ZeroMQ的研究与学习
2016-08-12 15:05
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ZeroMQ的研究与学习
简介工作模式
层级模型
实现原理
核心特点
与其他MQ的简单比较
ZeroMQ的一百字概括
ZeroMQ看起来想一个可嵌入的网络库，但其作用就像是一个并发框架。它为你提供了各种传输工具，如进程内，进程间，TCP和组播中进行原子消息传递的套接字。你可以使用各种模式实现N对N的套接字连接，这些模式包括发布订阅，请求应答，扇出模式，管道模式。它的速度足够快，因此可以充当集群产品的结构，他的异步IO模型提供了可扩展的多核应用程序，用异步消息来处理任务。它虽然是以C为源码进行开发，但是可以绑定多种语言。
1. 简介
ZeroMQ号称是“史上最快的消息队列”，基于c语言开发的，实时流处理sorm的task之间的通信就是用的zeroMQ。 引用官方说法，“ZMQ(以下ZeroMQ简称ZMQ)是一个简单好用的传输层，像框架一样的一个socket library，他使得Socket编程更加简单、简洁和性能更高。是一个消息处理队列库，可在多个线程、内核和主机盒之间弹性伸缩。ZMQ的明确目标是“成为标准网络协议栈的一部分，之后进入Linux内核”。现在还未看到它们的成功。但是，它无疑是极具前景的、并且是人们更加需要的“传统”BSD套接字之上的一 层封装。ZMQ让编写高性能网络应用程序极为简单和有趣。” 确实，它跟RabbitMQ，ActiveMQ之类有着相当本质的区别，ZeroMQ根本就不是一个消息队列服务器，更像是一组底层网络通讯库，对原有的Socket API加上一层封装，是我们操作更简便。使用时只需要引入相应的jar包即可。
2. 工作模式
ZeroMQ与其他MQ类似，也实现了3中最基本的工作模式：发布-订阅，请求-应答，管道
1.发布-订阅
“发布-订阅”模式下，“发布者”绑定一个指定的地址，例如“192.168.10.1：5500”，“订阅者”连接到该地址。该模式下消息流是单向的，只允许从“发布者”流向“订阅者”。且“发布者”只管发消息，不理会是否存在“订阅者”。上图只是“发布-订阅”的最基本的模型，一个“发布者”可以拥有多个订阅者，同样的，一个“订阅者”也可订阅多个发布者。下面给出“发布-订阅”模型的样例程序：
发布者：
<code class="language-java hljs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">import</span> org.zeromq.ZMQ;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">Publisher</span> {</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">main</span>(String args[]) {
ZMQ.Context context = ZMQ.context(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//创创建包含一个I/O线程的context </span>
ZMQ.Socket publisher = context.socket(ZMQ.PUB); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//创建一个publisher类型的socket，他可以向所有订阅的subscriber广播数据 </span>
publisher.bind(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"tcp://*:5555"</span>); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//将当前publisher绑定到5555端口上，可以接受subscriber的订阅 </span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">while</span> (!Thread.currentThread ().isInterrupted ()) {
String message = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"fjs hello"</span>; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//最开始可以理解为pub的channel，subscribe需要订阅fjs这个channel才能接收到消息 </span>
publisher.send(message.getBytes());
}
publisher.close();
context.term();
}
} </code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li></ul>订阅者
<code class="language-java hljs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">import</span> org.zeromq.ZMQ;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">Subscriber</span> {</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">main</span>(String args[]) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> j = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; j < <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">100</span>; j++) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Thread(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Runnable(){
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">run</span>() {
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// TODO Auto-generated method stub </span>
ZMQ.Context context = ZMQ.context(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//创建1个I/O线程的上下文 </span>
ZMQ.Socket subscriber = context.socket(ZMQ.SUB); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//创建一个sub类型，也就是subscriber类型的socket </span>
subscriber.connect(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"tcp://127.0.0.1:5555"</span>); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//与在5555端口监听的publisher建立连接 </span>
subscriber.subscribe(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"fjs"</span>.getBytes()); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//订阅fjs这个channel </span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> i = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; i < <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">100</span>; i++) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">byte</span>[] message = subscriber.recv(); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//接收publisher发送过来的消息 </span>
System.out.println(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"receive : "</span> + <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> String(message));
}
subscriber.close();
context.term();
}
}).start();
}
}
} </code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li></ul>虽然我们知道“发布者”在发送消息时是不关心“订阅者”的存在于否，所以先启动“发布者”，再启动“订阅者”是很容易导致部分消息丢失的。那么可能会提出一个说法“我先启动‘订阅者’，再启动‘发布者’，就能解决这个问题了？” 对于ZeroMQ而言，这种做法也并不能保证100%的可靠性。在ZeroMQ领域中有一个叫做“慢木匠”的术语，就是说即使我是先启动了“订阅者”，再启动“发布者”，“订阅者”总是会丢失第一批数据。因为在“订阅者”与端点建立TCP连接时，会包含几毫秒的握手时间，虽然时间短，但是是存在的。再加上ZeroMQ后台IO是以一部方式执行的，所以若不在双方之间施加同步策略，消息丢失是不可避免的。
关于“发布-订阅”模式在ZeroMQ中的一些其他特点：
1.公平排队，一个“订阅者”连接到多个发布者时，会均衡的从每个“发布者”读取消息，不会出现一个“发布者”淹没其他“发布者”的情况。
2.ZMQ3.0以上的版本，过滤规则发生在“发布方”. ZMQ3.0以下的版本，过滤规则发生在“订阅方”。其实也就是处理消息的位置。
2.请求-应答
说到“请求-应答”模式，不得不说的就是它的消息流动模型以及数据包装模型。
消息流动模型指的是该模式下，必须严格遵守“一问一答”的方式。
在源代码中Req存在两个重要的标志位：
<code class="language-java hljs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> receiving_reply; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//标志位，如果是ture的话，表示request已经发送了，正在等待reponse </span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> message_begins; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//如果是true的话，那么表示这里还需要发送第一个标志的空msg </span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li></ul>
发出消息后，若没有收到回复，再发出第二条消息时就会抛出异常。同样的，对于Rep也是，在没有接收到消息前，不允许发出消息。基于此构成“一问一答”的响应模式。
对于消息发送时的具体数据格式，引入两个图作为参照：
含有识别码：
不含识别码：
这种数据结构ZeroMQ称之为“封包”。一个封包由0个或多个“帧”组成。对于“请求-应答”模式，一个元封包一般由2-3个帧组成，可以看出，差别就是第一帧的存在与否。
对于含有目标地址的封包，第一帧存放消息接收端的身份识别码，该码在ZeroMQ内部维护的一个Map中作为key，Value是对应的地址。第二帧是一个分隔帧，没有任何意义，仅仅起分隔作用。第三帧是发送的数据。对于这类封包，通常第一帧，也就是识别码需要我们手动指定。
相比于前者，不含识别码的封包内的帧的含义还是一样，只是它的识别码直接有ZeroMQ默认生成，无需手动指定。
发送时，根据识别码在内存Map中对应的地址，将消息投递过去。
示例程序：
服务端
<code class="language-java hljs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">import</span> org.zeromq.ZMQ;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">Response</span> {</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">main</span> (String[] args) {
ZMQ.Context context = ZMQ.context(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//这个表示创建用于一个I/O线程的context </span>
ZMQ.Socket socket = context.socket(ZMQ.REP); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//创建一个response类型的socket，他可以接收request发送过来的请求，其实可以将其简单的理解为服务端 </span>
socket.bind (<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"tcp://*:5555"</span>); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//绑定端口 </span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> i = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> number = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">while</span> (!Thread.currentThread().isInterrupted()) {
i++;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (i == <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10000</span>) {
i = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;
System.out.println(++number);
}
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">byte</span>[] request = socket.recv(); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//获取request发送过来的数据 </span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//System.out.println("receive : " + new String(request)); </span>
String response = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"world"</span>;
socket.send(response.getBytes()); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//向request端发送数据 ，必须要要request端返回数据，没有返回就又recv，将会出错，这里可以理解为强制要求走完整个request/response流程 </span>
}
socket.close(); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//先关闭socket </span>
context.term(); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//关闭当前的上下文 </span>
}
} </code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li></ul>客户端
<code class="language-java hljs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">import</span> org.zeromq.ZMQ;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">Request</span> {</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">main</span>(String args[]) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> j = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; j < <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5</span>; j++) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Thread(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Runnable(){
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">run</span>() {
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// TODO Auto-generated method stub </span>
ZMQ.Context context = ZMQ.context(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//创建一个I/O线程的上下文 </span>
ZMQ.Socket socket = context.socket(ZMQ.REQ); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//创建一个request类型的socket，这里可以将其简单的理解为客户端，用于向response端发送数据 </span>
socket.connect(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"tcp://127.0.0.1:5555"</span>); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//与response端建立连接 </span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">long</span> now = System.currentTimeMillis();
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> i = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; i < <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">100000</span>; i++) {
String request = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"hello"</span>;
socket.send(request.getBytes()); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//向reponse端发送数据 </span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">byte</span>[] response = socket.recv(); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//接收response发送回来的数据 正在request/response模型中，send之后必须要recv之后才能继续send，这可能是为了保证整个request/response的流程走完 </span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// System.out.println("receive : " + new String(response)); </span>
}
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">long</span> after = System.currentTimeMillis();
System.out.println((after - now) / <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1000</span>);
}
}).start();;
}
}
} </code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li></ul>“请求-应答”模式中Req套接字是同步的，每次只跟一个节点交流，如果Req套接字连接了多个节点，请求会同时分发到每一个节点。
相应的Rep套接字也是同步的，每次只跟一个节点交流，如果连接了多个节点，则以公平的方式以此从每个节点读取请求，但是最先响应的是最后读取的请求。
在接下来的内部结构分析时，将以“请求-应答”模式为例。
3.管道模式
在说明“管道模式”前，需要明确的是在ZeroMQ中并没有绝对的服务端与客户端之分，所有的数据接收与发送都是以连接为单位的，只区分ZeroMQ定义的类型。就像套接字绑定地址时，可以使用“bind”，也可以使用“connect”，只是通常我们将理解中的服务端“bind”到一个地址，而理解中的客户端“connec”到该地址。
“管道模式”一般用于任务分发与结果收集，由一个任务发生器来产生任务，“公平”的派发到其管辖下的所有worker，完成后再由结果收集器来回收任务的执行结果。
任务发生器
<code class="language-java hljs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">import</span> org.zeromq.ZMQ;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">Push</span> {</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">main</span>(String args[]) {
ZMQ.Context context = ZMQ.context(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>);
ZMQ.Socket push = context.socket(ZMQ.PUSH);
push.bind(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"ipc://fjs"</span>);
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> i = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; i < <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10000000</span>; i++) {
push.send(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"hello"</span>.getBytes());
}
push.close();
context.term();
}
} </code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li></ul>Worker
<code class="language-java hljs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">import</span> java.util.concurrent.atomic.AtomicInteger;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">import</span> org.zeromq.ZMQ;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">Pull</span> {</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">main</span>(String args[]) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> AtomicInteger number = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> AtomicInteger(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>);
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> i = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; i < <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5</span>; i++) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Thread(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Runnable(){
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> here = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">run</span>() {
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// TODO Auto-generated method stub </span>
ZMQ.Context context = ZMQ.context(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>);
ZMQ.Socket pull = context.socket(ZMQ.PULL);
pull.connect(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"ipc://fjs"</span>);
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//pull.connect("ipc://fjs"); </span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">while</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>) {
String message = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> String(pull.recv());
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> now = number.incrementAndGet();
here++;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (now % <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1000000</span> == <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>) {
System.out.println(now + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">" here is : "</span> + here);
}
}
}
}).start();
}
}
} </code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li></ul>结果收集器
<code class="language-java hljs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">import</span> org.zeromq.ZMQ;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">Pull</span> {</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">main</span>(String args[]) {
ZMQ.Context context = ZMQ.context(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>);
ZMQ.Socket pull = context.socket(ZMQ.PULL);
pull.bind(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"ipc://fjs"</span>);
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> number = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">while</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>) {
String message = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> String(pull.recv());
number++;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (number % <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1000000</span> == <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>) {
System.out.println(number);
}
}
}
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li></ul>整体流程比较好理解，Worker连接到任务发生器上，等待任务的产生，完成后将结果发送至结果收集器。如果要以客户端服务端的概念来区分，这里的任务发生器与结果收集器是服务端，而worker是客户端。
前面说到了这里任务的派发是“公平的”，因为内部采用了LRU的算法来找到最近最久未工作的闲置worker。但是公平在这里是相对的，当任务发生器启动后，第一个连接到它的worker会在一瞬间承受整个任务发生器产生的tasks。
3. 层级模型与交互逻辑
这是ZeroMQ的主要的层级模型，以“请求-应答”为例。
由上而下，最顶层的是ZObject与IPollEvent。
ZObject是所有ZeroMQ体系中类的父类，它存在的意义是发送与接收命令（有别于消息，命令是告诉ZeroMQ该做什么，需要做什么）。
IPollEvent则是一个接口，定义了若干操作，包括读操作，写操作，客户端请求连接，服务端应答连接，超时操作等供5个操作，该操作的实现类包括Req，Rep等具体Socket。该接口的目的是定义终端间发生操作时的行为。
Ctx是一个上下文类，通常一个终端只需要创建一个上下文。
IOObject本身并没有太多的属性，主要是其内维护了一个IOThread。
IOThread是用于处理命令的一个类，内部持有一个MailBox实例与Poller实例。
MailBox是一个重要的类，它被用作处理命令，包括命令的发送与接收，需要注意的是，这里的命令其实是本地发送，也就是自己跟自己发，而不是端点间发送。
Pipe用于处理接收到或者需要发送的数据，是实际存储待处理数据的数据结构，其内部是用队列的形式实现。
LB、FQ这两者在官方给出的全名是“LoadBalance”，“FairQueue”。也就是负载均衡与公平排队，分别用于处理要发送的数据与要接收的数据。
SocketBase是例如Req，Rep，Pull等包装后Socket的父类。其内含有一对Pipe（与SessionBase公用），用于在SocketBase与SessionBase之间传递消息，具体传递过程在接下去或说明。
SessionBase是创建SocketChannel并与目标终端进行连接的地方，是与底层Poller最先进行交互的一层。具有超时重连，断线重连等功能。
Poller是整个ZeroMQ的核心，它实现了命令的发送与接收，数据的发送与接收。由他来真正的发送数据到其他终端，也是他处理来自其他终端的数据后交给SessionBase。
基于此层级模型的交互逻辑：
发送消息
Socket -> Session -> StreamEngine -> Poller
接收消息
Poller -> StreamEngine -> Session -> Socket
4. 实现原理
这部分将说明从创建一个Socket开始到发送或者接收数据的整个过程，ZeroMQ内部的处理流程。不过我个人觉得先了解一些在底层的原理，对于整体的实现理解会有更好的帮助。
先看一下Poller的一些重要定义
<code class="language-java hljs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">PollSet</span> {</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">protected</span> IPollEvents handler; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//事件的回调 </span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">protected</span> SelectionKey key; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//注册之后的key </span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">protected</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> ops; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//注册的事件 </span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">protected</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> cancelled; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//是否已经取消 </span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">protected</span> <span class="hljs-title" style="box-sizing: border-box;">PollSet</span>(IPollEvents handler) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>.handler = handler;
key = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>;
cancelled = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>;
ops = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;
}
}
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> Map<SelectableChannel, PollSet> fd_table; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//记录所有的注册，key是channel </span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> retired; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//当前注册的对象是否有更新，如果有更新的话，在执行select之前需要先更新注册 </span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">volatile</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> stopping; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//如果是true的话，那么执行线程将会停止 </span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">volatile</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> stopped; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//是否已经停止 </span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> Thread worker; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//worker线程 </span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> Selector selector; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//selector </span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> String name; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//名字 </span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li></ul>PollerSet是Poller的一个嵌套类，所有需要注册到selector上的channel都会先构建这个对象，将其当做附件注册到selector上。其中handler是事件回调（一般是一个IOObject实例），key是selector注册后取得的key，ops是注册的事件类型
fd_table用于维护注册的channel对象与其的PollSet对象之间的映射关系。
retired用于标识当前的注册的channel什么的是否有更新，若是需要更新，则可能会重新生成key。
接下来来看看如何在poller对象上面注册channel吧，有几个比较重要的方法：
<code class="language-java hljs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//用于在当前的集合里面添加需要注册的channel，第一个参数是channel，第二个参数是事件回调 </span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">add_fd</span> (SelectableChannel fd_, IPollEvents events_) {
fd_table.put(fd_, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> PollSet(events_)); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//直接把放到map里面就好了 </span>
adjust_load (<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//增加load值，这里所谓的负载其实就是在当前poller里面注册的channel的数量 </span>
}
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//在key上面注册事件，如果negate为true的话，那么表示是取消事件 </span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">register</span> (SelectableChannel handle_, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> ops, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> negate) {
PollSet pollset = fd_table.get(handle_); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//获取pollset对象 </span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (negate) {
pollset.ops = pollset.ops &~ ops; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//取反，相当于取消事件 </span>
} <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> {
pollset.ops = pollset.ops | ops; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//注册事件 </span>
}
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (pollset.key != <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//如果有key了，那么表示已经注册到selector上面了，那么只需要更新key就好了 </span>
pollset.key.interestOps(pollset.ops);
} <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> {
retired = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>;
}
} </code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li></ul>可见在Poller里注册一个事件主要分为两步 1.放入map中 2.设置PollerSet的相应属性
Poller本身作为一个线程，来看看它的run方法
<code class="language-java hljs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">run</span> () {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> returnsImmediately = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">while</span> (!stopping) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">long</span> timeout = execute_timers (); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//执行所有的超时，并且获取下一个超时的时间 </span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (retired) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//这里表示注册的东西有更新 </span>
Iterator <Map.Entry <SelectableChannel,PollSet>> it = fd_table.entrySet ().iterator ();
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">while</span> (it.hasNext ()) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//遍历所有需要注册的 </span>
Map.Entry <SelectableChannel,PollSet> entry = it.next ();
SelectableChannel ch = entry.getKey (); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//获取channel </span>
PollSet pollset = entry.getValue (); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//获取pollset </span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (pollset.key == <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//这里没有key的话，表示当前channel并没有注册到selector上面去 </span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> {
pollset.key = ch.register(selector, pollset.ops, pollset.handler); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//注册 </span>
} <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span> (ClosedChannelException e) {
}
}
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (pollset.cancelled || !ch.isOpen()) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//如果是取消注册，那么直接取消掉就可以了 </span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span>(pollset.key != <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>) {
pollset.key.cancel();
}
it.remove ();
}
}
retired = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>;
}
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Wait for events. </span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> rc;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">long</span> start = System.currentTimeMillis (); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//select之前的时间 </span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> {
rc = selector.select (timeout);
} <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span> (IOException e) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throw</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> ZError.IOException (e);
}
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (rc == <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//出错啦，好像 </span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Guess JDK epoll bug </span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (timeout == <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> ||
System.currentTimeMillis () - start < timeout / <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>)
returnsImmediately ++;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span>
returnsImmediately = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (returnsImmediately > <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>) {
rebuildSelector (); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//重建selector </span>
returnsImmediately = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;
}
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">continue</span>;
}
Iterator<SelectionKey> it = selector.selectedKeys().iterator(); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//所有select出来的key </span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">while</span> (it.hasNext()) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//遍历 </span>
SelectionKey key = it.next();
IPollEvents evt = (IPollEvents) key.attachment();
it.remove();
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//接下来就是判断事件的类型执行相应的方法就好了 </span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (key.isReadable() ) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//有数据可以读取了 </span>
evt.in_event();
} <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (key.isAcceptable()) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//有新的连接进来了 </span>
evt.accept_event();
} <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (key.isConnectable()) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//连接建立 </span>
evt.connect_event();
}
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (key.isWritable()) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//可写 </span>
evt.out_event();
}
} <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span> (CancelledKeyException e) {
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// channel might have been closed </span>
}
}
}
stopped = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>;
} </code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li><li style="box-sizing: border-box; padding: 0px 5px;">55</li><li style="box-sizing: border-box; padding: 0px 5px;">56</li><li style="box-sizing: border-box; padding: 0px 5px;">57</li><li style="box-sizing: border-box; padding: 0px 5px;">58</li><li style="box-sizing: border-box; padding: 0px 5px;">59</li><li style="box-sizing: border-box; padding: 0px 5px;">60</li><li style="box-sizing: border-box; padding: 0px 5px;">61</li><li style="box-sizing: border-box; padding: 0px 5px;">62</li><li style="box-sizing: border-box; padding: 0px 5px;">63</li><li style="box-sizing: border-box; padding: 0px 5px;">64</li><li style="box-sizing: border-box; padding: 0px 5px;">65</li><li style="box-sizing: border-box; padding: 0px 5px;">66</li><li style="box-sizing: border-box; padding: 0px 5px;">67</li><li style="box-sizing: border-box; padding: 0px 5px;">68</li><li style="box-sizing: border-box; padding: 0px 5px;">69</li><li style="box-sizing: border-box; padding: 0px 5px;">70</li><li style="box-sizing: border-box; padding: 0px 5px;">71</li><li style="box-sizing: border-box; padding: 0px 5px;">72</li><li style="box-sizing: border-box; padding: 0px 5px;">73</li><li style="box-sizing: border-box; padding: 0px 5px;">74</li><li style="box-sizing: border-box; padding: 0px 5px;">75</li><li style="box-sizing: border-box; padding: 0px 5px;">76</li><li style="box-sizing: border-box; padding: 0px 5px;">77</li><li style="box-sizing: border-box; padding: 0px 5px;">78</li><li style="box-sizing: border-box; padding: 0px 5px;">79</li><li style="box-sizing: border-box; padding: 0px 5px;">80</li><li style="box-sizing: border-box; padding: 0px 5px;">81</li><li style="box-sizing: border-box; padding: 0px 5px;">82</li><li style="box-sizing: border-box; padding: 0px 5px;">83</li><li style="box-sizing: border-box; padding: 0px 5px;">84</li><li style="box-sizing: border-box; padding: 0px 5px;">85</li></ul>这部分还是好理解的，首先是检查fd_table是否需要更新，其实就是有没有新插入的channel或者有channel已经失效，由retired标志位决定。如果需要更新，遍历map中每个元素，检查PollerSet里的key，如果没有，则在Selector上进行注册。
然后调用selector.select()，若是有事件到来，根据其事件类型以及注册事件时一并传入的handle来决定执行何种操作。
简单来说Poller就是一个轮询器，我们在它的Selector上注册相应的channel与事件。而Poller定期扫描来捕获channel的状态。同时我们也了解到一点，Poller才是真正的IO线程持有者。
粗浅的说明了Poller之后，再来看看MailBox
同样，先是介绍一些重要的属性
<code class="language-java hljs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> YPipe<Command> cpipe; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//一个用来保存command的队列，内部以链表的形式实现 </span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> Signaler signaler; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//其实也是一个实现了一个SocketChannel，但是不对外发送消息，而是向Poller发送空白消息，以提醒command队列中有命令需要处理 </span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> Lock sync; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//只有一个线程从mailbox里面收命令，但是会有很多线程向mialbox里面发送命令，用这个锁来进行同步 </span> </code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li></ul>
<code class="language-java hljs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> SelectableChannel <span class="hljs-title" style="box-sizing: border-box;">get_fd</span> () {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> signaler.get_fd (); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//这里其实获取的是signal用到的pipe的读channel </span>
}
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//向当前的mailbox发送命令，其实就是写到command队列里面去而已 </span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">send</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> Command cmd_) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> ok = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>;
sync.lock ();
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> {
cpipe.write (cmd_, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>);
ok = cpipe.flush (); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//pipeflush，这里将会被selector感应到，从而可以执行相应的处理，在执行线程里面执行命令 </span>
} <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">finally</span> {
sync.unlock ();
}
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (!ok) {
signaler.send (); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//通过写端写数据，这样子的话会被读端收到 </span>
}
}
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//收取命令，如果这里无法立刻获取命令的话，还可以有一个超时时间 </span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> Command <span class="hljs-title" style="box-sizing: border-box;">recv</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">long</span> timeout_) {
Command cmd_ = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>;
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Try to get the command straight away. </span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (active) {
cmd_ = cpipe.read (); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//从队列里面获取命令 </span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (cmd_ != <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> cmd_;
}
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// If there are no more commands available, switch into passive state. </span>
active = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>;
signaler.recv (); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//这里会从读端不断的读数据 </span>
}
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Wait for signal from the command sender. </span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> rc = signaler.wait_event (timeout_);
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (!rc)
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>;
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// We've got the signal. Now we can switch into active state. </span>
active = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>;
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Get a command. </span>
cmd_ = cpipe.read ();
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">assert</span> (cmd_ != <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>);
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> cmd_;
} </code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li></ul>MailBox，就像之前说过的，只是用于处理命令的一个东西。命令的读写都是对本地的一个队列进行操作。需要注意的是在写命令与读命令之间需要有Signaler来充当信号通知者。
Signaler内部有一组变量：
<code class="language-java hljs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> Pipe.SinkChannel w; 数据写入端 <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> Pipe.SourceChannel r; 数据读取端</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li></ul>
将SourceChannel 注册到了poller内。 这样，当命令写入到队列中，会触发SinkChannel的write操作，通过SinkChannel向SourceChannel写数据，此时会被poller内的selector感知到。
由于IOThred在向poller注册时，传入的回调是“this”，也就是本身，在发生in_event(读事件)时，实际调用的时IOThread的in_event。
然后IOThread中的in_event从MailBox中读取数据，实质是从YPipe中读取command。
对于Signaler的作用，只是用于提醒poller有命令，它向SinkChannel内写入的数据其实是一个大小为1没有意义的ByteBuffer。只是用于触发在poller内注册的SourceChannel的Readable事件。
需要明确的是，command都是针对于本地的。不会在两台不同的机器间传送command，因为send_command并没有走socketchannel，所以不可能通过网络发送。
MailBox里面的逻辑大致就是如此：
1.命令写入YPipe
2.Signaler提醒Poller，激活in_event
3.MailBox从YPipe读取命令并执行
ok，一些基本的概念说的差不多了，接下来开始说明Socket的创建以及消息的发送过程。
<code class="language-java hljs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//这是一个创建上下文，Socket，与目标端进行连接，发送数据以及接收数据的客户端代码</span> Context context = ZMQ.context(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>); Socket worker = context.socket(ZMQ.REQ); worker.connect(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"tcp://localhost:5671"</span>); worker.send (<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Hi Boss"</span>); String workload = worker.recvStr (); Sysout.out.println(workload);</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li></ul>
1.创建上下文
<code class="language-java hljs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> List<SocketBase> sockets; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> Deque<Integer> empty_slots; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">volatile</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> starting; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> terminating; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> Lock slot_sync; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> Reaper reaper; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> List<IOThread> io_threads; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> slot_count; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> Mailbox[] slots; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> Mailbox term_mailbox; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> Lock endpoints_sync; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> AtomicInteger max_socket_id = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> AtomicInteger(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> max_sockets; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> io_thread_count; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> Lock opt_sync; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> term_tid = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> reaper_tid = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>; </code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li></ul>
上面给出了Ctx内的一些重要的成员变量，初始化过程中调用了init_ctx()，返回一个Ctx对象，此时仅仅只是对部分成员变量做了一个初始赋值，并没有特殊操作。
2.创建Socket
<code class="language-java hljs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//截取部分代码，基本上能表示整个过程</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (starting) {
starting = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>;
opt_sync.lock ();
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> mazmq = max_sockets;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> ios = io_thread_count;
opt_sync.unlock ();
slot_count = mazmq + ios + <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>;
slots = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Mailbox[slot_count];
slots [term_tid] = term_mailbox;
reaper = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Reaper (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>, reaper_tid);
slots [reaper_tid] = reaper.get_mailbox ();
reaper.start ();
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//以上部分创建的Reaper对象与两个MailBox是作用于上下文销毁的时候处理剩余消息以及释放占用资源。</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//下面是需要关注的部分，ios是在创建Ctx时我们指定需要创建的IO线程数，通常情况1个就足够了。根据我们指定的数量创建相应的IOThread，每个IOThread都有他子身的MailBox。</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> i = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>; i != ios + <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>; i++) {
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//创建IOThread对象的时候会创建一个Poller，以及一个MailBox,同时，将MailBox对应的Signaler的SourceChannel注册到Poller中以监听有无command需要执行。</span>
IOThread io_thread = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> IOThread (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>, i);
io_threads.add(io_thread);
slots [i] = io_thread.get_mailbox ();
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//启动Poller</span>
io_thread.start ();
}
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> i = (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span>) slot_count - <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>;
i >= (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span>) ios + <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>; i--) {
empty_slots.add (i);
slots [i] = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>;
}
}
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//以上为if部分，只会在Ctx已经创建好，第一次创建Socket会进入的分支，由于是第一次创建Socket，所以需要对一些Ctx成员进行初始化。而之后只需要创建每个Socket对应的IOThread以及必要属性即可。</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> slot = empty_slots.pollLast();
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> sid = max_socket_id.incrementAndGet();
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//这一步比较重要，先创建一个SocketBase，它是所有Socket的父类</span>
s = SocketBase.create (type_, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>, slot, sid);
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (s == <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>) {
empty_slots.addLast(slot);
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>;
}
sockets.add (s);
slots [slot] = s.get_mailbox ();</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li></ul>来看看SocketBase.create(type_,this,slot,sid)都做了些什么。
<code class="language-java hljs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//省略了部分操作，实际是先根据我们要创建的Socket类型调用构造函数，然后在构造函数中用super调用父类也就是SocketBase的构造函数...</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//给出部分重要成员</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> tag;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> ctx_terminated;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> destroyed;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> Mailbox mailbox;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> List<Pipe> pipes;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> Poller poller;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> SelectableChannel handle
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> SocketBase monitor_socket;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">protected</span> <span class="hljs-title" style="box-sizing: border-box;">SocketBase</span> (Ctx parent_, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> tid_, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> sid_)
{
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//调了ZObject的构造函数，因为ZObject是所有类的父类</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">super</span> (parent_, tid_);
tag = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0xbaddecaf</span>;
ctx_terminated = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>;
destroyed = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>;
last_tsc = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;
ticks = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;
rcvmore = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>;
monitor_socket = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>;
monitor_events = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;
options.socket_id = sid_;
endpoints = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> MultiMap<String, Own>();
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//这个pipes在后期会起到非常大的作用</span>
pipes = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> ArrayList<Pipe>();
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//创建了一个MailBox</span>
mailbox = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Mailbox(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"socket-"</span> + sid_);
errno = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> ValueReference<Integer>(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>);
...
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> s;
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li></ul>那到这里为止，我们已经获得了所需的Socket，但是需要注意的是现在只是获得Socket，但是该Socket还没有跟地址进行绑定或者链接。
现在说connect部分，这部分比较长，所以分开说明。
<code class="language-java hljs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//这里就是先去看看有没有需要执行的command，有的话先执行。这样做的目的应该是假如我们关闭了上下文，理论上来说是不再处理任何请求。但是关闭上下文也是一个动作，发出一个command，经过之前对MailBox的讲解，我们知道处理一个command其实是先放到一个队列中，等待Poller的信号在从队列中取出command然后执行。这样如果Poller要处理较多事件时，可能会推迟command的执行，个人认为在ZeroMQ中，command的优先级是大于消息的。所以基本在执行大部分动作前会先去看看队列中有没有待执行的command。以避免command等待过久而不执行的尴尬。</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> brc = process_commands (<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (!brc) <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>; ... <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//这里没什么需要特别说明的，我们知道终端url的形式是像tcp://192.168.1.1:8000 这样的形式存在的。所以这里做的只是获取IP，端口以及协议。</span> String protocol = uri.getScheme(); String address = uri.getAuthority(); String path = uri.getPath(); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (address == <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>) address = path; check_protocol (protocol); ... <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//创建一个与该Socket对应的Session，一个Socket可以绑定多个Session</span> SessionBase session = SessionBase.create (io_thread, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>, options, paddr);</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li></ul>
在SessionBase中才是发生SocketChannel对接的地方，下面来看看它做了些什么。
<code class="language-java hljs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//与SocketBase类似，也是进行了一些基本的初始化工作</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> connect;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> Pipe pipe;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> Set<Pipe> terminating_pipes;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> incomplete_in;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> pending;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> SocketBase socket;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> IOThread io_thread;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> identity_sent;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> identity_received;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> Address addr;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> IOObject io_object;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-title" style="box-sizing: border-box;">SessionBase</span>(IOThread io_thread_, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> connect_,
SocketBase socket_, Options options_, Address addr_) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">super</span>(io_thread_, options_);
io_object = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> IOObject(io_thread_);
connect = connect_;
pipe = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>;
incomplete_in = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>;
pending = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>;
engine = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>;
socket = socket_;
io_thread = io_thread_;
has_linger_timer = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>;
identity_sent = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>;
identity_received = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>;
addr = addr_;
terminating_pipes = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> HashSet <Pipe> ();
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li></ul>继续看connect的过程。
<code class="language-java hljs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">...
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (options.delay_attach_on_connect != <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> || icanhasall) {
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//这个parents在回收资源的时候起作用，维护层级关系</span>
ZObject[] parents = {<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>, session};
Pipe[] pipes = {<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>};
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//这是一个高水位线数组，由于Socket根据不同类型会存在发送缓冲区，接收缓冲区，或者一个公用缓冲区。虽然ZeroMQ没有持久化操作。但是比如Req套接字，如果在Rep建立连接前就发送消息，实质是不会发出去的，会先缓存在本地发送缓存区。同时，接收缓冲区也一样，如果收到消息还没来的及处理，就会一直对方在接收缓存区中。高水位线的作用就是给缓冲区定义一个大小，防止撑爆内存。</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span>[] hwms = {options.sndhwm, options.rcvhwm};
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span>[] delays = {options.delay_on_disconnect, options.delay_on_close};
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//OK，接下去的3步操作，直接为Socket与Session进行数据交互奠定了基础。我们仔细看下。</span>
Pipe.pipepair (parents, pipes, hwms, delays);
attach_pipe (pipes [<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>], icanhasall);
session.attach_pipe (pipes [<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>]);
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li></ul><code class="language-java hljs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">pipepair</span>(ZObject[] parents_, Pipe[] pipes_, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span>[] hwms_, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span>[] delays_) {
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//从以下代码可以看到一个数据结构，它创建了2个YPipe对象（实质就是链表），然后又创建了2个Pipe，一般的1个Pipe需要一个写端一个读端，在这里这两个Pipe公用了2个YPipe。</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//也就是说，现有2个Pipe，分别是A,B；2个YPipe，分别是Y1，Y2 。A,B公用Y1,Y2，Y1作为A的读端，作为B的写端；Y2作为B的读端，作为A的写端。结构图如下</span>
YPipe<Msg> upipe1 = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> YPipe<Msg>(Msg.class, Config.message_pipe_granularity.getValue());
YPipe<Msg> upipe2 = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> YPipe<Msg>(Msg.class, Config.message_pipe_granularity.getValue());
pipes_ [<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>] = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Pipe(parents_ [<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>], upipe1, upipe2,
hwms_ [<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>], hwms_ [<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>], delays_ [<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>]);
pipes_ [<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>] = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Pipe(parents_ [<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>], upipe2, upipe1,
hwms_ [<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>], hwms_ [<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>], delays_ [<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>]);
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//两个Pipe相互持有对方的引用 </span>
pipes_ [<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>].set_peer (pipes_ [<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>]);
pipes_ [<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>].set_peer (pipes_ [<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>]);
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li></ul>
继续看剩下的两个操作
<code class="language-java hljs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//这两部操作就比较好说，因为我们有2个Pipe，但最后是SocketBase持有一个Pipe，另一个由SessionBase持有。这样，SessionBase才能通过此与SocketBase进行数据交互，而实际上，发送数据或者接收数据就是通过这两个Pipe来流动的。</span> attach_pipe (pipes [<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>], icanhasall); session.attach_pipe (pipes [<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>]);</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul>
发送时，Pipe1通过LB向YPipe1写入要发送的数据，并发送read_activated命令，传入参数为Pipe2，SessionBase中其实持有的就是Pipe2，所以Pipe2从YPipe读取数据后由StreamEngine发送
接收时，StreamEngine将消息写会SessionBase的Pipe，也就是Pipe2，从Pipe2写入数据，其实是写入到YPipe2，然后通知SocketBase中的Pipe1，Pipe1从YPipe2读取数据
其实我觉得比如直接把Pipe设计成队列的形式，同样是两个Pipe，SocketBase与SessionBase同时持有双方引用，也能做到一样的功能，也许是因为这样做的话双方要维护的Pipe对的引用数会加倍，所以没有采用这种做法。
继续讲connect的最后一步。
<code class="language-java hljs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"> add_endpoint (addr_, session);
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//调用了 launch_child (endpoint_);方法</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">protected</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">launch_child</span> (Own object_)
{
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//这步是设置层级关系，回收资源时用到</span>
object_.set_owner (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>);
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//其实质就是发送了一个plug命令，因为传进来的object_是SessionBase，所以plug操作最后由SessionBase来完成。</span>
send_plug (object_);
send_own (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>, object_);
}
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//SessionBase中的process_plug操作</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">protected</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">process_plug</span> ()
{
io_object.set_handler(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>);
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (connect)
start_connecting (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>);
}
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//看到这里似乎要发现了连接操作将要执行的细节了。</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">start_connecting</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> wait_)
{
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">assert</span> (connect);
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">assert</span> (io_thread != <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>);
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Create the connecter object.</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (addr.protocol().equals(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"tcp"</span>)) {
TcpConnecter connecter = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> TcpConnecter (
io_thread, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>, options, addr, wait_);
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//alloc_assert (connecter);</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//没错，又是 launch_child，不过这次传进去的对象是上面创建的 TcpConnecter。同样的一会来看看 TcpConnecter里的process_plug操作。</span>
launch_child (connecter);
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span>;
}
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (addr.protocol().equals(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"ipc"</span>)) {
IpcConnecter connecter = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> IpcConnecter (
io_thread, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>, options, addr, wait_);
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//alloc_assert (connecter);</span>
launch_child (connecter);
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span>;
}
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">assert</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>);
}
</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li></ul>简要说明下TcpConnector的重要成员以及部分操作
<code class="language-java hljs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> reconnect_timer_id = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> IOObject io_object;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> Address addr;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> SocketChannel handle;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> handle_valid;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> delayed_start;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> timer_started;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> SessionBase session;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> current_reconnect_ivl;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> String endpoint;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> SocketBase socket;
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//观察下发现他持有一个SessionBase引用，以及含有IOThread的一个IOObject</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-title" style="box-sizing: border-box;">TcpConnecter</span> (IOThread io_thread_,
SessionBase session_, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> Options options_,
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> Address addr_, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> delayed_start_) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">super</span> (io_thread_, options_);
io_object = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> IOObject(io_thread_);
addr = addr_;
handle = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>;
handle_valid = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>;
delayed_start = delayed_start_;
timer_started = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>;
session = session_;
current_reconnect_ivl = options.reconnect_ivl;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">assert</span> (addr != <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>);
endpoint = addr.toString ();
socket = session_.get_soket ();
}
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//接下去，我们要来看TcpConnector里的process_plug</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">protected</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">process_plug</span> ()
{
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//设置了回调句柄为TcpConnector</span>
io_object.set_handler(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>);
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (delayed_start)
add_reconnect_timer();
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> {
start_connecting ();
}
}
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//开始进行Socket连接</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">start_connecting</span> ()
{
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> {
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//open()操作，执行真正的连接</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> rc = open ();
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (rc) {
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//若是连接成功，那该SocketChannel注册到Poller中</span>
io_object.add_fd (handle);
handle_valid = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>;
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//ok，这里不用说，实际上肯定是执行了事件回调，在之前的process_plug里看到， io_object.set_handler(this);说明在IOObject内的回调句柄就是该TcpConnector，所以这里执行的就是TcpConnector的connect_event()，具体执行在下面有所介绍。</span>
io_object.connect_event();
}
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> {
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//进入该分支那明显就是说明连接未成功，采取的策略是延迟一段时间后继续尝试连接。</span>
io_object.add_fd (handle);
handle_valid = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>;
io_object.set_pollconnect (handle);
socket.event_connect_delayed (endpoint, -<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>);
}
} <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span> (IOException e) {
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Handle any other error condition by eventual reconnect.</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (handle != <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>)
close ();
add_reconnect_timer();
}
}
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//到此，终于看到了真正的Socket连接</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> <span class="hljs-title" style="box-sizing: border-box;">open</span> () <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throws</span> IOException
{
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">assert</span> (handle == <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>);
handle = SocketChannel.open();
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//设置为非阻塞模式</span>
Utils.unblock_socket(handle);
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> rc = handle.connect(addr.resolved().address());
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> rc;
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li><li style="box-sizing: border-box; padding: 0px 5px;">55</li><li style="box-sizing: border-box; padding: 0px 5px;">56</li><li style="box-sizing: border-box; padding: 0px 5px;">57</li><li style="box-sizing: border-box; padding: 0px 5px;">58</li><li style="box-sizing: border-box; padding: 0px 5px;">59</li><li style="box-sizing: border-box; padding: 0px 5px;">60</li><li style="box-sizing: border-box; padding: 0px 5px;">61</li><li style="box-sizing: border-box; padding: 0px 5px;">62</li><li style="box-sizing: border-box; padding: 0px 5px;">63</li><li style="box-sizing: border-box; padding: 0px 5px;">64</li><li style="box-sizing: border-box; padding: 0px 5px;">65</li><li style="box-sizing: border-box; padding: 0px 5px;">66</li><li style="box-sizing: border-box; padding: 0px 5px;">67</li><li style="box-sizing: border-box; padding: 0px 5px;">68</li><li style="box-sizing: border-box; padding: 0px 5px;">69</li><li style="box-sizing: border-box; padding: 0px 5px;">70</li><li style="box-sizing: border-box; padding: 0px 5px;">71</li><li style="box-sizing: border-box; padding: 0px 5px;">72</li><li style="box-sizing: border-box; padding: 0px 5px;">73</li><li style="box-sizing: border-box; padding: 0px 5px;">74</li><li style="box-sizing: border-box; padding: 0px 5px;">75</li><li style="box-sizing: border-box; padding: 0px 5px;">76</li><li style="box-sizing: border-box; padding: 0px 5px;">77</li><li style="box-sizing: border-box; padding: 0px 5px;">78</li><li style="box-sizing: border-box; padding: 0px 5px;">79</li><li style="box-sizing: border-box; padding: 0px 5px;">80</li><li style="box-sizing: border-box; padding: 0px 5px;">81</li><li style="box-sizing: border-box; padding: 0px 5px;">82</li></ul><code class="language-java hljs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">这里说明下connect_event()
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">connect_event</span> ()
{
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> err = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>;
SocketChannel fd = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> {
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//确认连接是否完成，因为之前将SocketChannel设置成了非阻塞模式，所以我们并不知道连接是否已经成功建立。</span>
fd = connect ();
} <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span> (){
...
}
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//这里是将成功连接得到的SocketChannel从Poller中主注销，可能大家觉得奇怪，都成功连接了干啥要注销呢，因为之前注册的时候监听的是connect_event，现在既然成功连接了，当然不再需要监听connect_event了。</span>
io_object.rm_fd (handle);
handle_valid = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (err) {
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//这里做的是失败重连机制，具体做法是延迟再尝试，指数式延迟。比如第一次延迟2s，第二次延迟4s...</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//至于close()执行的目的，那肯定就是关闭由于之前成功连接所打开的一些资源。</span>
close ();
add_reconnect_timer();
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span>;
}
handle = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> {
Utils.tune_tcp_socket (fd);
Utils.tune_tcp_keepalives (fd, options.tcp_keepalive, options.tcp_keepalive_cnt, options.tcp_keepalive_idle, options.tcp_keepalive_intvl);
} <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span> (SocketException e) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throw</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> RuntimeException(e);
}
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//StreamEngine这个东西之前没有讲过，不过等下会细讲，它是位于Poller与SessionBase之间的一层，用于数据处理。</span>
StreamEngine engine = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> {
engine = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> StreamEngine (fd, options, endpoint);
} <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span> (ZError.InstantiationException e) {
socket.event_connect_delayed (endpoint, -<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>);
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span>;
}
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//上面提到了，StreamEngine是用于SessionBase与Poller之间的，那么需要将SessionBase与StreamEngine联系起来，两者才能进行交互</span>
send_attach (session, engine);
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//以下是清扫一些由于connect而留下的未释放的资源。</span>
terminate ();
socket.event_connected (endpoint, fd);
}
</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li></ul>ok，讲了很多，那到了这里，Socket的连接基本也就完成了。
回顾一下这个过程：
1. connect的动作最初是发生在SocketBase的
2. 在SocketBase中它创建了一个SessionBase与之对应
3. 同时创建了一对Pipe，SocketBase与SessionBase各持一个，用来在两者间进行数据交互。
4. 调用了SessionBase中的process_plug方法，创建一个TcpConnector用来将SocketChannel进行连接
5. 又调用了TcpConnector中的process_plug方法开始进行真正的连接
6. 在连接过程中我们看到，它将SocketChannel设置成了非阻塞模式，所以需要在后续检查连接是否完成，当然未完成时它也有重连策略（指数后退再重连）。
7. 连接成功后，注销在Poller中原有的SocketChannel，在重新注册一个，因为原先的SocketChannel监听connect事件。
8. 我们看到，在整个过程中MailBox起到了至关重要的部分，因为无论是plug或者是connect_event()，都是通过命令来执行的，而不是直接通过引用调用。
过程大致如上，再来说说这个StreamEngine，之前也没有讲到这个东西。
关于Poller，SessionBase与StreamEngine的交互（数据接收与发送的处理）
通过之前的了解，ZeroMQ自底向上的层级结构是这样的：底层–>Poller–>StreamEngine–>Session–>Socket–>应用程序
Poller与StreamEngine的关系相当于是Poller需要发送的数据是由StreamEngine进行编码处理的，Poller接收到的数据是由StreamEngine来解码处理的。
首先StreamEngine何时被创建？
上面说的Tcp连接过程中，讲到了超时重连机制。如果连接过程中，成功建立连接，则会先删除原先TcpConnector在Poller注册的channel，因为他只针对事件connect，成功建立连接后就没有用了。然后创建StreamEngine对象，没有其余步骤，只是初始化一些基本变量。
接下来是重点
需要将当前的Session与Engine相互联系，这样Engine接收到数据后处理好之后能放到Pipe中供session获取，发送也是同样道理，所以这里需要发送attach命令.命令发送的过程不再赘述，上面已经讲过了。
接收到attach命令后，由SessionBase的process_attach来负责处理，比较重要的是Engine中的plug方法，该方法的作用是将Engine插到Session中，但是比较好理解的说法就是讲Engine与Session相互联系起来，并且在Poller中进行注册。
向poller注册的过程就是用将从tcpconnector中成功连接所获取到的SocketChannel注册到Poller中，Engine本身作为回调方法，里面实现了in_event,out_event事件，到这里poller与Engine已经可以交互，poller在轮询发现有输入或者输出事件时，StreamEngine中的in_event,out_event会去处理。
简单来说
StreamEngine与SessionBase的交互，是将一个session赋值给StreamEngine中的SessionBase
StreamEngine与Poller的交互，是将从TcpConnector中成功连接返回的SocketChannel注册到Poller中，并将本身作为回调事件加入其中。
值得一提的是，在StreamEngine中调用plug方法时，不仅仅是连接SessionBase与Poller，也会发生一次“握手”。
那进行到这里，剩下的就是一个发送与接收的过程了。
关于发送过程，入口仍就是SocketBase的send。
代码也有点长，我们还是老办法，分开看。
<code class="language-java hljs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//public boolean send (Msg msg_, int flags_)这是方法名，Msg是消息载体，封装了要发送的消息。flags_是一个标志位，表示消息是由多段组成，合并后一起发送或者单独发送</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> <span class="hljs-title" style="box-sizing: border-box;">send</span> (Msg msg_, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> flags_)
{
...
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//之前怎么说的，命令的优先级大于消息，所以在类似发送消息，接收消息之前都会先去看下有没有命令要执行，主要防止一些例如销毁上下文之类的命令被延迟执行。</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> brc = process_commands (<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>);
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (!brc)
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>;
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//没啥意义，设置Msg的初始标志位</span>
msg_.reset_flags (Msg.more);
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> ((flags_ & ZMQ.ZMQ_SNDMORE) > <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>)
msg_.set_flags (Msg.more);
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 尝试发送消息，经过对ZeroMQ的命名方法的研究，发现带有x都是调用其具体实现类方法。</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> rc = xsend(msg_);</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li></ul>那就来看下具体是哪个子类来执行这个发送动作的
<code class="language-java hljs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">protected</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> <span class="hljs-title" style="box-sizing: border-box;">xsend</span>(Msg msg_)
{
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//lb就是之前说的LB（LoadBalanced 用来管理发送的消息的）</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> lb.send(msg_, errno);
}
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//Req的父类是Dealer</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//来看看LB的send</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> <span class="hljs-title" style="box-sizing: border-box;">send</span>(Msg msg_, ValueReference<Integer> errno) {
...
more = msg_.has_more();
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (!more) {
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//flush是对于发送消息的准备</span>
pipes.get(current).flush ();
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (active > <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>)
current = (current + <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>) % active;
}
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>;
}
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">flush</span> ()
{
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (state == State.terminating)
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span>;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (outpipe != <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span> && !outpipe.flush ()) {
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//发送了一个command，告知已经有准备好发送的数据，请读取</span>
send_activate_read (peer);
}
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li></ul>之前提过SessionBase与SocketBase通过一对Pipe来进行数据交互，那到这里，发送数据的过程也已经能看出个大概，首先就是将准备好的数据进行封包，Req需要一个身份帧，一个空帧，一个内容帧。然后将封包后的Msg写入SocketBase的Pipe，同时向Poller发送一个命令，告知在SocketBase端的Pipe中有可读消息需要发送。随即执行SessionBase的read_activated方法，目的是从Pipe中读出要发送的数据后发送出去。
<code class="language-java hljs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">read_activated</span>(Pipe pipe_)
{
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Skip activating if we're detaching this pipe</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (pipe != pipe_) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">assert</span> (terminating_pipes.contains (pipe_));
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span>;
}
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (engine != <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>)
engine.activate_out ();
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span>
pipe.check_read ();
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li></ul>之前也讲过真正的数据发送是发生在StreamEngine中的,那么需要来看下activate_out中发生了什么。
<code class="language-java hljs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">out_event</span> ()
{
...
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//通过SessionBase的Pipe从SocketBase的Pipe中读取数据</span>
outbuf = encoder.get_data (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>);
outsize = outbuf.remaining();
...
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//发送数据</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> nbytes = write (outbuf);
...
}
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> <span class="hljs-title" style="box-sizing: border-box;">write</span> (Transfer buf)
{
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> nbytes = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> ;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> {
nbytes = buf.transferTo(handle);
} <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span> (IOException e) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> -<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>;
}
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> nbytes;
}
<span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> <span class="hljs-title" style="box-sizing: border-box;">transferTo</span> (WritableByteChannel s) <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throws</span> IOException {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> s.write (buf);
}
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//那看到这里我们已经看到了真正的发送过程，读取数据后，直接通过WritableByteChannel来想连接节点发送消息。</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li></ul>接收过程类似于发送过程，Poller轮询器里注册的channel监听到有事件发生，由于之前channel向selector注册的时候携带的附件基本都是一个IOObject对象，所以从IOObject对象开始逐层向内执行in_event()，最终到了StreamEngine中。
<code class="language-java hljs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> <span class="hljs-title" style="box-sizing: border-box;">read</span> (ByteBuffer buf)
{
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> nbytes = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> ;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> {
nbytes = handle.read (buf);
} <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span> (IOException e) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> -<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>;
}
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> nbytes;
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li></ul>在StreamEngine中的in_event()中通过一个read方法将其读到ByteBuffer中，然后解码后放到SessionBase的Pipe中。SocketBase通过他持有的Pipe来获取SessionBase中Pipe的数据，并最终返回给客户端。
对发送与接收部分的小结：
StreamEngine中的in_event与out_event两个方法，这两个方法是真正读，写数据的地方，抛开一些列数据长度的检查，ByteBuffer的设置填充等，
最终的就是调用了SocketChannel的read与write方法。
但是经过观察，似乎Poller轮询是如果isWriteable为true，走out_event方法时，只有在StreamEngine发送握手信息时才会发生。而其余，无论是客户端发送或者接收信息，走的都是Poller中的isReadable下的in_event。原因之后进行说明。
上面说到客户端的读写在Poller走的都是in_event。
读很好理解，另一个端点直接通过SocketChannel,write一个消息过来，因为我们的SocketChannel在Poller中注册了，所以自然就比较能检测到isReadable信号，从而进入in_event
但是写的话，由于我们表面上的写操作并不是直接通过SocketChannel来发送消息，而是先将要发送的消息放到Pipe中（其实就是放到一个队列中），然后由之前提过的Signaler发出一个activate_read信号，也就是告诉主机本地有需要发送的消息，请从Pipe中读取。上面也提过，Signaler的消息是通过SinkChannel发送的，对应的SourceChannel在Poller中也注册了。
如此，Poller轮询到一个读事件，促发in_event，IOThread从MailBox中读取命令后发现是activate_read命令，触发read_activated事件，该事件由SessionBase开始传播，最终传到StreamEngine中的activate_out事件，由该事件来执行out_event,来真正完成发送数据的过程。
就整个实现过程进行一个小总结
1.MailBox是核心组件，所有所有动作包括读，写最终都要通过命令传递，才会发生我们预期中的操作
2.命令的优先级高于消息，明显的在读写操作前都会先去读MailBox中有没有命令需要执行
3.Socket连接方式采用非阻塞模式，具有断线重连，超时重连的功能，重连方式是以指数退步的方式进行
4.纵观全局，其实所有的内容都包装在了一个IOObject中，所以层级拆分时还是比较容易的
5.整个消息组件用了大量的事件回调，几乎所有的动作都是通过时间回掉来完成的
6.整个发送或者或者接收过程，就像是有消息要发送，先发个命令到MailBox，读取命令后执行具体操作。有消息要接收，先发个命令到MailBox，读取命令后执行具体操作。
5. 核心特点
1.嵌入式消息组件
与rabbitMQ，ActiveMQ有很大的不同，如果说rabbitMQ已经近乎是一个小型操作系统，那么ZeroMQ就像是一个嵌入在操作系统内的一个组件，说白了ZeroMQ就是一组jar包，直接嵌入到项目中就可以运行，它不需要一台独立的服务器来承载整个消息系统。
ZeroMQ关注的不是消息的可靠送达，而是着眼于端到端的发送，接收…它希望的是尽快完成任务，而不介意部分消息的丢失。
但这也并不是说他完全没有持久化的功能，ZeroMQ是具有一定的本地持久化的功能的，但是能保存的数据量比较有限，而且是暂存于内存中的。
2.高的离谱的吞吐量
这是网上找到的一张关于MQ的性能分析的图表
显示的是每秒钟发送和接受的消息数。整个过程共产生1百万条1K的消息，测试环境为Windows Vista。从测试数据可以看出，ZeroMQ的性能远远高于其它3个MQ。或者说ZeroMQ与其他3各MQ根本就不再一个量级上比较合适。
至于这样的原因跟ZeroMQ的定位，以及对消息的处理方式有很大关联。
ZeroMQ对于消息的处理可以说除却请求-应答模式之外，基本就是不关系消息是否丢失，它只管发送。
ZeroMQ的定位，它的创始人一直在其社区表示，团队将立志于把ZeroMQ融入到Linux内核中去。
基于以上两点，高效的处理速度就成了它必不可少的特点之一。
3. 无锁队列与异步模式
之前我们提到了SessionBase与SocketBase之间通过一对Pipe来完成数据交互，在这对Pipe的内部持有的是YPipe的实例，YPipe本质上的实现是一个队列，而且还是一个采用无锁CAS技术的队列。我截出部分代码，供大家参考：
<code class="language-java hljs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> <span class="hljs-title" style="box-sizing: border-box;">flush</span> ()
{
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// If there are no un-flushed items, do nothing.</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (w == f) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>;
}
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Try to set 'c' to 'f'.</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (!c.compareAndSet(w, f)) {
c.set (f);
w = f;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>;
}
w = f;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>;
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li></ul>类似于这样的操作在YPipe中还有不少。
还是Pipe，我们知道Pipe有一个读端一个写端，这两端均在Poller中注册了异步事件，在该Pipe上发生读写操作时就会触发相应的具体读写事件实现方法。这样的做法提高的程序的响应速度。但是缺点是除非明确在Poller中注册的对象到底是什么，否则比较难判断出将要执行的回调事件将在哪里发生，比如同样是in_event()，IOObject实现了，SocketBase实现了，SessionBase也实现了，如果我们不知道注册时传入的handle是什么，判断起来就有些繁琐了。
4.多核下的线程绑定
传统的多线程并发模式一般会采用锁，临界区，信号量等技术来控制，而ZeroMQ给出的建议是：在创建IO时不要超出CPU核数。
当我们创建一个上下文时都会有这么一句代码“Context context = ZMQ.context(1);”这里就指定了IO线程数。通常来说一个线程足矣。但是如果希望创建多个IO线程，最好不要超出CPU核数，因为此时ZeroMQ会将工作线程其实就是那个Poller绑定到每一个核，免除了线程上下文切换带来的开销。
6. 与其他MQ的对比
关于ZeroMQ与其他几个MQ之间的比较，我们在TPS，并发性，持久化，技术点以及扩展性这几个方面进行展开。1.TPS
之前提过，这里在说一下。
显示的是每秒钟发送和接受的消息数。整个过程共产生1百万条1K的消息，测试环境为Windows Vista。
明显的ZeroMQ最好，其余三者差不多。
2.持久化消息比较
ZeroMq原生是不支持的，仅支持相当有限的本地缓存，如需要消息持久化需要自己进行扩展。
ActiveMq和rabbitMq都支持。
3.并发性
虽然ZeroMQ在高并发环境下不会出问题，但是有可能会导致本地的缓存区被塞满而导致消息丢失的情况。所以不推荐在并发量较高的情境下使用ZeroMQ.
查了下资料发现，ActiveMQ在发送到queue的消息并发较多时，消费端只能接收一部分，比如100条消息在较短的时间内发入，总有10来条接收不到，存放在服务器上，而且这些消息一直不能主动发送出来，后面继续进入的消息都能正常处理，最终只有重新启动服务消费端才能接收到那部分剩下的消息。
而RabbitMQ，从实现语言来看，它是并发性最好的，原因是它的实现语言是天生具备高并发高可用的erlang语言。
4.技术点以及扩展性
ok，首先就扩展性而言，那毫无疑问的是ZeroMQ最强，其余其中MQ都已经是成形的产品，已经是一款应用程序了。而ZeroMQ说白了就是一组库函数。基于这种情况，我们可以按自己的需要实现IPollEvent以及ZObject来开发适合自己的Socket组件，至于它对于消息持久化的不支持，只是原生不支持，因为它的定位不是吃保证可靠的消息传输。所以在可靠性这部分我们完全可以按自己的需求进行扩展。一组lib的扩展度明显是宽于产品级的rabbitMQ之类的产品。
技术上虽然ZeroMQ立志于成为Linux内核的消息组件，但是不得不说它的开源社区活跃度是远远不及RabbitMQ或者ActiveMQ。或许是处于它的可靠性考虑，它的应用场景比较受限制。
可靠性上虽然ActiveMQ也具备，只是性能上相比于RabbitMQ还是有一定差距，所以大部分的MQ选型都是RabbitMQ。
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