Quartz与Spring集成——QuartzSchedulerThread的执行分析

前言

前面说过当paused设置为false，QuartzSchedulerThread才正式启动，我们接着《Quartz与Spring集成——创建调度器》与《Quartz与Spring集成——启动调度器》中QuartzSchedulerThread启动的部分接着展开分析，QuartzSchedulerThread的run方法紧接着会从线程池获取可用的线程数，代码如下：

int availThreadCount = qsRsrcs.getThreadPool().blockForAvailableThreads();

只有availThreadCount大于0时才会进行真正的调度，否则将轮询等待线程的释放。所以我们来看看可用线程数充足的情况下的执行过程。

获取触发器

获取触发器的代码见代码清单1。其中调用了JobStore的acquireNextTriggers方法来获取触发器。

代码清单1

                    List<OperableTrigger> triggers = null;

                    long now = System.currentTimeMillis();

                    clearSignaledSchedulingChange();
                    try {
                        triggers = qsRsrcs.getJobStore().acquireNextTriggers(
                                now + idleWaitTime, Math.min(availThreadCount, qsRsrcs.getMaxBatchSize()), qsRsrcs.getBatchTimeWindow());
                        lastAcquireFailed = false;
                        if (log.isDebugEnabled()) 
                            log.debug("batch acquisition of " + (triggers == null ? 0 : triggers.size()) + " triggers");
                    } catch (JobPersistenceException jpe) {
                        //省略异常信息
                    } catch (RuntimeException e) {
                        //省略异常信息
                    }

以JobStore的实现类LocalDataSourceJobStore来具体看看acquireNextTriggers方法的执行内容。LocalDataSourceJobStore继承了父类JobStoreSupport的acquireNextTriggers方法（见代码清单2），此方法用于从数据源获取触发器。

代码清单2

    public List<OperableTrigger> acquireNextTriggers(final long noLaterThan, final int maxCount, final long timeWindow)
        throws JobPersistenceException {
        
        String lockName;
        if(isAcquireTriggersWithinLock() || maxCount > 1) { 
            lockName = LOCK_TRIGGER_ACCESS;
        } else {
            lockName = null;
        }
        return executeInNonManagedTXLock(lockName, 
                new TransactionCallback<List<OperableTrigger>>() {
                    public List<OperableTrigger> execute(Connection conn) throws JobPersistenceException {
                        return acquireNextTrigger(conn, noLaterThan, maxCount, timeWindow);
                    }
                },
                new TransactionValidator<List<OperableTrigger>>() {
                    public Boolean validate(Connection conn, List<OperableTrigger> result) throws JobPersistenceException {
                        try {
                            List<FiredTriggerRecord> acquired = getDelegate().selectInstancesFiredTriggerRecords(conn, getInstanceId());
                            Set<String> fireInstanceIds = new HashSet<String>();
                            for (FiredTriggerRecord ft : acquired) {
                                fireInstanceIds.add(ft.getFireInstanceId());
                            }
                            for (OperableTrigger tr : result) {
                                if (fireInstanceIds.contains(tr.getFireInstanceId())) {
                                    return true;
                                }
                            }
                            return false;
                        } catch (SQLException e) {
                            throw new JobPersistenceException("error validating trigger acquisition", e);
                        }
                    }
                });
    }

JobStoreSupport的acquireNextTriggers方法，主要调用了executeInNonManagedTXLock方法（见代码清单3），其执行逻辑如下：

1. 获取数据库连接；
2. 回调txCallback（即代码清单2中的TransactionCallback的匿名类）的execute方法，因此调用了acquireNextTrigger方法获取触发器；
3. 调用commitConnection方法提交第2步中的所有sql；
4. 返回获取的触发器集合；

代码清单3

    protected <T> T executeInNonManagedTXLock(
            String lockName, 
            TransactionCallback<T> txCallback, final TransactionValidator<T> txValidator) throws JobPersistenceException {
        boolean transOwner = false;
        Connection conn = null;
        try {
            if (lockName != null) {
                // If we aren't using db locks, then delay getting DB connection 
                // until after acquiring the lock since it isn't needed.
                if (getLockHandler().requiresConnection()) {
                    conn = getNonManagedTXConnection();
                }
                
                transOwner = getLockHandler().obtainLock(conn, lockName);
            }
            
            if (conn == null) {
                conn = getNonManagedTXConnection();
            }
            
            final T result = txCallback.execute(conn);
            try {
                commitConnection(conn);
            } catch (JobPersistenceException e) {
                rollbackConnection(conn);
                if (txValidator == null || !retryExecuteInNonManagedTXLock(lockName, new TransactionCallback<Boolean>() {
                    @Override
                    public Boolean execute(Connection conn) throws JobPersistenceException {
                        return txValidator.validate(conn, result);
                    }
                })) {
                    throw e;
                }
            }

            Long sigTime = clearAndGetSignalSchedulingChangeOnTxCompletion();
            if(sigTime != null && sigTime >= 0) {
                signalSchedulingChangeImmediately(sigTime);
            }
            
            return result;
        } catch (JobPersistenceException e) {
            rollbackConnection(conn);
            throw e;
        } catch (RuntimeException e) {
            rollbackConnection(conn);
            throw new JobPersistenceException("Unexpected runtime exception: "
                    + e.getMessage(), e);
        } finally {
            try {
                releaseLock(lockName, transOwner);
            } finally {
                cleanupConnection(conn);
            }
        }
    }

acquireNextTrigger方法用于获取触发器，它的执行步骤如下：

首先，查询状态为WAITING的触发器（见代码清单4），以StdJDBCDelegate为例，其selectTriggerToAcquire方法（使用JDBC的API，留给读者自己去看）实际就是执行sql查询触发器，执行的sql为：

SELECT TRIGGER_NAME, TRIGGER_GR