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     */
017    package org.apache.camel.processor.aggregate;
018    
019    import org.apache.camel.Exchange;
020    
021    /**
022     * A specialized {@link AggregationStrategy} which gets a callback when the aggregated {@link Exchange} fails to add
023     * in the {@link org.apache.camel.spi.OptimisticLockingAggregationRepository} because of
024     * an {@link org.apache.camel.spi.OptimisticLockingAggregationRepository.OptimisticLockingException}.
025     * <p/>
026     * Please note that when aggregating {@link Exchange}'s to be careful not to modify and return the {@code oldExchange}
027     * from the {@link AggregationStrategy#aggregate(org.apache.camel.Exchange, org.apache.camel.Exchange)} method.
028     * If you are using the default MemoryAggregationRepository this will mean you have modified the value of an object
029     * already referenced/stored by the MemoryAggregationRepository. This makes it impossible for optimistic locking
030     * to work correctly with the MemoryAggregationRepository.
031     * <p/>
032     * You should instead return either the new {@code newExchange} or a completely new instance of {@link Exchange}. This
033     * is due to the nature of how the underlying {@link java.util.concurrent.ConcurrentHashMap} performs CAS operations
034     * on the value identity.
035     *
036     * @see java.util.concurrent.ConcurrentHashMap
037     *
038     * @version
039     */
040    public interface OptimisticLockingAwareAggregationStrategy extends AggregationStrategy {
041    
042        // TODO: In Camel 3.0 we should move this to org.apache.camel package
043    
044        void onOptimisticLockFailure(Exchange oldExchange, Exchange newExchange);
045    }