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.lib;
020    
021    import org.apache.hadoop.classification.InterfaceAudience;
022    import org.apache.hadoop.classification.InterfaceStability;
023    import org.apache.hadoop.metrics2.MetricsRecordBuilder;
024    
025    /**
026     * The mutable metric interface
027     */
028    @InterfaceAudience.Public
029    @InterfaceStability.Evolving
030    public abstract class MutableMetric {
031      private volatile boolean changed = true;
032    
033      /**
034       * Get a snapshot of the metric
035       * @param builder the metrics record builder
036       * @param all if true, snapshot unchanged metrics as well
037       */
038      public abstract void snapshot(MetricsRecordBuilder builder, boolean all);
039    
040      /**
041       * Get a snapshot of metric if changed
042       * @param builder the metrics record builder
043       */
044      public void snapshot(MetricsRecordBuilder builder) {
045        snapshot(builder, false);
046      }
047    
048      /**
049       * Set the changed flag in mutable operations
050       */
051      protected void setChanged() { changed = true; }
052    
053      /**
054       * Clear the changed flag in the snapshot operations
055       */
056      protected void clearChanged() { changed = false; }
057    
058      /**
059       * @return  true if metric is changed since last snapshot/snapshot
060       */
061      public boolean changed() { return changed; }
062    }