在xxl-job中，有三个角色，一个是执行器，一个人服务端（注册中心），另一个就是调度中心了。而任务调度器可以说是调度中心的最核心，我们发往执行器的任务，都是从任务调度器发出来的（除手动执行的）。
调度中心在服务启动初始化Bean时，执行了com.xxl.job.admin.core.conf.XxlJobAdminConfig#afterPropertiesSet方法
其中XxlJobScheduler的init方法
public void init() throws Exception {
// init i18n
initI18n();
// admin trigger pool start
JobTriggerPoolHelper.toStart();
// admin registry monitor run
JobRegistryHelper.getInstance().start();
// admin fail-monitor run
JobFailMonitorHelper.getInstance().start();
// admin lose-monitor run ( depend on JobTriggerPoolHelper )
JobCompleteHelper.getInstance().start();
// admin log report start
JobLogReportHelper.getInstance().start();
// 启动任务调度
JobScheduleHelper.getInstance().start();
logger.info(">>>>>>>>> init xxl-job admin success.");
}
在最下一行，启动了任务调度com.xxl.job.admin.core.thread.JobScheduleHelper#start，该方法分了两部分：scheduleThread和ringThread
第一部分：调度线程scheduleThread
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();
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();
//<1>：扫描任务
List<XxlJobInfo> scheduleList = XxlJobAdminConfig.getAdminConfig().getXxlJobInfoDao().scheduleJobQuery(nowTime + PRE_READ_MS, preReadCount);
if (scheduleList!=null && scheduleList.size()>0) {
// 2、push time-ring
for (XxlJobInfo jobInfo: scheduleList) {
// <2>: 调度时间过了5s
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
//过期策略
MisfireStrategyEnum misfireStrategyEnum = MisfireStrategyEnum.match(jobInfo.getMisfireStrategy(), MisfireStrategyEnum.DO_NOTHING);
if (MisfireStrategyEnum.FIRE_ONCE_NOW == misfireStrategyEnum) {
// FIRE_ONCE_NOW 》 trigger
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());
//<3>: 调度时间在5s内
} 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
// 添加到时间刻度轮
pushTimeRing(ringSecond, jobInfo.getId());
// 3、fresh next
refreshNextValidTime(jobInfo, new Date(jobInfo.getTriggerNextTime()));
}
} else { // <4>: 还差点时间才能执行
// 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) {
} finally {
}
long cost = System.currentTimeMillis()-start;
// <5>:控制速度
if (cost < 1000) {
TimeUnit.MILLISECONDS.sleep();
}
}
}
});
scheduleThread.setDaemon(true);
scheduleThread.setName("xxl-job, admin JobScheduleHelper#scheduleThread");
scheduleThread.start();
<1>：获取5s内要执行的任务配置
<2>：任务超过了当前执行时间5s（前面耽误超时了）：
按照配置的过期策略（立刻执行一次 or 丢弃）来判断是否继续执行任务，并计算好下一次执行时间更新到数据库
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;
}
解析corn表达式
<3>：任务调度时间在当前时间5s内：先执行一次，刷新下次执行时间。如果下次执行时间还在5s内，则加到上
// 1、make ring second int ringSecond = (int)((jobInfo.getTriggerNextTime()/1000)%60); // 2、push time ring pushTimeRing(ringSecond, jobInfo.getId());
时间刻度轮根据下次执行时间，按时钟满60个刻度 ，取任务id放到 volatile修饰的Map<Integer, List<Integer>>中，供ringThread线程来调度。
private void pushTimeRing(int ringSecond, int jobId){
// push async ring
List<Integer> ringItemData = ringData.get(ringSecond);
if (ringItemData == null) {
ringItemData = new ArrayList<Integer>();
ringData.put(ringSecond, ringItemData);
}
ringItemData.add(jobId);
}
<4>：还没到任务执行时间，也给塞到时间刻度轮上
<5>：控制调度速度
第二部分：扫描ringData刻度环上的数据 ringThread
ringThread = new Thread(new Runnable() {
@Override
public void run() {
while (!ringThreadToStop) {
// 1：align second
try {
TimeUnit.MILLISECONDS.sleep(1000 - System.currentTimeMillis() % 1000);
} catch (InterruptedException e) {
if (!ringThreadToStop) {
logger.error(e.getMessage(), e);
}
}
try {
// 2：second data
List<Integer> 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<Integer> tmpData = ringData.remove( (nowSecond+60-i)%60 );
if (tmpData != null) {
ringItemData.addAll(tmpData);
}
}
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) {
}
}
});
ringThread.setDaemon(true);
ringThread.setName("xxl-job, admin JobScheduleHelper#ringThread");
ringThread.start();
}
该线程扫描调度线程扫描调度线上扔到ringData上的数据
1：一秒内扫描一次
2：按照时钟刻度取数，并取上一刻度的任务，避免因卡壳导致的取不到数据