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    
019    package org.apache.hadoop.metrics2.annotation;
020    
021    import java.lang.annotation.*;
022    
023    import org.apache.hadoop.classification.InterfaceAudience;
024    import org.apache.hadoop.classification.InterfaceStability;
025    
026    /**
027     * Annotation interface for a single metric
028     */
029    @InterfaceAudience.Public
030    @InterfaceStability.Evolving
031    @Documented
032    @Target({ElementType.FIELD, ElementType.METHOD})
033    @Retention(RetentionPolicy.RUNTIME)
034    public @interface Metric {
035    
036      public enum Type {
037        DEFAULT, COUNTER, GAUGE, TAG
038      }
039    
040      /**
041       * Shorthand for optional name and description
042       * @return {description} or {name, description}
043       */
044      String[] value() default {};
045    
046      /**
047       * @return optional description of the metric
048       */
049      String about() default "";
050    
051      /**
052       * @return optional sample name for MutableStat/Rate/Rates
053       */
054      String sampleName() default "Ops";
055    
056      /**
057       * @return optional value name for MutableStat/Rate/Rates
058       */
059      String valueName() default "Time";
060    
061      /**
062       * @return true to create a metric snapshot even if unchanged.
063       */
064      boolean always() default false;
065    
066      /**
067       * @return optional type (counter|gauge) of the metric
068       */
069      Type type() default Type.DEFAULT;
070    }