Tomcat NIO源代码分析(一) -- Acceptor

当Tomcat配置成使用NIO时，启动过程其实和过去差不多，也是Connector#startInternal -> Protocol(Http11NioProtocol)#start() -> Endpoint(NioEndPoint)#start()的过程，这里主要看一下NioEndPoint：

 1      public   void  start()  throws  Exception  {
 2          //  初始化
 3          if  ( ! initialized)  {
 4             init();
 5         }
 6          if  ( ! running)  {
 7             running  =   true ;
 8             paused  =   false ;
 9
10              //  创建一个ThreadPoolExecutor对象，和JDK里的功能一样，只不过进行了一些扩展
11              if  (getExecutor()  ==   null )  {
12                 createExecutor();
13             }
14
15              //  开启poll的线程
16             pollers  =   new  Poller[getPollerThreadCount()];
17              for  ( int  i  =   0 ; i  <  pollers.length; i ++ )  {
18                 pollers[i]  =   new  Poller();
19                 Thread pollerThread  =   new  Thread(pollers[i], getName()  +   " -ClientPoller- "   +  i);
20                 pollerThread.setPriority(threadPriority);
21                 pollerThread.setDaemon( true );
22                 pollerThread.start();
23             }
24
25              //  开启Acceptor的线程
26              for  ( int  i  =   0 ; i  <  acceptorThreadCount; i ++ )  {
27                 Thread acceptorThread  =   new  Thread( new  Acceptor(), getName()  +   " -Acceptor- "   +  i);
28                 acceptorThread.setPriority(threadPriority);
29                 acceptorThread.setDaemon(getDaemon());
30                 acceptorThread.start();
31             }
32         }
33     }

这里先看一下init()方法，没有全列出来，最主要的一点就是初始化ServerSocketChannel：

 1      public   void  init()  throws  Exception  {
 2
 3          if  (initialized)
 4              return ;
 5
 6          //  初始化ServerSocketChannel，这里用的是阻塞的方式，没有用Selector
 7         serverSock  =  ServerSocketChannel.open();
 8         socketProperties.setProperties(serverSock.socket());
 9         InetSocketAddress addr  =  (getAddress()  !=   null   ?   new  InetSocketAddress(getAddress(), getPort())
10                 :  new  InetSocketAddress(getPort()));
11         serverSock.socket().bind(addr, getBacklog());
12         serverSock.configureBlocking( true );  //  mimic APR behavior
13         serverSock.socket().setSoTimeout(getSocketProperties().getSoTimeout());
14
15         ......
16
17     }

Tomcat每种Endpoint的Acceptor线程其实作用都一样，对来访的请求进行最初的处理之用，NioEndpoint的Acceptor也不例外，它内部也只定义一个继承自Runnable的方法

 1          public   void  run()  {
 2              while  (running)  {
 3                 
 4                  while  (paused  &&  running)  {
 5                      try   {
 6                         Thread.sleep( 1000 );
 7                     }   catch  (InterruptedException e)  {
 8                          //  Ignore
 9                     }
10                 }
11
12                  if  ( ! running)  {
13                      break ;
14                 }
15                  try   {
16              //  接受请求
17                     SocketChannel socket  =  serverSock.accept();
18                      if  ( running  &&  ( ! paused)  &&  socket  !=   null  )  {
19                          //  将SocketChannel给pollor处理
20                          if  ( ! setSocketOptions(socket))  {
21                              try   {
22                                 socket.socket().close();
23                                 socket.close();
24                             }   catch  (IOException ix)  {
25                                  if  (log.isDebugEnabled())
26                                     log.debug( "" , ix);
27                             }
28                         }  
29                     }
30                 }   catch  (SocketTimeoutException sx)  {
31                      // normal condition
32                 }   catch  (IOException x)  {
33                      if  (running)  {
34                         log.error(sm.getString( " endpoint.accept.fail " ), x);
35                     }
36                 }   catch  (OutOfMemoryError oom)  {
37                      try   {
38                         oomParachuteData  =   null ;
39                         releaseCaches();
40                         log.error( "" , oom);
41                     } catch  ( Throwable oomt )  {
42                          try   {
43                              try   {
44                                 System.err.println(oomParachuteMsg);
45                                 oomt.printStackTrace();
46                             } catch  (Throwable letsHopeWeDontGetHere) {
47                                 ExceptionUtils.handleThrowable(letsHopeWeDontGetHere);
48                             }
49                         } catch  (Throwable letsHopeWeDontGetHere) {
50                             ExceptionUtils.handleThrowable(letsHopeWeDontGetHere);
51                         }
52                     }
53                 }   catch  (Throwable t)  {
54                     ExceptionUtils.handleThrowable(t);
55                     log.error(sm.getString( " endpoint.accept.fail " ), t);
56                 }
57             }
58         }
59     }

方法其实挺容易理解，就是得到请求用的SocketChannel后交给Poller处理，这里poll是一个UNIX的系统调用名字，Java开发者可 以google下，我也是才准备开始啃《UNIX网络编程》，闲言少叙，看一下#setSocketOptions()方法吧：

 1      protected   boolean  setSocketOptions(SocketChannel socket)  {
 2          //  Process the connection
 3          try   {
 4              //  disable blocking, APR style, we are gonna be polling it
 5              //  这里终于看到了印象中的NIO的影子了
 6             socket.configureBlocking( false );
 7             Socket sock  =  socket.socket();
 8             socketProperties.setProperties(sock);
 9
10              //  NioChannel是ByteChannel的子类
11              //  从队列里取出第一个可用的Channel，这样的话NioChannel应该是设计成非GC的
12              //  感觉其目的主要是对SocketChannel进行下封装
13             NioChannel channel  =  nioChannels.poll();
14              if  (channel  ==   null )  {
15                  //  不过这里如果没有可用的就初始化一个的话请求数陡然增高再慢慢回落的时候不就浪费了内存了吗？
16                  //  NioBufferHandler里分别分配了读缓冲区和写缓冲区
17                  //  SSL setup
18                  if  (sslContext  !=   null )  {
19                     SSLEngine engine  =  createSSLEngine();
20                      int  appbufsize  =  engine.getSession().getApplicationBufferSize();
21                     NioBufferHandler bufhandler  =   new  NioBufferHandler(Math.max(appbufsize,
22                             socketProperties.getAppReadBufSize()), Math.max(appbufsize,
23                             socketProperties.getAppWriteBufSize()), socketProperties.getDirectBuffer());
24                     channel  =   new  SecureNioChannel(socket, engine, bufhandler, selectorPool);
25                 }   else   {
26                      //  normal tcp setup
27                     NioBufferHandler bufhandler  =   new  NioBufferHandler(socketProperties.getAppReadBufSize(),
28                             socketProperties.getAppWriteBufSize(), socketProperties.getDirectBuffer());
29
30                     channel  =   new  NioChannel(socket, bufhandler);
31                 }
32             }   else   {
33                  //  这里就是对Channel的重用了
34                 channel.setIOChannel(socket);
35                  if  (channel  instanceof  SecureNioChannel)  {
36                     SSLEngine engine  =  createSSLEngine();
37                     ((SecureNioChannel) channel).reset(engine);
38                 }   else   {
39                     channel.reset();
40                 }
41             }
42              //  这里就是将SocketChannel注册到Poller了。
43              //  getPoller0用的循环的方式来返回Poller，即Poller 1, 2, 3 ... n 然后再回到1, 2, 3.
44             getPoller0().register(channel);
45         }   catch  (Throwable t)  {
46             ExceptionUtils.handleThrowable(t);
47