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 */
031public interface OptimisticLockingAggregationRepository extends AggregationRepository {
032
033    /**
034     * {@link Exception} used by an {@code AggregationRepository} to indicate that an optimistic
035     * update error has occurred and that the operation should be retried by the caller.
036     * <p/>
037     */
038    class OptimisticLockingException extends RuntimeException {
039        private static final long serialVersionUID = 1L;
040    }
041
042    /**
043     * Add the given {@link org.apache.camel.Exchange} under the correlation key.
044     * <p/>
045     * Will perform optimistic locking to replace expected existing exchange with the new supplied exchange.
046     * <p/>
047     * If the {@code oldExchange} is null the underlying implementation is to assume this is the very first Exchange for the
048     * supplied correlation key. When the implementation comes to store to the Exchange if there is already an existing
049     * Exchange present for this correlation key the implementation should throw an OptimisticLockingException.
050     * <p/>
051     * If the {@code oldExchange} is not null the underlying implementation should use it to compare with the existing exchange
052     * when doing an atomic compare-and-set/swap operation.
053     * <p/>
054     * The implementation may achieve this by storing a version identifier in the Exchange as a parameter. Set before
055     * returning from {@link AggregationRepository#get(org.apache.camel.CamelContext, String)}} and retrieved from the
056     * exchange when passed to {@link AggregationRepository#add(org.apache.camel.CamelContext, String, org.apache.camel.Exchange)}.
057     * <p/>
058     * Note: The {@link org.apache.camel.processor.aggregate.MemoryAggregationRepository} is an exception to this recommendation.
059     * It uses the {@code oldExchange}'s Object identify to perform it's compare-and-set/swap operation, instead of a version
060     * parameter. This is not the recommended approach, and should be avoided.
061     * <p/>
062     * The {@link org.apache.camel.processor.aggregate.AggregateProcessor} will ensure that the exchange received from
063     * {@link OptimisticLockingAggregationRepository#get(org.apache.camel.CamelContext, String)} is passed as {@code oldExchange},
064     * and that the aggregated exchange received from the {@link org.apache.camel.processor.aggregate.AggregationStrategy}
065     * is passed as the {@code newExchange}.
066     *
067     * @param camelContext   the current CamelContext
068     * @param key            the correlation key
069     * @param oldExchange    the old exchange that is expected to exist when replacing with the new exchange
070     * @param newExchange    the new aggregated exchange, to replace old exchange
071     * @return the old exchange if any existed
072     * @throws OptimisticLockingException This should be thrown when the currently stored exchange differs from the supplied oldExchange.
073     */
074    Exchange add(CamelContext camelContext, String key, Exchange oldExchange, Exchange newExchange) throws OptimisticLockingException;
075
076    /**
077     * Removes the given Exchange when both the supplied key and Exchange are present in the repository. If the supplied Exchange
078     * does not match the Exchange actually stored against the key this method should throw an OptimisticLockingException
079     * to indicate that the value of the correlation key has changed from the expected value.
080     * <p/>
081     * @param camelContext   the current CamelContext
082     * @param key            the correlation key
083     * @param exchange       the exchange to remove
084     * @throws OptimisticLockingException This should be thrown when the exchange has already been deleted, or otherwise modified.
085     */
086    void remove(CamelContext camelContext, String key, Exchange exchange) throws OptimisticLockingException;
087}