一文揭秘定时任务调度框架quartz

之前写过quartz或者引用过quartz的一些文章，有很多人给我发消息问quartz的相关问题，

quartz 报错：java.lang.classNotFoundException

quartz源码分析之深刻理解job，sheduler，calendar，trigger及listener之间的关系

Quartz框架多个trigger任务执行出现漏执行的问题分析--转

quartz集群调度机制调研及源码分析---转载

分布式定时任务调度系统技术选型--转

趁着年底比较清闲，把quartz的问题整理了一下，顺带翻了翻源码，做了一些总结，希望能帮助到一些人或者减少人们探索的时间。

注意，使用版本为quartz2.2.3  spring boot2.1.3

1.quartz的核心组件

1.1 Job组件

1.1.1Job

Job负责任务执行的逻辑，所有逻辑在execute()方法中，执行所需要的数据存放在JobExecutionContext 中

Job实例：

@PersistJobDataAfterExecution
@DisallowConcurrentExecution
public class ColorJob implements Job {

    private static Logger _log = LoggerFactory.getLogger(ColorJob.class);

    // parameter names specific to this job
    public static final String FAVORITE_COLOR = "favorite color";
    public static final String EXECUTION_COUNT = "count";

    // Since Quartz will re-instantiate a class every time it
    // gets executed, members non-static member variables can
    // not be used to maintain state!
    private int _counter = 1;

    /**
     * <p>
     * Empty constructor for job initialization
     * </p>
     * <p>
     * Quartz requires a public empty constructor so that the
     * scheduler can instantiate the class whenever it needs.
     * </p>
     */
    public ColorJob() {
    }

    /**
     * <p>
     * Called by the <code>{@link org.quartz.Scheduler}</code> when a
     * <code>{@link org.quartz.Trigger}</code> fires that is associated with
     * the <code>Job</code>.
     * </p>
     *
     * @throws JobExecutionException
     *             if there is an exception while executing the job.
     */
    public void execute(JobExecutionContext context)
        throws JobExecutionException {

        // This job simply prints out its job name and the
        // date and time that it is running
        JobKey jobKey = context.getJobDetail().getKey();

        // Grab and print passed parameters
        JobDataMap data = context.getJobDetail().getJobDataMap();
        String favoriteColor = data.getString(FAVORITE_COLOR);
        int count = data.getInt(EXECUTION_COUNT);
        _log.info("ColorJob: " + jobKey + " executing at " + new Date() + "\n" +
            "  favorite color is " + favoriteColor + "\n" +
            "  execution count (from job map) is " + count + "\n" +
            "  execution count (from job member variable) is " + _counter);

        // increment the count and store it back into the
        // job map so that job state can be properly maintained
        count++;
        data.put(EXECUTION_COUNT, count);

        // Increment the local member variable
        // This serves no real purpose since job state can not
        // be maintained via member variables!
        _counter++;
    }

}

1.1.2 JobDetail存储Job的信息

主要负责

1.指定执行的Job类，唯一标识（job名称和组别 名称）

2.存储JobDataMap信息

    // job1 will only run 5 times (at start time, plus 4 repeats), every 10 seconds
    JobDetail job1 = newJob(ColorJob.class).withIdentity("job1", "group1").build();

    // pass initialization parameters into the job
    job1.getJobDataMap().put(ColorJob.FAVORITE_COLOR, "Green");
    job1.getJobDataMap().put(ColorJob.EXECUTION_COUNT, 1);

数据库存储如下：

1.1.3 Quartz JobBuilder提供了一个链式api创建JobDetail

@Bean
public JobDetail jobDetail() {
    return JobBuilder.newJob().ofType(SampleJob.class)
      .storeDurably()
      .withIdentity("Qrtz_Job_Detail")
      .withDescription("Invoke Sample Job service...")
      .build();
}

1.1.4 Spring JobDetailFactoryBean

spring提供的一个创建JobDetail的方式工厂bean

@Bean
public JobDetailFactoryBean jobDetail() {
    JobDetailFactoryBean jobDetailFactory = new JobDetailFactoryBean();
    jobDetailFactory.setJobClass(SampleJob.class);
    jobDetailFactory.setDescription("Invoke Sample Job service...");
    jobDetailFactory.setDurability(true);
    return jobDetailFactory;
}

1.2 Trigger组件

trigger的状态不同

trigger的状态

    // STATES
    String STATE_WAITING = "WAITING";

    String STATE_ACQUIRED = "ACQUIRED";

    String STATE_EXECUTING = "EXECUTING";

    String STATE_COMPLETE = "COMPLETE";

    String STATE_BLOCKED = "BLOCKED";

    String STATE_ERROR = "ERROR";

    String STATE_PAUSED = "PAUSED";

    String STATE_PAUSED_BLOCKED = "PAUSED_BLOCKED";

    String STATE_DELETED = "DELETED";

状态的表结构

trigger的类型

    // TRIGGER TYPES
    /** Simple Trigger type. */
    String TTYPE_SIMPLE = "SIMPLE";

    /** Cron Trigger type. */
    String TTYPE_CRON = "CRON";

    /** Calendar Interval Trigger type. */
    String TTYPE_CAL_INT = "CAL_INT";

    /** Daily Time Interval Trigger type. */
    String TTYPE_DAILY_TIME_INT = "DAILY_I";

    /** A general blob Trigger type. */
    String TTYPE_BLOB = "BLOB";

对应表结构

1.2.1 trigger实例

    SimpleTrigger trigger1 = newTrigger().withIdentity("trigger1", "group1").startAt(startTime)
        .withSchedule(simpleSchedule().withIntervalInSeconds(10).withRepeatCount(4)).build();

Trigger存储在mysql中

1.2.2 Quartz TriggerBuilder

提供了一个链式创建Trigger的api

@Bean
public Trigger trigger(JobDetail job) {
    return TriggerBuilder.newTrigger().forJob(job)
      .withIdentity("Qrtz_Trigger")
      .withDescription("Sample trigger")
      .withSchedule(simpleSchedule().repeatForever().withIntervalInHours(1))
      .build();
}

1.2.3 Spring SimpleTriggerFactoryBean

spring提供的一个创建SimpleTrigger的工厂类

@Bean
public SimpleTriggerFactoryBean trigger(JobDetail job) {
    SimpleTriggerFactoryBean trigger = new SimpleTriggerFactoryBean();
    trigger.setJobDetail(job);
    trigger.setRepeatInterval(3600000);
    trigger.setRepeatCount(SimpleTrigger.REPEAT_INDEFINITELY);
    return trigger;
}

1.3 调度组件

1.3.1 quartz提供的工厂类

@Bean
public Scheduler scheduler(Trigger trigger, JobDetail job) {
    StdSchedulerFactory factory = new StdSchedulerFactory();
    factory.initialize(new ClassPathResource("quartz.properties").getInputStream());
 
    Scheduler scheduler = factory.getScheduler();
    scheduler.setJobFactory(springBeanJobFactory());
    scheduler.scheduleJob(job, trigger);
 
    scheduler.start();
    return scheduler;
}

1.3.2 spring提供的工厂bean

@Bean
public SchedulerFactoryBean scheduler(Trigger trigger, JobDetail job) {
    SchedulerFactoryBean schedulerFactory = new SchedulerFactoryBean();
    schedulerFactory.setConfigLocation(new ClassPathResource("quartz.properties"));

    schedulerFactory.setJobFactory(springBeanJobFactory());
    schedulerFactory.setJobDetails(job);
    schedulerFactory.setTriggers(trigger);
    return schedulerFactory;
}

2.工作原理

2.1 核心类QuartzScheduler

Scheduler实现类StdScheduler封装了核心工作类QuartzScheduler

    /**
     * <p>
     * Construct a <code>StdScheduler</code> instance to proxy the given
     * <code>QuartzScheduler</code> instance, and with the given <code>SchedulingContext</code>.
     * </p>
     */
    public StdScheduler(QuartzScheduler sched) {
        this.sched = sched;
    }

2.2 JobDetail的存取

    public void addJob(JobDetail jobDetail, boolean replace, boolean storeNonDurableWhileAwaitingScheduling) throws SchedulerException {
        validateState();

        if (!storeNonDurableWhileAwaitingScheduling && !jobDetail.isDurable()) {
            throw new SchedulerException(
                    "Jobs added with no trigger must be durable.");
        }

        resources.getJobStore().storeJob(jobDetail, replace);
        notifySchedulerThread(0L);
        notifySchedulerListenersJobAdded(jobDetail);
    }

2.2.1 存储JobDetail信息(以mysql Jdbc方式为例)

    /**
     * <p>
     * Insert or update a job.
     * </p>
     */
    protected void storeJob(Connection conn,
            JobDetail newJob, boolean replaceExisting)
        throws JobPersistenceException {

        boolean existingJob = jobExists(conn, newJob.getKey());
        try {
            if (existingJob) {
                if (!replaceExisting) {
                    throw new ObjectAlreadyExistsException(newJob);
                }
                getDelegate().updateJobDetail(conn, newJob);
            } else {
                getDelegate().insertJobDetail(conn, newJob);
            }
        } catch (IOException e) {
            throw new JobPersistenceException("Couldn't store job: "
                    + e.getMessage(), e);
        } catch (SQLException e) {
            throw new JobPersistenceException("Couldn't store job: "
                    + e.getMessage(), e);
        }
    }

调用StdJDBCDelegate实现

    /**
     * <p>
     * Insert the job detail record.
     * </p>
     *
     * @param conn
     *          the DB Connection
     * @param job
     *          the job to insert
     * @return number of rows inserted
     * @throws IOException
     *           if there were problems serializing the JobDataMap
     */
    public int insertJobDetail(Connection conn, JobDetail job)
        throws IOException, SQLException {
        ByteArrayOutputStream baos = serializeJobData(job.getJobDataMap());

        PreparedStatement ps = null;

        int insertResult = 0;

        try {
            ps = conn.prepareStatement(rtp(INSERT_JOB_DETAIL));
            ps.setString(1, job.getKey().getName());
            ps.setString(2, job.getKey().getGroup());
            ps.setString(3, job.getDescription());
            ps.setString(4, job.getJobClass().getName());
            setBoolean(ps, 5, job.isDurable());
            setBoolean(ps, 6, job.isConcurrentExectionDisallowed());
            setBoolean(ps, 7, job.isPersistJobDataAfterExecution());
            setBoolean(ps, 8, job.requestsRecovery());
            setBytes(ps, 9, baos);

            insertResult = ps.executeUpdate();
        } finally {
            closeStatement(ps);
        }

        return insertResult;
    }

注意：JobDataMap序列化后以Blob形式存储到数据库中

StdJDBCConstants中执行sql如下：

    String INSERT_JOB_DETAIL = "INSERT INTO "
            + TABLE_PREFIX_SUBST + TABLE_JOB_DETAILS + " ("
            + COL_SCHEDULER_NAME + ", " + COL_JOB_NAME
            + ", " + COL_JOB_GROUP + ", " + COL_DESCRIPTION + ", "
            + COL_JOB_CLASS + ", " + COL_IS_DURABLE + ", "
            + COL_IS_NONCONCURRENT +  ", " + COL_IS_UPDATE_DATA + ", "
            + COL_REQUESTS_RECOVERY + ", "
            + COL_JOB_DATAMAP + ") " + " VALUES(" + SCHED_NAME_SUBST + ", ?, ?, ?, ?, ?, ?, ?, ?, ?)";

2.2.2  查询JobDetail

强调一下，因JobDetail中的JobDataMap是以Blob形式存放到数据库中的(也可以通过useProperties属性修改成string存储，默认是false，Blob形式存储)，所以查询时需要特殊处理：StdJDBCDelegate.java

/**
     * <p>
     * Select the JobDetail object for a given job name / group name.
     * </p>
     *
     * @param conn
     *          the DB Connection
     * @return the populated JobDetail object
     * @throws ClassNotFoundException
     *           if a class found during deserialization cannot be found or if
     *           the job class could not be found
     * @throws IOException
     *           if deserialization causes an error
     */
    public JobDetail selectJobDetail(Connection conn, JobKey jobKey,
            ClassLoadHelper loadHelper)
        throws ClassNotFoundException, IOException, SQLException {
        PreparedStatement ps = null;
        ResultSet rs = null;

        try {
            ps = conn.prepareStatement(rtp(SELECT_JOB_DETAIL));
            ps.setString(1, jobKey.getName());
            ps.setString(2, jobKey.getGroup());
            rs = ps.executeQuery();

            JobDetailImpl job = null;

            if (rs.next()) {
                job = new JobDetailImpl();

                job.setName(rs.getString(COL_JOB_NAME));
                job.setGroup(rs.getString(COL_JOB_GROUP));
                job.setDescription(rs.getString(COL_DESCRIPTION));
                job.setJobClass( loadHelper.loadClass(rs.getString(COL_JOB_CLASS), Job.class));
                job.setDurability(getBoolean(rs, COL_IS_DURABLE));
                job.setRequestsRecovery(getBoolean(rs, COL_REQUESTS_RECOVERY));

                Map<?, ?> map = null;
                if (canUseProperties()) {
                    map = getMapFromProperties(rs);
                } else {
                    map = (Map<?, ?>) getObjectFromBlob(rs, COL_JOB_DATAMAP);
                }

                if (null != map) {
                    job.setJobDataMap(new JobDataMap(map));
                }
            }

            return job;
        } finally {
            closeResultSet(rs);
            closeStatement(ps);
        }
    }

2.3 查询trigger

    /**
     * <p>
     * Retrieve the given <code>{@link org.quartz.Trigger}</code>.
     * </p>
     *
     * @return The desired <code>Trigger</code>, or null if there is no
     *         match.
     */
    public OperableTrigger retrieveTrigger(final TriggerKey triggerKey) throws JobPersistenceException {
        return (OperableTrigger)executeWithoutLock( // no locks necessary for read...
            new TransactionCallback() {
                public Object execute(Connection conn) throws JobPersistenceException {
                    return retrieveTrigger(conn, triggerKey);
                }
            });
    }

    protected OperableTrigger retrieveTrigger(Connection conn, TriggerKey key)
        throws JobPersistenceException {
        try {

            return getDelegate().selectTrigger(conn, key);
        } catch (Exception e) {
            throw new JobPersistenceException("Couldn't retrieve trigger: "
                    + e.getMessage(), e);
        }
    }

StdJDBCDelegate.java

   /**
     * <p>
     * Select a trigger.
     * </p>
     *
     * @param conn
     *          the DB Connection
     * @return the <code>{@link org.quartz.Trigger}</code> object
     * @throws JobPersistenceException
     */
    public OperableTrigger selectTrigger(Connection conn, TriggerKey triggerKey) throws SQLException, ClassNotFoundException,
            IOException, JobPersistenceException {
        PreparedStatement ps = null;
        ResultSet rs = null;

        try {
            OperableTrigger trigger = null;

            ps = conn.prepareStatement(rtp(SELECT_TRIGGER));
            ps.setString(1, triggerKey.getName());
            ps.setString(2, triggerKey.getGroup());
            rs = ps.executeQuery();

            if (rs.next()) {
                String jobName = rs.getString(COL_JOB_NAME);
                String jobGroup = rs.getString(COL_JOB_GROUP);
                String description = rs.getString(COL_DESCRIPTION);
                long nextFireTime = rs.getLong(COL_NEXT_FIRE_TIME);
                long prevFireTime = rs.getLong(COL_PREV_FIRE_TIME);
                String triggerType = rs.getString(COL_TRIGGER_TYPE);
                long startTime = rs.getLong(COL_START_TIME);
                long endTime = rs.getLong(COL_END_TIME);
                String calendarName = rs.getString(COL_CALENDAR_NAME);
                int misFireInstr = rs.getInt(COL_MISFIRE_INSTRUCTION);
                int priority = rs.getInt(COL_PRIORITY);

                Map<?, ?> map = null;
                if (canUseProperties()) {
                    map = getMapFromProperties(rs);
                } else {
                    map = (Map<?, ?>) getObjectFromBlob(rs, COL_JOB_DATAMAP);
                }

                Date nft = null;
                if (nextFireTime > 0) {
                    nft = new Date(nextFireTime);
                }

                Date pft = null;
                if (prevFireTime > 0) {
                    pft = new Date(prevFireTime);
                }
                Date startTimeD = new Date(startTime);
                Date endTimeD = null;
                if (endTime > 0) {
                    endTimeD = new Date(endTime);
                }

                if (triggerType.equals(TTYPE_BLOB)) {
                    rs.close(); rs = null;
                    ps.close(); ps = null;

                    ps = conn.prepareStatement(rtp(SELECT_BLOB_TRIGGER));
                    ps.setString(1, triggerKey.getName());
                    ps.setString(2, triggerKey.getGroup());
                    rs = ps.executeQuery();

                    if (rs.next()) {
                        trigger = (OperableTrigger) getObjectFromBlob(rs, COL_BLOB);
                    }
                }
                else {
                    TriggerPersistenceDelegate tDel = findTriggerPersistenceDelegate(triggerType);

                    if(tDel == null)
                        throw new JobPersistenceException("No TriggerPersistenceDelegate for trigger discriminator type: " + triggerType);

                    TriggerPropertyBundle triggerProps = null;
                    try {
                        triggerProps = tDel.loadExtendedTriggerProperties(conn, triggerKey);
                    } catch (IllegalStateException isex) {
                        if (isTriggerStillPresent(ps)) {
                            throw isex;
                        } else {
                            // QTZ-386 Trigger has been deleted
                            return null;
                        }
                    }

                    TriggerBuilder<?> tb = newTrigger()
                        .withDescription(description)
                        .withPriority(priority)
                        .startAt(startTimeD)
                        .endAt(endTimeD)
                        .withIdentity(triggerKey)
                        .modifiedByCalendar(calendarName)
                        .withSchedule(triggerProps.getScheduleBuilder())
                        .forJob(jobKey(jobName, jobGroup));

                    if (null != map) {
                        tb.usingJobData(new JobDataMap(map));
                    }

                    trigger = (OperableTrigger) tb.build();

                    trigger.setMisfireInstruction(misFireInstr);
                    trigger.setNextFireTime(nft);
                    trigger.setPreviousFireTime(pft);

                    setTriggerStateProperties(trigger, triggerProps);
                }
            }

            return trigger;
        } finally {
            closeResultSet(rs);
            closeStatement(ps);
        }
    }

执行的sql：

    String SELECT_TRIGGER = "SELECT * FROM "
            + TABLE_PREFIX_SUBST + TABLE_TRIGGERS + " WHERE "
            + COL_SCHEDULER_NAME + " = " + SCHED_NAME_SUBST
            + " AND " + COL_TRIGGER_NAME + " = ? AND " + COL_TRIGGER_GROUP + " = ?";

和JobDetail一样，也存在Blob的问题，不再赘述。

2.4 调度执行线程QuartzSchedulerThread

 /**
     * <p>
     * The main processing loop of the <code>QuartzSchedulerThread</code>.
     * </p>
     */
    @Override
    public void run() {
        boolean lastAcquireFailed = false;

        while (!halted.get()) {
            try {
                // check if we're supposed to pause...
                synchronized (sigLock) {
                    while (paused && !halted.get()) {
                        try {
                            // wait until togglePause(false) is called...
                            sigLock.wait(1000L);
                        } catch (InterruptedException ignore) {
                        }
                    }

                    if (halted.get()) {
                        break;
                    }
                }

                int availThreadCount = qsRsrcs.getThreadPool().blockForAvailableThreads();
                if(availThreadCount > 0) { // will always be true, due to semantics of blockForAvailableThreads...

                    List<OperableTrigger> triggers = null;

                    long now = System.currentTimeMillis();

                    clearSignaledSchedulingChange();
                    try {
                        triggers = qsRsrcs.getJobStore().acquireNextTriggers(
                                now + idleWaitTime, Math.min(availThreadCount, qsRsrcs.getMaxBatchSize()), qsRsrcs.getBatchTimeWindow()); //1.
                        lastAcquireFailed = false;
                        if (log.isDebugEnabled())
                            log.debug("batch acquisition of " + (triggers == null ? 0 : triggers.size()) + " triggers");
                    } catch (JobPersistenceException jpe) {
                        if(!lastAcquireFailed) {
                            qs.notifySchedulerListenersError(
                                "An error occurred while scanning for the next triggers to fire.",
                                jpe);
                        }
                        lastAcquireFailed = true;
                        continue;
                    } catch (RuntimeException e) {
                        if(!lastAcquireFailed) {
                            getLog().error("quartzSchedulerThreadLoop: RuntimeException "
                                    +e.getMessage(), e);
                        }
                        lastAcquireFailed = true;
                        continue;
                    }

                    if (triggers != null && !triggers.isEmpty()) {

                        now = System.currentTimeMillis();
                        long triggerTime = triggers.get(0).getNextFireTime().getTime();
                        long timeUntilTrigger = triggerTime - now;
                        while(timeUntilTrigger > 2) {
                            synchronized (sigLock) {
                                if (halted.get()) {
                                    break;
                                }
                                if (!isCandidateNewTimeEarlierWithinReason(triggerTime, false)) {
                                    try {
                                        // we could have blocked a long while
                                        // on 'synchronize', so we must recompute
                                        now = System.currentTimeMillis();
                                        timeUntilTrigger = triggerTime - now;
                                        if(timeUntilTrigger >= 1)
                                            sigLock.wait(timeUntilTrigger);
                                    } catch (InterruptedException ignore) {
                                    }
                                }
                            }
                            if(releaseIfScheduleChangedSignificantly(triggers, triggerTime)) {
                                break;
                            }
                            now = System.currentTimeMillis();
                            timeUntilTrigger = triggerTime - now;
                        }

                        // this happens if releaseIfScheduleChangedSignificantly decided to release triggers
                        if(triggers.isEmpty())
                            continue;

                        // set triggers to 'executing'
                        List<TriggerFiredResult> bndles = new ArrayList<TriggerFiredResult>();

                        boolean goAhead = true;
                        synchronized(sigLock) {
                            goAhead = !halted.get();
                        }
                        if(goAhead) {
                            try {
                                List<TriggerFiredResult> res = qsRsrcs.getJobStore().triggersFired(triggers); //2
                                if(res != null)
                                    bndles = res;
                            } catch (SchedulerException se) {
                                qs.notifySchedulerListenersError(
                                        "An error occurred while firing triggers '"
                                                + triggers + "'", se);
                                //QTZ-179 : a problem occurred interacting with the triggers from the db
                                //we release them and loop again
                                for (int i = 0; i < triggers.size(); i++) {
                                    qsRsrcs.getJobStore().releaseAcquiredTrigger(triggers.get(i));
                                }
                                continue;
                            }

                        }

                        for (int i = 0; i < bndles.size(); i++) {
                            TriggerFiredResult result =  bndles.get(i);
                            TriggerFiredBundle bndle =  result.getTriggerFiredBundle();
                            Exception exception = result.getException();

                            if (exception instanceof RuntimeException) {
                                getLog().error("RuntimeException while firing trigger " + triggers.get(i), exception);
                                qsRsrcs.getJobStore().releaseAcquiredTrigger(triggers.get(i));
                                continue;
                            }

                            // it's possible to get 'null' if the triggers was paused,
                            // blocked, or other similar occurrences that prevent it being
                            // fired at this time...  or if the scheduler was shutdown (halted)
                            if (bndle == null) {
                                qsRsrcs.getJobStore().releaseAcquiredTrigger(triggers.get(i));
                                continue;
                            }

                            JobRunShell shell = null;
                            try {
                                shell = qsRsrcs.getJobRunShellFactory().createJobRunShell(bndle);
                                shell.initialize(qs);
                            } catch (SchedulerException se) {
                                qsRsrcs.getJobStore().triggeredJobComplete(triggers.get(i), bndle.getJobDetail(), CompletedExecutionInstruction.SET_ALL_JOB_TRIGGERS_ERROR);
                                continue;
                            }

                            if (qsRsrcs.getThreadPool().runInThread(shell) == false) {
                                // this case should never happen, as it is indicative of the
                                // scheduler being shutdown or a bug in the thread pool or
                                // a thread pool being used concurrently - which the docs
                                // say not to do...
                                getLog().error("ThreadPool.runInThread() return false!");
                                qsRsrcs.getJobStore().triggeredJobComplete(triggers.get(i), bndle.getJobDetail(), CompletedExecutionInstruction.SET_ALL_JOB_TRIGGERS_ERROR);
                            }

                        }

                        continue; // while (!halted)
                    }
                } else { // if(availThreadCount > 0)
                    // should never happen, if threadPool.blockForAvailableThreads() follows contract
                    continue; // while (!halted)
                }

                long now = System.currentTimeMillis();
                long waitTime = now + getRandomizedIdleWaitTime();
                long timeUntilContinue = waitTime - now;
                synchronized(sigLock) {
                    try {
                      if(!halted.get()) {
                        // QTZ-336 A job might have been completed in the mean time and we might have
                        // missed the scheduled changed signal by not waiting for the notify() yet
                        // Check that before waiting for too long in case this very job needs to be
                        // scheduled very soon
                        if (!isScheduleChanged()) {
                          sigLock.wait(timeUntilContinue);
                        }
                      }
                    } catch (InterruptedException ignore) {
                    }
                }

            } catch(RuntimeException re) {
                getLog().error("Runtime error occurred in main trigger firing loop.", re);
            }
        } // while (!halted)

        // drop references to scheduler stuff to aid garbage collection...
        qs = null;
        qsRsrcs = null;
    }

2.4.1 获取trigger(红色1)

protected List<OperableTrigger> acquireNextTrigger(Connection conn, long noLaterThan, int maxCount, long timeWindow)
        throws JobPersistenceException {
        if (timeWindow < 0) {
          throw new IllegalArgumentException();
        }

        List<OperableTrigger> acquiredTriggers = new ArrayList<OperableTrigger>();
        Set<JobKey> acquiredJobKeysForNoConcurrentExec = new HashSet<JobKey>();
        final int MAX_DO_LOOP_RETRY = 3;
        int currentLoopCount = 0;
        do {
            currentLoopCount ++;
            try {
                List<TriggerKey> keys = getDelegate().selectTriggerToAcquire(conn, noLaterThan + timeWindow, getMisfireTime(), maxCount);

                // No trigger is ready to fire yet.
                if (keys == null || keys.size() == 0)
                    return acquiredTriggers;

                long batchEnd = noLaterThan;

                for(TriggerKey triggerKey: keys) {
                    // If our trigger is no longer available, try a new one.
                    OperableTrigger nextTrigger = retrieveTrigger(conn, triggerKey);
                    if(nextTrigger == null) {
                        continue; // next trigger
                    }

                    // If trigger's job is set as @DisallowConcurrentExecution, and it has already been added to result, then
                    // put it back into the timeTriggers set and continue to search for next trigger.
                    JobKey jobKey = nextTrigger.getJobKey();
                    JobDetail job;
                    try {
                        job = retrieveJob(conn, jobKey);
                    } catch (JobPersistenceException jpe) {
                        try {
                            getLog().error("Error retrieving job, setting trigger state to ERROR.", jpe);
                            getDelegate().updateTriggerState(conn, triggerKey, STATE_ERROR);
                        } catch (SQLException sqle) {
                            getLog().error("Unable to set trigger state to ERROR.", sqle);
                        }
                        continue;
                    }

                    if (job.isConcurrentExectionDisallowed()) {
                        if (acquiredJobKeysForNoConcurrentExec.contains(jobKey)) {
                            continue; // next trigger
                        } else {
                            acquiredJobKeysForNoConcurrentExec.add(jobKey);
                        }
                    }

                    if (nextTrigger.getNextFireTime().getTime() > batchEnd) {
                      break;
                    }
                    // We now have a acquired trigger, let's add to return list.
                    // If our trigger was no longer in the expected state, try a new one.
                    int rowsUpdated = getDelegate().updateTriggerStateFromOtherState(conn, triggerKey, STATE_ACQUIRED, STATE_WAITING);
                    if (rowsUpdated <= 0) {
                        continue; // next trigger
                    }
                    nextTrigger.setFireInstanceId(getFiredTriggerRecordId());
                    getDelegate().insertFiredTrigger(conn, nextTrigger, STATE_ACQUIRED, null);

                    if(acquiredTriggers.isEmpty()) {
                        batchEnd = Math.max(nextTrigger.getNextFireTime().getTime(), System.currentTimeMillis()) + timeWindow;
                    }
                    acquiredTriggers.add(nextTrigger);
                }

                // if we didn't end up with any trigger to fire from that first
                // batch, try again for another batch. We allow with a max retry count.
                if(acquiredTriggers.size() == 0 && currentLoopCount < MAX_DO_LOOP_RETRY) {
                    continue;
                }

                // We are done with the while loop.
                break;
            } catch (Exception e) {
                throw new JobPersistenceException(
                          "Couldn't acquire next trigger: " + e.getMessage(), e);
            }
        } while (true);

        // Return the acquired trigger list
        return acquiredTriggers;
    }

2.4.2 触发trigger(红色2)

 protected TriggerFiredBundle triggerFired(Connection conn,
            OperableTrigger trigger)
        throws JobPersistenceException {
        JobDetail job;
        Calendar cal = null;

        // Make sure trigger wasn't deleted, paused, or completed...
        try { // if trigger was deleted, state will be STATE_DELETED
            String state = getDelegate().selectTriggerState(conn,
                    trigger.getKey());
            if (!state.equals(STATE_ACQUIRED)) {
                return null;
            }
        } catch (SQLException e) {
            throw new JobPersistenceException("Couldn't select trigger state: "
                    + e.getMessage(), e);
        }

        try {
            job = retrieveJob(conn, trigger.getJobKey());
            if (job == null) { return null; }
        } catch (JobPersistenceException jpe) {
            try {
                getLog().error("Error retrieving job, setting trigger state to ERROR.", jpe);
                getDelegate().updateTriggerState(conn, trigger.getKey(),
                        STATE_ERROR);
            } catch (SQLException sqle) {
                getLog().error("Unable to set trigger state to ERROR.", sqle);
            }
            throw jpe;
        }

        if (trigger.getCalendarName() != null) {
            cal = retrieveCalendar(conn, trigger.getCalendarName());
            if (cal == null) { return null; }
        }

        try {
            getDelegate().updateFiredTrigger(conn, trigger, STATE_EXECUTING, job);
        } catch (SQLException e) {
            throw new JobPersistenceException("Couldn't insert fired trigger: "
                    + e.getMessage(), e);
        }

        Date prevFireTime = trigger.getPreviousFireTime();

        // call triggered - to update the trigger's next-fire-time state...
        trigger.triggered(cal);

        String state = STATE_WAITING;
        boolean force = true;

        if (job.isConcurrentExectionDisallowed()) {
            state = STATE_BLOCKED;
            force = false;
            try {
                getDelegate().updateTriggerStatesForJobFromOtherState(conn, job.getKey(),
                        STATE_BLOCKED, STATE_WAITING);
                getDelegate().updateTriggerStatesForJobFromOtherState(conn, job.getKey(),
                        STATE_BLOCKED, STATE_ACQUIRED);
                getDelegate().updateTriggerStatesForJobFromOtherState(conn, job.getKey(),
                        STATE_PAUSED_BLOCKED, STATE_PAUSED);
            } catch (SQLException e) {
                throw new JobPersistenceException(
                        "Couldn't update states of blocked triggers: "
                                + e.getMessage(), e);
            }
        } 

        if (trigger.getNextFireTime() == null) {
            state = STATE_COMPLETE;
            force = true;
        }

        storeTrigger(conn, trigger, job, true, state, force, false);

        job.getJobDataMap().clearDirtyFlag();

        return new TriggerFiredBundle(job, trigger, cal, trigger.getKey().getGroup()
                .equals(Scheduler.DEFAULT_RECOVERY_GROUP), new Date(), trigger
                .getPreviousFireTime(), prevFireTime, trigger.getNextFireTime());
    }

2.4.3 数据库锁

StdRowLockSemaphore针对支持select for update的数据库如mysql

UpdateLockRowSemaphore针对不支持select for update的数据库如mssqlserver

StdRowLockSemaphore的实现如下：

    public static final String SELECT_FOR_LOCK = "SELECT * FROM "
            + TABLE_PREFIX_SUBST + TABLE_LOCKS + " WHERE " + COL_SCHEDULER_NAME + " = " + SCHED_NAME_SUBST
            + " AND " + COL_LOCK_NAME + " = ? FOR UPDATE";

    public static final String INSERT_LOCK = "INSERT INTO "
        + TABLE_PREFIX_SUBST + TABLE_LOCKS + "(" + COL_SCHEDULER_NAME + ", " + COL_LOCK_NAME + ") VALUES ("
        + SCHED_NAME_SUBST + ", ?)"; 

总结：

1.quartz的三大组件Job/trigger/scheduler，job负责业务逻辑，trigger负责执行时机，scheduler负责调度Job和trigger来执行。

2.使用mysql作为存储的话，使用StdJDBCDelegate和数据库进行交互，交互的sql在StdJDBCConstants中定义

3.QuartzScheduler是核心类，Scheduler做其代理，真正执行的是QuartzSchedulerThread

4.JobStore存储控制，JobStoreSupport的两个实现JobStoreCMT容器管理事务，不需要使用commit和rollback；JobStoreTX用在单机环境，需要处理commit和rollback

5.数据库锁使用了悲观锁select for update，定义为Semaphore

6.qrtz_scheduler_state定义了扫描间隔集群扫描间隔

参考文献：

【1】https://www.baeldung.com/spring-quartz-schedule

【2】https://blog.csdn.net/xiaojin21cen/article/details/79298883