核心代码逻辑：
org.apache.dolphinscheduler.server.master.registry.MasterSlotManager.SlotChangeListener#notify
public void notify(Map<String, MasterHeartBeat> masterNodeInfo) { List<Server> serverList = masterNodeInfo.values().stream() // TODO 这里其实就是过滤掉buzy的master节点 .filter(heartBeat -> !heartBeat.getServerStatus().equals(ServerStatus.BUSY)) .map(this::convertHeartBeatToServer).collect(Collectors.toList()); // TODO 同步master节点 syncMasterNodes(serverList);}计算 totalSlot和currentSlot
private void syncMasterNodes(List<Server> masterNodes) { slotLock.lock(); try { this.masterPriorityQueue.clear(); // TODO 这里会把所有的master节点都放入到masterPriorityQueue中，比如说 [192.168.220.1:12345,192.168.220.2:12345] this.masterPriorityQueue.putAll(masterNodes); // TODO 就是获取到本地ip的在队列中的位置 int tempCurrentSlot = masterPriorityQueue.getIndex(masterConfig.getMasterAddress()); // TODO 所有节点数量 int tempTotalSlot = masterNodes.size(); // TODO 正常情况下不会小于0 if (tempCurrentSlot < 0) { totalSlot = 0; currentSlot = 0; log.warn("Current master is not in active master list"); } else if (tempCurrentSlot != currentSlot || tempTotalSlot != totalSlot) { // TODO 这里其实就是记录的是比如说一共有两个slot，我的slot是0或者1 totalSlot = tempTotalSlot; currentSlot = tempCurrentSlot; log.info("Update master nodes, total master size: {}, current slot: {}", totalSlot, currentSlot); } } finally { slotLock.unlock(); }}this.masterPriorityQueue.putAll(masterNodes); 会计算索引
public void putAll(Collection<Server> serverList) { for (Server server : serverList) { this.queue.put(server); } // TODO 这里更新了hostIndexMap，存放的是 <host:port> -> 索引 refreshMasterList();}private void refreshMasterList() { hostIndexMap.clear(); Iterator<Server> iterator = queue.iterator(); int index = 0; while (iterator.hasNext()) { Server server = iterator.next(); String addr = NetUtils.getAddr(server.getHost(), server.getPort()); hostIndexMap.put(addr, index); index += 1; }}
command最终的获取逻辑:
比如说两个Master节点 : masterCount=2 thisMasterSlot=0 master1masterCount=2 thisMasterSlot=1 master2command中的数据如下 :1 master22 master13 master24 master1select * from t_ds_command where id % #{masterCount} = #{thisMasterSlot} order by process_instance_priority, id asc limit #{limit}有没有感到疑惑，就是如果一个master更新到的最新的，一个没有更新到，怎么办？
比如说，master1节点是这样的1 master22 master13 master24 master1比如说，master2节点是这样的，是不是发现master2节点都是他的，都可以拉取消费？那就导致重复消费，比如说1这个command1 master12 master13 master14 master1
org.apache.dolphinscheduler.service.process.ProcessServiceImpl#handleCommand
@Transactionalpublic @Nullable ProcessInstance handleCommand(String host, Command command) throws CronParseException, CodeGenerateException { // TODO 创建流程实例 ProcessInstance processInstance = constructProcessInstance(command, host); // cannot construct process instance, return null if (processInstance == null) { log.error("scan command, command parameter is error: {}", command); commandService.moveToErrorCommand(command, "process instance is null"); return null; } processInstance.setCommandType(command.getCommandType()); processInstance.addHistoryCmd(command.getCommandType()); processInstance.setTestFlag(command.getTestFlag()); // if the processDefinition is serial ProcessDefinition processDefinition = this.findProcessDefinition(processInstance.getProcessDefinitionCode(), processInstance.getProcessDefinitionVersion()); // TODO 是否是串行执行 if (processDefinition.getExecutionType().typeIsSerial()) { saveSerialProcess(processInstance, processDefinition); if (processInstance.getState() != WorkflowExecutionStatus.RUNNING_EXECUTION) { setSubProcessParam(processInstance); triggerRelationService.saveProcessInstanceTrigger(command.getId(), processInstance.getId()); deleteCommandWithCheck(command.getId()); // todo: this is a bad design to return null here, whether trigger the task return null; } } else { // TODO 并行执行 processInstanceDao.upsertProcessInstance(processInstance); } // TODO 这里其实还会向triggerRelation表中插入一条数据，是流程实例和triggerCode的关系 triggerRelationService.saveProcessInstanceTrigger(command.getId(), processInstance.getId()); // TODO 设置子流程参数 setSubProcessParam(processInstance); // TODO 删除command deleteCommandWithCheck(command.getId()); return processInstance;}注意：这个方法是加@Transactional的，所以说创建流程实例和删除Command是在一个事物里面的，如果不同的Master消费到同一个Command。肯定会有一个删除Command失败，这时会抛出一个异常，这样就会让数据库进行回滚。
图连接 : Master事件状态流转
TaskEventService组件中的TaskEventDispatchThread(线程)和TaskEventHandlerThread(线程)解析
其实就是Master自己状态(DISPATCH)和Worker汇报上来的状态(RUNNING、UPDATE_PID、RESULT)都会放入到eventQueue，TaskEventDispatchThread(线程)会阻塞的方式进行获取，然后放入到对应的TaskExecuteRunnable中(注意 : 不执行的)，只有通过TaskEventHandlerThread(线程)才会使用TaskExecuteThreadPool线程进行TaskExecuteRunnable的提交。
转载自Journey
原文链接：https://segmentfault.com/a/1190000044992842