Netty中 什么是NioEventLoop源码分析

​​interface Executor
public interface ExecutorService extends Executor
public abstract class AbstractExecutorService implements ExecutorService
public abstract class AbstractEventExecutor extends AbstractExecutorService
public abstract class AbstractScheduledEventExecutor extends AbstractEventExecutor
public abstract class SingleThreadEventExecutor extends AbstractScheduledEventExecutor ->//这个类实现了具体的execute方法，方法实现中调用了run方法
public abstract class SingleThreadEventLoop extends SingleThreadEventExecutor
public final class NioEventLoop extends SingleThreadEventLoop ->//这个类中实现了run方法，被execute方法调用

Exector接口最重要的就是execute方法，我们找下这个方法的实现

EventLoopContext.executeAsync
    ->nettyEventLoop().execute(task);
         ->AbstractScheduledEventExecutor.execute(task)
              -> AbstractScheduledEventExecutor.startThread() / addTask(task)

                      ->NioEventLoop.run()
                           ->AbstractScheduledEventExecutor.runAllTasks()

public abstract class SingleThreadEventExecutor extends AbstractScheduledEventExecutor{

    @Override
    public void execute(Runnable task) {
        if (task == null) {
            throw new NullPointerException("task");
        }

        boolean inEventLoop = inEventLoop();
        if (inEventLoop) {
            addTask(task);
        } else {
            startThread();
            addTask(task);
            if (isShutdown() && removeTask(task)) {
                reject();
            }
        }

        if (!addTaskWakesUp && wakesUpForTask(task)) {
            wakeup(inEventLoop);
        }
    }

     private void startThread() {
        if (STATE_UPDATER.get(this) == ST_NOT_STARTED) {
            if (STATE_UPDATER.compareAndSet(this, ST_NOT_STARTED, ST_STARTED)) {
                doStartThread();
            }
        }
    }

    private void doStartThread() {
        assert thread == null;
        executor.execute(new Runnable() {
            @Override
            public void run() {
                thread = Thread.currentThread();
                if (interrupted) {
                    thread.interrupt();
                }

                boolean success = false;
                updateLastExecutionTime();
                try {
                    //调用了run方法，这个run方法的实现如下
                    SingleThreadEventExecutor.this.run();
                    success = true;
                } catch (Throwable t) {
                    logger.warn("Unexpected exception from an event executor: ", t);
                } 
    }    

}

public final class NioEventLoop extends SingleThreadEventLoop {
    @Override
    protected void run() {
        for (;;) {
            try {
                switch (selectStrategy.calculateStrategy(selectNowSupplier, hasTasks())) {
                    case SelectStrategy.CONTINUE:
                        continue;
                    case SelectStrategy.SELECT:
                        select(wakenUp.getAndSet(false));                    
                        if (wakenUp.get()) {
                            selector.wakeup();
                        }
                    default:
                        // fallthrough
                }

                cancelledKeys = 0;
                needsToSelectAgain = false;
                final int ioRatio = this.ioRatio;
                if (ioRatio == 100) {
                    try {
                        processSelectedKeys();
                    } finally {
                        // Ensure we always run tasks.
                        runAllTasks();
                    }
                } else {
                    final long ioStartTime = System.nanoTime();
                    try {
                        processSelectedKeys();
                    } finally {
                        // Ensure we always run tasks.
                        final long ioTime = System.nanoTime() - ioStartTime;
                        //execute()-> startThread->run()->runAllTasks
                        runAllTasks(ioTime * (100 - ioRatio) / ioRatio);
                    }
                }
            } catch (Throwable t) {
                handleLoopException(t);
            }
            // Always handle shutdown even if the loop processing threw an exception.
            try {
                if (isShuttingDown()) {
                    closeAll();
                    if (confirmShutdown()) {
                        return;
                    }
                }
            } catch (Throwable t) {
                handleLoopException(t);
            }
        }
    }
}