NIO框架之MINA源码解析（二）：mina核心引擎

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NIO框架之MINA源码解析（一）：背景

MINA的底层还是利用了jdk提供了nio功能，mina只是对nio进行封装，包括MINA用的线程池都是jdk直接提供的。

MINA的server端主要有accept、processor、session三部分组成的。其中accept主要负责在指定的端口监听，若有新连接则建立一个新的session；processor则负责处理session对应的发送数据和接收数据并调用上层处理；session则缓存当前连接数据。

MINA采用了线程懒启动的技术，即最少启动线程，在MINA server启动的时候，只有一个线程-accept,并且accept线程只有一个，在指定的端口进行监听（可以同时监听多个端口，mina可以绑定多端口）。

1、acceptor

先看下acceptor的主要类图吧。

mina server的启动入口是在NioSocketAcceptor.bind（InetSocketAddress）或者NioSocketAcceptor.bind（SocketAddress...）方法， acceptor.bind(new InetSocketAddress(1234));
然后会调用AbstractPollingIoAcceptor.bindInternal（List<? extends SocketAddress>）方法，在bindInternal方法里面会调用startupAcceptor()方法提交一个accept线程到线程池里面（只提交一次），并初始化acceptor端的Selector，就这样一个acceptor线程启动了。

acceptor端业务相对简单，相当于在当前Selector里面监听acceptor事件，处理新连接并新建一个session放到对应的processor里面。

acceptor 代码，很简单。

 private class Acceptor implements Runnable {        public void run() {            assert (acceptorRef.get() == this);            int nHandles = 0;            // Release the lock            lock.release();            while (selectable) {                try {                    // 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                    int selected = select();                    // this actually sets the selector to OP_ACCEPT,                    // and binds to the port on which this class will                    // listen on  在通道里面注册连接事件                    nHandles += registerHandles();                    // 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) {                        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.处理连接                        processHandles(selectedHandles());                    }                    // check to see if any cancellation request has been made.                    nHandles -= unregisterHandles();                } catch (ClosedSelectorException cse) {                    // If the selector has been closed, we can exit the loop                    break;                } catch (Throwable 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()) {                selectable = false;                try {                    if (createdProcessor) {                        processor.dispose();                    }                } finally {                    try {                        synchronized (disposalLock) {                            if (isDisposing()) {                                destroy();                            }                        }                    } catch (Exception e) {                        ExceptionMonitor.getInstance().exceptionCaught(e);                    } finally {                        disposalFuture.setDone();                    }                }            }        }

2、processor

processor顾名思义，就是进行IO处理，处理当前session的数据读写，并进行业务处理。

在mina server初始化的时候，会初始化一个processor池，通过NioSocketAcceptor的构造器传入池的大小，默认是当前处理器的个数+1。

processor池里面有一个jdk提供的线程池 - Executors.newCachedThreadPool()。各个processor线程会引用此线程池，即每个processor线程都在这个线程池里面运行。

在mina server实际处理时，每个processor相当于一个线程，轮流处理当前的session队列里面的数据（每个processor里面的session相当于顺序处理，共享一个线程）。

每个processor有一个Selector对象。

processor类图

processor端的处理逻辑相对有点复杂，看下面的流程图。

1、把新添加进来的session注册到当前processor的Selector里面的read事件，并初始化session；
2、判断当前Selector是否有读写事件；
3、若第2步有读事件时，进入步骤4，若没有的话，直接到第6步；
4、处理当前读事件，并把处理后的数据放入到flush队列里面；
5、把第4步执行的结果flush到客户端；
6、处理session，比如session idle时间等。
7、重新执行第1步，循环执行。

processor端代码。

 private class Processor implements Runnable {        public void run() {            assert (processorRef.get() == this);            int nSessions = 0;            lastIdleCheckTime = System.currentTimeMillis();            for (;;) {                try {                    // This select has a timeout so that we can manage                    // idle session when we get out of the select every                    // second. (note : this is a hack to avoid creating                    // a dedicated thread).                    long t0 = System.currentTimeMillis();                    int selected = select(SELECT_TIMEOUT);                    long t1 = System.currentTimeMillis();                    long delta = (t1 - t0);                    if ((selected == 0) && !wakeupCalled.get() && (delta < 100)) {                        // Last chance : the select() may have been                        // interrupted because we have had an closed channel.                        if (isBrokenConnection()) {                            LOG.warn("Broken connection");                            // we can reselect immediately                            // set back the flag to false                            wakeupCalled.getAndSet(false);                            continue;                        } else {                            LOG.warn("Create a new selector. Selected is 0, delta = " + (t1 - t0));                            // Ok, we are hit by the nasty epoll                            // spinning.                            // Basically, there is a race condition                            // which causes a closing file descriptor not to be                            // considered as available as a selected channel, but                            // it stopped the select. The next time we will                            // call select(), it will exit immediately for the same                            // reason, and do so forever, consuming 100%                            // CPU.                            // We have to destroy the selector, and                            // register all the socket on a new one.                            registerNewSelector();                        }                        // Set back the flag to false                        wakeupCalled.getAndSet(false);                        // and continue the loop                        continue;                    }                    // Manage newly created session first  处理新添加进来的session，并注册到当前processor的Selector读事件                    nSessions += handleNewSessions();                    updateTrafficMask();                    // Now, if we have had some incoming or outgoing events,                    // deal with them                    if (selected > 0) {                        //LOG.debug("Processing ..."); // This log hurts one of the MDCFilter test...处理读事件，并把结果放入flush队列里面                        process();                    }                    // Write the pending requests  把flush队列里面的session的处理完的数据发送给客户端                    long currentTime = System.currentTimeMillis();                    flush(currentTime);                    // And manage removed sessions                    nSessions -= removeSessions();                    // Last, not least, send Idle events to the idle sessions                    notifyIdleSessions(currentTime);                    // Get a chance to exit the infinite loop if there are no                    // more sessions on this Processor                    if (nSessions == 0) {                        processorRef.set(null);                        if (newSessions.isEmpty() && isSelectorEmpty()) {                            // newSessions.add() precedes startupProcessor                            assert (processorRef.get() != this);                            break;                        }                        assert (processorRef.get() != this);                        if (!processorRef.compareAndSet(null, this)) {                            // startupProcessor won race, so must exit processor                            assert (processorRef.get() != this);                            break;                        }                        assert (processorRef.get() == this);                    }                    // Disconnect all sessions immediately if disposal has been                    // requested so that we exit this loop eventually.                    if (isDisposing()) {                        for (Iterator<S> i = allSessions(); i.hasNext();) {                            scheduleRemove(i.next());                        }                        wakeup();                    }                } catch (ClosedSelectorException cse) {                    // If the selector has been closed, we can exit the loop                    break;                } catch (Throwable t) {                    ExceptionMonitor.getInstance().exceptionCaught(t);                    try {                        Thread.sleep(1000);                    } catch (InterruptedException e1) {                        ExceptionMonitor.getInstance().exceptionCaught(e1);                    }                }            }            try {                synchronized (disposalLock) {                    if (disposing) {                        doDispose();                    }                }            } catch (Throwable t) {                ExceptionMonitor.getInstance().exceptionCaught(t);            } finally {                disposalFuture.setValue(true);            }        }    }

3、session

session做为一个连接的具体对象，缓存当前连接用户的一些信息。

session类图

session对象是绑定在SelectableChannel的一个attach。

class  NioProcessor @Override    protected void init(NioSession session) throws Exception {        SelectableChannel ch = (SelectableChannel) session.getChannel();        ch.configureBlocking(false);        session.setSelectionKey(ch.register(selector, SelectionKey.OP_READ, session));//chanel 注册读事件，并把session当做一个attach辅导SelectableChannel里面。    }

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