MIT 2012 分布式课程基础源码解析-底层通讯实现

本节内容和前节事件管理封装是息息相关的，本节内容主要包含的代码在connection{.h, .cc}中。

这里面最主要的有两个类:connection类和tcpsconn类，connetion类主要服务于单个套接字，包括套接字上的数据读取写入等，而tcpsconn类则是服务于套接字集合，如接收连接，更新失效套接字等。具体我们看头文件。

<span style="color: #0000ff;">class</span><span style="color: #000000;"> chanmgr {
    </span><span style="color: #0000ff;">public</span><span style="color: #000000;">:
        </span><span style="color: #0000ff;">virtual</span> <span style="color: #0000ff;">bool</span> got_pdu(connection *c, <span style="color: #0000ff;">char</span> *b, <span style="color: #0000ff;">int</span> sz) = <span style="color: #800080;">0</span><span style="color: #000000;">;
        </span><span style="color: #0000ff;">virtual</span> ~<span style="color: #000000;">chanmgr() {}
};</span>

我们首先看到的是这个虚基类类，这个类会以委托的形式用在connection和tcpsconn类中，它只有一个方法即got_pdu，它在RPC实现中扮演着重要角色，后面使用的时候会再次介绍它。

connection类

<span style="color: #008080;"> 1</span> <span style="color: #0000ff;">class</span> connection : <span style="color: #0000ff;">public</span><span style="color: #000000;"> aio_callback {
</span><span style="color: #008080;"> 2</span>     <span style="color: #0000ff;">public</span><span style="color: #000000;">:
</span><span style="color: #008080;"> 3</span>         <span style="color: #008000;">//</span><span style="color: #008000;">内部buffer类，主要用于接收/写入数据的buffer</span>
<span style="color: #008080;"> 4</span>         <span style="color: #0000ff;">struct</span><span style="color: #000000;"> charbuf {
</span><span style="color: #008080;"> 5</span>             charbuf(): buf(NULL), sz(<span style="color: #800080;">0</span>), solong(<span style="color: #800080;">0</span><span style="color: #000000;">) {}
</span><span style="color: #008080;"> 6</span>             charbuf (<span style="color: #0000ff;">char</span> *b, <span style="color: #0000ff;">int</span> s) : buf(b), sz(s), solong(<span style="color: #800080;">0</span><span style="color: #000000;">){}
</span><span style="color: #008080;"> 7</span>             <span style="color: #0000ff;">char</span> *<span style="color: #000000;">buf;
</span><span style="color: #008080;"> 8</span>             <span style="color: #0000ff;">int</span><span style="color: #000000;"> sz;
</span><span style="color: #008080;"> 9</span>             <span style="color: #0000ff;">int</span> solong; <span style="color: #008000;">//</span><span style="color: #008000;">amount of bytes written or read so far</span>
<span style="color: #008080;">10</span> <span style="color: #000000;">        };
</span><span style="color: #008080;">11</span>         <span style="color: #008000;">//</span><span style="color: #008000;">m1: chanmgr, f1: socket or file, </span>
<span style="color: #008080;">12</span>         connection(chanmgr *m1, <span style="color: #0000ff;">int</span> f1, <span style="color: #0000ff;">int</span> lossytest=<span style="color: #800080;">0</span><span style="color: #000000;">);
</span><span style="color: #008080;">13</span>         ~<span style="color: #000000;">connection();
</span><span style="color: #008080;">14</span> 
<span style="color: #008080;">15</span>         <span style="color: #0000ff;">int</span> channo() { <span style="color: #0000ff;">return</span><span style="color: #000000;"> fd_; }
</span><span style="color: #008080;">16</span>         <span style="color: #0000ff;">bool</span><span style="color: #000000;"> isdead();
</span><span style="color: #008080;">17</span>         <span style="color: #0000ff;">void</span><span style="color: #000000;"> closeconn();
</span><span style="color: #008080;">18</span> 
<span style="color: #008080;">19</span>         <span style="color: #0000ff;">bool</span> send(<span style="color: #0000ff;">char</span> *b, <span style="color: #0000ff;">int</span><span style="color: #000000;"> sz);
</span><span style="color: #008080;">20</span>         <span style="color: #0000ff;">void</span> write_cb(<span style="color: #0000ff;">int</span><span style="color: #000000;"> s);
</span><span style="color: #008080;">21</span>         <span style="color: #0000ff;">void</span> read_cb(<span style="color: #0000ff;">int</span><span style="color: #000000;"> s);
</span><span style="color: #008080;">22</span>         <span style="color: #008000;">//</span><span style="color: #008000;">增加/减少引用计数</span>
<span style="color: #008080;">23</span>         <span style="color: #0000ff;">void</span><span style="color: #000000;"> incref();
</span><span style="color: #008080;">24</span>         <span style="color: #0000ff;">void</span><span style="color: #000000;"> decref();
</span><span style="color: #008080;">25</span>         <span style="color: #0000ff;">int</span> <span style="color: #0000ff;">ref</span><span style="color: #000000;">();
</span><span style="color: #008080;">26</span>                 
<span style="color: #008080;">27</span>         <span style="color: #0000ff;">int</span> compare(connection *<span style="color: #000000;">another);
</span><span style="color: #008080;">28</span>     <span style="color: #0000ff;">private</span><span style="color: #000000;">:
</span><span style="color: #008080;">29</span> 
<span style="color: #008080;">30</span>         <span style="color: #0000ff;">bool</span><span style="color: #000000;"> readpdu();
</span><span style="color: #008080;">31</span>         <span style="color: #0000ff;">bool</span><span style="color: #000000;"> writepdu();
</span><span style="color: #008080;">32</span> 
<span style="color: #008080;">33</span>         chanmgr *<span style="color: #000000;">mgr_;
</span><span style="color: #008080;">34</span>         <span style="color: #0000ff;">const</span> <span style="color: #0000ff;">int</span><span style="color: #000000;"> fd_;
</span><span style="color: #008080;">35</span>         <span style="color: #0000ff;">bool</span><span style="color: #000000;"> dead_;
</span><span style="color: #008080;">36</span> 
<span style="color: #008080;">37</span>         charbuf wpdu_; <span style="color: #008000;">//</span><span style="color: #008000;">write pdu</span>
<span style="color: #008080;">38</span>         charbuf rpdu_; <span style="color: #008000;">//</span><span style="color: #008000;">read pdu</span>
<span style="color: #008080;">39</span>                 
<span style="color: #008080;">40</span>         <span style="color: #0000ff;">struct</span><span style="color: #000000;"> timeval create_time_;
</span><span style="color: #008080;">41</span> 
<span style="color: #008080;">42</span>         <span style="color: #0000ff;">int</span><span style="color: #000000;"> waiters_;
</span><span style="color: #008080;">43</span>         <span style="color: #0000ff;">int</span><span style="color: #000000;"> refno_;
</span><span style="color: #008080;">44</span>         <span style="color: #0000ff;">const</span> <span style="color: #0000ff;">int</span><span style="color: #000000;"> lossy_;
</span><span style="color: #008080;">45</span> 
<span style="color: #008080;">46</span> <span style="color: #000000;">        pthread_mutex_t m_;
</span><span style="color: #008080;">47</span>         pthread_mutex_t ref_m_; <span style="color: #008000;">//</span><span style="color: #008000;">保护更新引用计数的安全性</span>
<span style="color: #008080;">48</span> <span style="color: #000000;">        pthread_cond_t send_complete_;
</span><span style="color: #008080;">49</span> <span style="color: #000000;">        pthread_cond_t send_wait_;
</span><span style="color: #008080;">50</span> };

View Code

这段代码即是connetion类的定义，它继承至aio_callback，在上一节说过，aio_callback在事件管理类中作为回调类，读取或写入数据，现在connection类就相当于一个回调类。

我们从connection的构造函数中便可以得知。

connection::connection(chanmgr *m1, <span style="color: #0000ff;">int</span> f1, <span style="color: #0000ff;">int</span><span style="color: #000000;"> l1) 
: mgr_(m1), fd_(f1), dead_(</span><span style="color: #0000ff;">false</span>),waiters_(<span style="color: #800080;">0</span>), refno_(<span style="color: #800080;">1</span><span style="color: #000000;">),lossy_(l1)
{

    </span><span style="color: #0000ff;">int</span> flags =<span style="color: #000000;"> fcntl(fd_, F_GETFL, NULL);
    flags </span>|= O_NONBLOCK;  <span style="color: #008000;">//</span><span style="color: #008000;">no blocking</span>
<span style="color: #000000;">    fcntl(fd_, F_SETFL, flags);
    </span><span style="color: #008000;">//</span><span style="color: #008000;">ignore信号</span>
<span style="color: #000000;">    signal(SIGPIPE, SIG_IGN);
    VERIFY(pthread_mutex_init(</span>&m_,<span style="color: #800080;">0</span>)==<span style="color: #800080;">0</span><span style="color: #000000;">);
    VERIFY(pthread_mutex_init(</span>&ref_m_,<span style="color: #800080;">0</span>)==<span style="color: #800080;">0</span><span style="color: #000000;">);
    VERIFY(pthread_cond_init(</span>&send_wait_,<span style="color: #800080;">0</span>)==<span style="color: #800080;">0</span><span style="color: #000000;">);
    VERIFY(pthread_cond_init(</span>&send_complete_,<span style="color: #800080;">0</span>)==<span style="color: #800080;">0</span><span style="color: #000000;">);
 
       VERIFY(gettimeofday(</span>&create_time_, NULL) == <span style="color: #800080;">0</span><span style="color: #000000;">); 
       </span><span style="color: #008000;">//</span><span style="color: #008000;">事件管理类将本类作为回调类添加到相应的事件管理数组中</span>
    PollMgr::Instance()->add_callback(fd_, CB_RDONLY, <span style="color: #0000ff;">this</span><span style="color: #000000;">);
}</span>

 那这个类的具体作用是啥呢？其实它就是用于在给定套接字上通信用的，对于发送数据，会发送直到数据发送完成为止，未发送完成则会将该事件添加到事件管理中，在下一轮事件循环中继续发送，这一点我们可以从send函数中看出：

<span style="color: #0000ff;">bool</span><span style="color: #000000;">
connection::send(</span><span style="color: #0000ff;">char</span> *b, <span style="color: #0000ff;">int</span><span style="color: #000000;"> sz)
{
    ScopedLock ml(</span>&<span style="color: #000000;">m_);
    waiters_</span>++<span style="color: #000000;">;
    </span><span style="color: #008000;">//</span><span style="color: #008000;">当活着，且write pdu中还有数据时等待数据清空(发送完)</span>
    <span style="color: #0000ff;">while</span> (!dead_ &&<span style="color: #000000;"> wpdu_.buf) {
        VERIFY(pthread_cond_wait(</span>&send_wait_, &m_)==<span style="color: #800080;">0</span><span style="color: #000000;">);
    }
    waiters_</span>--<span style="color: #000000;">;
    </span><span style="color: #0000ff;">if</span><span style="color: #000000;"> (dead_) {
        </span><span style="color: #0000ff;">return</span> <span style="color: #0000ff;">false</span><span style="color: #000000;">;
    }
    wpdu_.buf </span>=<span style="color: #000000;"> b;
    wpdu_.sz </span>=<span style="color: #000000;"> sz;
    wpdu_.solong </span>= <span style="color: #800080;">0</span><span style="color: #000000;">;

    </span><span style="color: #0000ff;">if</span><span style="color: #000000;"> (lossy_) {
        </span><span style="color: #0000ff;">if</span> ((random()%<span style="color: #800080;">100</span>)  lossy_) {
            jsl_log(JSL_DBG_1, <span style="color: #800000;">"</span><span style="color: #800000;">connection::send LOSSY TEST shutdown fd_ %d\n</span><span style="color: #800000;">"</span><span style="color: #000000;">, fd_);
            shutdown(fd_,SHUT_RDWR);
        }
    }

    </span><span style="color: #008000;">//</span><span style="color: #008000;">发送失败时</span>
    <span style="color: #0000ff;">if</span> (!<span style="color: #000000;">writepdu()) {
        dead_ </span>= <span style="color: #0000ff;">true</span><span style="color: #000000;">;
        VERIFY(pthread_mutex_unlock(</span>&m_) == <span style="color: #800080;">0</span><span style="color: #000000;">);
        PollMgr::Instance()</span>-><span style="color: #000000;">block_remove_fd(fd_);
        VERIFY(pthread_mutex_lock(</span>&m_) == <span style="color: #800080;">0</span><span style="color: #000000;">);
    }</span><span style="color: #0000ff;">else</span><span style="color: #000000;">{
        </span><span style="color: #0000ff;">if</span> (wpdu_.solong ==<span style="color: #000000;"> wpdu_.sz) {
        }</span><span style="color: #0000ff;">else</span><span style="color: #000000;">{
            </span><span style="color: #008000;">//</span><span style="color: #008000;">should be rare to need to explicitly add write callback
            </span><span style="color: #008000;">//</span><span style="color: #008000;">这会继续写，因为这会添加本类（回调），然后调用里面的回调函数write_cb,
            </span><span style="color: #008000;">//</span><span style="color: #008000;">就像是一个递归</span>
            PollMgr::Instance()->add_callback(fd_, CB_WRONLY, <span style="color: #0000ff;">this</span><span style="color: #000000;">); 
            </span><span style="color: #0000ff;">while</span> (!dead_ && wpdu_.solong >= <span style="color: #800080;">0</span> && wpdu_.solong  wpdu_.sz) {
                VERIFY(pthread_cond_wait(&send_complete_,&m_) == <span style="color: #800080;">0</span><span style="color: #000000;">);
            }
        }
    }
    </span><span style="color: #008000;">//</span><span style="color: #008000;">清空写buffer</span>
    <span style="color: #0000ff;">bool</span> ret = (!dead_ && wpdu_.solong ==<span style="color: #000000;"> wpdu_.sz);
    wpdu_.solong </span>= wpdu_.sz = <span style="color: #800080;">0</span><span style="color: #000000;">;
    wpdu_.buf </span>=<span style="color: #000000;"> NULL;
    </span><span style="color: #0000ff;">if</span> (waiters_ > <span style="color: #800080;">0</span><span style="color: #000000;">)
        pthread_cond_broadcast(</span>&send_wait_);  <span style="color: #008000;">//</span><span style="color: #008000;">唤醒上面的等待</span>
    <span style="color: #0000ff;">return</span><span style="color: #000000;"> ret;
}</span>

send

对于读取数据，则当rpdu_（read buffer）未满时继续读，读取完成后就是用chanmgr类的got_pdu处理读取后的数据。

注意发送数据/接收数据都会首先发送数据大小/接收数据大小，然后再做后续发送数据/接收数据的工作。

除了connection类的发送/接收数据的功能外，我们还看到一个私有变量refno_变量，该变量的作用是用于引用计数，引用计数是一种很常见的编程技巧，例如在python中，引用计数用于对象的管理，当引用计数为0时，对象便会销毁，这里的引用计数也是也是同样的道理，这一点可以从decref函数中得知

<span style="color: #0000ff;">void</span><span style="color: #000000;">
connection::decref()
{
    VERIFY(pthread_mutex_lock(</span>&ref_m_)==<span style="color: #800080;">0</span><span style="color: #000000;">);
    refno_ </span>--<span style="color: #000000;">;
    VERIFY(refno_</span>>=<span style="color: #800080;">0</span><span style="color: #000000;">);
    </span><span style="color: #008000;">//</span><span style="color: #008000;">当引用计数为0时，销毁对象</span>
    <span style="color: #0000ff;">if</span> (refno_==<span style="color: #800080;">0</span><span style="color: #000000;">) {
        VERIFY(pthread_mutex_lock(</span>&m_)==<span style="color: #800080;">0</span><span style="color: #000000;">);
        </span><span style="color: #0000ff;">if</span><span style="color: #000000;"> (dead_) {
            VERIFY(pthread_mutex_unlock(</span>&ref_m_)==<span style="color: #800080;">0</span><span style="color: #000000;">);
            VERIFY(pthread_mutex_unlock(</span>&m_)==<span style="color: #800080;">0</span><span style="color: #000000;">);
            </span><span style="color: #0000ff;">delete</span> <span style="color: #0000ff;">this</span><span style="color: #000000;">;
            </span><span style="color: #0000ff;">return</span><span style="color: #000000;">;
        }
        VERIFY(pthread_mutex_unlock(</span>&m_)==<span style="color: #800080;">0</span><span style="color: #000000;">);
    }
    pthread_mutex_unlock(</span>&<span style="color: #000000;">ref_m_);
}</span>

tcpscon类：

这个类则是用于管理connection的，我们先看它的定义

<span style="color: #008000;">/*</span><span style="color: #008000;">*
 *  管理客户连接，将连接放入一个map中map<int connection>
 *
 </int></span><span style="color: #008000;">*/</span>
<span style="color: #0000ff;">class</span><span style="color: #000000;"> tcpsconn {
    </span><span style="color: #0000ff;">public</span><span style="color: #000000;">:
        tcpsconn(chanmgr </span>*m1, <span style="color: #0000ff;">int</span> port, <span style="color: #0000ff;">int</span> lossytest=<span style="color: #800080;">0</span><span style="color: #000000;">);
        </span>~<span style="color: #000000;">tcpsconn();

        </span><span style="color: #0000ff;">void</span><span style="color: #000000;"> accept_conn();
    </span><span style="color: #0000ff;">private</span><span style="color: #000000;">:

        pthread_mutex_t m_;
        pthread_t th_;
        </span><span style="color: #0000ff;">int</span> pipe_[<span style="color: #800080;">2</span><span style="color: #000000;">];

        </span><span style="color: #0000ff;">int</span> tcp_; <span style="color: #008000;">//</span><span style="color: #008000;">file desciptor for accepting connection</span>
        chanmgr *<span style="color: #000000;">mgr_;
        </span><span style="color: #0000ff;">int</span><span style="color: #000000;"> lossy_;
        std::map</span>int, connection *><span style="color: #000000;"> conns_;

        </span><span style="color: #0000ff;">void</span><span style="color: #000000;"> process_accept();
};</span>

可看到里面定义了一个map，该map的key其实是connection类指针对应的套接字，我们看构造函数实现

tcpsconn::tcpsconn(chanmgr *m1, <span style="color: #0000ff;">int</span> port, <span style="color: #0000ff;">int</span><span style="color: #000000;"> lossytest) 
: mgr_(m1), lossy_(lossytest)
{

    VERIFY(pthread_mutex_init(</span>&m_,NULL) == <span style="color: #800080;">0</span><span style="color: #000000;">);

    </span><span style="color: #0000ff;">struct</span><span style="color: #000000;"> sockaddr_in sin;
    memset(</span>&sin, <span style="color: #800080;">0</span>, <span style="color: #0000ff;">sizeof</span><span style="color: #000000;">(sin));
    sin.sin_family </span>=<span style="color: #000000;"> AF_INET;
    sin.sin_port </span>=<span style="color: #000000;"> htons(port);

    tcp_ </span>= socket(AF_INET, SOCK_STREAM, <span style="color: #800080;">0</span><span style="color: #000000;">);
    </span><span style="color: #0000ff;">if</span>(tcp_ 0<span style="color: #000000;">){
        perror(</span><span style="color: #800000;">"</span><span style="color: #800000;">tcpsconn::tcpsconn accept_loop socket:</span><span style="color: #800000;">"</span><span style="color: #000000;">);
        VERIFY(</span><span style="color: #800080;">0</span><span style="color: #000000;">);
    }

    </span><span style="color: #0000ff;">int</span> yes = <span style="color: #800080;">1</span><span style="color: #000000;">;
    </span><span style="color: #008000;">//</span><span style="color: #008000;">设置TCP参数， reuseaddr, nodelay</span>
    setsockopt(tcp_, SOL_SOCKET, SO_REUSEADDR, &yes, <span style="color: #0000ff;">sizeof</span><span style="color: #000000;">(yes));
    setsockopt(tcp_, IPPROTO_TCP, TCP_NODELAY, </span>&yes, <span style="color: #0000ff;">sizeof</span><span style="color: #000000;">(yes));

    </span><span style="color: #0000ff;">if</span>(bind(tcp_, (sockaddr *)&sin, <span style="color: #0000ff;">sizeof</span>(sin)) 0<span style="color: #000000;">){
        perror(</span><span style="color: #800000;">"</span><span style="color: #800000;">accept_loop tcp bind:</span><span style="color: #800000;">"</span><span style="color: #000000;">);
        VERIFY(</span><span style="color: #800080;">0</span><span style="color: #000000;">);
    }

    </span><span style="color: #0000ff;">if</span>(listen(tcp_, <span style="color: #800080;">1000</span>) 0<span style="color: #000000;">) {
        perror(</span><span style="color: #800000;">"</span><span style="color: #800000;">tcpsconn::tcpsconn listen:</span><span style="color: #800000;">"</span><span style="color: #000000;">);
        VERIFY(</span><span style="color: #800080;">0</span><span style="color: #000000;">);
    }

    jsl_log(JSL_DBG_2, </span><span style="color: #800000;">"</span><span style="color: #800000;">tcpsconn::tcpsconn listen on %d %d\n</span><span style="color: #800000;">"</span><span style="color: #000000;">, port, 
        sin.sin_port);

    </span><span style="color: #0000ff;">if</span> (pipe(pipe_) 0<span style="color: #000000;">) {
        perror(</span><span style="color: #800000;">"</span><span style="color: #800000;">accept_loop pipe:</span><span style="color: #800000;">"</span><span style="color: #000000;">);
        VERIFY(</span><span style="color: #800080;">0</span><span style="color: #000000;">);
    }

    </span><span style="color: #0000ff;">int</span> flags = fcntl(pipe_[<span style="color: #800080;">0</span><span style="color: #000000;">], F_GETFL, NULL);
    flags </span>|=<span style="color: #000000;"> O_NONBLOCK;
    fcntl(pipe_[</span><span style="color: #800080;">0</span>], F_SETFL, flags);  <span style="color: #008000;">//</span><span style="color: #008000;">无阻塞管道</span>
<span style="color: #000000;">
    VERIFY((th_ </span>= method_thread(<span style="color: #0000ff;">this</span>, <span style="color: #0000ff;">false</span>, &tcpsconn::accept_conn)) != <span style="color: #800080;">0</span><span style="color: #000000;">); 
}</span>

View Code

该构造函数主要是初始化服务器端连接，然后创建一个线程来等待客户端的连接，后面处理客户端连接时，会将连接的客户端套接字添加到conns_的map中，即创建套接字到connection指针的对应关系，然后遍历conns_，清除死亡的connection，从而达到及时处理死亡连接的效果。