content: 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);
  }
  