ITransactionalSpout.java

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);
        
        /**
         * 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);
}