超详解讲解xxl-job分布式框架源码 JobScheduleHelper详解

 

1.JobScheduleHelper类的作用

JobScheduleHelper就是xxl-job框架的核心代码，是调度中心执行任务调度的核心代码，主要功能就是进行任务的调度，计算任务下一次执行的有效时间，下图说明了

xxl-job如何保证高可用，如何保证数据一致性，同一时刻只有一个调度中心处理任务调度。

JobScheduleHelper这个类是非常重要的类，保证了后续集群的高可用和调度任务的一致性。

2.JobScheduleHelper如何知道新任务，如何判断任务何时执行

以上代码说明了任务何时开始添加到准备执行（并不是真正的执行，只是当前任务已经修改了状态既triggerStatus这个字段0 设置为1（启动）），就是简单来说只在数据库修改了当前任务的状态和当前任务第一次执行的时间。

真正开始执行任务的是JobScheduleHelper这个类，这个类有两个线程scheduleThread和ringThread。

1）scheduleThread负责筛选任务，挑选还没有触发或者快要触发的任务，挑选的方法是通过数据库查询job_info这个表，判断触发任务的时间是否小于当前时间+5s

2）ringThread线程负责scheduleThread筛选出来的任务进行一个个执行，具体看代码分析。

3.JobScheduleHelper源码解析

package com.xxl.job.admin.core.thread;

import com.xxl.job.admin.core.conf.XxlJobAdminConfig;
import com.xxl.job.admin.core.cron.CronExpression;
import com.xxl.job.admin.core.model.XxlJobInfo;
import com.xxl.job.admin.core.scheduler.MisfireStrategyEnum;
import com.xxl.job.admin.core.scheduler.ScheduleTypeEnum;
import com.xxl.job.admin.core.trigger.TriggerTypeEnum;
import com.xxl.job.core.util.DateUtil;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.SQLException;
import java.text.ParseException;
import java.util.*;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.TimeUnit;

/**
 * @author xuxueli 2019-05-21
 * 任务调度器
 * 工作流程：
 * 周期性的遍历所有的jobInfo这个表，通过数据库的行锁和事务一致性，通过for update 来保证多个调度中心集群在同一时间内只有一个调度中心在调度任务
 * 周期性的遍历所有的jobInfo这个表，读取触发时间小于nowtime+5s这个时间之前的所有任务，然后进行引入以下触发机制判断
 * 三种触发任务机制： 1）nowtime-TriggerNextTime()>PRE_READ_MS(5s) 既超过有效误差内，则查看当前任务的失效调度策略，若为立即重试一次，则立即触发调度任务，且触发类型为misfire
 *                  2)nowtime-TriggerNextTime()> ringData = new ConcurrentHashMap<>();

    public void start(){

        // schedule thread
        scheduleThread = new Thread(new Runnable() {
            @Override
            public void run() {

                try {
                    TimeUnit.MILLISECONDS.sleep(5000 - System.currentTimeMillis()%1000 );
                } catch (InterruptedException e) {
                    if (!scheduleThreadToStop) {
                        logger.error(e.getMessage(), e);
                    }
                }
                logger.info(">>>>>>>>> init xxl-job admin scheduler success.");

                // pre-read count: treadpool-size * trigger-qps (each trigger cost 50ms, qps = 1000/50 = 20)
                int preReadCount = (XxlJobAdminConfig.getAdminConfig().getTriggerPoolFastMax() + XxlJobAdminConfig.getAdminConfig().getTriggerPoolSlowMax()) * 20;

                while (!scheduleThreadToStop) {

                    // Scan Job
                    long start = System.currentTimeMillis();

                    Connection conn = null;
                    Boolean connAutoCommit = null;
                    PreparedStatement preparedStatement = null;

                    boolean preReadSuc = true;
                    try {

                        conn = XxlJobAdminConfig.getAdminConfig().getDataSource().getConnection();
                        connAutoCommit = conn.getAutoCommit();
                        //关闭自动提交
                        conn.setAutoCommit(false);

                        preparedStatement = conn.prepareStatement(  "select * from xxl_job_lock where lock_name = 'schedule_lock' for update" );
                        preparedStatement.execute();

                        // tx start

                        // 1、pre read
                        long nowTime = System.currentTimeMillis();
                        //关键部分，预读出 当前时间+5s 的所有触发任务的时间小于这个时间预读出时间的任务
                        List scheduleList = XxlJobAdminConfig.getAdminConfig().getXxlJobInfoDao().scheduleJobQuery(nowTime + PRE_READ_MS, preReadCount);
                        if (scheduleList!=null && scheduleList.size()>0) {
                            // 2、push time-ring
                            for (XxlJobInfo jobInfo: scheduleList) {

                                // time-ring jump
                                //遍历所有任务，过滤出所有过期任务
                                //过期任务的判断方式 当前时间>任务下一次触发时间+空闲间隔周期5s (在这段时间内任务还没触发的话说明任务超时过期了，既在5s的误差内还没出发任务)
                                if (nowTime > jobInfo.getTriggerNextTime() + PRE_READ_MS) {
                                    // 2.1、trigger-expire > 5s：pass && make next-trigger-time
                                    logger.warn(">>>>>>>>>>> xxl-job, schedule misfire, jobId = " + jobInfo.getId());

                                    // 1、misfire match  查询当前任务的过期策略
                                    MisfireStrategyEnum misfireStrategyEnum = MisfireStrategyEnum.match(jobInfo.getMisfireStrategy(), MisfireStrategyEnum.DO_NOTHING);
                                    if (MisfireStrategyEnum.FIRE_ONCE_NOW == misfireStrategyEnum) {
                                        // FIRE_ONCE_NOW 》 trigger  执行过期策略，过期立即执行一次
                                        JobTriggerPoolHelper.trigger(jobInfo.getId(), TriggerTypeEnum.MISFIRE, -1, null, null, null);
                                        logger.debug(">>>>>>>>>>> xxl-job, schedule push trigger : jobId = " + jobInfo.getId() );
                                    }

                                    // 2、fresh next
                                    refreshNextValidTime(jobInfo, new Date());
                                //否则不是过期任务  任务下一次触发时间+空闲间隔周期5s>当前时间>下一次任务触发时间  （在允许的误差之内都不算过期任务）
                                } else if (nowTime > jobInfo.getTriggerNextTime()) {
                                    // 2.2、trigger-expire < 5s：direct-trigger && make next-trigger-time
                                    // 1、trigger
                                    JobTriggerPoolHelper.trigger(jobInfo.getId(), TriggerTypeEnum.CRON, -1, null, null, null);
                                    logger.debug(">>>>>>>>>>> xxl-job, schedule push trigger : jobId = " + jobInfo.getId() );

                                    // 2、fresh next
                                    refreshNextValidTime(jobInfo, new Date());

                                    // next-trigger-time in 5s, pre-read again
                                    if (jobInfo.getTriggerStatus()==1 && nowTime + PRE_READ_MS > jobInfo.getTriggerNextTime()) {

                                        // 1、make ring second
                                        int ringSecond = (int)((jobInfo.getTriggerNextTime()/1000)%60);

                                        // 2、push time ring
                                        pushTimeRing(ringSecond, jobInfo.getId());

                                        // 3、fresh next
                                        refreshNextValidTime(jobInfo, new Date(jobInfo.getTriggerNextTime()));

                                    }

                                } else {
                                    // 2.3、trigger-pre-read：time-ring trigger && make next-trigger-time

                                    // 1、make ring second
                                    int ringSecond = (int)((jobInfo.getTriggerNextTime()/1000)%60);

                                    // 2、push time ring
                                    pushTimeRing(ringSecond, jobInfo.getId());

                                    // 3、fresh next
                                    refreshNextValidTime(jobInfo, new Date(jobInfo.getTriggerNextTime()));

                                }

                            }

                            // 3、update trigger info
                            for (XxlJobInfo jobInfo: scheduleList) {
                                XxlJobAdminConfig.getAdminConfig().getXxlJobInfoDao().scheduleUpdate(jobInfo);
                            }

                        } else {
                            preReadSuc = false;
                        }

                        // tx stop


                    } catch (Exception e) {
                        if (!scheduleThreadToStop) {
                            logger.error(">>>>>>>>>>> xxl-job, JobScheduleHelper#scheduleThread error:{}", e);
                        }
                    } finally {

                        // commit
                        if (conn != null) {
                            try {
                                conn.commit();
                            } catch (SQLException e) {
                                if (!scheduleThreadToStop) {
                                    logger.error(e.getMessage(), e);
                                }
                            }
                            try {
                                conn.setAutoCommit(connAutoCommit);
                            } catch (SQLException e) {
                                if (!scheduleThreadToStop) {
                                    logger.error(e.getMessage(), e);
                                }
                            }
                            try {
                                conn.close();
                            } catch (SQLException e) {
                                if (!scheduleThreadToStop) {
                                    logger.error(e.getMessage(), e);
                                }
                            }
                        }

                        // close PreparedStatement
                        if (null != preparedStatement) {
                            try {
                                preparedStatement.close();
                            } catch (SQLException e) {
                                if (!scheduleThreadToStop) {
                                    logger.error(e.getMessage(), e);
                                }
                            }
                        }
                    }
                    long cost = System.currentTimeMillis()-start;


                    // Wait seconds, align second
                    if (cost < 1000) {  // scan-overtime, not wait
                        try {
                            // pre-read period: success > scan each second; fail > skip this period;
                            TimeUnit.MILLISECONDS.sleep((preReadSuc?1000:PRE_READ_MS) - System.currentTimeMillis()%1000);
                        } catch (InterruptedException e) {
                            if (!scheduleThreadToStop) {
                                logger.error(e.getMessage(), e);
                            }
                        }
                    }

                }

                logger.info(">>>>>>>>>>> xxl-job, JobScheduleHelper#scheduleThread stop");
            }
        });
        scheduleThread.setDaemon(true);
        scheduleThread.setName("xxl-job, admin JobScheduleHelper#scheduleThread");
        scheduleThread.start();


        // ring thread
        ringThread = new Thread(new Runnable() {
            @Override
            public void run() {

                // align second
                try {
                    TimeUnit.MILLISECONDS.sleep(1000 - System.currentTimeMillis()%1000 );
                } catch (InterruptedException e) {
                    if (!ringThreadToStop) {
                        logger.error(e.getMessage(), e);
                    }
                }

                while (!ringThreadToStop) {
                    try {
                        synchronized (ringData){
                            if(ringData.isEmpty()){
                                     ringData.wait();
                            }
                        }

                        // second data
                        List ringItemData = new ArrayList<>();
                        int nowSecond = Calendar.getInstance().get(Calendar.SECOND);   // 避免处理耗时太长，跨过刻度，向前校验一个刻度；
                        for (int i = 0; i < 2; i++) {
                            List tmpData = ringData.remove( (nowSecond+60-i)%60 );
                            if (tmpData != null) {
                                ringItemData.addAll(tmpData);
                            }
                        }

                        // ring trigger
                        logger.debug(">>>>>>>>>>> xxl-job, time-ring beat : " + nowSecond + " = " + Arrays.asList(ringItemData) );
                        if (ringItemData.size() > 0) {
                            // do trigger
                            for (int jobId: ringItemData) {
                                // do trigger
                                JobTriggerPoolHelper.trigger(jobId, TriggerTypeEnum.CRON, -1, null, null, null);
                            }
                            // clear
                            ringItemData.clear();
                        }
                    } catch (Exception e) {
                        if (!ringThreadToStop) {
                            logger.error(">>>>>>>>>>> xxl-job, JobScheduleHelper#ringThread error:{}", e);
                        }
                    }

                    // next second, align second
                    try {
                        TimeUnit.MILLISECONDS.sleep(1000 - System.currentTimeMillis()%1000);
                    } catch (InterruptedException e) {
                        if (!ringThreadToStop) {
                            logger.error(e.getMessage(), e);
                        }
                    }
                }
                logger.info(">>>>>>>>>>> xxl-job, JobScheduleHelper#ringThread stop");
            }
        });
        ringThread.setDaemon(true);
        ringThread.setName("xxl-job, admin JobScheduleHelper#ringThread");
        ringThread.start();
    }

    private void refreshNextValidTime(XxlJobInfo jobInfo, Date fromTime) throws Exception {
        Date nextValidTime = generateNextValidTime(jobInfo, fromTime);
        if (nextValidTime != null) {
            jobInfo.setTriggerLastTime(jobInfo.getTriggerNextTime());
            jobInfo.setTriggerNextTime(nextValidTime.getTime());
        } else {
            jobInfo.setTriggerStatus(0);
            jobInfo.setTriggerLastTime(0);
            jobInfo.setTriggerNextTime(0);
            logger.warn(">>>>>>>>>>> xxl-job, refreshNextValidTime fail for job: jobId={}, scheduleType={}, scheduleConf={}",
                    jobInfo.getId(), jobInfo.getScheduleType(), jobInfo.getScheduleConf());
        }
    }

    private void pushTimeRing(int ringSecond, int jobId){
        synchronized (ringData){
        // push async ring
        List ringItemData = ringData.get(ringSecond);
        if (ringItemData == null) {
            ringItemData = new ArrayList();
            ringData.put(ringSecond, ringItemData);
        }
        ringItemData.add(jobId);
        ringData.notify();
        logger.debug(">>>>>>>>>>> xxl-job, schedule push time-ring : " + ringSecond + " = " + Arrays.asList(ringItemData) );
        }

    }

    public void toStop(){

        // 1、stop schedule
        scheduleThreadToStop = true;
        try {
            TimeUnit.SECONDS.sleep(1);  // wait
        } catch (InterruptedException e) {
            logger.error(e.getMessage(), e);
        }
        if (scheduleThread.getState() != Thread.State.TERMINATED){
            // interrupt and wait
            scheduleThread.interrupt();
            try {
                scheduleThread.join();
            } catch (InterruptedException e) {
                logger.error(e.getMessage(), e);
            }
        }

        // if has ring data
        boolean hasRingData = false;
        if (!ringData.isEmpty()) {
            for (int second : ringData.keySet()) {
                List tmpData = ringData.get(second);
                if (tmpData!=null && tmpData.size()>0) {
                    hasRingData = true;
                    break;
                }
            }
        }
        if (hasRingData) {
            try {
                TimeUnit.SECONDS.sleep(8);
            } catch (InterruptedException e) {
                logger.error(e.getMessage(), e);
            }
        }

        // stop ring (wait job-in-memory stop)
        ringThreadToStop = true;
        try {
            TimeUnit.SECONDS.sleep(1);
        } catch (InterruptedException e) {
            logger.error(e.getMessage(), e);
        }
        if (ringThread.getState() != Thread.State.TERMINATED){
            // interrupt and wait
            ringThread.interrupt();
            try {
                ringThread.join();
            } catch (InterruptedException e) {
                logger.error(e.getMessage(), e);
            }
        }

        logger.info(">>>>>>>>>>> xxl-job, JobScheduleHelper stop");
    }


    // ---------------------- tools ----------------------
    public static Date generateNextValidTime(XxlJobInfo jobInfo, Date fromTime) throws Exception {
        ScheduleTypeEnum scheduleTypeEnum = ScheduleTypeEnum.match(jobInfo.getScheduleType(), null);
        if (ScheduleTypeEnum.CRON == scheduleTypeEnum) {
            Date nextValidTime = new CronExpression(jobInfo.getScheduleConf()).getNextValidTimeAfter(fromTime);
            return nextValidTime;
        } else if (ScheduleTypeEnum.FIX_RATE == scheduleTypeEnum /*|| ScheduleTypeEnum.FIX_DELAY == scheduleTypeEnum*/) {
            return new Date(fromTime.getTime() + Integer.valueOf(jobInfo.getScheduleConf())*1000 );
        }
        return null;
    }



}

源码注释已经很详细了，如果不懂得话，欢迎留言区评论