摘要：
=null&&now lastRead˃heartbeat）||（lastWrite！
- 目的：
- 维持provider和consumer之间的长连接
- 实现：
- dubbo心跳时间heartbeat默认是60s，超过heartbeat时间没有收到消息，就发送心跳消息(provider，consumer一样),如果连着3次(heartbeatTimeout为heartbeat*3)没有收到心跳响应，provider会关闭channel，而consumer会进行重连;不论是provider还是consumer的心跳检测都是通过启动定时任务的方式实现；
- provider绑定和consumer连接的入口：
public class HeaderExchanger implements Exchanger { public static final String NAME = "header"; @Override public ExchangeClient connect(URL url, ExchangeHandler handler) throws RemotingException { return new HeaderExchangeClient(Transporters.connect(url, new DecodeHandler(new HeaderExchangeHandler(handler))), true); } @Override public ExchangeServer bind(URL url, ExchangeHandler handler) throws RemotingException { return new HeaderExchangeServer(Transporters.bind(url, new DecodeHandler(new HeaderExchangeHandler(handler)))); } }
- provider启动心跳检测：
public HeaderExchangeServer(Server server) { if (server == null) { throw new IllegalArgumentException("server == null"); } this.server = server; this.heartbeat = server.getUrl().getParameter(Constants.HEARTBEAT_KEY, 0); //心跳超时时间默认为心跳时间的3倍 this.heartbeatTimeout = server.getUrl().getParameter(Constants.HEARTBEAT_TIMEOUT_KEY, heartbeat * 3); //如果心跳超时时间小于心跳时间的两倍则抛异常 if (heartbeatTimeout < heartbeat * 2) { throw new IllegalStateException("heartbeatTimeout < heartbeatInterval * 2"); } startHeatbeatTimer(); }
- startHeatbeatTimer的实现
- 先停止已有的定时任务，启动新的定时任务：
private void startHeatbeatTimer() { // 停止原有定时任务 stopHeartbeatTimer(); // 发起新的定时任务 if (heartbeat > 0) { heatbeatTimer = scheduled.scheduleWithFixedDelay( new HeartBeatTask(new HeartBeatTask.ChannelProvider() { public Collection<Channel> getChannels() { return Collections.unmodifiableCollection(HeaderExchangeServer.this.getChannels()); } }, heartbeat, heartbeatTimeout), heartbeat, heartbeat, TimeUnit.MILLISECONDS); } }
- HeartBeatTask的实现
- 遍历所有的channel，检测心跳间隔,如果超过心跳间隔没有读或写，则发送需要回复的心跳消息,最有判断是否心跳超时(heartbeatTimeout),如果超时，provider关闭channel，consumer进行重连
public void run() { try { long now = System.currentTimeMillis(); for (Channel channel : channelProvider.getChannels()) { if (channel.isClosed()) { continue; } try { Long lastRead = (Long) channel.getAttribute(HeaderExchangeHandler.KEY_READ_TIMESTAMP); Long lastWrite = (Long) channel.getAttribute(HeaderExchangeHandler.KEY_WRITE_TIMESTAMP); // 读写的时间，任一超过心跳间隔，发送心跳 if ((lastRead != null && now - lastRead > heartbeat) || (lastWrite != null && now - lastWrite > heartbeat)) { Request req = new Request(); req.setVersion("2.0.0"); req.setTwoWay(true); // 需要响应的心跳事件 req.setEvent(Request.HEARTBEAT_EVENT); channel.send(req); if (logger.isDebugEnabled()) { logger.debug("Send heartbeat to remote channel " + channel.getRemoteAddress() + ", cause: The channel has no data-transmission exceeds a heartbeat period: " + heartbeat + "ms"); } } // 最后读的时间，超过心跳超时时间 if (lastRead != null && now - lastRead > heartbeatTimeout) { logger.warn("Close channel " + channel + ", because heartbeat read idle time out: " + heartbeatTimeout + "ms"); // 客户端侧，重新连接服务端 if (channel instanceof Client) { try { ((Client) channel).reconnect(); } catch (Exception e) { //do nothing } // 服务端侧，关闭客户端连接 } else { channel.close(); } } } catch (Throwable t) { logger.warn("Exception when heartbeat to remote channel " + channel.getRemoteAddress(), t); } } } catch (Throwable t) { logger.warn("Unhandled exception when heartbeat, cause: " + t.getMessage(), t); } }
- consumer端的实现
- 默认需要心跳检测
public HeaderExchangeClient(Client client, boolean needHeartbeat) { if (client == null) { throw new IllegalArgumentException("client == null"); } this.client = client; // 创建 HeaderExchangeChannel 对象 this.channel = new HeaderExchangeChannel(client); // 读取心跳相关配置 String dubbo = client.getUrl().getParameter(Constants.DUBBO_VERSION_KEY); this.heartbeat = client.getUrl().getParameter(Constants.HEARTBEAT_KEY, dubbo != null && dubbo.startsWith("1.0.") ? Constants.DEFAULT_HEARTBEAT : 0); this.heartbeatTimeout = client.getUrl().getParameter(Constants.HEARTBEAT_TIMEOUT_KEY, heartbeat * 3); if (heartbeatTimeout < heartbeat * 2) { // 避免间隔太短 throw new IllegalStateException("heartbeatTimeout < heartbeatInterval * 2"); } // 发起心跳定时器 if (needHeartbeat) { startHeatbeatTimer(); } }
我们可以看到dubbo的心跳检测，服务端会发送发送心跳包，客户端也会发送心跳包，与一般只有客户端发送心跳包，服务端接受心跳是有所不同的。