src/core/org/apache/hadoop/metrics2/MetricsSystem.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.hadoop.metrics2;

/**
 * The metrics system interface
 */
public interface MetricsSystem extends MetricsSystemMXBean {

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

  /**
   * 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
   */
  <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.
   */
  void register(Callback callback);

  /**
   * Shutdown the metrics system completely (usually during server shutdown.)
   * The MetricsSystemMXBean will be unregistered.
   */
  void shutdown();

  /**
   * The metrics system callback interface
   */
  @SuppressWarnings("PublicInnerClass")
  static 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
   */
  @SuppressWarnings("PublicInnerClass")
  public static abstract class AbstractCallback implements Callback {

    public void preStart() {}
    public void postStart() {}
    public void preStop() {}
    public void postStop() {}

  }

}