private void register0(ChannelPromise promise) {
    try {
        //省略代碼
        //做實(shí)際的注冊(cè)
        doRegister();
        neverRegistered = false;
        registered = true;
        //觸發(fā)事件
        pipeline.invokeHandlerAddedIfNeeded();
        safeSetSuccess(promise);
        //觸發(fā)注冊(cè)成功事件
        pipeline.fireChannelRegistered();
        if (isActive()) {
            if (firstRegistration) {
                //傳播active事件(4)
                pipeline.fireChannelActive();
            } else if (config().isAutoRead()) {
                beginRead();
            }
        }
    } catch (Throwable t) {
        //省略代碼
    }
}

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

protected void doBeginRead() throws Exception {
    //拿到selectionKey
    final SelectionKey selectionKey = this.selectionKey;
    if (!selectionKey.isValid()) {
        return;
    }
    readPending = true;
    //獲得感興趣的事件
    final int interestOps = selectionKey.interestOps();
    //判斷是不是對(duì)任何事件都不監(jiān)聽
    if ((interestOps & readInterestOp) == 0) {
        //此條件成立
        //將之前的accept事件注冊(cè), readInterest代表可以讀取一個(gè)新連接的意思
        selectionKey.interestOps(interestOps | readInterestOp);
    }
}