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/*
*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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/BrokerImportExport.h"
#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::shared_ptr>::iterator op_iterator;
std::vector<TxOp::shared_ptr> ops;
protected:
public:
typedef boost::shared_ptr<TxBuffer> shared_ptr;
/**
* Adds an operation to the transaction.
*/
QPID_BROKER_EXTERN void enlist(TxOp::shared_ptr op);
/**
* Requests that all ops are prepared. This should
* primarily involve making sure that a persistent record
* of the operations is stored where necessary.
*
* 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.
*/
QPID_BROKER_EXTERN bool prepare(TransactionContext* const ctxt);
/**
* Signals that the ops all prepared 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.
*/
QPID_BROKER_EXTERN void commit();
/**
* Signals that all ops can be rolled back.
*
* Should only be called either after a call to prepare()
* returns true (2pc) or instead of a prepare call
* ('server-local')
*/
QPID_BROKER_EXTERN void rollback();
/**
* Helper method for managing the process of server local
* commit
*/
QPID_BROKER_EXTERN bool commitLocal(TransactionalStore* const store);
// Used by cluster to replicate transaction status.
void accept(TxOpConstVisitor& v) const;
};
}
}
#endif
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