org.apache.hadoop.mapred.Reporter.java Source code

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Here is the source code for org.apache.hadoop.mapred.Reporter.java

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/**
 * 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.hadoop.mapred;

import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.mapred.Counters.Counter;
import org.apache.hadoop.util.Progressable;

/** 
 * A facility for Map-Reduce applications to report progress and update 
 * counters, status information etc.
 * 
 * <p>{@link Mapper} and {@link Reducer} can use the <code>Reporter</code>
 * provided to report progress or just indicate that they are alive. In 
 * scenarios where the application takes significant amount of time to
 * process individual key/value pairs, this is crucial since the framework 
 * might assume that the task has timed-out and kill that task.
 *
 * <p>Applications can also update {@link Counters} via the provided 
 * <code>Reporter</code> .</p>
 * 
 * @see Progressable
 * @see Counters
 */
@InterfaceAudience.Public
@InterfaceStability.Stable
public interface Reporter extends Progressable {

    /**
     * A constant of Reporter type that does nothing.
     */
    public static final Reporter NULL = new Reporter() {
        public void setStatus(String s) {
        }

        public void progress() {
        }

        public Counter getCounter(Enum<?> name) {
            return null;
        }

        public Counter getCounter(String group, String name) {
            return null;
        }

        public void incrCounter(Enum<?> key, long amount) {
        }

        public void incrCounter(String group, String counter, long amount) {
        }

        public InputSplit getInputSplit() throws UnsupportedOperationException {
            throw new UnsupportedOperationException("NULL reporter has no input");
        }

        @Override
        public float getProgress() {
            return 0;
        }
    };

    /**
     * Set the status description for the task.
     * 
     * @param status brief description of the current status.
     */
    public abstract void setStatus(String status);

    /**
     * Get the {@link Counter} of the given group with the given name.
     * 
     * @param name counter name
     * @return the <code>Counter</code> of the given group/name.
     */
    public abstract Counter getCounter(Enum<?> name);

    /**
     * Get the {@link Counter} of the given group with the given name.
     * 
     * @param group counter group
     * @param name counter name
     * @return the <code>Counter</code> of the given group/name.
     */
    public abstract Counter getCounter(String group, String name);

    /**
     * Increments the counter identified by the key, which can be of
     * any {@link Enum} type, by the specified amount.
     * 
     * @param key key to identify the counter to be incremented. The key can be
     *            be any <code>Enum</code>. 
     * @param amount A non-negative amount by which the counter is to 
     *               be incremented.
     */
    public abstract void incrCounter(Enum<?> key, long amount);

    /**
     * Increments the counter identified by the group and counter name
     * by the specified amount.
     * 
     * @param group name to identify the group of the counter to be incremented.
     * @param counter name to identify the counter within the group.
     * @param amount A non-negative amount by which the counter is to 
     *               be incremented.
     */
    public abstract void incrCounter(String group, String counter, long amount);

    /**
     * Get the {@link InputSplit} object for a map.
     * 
     * @return the <code>InputSplit</code> that the map is reading from.
     * @throws UnsupportedOperationException if called outside a mapper
     */
    public abstract InputSplit getInputSplit() throws UnsupportedOperationException;

    /**
     * Get the progress of the task. Progress is represented as a number between
     * 0 and 1 (inclusive).
     */
    public float getProgress();
}