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引言

随着大数据的发展，任务调度系统成为了数据处理和管理中至关重要的部分。Apache DolphinScheduler 是一款优秀的开源分布式工作流调度平台，在大数据场景中得到广泛应用。

在本文中，我们将对 Apache DolphinScheduler 1.3.9 版本的源码进行深入分析，介绍 Master 启动以及调度流程。

通过这些分析，开发者可以更好地理解 DolphinScheduler 的工作机制，并在实际使用中更高效地进行二次开发或优化。

Master Server启动

启动流程图

Master调度工作流流程图

MasterServer启动方法

public void run() {// init remoting serverNettyServerConfig serverConfig = new NettyServerConfig();serverConfig.setListenPort(masterConfig.getListenPort());this.nettyRemotingServer = new NettyRemotingServer(serverConfig);this.nettyRemotingServer.registerProcessor(CommandType.TASK_EXECUTE_RESPONSE, new TaskResponseProcessor());this.nettyRemotingServer.registerProcessor(CommandType.TASK_EXECUTE_ACK, new TaskAckProcessor());this.nettyRemotingServer.registerProcessor(CommandType.TASK_KILL_RESPONSE, new TaskKillResponseProcessor());this.nettyRemotingServer.start();// self tolerantthis.zkMasterClient.start();this.zkMasterClient.setStoppable(this);// scheduler startthis.masterSchedulerService.start();// start QuartzExecutors// what system should do if exceptiontry {logger.info("start Quartz server...");QuartzExecutors.getInstance().start();} catch (Exception e) {try {QuartzExecutors.getInstance().shutdown();} catch (SchedulerException e1) {logger.error("QuartzExecutors shutdown failed : " + e1.getMessage(), e1);}logger.error("start Quartz failed", e);}/*** register hooks, which are called before the process exits*/Runtime.getRuntime().addShutdownHook(new Thread(() -> {if (Stopper.isRunning()) {close("shutdownHook");}}));}

• nettyServer会注册三种Command

1. TASK_EXECUTE_ACK：Worker在接收到Master执行任务的请求后，会给Master发送一条Ack Command，告诉Master已经开始执行Task了。
2. TASK_EXECUTE_RESPONSE：Worker在执行完Task之后，会给Master发送一条Response Command，告诉Master任务调度/执行结果。
3. TASK_KILL_RESPONSE：Master接收到Task停止的请求会，会给Worker发送TASK_KILL_REQUEST Command，之后Worker会把Task_KILL_RESPONSE Command返回给Master。

• 启动调度和定时器。
• 添加ShutdownHook，关闭资源。

Master 配置文件

master.listen.port=5678# 限制Process Instance并发调度的线程数
master.exec.threads=100# 限制每个ProcessInstance可以执行的任务数
master.exec.task.num=20# 每一批次可以分发的任务数
master.dispatch.task.num=3# master需要选择一个稳定的worker去执行任务
# 算法有：Random，RoundRobin，LowerWeight。默认是LowerWeight
master.host.selector=LowerWeight# master需要向Zookeeper发送心跳，单位：秒
master.heartbeat.interval=10# master提交任务失败，重试次数
master.task.commit.retryTimes=5# master提交任务失败，重试时间间隔
master.task.commit.interval=1000# master最大cpu平均负载，只有当系统cpu平均负载还没有达到这个值，master才能调度任务
# 默认值为-1，系统cpu核数 * 2
master.max.cpuload.avg=-1# master为其他进程保留内存，只有当系统可用内存大于这个值，master才能调度
# 默认值0.3G
master.reserved.memory=0.3

Master Scheduler启动

MasterSchedulerService初始化方法

public void init(){// masterConfig.getMasterExecThreads()，master.properties里master.exec.threads=100// 该线程池的核心线程数和最大线程数为100this.masterExecService = (ThreadPoolExecutor)ThreadUtils.newDaemonFixedThreadExecutor("Master-Exec-Thread", masterConfig.getMasterExecThreads());NettyClientConfig clientConfig = new NettyClientConfig();this.nettyRemotingClient = new NettyRemotingClient(clientConfig);
}

MasterSchedulerService启动方法

public void run() {logger.info("master scheduler started");while (Stopper.isRunning()){try {// 这个方法是用来检查master cpu load和memory，判断master是否还有资源进行调度// 如果不能调度，Sleep 1 秒种boolean runCheckFlag = OSUtils.checkResource(masterConfig.getMasterMaxCpuloadAvg(), masterConfig.getMasterReservedMemory());if(!runCheckFlag) {Thread.sleep(Constants.SLEEP_TIME_MILLIS);continue;}if (zkMasterClient.getZkClient().getState() == CuratorFrameworkState.STARTED) {// 这里才是真正去执行调度的方法scheduleProcess();}} catch (Exception e) {logger.error("master scheduler thread error", e);}}
}

MasterSchedulerService调度方法

private void scheduleProcess() throws Exception {InterProcessMutex mutex = null;try {// 阻塞式获取分布式锁mutex = zkMasterClient.blockAcquireMutex();// 获取线程池的活跃线程数int activeCount = masterExecService.getActiveCount();// make sure to scan and delete command  table in one transaction// 获取其中一个command，必须保证操作都在一个事务里Command command = processService.findOneCommand();if (command != null) {logger.info("find one command: id: {}, type: {}", command.getId(),command.getCommandType());try{// 获取ProcessInstance，// 这个方法会根据master.exec.threads配置和活跃线程数来判断是否可以调度processInstanceProcessInstance processInstance = processService.handleCommand(logger,getLocalAddress(),this.masterConfig.getMasterExecThreads() - activeCount, command);if (processInstance != null) {logger.info("start master exec thread , split DAG ...");masterExecService.execute(new MasterExecThread(processInstance, processService, nettyRemotingClient));}}catch (Exception e){logger.error("scan command error ", e);processService.moveToErrorCommand(command, e.toString());}} else{//indicate that no command ,sleep for 1sThread.sleep(Constants.SLEEP_TIME_MILLIS);}} finally{// 释放分布式锁zkMasterClient.releaseMutex(mutex);}
}

ProcessService处理Command的方法

public ProcessInstance handleCommand(Logger logger, String host, int validThreadNum, Command command) {// 这里是去构造ProcessInstanceProcessInstance processInstance = constructProcessInstance(command, host);//cannot construct process instance, return null;if(processInstance == null){logger.error("scan command, command parameter is error: {}", command);moveToErrorCommand(command, "process instance is null");return null;}// 这里是检测当前剩余线程数是否大于等于该ProcessDefinition及其所有子Process的数量// 如果检测不通过，process instance的状态变为wait thread.并且返回空的process instanceif(!checkThreadNum(command, validThreadNum)){logger.info("there is not enough thread for this command: {}", command);return setWaitingThreadProcess(command, processInstance);}processInstance.setCommandType(command.getCommandType());processInstance.addHistoryCmd(command.getCommandType());saveProcessInstance(processInstance);this.setSubProcessParam(processInstance);delCommandByid(command.getId());return processInstance;
}

MasterExecThread初始化方法

public MasterExecThread(ProcessInstance processInstance, ProcessService processService, NettyRemotingClient nettyRemotingClient){this.processService = processService;this.processInstance = processInstance;this.masterConfig = SpringApplicationContext.getBean(MasterConfig.class);// master.properties文件里的master.task.exec.numint masterTaskExecNum = masterConfig.getMasterExecTaskNum();this.taskExecService = ThreadUtils.newDaemonFixedThreadExecutor("Master-Task-Exec-Thread",masterTaskExecNum);this.nettyRemotingClient = nettyRemotingClient;
}

MasterExecThread启动方法

public void run() {// 省略...try {if (processInstance.isComplementData() &&  Flag.NO == processInstance.getIsSubProcess()){// 补数逻辑... 暂不看executeComplementProcess();}else{// 执行task方法executeProcess();}}catch (Exception e){logger.error("master exec thread exception", e);logger.error("process execute failed, process id:{}", processInstance.getId());processInstance.setState(ExecutionStatus.FAILURE);processInstance.setEndTime(new Date());processService.updateProcessInstance(processInstance);}finally {taskExecService.shutdown();}
}private void executeProcess() throws Exception {// 前置prepareProcess();// 执行runProcess();// 后置endProcess();
}private void runProcess(){// 从根task开始提交submitPostNode(null);boolean sendTimeWarning = false;while(!processInstance.isProcessInstanceStop() && Stopper.isRunning()){// 省略部分代码...// 根据cpu load avg和Memorry判断是否可以调度if(canSubmitTaskToQueue()){submitStandByTask();}try {Thread.sleep(Constants.SLEEP_TIME_MILLIS);} catch (InterruptedException e) {logger.error(e.getMessage(),e);}updateProcessInstanceState();}logger.info("process:{} end, state :{}", processInstance.getId(), processInstance.getState());
}// 获取可以并行的task
/**
* task 1 -> task 2 -> task3
* task 4 -> task 5
* task 6
* task 1,task4,task6可以并行跑
*/
private void submitPostNode(String parentNodeName){Set<String> submitTaskNodeList = DagHelper.parsePostNodes(parentNodeName, skipTaskNodeList, dag, completeTaskList);List<TaskInstance> taskInstances = new ArrayList<>();for(String taskNode : submitTaskNodeList){taskInstances.add(createTaskInstance(processInstance, taskNode,dag.getNode(taskNode)));}// if previous node success , post node submitfor(TaskInstance task : taskInstances){if(readyToSubmitTaskQueue.contains(task)){continue;}if(completeTaskList.containsKey(task.getName())){logger.info("task {} has already run success", task.getName());continue;}if(task.getState().typeIsPause() || task.getState().typeIsCancel()){logger.info("task {} stopped, the state is {}", task.getName(), task.getState());}else{// task添加到priorityQueueaddTaskToStandByList(task);}}
}/*** handling the list of tasks to be submitted*/
private void submitStandByTask(){try {int length = readyToSubmitTaskQueue.size();for (int i=0;i<length;i++) {// 从队列里面取task, 提交给worker执行TaskInstance task = readyToSubmitTaskQueue.peek();// 先判断task的前置依赖有没有都运行成功，如果运行成功，在提交该task运行// 如果运行失败，或者没有执行，则不提交DependResult dependResult = getDependResultForTask(task);if(DependResult.SUCCESS == dependResult){if(retryTaskIntervalOverTime(task)){submitTaskExec(task);removeTaskFromStandbyList(task);}}else if(DependResult.FAILED == dependResult){// if the dependency fails, the current node is not submitted and the state changes to failure.dependFailedTask.put(task.getName(), task);removeTaskFromStandbyList(task);logger.info("task {},id:{} depend result : {}",task.getName(), task.getId(), dependResult);} else if (DependResult.NON_EXEC == dependResult) {// for some reasons(depend task pause/stop) this task would not be submitremoveTaskFromStandbyList(task);logger.info("remove task {},id:{} , because depend result : {}", task.getName(), task.getId(), dependResult);}}} catch (Exception e) {logger.error("submit standby task error",e);}
}/**
* 创建TaskExecThread
*/
private TaskInstance submitTaskExec(TaskInstance taskInstance) {MasterBaseTaskExecThread abstractExecThread = null;if(taskInstance.isSubProcess()){abstractExecThread = new SubProcessTaskExecThread(taskInstance);}else if(taskInstance.isDependTask()){abstractExecThread = new DependentTaskExecThread(taskInstance);}else if(taskInstance.isConditionsTask()){abstractExecThread = new ConditionsTaskExecThread(taskInstance);}else {abstractExecThread = new MasterTaskExecThread(taskInstance);}Future<Boolean> future = taskExecService.submit(abstractExecThread);activeTaskNode.putIfAbsent(abstractExecThread, future);return abstractExecThread.getTaskInstance();
}

MasterBaseTaskExecThread

MasterBaseTaskExecThread是SubProcessTaskExecThread，DependentTaskExecThread，ConditionsTaskExecThread，MasterTaskExecThread的父类，实现Callable接口。

• SubProcessTaskExecThread

  任务实例不会下发到worker节点执行，在submitTask(TaskInstance taskInstance)方法中，针对子流程，会增加一条子流程实例命令，然后在waitTaskQuit方法中循环等待子流程执行完成。在当前工作流运行结束后会继续运行子工作流并做相关状态更新，子工作流完全完成才同步状态为子工作流的状态。

• DependentTaskExecThread

  Dependent 节点，就是依赖检查节点。比如 A 流程依赖昨天的 B 流程执行成功，依赖节点会去检查 B 流程在昨天是否有执行成功的实例。

• ConditionsTaskExecThrea

  Conditions 是一个条件节点，根据上游任务运行状态，判断应该运行哪个下游任务。截止目前 Conditions 支持多个上游任务，但只支持两个下游任务。当上游任务数超过一个时，可以通过且以及或操作符实现复杂上游依赖。

• MasterTaskExecThread

  将任务实例下发到worker节点执行，并在waitTaskQuit方法中循环等待任务实例执行完成，任务完成后则即出。例如SQKL，Shell等任务类型。

MasterBaseTaskExecThread初始化方法

public MasterBaseTaskExecThread(TaskInstance taskInstance){this.processService = SpringApplicationContext.getBean(ProcessService.class);this.alertDao = SpringApplicationContext.getBean(AlertDao.class);this.cancel = false;this.taskInstance = taskInstance;this.masterConfig = SpringApplicationContext.getBean(MasterConfig.class);this.taskUpdateQueue = SpringApplicationContext.getBean(TaskPriorityQueueImpl.class);initTaskParams();
}

MasterBaseTaskExecThread执行方法

@Override
public Boolean call() throws Exception {this.processInstance = processService.findProcessInstanceById(taskInstance.getProcessInstanceId());return submitWaitComplete(); // 由各子类实现
}

MasterBaseTaskExecThread公共方法

submit()

protected TaskInstance submit(){// 提交任务重试次数. master.task.commit.retryTimes=5Integer commitRetryTimes = masterConfig.getMasterTaskCommitRetryTimes();// 提交任务失败，重试间隔时间 master.task.commit.interval=1000Integer commitRetryInterval = masterConfig.getMasterTaskCommitInterval();int retryTimes = 1;boolean submitDB = false;boolean submitTask = false;TaskInstance task = null;while (retryTimes <= commitRetryTimes){try {if(!submitDB){// 持久化TaskInstance到数据库task = processService.submitTask(taskInstance);if(task != null && task.getId() != 0){submitDB = true;}}if(submitDB && !submitTask){// 分发任务到Woroker执行submitTask = dispatchTask(task);}if(submitDB && submitTask){return task;}if(!submitDB){logger.error("task commit to db failed , taskId {} has already retry {} times, please check the database", taskInstance.getId(), retryTimes);}else if(!submitTask){logger.error("task commit  failed , taskId {} has already retry {} times, please check", taskInstance.getId(), retryTimes);}Thread.sleep(commitRetryInterval);} catch (Exception e) {logger.error("task commit to mysql and dispatcht task failed",e);}retryTimes += 1;}return task;
}

dispatchTask(TaskInstance task)

public Boolean dispatchTask(TaskInstance taskInstance) {try{// 如果是子流程，条件任务，依赖任务，直接返回true，不提交给worker执行if(taskInstance.isConditionsTask()|| taskInstance.isDependTask()|| taskInstance.isSubProcess()){return true;}if(taskInstance.getState().typeIsFinished()){logger.info(String.format("submit task , but task [%s] state [%s] is already  finished. ", taskInstance.getName(), taskInstance.getState().toString()));return true;}// task cannot submit when runningif(taskInstance.getState() == ExecutionStatus.RUNNING_EXECUTION){logger.info(String.format("submit to task, but task [%s] state already be running. ", taskInstance.getName()));return true;}logger.info("task ready to submit: {}", taskInstance);/***  taskPriority*/TaskPriority taskPriority = buildTaskPriority(processInstance.getProcessInstancePriority().getCode(),processInstance.getId(),taskInstance.getProcessInstancePriority().getCode(),taskInstance.getId(),org.apache.dolphinscheduler.common.Constants.DEFAULT_WORKER_GROUP);// 放入TaskPriorityQueue中，// org.apache.dolphinscheduler.service.queue.TaskPriorityQueueImpl用于消费，从队列里取出TaskInstance，提交给Worker执行taskUpdateQueue.put(taskPriority);logger.info(String.format("master submit success, task : %s", taskInstance.getName()) );return true;}catch (Exception e){logger.error("submit task  Exception: ", e);logger.error("task error : %s", JSONUtils.toJson(taskInstance));return false;}
}

MasterTaskExecThread

submitWaitComplete()

public Boolean submitWaitComplete() {Boolean result = false;// 提交任务this.taskInstance = submit();if(this.taskInstance == null){logger.error("submit task instance to mysql and queue failed , please check and fix it");return result;}if(!this.taskInstance.getState().typeIsFinished()) {// 等待任务执行结果result = waitTaskQuit();}taskInstance.setEndTime(new Date());processService.updateTaskInstance(taskInstance);logger.info("task :{} id:{}, process id:{}, exec thread completed ",this.taskInstance.getName(),taskInstance.getId(), processInstance.getId() );return result;
}

waitTaskQuit()

public Boolean waitTaskQuit(){// query new statetaskInstance = processService.findTaskInstanceById(taskInstance.getId());logger.info("wait task: process id: {}, task id:{}, task name:{} complete",this.taskInstance.getProcessInstanceId(), this.taskInstance.getId(), this.taskInstance.getName());while (Stopper.isRunning()){try {if(this.processInstance == null){logger.error("process instance not exists , master task exec thread exit");return true;}// task instance add queue , waiting worker to killif(this.cancel || this.processInstance.getState() == ExecutionStatus.READY_STOP){cancelTaskInstance();}if(processInstance.getState() == ExecutionStatus.READY_PAUSE){pauseTask();}// task instance finishedif (taskInstance.getState().typeIsFinished()){// if task is final result , then remove taskInstance from cache// taskInstanceCacheManager其实现类为：org.apache.dolphinscheduler.server.master.cache.impl.TaskInstanceCacheManagerImpl// taskInstance在触发ack和response Command会被添加到taskInstanceCache里taskInstanceCacheManager.removeByTaskInstanceId(taskInstance.getId());break;}if (checkTaskTimeout()) {this.checkTimeoutFlag = !alertTimeout();}// updateProcessInstance task instancetaskInstance = processService.findTaskInstanceById(taskInstance.getId());processInstance = processService.findProcessInstanceById(processInstance.getId());Thread.sleep(Constants.SLEEP_TIME_MILLIS);} catch (Exception e) {logger.error("exception",e);if (processInstance != null) {logger.error("wait task quit failed, instance id:{}, task id:{}",processInstance.getId(), taskInstance.getId());}}}return true;
}

SubProcessTaskExecThread

submitWaitComplete()

public Boolean submitWaitComplete() {Boolean result = false;try{// submit task instancethis.taskInstance = submit();if(taskInstance == null){logger.error("sub work flow submit task instance to mysql and queue failed , please check and fix it");return result;}setTaskInstanceState();waitTaskQuit();subProcessInstance = processService.findSubProcessInstance(processInstance.getId(), taskInstance.getId());// at the end of the subflow , the task state is changed to the subflow stateif(subProcessInstance != null){if(subProcessInstance.getState() == ExecutionStatus.STOP){this.taskInstance.setState(ExecutionStatus.KILL);}else{this.taskInstance.setState(subProcessInstance.getState());}}taskInstance.setEndTime(new Date());processService.updateTaskInstance(taskInstance);logger.info("subflow task :{} id:{}, process id:{}, exec thread completed ",this.taskInstance.getName(),taskInstance.getId(), processInstance.getId() );result = true;}catch (Exception e){logger.error("exception: ",e);if (null != taskInstance) {logger.error("wait task quit failed, instance id:{}, task id:{}",processInstance.getId(), taskInstance.getId());}}return result;
}

waitTaskQuit()

private void waitTaskQuit() throws InterruptedException {logger.info("wait sub work flow: {} complete", this.taskInstance.getName());if (taskInstance.getState().typeIsFinished()) {logger.info("sub work flow task {} already complete. task state:{}, parent work flow instance state:{}",this.taskInstance.getName(),this.taskInstance.getState(),this.processInstance.getState());return;}while (Stopper.isRunning()) {// waiting for subflow process instance establishmentif (subProcessInstance == null) {Thread.sleep(Constants.SLEEP_TIME_MILLIS);if(!setTaskInstanceState()){continue;}}subProcessInstance = processService.findProcessInstanceById(subProcessInstance.getId());if (checkTaskTimeout()) {this.checkTimeoutFlag = !alertTimeout();handleTimeoutFailed();}updateParentProcessState();if (subProcessInstance.getState().typeIsFinished()){break;}if(this.processInstance.getState() == ExecutionStatus.READY_PAUSE){// parent process "ready to pause" , child process "pause"pauseSubProcess();}else if(this.cancel || this.processInstance.getState() == ExecutionStatus.READY_STOP){// parent Process "Ready to Cancel" , subflow "Cancel"stopSubProcess();}Thread.sleep(Constants.SLEEP_TIME_MILLIS);}
}

ConditionsTaskExecThread

submitWaitComplete()

public Boolean submitWaitComplete() {try{this.taskInstance = submit();logger = LoggerFactory.getLogger(LoggerUtils.buildTaskId(LoggerUtils.TASK_LOGGER_INFO_PREFIX,taskInstance.getProcessDefinitionId(),taskInstance.getProcessInstanceId(),taskInstance.getId()));String threadLoggerInfoName = String.format(Constants.TASK_LOG_INFO_FORMAT, processService.formatTaskAppId(this.taskInstance));Thread.currentThread().setName(threadLoggerInfoName);initTaskParameters();logger.info("dependent task start");// 等待判断waitTaskQuit();// 更新最终依赖结果updateTaskState();}catch (Exception e){logger.error("conditions task run exception" , e);}return true;
}

waitTaskQuit

private void waitTaskQuit() {List<TaskInstance> taskInstances = processService.findValidTaskListByProcessId(taskInstance.getProcessInstanceId());for(TaskInstance task : taskInstances){completeTaskList.putIfAbsent(task.getName(), task.getState());}// 获取所有依赖结果List<DependResult> modelResultList = new ArrayList<>();for(DependentTaskModel dependentTaskModel : dependentParameters.getDependTaskList()){List<DependResult> itemDependResult = new ArrayList<>();for(DependentItem item : dependentTaskModel.getDependItemList()){itemDependResult.add(getDependResultForItem(item));}DependResult modelResult = DependentUtils.getDependResultForRelation(dependentTaskModel.getRelation(), itemDependResult);modelResultList.add(modelResult);}// 根据逻辑运算符，合并依赖结果conditionResult = DependentUtils.getDependResultForRelation(dependentParameters.getRelation(), modelResultList);logger.info("the conditions task depend result : {}", conditionResult);
}

DependentTaskExecThread

submitWaitComplete()

public Boolean submitWaitComplete() {try{logger.info("dependent task start");this.taskInstance = submit();logger = LoggerFactory.getLogger(LoggerUtils.buildTaskId(LoggerUtils.TASK_LOGGER_INFO_PREFIX,taskInstance.getProcessDefinitionId(),taskInstance.getProcessInstanceId(),taskInstance.getId()));String threadLoggerInfoName = String.format(Constants.TASK_LOG_INFO_FORMAT, processService.formatTaskAppId(this.taskInstance));Thread.currentThread().setName(threadLoggerInfoName);initTaskParameters();initDependParameters();waitTaskQuit();updateTaskState();}catch (Exception e){logger.error("dependent task run exception" , e);}return true;
}

waitTaskQuit()

private Boolean waitTaskQuit() {logger.info("wait depend task : {} complete", this.taskInstance.getName());if (taskInstance.getState().typeIsFinished()) {logger.info("task {} already complete. task state:{}",this.taskInstance.getName(),this.taskInstance.getState());return true;}while (Stopper.isRunning()) {try{if(this.processInstance == null){logger.error("process instance not exists , master task exec thread exit");return true;}// 省略部分代码// allDependentTaskFinish()等待所有依赖任务执行结束if ( allDependentTaskFinish() || taskInstance.getState().typeIsFinished()){break;}// update process tasktaskInstance = processService.findTaskInstanceById(taskInstance.getId());processInstance = processService.findProcessInstanceById(processInstance.getId());Thread.sleep(Constants.SLEEP_TIME_MILLIS);} catch (Exception e) {logger.error("exception",e);if (processInstance != null) {logger.error("wait task quit failed, instance id:{}, task id:{}",processInstance.getId(), taskInstance.getId());}}}return true;
}

TaskPriorityQueueConsumer

@Override
public void run() {List<TaskPriority> failedDispatchTasks = new ArrayList<>();while (Stopper.isRunning()){try {// 每一批次分发任务数量，master.dispatch.task.num = 3int fetchTaskNum = masterConfig.getMasterDispatchTaskNumber();failedDispatchTasks.clear();for(int i = 0; i < fetchTaskNum; i++){if(taskPriorityQueue.size() <= 0){Thread.sleep(Constants.SLEEP_TIME_MILLIS);continue;}// if not task , blocking here// 从队列里面获取taskTaskPriority taskPriority = taskPriorityQueue.take();// 分发给worker执行boolean dispatchResult = dispatch(taskPriority);if(!dispatchResult){failedDispatchTasks.add(taskPriority);}}if (!failedDispatchTasks.isEmpty()) {// 分发失败的任务，需要重新加入队列中，等待重新分发for (TaskPriority dispatchFailedTask : failedDispatchTasks) {taskPriorityQueue.put(dispatchFailedTask);}// If there are tasks in a cycle that cannot find the worker group,// sleep for 1 secondif (taskPriorityQueue.size() <= failedDispatchTasks.size()) {TimeUnit.MILLISECONDS.sleep(Constants.SLEEP_TIME_MILLIS);}}}catch (Exception e){logger.error("dispatcher task error",e);}}
}/*** dispatch task** @param taskPriority taskPriority* @return result*/
protected boolean dispatch(TaskPriority taskPriority) {boolean result = false;try {int taskInstanceId = taskPriority.getTaskId();TaskExecutionContext context = getTaskExecutionContext(taskInstanceId);ExecutionContext executionContext = new ExecutionContext(context.toCommand(), ExecutorType.WORKER, context.getWorkerGroup());if (taskInstanceIsFinalState(taskInstanceId)){// when task finish, ignore this task, there is no need to dispatch anymorereturn true;}else{// 分发任务// 分发算法支持：低负载优先算法，随机算法， 轮询算法。result = dispatcher.dispatch(executionContext);}} catch (ExecuteException e) {logger.error("dispatch error: {}",e.getMessage());}return result;
}

通过对 Apache DolphinScheduler 1.3.9 的源码分析，我们深入了解了其核心模块的设计和实现。DolphinScheduler 的 Master 架构充分保证了任务调度的高可用性和扩展性，而通过 Zookeeper 实现的集群协调则为系统提供了强大的容错机制。

如果你对 Apache DolphinScheduler 的源码有兴趣，可以深入研究其任务调度策略的细节部分，或者根据自身业务场景进行二次开发，充分发挥 DolphinScheduler 的调度能力。

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