com.chinamobile.bcbsp.subgraph.SGAHashPartitioner.java Source code

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Here is the source code for com.chinamobile.bcbsp.subgraph.SGAHashPartitioner.java

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package com.chinamobile.bcbsp.subgraph;

/*
 * 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.
 */

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.HashMap;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import com.chinamobile.bcbsp.api.Partitioner;

/**
 * HashPartitioner is partitioning by the MD5-based hash code of the vertex id.
 * 
 * @param <IDT>
 *        the type of the vertex
 */
public class SGAHashPartitioner<IDT> extends Partitioner<IDT> {
    public static final Log LOG = LogFactory.getLog(SGAHashPartitioner.class);
    /** the index of the array. */
    private static final int INDEX_0 = 0;
    /** the index of the array. */
    private static final int INDEX_1 = 1;
    /** the index of the array. */
    private static final int INDEX_2 = 2;
    /** the index of the array. */
    private static final int INDEX_3 = 3;
    /** the offset of the number. */
    private static final int OFFSET_1 = 8;
    /** the offset of the number. */
    private static final int OFFSET_2 = 16;
    /** the offset of the number. */
    private static final int OFFSET_3 = 24;
    /** the compared number. */
    private static final int NUMBER = 0xFF;

    private HashMap<IDT, Integer> migrateVertexPartition = new HashMap<IDT, Integer>(16384);

    /**
     * Constructor method.
     */
    public SGAHashPartitioner() {
    }

    /**
     * Constructor method.
     * 
     * @param numpartition
     *        the number of the partition.
     */
    public SGAHashPartitioner(int numpartition) {
        this.numPartition = numpartition;
    }

    /**
     * Partitions a vertex according the id mapping to a partition.
     * 
     * @return a number between 0 and numPartition that tells which partition it
     *         belongs to.
     * @param id
     *        the vertex id
     */
    @Override
    public int getPartitionID(IDT id) {

        if (migrateVertexPartition.size() != 0) {
            if (this.migrateVertexPartition.containsKey(id)) {
                return this.migrateVertexPartition.get(id);
            }
        }
        String url = id.toString();
        MessageDigest md5 = null;
        if (md5 == null) {
            try {
                md5 = MessageDigest.getInstance("MD5");
            } catch (NoSuchAlgorithmException e) {
                throw new IllegalStateException("++++ no md5 algorythm found");
            }
        }
        md5.reset();
        md5.update(url.getBytes());
        byte[] bKey = md5.digest();
        long hashcode = ((long) (bKey[INDEX_3] & NUMBER) << OFFSET_3)
                | ((long) (bKey[INDEX_2] & NUMBER) << OFFSET_2) | ((long) (bKey[INDEX_1] & NUMBER) << OFFSET_1)
                | bKey[INDEX_0] & NUMBER;
        int result = (int) (hashcode % this.numPartition);
        if (result < 0) {
            result = result + this.numPartition;
        }
        return result;
    }

    @Override
    public void updateMigratePartition(IDT id, int partitionID) {
        this.migrateVertexPartition.put(id, partitionID);
    }
}