时钟不同步造成的异常

异常信息：

This scheduler instance () is still active but was recovered by another instance in the cluster

对应源码：

protected boolean doCheckin() throws JobPersistenceException {
     boolean transOwner = false;
     boolean transStateOwner = false;
     boolean recovered = false;

     Connection conn = getNonManagedTXConnection();
     try {
         // Other than the first time, always checkin first to make sure there is 
         // work to be done before we acquire the lock (since that is expensive, 
         // and is almost never necessary).  This must be done in a separate
         // transaction to prevent a deadlock under recovery conditions.
         List<SchedulerStateRecord> failedRecords = null;
         if (!firstCheckIn) {
             failedRecords = clusterCheckIn(conn);
             commitConnection(conn);
         }
         
         if (firstCheckIn || (failedRecords.size() > 0)) {
             getLockHandler().obtainLock(conn, LOCK_STATE_ACCESS);
             transStateOwner = true;
 
             // Now that we own the lock, make sure we still have work to do. 
             // The first time through, we also need to make sure we update/create our state record
             failedRecords = (firstCheckIn) ? clusterCheckIn(conn) : findFailedInstances(conn);
 
             if (failedRecords.size() > 0) {
                 getLockHandler().obtainLock(conn, LOCK_TRIGGER_ACCESS);
                 //getLockHandler().obtainLock(conn, LOCK_JOB_ACCESS);
                 transOwner = true;
 
                 clusterRecover(conn, failedRecords);
                 recovered = true;
             }
         }
         
         commitConnection(conn);
     } catch (JobPersistenceException e) {
         rollbackConnection(conn);
         throw e;
     } finally {
         try {
             releaseLock(LOCK_TRIGGER_ACCESS, transOwner);
         } finally {
             try {
                 releaseLock(LOCK_STATE_ACCESS, transStateOwner);
             } finally {
                 cleanupConnection(conn);
             }
         }
     }

     firstCheckIn = false;

     return recovered;
 }

protected List<SchedulerStateRecord> findFailedInstances(Connection conn)
        throws JobPersistenceException {
        try {
            List<SchedulerStateRecord> failedInstances = new LinkedList<SchedulerStateRecord>();
            boolean foundThisScheduler = false;
            long timeNow = System.currentTimeMillis();
            
            // 获取 qrzt_scheduler_state 表中，记录。对应sql是：SELECT * FROM QRTZ_SCHEDULER_STATE WHERE SCHED_NAME = 'zl'，其中SCHED_NAME是配置文件中的org.quartz.scheduler.instanceName值
            List<SchedulerStateRecord> states = getDelegate().selectSchedulerStateRecords(conn, null);

            for(SchedulerStateRecord rec: states) {
        
                // find own record...
                if (rec.getSchedulerInstanceId().equals(getInstanceId())) {
                    foundThisScheduler = true;
                    if (firstCheckIn) {
                        failedInstances.add(rec);
                    }
                } else {
                    // find failed instances...
                    if (calcFailedIfAfter(rec) < timeNow) {
                        failedInstances.add(rec);
                    }
                }
            }
            
            // The first time through, also check for orphaned fired triggers.
            if (firstCheckIn) {
                failedInstances.addAll(findOrphanedFailedInstances(conn, states));
            }
            
            // If not the first time but we didn't find our own instance, then
            // Someone must have done recovery for us.
            // !foundThisScheduler 表示 应用程序没有找到 自己的 instance
            // !firstCheckIn       表示 应该表示 应用程序是否为第一次checkIn
            if ((!foundThisScheduler) && (!firstCheckIn)) {
                // FUTURE_TODO: revisit when handle self-failed-out impl'ed (see FUTURE_TODO in clusterCheckIn() below)
                getLog().warn(
                    "This scheduler instance (" + getInstanceId() + ") is still " + 
                    "active but was recovered by another instance in the cluster.  " +
                    "This may cause inconsistent behavior.");
            }
            
            return failedInstances;
        } catch (Exception e) {
            lastCheckin = System.currentTimeMillis();
            throw new JobPersistenceException("Failure identifying failed instances when checking-in: "
                    + e.getMessage(), e);
        }
    }