Netty笔记-Channel的Register

这一篇介绍了如何Channel如何接受SelectionKey.OP_ACCEPT的流程,接下就是接受SelectionKey.OP_READ的流程

1.NioEventLoop的processSelectedKey

当readyOps为SelectionKey.OP_ACCEPT则进入AbstractNioMessageChannel中的unsafe的read流程

private void processSelectedKey(SelectionKey k, AbstractNioChannel ch) {
         int readyOps = k.readyOps();
         if ((readyOps & (SelectionKey.OP_READ | SelectionKey.OP_ACCEPT)) != 0 || readyOps == 0) {
                unsafe.read();
            }
    }

2. 回顾ServerSocketChannel的accept方法

我们先回顾下nio中ServerSocketChannel的accept方法,在接受到SelectionKey.OP_ACCEPT时,调用该方法获取新连接的SocketChannel,并将SelectionKey.OP_READ注册到selector当中去,Netty中封装势必有这样处理的代码

private void handleInput(final SelectionKey key) throws IOException {
        if (key.isValid()) {
            // 处理新接入的请求消息
            if (key.isAcceptable()) {
                // Accept the new connection
                ServerSocketChannel ssc = (ServerSocketChannel) key.channel();
                SocketChannel sc = ssc.accept();
                sc.configureBlocking(false);
                // Add the new connection to the selector
                sc.register(selector, SelectionKey.OP_READ);
            }
        }
    }

2. NioMessageUnsafe的read方法

    private final class NioMessageUnsafe extends AbstractNioUnsafe {

        private final List<Object> readBuf = new ArrayList<Object>();

        @Override
        public void read() {
            assert eventLoop().inEventLoop();
            final ChannelConfig config = config();
            final ChannelPipeline pipeline = pipeline();
            final RecvByteBufAllocator.Handle allocHandle = unsafe().recvBufAllocHandle();
            allocHandle.reset(config);

            boolean closed = false;
            Throwable exception = null;
            try {
                try {
                    do {
                        int localRead = doReadMessages(readBuf);
                        if (localRead == 0) {
                            break;
                        }
                        if (localRead < 0) {
                            closed = true;
                            break;
                        }

                        allocHandle.incMessagesRead(localRead);
                    } while (allocHandle.continueReading());
                } catch (Throwable t) {
                    exception = t;
                }

                int size = readBuf.size();
                for (int i = 0; i < size; i ++) {
                    readPending = false;
                    pipeline.fireChannelRead(readBuf.get(i));
                }
                readBuf.clear();
                allocHandle.readComplete();
                pipeline.fireChannelReadComplete();

                if (exception != null) {
                    closed = closeOnReadError(exception);

                    pipeline.fireExceptionCaught(exception);
                }

                if (closed) {
                    inputShutdown = true;
                    if (isOpen()) {
                        close(voidPromise());
                    }
                }
            } finally {
                // Check if there is a readPending which was not processed yet.
                // This could be for two reasons:
                // * The user called Channel.read() or ChannelHandlerContext.read() in channelRead(...) method
                // * The user called Channel.read() or ChannelHandlerContext.read() in channelReadComplete(...) method
                //
                // See https://github.com/netty/netty/issues/2254
                if (!readPending && !config.isAutoRead()) {
                    removeReadOp();
                }
            }
        }
    }

read方法最需要关注的readBuf,readBuf是NioSocketChannel的数组,其由doReadMessages处理获取,doReadMessages中调用了SocketUtils.accept方法,其内部调用了ServerSocketChannel的accept方法,NioSocketChannel对ServerSocketChannel进行了包装

@Override
    protected int doReadMessages(List<Object> buf) throws Exception {
        SocketChannel ch = SocketUtils.accept(javaChannel());

        try {
            if (ch != null) {
                buf.add(new NioSocketChannel(this, ch));
                return 1;
            }
        } catch (Throwable t) {
            logger.warn("Failed to create a new channel from an accepted socket.", t);

            try {
                ch.close();
            } catch (Throwable t2) {
                logger.warn("Failed to close a socket.", t2);
            }
        }

        return 0;
    }

   //SocketUtils
    public static SocketChannel accept(final ServerSocketChannel serverSocketChannel) throws IOException {
        try {
            return AccessController.doPrivileged(new PrivilegedExceptionAction<SocketChannel>() {
                @Override
                public SocketChannel run() throws IOException {
                    return serverSocketChannel.accept();
                }
            });
        } catch (PrivilegedActionException e) {
            throw (IOException) e.getCause();
        }
    }

3.NioSocketChannel

NioSocketChannel调用了父类AbstractNioByteChannel的构造函数,其监听的事件是SelectionKey.OP_READ

    protected AbstractNioByteChannel(Channel parent, SelectableChannel ch) {
        super(parent, ch, SelectionKey.OP_READ);
    }

4.ServerBootstrapAcceptor中register

ServerBootstrapAcceptor是在ServerBootstrap初始化时作为一个ChannelInboundHandler添加到Pineline中,其用于处理接收的Channel

在channelRead方法中调用了EventLoopGroup的register方法,将Channel注册到work线程中(监听SelectionKey.OP_READ事件)

 @Override
        @SuppressWarnings("unchecked")
        public void channelRead(ChannelHandlerContext ctx, Object msg) {
            final Channel child = (Channel) msg;

            child.pipeline().addLast(childHandler);

            setChannelOptions(child, childOptions, logger);

            for (Entry<AttributeKey<?>, Object> e: childAttrs) {
                child.attr((AttributeKey<Object>) e.getKey()).set(e.getValue());
            }

            try {
                childGroup.register(child).addListener(new ChannelFutureListener() {
                    @Override
                    public void operationComplete(ChannelFuture future) throws Exception {
                        if (!future.isSuccess()) {
                            forceClose(child, future.cause());
                        }
                    }
                });
            } catch (Throwable t) {
                forceClose(child, t);
            }
        }

参考:
Netty 接受请求过程源码分析 (基于4.1.23)
Netty源码分析-Server端启动