jstorm-core/src/main/java/backtype/storm/transactional/ITransactionalSpout.java

/**
 * 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.
 */
package backtype.storm.transactional;

import backtype.storm.coordination.BatchOutputCollector;
import backtype.storm.task.TopologyContext;
import backtype.storm.topology.IComponent;
import java.math.BigInteger;
import java.util.Map;

public interface ITransactionalSpout<T> extends IComponent {
    public interface Coordinator<X> {
        /**
         * Create metadata for this particular transaction id which has never been emitted before. The metadata should contain whatever is necessary to be able
         * to replay the exact batch for the transaction at a later point.
         * 
         * The metadata is stored in Zookeeper.
         * 
         * Storm uses the Kryo serializations configured in the component configuration for this spout to serialize and deserialize the metadata.
         * 
         * @param txid The id of the transaction.
         * @param prevMetadata The metadata of the previous transaction
         * @return the metadata for this new transaction
         */
        X initializeTransaction(BigInteger txid, X prevMetadata);

        /**
         * Returns true if its ok to emit start a new transaction, false otherwise (will skip this transaction).
         * 
         * You should sleep here if you want a delay between asking for the next transaction (this will be called repeatedly in a loop).
         */
        boolean isReady();

        /**
         * Release any resources from this coordinator.
         */
        void close();
    }

    public interface Emitter<X> {
        /**
         * Emit a batch for the specified transaction attempt and metadata for the transaction. The metadata was created by the Coordinator in the
         * initializeTranaction method. This method must always emit the same batch of tuples across all tasks for the same transaction id.
         * 
         * The first field of all emitted tuples must contain the provided TransactionAttempt.
         * 
         */
        void emitBatch(TransactionAttempt tx, X coordinatorMeta, BatchOutputCollector collector);

        /**
         * Any state for transactions prior to the provided transaction id can be safely cleaned up, so this method should clean up that state.
         */
        void cleanupBefore(BigInteger txid);

        /**
         * Release any resources held by this emitter.
         */
        void close();
    }

    /**
     * The coordinator for a TransactionalSpout runs in a single thread and indicates when batches of tuples should be emitted and when transactions should
     * commit. The Coordinator that you provide in a TransactionalSpout provides metadata for each transaction so that the transactions can be replayed.
     */
    Coordinator<T> getCoordinator(Map conf, TopologyContext context);

    /**
     * The emitter for a TransactionalSpout runs as many tasks across the cluster. Emitters are responsible for emitting batches of tuples for a transaction and
     * must ensure that the same batch of tuples is always emitted for the same transaction id.
     */
    Emitter<T> getEmitter(Map conf, TopologyContext context);
}