giraph-core/src/main/java/org/apache/giraph/partition/PartitionStore.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 org.apache.giraph.partition;

import org.apache.hadoop.io.Writable;
import org.apache.hadoop.io.WritableComparable;

/**
 * Structure that stores partitions for a worker.
 *
 * @param <I> Vertex id
 * @param <V> Vertex data
 * @param <E> Edge data
 */
public abstract class PartitionStore<I extends WritableComparable,
    V extends Writable, E extends Writable> {
  /**
   * Add a new partition to the store or just the vertices from the partition
   * to the old partition.
   *
   * @param partition Partition to add
   */
  public abstract void addPartition(Partition<I, V, E> partition);

  /**
   * Get or create a partition. Note: user has to put back
   * it to the store through {@link #putPartition(Partition)} after use.
   *
   * @param partitionId Partition id
   * @return The requested partition (never null)
   */
  public abstract Partition<I, V, E> getOrCreatePartition(Integer partitionId);

  /**
   * Put a partition back to the store. Use this method to be put a partition
   * back after it has been retrieved through
   * {@link #getOrCreatePartition(Integer)}.
   *
   * @param partition Partition
   */
  public abstract void putPartition(Partition<I, V, E> partition);

  /**
   * Remove a partition and return it.
   *
   * @param partitionId Partition id
   * @return The removed partition
   */
  public abstract Partition<I, V, E> removePartition(Integer partitionId);

  /**
   * Just delete a partition
   * (more efficient than {@link #removePartition(Integer partitionID)} if the
   * partition is out of core).
   *
   * @param partitionId Partition id
   */
  public abstract void deletePartition(Integer partitionId);

  /**
   * Whether a specific partition is present in the store.
   *
   * @param partitionId Partition id
   * @return True iff the partition is present
   */
  public abstract boolean hasPartition(Integer partitionId);

  /**
   * Return the ids of all the stored partitions as an Iterable.
   *
   * @return The partition ids
   */
  public abstract Iterable<Integer> getPartitionIds();

  /**
   * Return the number of stored partitions.
   *
   * @return The number of partitions
   */
  public abstract int getNumPartitions();

  /**
   * Whether the partition store is empty.
   *
   * @return True iff there are no partitions in the store
   */
  public boolean isEmpty() {
    return getNumPartitions() == 0;
  }

  /**
   * Called at the end of the computation.
   */
  public void shutdown() { }
}