src/main/java/org/apache/giraph/bsp/CentralizedServiceMaster.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.bsp;

import java.io.IOException;

import org.apache.hadoop.io.Writable;
import org.apache.hadoop.io.WritableComparable;
import org.apache.hadoop.mapreduce.InputSplit;
import org.apache.zookeeper.KeeperException;

/**
 * At most, there will be one active master at a time, but many threads can
 * be trying to be the active master.
 */
@SuppressWarnings("rawtypes")
public interface CentralizedServiceMaster<
        I extends WritableComparable,
        V extends Writable,
        E extends Writable,
        M extends Writable>
        extends CentralizedService<I, V, E, M> {
    /**
     * Become the master.
     * @return true if became the master, false if the application is done.
     */
    boolean becomeMaster();

    /**
     * Create the {@link InputSplit} objects from the index range based on the
     * user-defined VertexInputFormat.  The {@link InputSplit} objects will
     * processed by the workers later on during the INPUT_SUPERSTEP.
     *
     * @return Number of partitions. Returns -1 on failure to create
     *         valid input splits.
     */
    int createInputSplits();

    /**
     * Master coordinates the superstep
     *
     * @return State of the application as a result of this superstep
     * @throws InterruptedException
     * @throws KeeperException
     */
    SuperstepState coordinateSuperstep()
        throws KeeperException, InterruptedException;

    /**
     * Master can decide to restart from the last good checkpoint if a
     * worker fails during a superstep.
     *
     * @param checkpoint Checkpoint to restart from
     */
    void restartFromCheckpoint(long checkpoint);

    /**
     * Get the last known good checkpoint
     * @throws IOException
     */
    long getLastGoodCheckpoint() throws IOException;

    /**
     * If the master decides that this job doesn't have the resources to
     * continue, it can fail the job.  It can also designate what to do next.
     * Typically this is mainly informative.
     *
     * @param state
     * @param applicationAttempt attempt to start on
     * @param desiredSuperstep Superstep to restart from (if applicable)
     */
    void setJobState(ApplicationState state,
                     long applicationAttempt,
                     long desiredSuperstep);
}