&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span><span class="keyword">func</span>&nbsp;main()&nbsp;{&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;done&nbsp;:=&nbsp;<span class="keyword">make</span>(<span class="keyword">chan</span>&nbsp;<span class="keyword">bool</span>)&nbsp;&nbsp;</span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;nums&nbsp;:=&nbsp;[]<span class="keyword">int</span><span>{</span><span class="number">2</span><span>,&nbsp;</span><span class="number">1</span><span>,&nbsp;</span><span class="number">3</span><span>,&nbsp;</span><span class="number">5</span><span>,&nbsp;</span><span class="number">4</span><span>}&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">go</span>&nbsp;<span class="keyword">func</span>()&nbsp;{&nbsp;&nbsp;</span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;time.Sleep(time.Second)&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;sort.Ints(nums)&nbsp;&nbsp;</span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;done&nbsp;&lt;-&nbsp;<span class="keyword">true</span><span>&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;}()&nbsp;&nbsp;</span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;&lt;-done&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;fmt.Println(nums)&nbsp;&nbsp;</span></li><li class="alt"><span>}&nbsp;&nbsp;</span></li></ol></div> <br /> <strong>1.2 Buffered channels</strong> <br /> 如下代码中,messages chan的缓冲区大小为2,因其为Buffered channel,所以消息发送与接收无须分开到两个并发的goroutine中。 <div class="dp-highlighter"><div class="bar"></div><ol start="1" class="dp-j"><li class="alt"><span><span class="keyword">package</span><span>&nbsp;main&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span><span class="keyword">import</span><span>&nbsp;(&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;<span class="string">"fmt"</span><span>&nbsp;&nbsp;</span></span></li><li class="alt"><span>)&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span><span class="keyword">func</span>&nbsp;main()&nbsp;{&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;messages&nbsp;:=&nbsp;<span class="keyword">make</span>(<span class="keyword">chan</span>&nbsp;string,&nbsp;<span class="number">2</span><span>)&nbsp;&nbsp;</span></span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;messages&nbsp;&lt;-&nbsp;<span class="string">"hello"</span><span>&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;messages&nbsp;&lt;-&nbsp;<span class="string">"world"</span><span>&nbsp;&nbsp;</span></span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;fmt.Println(&lt;-messages,&nbsp;&lt;-messages)&nbsp;&nbsp;</span></li><li class=""><span>}&nbsp;&nbsp;</span></li></ol></div> <br /> <strong>2 配套使用</strong> <br /> <strong>2.1 指明channel direction</strong> <br /> 函数封装时,对仅作消息接收或仅作消息发送的chan标识direction可以借用编译器检查增强类型使用安全。如下代码中,ping函数中pings chan仅用来接收消息,所以参数列表中将其标识为接收者。pong函数中,pings chan仅用来发送消息,pongs chan仅用来接收消息,所以参数列表中二者分别标识为发送者与接收者。 <div class="dp-highlighter"><div class="bar"></div><ol start="1" class="dp-j"><li class="alt"><span><span class="keyword">package</span><span>&nbsp;main&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span><span class="keyword">import</span><span>&nbsp;</span><span class="string">"fmt"</span><span>&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span><span class="keyword">func</span>&nbsp;ping(pings&nbsp;<span class="keyword">chan</span>&lt;-&nbsp;string,&nbsp;msg&nbsp;string)&nbsp;{&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;pings&nbsp;&lt;-&nbsp;msg&nbsp;&nbsp;</span></li><li class="alt"><span>}&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span><span class="keyword">func</span>&nbsp;pong(pings&nbsp;&lt;-<span class="keyword">chan</span>&nbsp;string,&nbsp;pongs&nbsp;<span class="keyword">chan</span>&lt;-&nbsp;string)&nbsp;{&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;pongs&nbsp;&lt;-&nbsp;&lt;-pings&nbsp;&nbsp;</span></li><li class="alt"><span>}&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span><span class="keyword">func</span>&nbsp;main()&nbsp;{&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;pings,&nbsp;pongs&nbsp;:=&nbsp;<span class="keyword">make</span>(<span class="keyword">chan</span>&nbsp;string,&nbsp;<span class="number">1</span><span>),&nbsp;<span class="keyword">make</span>(<span class="keyword">chan</span>&nbsp;string,&nbsp;</span><span class="number">1</span><span>)&nbsp;&nbsp;</span></span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;ping(pings,&nbsp;<span class="string">"ping"</span><span>)&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;pong(pings,&nbsp;pongs)&nbsp;&nbsp;</span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;fmt.Println(&lt;-pongs)&nbsp;&nbsp;</span></li><li class=""><span>}&nbsp;&nbsp;</span></li></ol></div> <br /> <strong>2.2 select</strong> <br /> 使用select可以用来等待多个channel的消息,如下代码,创建两个chan,启动两个goroutine耗费不等时间计算结果,主routine监听消息,使用两次select,第一次接收到了ch2的消息,第二次接收到了ch1的消息,用时2.000521146s。 <div class="dp-highlighter"><div class="bar"></div><ol start="1" class="dp-j"><li class="alt"><span><span class="keyword">package</span><span>&nbsp;main&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span><span class="keyword">import</span><span>&nbsp;(&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;<span class="string">"fmt"</span><span>&nbsp;&nbsp;</span></span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;<span class="string">"time"</span><span>&nbsp;&nbsp;</span></span></li><li class=""><span>)&nbsp;&nbsp;</span></li><li class="alt"><span>&nbsp;&nbsp;</span></li><li class=""><span><span class="keyword">func</span>&nbsp;main()&nbsp;{&nbsp;&nbsp;</span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;c1,&nbsp;c2&nbsp;:=&nbsp;<span class="keyword">make</span>(<span class="keyword">chan</span>&nbsp;<span class="keyword">int</span><span>,&nbsp;</span><span class="number">1</span><span>),&nbsp;<span class="keyword">make</span>(<span class="keyword">chan</span>&nbsp;</span><span class="keyword">int</span><span>,&nbsp;</span><span class="number">1</span><span>)&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;go&nbsp;<span class="keyword">func</span>()&nbsp;{&nbsp;&nbsp;</span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;time.Sleep(<span class="number">2</span><span>&nbsp;*&nbsp;time.Second)&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;c1&nbsp;&lt;-&nbsp;<span class="number">1</span><span>&nbsp;&nbsp;</span></span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;}()&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;go&nbsp;<span class="keyword">func</span>()&nbsp;{&nbsp;&nbsp;</span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;time.Sleep(time.Second)&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;c2&nbsp;&lt;-&nbsp;<span class="number">2</span><span>&nbsp;&nbsp;</span></span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;}()&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">for</span><span>&nbsp;i&nbsp;:=&nbsp;</span><span class="number">0</span><span>;&nbsp;i&nbsp;&lt;&nbsp;</span><span class="number">2</span><span>;&nbsp;i++&nbsp;{&nbsp;&nbsp;</span></span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">select</span>&nbsp;{&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">case</span><span>&nbsp;msg1&nbsp;:=&nbsp;&lt;-c1:&nbsp;&nbsp;</span></span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;fmt.Println(<span class="string">"received&nbsp;msg&nbsp;from&nbsp;c1"</span><span>,&nbsp;msg1)&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">case</span><span>&nbsp;msg2&nbsp;:=&nbsp;&lt;-c2:&nbsp;&nbsp;</span></span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;fmt.Println(<span class="string">"received&nbsp;msg&nbsp;from&nbsp;c2"</span><span>,&nbsp;msg2)&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}&nbsp;&nbsp;</span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;}&nbsp;&nbsp;</span></li><li class=""><span>}&nbsp;&nbsp;</span></li></ol></div> <br /> <strong>2.3 select with default</strong> <br /> select with default可以用来处理非阻塞式消息发送、接收及多路选择。如下代码中,第一个select为非阻塞式消息接收,若收到消息,则落入<-messages case,否则落入default。第二个select为非阻塞式消息发送,与非阻塞式消息接收类似,因messages chan为Unbuffered channel且无异步消息接收者,因此落入default case。第三个select为多路非阻塞式消息接收。 <div class="dp-highlighter"><div class="bar"></div><ol start="1" class="dp-j"><li class="alt"><span><span class="keyword">package</span><span>&nbsp;main&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span><span class="keyword">import</span><span>&nbsp;</span><span class="string">"fmt"</span><span>&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span><span class="keyword">func</span>&nbsp;main()&nbsp;{&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;messages&nbsp;:=&nbsp;<span class="keyword">make</span>(<span class="keyword">chan</span>&nbsp;string)&nbsp;&nbsp;</span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;signal&nbsp;:=&nbsp;<span class="keyword">make</span>(<span class="keyword">chan</span>&nbsp;<span class="keyword">bool</span>)&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;<span class="comment">//&nbsp;receive&nbsp;with&nbsp;default</span><span>&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">select</span>&nbsp;{&nbsp;&nbsp;</span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">case</span><span>&nbsp;&lt;-messages:&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;fmt.Println(<span class="string">"message&nbsp;received"</span><span>)&nbsp;&nbsp;</span></span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">default</span><span>:&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;fmt.Println(<span class="string">"no&nbsp;message&nbsp;received"</span><span>)&nbsp;&nbsp;</span></span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;}&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;<span class="comment">//&nbsp;send&nbsp;with&nbsp;default</span><span>&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">select</span>&nbsp;{&nbsp;&nbsp;</span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">case</span><span>&nbsp;messages&nbsp;&lt;-&nbsp;</span><span class="string">"message"</span><span>:&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;fmt.Println(<span class="string">"message&nbsp;sent&nbsp;successfully"</span><span>)&nbsp;&nbsp;</span></span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">default</span><span>:&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;fmt.Println(<span class="string">"message&nbsp;sent&nbsp;failed"</span><span>)&nbsp;&nbsp;</span></span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;}&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;<span class="comment">//&nbsp;muti-way&nbsp;<span class="keyword">select</span></span><span>&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">select</span>&nbsp;{&nbsp;&nbsp;</span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">case</span><span>&nbsp;&lt;-messages:&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;fmt.Println(<span class="string">"message&nbsp;received"</span><span>)&nbsp;&nbsp;</span></span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">case</span><span>&nbsp;&lt;-signal:&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;fmt.Println(<span class="string">"signal&nbsp;received"</span><span>)&nbsp;&nbsp;</span></span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">default</span><span>:&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;fmt.Println(<span class="string">"no&nbsp;message&nbsp;or&nbsp;signal&nbsp;received"</span><span>)&nbsp;&nbsp;</span></span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;}&nbsp;&nbsp;</span></li><li class=""><span>}&nbsp;&nbsp;</span></li></ol></div> <br /> <strong>2.4 close</strong> <br /> 当无需再给channel发送消息时,可将其close。如下代码中,创建一个Buffered channel,首先启动一个异步goroutine循环消费消息,然后主routine完成消息发送后关闭chan,消费goroutine检测到chan关闭后,退出循环。 <div class="dp-highlighter"><div class="bar"></div><ol start="1" class="dp-j"><li class="alt"><span><span class="keyword">package</span><span>&nbsp;main&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span><span class="keyword">import</span><span>&nbsp;</span><span class="string">"fmt"</span><span>&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span><span class="keyword">func</span>&nbsp;main()&nbsp;{&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;messages&nbsp;:=&nbsp;<span class="keyword">make</span>(<span class="keyword">chan</span>&nbsp;<span class="keyword">int</span><span>,&nbsp;</span><span class="number">10</span><span>)&nbsp;&nbsp;</span></span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;done&nbsp;:=&nbsp;<span class="keyword">make</span>(<span class="keyword">chan</span>&nbsp;<span class="keyword">bool</span>)&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;<span class="comment">//&nbsp;consumer</span><span>&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">go</span>&nbsp;<span class="keyword">func</span>()&nbsp;{&nbsp;&nbsp;</span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">for</span><span>&nbsp;{&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;msg,&nbsp;more&nbsp;:=&nbsp;&lt;-messages&nbsp;&nbsp;</span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">if</span><span>&nbsp;!more&nbsp;{&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;fmt.Println(<span class="string">"no&nbsp;more&nbsp;message"</span><span>)&nbsp;&nbsp;</span></span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;done&nbsp;&lt;-&nbsp;<span class="keyword">true</span><span>&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">break</span><span>&nbsp;&nbsp;</span></span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;fmt.Println(<span class="string">"message&nbsp;received"</span><span>,&nbsp;msg)&nbsp;&nbsp;</span></span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;}()&nbsp;&nbsp;</span></li><li class="alt"><span>&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;<span class="comment">//&nbsp;producer</span><span>&nbsp;&nbsp;</span></span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">for</span><span>&nbsp;i&nbsp;:=&nbsp;</span><span class="number">0</span><span>;&nbsp;i&nbsp;&lt;&nbsp;</span><span class="number">5</span><span>;&nbsp;i++&nbsp;{&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;messages&nbsp;&lt;-&nbsp;i&nbsp;&nbsp;</span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;}&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;close(messages)&nbsp;&nbsp;</span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;&lt;-done&nbsp;&nbsp;</span></li><li class=""><span>}&nbsp;&nbsp;</span></li></ol></div> <br /> <strong>2.5 for range</strong> <br /> for range语法不仅可对基础数据结构(slice、map等)作迭代,还可对channel作消息接收迭代。如下代码中,给messages chan发送两条消息后将其关闭,然后迭代messages chan打印消息。 <div class="dp-highlighter"><div class="bar"></div><ol start="1" class="dp-j"><li class="alt"><span><span class="keyword">package</span><span>&nbsp;main&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span><span class="keyword">import</span><span>&nbsp;</span><span class="string">"fmt"</span><span>&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span><span class="keyword">func</span>&nbsp;main()&nbsp;{&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;messages&nbsp;:=&nbsp;<span class="keyword">make</span>(<span class="keyword">chan</span>&nbsp;string,&nbsp;<span class="number">2</span><span>)&nbsp;&nbsp;</span></span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;messages&nbsp;&lt;-&nbsp;<span class="string">"hello"</span><span>&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;messages&nbsp;&lt;-&nbsp;<span class="string">"world"</span><span>&nbsp;&nbsp;</span></span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;close(messages)&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">for</span><span>&nbsp;msg&nbsp;:=&nbsp;<span class="keyword">range</span>&nbsp;messages&nbsp;{&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;fmt.Println(msg)&nbsp;&nbsp;</span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;}&nbsp;&nbsp;</span></li><li class=""><span>}&nbsp;&nbsp;</span></li></ol></div> <br /> <strong>3 应用场景</strong> <br /> <strong>3.1 超时控制</strong> <br /> 资源访问、网络请求等场景作超时控制是非常必要的,可以使用channel结合select来实现。如下代码,对常规sum函数增加超时限制,sumWithTimeout函数中,select的v := <-rlt在等待计算结果,若在时限范围内计算完成,则正常返回计算结果,若超过时限则落入<-time.After(timeout) case,抛出timeout error。 <div class="dp-highlighter"><div class="bar"></div><ol start="1" class="dp-j"><li class="alt"><span><span class="keyword">package</span><span>&nbsp;main&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span><span class="keyword">import</span><span>&nbsp;(&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;<span class="string">"errors"</span><span>&nbsp;&nbsp;</span></span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;<span class="string">"fmt"</span><span>&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;<span class="string">"time"</span><span>&nbsp;&nbsp;</span></span></li><li class="alt"><span>)&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span><span class="keyword">func</span>&nbsp;sum(nums&nbsp;[]<span class="keyword">int</span><span>)&nbsp;</span><span class="keyword">int</span><span>&nbsp;{&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;rlt&nbsp;:=&nbsp;<span class="number">0</span><span>&nbsp;&nbsp;</span></span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">for</span><span>&nbsp;_,&nbsp;num&nbsp;:=&nbsp;<span class="keyword">range</span>&nbsp;nums&nbsp;{&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;rlt&nbsp;+=&nbsp;num&nbsp;&nbsp;</span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;}&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">return</span><span>&nbsp;rlt&nbsp;&nbsp;</span></span></li><li class="alt"><span>}&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span><span class="keyword">func</span>&nbsp;sumWithTimeout(nums&nbsp;[]<span class="keyword">int</span><span>,&nbsp;timeout&nbsp;time.Duration)&nbsp;(</span><span class="keyword">int</span><span>,&nbsp;error)&nbsp;{&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;rlt&nbsp;:=&nbsp;<span class="keyword">make</span>(<span class="keyword">chan</span>&nbsp;<span class="keyword">int</span><span>)&nbsp;&nbsp;</span></span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">go</span>&nbsp;<span class="keyword">func</span>()&nbsp;{&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;time.Sleep(<span class="number">2</span><span>&nbsp;*&nbsp;time.Second)&nbsp;&nbsp;</span></span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;rlt&nbsp;&lt;-&nbsp;sum(nums)&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;}()&nbsp;&nbsp;</span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">select</span>&nbsp;{&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">case</span><span>&nbsp;v&nbsp;:=&nbsp;&lt;-rlt:&nbsp;&nbsp;</span></span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">return</span><span>&nbsp;v,&nbsp;nil&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">case</span><span>&nbsp;&lt;-time.After(timeout):&nbsp;&nbsp;</span></span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">return</span><span>&nbsp;</span><span class="number">0</span><span>,&nbsp;errors.New(</span><span class="string">"timeout"</span><span>)&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;}&nbsp;&nbsp;</span></li><li class="alt"><span>}&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span><span class="keyword">func</span>&nbsp;main()&nbsp;{&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;nums&nbsp;:=&nbsp;[]<span class="keyword">int</span><span>{</span><span class="number">1</span><span>,&nbsp;</span><span class="number">2</span><span>,&nbsp;</span><span class="number">3</span><span>,&nbsp;</span><span class="number">4</span><span>,&nbsp;</span><span class="number">5</span><span>}&nbsp;&nbsp;</span></span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;timeout&nbsp;:=&nbsp;<span class="number">3</span><span>&nbsp;*&nbsp;time.Second&nbsp;</span><span class="comment">//&nbsp;time.Second</span><span>&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;rlt,&nbsp;err&nbsp;:=&nbsp;sumWithTimeout(nums,&nbsp;timeout)&nbsp;&nbsp;</span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">if</span><span>&nbsp;nil&nbsp;!=&nbsp;err&nbsp;{&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;fmt.Println(<span class="string">"error"</span><span>,&nbsp;err)&nbsp;&nbsp;</span></span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">return</span><span>&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;}&nbsp;&nbsp;</span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;fmt.Println(rlt)&nbsp;&nbsp;</span></li><li class=""><span>}&nbsp;&nbsp;</span></li></ol></div> <br /> 本文代码托管地址:<a href="https://github.com/olzhy/go-excercises/tree/master/channels" target="blank">https://github.com/olzhy/go-excercises/tree/master/channels</a> 原文地址:https://leileiluoluo.com/posts/golang-channels.html

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