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/*
*
* Copyright (c) 2006 The Apache Software Foundation
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
*/
#ifndef _TxBuffer_
#define _TxBuffer_
#include <algorithm>
#include <functional>
#include <vector>
#include <qpid/broker/TransactionalStore.h>
#include <qpid/broker/TxOp.h>
/**
* Represents a single transaction. As such, an instance of this class
* will hold a list of operations representing the workload of the
* transaction. This work can be committed or rolled back. Committing
* is a two-stage process: first all the operations should be
* prepared, then if that succeeds they can be committed.
*
* In the 2pc case, a successful prepare may be followed by either a
* commit or a rollback.
*
* Atomicity of prepare is ensured by using a lower level
* transactional facility. This saves explicitly rolling back all the
* successfully prepared ops when one of them fails. i.e. we do not
* use 2pc internally, we instead ensure that prepare is atomic at a
* lower level. This makes individual prepare operations easier to
* code.
*
* Transactions on a messaging broker effect three types of 'action':
* (1) updates to persistent storage (2) updates to transient storage
* or cached data (3) network writes.
*
* Of these, (1) should always occur atomically during prepare to
* ensure that if the broker crashes while a transaction is being
* completed the persistent state (which is all that then remains) is
* consistent. (3) can only be done on commit, after a successful
* prepare. There is a little more flexibility with (2) but any
* changes made during prepare should be subject to the control of the
* TransactionalStore in use.
*/
namespace qpid {
namespace broker {
class TxBuffer{
typedef std::vector<TxOp*>::iterator op_iterator;
std::vector<TxOp*> ops;
public:
/**
* Requests that all ops are prepared. This should
* primarily involve making sure that a persistent record
* of the operations is stored where necessary.
*
* All ops will be prepared under a transaction on the
* specified store. If any operation fails on prepare,
* this transaction will be rolled back.
*
* Once prepared, a transaction can be committed (or in
* the 2pc case, rolled back).
*
* @returns true if all the operations prepared
* successfully, false if not.
*/
bool prepare(TransactionalStore* const store);
/**
* Signals that the ops all prepared all completed
* successfully and can now commit, i.e. the operation can
* now be fully carried out.
*
* Should only be called after a call to prepare() returns
* true.
*/
void commit();
/**
* Rolls back all the operations.
*
* Should only be called either after a call to prepare()
* returns true (2pc) or instead of a prepare call
* ('server-local')
*/
void rollback();
/**
* Adds an operation to the transaction.
*/
void enlist(TxOp* const op);
};
}
}
#endif
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