001    /*
002     * NullContext.java
003     * Licensed to the Apache Software Foundation (ASF) under one
004     * or more contributor license agreements.  See the NOTICE file
005     * distributed with this work for additional information
006     * regarding copyright ownership.  The ASF licenses this file
007     * to you under the Apache License, Version 2.0 (the
008     * "License"); you may not use this file except in compliance
009     * with the License.  You may obtain a copy of the License at
010     *
011     *     http://www.apache.org/licenses/LICENSE-2.0
012     *
013     * Unless required by applicable law or agreed to in writing, software
014     * distributed under the License is distributed on an "AS IS" BASIS,
015     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
016     * See the License for the specific language governing permissions and
017     * limitations under the License.
018     */
019    
020    package org.apache.hadoop.metrics.spi;
021    
022    import org.apache.hadoop.classification.InterfaceAudience;
023    import org.apache.hadoop.classification.InterfaceStability;
024    
025    /**
026     * Null metrics context: a metrics context which does nothing.  Used as the
027     * default context, so that no performance data is emitted if no configuration
028     * data is found.
029     * 
030     */
031    @InterfaceAudience.Public
032    @InterfaceStability.Evolving
033    public class NullContext extends AbstractMetricsContext {
034        
035      /** Creates a new instance of NullContext */
036      @InterfaceAudience.Private
037      public NullContext() {
038      }
039        
040      /**
041       * Do-nothing version of startMonitoring
042       */
043      @InterfaceAudience.Private
044      public void startMonitoring() {
045      }
046        
047      /**
048       * Do-nothing version of emitRecord
049       */
050      @InterfaceAudience.Private
051      protected void emitRecord(String contextName, String recordName,
052                                OutputRecord outRec) 
053      {}
054        
055      /**
056       * Do-nothing version of update
057       */
058      @InterfaceAudience.Private
059      protected void update(MetricsRecordImpl record) {
060      }
061        
062      /**
063       * Do-nothing version of remove
064       */
065      @InterfaceAudience.Private
066      protected void remove(MetricsRecordImpl record) {
067      }
068    }