Tomcat NIO源代码分析(二) -- Poller

接着上面的流程，现在请求到了Poller的#register()方法。

     public   void  register( final  NioChannel socket)  {
        socket.setPoller( this );
         //  KeyAttachment是对NioChannel信息的包装，同样是非GC
        KeyAttachment key  =  keyCache.poll();
         final  KeyAttachment ka  =  key  !=   null   ?  key :  new  KeyAttachment(socket);
        ka.reset( this , socket, getSocketProperties().getSoTimeout());
        ka.setKeepAliveLeft(NioEndpoint. this .getMaxKeepAliveRequests());
        
         //  PollerEvent的初始化，非GC Again
        PollerEvent r  =  eventCache.poll();
         //  this is what OP_REGISTER turns into.
         //  读取数据的事件
        ka.interestOps(SelectionKey.OP_READ);
         if  (r  ==   null )
            r  =   new  PollerEvent(socket, ka, OP_REGISTER);
         else
            r.reset(socket, ka, OP_REGISTER);
        
         //  把事件加到Poller
        addEvent(r);
    }

     public   void  addEvent(Runnable event)  {
         //  把事件加入到队列中
        events.offer(event);
         //  ++wakeupCounter
         if  (wakeupCounter.incrementAndGet()  ==   0 ) selector.wakeup();
    }

其实也挺好懂的，就是把NioChannel作为OP_REGISTER事件注册到Poller，这样在Poller的#run()方法中就可以对加入Poller的事件进行处理了。

     public   void  run()  {
         while  (running)  {
             try   {
                 while  (paused  &&  ( ! close))  {
                     try   {
                        Thread.sleep( 100 );
                    }   catch  (InterruptedException e)  {
                         //  Ignore
                    }
                }
                 boolean  hasEvents  =   false ;

                hasEvents  =  (hasEvents  |  events());
                 //  Time to terminate?
                 if  (close)  {
                    timeout( 0 ,  false );
                     break ;
                }
                 try   {
                     if  ( ! close)  {
                         if  (wakeupCounter.get()  >   0 )  {
                             //  立刻返回 I/O 就绪的那些通道的键
                            keyCount  =  selector.selectNow();
                        }   else   {
                            keyCount  =  selector.keys().size();
                             //  这里把wakeupCounter设成-1，在addEvent的时候就会唤醒selector
                            wakeupCounter.set( - 1 );
                             //  使用阻塞的方式
                            keyCount  =  selector.select(selectorTimeout);
                        }
                        wakeupCounter.set( 0 );
                    }
                     if  (close)  {
                        timeout( 0 ,  false );
                        selector.close();
                         break ;
                    }
                }   catch  (NullPointerException x)  {
                     //  sun bug 5076772 on windows JDK 1.5
                     if  (log.isDebugEnabled())
                        log.debug( " Possibly encountered sun bug 5076772 on windows JDK 1.5 " , x);
                     if  (wakeupCounter  ==   null   ||  selector  ==   null )
                         throw  x;
                     continue ;
                }   catch  (CancelledKeyException x)  {
                     //  sun bug 5076772 on windows JDK 1.5
                     if  (log.isDebugEnabled())
                        log.debug( " Possibly encountered sun bug 5076772 on windows JDK 1.5 " , x);
                     if  (wakeupCounter  ==   null   ||  selector  ==   null )
                         throw  x;
                     continue ;
                }   catch  (Throwable x)  {
                    ExceptionUtils.handleThrowable(x);
                    log.error( "" , x);
                     continue ;
                }
                 //  either we timed out or we woke up, process events first
                 if  (keyCount  ==   0 )
                    hasEvents  =  (hasEvents  |  events());

                Iterator < SelectionKey >  iterator  =  keyCount  >   0   ?  selector.selectedKeys().iterator()
                        :  null ;
                 //  Walk through the collection of ready keys and dispatch
                 //  any active event.
                 while  (iterator  !=   null   &&  iterator.hasNext())  {
                    SelectionKey sk  =  iterator.next();
                     //  这里的KeyAttachment实在#register()方法中注册的
                    KeyAttachment attachment  =  (KeyAttachment) sk.attachment();
                    attachment.access();
                    iterator.remove();
                     //  继续流程
                    processKey(sk, attachment);
                } //  while

                 //  process timeouts
                timeout(keyCount, hasEvents);
                 if  (oomParachute  >   0   &&  oomParachuteData  ==   null )
                    checkParachute();
            }   catch  (OutOfMemoryError oom)  {
                 try   {
                    oomParachuteData  =   null ;
                    releaseCaches();
                    log.error( "" , oom);
                }   catch  (Throwable oomt)  {
                     try   {
                        System.err.println(oomParachuteMsg);
                        oomt.printStackTrace();
                    }   catch  (Throwable letsHopeWeDontGetHere)  {
                        ExceptionUtils.handleThrowable(letsHopeWeDontGetHere);
                    }
                }
            }
        } //  while
         synchronized  ( this )  {
             this .notifyAll();
        }
        stopLatch.countDown();

    }

这个方法有2个方法需要关注一下：#events()和#processKey()：

     public   boolean  events()  {
         boolean  result  =   false ;
         //  synchronized (events) {
        Runnable r  =   null ;
         //  返回是事件队列中是否有事件
        result  =  (events.size()  >   0 );
         while  ((r  =  events.poll())  !=   null )  {
             try   {
                 //  执行KeyEvent的#run()
                r.run();
                 if  (r  instanceof  PollerEvent)  {
                    ((PollerEvent) r).reset();
                     //  对KeyEvent进行回收
                    eventCache.offer((PollerEvent) r);
                }
            }   catch  (Throwable x)  {
                log.error( "" , x);
            }
        }
         //  events.clear();
         //  }
         return  result;
    }

这里执行了SocketChannel对应的KeyEvent的#run()方法，在这个方法里给SocketChannel注册了OP_READ：

     public   void  run()  {
         if  (interestOps  ==  OP_REGISTER)  {
             try   {
                 //  给SocketChannel注册OP_READ
                socket.getIOChannel().register(socket.getPoller().getSelector(), SelectionKey.OP_READ,
                        key);
            }   catch  (Exception x)  {
                log.error( "" , x);
            }
        }   else   {
             //  这里应该是对comet进行支持的，暂时先不看

            ......

        } //  end if
    } //  run

第二个是#processKey()方法，里边的很多流程我现在不是很关心，都略去了，

     protected   boolean  processKey(SelectionKey sk, KeyAttachment attachment)  {
         boolean  result  =   true ;
         try   {
             if  (close)  {
                cancelledKey(sk, SocketStatus.STOP,  false );
            }   else   if  (sk.isValid()  &&  attachment  !=   null )  {
                attachment.access(); //  make sure we don't time out valid sockets
                sk.attach(attachment); //  cant remember why this is here
                NioChannel channel  =  attachment.getChannel();
                 if  (sk.isReadable()  ||  sk.isWritable())  {
                     if  (attachment.getSendfileData()  !=   null )  {
                        processSendfile(sk, attachment,  true ,  false );
                    }   else   if  (attachment.getComet())  { //  这里应该是对comet的支持
                        ......
                    }   else   {
                         //  这个分支是现在比较关心的
                         if  (isWorkerAvailable())  { //  这个好像还没实现
                             //  这个#unreg()很巧妙，防止了通道对同一个事件不断select的问题
                            unreg(sk, attachment, sk.readyOps());
                             boolean  close  =  ( ! processSocket(channel,  null ,  true ));
                             color: #000

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• 2010-12-27 13:52
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