【转载】erlang 如何自定义 behaviour

偏执的太偏执、 2022-01-26 03:35 211阅读 0赞

## **什么是 behaviour ？** ##

使用 erlang 编程的人都知道 OTP，而基于 OTP 框架创建进程的时候，常用的有四大 behaviour：

*  supervisor
 *  gen\_server
 *  gen\_fsm
 *  gen\_event

那么什么是 behaviour？是做什么用的呢？    
  
      首先，写这篇文章之前我上谷歌查过人家对 behaviour 的定义，当然，是非官方定义，我一直没找着官方定义，如果有人有一个比较确切的定义，麻烦告诉我，大家共同学习嘛。    
      在 StackOverFlow 上这篇   [文章][Link 1]   中指明了，在 erlang 的编译器中，**behaviour 的作用是用来定义一个规约**。定义好这个规约之后，任何遵守这个规约的模块，必须按照规约中的要求，使用 -export(\[\]). 导出对应的函数，导出完这些函数后，这些导出函数的调用将由 behaviour 统一支配。    
  
为什么要这么做呢？   参照一句话：

> The OTP Design Principles is a set of principles for how to structure Erlang code in terms of processes, modules and directories.

这句话来自官方文档 OTP 设计原则的第一句话。那么，**behaviour 只不过是实现代码组织的一种手段而已**。那么，再应用一句：

> The idea is to divide the code for a process in a generic part (a behaviour module) and a specific part (a callback module).

behaviour 就是把代码分成   **通用部分**   ，以及每一个回调模块需要去做的   **特殊部分**   。这样就好理解了，于是   **使用 -behaviour() 定义的模块都是这个 behaviour 所要求实现的回调模块**   。

## **erlang 可以自定义 behaviour 吗？** ##

这是可以的，如果大家代码读得多了，就应该发现，很多优秀的开源项目中就自定义了 behaviour。例如经典的 rabbitmq 中，就将 erlang 自带的 gen\_server 进行了改进，写了一个 gen\_server2 的 behaviour，因为 **gen\_server 中的消息队列是一个普通消息队列**不能满足需要，**改进后的 gen\_server2 使用了带优先级的消息队列**。当然了，在 erlang 本身的底层代码里面，也有写过很多 behaviour，不细说了，总之 erlang 可以自定义 behaviour 。

## **关键字究竟是 behavior 还是 behaviour？** ##

在写代码的时候发现有时候用的是 behaviour，而又有的时候用的是 behavior。这两个词应该是美式英语和英式英语的区别吧。说明一点，**在定义 behaviour 的时候**，erlang 是亲美一派的，**必须用 behaviour**，使用 behavior 将报错。而在使用已经定义好的 behavior 模块的时候，对编译器而言，两个词都可以用.....真是很诡异的。

## **怎么定义一个 behaviour？** ##

要定义一个 behaviour，首先你要创建一个模块，它必须导出 behaviour\_info/1 这个函数（注意   behaviour 是   带 u 的），函数定义如下：

[?][Link 2]

传入 callbacks 参数，必须返回一个包含导出函数和参数个数的列表。    
  
      这些导出函数，就是这些回调模块所特有的部分，而通用部分，则写在 behaviour 中。比如在 gen\_server 中，当一个进程收到一个消息，在 behaviour 行为模型中，它会处理大部分通用的逻辑，例如，如果是 call 消息，它会根据 handle\_call 函数的返回值对 From 进程发送返回消息，同时，处理完消息后，它会继续循环进行消息处理，不多说，亮代码：

[?][Link 2]

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   <td style="border:0px;line-height:1.1em;vertical-align:baseline;font-size:1em;background:none;"> 
    <div style="border:0px;line-height:1.1em;vertical-align:baseline;font-size:1em;background:none;"> 
     <div style="border:0px;line-height:1.1em;vertical-align:baseline;font-size:1em;background-image:none;"> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">handle_msg({ </code> 
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      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">, From, Msg}, GS2State = </code> 
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      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">state = State,&nbsp; </code> 
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     <div style="border:0px;line-height:1.1em;vertical-align:baseline;font-size:1em;background-image:none;"> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">name = Name,&nbsp; </code> 
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     <div style="border:0px;line-height:1.1em;vertical-align:baseline;font-size:1em;background-image:none;"> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">debug = Debug }) -&gt;&nbsp; </code> 
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     <div style="border:0px;line-height:1.1em;vertical-align:baseline;font-size:1em;background-image:none;"> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-weight:bold;font-size:1em;color:rgb(0,102,153);background:none;">case</code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">catch Mod:handle_call(Msg, From, State) of %%大家注意了，这里就是调用了模块中的handle_call()函数，并且获取它的返回值&nbsp; </code> 
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      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">{reply, Reply, NState} -&gt;&nbsp; </code> 
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     <div style="border:0px;line-height:1.1em;vertical-align:baseline;font-size:1em;background-image:none;"> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">Debug1 = common_reply(Name, From, Reply, NState, Debug),&nbsp; </code> 
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     <div style="border:0px;line-height:1.1em;vertical-align:baseline;font-size:1em;background-image:none;"> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">loop(GS2State </code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;color:rgb(0,130,0);background:none;">#gs2_state { state = NState,%%在这里，处理完一条消息之后，继续转入到循环中去&nbsp; </code> 
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     <div style="border:0px;line-height:1.1em;vertical-align:baseline;font-size:1em;background-image:none;"> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">time</code>&nbsp; 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">= infinity,&nbsp; </code> 
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     <div style="border:0px;line-height:1.1em;vertical-align:baseline;font-size:1em;background-image:none;"> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">debug = Debug1 });&nbsp; </code> 
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     <div style="border:0px;line-height:1.1em;vertical-align:baseline;font-size:1em;background-image:none;"> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">{reply, Reply, NState, Time1} -&gt;&nbsp; </code> 
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     <div style="border:0px;line-height:1.1em;vertical-align:baseline;font-size:1em;background-image:none;"> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">Debug1 = common_reply(Name, From, Reply, NState, Debug),&nbsp; </code> 
     </div> 
     <div style="border:0px;line-height:1.1em;vertical-align:baseline;font-size:1em;background-image:none;"> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">loop(GS2State </code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;color:rgb(0,130,0);background:none;">#gs2_state { state = NState,&nbsp; </code> 
     </div> 
     <div style="border:0px;line-height:1.1em;vertical-align:baseline;font-size:1em;background-image:none;"> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">time</code>&nbsp; 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">= Time1,&nbsp; </code> 
     </div> 
     <div style="border:0px;line-height:1.1em;vertical-align:baseline;font-size:1em;background-image:none;"> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">debug = Debug1});&nbsp; </code> 
     </div> 
     <div style="border:0px;line-height:1.1em;vertical-align:baseline;font-size:1em;background-image:none;"> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">{noreply, NState} -&gt;&nbsp; </code> 
     </div> 
     <div style="border:0px;line-height:1.1em;vertical-align:baseline;font-size:1em;background-image:none;"> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">Debug1 = common_debug(Debug, fun print_event</code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">/3</code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">, Name,&nbsp; </code> 
     </div> 
     <div style="border:0px;line-height:1.1em;vertical-align:baseline;font-size:1em;background-image:none;"> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">{noreply, NState}),&nbsp; </code> 
     </div> 
     <div style="border:0px;line-height:1.1em;vertical-align:baseline;font-size:1em;background-image:none;"> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">loop(GS2State </code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;color:rgb(0,130,0);background:none;">#gs2_state {state = NState,&nbsp; </code> 
     </div> 
     <div style="border:0px;line-height:1.1em;vertical-align:baseline;font-size:1em;background-image:none;"> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">time</code>&nbsp; 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">= infinity,&nbsp; </code> 
     </div> 
     <div style="border:0px;line-height:1.1em;vertical-align:baseline;font-size:1em;background-image:none;"> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">debug = Debug1});&nbsp; </code> 
     </div> 
     <div style="border:0px;line-height:1.1em;vertical-align:baseline;font-size:1em;background-image:none;"> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">{noreply, NState, Time1} -&gt;&nbsp; </code> 
     </div> 
     <div style="border:0px;line-height:1.1em;vertical-align:baseline;font-size:1em;background-image:none;"> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">Debug1 = common_debug(Debug, fun print_event</code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">/3</code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">, Name,&nbsp; </code> 
     </div> 
     <div style="border:0px;line-height:1.1em;vertical-align:baseline;font-size:1em;background-image:none;"> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">{noreply, NState}),&nbsp; </code> 
     </div> 
     <div style="border:0px;line-height:1.1em;vertical-align:baseline;font-size:1em;background-image:none;"> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">loop(GS2State </code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;color:rgb(0,130,0);background:none;">#gs2_state {state = NState,&nbsp; </code> 
     </div> 
     <div style="border:0px;line-height:1.1em;vertical-align:baseline;font-size:1em;background-image:none;"> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">time</code>&nbsp; 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">= Time1,&nbsp; </code> 
     </div> 
     <div style="border:0px;line-height:1.1em;vertical-align:baseline;font-size:1em;background-image:none;"> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">debug = Debug1});&nbsp; </code> 
     </div> 
     <div style="border:0px;line-height:1.1em;vertical-align:baseline;font-size:1em;background-image:none;"> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">{stop, Reason, Reply, NState} -&gt;&nbsp; </code> 
     </div> 
     <div style="border:0px;line-height:1.1em;vertical-align:baseline;font-size:1em;background-image:none;"> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">{ </code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;color:#0000FF;background:none;">'EXIT'</code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">, R} =&nbsp; </code> 
     </div> 
     <div style="border:0px;line-height:1.1em;vertical-align:baseline;font-size:1em;background-image:none;"> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">(catch terminate(Reason, Msg,&nbsp; </code> 
     </div> 
     <div style="border:0px;line-height:1.1em;vertical-align:baseline;font-size:1em;background-image:none;"> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">GS2State </code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;color:rgb(0,130,0);background:none;">#gs2_state { state = NState })),&nbsp; </code> 
     </div> 
     <div style="border:0px;line-height:1.1em;vertical-align:baseline;font-size:1em;background-image:none;"> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">reply(Name, From, Reply, NState, Debug),&nbsp; </code> 
     </div> 
     <div style="border:0px;line-height:1.1em;vertical-align:baseline;font-size:1em;background-image:none;"> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">exit</code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">(R);&nbsp; </code> 
     </div> 
     <div style="border:0px;line-height:1.1em;vertical-align:baseline;font-size:1em;background-image:none;"> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">Other -&gt;&nbsp; </code> 
     </div> 
     <div style="border:0px;line-height:1.1em;vertical-align:baseline;font-size:1em;background-image:none;"> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">handle_common_reply(Other, Msg, GS2State)&nbsp; </code> 
     </div> 
     <div style="border:0px;line-height:1.1em;vertical-align:baseline;font-size:1em;background-image:none;"> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:1em;background:none;">end;</code> 
     </div> 
    </div> </td> 
  </tr> 
 </tbody> 
</table>

源代码是最好的老师！有时候我想，想要了解 gen\_server ，为什么放着 gen\_server.erl 这个源代码不去读，却宁愿相信百度上，或者谷歌上，或者别人说的话呢？还有什么比代码中的事实更真实吗？更可信的吗？

## **怎么使用 behaviour?** ##

使用的时候，需要在模块开头 使用：

[?][Link 2]

同时需要定义并且使用 -export(\[\]) 导出这个 behaviour 所要求的导出函数。    
注意了，   **一个模块是可以有多个 -behaviour(behaviour\_name). 的**   ，也就是说，这个模块的一部分函数可以既是 A behaviour 的回调模块，又是 B behaviour 的回调模块。

## **何时使用 behaviour？** ##

最后这个话题就比较广了，这是一个没有绝对意义正确的问题，在 erlang OTP 中，那几个主要进程的实现都是使用 behaviour 封装了基本的操作。

对于 behaviour 和进程的关系，我曾经有过这样的疑惑，只有在创建进程的时候才能用 behaviour 吗？最后得到的结论是：没有关系！ 因为在 erlang 的设计理念当中，模块与进程，这是两个概念，而 behaviour 与模块的组织相关，因此它与进程没有必然联系。

原文地址： [http://blog.csdn.net/zhangzhizhen1988/article/details/8499871][http_blog.csdn.net_zhangzhizhen1988_article_details_8499871]

[Link 1]: http://stackoverflow.com/questions/6488002/how-to-define-customized-behavior-in-erlang-and-what-can-it-do-for-you
[Link 2]: http://my.oschina.net/moooofly/blog/262723#
[http_blog.csdn.net_zhangzhizhen1988_article_details_8499871]: http://blog.csdn.net/zhangzhizhen1988/article/details/8499871