NioEventLoop

上一篇文章提到了NioEventLoopGroup，那么这篇文章就要提到NioEventLoop了，可以简单的理解为一个NioEventLoopGroup中有很多NioEventLoop真正的执行工作。

首先我们还是来看一下NioEventLoop的继承体系：

其实相对还是比较直线型的集成体系。。

首先在AbstractEventExecutor中定义了一些基本的executor的方法，例如submit任务，调度任务等。

接着，在SingleThreadEventExecutor中则进行了一些详细的定义，我们来看看它的构造函数，基本上就明白了：

    //构造函数    protected SingleThreadEventExecutor(            EventExecutorGroup parent, ThreadFactory threadFactory, boolean addTaskWakesUp) {        if (threadFactory == null) {            throw new NullPointerException("threadFactory");        }        this.parent = parent;        this.addTaskWakesUp = addTaskWakesUp;        thread = threadFactory.newThread(new Runnable() {    //创建线程            @Override   //线程的执行函数            public void run() {                CURRENT_EVENT_LOOP.set(SingleThreadEventExecutor.this);                boolean success = false;                updateLastExecutionTime();                try {                    SingleThreadEventExecutor.this.run();  //开始当前executor的执行函数                    success = true;                } catch (Throwable t) {                    logger.warn("Unexpected exception from an event executor: ", t);                } finally {                    if (state < ST_SHUTTING_DOWN) {                        state = ST_SHUTTING_DOWN;                    }                    // Check if confirmShutdown() was called at the end of the loop.                    if (success && gracefulShutdownStartTime == 0) {                        logger.error(                                "Buggy " + EventExecutor.class.getSimpleName() + " implementation; " +                                SingleThreadEventExecutor.class.getSimpleName() + ".confirmShutdown() must be called " +                                "before run() implementation terminates.");                    }                    try {                        // Run all remaining tasks and shutdown hooks.                        for (;;) {                            if (confirmShutdown()) {                                break;                            }                        }                    } finally {                        try {                            cleanup();                        } finally {                            synchronized (stateLock) {                                state = ST_TERMINATED;                            }                            threadLock.release();                            if (!taskQueue.isEmpty()) {                                logger.warn(                                        "An event executor terminated with " +                                        "non-empty task queue (" + taskQueue.size() + ')');                            }                        }                    }                }            }        });        taskQueue = newTaskQueue();   //构造任务队列    }

在构造函数中定义了执行线程，并且还构造了任务队列，用于保存当前executor需要执行的所有任务。

接下来就是SingleThreadEventLoop，它继承自SingleThreadEventExecutor，这其实和group里面的差不多，我们最终用的是eventloop，但是eventloop本身也是一个eventexecutor。

在SingleThreadEventLoop中，定一些一些eventloop的基本方法，例如register方法。

最后就是NioEventLoop了，在它里面实现了各种事件循环的方法，其实最重要的还是run方法，这也是在singlethreadexecutor中线程要执行的方法，我们来看看它的定义吧：

 protected void run() {        for (;;) {            oldWakenUp = wakenUp.getAndSet(false);            try {                if (hasTasks()) {                    selectNow();                } else {                    select();                        // 'wakenUp.compareAndSet(false, true)' is always evaluated                    // before calling 'selector.wakeup()' to reduce the wake-up                    // overhead. (Selector.wakeup() is an expensive operation.)                    //                    // However, there is a race condition in this approach.                    // The race condition is triggered when 'wakenUp' is set to                    // true too early.                    //                    // 'wakenUp' is set to true too early if:                    // 1) Selector is waken up between 'wakenUp.set(false)' and                    //    'selector.select(...)'. (BAD)                    // 2) Selector is waken up between 'selector.select(...)' and                    //    'if (wakenUp.get()) { ... }'. (OK)                    //                    // In the first case, 'wakenUp' is set to true and the                    // following 'selector.select(...)' will wake up immediately.                    // Until 'wakenUp' is set to false again in the next round,                    // 'wakenUp.compareAndSet(false, true)' will fail, and therefore                    // any attempt to wake up the Selector will fail, too, causing                    // the following 'selector.select(...)' call to block                    // unnecessarily.                    //                    // To fix this problem, we wake up the selector again if wakenUp                    // is true immediately after selector.select(...).                    // It is inefficient in that it wakes up the selector for both                    // the first case (BAD - wake-up required) and the second case                    // (OK - no wake-up required).                    if (wakenUp.get()) {                        selector.wakeup();                    }                }                cancelledKeys = 0;                final long ioStartTime = System.nanoTime();                processSelectedKeys();   //处理所有选出来的key                final long ioTime = System.nanoTime() - ioStartTime;                final int ioRatio = this.ioRatio;                runAllTasks(ioTime * (100 - ioRatio) / ioRatio);   //执行所有的任务                if (isShuttingDown()) {                    closeAll();                    if (confirmShutdown()) {                        break;                    }                }            } catch (Throwable t) {                logger.warn("Unexpected exception in the selector loop.", t);                // Prevent possible consecutive immediate failures that lead to                // excessive CPU consumption.                try {                    Thread.sleep(1000);                } catch (InterruptedException e) {                    // Ignore.                }            }        }    }

就这样，NioEventLoop和NioEventLoopGroup两条主线就差不多了，可以有以下总结，

EventLoop里面会包含EventExecutor，也就是说事件循环同时也是一个事件的执行器，group可以把它看做是一个容器。。。。

接下来可以分析Netty里面channel的定义了。。。。。