org.apache.hadoop.metrics2.MetricsSystem.java Source code

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Here is the source code for org.apache.hadoop.metrics2.MetricsSystem.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.metrics2;

import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;

/**
 * The metrics system interface.
 * 
 * The following components are used for metrics.
 * <ul>
 * <li>{@link MetricsSource} generate and update metrics information.</li>
 * <li>{@link MetricsSink} consume the metrics information</li>
 * </ul>
 * 
 * {@link MetricsSource} and {@link MetricsSink} register with the metrics
 * system. Implementations of {@link MetricsSystem} polls the
 * {@link MetricsSource}s periodically and pass the {@link MetricsRecord}s to
 * {@link MetricsSink}.
 */
@InterfaceAudience.Public
@InterfaceStability.Evolving
public abstract class MetricsSystem implements MetricsSystemMXBean {

    @InterfaceAudience.Private
    public abstract MetricsSystem init(String prefix);

    /**
     * Register a metrics source
     * @param <T>   the actual type of the source object
     * @param source object to register
     * @param name  of the source. Must be unique or null (then extracted from
     *              the annotations of the source object.)
     * @param desc  the description of the source (or null. See above.)
     * @return the source object
     * @exception MetricsException
     */
    public abstract <T> T register(String name, String desc, T source);

    /**
     * Unregister a metrics source
     * @param name of the source. This is the name you use to call register()
     */
    public abstract void unregisterSource(String name);

    /**
     * Register a metrics source (deriving name and description from the object)
     * @param <T>   the actual type of the source object
     * @param source  object to register
     * @return  the source object
     * @exception MetricsException
     */
    public <T> T register(T source) {
        return register(null, null, source);
    }

    /**
     * @param name  of the metrics source
     * @return the metrics source (potentially wrapped) object
     */
    @InterfaceAudience.Private
    public abstract MetricsSource getSource(String name);

    /**
     * Register a metrics sink
     * @param <T>   the type of the sink
     * @param sink  to register
     * @param name  of the sink. Must be unique.
     * @param desc  the description of the sink
     * @return the sink
     * @exception MetricsException
     */
    public abstract <T extends MetricsSink> T register(String name, String desc, T sink);

    /**
     * Register a callback interface for JMX events
     * @param callback  the callback object implementing the MBean interface.
     */
    public abstract void register(Callback callback);

    /**
     * Requests an immediate publish of all metrics from sources to sinks.
     * 
     * This is a "soft" request: the expectation is that a best effort will be
     * done to synchronously snapshot the metrics from all the sources and put
     * them in all the sinks (including flushing the sinks) before returning to
     * the caller. If this can't be accomplished in reasonable time it's OK to
     * return to the caller before everything is done. 
     */
    public abstract void publishMetricsNow();

    /**
     * Shutdown the metrics system completely (usually during server shutdown.)
     * The MetricsSystemMXBean will be unregistered.
     * @return true if shutdown completed
     */
    public abstract boolean shutdown();

    /**
     * The metrics system callback interface (needed for proxies.)
     */
    public interface Callback {
        /**
         * Called before start()
         */
        void preStart();

        /**
         * Called after start()
         */
        void postStart();

        /**
         * Called before stop()
         */
        void preStop();

        /**
         * Called after stop()
         */
        void postStop();
    }

    /**
     * Convenient abstract class for implementing callback interface
     */
    public static abstract class AbstractCallback implements Callback {
        @Override
        public void preStart() {
        }

        @Override
        public void postStart() {
        }

        @Override
        public void preStop() {
        }

        @Override
        public void postStop() {
        }
    }
}