Mina 抽象polling监听器

Mina Io监听器接口定义及抽象实现：http://donald-draper.iteye.com/blog/2378315
引言：
    IoAcceptor与IoService不同的是，添加了监听连接请求和地址绑定功能。抽象Io监听器AbstractIoAcceptor绑定地址首先要检查绑定的socket地址与传输元数据的地址类型是否相同，相同则通过bindInternal完成实际的绑定，然后通知Service监听器，Service已激活fireServiceActivated。解绑地址方法，主要是委托unbind0方法完成实际解绑工作，清空绑定地址集合boundAddresses，触发Service监听器无效事件fireServiceDeactivated。

/**
 * A base class for implementing transport using a polling strategy. The
 * underlying sockets will be checked in an active loop and woke up when an
 * socket needed to be processed. This class handle the logic behind binding,
 * accepting and disposing the server sockets. An {@link Executor} will be used
 * for running client accepting and an {@link AbstractPollingIoProcessor} will
 * be used for processing client I/O operations like reading, writing and
 * closing.
 * AbstractPollingIoAcceptor为传输层拉取策略的基本实现。底层socket将在一个循环中检查，连接请求事件，当一个以个socket连接请求时，唤醒监听器线程，处理连接请求。此类处理地址绑定，接收连接请求，释放server socket。一个执行器将会运行接收客户端连接，AbstractPollingIoProcessor将用于处理客户端的IO操作事件。
 * All the low level methods for binding, accepting, closing need to be provided
 * by the subclassing implementation.
 * 
 * @see NioSocketAcceptor for a example of implementation
 * @param <H> The type of IoHandler
 * @param <S> The type of IoSession
 * 
 * @author [url=http://mina.apache.org]Apache MINA Project[/url]
 */
public abstract class AbstractPollingIoAcceptor<S extends AbstractIoSession, H> extends AbstractIoAcceptor {
    /** A lock used to protect the selector to be waked up before it's created */
    //信号量用于在选择器被创建前，保护选择器被唤醒
    private final Semaphore lock = new Semaphore(1);
    private final IoProcessor<S> processor;//Io处理器
    private final boolean createdProcessor;//Io处理器是否创建
    //地址绑定请求队列，地址绑定时，添加绑定请求AcceptorOperationFuture到队列
    private final Queue<AcceptorOperationFuture> registerQueue = new ConcurrentLinkedQueue<>();
    //解绑队列，解绑地址时，添加地址解绑请求AcceptorOperationFuture到队列
    private final Queue<AcceptorOperationFuture> cancelQueue = new ConcurrentLinkedQueue<>();
    //监听器绑定的socket地址，与ServerSocketChannel映射关系
    //绑定地址后，添加地址与ServerSocketChannel映射关系到boundHandles
    private final Map<SocketAddress, H> boundHandles = Collections.synchronizedMap(new HashMap<SocketAddress, H>());
    private final ServiceOperationFuture disposalFuture = new ServiceOperationFuture();//Service关闭结果
    /** A flag set when the acceptor has been created and initialized */
    private volatile boolean selectable;//当acceptor创建和初始化设置
    /** The thread responsible of accepting incoming requests 监听连接请求线程Acceptor*/
    private AtomicReference<Acceptor> acceptorRef = new AtomicReference<>();
    protected boolean reuseAddress = false;//地址是否重用
    /**
     * Define the number of socket that can wait to be accepted. Default
     * to 50 (as in the SocketServer default).
     SocketServer默认可以接收的连接数。
     */
    protected int backlog = 50;
 }

来看AbstractPollingIoAcceptor的构造:
    

/**
     * Constructor for {@link AbstractPollingIoAcceptor}. You need to provide a default
     * session configuration, a class of {@link IoProcessor} which will be instantiated in a
     * {@link SimpleIoProcessorPool} for better scaling in multiprocessor systems. The default
     * pool size will be used.
     * 构造AbstractPollingIoAcceptor，需要提供默认的会话配置，在IO简单处理器线程池当中，执行的Io处理器类型。
     默认的线程池大小将会被使用
     * @see SimpleIoProcessorPool
     * 
     * @param sessionConfig
     *            the default configuration for the managed {@link IoSession}
     * @param processorClass a {@link Class} of {@link IoProcessor} for the associated {@link IoSession}
     *            type.
     */
    protected AbstractPollingIoAcceptor(IoSessionConfig sessionConfig, Class<? extends IoProcessor<S>> processorClass) {
        this(sessionConfig, null, new SimpleIoProcessorPool<S>(processorClass), true, null);
    }

    /**
     * Constructor for {@link AbstractPollingIoAcceptor}. You need to provide a default
     * session configuration, a class of {@link IoProcessor} which will be instantiated in a
     * {@link SimpleIoProcessorPool} for using multiple thread for better scaling in multiprocessor
     * systems.
     * 与上面的方法不同的时，指定Io处理器线程池大小，即Io处理器的个数。
     * @see SimpleIoProcessorPool
     * 
     * @param sessionConfig
     *            the default configuration for the managed {@link IoSession}
     * @param processorClass a {@link Class} of {@link IoProcessor} for the associated {@link IoSession}
     *            type.
     * @param processorCount the amount of processor to instantiate for the pool
     */
    protected AbstractPollingIoAcceptor(IoSessionConfig sessionConfig, Class<? extends IoProcessor<S>> processorClass,
            int processorCount) {
        this(sessionConfig, null, new SimpleIoProcessorPool<S>(processorClass, processorCount), true, null);
    }

    /**
     * Constructor for {@link AbstractPollingIoAcceptor}. You need to provide a default
     * session configuration, a class of {@link IoProcessor} which will be instantiated in a
     * {@link SimpleIoProcessorPool} for using multiple thread for better scaling in multiprocessor
     * systems.
     *与上面不同的时，多个一个选择器提供者参数
     * @see SimpleIoProcessorPool
     *
     * @param sessionConfig
     *            the default configuration for the managed {@link IoSession}
     * @param processorClass a {@link Class} of {@link IoProcessor} for the associated {@link IoSession}
     *            type.
     * @param processorCount the amount of processor to instantiate for the pool
     * @param selectorProvider The SelectorProvider to use
     */
    protected AbstractPollingIoAcceptor(IoSessionConfig sessionConfig, Class<? extends IoProcessor<S>> processorClass,
            int processorCount, SelectorProvider selectorProvider ) {
        this(sessionConfig, null, new SimpleIoProcessorPool<S>(processorClass, processorCount, selectorProvider), true, selectorProvider);
    }

    /**
     * Constructor for {@link AbstractPollingIoAcceptor}. You need to provide a default
     * session configuration, a default {@link Executor} will be created using
     * {@link Executors#newCachedThreadPool()}.
     * 此方法的Io处理器执行器，为 Executors#newCachedThreadPool
     * @see AbstractIoService
     * 
     * @param sessionConfig
     *            the default configuration for the managed {@link IoSession}
     * @param processor the {@link IoProcessor} for processing the {@link IoSession} of this transport, triggering
     *            events to the bound {@link IoHandler} and processing the chains of {@link IoFilter}
     */
    protected AbstractPollingIoAcceptor(IoSessionConfig sessionConfig, IoProcessor<S> processor) {
        this(sessionConfig, null, processor, false, null);
    }

    /**
     * Constructor for {@link AbstractPollingIoAcceptor}. You need to provide a
     * default session configuration and an {@link Executor} for handling I/O
     * events. If a null {@link Executor} is provided, a default one will be
     * created using {@link Executors#newCachedThreadPool()}.
     * 如果线程池为空，默认为Executors#newCachedThreadPool
     * @see AbstractIoService#AbstractIoService(IoSessionConfig, Executor)
     * 
     * @param sessionConfig
     *            the default configuration for the managed {@link IoSession}
     * @param executor
     *            the {@link Executor} used for handling asynchronous execution
     *            of I/O events. Can be <code>null</code>.
     * @param processor
     *            the {@link IoProcessor} for processing the {@link IoSession}
     *            of this transport, triggering events to the bound
     *            {@link IoHandler} and processing the chains of
     *            {@link IoFilter}
     */
    protected AbstractPollingIoAcceptor(IoSessionConfig sessionConfig, Executor executor, IoProcessor<S> processor) {
        this(sessionConfig, executor, processor, false, null);
    }

    /**
     * Constructor for {@link AbstractPollingIoAcceptor}. You need to provide a
     * default session configuration and an {@link Executor} for handling I/O
     * events. If a null {@link Executor} is provided, a default one will be
     * created using {@link Executors#newCachedThreadPool()}.
     * 这个就是最终的构造方法了。
     * @see #AbstractIoService(IoSessionConfig, Executor)
     * 
     * @param sessionConfig 默认会话配置
     *            the default configuration for the managed {@link IoSession}
     * @param executor 异步IO事件执行器
     *            the {@link Executor} used for handling asynchronous execution
     *            of I/O events. Can be <code>null</code>.
     * @param processor 会话处理器器，触发IoHander和过滤器的相关事件
     *            the {@link IoProcessor} for processing the {@link IoSession}
     *            of this transport, triggering events to the bound
     *            {@link IoHandler} and processing the chains of
     *            {@link IoFilter}
     * @param createdProcessor
     *            tagging the processor as automatically created, so it will be
     *            automatically disposed
     */
    private AbstractPollingIoAcceptor(IoSessionConfig sessionConfig, Executor executor, IoProcessor<S> processor,
            boolean createdProcessor, SelectorProvider selectorProvider) {
        super(sessionConfig, executor);
        if (processor == null) {
            throw new IllegalArgumentException("processor");
        }
        this.processor = processor;
        this.createdProcessor = createdProcessor;
        try {
            // Initialize the selector
            init(selectorProvider);初始化选择器
            // The selector is now ready, we can switch the
            // flag to true so that incoming connection can be accepted
            selectable = true;
        } catch (RuntimeException e) {
            throw e;
        } catch (Exception e) {
            throw new RuntimeIoException("Failed to initialize.", e);
        } finally {
            if (!selectable) {
                try {
                    destroy();
                } catch (Exception e) {
                    ExceptionMonitor.getInstance().exceptionCaught(e);
                }
            }
        }
    }

  /**
     * Initialize the polling system, will be called at construction time.
     * 
     * @param selectorProvider The Selector Provider that will be used by this polling acceptor
     * @throws Exception any exception thrown by the underlying system calls
     */
    protected abstract void init(SelectorProvider selectorProvider) throws Exception;

从上面来看，构造AbstractPollingIoAcceptor，主要是初始化会话配置，Io处理器类型，IO异步事件执行器为空的话默认为CachedThreadPool，然后初始化选择器。
再来看其他方法:

  

 /**
     * Initialize the polling system, will be called at construction time.
     * @throws Exception any exception thrown by the underlying system calls
     初始化拉取系统，在构造是调用
     */
    protected abstract void init() throws Exception;

  
    /**
     * Destroy the polling system, will be called when this {@link IoAcceptor}
     * implementation will be disposed.
     销毁拉取系统，在IO监听器销毁时，调用
     * @throws Exception any exception thrown by the underlying systems calls
     */
    protected abstract void destroy() throws Exception;

    /**
     * Check for acceptable connections, interrupt when at least a server is ready for accepting.
     * All the ready server socket descriptors need to be returned by {@link #selectedHandles()}
     检查已接收的连接，当至少有一个准备好接收时，中断。所有的就绪serversocket描述符需要通过
     #selectedHandles方法返回
     * @return The number of sockets having got incoming client 接收的客户端连接数
     * @throws Exception any exception thrown by the underlying systems calls
     */
    protected abstract int select() throws Exception;

    /**
     * Interrupt the {@link #select()} method. Used when the poll set need to be modified.
     唤醒，选择操作。当poll及修改时
     */
    protected abstract void wakeup();

    /**
     * {@link Iterator} for the set of server sockets found with acceptable incoming connections
     *  during the last {@link #select()} call.
     返回在上一次选择操作中，服务端接收连接数
     * @return the list of server handles ready
     */
    protected abstract Iterator<H> selectedHandles();
    
    /**
     * Open a server socket for a given local address.
     打开一个给定socket地址的serversocket
     * @param localAddress the associated local address
     * @return the opened server socket
     * @throws Exception any exception thrown by the underlying systems calls
     */
    protected abstract H open(SocketAddress localAddress) throws Exception;

    /**
     * Get the local address associated with a given server socket
     获取给定serversocket的本地地址
     * @param handle the server socket
     * @return the local {@link SocketAddress} associated with this handle
     * @throws Exception any exception thrown by the underlying systems calls
     */
    protected abstract SocketAddress localAddress(H handle) throws Exception;

    /**
     * Accept a client connection for a server socket and return a new {@link IoSession}
     * associated with the given {@link IoProcessor}
     serversocket接收一个客户端连接请求，返回一个关联指定IO处理器的会话。
     * @param processor the {@link IoProcessor} to associate with the {@link IoSession}
     * @param handle the server handle
     * @return the created {@link IoSession}
     * @throws Exception any exception thrown by the underlying systems calls
     */
    protected abstract S accept(IoProcessor<S> processor, H handle) throws Exception;

    /**
     * Close a server socket. 关闭一个serversocket
     * @param handle the server socket
     * @throws Exception any exception thrown by the underlying systems calls
     */
    protected abstract void close(H handle) throws Exception;

再来绑定socket地址：

/**
 * {@inheritDoc}
 */
@Override
protected final Set<SocketAddress> bindInternal(List<? extends SocketAddress> localAddresses) throws Exception {
    // Create a bind request as a Future operation. When the selector
    // have handled the registration, it will signal this future.
    //创建绑定操作结果。当选择器处理注册时，将会通知操作结果。
    AcceptorOperationFuture request = new AcceptorOperationFuture(localAddresses);
    // adds the Registration request to the queue for the Workers
    // to handle 注册请求到注册队列，以便工作线程处理
    registerQueue.add(request);

    // creates the Acceptor instance and has the local
    // executor kick it off.
    //创建监听器实例，本地执行器将会执行实例
    startupAcceptor();

    // As we just started the acceptor, we have to unblock the select()
    // in order to process the bind request we just have added to the
    // registerQueue.
    //由于我们刚启动监听器，不得不unblock选择操作，处理刚刚添加到注册队列的绑定请求
    try {
        lock.acquire();

        wakeup();
    } finally {
        lock.release();
    }

    // Now, we wait until this request is completed.
    request.awaitUninterruptibly();

    if (request.getException() != null) {
        throw request.getException();
    }
    // Update the local addresses.
    // setLocalAddresses() shouldn't be called from the worker thread
    // because of deadlock.
    Set<SocketAddress> newLocalAddresses = new HashSet<>();
    for (H handle : boundHandles.values()) {
        newLocalAddresses.add(localAddress(handle));
    }
    return newLocalAddresses;
}

地址绑定有一点要关注：

// creates the Acceptor instance and has the local 
// executor kick it off.                           
//创建监听器实例，本地执行器将会执行实例           
startupAcceptor();  

 /**
 * This method is called by the doBind() and doUnbind()
 * methods.  If the acceptor is null, the acceptor object will
 * be created and kicked off by the executor.  If the acceptor
 * object is null, probably already created and this class
 * is now working, then nothing will happen and the method
 * will just return.
 */
private void startupAcceptor() throws InterruptedException {
    // If the acceptor is not ready, clear the queues
    // TODO : they should already be clean : do we have to do that ?
    if (!selectable) {
        //如果acceptor没有准备好，则清空注册队列和取消队列
        registerQueue.clear();
        cancelQueue.clear();
    }
    // start the acceptor if not already started,
    //获取当前正在运行的acceptor，没有这创建一个，有执行器执行。
    Acceptor acceptor = acceptorRef.get();
    if (acceptor == null) {
        lock.acquire();
        acceptor = new Acceptor();

        if (acceptorRef.compareAndSet(null, acceptor)) {
            executeWorker(acceptor);
        } else {
            lock.release();
        }
    }
}

我们再来看监听器Acceptor的定义：

 /**
   * This class is called by the startupAcceptor() method and is
   * placed into a NamePreservingRunnable class.
  * It's a thread accepting incoming connections from clients.
  * The loop is stopped when all the bound handlers are unbound.
  Acceptor监听器，在startupAcceptor方法，创建被包装成NamePreservingRunnable线程
  执行。Acceptor是一个线程，接收来自客户端的连接。当所有绑定的Handler解绑时，循环停止。
  */
 private class Acceptor implements Runnable {
     /**
      * {@inheritDoc}
      */
     @Override
     public void run() {
         assert acceptorRef.get() == this;
         int nHandles = 0;
         // Release the lock
         lock.release();
         //当监听器已经准备好
         while (selectable) {
             try {
                 // Process the bound sockets to this acceptor.
                 // this actually sets the selector to OP_ACCEPT,
                 // and binds to the port on which this class will
                 // listen on. We do that before the select because 
                 // the registerQueue containing the new handler is
                 // already updated at this point.
		 //根据地址绑定队列中的绑定请求，打开一个ServerSocketChannle，
		 //注册接收事件OP_ACCEPT到选择器
                 nHandles += registerHandles();

                 // Detect if we have some keys ready to be processed
                 // The select() will be woke up if some new connection
                 // have occurred, or if the selector has been explicitly
                 // woke up
		 //探测是否存在选择key就绪待处理，及一个新的连接请求发生，或者
		 //选择操作被显示唤醒，执行选择操作
                 int selected = select();

                 // Now, if the number of registred handles is 0, we can
                 // quit the loop: we don't have any socket listening
                 // for incoming connection.
                 if (nHandles == 0) {
		     //如果绑定地址为空，则置空acceptorRef
                     acceptorRef.set(null);

                     if (registerQueue.isEmpty() && cancelQueue.isEmpty()) {
                         assert acceptorRef.get() != this;
                         break;
                     }

                     if (!acceptorRef.compareAndSet(null, this)) {
                         assert acceptorRef.get() != this;
                         break;
                     }

                     assert acceptorRef.get() == this;
                 }

                 if (selected > 0) {
                     // We have some connection request, let's process
                     // them here.
		     //有接收连接事件发生，则处理连接请求
                     processHandles(selectedHandles());
                 }

                 // check to see if any cancellation request has been made.
		 //unbind解绑队列的解绑地址请求
                 nHandles -= unregisterHandles();
             } catch (ClosedSelectorException cse) {
                 // If the selector has been closed, we can exit the loop
                 ExceptionMonitor.getInstance().exceptionCaught(cse);
                 break;
             } catch (Exception e) {
                 ExceptionMonitor.getInstance().exceptionCaught(e);

                 try {
                     Thread.sleep(1000);
                 } catch (InterruptedException e1) {
                     ExceptionMonitor.getInstance().exceptionCaught(e1);
                 }
             }
         }

         // Cleanup all the processors, and shutdown the acceptor.
         if (selectable && isDisposing()) {
	    //如果acceptor正在关闭，则关闭关联processor
             selectable = false;
             try {
                 if (createdProcessor) {
                     processor.dispose();
                 }
             } finally {
                 try {
                     synchronized (disposalLock) {
                         if (isDisposing()) {
                             destroy();
                         }
                     }
                 } catch (Exception e) {
                     ExceptionMonitor.getInstance().exceptionCaught(e);
                 } finally {
                     disposalFuture.setDone();
                 }
             }
         }
     }
     /**
      * This method will process new sessions for the Worker class.  All
      * keys that have had their status updates as per the Selector.selectedKeys()
      * method will be processed here.  Only keys that are ready to accept
      * connections are handled here.
      * <p/>
      * Session objects are created by making new instances of SocketSessionImpl
      * and passing the session object to the SocketIoProcessor class.
      */
     @SuppressWarnings("unchecked")
     private void processHandles(Iterator<H> handles) throws Exception {
        //遍历接收事件就绪的ServerSocketChannel
         while (handles.hasNext()) {
             H handle = handles.next();
             handles.remove();

             // Associates a new created connection to a processor,
             // and get back a session
	     //ServerSocketChannel创建一个关联processor的会话
             S session = accept(processor, handle);
             if (session == null) {
                 continue;
             }
	     //初始化会话
             initSession(session, null, null);
             // add the session to the SocketIoProcessor
	     //添加会话到会话关联io处理器
             session.getProcessor().add(session);
         }
     }
     /**
      * Sets up the socket communications.  Sets items such as:
     绑定socket地址，打开一个ServerSocketChannle，注册接收事件OP_ACCEPT到选择器
      * <p/>
      * Blocking
      * Reuse address
      * Receive buffer size
      * Bind to listen port
      * Registers OP_ACCEPT for selector
      */
     private int registerHandles() {
         for (;;) {
             // The register queue contains the list of services to manage
             // in this acceptor.
	     //从socket地址绑定请求队列，poll一个地址绑定请求
             AcceptorOperationFuture future = registerQueue.poll();

             if (future == null) {
                 return 0;
             }

             // We create a temporary map to store the bound handles,
             // as we may have to remove them all if there is an exception
             // during the sockets opening.
             Map<SocketAddress, H> newHandles = new ConcurrentHashMap<>();
	     //获取需要绑定的地址
             List<SocketAddress> localAddresses = future.getLocalAddresses();
             try {
                 // Process all the addresses
                 for (SocketAddress a : localAddresses) {
                     H handle = open(a);//根据Socket地址，打开一个ServerSocketChannle
                     newHandles.put(localAddress(handle), handle);
                 }

                 // Everything went ok, we can now update the map storing
                 // all the bound sockets.
		 //将绑定地址与ServerSocketChannle映射管理添加到地址绑定映射集合
                 boundHandles.putAll(newHandles);

                 // and notify.
                 future.setDone();
                 
                 return newHandles.size();
             } catch (Exception e) {
                 // We store the exception in the future
                 future.setException(e);
             } finally {
                 // Roll back if failed to bind all addresses.
                 if (future.getException() != null) {
		     //如果绑定地址有异常，则关闭打开的ServerSocketChannle
                     for (H handle : newHandles.values()) {
                         try {
                             close(handle);
                         } catch (Exception e) {
                             ExceptionMonitor.getInstance().exceptionCaught(e);
                         }
                     }

                     // Wake up the selector to be sure we will process the newly bound handle
                     // and not block forever in the select()
		     //唤醒选择器处理新创建的ServerSocketChannle，不在阻塞在选择操作
                     wakeup();
                 }
             }
         }
     }

     /**
      * This method just checks to see if anything has been placed into the
      * cancellation queue.  The only thing that should be in the cancelQueue
      * is CancellationRequest objects and the only place this happens is in
      * the doUnbind() method.
      unregisterHandles方法，检查是否有地址解绑请求。如果有解绑请求CancellationRequest，
      解绑请求在doUnbind方法中产生
      */
     private int unregisterHandles() {
         int cancelledHandles = 0;
         for (;;) {
	 //从解绑队列中poll解绑请求
             AcceptorOperationFuture future = cancelQueue.poll();
             if (future == null) {
                 break;
             }
             // close the channels
	     //获取ServerSocketChannle绑定的地址
             for (SocketAddress a : future.getLocalAddresses()) {
	        //从绑定socket地址与ServerSocketChannle映射map中，移除绑定的socket地址
                 H handle = boundHandles.remove(a);
                 if (handle == null) {
                     continue;
                 }
                 try {
		     //关闭ServerSocketChannle
                     close(handle);
		     //唤醒，触发ServerSocketChannle线程death
                     wakeup(); // wake up again to trigger thread death
                 } catch (Exception e) {
                     ExceptionMonitor.getInstance().exceptionCaught(e);
                 } finally {
                     cancelledHandles++;
                 }
             }
             //解绑成功
             future.setDone();
         }

         return cancelledHandles;
     }
}

从Acceptor的源码可以看出，如果监听器AbstractPollingIoAcceptor已经初始化，首先
根据地址绑定队列中的绑定请求，打开一个ServerSocketChannle，注册接收事件OP_ACCEPT到选择器，并将绑定地址与ServerSocketChannle映射管理添加到地址绑定映射集合；执行选择操作，如果实际绑定地址为空，则置空acceptorRef；如果接收连接事件发生，则处理连接请求，遍历接收事件就绪的ServerSocketChannel，ServerSocketChannel创建一个关联processor的会话，初始化会话，添加会话到会话关联io处理器；检查是否有地址解绑请求，如果有解绑请求CancellationRequest，从绑定socket地址与ServerSocketChannle映射map中，移除绑定的socket地址，关闭ServerSocketChannle；最后检查监听器是否正在关闭，如果acceptor正在关闭，则关闭关联processor。
回到地址绑定方法：

protected final Set<SocketAddress> bindInternal(List<? extends SocketAddress> localAddresses) throws Exception {
    // Create a bind request as a Future operation. When the selector
    // have handled the registration, it will signal this future.
    //创建绑定操作结果。当选择器处理注册时，将会通知操作结果。
    AcceptorOperationFuture request = new AcceptorOperationFuture(localAddresses);
    // adds the Registration request to the queue for the Workers
    // to handle 注册请求到注册队列，以便工作线程处理
    registerQueue.add(request);

    // creates the Acceptor instance and has the local
    // executor kick it off.
    //创建监听器实例，本地执行器将会执行实例
    startupAcceptor();

    // As we just started the acceptor, we have to unblock the select()
    // in order to process the bind request we just have added to the
    // registerQueue.
    //由于我们刚启动监听器，不得不unblock选择操作，处理刚刚添加到注册队列的绑定请求
    try {
        lock.acquire();

        wakeup();
    } finally {
        lock.release();
    }

    // Now, we wait until this request is completed.
    request.awaitUninterruptibly();

    if (request.getException() != null) {
        throw request.getException();
    }
    // Update the local addresses.
    // setLocalAddresses() shouldn't be called from the worker thread
    // because of deadlock.
    Set<SocketAddress> newLocalAddresses = new HashSet<>();
    for (H handle : boundHandles.values()) {
        newLocalAddresses.add(localAddress(handle));
    }
    return newLocalAddresses;
}

 /**
 * This method is called by the doBind() and doUnbind()
 * methods.  If the acceptor is null, the acceptor object will
 * be created and kicked off by the executor.  If the acceptor
 * object is null, probably already created and this class
 * is now working, then nothing will happen and the method
 * will just return.
 */
private void startupAcceptor() throws InterruptedException {
    // If the acceptor is not ready, clear the queues
    // TODO : they should already be clean : do we have to do that ?
    if (!selectable) {
        //如果acceptor没有准备好，则清空注册队列和取消队列
        registerQueue.clear();
        cancelQueue.clear();
    }
    // start the acceptor if not already started,
    //获取当前正在运行的acceptor，没有这创建一个，有执行器执行。
    Acceptor acceptor = acceptorRef.get();
    if (acceptor == null) {
        lock.acquire();
        acceptor = new Acceptor();

        if (acceptorRef.compareAndSet(null, acceptor)) {
            executeWorker(acceptor);
        } else {
            lock.release();
        }
    }
}

从上面来看，地址绑定过程为，创建绑定操作结果，注册绑定请求到注册地址绑定请求队列，
创建监听器Acceptor实例并执行。
再来看地址解绑等操作:
  

 /**
     * {@inheritDoc}
     */
    @Override
    protected final void unbind0(List<? extends SocketAddress> localAddresses) throws Exception {
        //根据解绑地址创建AcceptorOperationFuture，添加到解绑队列，启动Acceptor线程，完成实际解绑工作。
        AcceptorOperationFuture future = new AcceptorOperationFuture(localAddresses);
        cancelQueue.add(future);
        startupAcceptor();
        wakeup();
        future.awaitUninterruptibly();
        if (future.getException() != null) {
            throw future.getException();
        }
    }
    /**
     * {@inheritDoc}
     */
    @Override
    protected void dispose0() throws Exception {
        unbind();//解绑地址
        startupAcceptor();//启动Acceptor线程，完成实际清理工作。
        wakeup();
    }
    /**
     * {@inheritDoc}
     默认不支持根据远端地址和本地地址创建会话
     */
    @Override
    public final IoSession newSession(SocketAddress remoteAddress, SocketAddress localAddress) {
        throw new UnsupportedOperationException();
    }
    /**
     * @return the backLog
     */
    public int getBacklog() {
        return backlog;
    }
    /**
     * Sets the Backlog parameter
     * 
     * @param backlog
     *            the backlog variable
     */
    public void setBacklog(int backlog) {
        synchronized (bindLock) {
            if (isActive()) {
                throw new IllegalStateException("backlog can't be set while the acceptor is bound.");
            }

            this.backlog = backlog;
        }
    }
    /**
     * @return the flag that sets the reuseAddress information
     */
    public boolean isReuseAddress() {
        return reuseAddress;
    }
    /**
     * Set the Reuse Address flag
     * 
     * @param reuseAddress
     *            The flag to set
     */
    public void setReuseAddress(boolean reuseAddress) {
        synchronized (bindLock) {
            if (isActive()) {
                throw new IllegalStateException("backlog can't be set while the acceptor is bound.");
            }
            this.reuseAddress = reuseAddress;
        }
    }
    /**
     * {@inheritDoc}
     */
    @Override
    public SocketSessionConfig getSessionConfig() {
        return (SocketSessionConfig)sessionConfig;
    }

总结：
AbstractPollingIoAcceptor主要变量为Io处理器processor，地址绑定请求队列registerQueue，地址解绑请求队列cancelQueue，监听器绑定的socket地址，与ServerSocketChannel映射关系boundHandles-Map，监听工作线程Acceptor引用acceptorRef。
构造AbstractPollingIoAcceptor，主要是初始化会话配置，Io处理器类型，IO异步事件执行器为空的话默认为CachedThreadPool，然后初始化选择器。地址绑定过程为，创建绑定操作结果，注册绑定请求到注册地址绑定请求队列，创建监听器Acceptor实例并执行。Acceptor主要功能为，地址绑定，监听连接请求，解绑地址，实际工作逻辑为：如果监听器AbstractPollingIoAcceptor已经初始化，首先根据地址绑定队列中的绑定请求，打开一个ServerSocketChannle，注册接收事件OP_ACCEPT到选择器，并将绑定地址与ServerSocketChannle映射管理添加到地址绑定映射集合；执行选择操作，如果实际绑定地址为空，则置空acceptorRef；如果接收连接事件发生，则处理连接请求，遍历接收事件就绪的ServerSocketChannel，ServerSocketChannel创建一个关联processor的会话，初始化会话，添加会话到会话关联io处理器；检查是否有地址解绑请求，如果有解绑请求CancellationRequest，从绑定socket地址与ServerSocketChannle映射map中，移除绑定的socket地址，关闭ServerSocketChannle；最后检查监听器是否正在关闭，如果acceptor正在关闭，则关闭关联processor。Acceptor和AbstractPollingIoAcceptor的关系，与AbstractPollingIoProcessor和Processor的关系很像。地址解绑过程，首先根据解绑地址创建AcceptorOperationFuture，添加到解绑队列，启动Acceptor线程，完成实际解绑工作。
AbstractPollingIoAcceptor所有的工作（地址绑定，接收连接，创建会话，添加会话到IO处理器，解绑地址，释放监听器资源）都是在Acceptor线程里完成。


附：
//SimpleIoProcessorPool,简单的IO处理器线程池，这一步，可以做个了解。
简单的IO处理器线程池SimpleIoProcessorPool，将一个会话的相关事件在多个Io处理器执行。当前的transport内部实现用SimpleIoProcessorPool，在多处理器环境下，具有良好的性能，因此不需要直接使用SimpleIoProcessorPool，除非在同个虚拟机中运行多个IoService。
Io处理器线程池，主要是创建size个IO处理器线程处理会话和过滤器相关事件。如果在同一虚拟机中运行多个Io服务，你需要共享处理器线程池。为了达到这个效果，你需要构造
SimpleIoProcessorPool实例，在创建IO服务时，作为参数传入。会话与IO处理器线程池，主要通过会话的处理器属性关联，获取会话关联的处理器，如果会话属性没有存储关联处理器，则从处理器线程池中获取一个，添加会话属性中。SimpleIoProcessorPool的其他方法发送写请求，刷新会话，添加移除会话等操作都是通过会话关联的处理器线程池中的处理器。简单的说，SimpleIoProcessorPool使用与再同一个虚拟机下启动多个IO服务的情况，简单处理器线程池，就是一个处理器集合，添加会话时，从会话属性中，获会话关联的处理器，如果会话属性没有存储关联处理器，则从处理器线程池中获取一个，添加会话属性中。

/**
 * An {@link IoProcessor} pool that distributes {@link IoSession}s into one or more
 * {@link IoProcessor}s. Most current transport implementations use this pool internally
 * to perform better in a multi-core environment, and therefore, you won't need to 
 * use this pool directly unless you are running multiple {@link IoService}s in the
 * same JVM.
简单的IO处理器线程池SimpleIoProcessorPool，将一个会话的相关事件在多个Io处理器执行。
当前的transport内部实现用SimpleIoProcessorPool，在多处理器环境下，具有良好的性能，
因此不需要直接使用SimpleIoProcessorPool，除非在同个虚拟机中运行多个IoService。
 * <p>
 * If you are running multiple {@link IoService}s, you could want to share the pool
 * among all services.  To do so, you can create a new {@link SimpleIoProcessorPool}
 * instance by yourself and provide the pool as a constructor parameter when you
 * create the services.
 如果在同一虚拟机中运行多个Io服务，你需要共享处理器线程池。为了达到这个效果，你需要构造
SimpleIoProcessorPool实例，在创建IO服务时，作为参数传入。
 * <p>
 * This pool uses Java reflection API to create multiple {@link IoProcessor} instances.
 * It tries to instantiate the processor in the following order:
Io处理器线程池默认通过反射创建io处理器实例，有一下三中形式
 * [list=1]
 * [*]A public constructor with one {@link ExecutorService} parameter.

 * [*]A public constructor with one {@link Executor} parameter.

 * [*]A public default constructor

 * [/list]
 * The following is an example for the NIO socket transport:
 * <pre><code>
 下面是创建TCP服务端的一个实例
 * // Create a shared pool.
 * SimpleIoProcessorPool<NioSession> pool = 
 *         new SimpleIoProcessorPool<NioSession>(NioProcessor.class, 16);
 * 
 * // Create two services that share the same pool.
 * SocketAcceptor acceptor = new NioSocketAcceptor(pool);
 * SocketConnector connector = new NioSocketConnector(pool);
 * 
 * ...
 * 
 * // Release related resources.
 * connector.dispose();
 * acceptor.dispose();
 * pool.dispose();
 * </code></pre>
 * 
 * @author [url=http://mina.apache.org]Apache MINA Project[/url]
 * 
 * @param <S> the type of the {@link IoSession} to be managed by the specified
 *            {@link IoProcessor}.
 */
public class SimpleIoProcessorPool<S extends AbstractIoSession> implements IoProcessor<S> {
    /** A logger for this class */
    private static final Logger LOGGER = LoggerFactory.getLogger(SimpleIoProcessorPool.class);
    /** The default pool size, when no size is provided.默认处理器实例数为运行时环境可以利用处理器数量+1 */
    private static final int DEFAULT_SIZE = Runtime.getRuntime().availableProcessors() + 1;
    /** A key used to store the processor pool in the session's Attributes */
    private static final AttributeKey PROCESSOR = new AttributeKey(SimpleIoProcessorPool.class, "processor");
    /** The pool table */
    private final IoProcessor<S>[] pool;//io处理器集会话的相关事件。
    /** The contained  which is passed to the IoProcessor when they are created */
    private final Executor executor;//io异步事件执行器
    /** A flag set to true if we had to create an executor */
    private final boolean createdExecutor;
    /** A lock to protect the disposal against concurrent calls */
    private final Object disposalLock = new Object();
    /** A flg set to true if the IoProcessor in the pool are being disposed */
    private volatile boolean disposing;
    /** A flag set to true if all the IoProcessor contained in the pool have been disposed */
    private volatile boolean disposed;

    /**
     * Creates a new instance of SimpleIoProcessorPool with a default
     * size of NbCPUs +1.
     *
     * @param processorType The type of IoProcessor to use
     */
    public SimpleIoProcessorPool(Class<? extends IoProcessor<S>> processorType) {
        this(processorType, null, DEFAULT_SIZE, null);
    }
    /**
     * Creates a new instance of SimpleIoProcessorPool with a defined
     * number of IoProcessors in the pool
     *
     * @param processorType The type of IoProcessor to use
     * @param size The number of IoProcessor in the pool
     */
    public SimpleIoProcessorPool(Class<? extends IoProcessor<S>> processorType, int size) {
        this(processorType, null, size, null);
    }
    /**
     * Creates a new instance of SimpleIoProcessorPool with a defined
     * number of IoProcessors in the pool
     *
     * @param processorType The type of IoProcessor to use
     * @param size The number of IoProcessor in the pool
     * @param selectorProvider The SelectorProvider to use
     */
    public SimpleIoProcessorPool(Class<? extends IoProcessor<S>> processorType, int size, SelectorProvider selectorProvider) {
        this(processorType, null, size, selectorProvider);
    }
    /**
     * Creates a new instance of SimpleIoProcessorPool with an executor
     *
     * @param processorType The type of IoProcessor to use
     * @param executor The {@link Executor}
     */
    public SimpleIoProcessorPool(Class<? extends IoProcessor<S>> processorType, Executor executor) {
        this(processorType, executor, DEFAULT_SIZE, null);
    }
    /**
     * Creates a new instance of SimpleIoProcessorPool with an executor
     *
     * @param processorType The type of IoProcessor to use
     * @param executor The {@link Executor}
     * @param size The number of IoProcessor in the pool
     * @param selectorProvider The SelectorProvider to used
     */
    @SuppressWarnings("unchecked")
    public SimpleIoProcessorPool(Class<? extends IoProcessor<S>> processorType, Executor executor, int size, 
            SelectorProvider selectorProvider) {
        if (processorType == null) {
            throw new IllegalArgumentException("processorType");
        }
        if (size <= 0) {
            throw new IllegalArgumentException("size: " + size + " (expected: positive integer)");
        }
        // Create the executor if none is provided
        createdExecutor = executor == null;
        if (createdExecutor) {
            this.executor = Executors.newCachedThreadPool();
            // Set a default reject handler
            ((ThreadPoolExecutor) this.executor).setRejectedExecutionHandler(new ThreadPoolExecutor.CallerRunsPolicy());
        } else {
            this.executor = executor;
        }
        pool = new IoProcessor[size];//初始化IO处理器集
        boolean success = false;
        Constructor<? extends IoProcessor<S>> processorConstructor = null;
        boolean usesExecutorArg = true;
        try {
            // We create at least one processor
            try {
                try {
		    //创建处理器
                    processorConstructor = processorType.getConstructor(ExecutorService.class);
                    pool[0] = processorConstructor.newInstance(this.executor);
                } catch (NoSuchMethodException e1) {
                    // To the next step...
                    try {
		        //如果处理器没有相关构造方法，重新构造Io处理器
                        if(selectorProvider==null) {
                            processorConstructor = processorType.getConstructor(Executor.class);
                            pool[0] = processorConstructor.newInstance(this.executor);
                        } else {
                            processorConstructor = processorType.getConstructor(Executor.class, SelectorProvider.class);
                            pool[0] = processorConstructor.newInstance(this.executor,selectorProvider);
                        }
                    } catch (NoSuchMethodException e2) {
                        // To the next step...
                        try {
                            processorConstructor = processorType.getConstructor();
                            usesExecutorArg = false;
                            pool[0] = processorConstructor.newInstance();
                        } catch (NoSuchMethodException e3) {
                            // To the next step...
                        }
                    }
                }
            } catch (RuntimeException re) {
                LOGGER.error("Cannot create an IoProcessor :{}", re.getMessage());
                throw re;
            } catch (Exception e) {
                String msg = "Failed to create a new instance of " + processorType.getName() + ":" + e.getMessage();
                LOGGER.error(msg, e);
                throw new RuntimeIoException(msg, e);
            }

            if (processorConstructor == null) {
                // Raise an exception if no proper constructor is found.
                String msg = String.valueOf(processorType) + " must have a public constructor with one "
                        + ExecutorService.class.getSimpleName() + " parameter, a public constructor with one "
                        + Executor.class.getSimpleName() + " parameter or a public default constructor.";
                LOGGER.error(msg);
                throw new IllegalArgumentException(msg);
            }

            // Constructor found now use it for all subsequent instantiations
            for (int i = 1; i < pool.length; i++) {
                try {
                    if (usesExecutorArg) {
                        if(selectorProvider==null) {
                            pool[i] = processorConstructor.newInstance(this.executor);
                        } else {
                            pool[i] = processorConstructor.newInstance(this.executor, selectorProvider);
                        }
                    } else {
                        pool[i] = processorConstructor.newInstance();
                    }
                } catch (Exception e) {
                    // Won't happen because it has been done previously
                }
            }

            success = true;
        } finally {
            if (!success) {
                dispose();
            }
        }
    }
   //从上来看，构造Io处理器线程池，主要是创建size个IO处理器线程处理会话和过滤器相关事件
    /**
     * {@inheritDoc}
     */
    @Override
    public final void add(S session) {
        getProcessor(session).add(session);
    }
     /**
     * Find the processor associated to a session. If it hasen't be stored into
     * the session's attributes, pick a new processor and stores it.
     获取会话关联的处理器，如果会话属性没有存储关联处理器，则从处理器线程池中获取一个，添加
     会话属性中。
     */
    @SuppressWarnings("unchecked")
    private IoProcessor<S> getProcessor(S session) {
        IoProcessor<S> processor = (IoProcessor<S>) session.getAttribute(PROCESSOR);
        if (processor == null) {
            if (disposed || disposing) {
                throw new IllegalStateException("A disposed processor cannot be accessed.");
            }
            processor = pool[Math.abs((int) session.getId()) % pool.length];

            if (processor == null) {
                throw new IllegalStateException("A disposed processor cannot be accessed.");
            }
            session.setAttributeIfAbsent(PROCESSOR, processor);
        }

        return processor;
    }
    /**
     * {@inheritDoc}
     */
    @Override
    public final void flush(S session) {
        getProcessor(session).flush(session);
    }
    /**
     * {@inheritDoc}
     */
    @Override
    public final void write(S session, WriteRequest writeRequest) {
        getProcessor(session).write(session, writeRequest);
    }
    /**
     * {@inheritDoc}
     */
    @Override
    public final void remove(S session) {
        getProcessor(session).remove(session);
    }
    /**
     * {@inheritDoc}
     */
    @Override
    public final void updateTrafficControl(S session) {
        getProcessor(session).updateTrafficControl(session);
    }
    /**
     * {@inheritDoc}
     */
    @Override
    public boolean isDisposed() {
        return disposed;
    }
    /**
     * {@inheritDoc}
     */
    @Override
    public boolean isDisposing() {
        return disposing;
    }
    /**
     * {@inheritDoc}
     */
    @Override
    public final void dispose() {
        if (disposed) {
            return;
        }
        synchronized (disposalLock) {
            if (!disposing) {
                disposing = true;
                //遍历处理器集，释放处理器资源
                for (IoProcessor<S> ioProcessor : pool) {
                    if (ioProcessor == null) {
                        // Special case if the pool has not been initialized properly
                        continue;
                    }

                    if (ioProcessor.isDisposing()) {
                        continue;
                    }

                    try {
                        ioProcessor.dispose();
                    } catch (Exception e) {
                        LOGGER.warn("Failed to dispose the {} IoProcessor.", ioProcessor.getClass().getSimpleName(), e);
                    }
                }

                if (createdExecutor) {
                    ((ExecutorService) executor).shutdown();
                }
            }

            Arrays.fill(pool, null);
            disposed = true;
        }
    }
}