netty源码分析之线程模型

MultithreadEventExecutorGroup里面是EventExecutor的数组，该类的构造器最数组进行初始化，初始化过程交给newChild抽象方法

该抽象方法是由具体实现，下面是NioEventLoopGroup的具体实现如下

 @Override
    protected EventLoop newChild(Executor executor, Object... args) throws Exception {
        return new NioEventLoop(this, executor, (SelectorProvider) args[0],
            ((SelectStrategyFactory) args[1]).newSelectStrategy(), (RejectedExecutionHandler) args[2]);
    }

NioEventLoopGroup其实就是一组NioEventLoop的管理，具体执行执行任务时都是调用相应的某个EventExecutor实现类来执行

那这里到底选择哪个EventExecutor来执行呢？原来MultithreadEventExecutorGroup有个选择器chooser，netty支持选择器如下

/**
 * Default implementation which uses simple round-robin to choose next {@link EventExecutor}.
 *默认的实现是是简单的轮询选择器
 */
@UnstableApi
public final class DefaultEventExecutorChooserFactory implements EventExecutorChooserFactory {

    public static final DefaultEventExecutorChooserFactory INSTANCE = new DefaultEventExecutorChooserFactory();

    private DefaultEventExecutorChooserFactory() { }

    @SuppressWarnings("unchecked")
    @Override
    public EventExecutorChooser newChooser(EventExecutor[] executors) {
        if (isPowerOfTwo(executors.length)) {
            return new PowerOfTwoEventExecutorChooser(executors);
        } else {
            return new GenericEventExecutorChooser(executors);
        }
    }

    private static boolean isPowerOfTwo(int val) {
        return (val & -val) == val;
    }

    private static final class PowerOfTwoEventExecutorChooser implements EventExecutorChooser {
        private final AtomicInteger idx = new AtomicInteger();
        private final EventExecutor[] executors;

        PowerOfTwoEventExecutorChooser(EventExecutor[] executors) {
            this.executors = executors;
        }

        @Override
        public EventExecutor next() {
            return executors[idx.getAndIncrement() & executors.length - 1];
        }
    }

    private static final class GenericEventExecutorChooser implements EventExecutorChooser {
        private final AtomicInteger idx = new AtomicInteger();
        private final EventExecutor[] executors;

        GenericEventExecutorChooser(EventExecutor[] executors) {
            this.executors = executors;
        }

        @Override
        public EventExecutor next() {
            return executors[Math.abs(idx.getAndIncrement() % executors.length)];
        }
    }
}

该类是EventExecutorChooser的工厂类，根据数组大小，当数量是2的n次方的时候，用PowerOfTwoEventExecutorChooser，其他用GenericEventExecutorChooser。二个都是简单轮询的方式，只是当数量是2的n次方的时候可以用&的方式比取模的时候性能高而已。