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.metrics.spi;
020    
021    import org.apache.hadoop.classification.InterfaceAudience;
022    import org.apache.hadoop.classification.InterfaceStability;
023    import org.apache.hadoop.metrics.ContextFactory;
024    import 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
040    public 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    }