001/**
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018
019package org.apache.hadoop.metrics2.annotation;
020
021import java.lang.annotation.*;
022
023import org.apache.hadoop.classification.InterfaceAudience;
024import org.apache.hadoop.classification.InterfaceStability;
025
026/**
027 * Annotation interface for a single metric used to annotate a field or a method
028 * in the class.
029 */
030@InterfaceAudience.Public
031@InterfaceStability.Evolving
032@Documented
033@Target({ElementType.FIELD, ElementType.METHOD})
034@Retention(RetentionPolicy.RUNTIME)
035public @interface Metric {
036
037  public enum Type {
038    DEFAULT, COUNTER, GAUGE, TAG
039  }
040
041  /**
042   * Shorthand for optional name and description
043   * @return {description} or {name, description}
044   */
045  String[] value() default {};
046
047  /**
048   * @return optional description of the metric
049   */
050  String about() default "";
051
052  /**
053   * @return optional sample name for MutableStat/Rate/Rates
054   */
055  String sampleName() default "Ops";
056
057  /**
058   * @return optional value name for MutableStat/Rate/Rates
059   */
060  String valueName() default "Time";
061
062  /**
063   * @return true to create a metric snapshot even if unchanged.
064   */
065  boolean always() default false;
066
067  /**
068   * @return optional type (counter|gauge) of the metric
069   */
070  Type type() default Type.DEFAULT;
071}