RocketMQ中的通信模块详解
作者:潜水路人甲
通信机制
RocketMQ消息队列集群主要包括NameServer、Broker(Master/Slave)、Producer、Consumer4个角色,基本通讯流程如下:
(1) Broker启动后需要完成一次将自己注册至NameServer的操作;随后每隔30s时间定时向NameServer上报Topic路由信息。
(2) 消息生产者Producer作为客户端发送消息时候,需要根据消息的Topic从本地缓存的TopicPublishInfoTable获取路由信息。如果没有则更新路由信息会从NameServer上重新拉取,同时Producer会默认每隔30s向NameServer拉取一次路由信息。
(3) 消息生产者Producer根据2)中获取的路由信息选择一个队列(MessageQueue)进行消息发送;Broker作为消息的接收者接收消息并落盘存储。
(4) 消息消费者Consumer根据2)中获取的路由信息,并再完成客户端的负载均衡后,选择其中的某一个或者某几个消息队列来拉取消息并进行消费。
从上面1)~3)中可以看出在消息生产者, Broker和NameServer之间都会发生通信(这里只说了MQ的部分通信),因此如何设计一个良好的网络通信模块在MQ中至关重要,它将决定RocketMQ集群整体的消息传输能力与最终的性能。
rocketmq-remoting 模块是 RocketMQ消息队列中负责网络通信的模块,它几乎被其他所有需要网络通信的模块(诸如rocketmq-client、rocketmq-broker、rocketmq-namesrv)所依赖和引用。为了实现客户端与服务器之间高效的数据请求与接收,RocketMQ消息队列自定义了通信协议并在Netty的基础之上扩展了通信模块。
Remoting通信类
通信类结构:
NettyRemotingServer
NettyRemotingServer为服务端实现类,在NamesrvController中被构造。
NettyRemotingServer构造时主要工作是初始化下列属性,构造时判断useEpoll来决定EventLoopGroup的实现。
private final ServerBootstrap serverBootstrap; private final EventLoopGroup eventLoopGroupSelector; private final EventLoopGroup eventLoopGroupBoss; private final NettyServerConfig nettyServerConfig; private final ExecutorService publicExecutor; private final ChannelEventListener channelEventListener;
NettyRemotingServer启动
@Override public void start() { this.defaultEventExecutorGroup = new DefaultEventExecutorGroup( nettyServerConfig.getServerWorkerThreads(), new ThreadFactory() { private AtomicInteger threadIndex = new AtomicInteger(0); @Override public Thread newThread(Runnable r) { return new Thread(r, "NettyServerCodecThread_" + this.threadIndex.incrementAndGet()); } }); prepareSharableHandlers(); ServerBootstrap childHandler = this.serverBootstrap.group(this.eventLoopGroupBoss, this.eventLoopGroupSelector) .channel(useEpoll() ? EpollServerSocketChannel.class : NioServerSocketChannel.class) .option(ChannelOption.SO_BACKLOG, 1024) .option(ChannelOption.SO_REUSEADDR, true) .option(ChannelOption.SO_KEEPALIVE, false) .childOption(ChannelOption.TCP_NODELAY, true) .childOption(ChannelOption.SO_SNDBUF, nettyServerConfig.getServerSocketSndBufSize()) .childOption(ChannelOption.SO_RCVBUF, nettyServerConfig.getServerSocketRcvBufSize()) .localAddress(new InetSocketAddress(this.nettyServerConfig.getListenPort())) .childHandler(new ChannelInitializer<SocketChannel>() { @Override public void initChannel(SocketChannel ch) throws Exception { //添加handler,握手、编解码、idle检测、连接管理、消息处理 ch.pipeline() .addLast(defaultEventExecutorGroup, HANDSHAKE_HANDLER_NAME, handshakeHandler) .addLast(defaultEventExecutorGroup, encoder, new NettyDecoder(), new IdleStateHandler(0, 0, nettyServerConfig.getServerChannelMaxIdleTimeSeconds()), connectionManageHandler, serverHandler ); } }); if (nettyServerConfig.isServerPooledByteBufAllocatorEnable()) { childHandler.childOption(ChannelOption.ALLOCATOR, PooledByteBufAllocator.DEFAULT); } try { ChannelFuture sync = this.serverBootstrap.bind().sync(); InetSocketAddress addr = (InetSocketAddress) sync.channel().localAddress(); this.port = addr.getPort(); } catch (InterruptedException e1) { throw new RuntimeException("this.serverBootstrap.bind().sync() InterruptedException", e1); } if (this.channelEventListener != null) { this.nettyEventExecutor.start(); } this.timer.scheduleAtFixedRate(new TimerTask() { @Override public void run() { try { NettyRemotingServer.this.scanResponseTable(); } catch (Throwable e) { log.error("scanResponseTable exception", e); } } }, 1000 * 3, 1000); }
主要关注initChannel方法中添加的handler,NettyConnectManageHandler
//消息处理核心类 @ChannelHandler.Sharable class NettyServerHandler extends SimpleChannelInboundHandler<RemotingCommand> { @Override protected void channelRead0(ChannelHandlerContext ctx, RemotingCommand msg) throws Exception { processMessageReceived(ctx, msg); } } //连接管理处理类 @ChannelHandler.Sharable class NettyConnectManageHandler extends ChannelDuplexHandler { @Override public void channelActive(ChannelHandlerContext ctx) throws Exception { final String remoteAddress = RemotingHelper.parseChannelRemoteAddr(ctx.channel()); log.info("NETTY SERVER PIPELINE: channelActive, the channel[{}]", remoteAddress); super.channelActive(ctx); if (NettyRemotingServer.this.channelEventListener != null) { NettyRemotingServer.this.putNettyEvent(new NettyEvent(NettyEventType.CONNECT, remoteAddress, ctx.channel())); } } @Override public void channelInactive(ChannelHandlerContext ctx) throws Exception { final String remoteAddress = RemotingHelper.parseChannelRemoteAddr(ctx.channel()); log.info("NETTY SERVER PIPELINE: channelInactive, the channel[{}]", remoteAddress); super.channelInactive(ctx); if (NettyRemotingServer.this.channelEventListener != null) { NettyRemotingServer.this.putNettyEvent(new NettyEvent(NettyEventType.CLOSE, remoteAddress, ctx.channel())); } } @Override public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception { if (evt instanceof IdleStateEvent) { IdleStateEvent event = (IdleStateEvent) evt; if (event.state().equals(IdleState.ALL_IDLE)) { final String remoteAddress = RemotingHelper.parseChannelRemoteAddr(ctx.channel()); log.warn("NETTY SERVER PIPELINE: IDLE exception [{}]", remoteAddress); RemotingUtil.closeChannel(ctx.channel()); if (NettyRemotingServer.this.channelEventListener != null) { NettyRemotingServer.this .putNettyEvent(new NettyEvent(NettyEventType.IDLE, remoteAddress, ctx.channel())); } } } ctx.fireUserEventTriggered(evt); } @Override public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception { final String remoteAddress = RemotingHelper.parseChannelRemoteAddr(ctx.channel()); log.warn("NETTY SERVER PIPELINE: exceptionCaught {}", remoteAddress); log.warn("NETTY SERVER PIPELINE: exceptionCaught exception.", cause); if (NettyRemotingServer.this.channelEventListener != null) { NettyRemotingServer.this.putNettyEvent(new NettyEvent(NettyEventType.EXCEPTION, remoteAddress, ctx.channel())); } RemotingUtil.closeChannel(ctx.channel()); } }
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