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;
024import org.apache.hadoop.metrics.MetricsException;
025
026/**
027 * A null context which has a thread calling 
028 * periodically when monitoring is started. This keeps the data sampled 
029 * correctly.
030 * In all other respects, this is like the NULL context: No data is emitted.
031 * This is suitable for Monitoring systems like JMX which reads the metrics
032 *  when someone reads the data from JMX.
033 * 
034 * The default impl of start and stop monitoring:
035 *  is the AbstractMetricsContext is good enough.
036 * 
037 */
038@InterfaceAudience.Public
039@InterfaceStability.Evolving
040public class NullContextWithUpdateThread extends AbstractMetricsContext {
041  
042  private static final String PERIOD_PROPERTY = "period";
043    
044  /** Creates a new instance of NullContextWithUpdateThread */
045  @InterfaceAudience.Private
046  public NullContextWithUpdateThread() {
047  }
048  
049  @InterfaceAudience.Private
050  public void init(String contextName, ContextFactory factory) {
051    super.init(contextName, factory);
052    parseAndSetPeriod(PERIOD_PROPERTY);
053  }
054   
055    
056  /**
057   * Do-nothing version of emitRecord
058   */
059  @InterfaceAudience.Private
060  protected void emitRecord(String contextName, String recordName,
061                            OutputRecord outRec) 
062  {}
063    
064  /**
065   * Do-nothing version of update
066   */
067  @InterfaceAudience.Private
068  protected void update(MetricsRecordImpl record) {
069  }
070    
071  /**
072   * Do-nothing version of remove
073   */
074  @InterfaceAudience.Private
075  protected void remove(MetricsRecordImpl record) {
076  }
077}