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JobStoreCMT 控制并发代码

	/**
     * Execute the given callback having optionally acquired the given lock.  
     * Because CMT assumes that the connection is already part of a managed
     * transaction, it does not attempt to commit or rollback the 
     * enclosing transaction.
     * 
     * @param lockName The name of the lock to acquire, for example 
     * "TRIGGER_ACCESS".  If null, then no lock is acquired, but the
     * txCallback is still executed in a transaction.
     * 
     * @see JobStoreSupport#executeInNonManagedTXLock(String, TransactionCallback)
     * @see JobStoreTX#executeInLock(String, TransactionCallback)
     * @see JobStoreSupport#getNonManagedTXConnection()
     * @see JobStoreSupport#getConnection()
     */

    protected Object executeInLock(String lockName, TransactionCallback txCallback) 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 = getConnection();
                }
                transOwner = getLockHandler().obtainLock(conn, lockName);
            }

            if (conn == null) {
                conn = getConnection();
            }
			//没有事务提交操作，与任务共享一个事务
            return txCallback.execute(conn);
        } finally {
            try {
                releaseLock(conn, LOCK_TRIGGER_ACCESS, transOwner);
            } finally {
                cleanupConnection(conn);
            }
        }
    }

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