hbase-common/src/main/java/org/apache/hadoop/hbase/util/MovingAverage.java

   1 /*
   2  * Licensed to the Apache Software Foundation (ASF) under one
   3  * or more contributor license agreements.  See the NOTICE file
   4  * distributed with this work for additional information
   5  * regarding copyright ownership.  The ASF licenses this file
   6  * to you under the Apache License, Version 2.0 (the
   7  * "License"); you may not use this file except in compliance
   8  * with the License.  You may obtain a copy of the License at
   9  *
  10  *     http://www.apache.org/licenses/LICENSE-2.0
  11  *
  12  * Unless required by applicable law or agreed to in writing, software
  13  * distributed under the License is distributed on an "AS IS" BASIS,
  14  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  15  * See the License for the specific language governing permissions and
  16  * limitations under the License.
  17  */
  18
  19 package org.apache.hadoop.hbase.util;
  20
  21 import org.apache.yetus.audience.InterfaceAudience;
  22 import org.slf4j.Logger;
  23 import org.slf4j.LoggerFactory;
  24
  25 /**
  26  * The purpose of introduction of {@link MovingAverage} mainly is to measure execution time of a
  27  * specific method, which can help us to know its performance fluctuation in response to different
  28  * machine states or situations, better case, then to act accordingly.
  29  * <br>
  30  * In different situation, different {@link MovingAverage} algorithm can be used based on needs.
  31  */
  32 @InterfaceAudience.Private
  33 public abstract class MovingAverage<T> {
  34   private final static Logger LOG = LoggerFactory.getLogger(MovingAverage.class);
  35
  36   protected final String label;
  37
  38   protected MovingAverage(String label) {
  39     this.label = label;
  40   }
  41
  42   /**
  43    * Mark start time of an execution.
  44    * @return time in ns.
  45    */
  46   protected long start() {
  47     return System.nanoTime();
  48   }
  49
  50   /**
  51    * Mark end time of an execution, and return its interval.
  52    * @param startTime start time of an execution
  53    * @return elapsed time
  54    */
  55   protected long stop(long startTime) {
  56     return System.nanoTime() - startTime;
  57   }
  58
  59   /**
  60    * Measure elapsed time of a measurable method.
  61    * @param measurable method implements {@link TimeMeasurable}
  62    * @return T it refers to the original return type of the measurable method
  63    */
  64   public T measure(TimeMeasurable<T> measurable) {
  65     long startTime = start();
  66     LOG.trace("{} - start to measure at: {} ns.", label, startTime);
  67     // Here may throw exceptions which should be taken care by caller, not here.
  68     // If exception occurs, this time wouldn't count.
  69     T result = measurable.measure();
  70     long elapsed = stop(startTime);
  71     LOG.trace("{} - elapse: {} ns.", label, elapsed);
  72     updateMostRecentTime(elapsed);
  73     return result;
  74   }
  75
  76   /**
  77    * Update the most recent data.
  78    * @param elapsed elapsed time of the most recent measurement
  79    */
  80   protected abstract void updateMostRecentTime(long elapsed);
  81
  82   /**
  83    * Get average execution time of the measured method.
  84    * @return average time in ns
  85    */
  86   public abstract double getAverageTime();
  87 }