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);

		/**
		 * 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);
}