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.metrics.spi;
020
021import org.apache.hadoop.classification.InterfaceAudience;
022import org.apache.hadoop.classification.InterfaceStability;
023import org.apache.hadoop.metrics.ContextFactory;
024
025/**
026 * A null context which has a thread calling 
027 * periodically when monitoring is started. This keeps the data sampled 
028 * correctly.
029 * In all other respects, this is like the NULL context: No data is emitted.
030 * This is suitable for Monitoring systems like JMX which reads the metrics
031 *  when someone reads the data from JMX.
032 * 
033 * The default impl of start and stop monitoring:
034 *  is the AbstractMetricsContext is good enough.
035 * 
036 */
037@InterfaceAudience.Public
038@InterfaceStability.Evolving
039public class NullContextWithUpdateThread extends AbstractMetricsContext {
040  
041  private static final String PERIOD_PROPERTY = "period";
042    
043  /** Creates a new instance of NullContextWithUpdateThread */
044  @InterfaceAudience.Private
045  public NullContextWithUpdateThread() {
046  }
047  
048  @InterfaceAudience.Private
049  public void init(String contextName, ContextFactory factory) {
050    super.init(contextName, factory);
051    parseAndSetPeriod(PERIOD_PROPERTY);
052  }
053   
054    
055  /**
056   * Do-nothing version of emitRecord
057   */
058  @InterfaceAudience.Private
059  protected void emitRecord(String contextName, String recordName,
060                            OutputRecord outRec) 
061  {}
062    
063  /**
064   * Do-nothing version of update
065   */
066  @InterfaceAudience.Private
067  protected void update(MetricsRecordImpl record) {
068  }
069    
070  /**
071   * Do-nothing version of remove
072   */
073  @InterfaceAudience.Private
074  protected void remove(MetricsRecordImpl record) {
075  }
076}