/*
 *
 * 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.
 *
 */
package org.apache.qpid.server.txn;

import org.apache.qpid.AMQException;

/**
 * This provides the abstraction of an individual operation within a
 * transaction. It is used by the TxnBuffer class.
 */
public interface TxnOp
{
    /**
     * Do the part of the operation that updates persistent state 
     */
    public void prepare() throws AMQException;
    /**
     * Complete the operation started by prepare. Can now update in
     * memory state or make netork transfers.
     */
    public void commit();
    /**
     * This is not the same as rollback. Unfortunately the use of an
     * in memory reference count as a locking mechanism and a test for
     * whether a message should be deleted means that as things are,
     * handling an acknowledgement unavoidably alters both memory and
     * persistent state on prepare. This is needed to 'compensate' or
     * undo the in-memory change if the peristent update of later ops
     * fails.
     */
    public void undoPrepare();
    /**
     * Rolls back the operation.
     */
    public void rollback();
}
