Netty分布式源码分析监听读事件

private void register0(ChannelPromise promise) {
    try {
        //省略代码
        //做实际的注册
        doRegister();
        neverRegistered = false;
        registered = true;
        //触发事件
        pipeline.invokeHandlerAddedIfNeeded();
        safeSetSuccess(promise);
        //触发注册成功事件
        pipeline.fireChannelRegistered();
        if (isActive()) {
            if (firstRegistration) {
                //传播active事件(4)
                pipeline.fireChannelActive();
            } else if (config().isAutoRead()) {
                beginRead();
            }
        }
    } catch (Throwable t) {
        //省略代码
    }
}

public final void beginRead() {
    assertEventLoop();
    if (!isActive()) {
        return;
    }
    try {
        doBeginRead();
    } catch (final Exception e) {
        //代码省略
    }
}

protected void doBeginRead() throws Exception {
    //拿到selectionKey
    final SelectionKey selectionKey = this.selectionKey;
    if (!selectionKey.isValid()) {
        return;
    }
    readPending = true;
    //获得感兴趣的事件
    final int interestOps = selectionKey.interestOps();
    //判断是不是对任何事件都不监听
    if ((interestOps & readInterestOp) == 0) {
        //此条件成立
        //将之前的accept事件注册, readInterest代表可以读取一个新连接的意思
        selectionKey.interestOps(interestOps | readInterestOp);
    }
}