背景

我們一個服務端的程序，啟動的時候就可以做兩個事情： 一是綁定本地地址，二是監聽端口

簡單版本

監聽

io.netty.channel.nio.AbstractNioChannel.java

  protected void doRegister() throws Exception {
        boolean selected = false;
        for (;;) {
            try {
                selectionKey = javaChannel().register(eventLoop().selector, 0, this);
                return;
            } catch (CancelledKeyException e) {
                if (!selected) {
                    // Force the Selector to select now as the "canceled" SelectionKey may still be
                    // cached and not removed because no Select.select(..) operation was called yet.
                    eventLoop().selectNow();
                    selected = true;
                } else {
                    // We forced a select operation on the selector before but the SelectionKey is still cached
                    // for whatever reason. JDK bug ?
                    throw e;
                }
            }
        }
    }

核心就是 selectionKey = javaChannel().register(eventLoop().selector, 0, this);
首先，javaChannel()返回的是一個SelectableChannel對象，然后注冊到當前線程的 selector，此時監聽的事件還是0（不監聽？），并且帶上了當前的對象，這個作為異步場景下數據的載體，用于數據的透傳

添加監聽的事件 (op_accept)

io.netty.channel.nio.AbstractNioChannel.java

  protected void doBeginRead() throws Exception {
        // Channel.read() or ChannelHandlerContext.read() was called
        if (inputShutdown) {
            return;
        }

        final SelectionKey selectionKey = this.selectionKey;
        if (!selectionKey.isValid()) {
            return;
        }

        readPending = true;

        final int interestOps = selectionKey.interestOps();
        if ((interestOps & readInterestOp) == 0) {
            selectionKey.interestOps(interestOps | readInterestOp);
        }
    }

在上面的函數中，主要是看監聽的時間是否有readInterestOp，如果沒有，那么就添加上。那么這個readInterestOp值是什么呢？從這里可以看出他是AbstractNioChannel中的成員，我們看他是在哪里賦值的