mina2的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类源码：

    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
                    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...
                        process();
                    }

                    // Write the pending requests
                    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);
            }
        }
    }