netty源码阅读之客户端新连接之读事件的注册

比眉伴天荒 2022-05-16 00:29 191阅读 0赞

上一篇文章《[netty源码阅读之客户端新连接之分配线程并注册selector][netty_selector]》这里，我们最后分析到AbstractChannel的register0()的代码：

private void register0(ChannelPromise promise) {
                try {
                    // check if the channel is still open as it could be closed in the mean time when the register
                    // call was outside of the eventLoop
                    if (!promise.setUncancellable() || !ensureOpen(promise)) {
                        return;
                    }
                    boolean firstRegistration = neverRegistered;
                    doRegister();
                    neverRegistered = false;
                    registered = true;
    
                    // Ensure we call handlerAdded(...) before we actually notify the promise. This is needed as the
                    // user may already fire events through the pipeline in the ChannelFutureListener.
                    pipeline.invokeHandlerAddedIfNeeded();
    
                    safeSetSuccess(promise);
                    pipeline.fireChannelRegistered();
                    // Only fire a channelActive if the channel has never been registered. This prevents firing
                    // multiple channel actives if the channel is deregistered and re-registered.
                    if (isActive()) {
                        if (firstRegistration) {
                            pipeline.fireChannelActive();
                        } else if (config().isAutoRead()) {
                            // This channel was registered before and autoRead() is set. This means we need to begin read
                            // again so that we process inbound data.
                            //
                            // See https://github.com/netty/netty/issues/4805
                            beginRead();
                        }
                    }
                } catch (Throwable t) {
                    // Close the channel directly to avoid FD leak.
                    closeForcibly();
                    closeFuture.setClosed();
                    safeSetFailure(promise, t);
                }
            }

注册完成之后isActive()已经为true了,然后我们这个是第一次注册（新连接已经接入并且注册到selector上面了所以isActive()为true），所以会进入到pipeline.fireChannelActive().点击进入，和服务端一样，最后会进入HeadContext的channelActive函数：

@Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
           ctx.fireChannelActive();
    
            readIfIsAutoRead();
        }

ctx.fireChannel就是继续传播事件，readInfIsAutoRead()就是注册读事件，进入：

private void readIfIsAutoRead() {
                if (channel.config().isAutoRead()) {
                    channel.read();
                }
            }

channel.config().isAutoRead()就是是否自动阅读，默认是自动读取的。所以继续不停进入来到HeadContext的read方法：

@Override
       public void read(ChannelHandlerContext ctx) {
            unsafe.beginRead();
        }

继续进入AbstractNioChannel的doBeginRead():

@Override
        protected void doBeginRead() throws Exception {
            // Channel.read() or ChannelHandlerContext.read() was called
            final SelectionKey selectionKey = this.selectionKey;
            if (!selectionKey.isValid()) {
                return;
            }
    
            readPending = true;
    
            final int interestOps = selectionKey.interestOps();
            if ((interestOps & readInterestOp) == 0) {
                selectionKey.interestOps(interestOps | readInterestOp);
            }
        }

在这一篇文章《[netty源码阅读之客户端新连接之分配线程并注册selector][netty_selector]》的最后，我们注册进去的事件是0，也就是什么也不注册，所以这里final int interestOps = selectionKey.interestOps();返回0。

然后readInterestOp这个值又是什么呢，我们回顾《[netty源码阅读之客户端新连接之创建NioSocketChannel][netty_NioSocketChannel]》第一段，创建AbstractNioByteChannel的时候，传入了SelectionKey.OP\_READ，然后父类AbstractNioChannel的方法里面

this.readInterestOp = readInterestOp;

`赋值了`SelectionKey.OP\_READ`。所以readInterestOp就是赋值的值，查看源码是1。0&1是0，所以就相当于把readInterestOp这个读事件，注册进去了（在原来没有读事件的基础上，并且在不修改之前已有事件的基础上，把OP_READ事件注册进去）。`

perfect。

[netty_selector]: https://blog.csdn.net/fst438060684/article/details/81606266
[netty_NioSocketChannel]: https://blog.csdn.net/fst438060684/article/details/81586156