Netty 源码阅读笔记（1） NioEventLoopGroup

最新推荐文章于 2024-05-03 19:19:09 发布

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最新推荐文章于 2024-05-03 19:19:09 发布

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分类专栏： # Netty 源码

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本文深入解析了NioEventLoopGroup的构造方法及其内部类结构，详细介绍了如何通过不同的构造参数创建线程组，特别关注了线程数量的默认设定及bossEventLoopGroup的创建过程。

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类结构图

在这里插入图片描述

1.1 构造方法

public NioEventLoopGroup() {
    this(0);
}

public NioEventLoopGroup(int nThreads) {
    this(nThreads, (Executor) null);
}

public NioEventLoopGroup(int nThreads, Executor executor) {
    this(nThreads, executor, SelectorProvider.provider());
}

public NioEventLoopGroup(
        int nThreads, Executor executor, final SelectorProvider selectorProvider) {
    this(nThreads, executor, selectorProvider, DefaultSelectStrategyFactory.INSTANCE);
}

public NioEventLoopGroup(int nThreads, Executor executor, final SelectorProvider selectorProvider,
                         final SelectStrategyFactory selectStrategyFactory) {
    super(nThreads, executor, selectorProvider, selectStrategyFactory, RejectedExecutionHandlers.reject());
}

类 MultithreadEventLoopGroup

protected MultithreadEventLoopGroup(int nThreads, Executor executor, Object... args) {
    super(nThreads == 0 ? DEFAULT_EVENT_LOOP_THREADS : nThreads, executor, args);
}

private static final int DEFAULT_EVENT_LOOP_THREADS;

static {
    DEFAULT_EVENT_LOOP_THREADS = Math.max(1, SystemPropertyUtil.getInt(
            "io.netty.eventLoopThreads", NettyRuntime.availableProcessors() * 2));

    if (logger.isDebugEnabled()) {
        logger.debug("-Dio.netty.eventLoopThreads: {}", DEFAULT_EVENT_LOOP_THREADS);
    }
}

可以看到如果调用无参构造，线程数会是 2*Ncpu，这适合 workerEventLoopGroup。
创建 bossEventLoopGroup 就需要加个参数 1。

类 MultithreadEventExecutorGroup

protected MultithreadEventExecutorGroup(int nThreads, Executor executor, Object... args) {
    this(nThreads, executor, DefaultEventExecutorChooserFactory.INSTANCE, args);
}

protected MultithreadEventExecutorGroup(int nThreads, Executor executor,
                                       EventExecutorChooserFactory chooserFactory, Object... args) {
    if (nThreads <= 0) {
        throw new IllegalArgumentException(String.format("nThreads: %d (expected: > 0)", nThreads));
    }

    if (executor == null) {
    	//实例化每个EventLoop所需要的执行器Executor 见（2）
        executor = new ThreadPerTaskExecutor(newDefaultThreadFactory());
    }

	//NioEventLoop是EventExecutor的实现类 
    children = new EventExecutor[nThreads];

    for (int i = 0; i < nThreads; i ++) {
        boolean success = false;
        try {
        					//见1.1.1
            children[i] = newChild(executor, args);
            success = true;
        } catch (Exception e) {
            // TODO: Think about if this is a good exception type
            throw new IllegalStateException("failed to create a child event loop", e);
        } finally {
            if (!success) {
                for (int j = 0; j < i; j ++) {
                    children[j].shutdownGracefully();
                }

                for (int j = 0; j < i; j ++) {
                    EventExecutor e = children[j];
                    try {
                        while (!e.isTerminated()) {
                            e.awaitTermination(Integer.MAX_VALUE, TimeUnit.SECONDS);
                        }
                    } catch (InterruptedException interrupted) {
                        // Let the caller handle the interruption.
                        Thread.currentThread().interrupt();
                        break;
                    }
                }
            }
        }
    }

    chooser = chooserFactory.newChooser(children);

    final FutureListener<Object> terminationListener = new FutureListener<Object>() {
        @Override
        public void operationComplete(Future<Object> future) throws Exception {
            if (terminatedChildren.incrementAndGet() == children.length) {
                terminationFuture.setSuccess(null);
            }
        }
    };

    for (EventExecutor e: children) {
        e.terminationFuture().addListener(terminationListener);
    }

    Set<EventExecutor> childrenSet = new LinkedHashSet<EventExecutor>(children.length);
    Collections.addAll(childrenSet, children);
    readonlyChildren = Collections.unmodifiableSet(childrenSet);
}

1.1.1 newChild

类 MultithreadEventExecutorGroup

protected abstract EventExecutor newChild(Executor executor, Object... args) throws Exception;

这是一个接口

类 NioEventLoopGroup

@Override
protected EventLoop newChild(Executor executor, Object... args) throws Exception {
				//见（3）
    return new NioEventLoop(this, executor, (SelectorProvider) args[0],
        ((SelectStrategyFactory) args[1]).newSelectStrategy(), (RejectedExecutionHandler) args[2]);
}