001/**
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.camel.spi;
018
019import org.apache.camel.CamelContext;
020import org.apache.camel.Exchange;
021
022/**
023 * A specialized {@link org.apache.camel.spi.AggregationRepository} which also supports
024 * optimistic locking.
025 *
026 * If the underlying implementation cannot perform optimistic locking, it should
027 * not implement this interface.
028 *
029 * @see org.apache.camel.processor.aggregate.MemoryAggregationRepository
030 *
031 * @version
032 */
033public interface OptimisticLockingAggregationRepository extends AggregationRepository {
034
035    /**
036     * {@link Exception} used by an {@code AggregationRepository} to indicate that an optimistic
037     * update error has occurred and that the operation should be retried by the caller.
038     * <p/>
039     */
040    class OptimisticLockingException extends RuntimeException {
041        private static final long serialVersionUID = 1L;
042    }
043
044    /**
045     * Add the given {@link org.apache.camel.Exchange} under the correlation key.
046     * <p/>
047     * Will perform optimistic locking to replace expected existing exchange with the new supplied exchange.
048     * <p/>
049     * If the {@code oldExchange} is null the underlying implementation is to assume this is the very first Exchange for the
050     * supplied correlation key. When the implementation comes to store to the Exchange if there is already an existing
051     * Exchange present for this correlation key the implementation should throw an OptimisticLockingException.
052     * <p/>
053     * If the {@code oldExchange} is not null the underlying implementation should use it to compare with the existing exchange
054     * when doing an atomic compare-and-set/swap operation.
055     * <p/>
056     * The implementation may achieve this by storing a version identifier in the Exchange as a parameter. Set before
057     * returning from {@link AggregationRepository#get(org.apache.camel.CamelContext, String)}} and retrieved from the
058     * exchange when passed to {@link AggregationRepository#add(org.apache.camel.CamelContext, String, org.apache.camel.Exchange)}.
059     * <p/>
060     * Note: The {@link org.apache.camel.processor.aggregate.MemoryAggregationRepository} is an exception to this recommendation.
061     * It uses the {@code oldExchange}'s Object identify to perform it's compare-and-set/swap operation, instead of a version
062     * parameter. This is not the recommended approach, and should be avoided.
063     * <p/>
064     * The {@link org.apache.camel.processor.aggregate.AggregateProcessor} will ensure that the exchange received from
065     * {@link OptimisticLockingAggregationRepository#get(org.apache.camel.CamelContext, String)} is passed as {@code oldExchange},
066     * and that the aggregated exchange received from the {@link org.apache.camel.processor.aggregate.AggregationStrategy}
067     * is passed as the {@code newExchange}.
068     *
069     * @param camelContext   the current CamelContext
070     * @param key            the correlation key
071     * @param oldExchange    the old exchange that is expected to exist when replacing with the new exchange
072     * @param newExchange    the new aggregated exchange, to replace old exchange
073     * @return the old exchange if any existed
074     * @throws OptimisticLockingException This should be thrown when the currently stored exchange differs from the supplied oldExchange.
075     */
076    Exchange add(CamelContext camelContext, String key, Exchange oldExchange, Exchange newExchange) throws OptimisticLockingException;
077
078    /**
079     * Removes the given Exchange when both the supplied key and Exchange are present in the repository. If the supplied Exchange
080     * does not match the Exchange actually stored against the key this method should throw an OptimisticLockingException
081     * to indicate that the value of the correlation key has changed from the expected value.
082     * <p/>
083     * @param camelContext   the current CamelContext
084     * @param key            the correlation key
085     * @param exchange       the exchange to remove
086     * @throws OptimisticLockingException This should be thrown when the exchange has already been deleted, or otherwise modified.
087     */
088    void remove(CamelContext camelContext, String key, Exchange exchange) throws OptimisticLockingException;
089}