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.metrics2;
020
021 import org.apache.hadoop.classification.InterfaceAudience;
022 import org.apache.hadoop.classification.InterfaceStability;
023
024 /**
025 * The metrics system interface
026 */
027 @InterfaceAudience.Public
028 @InterfaceStability.Evolving
029 public abstract class MetricsSystem implements MetricsSystemMXBean {
030
031 @InterfaceAudience.Private
032 public abstract MetricsSystem init(String prefix);
033
034 /**
035 * Register a metrics source
036 * @param <T> the actual type of the source object
037 * @param source object to register
038 * @param name of the source. Must be unique or null (then extracted from
039 * the annotations of the source object.)
040 * @param desc the description of the source (or null. See above.)
041 * @return the source object
042 * @exception MetricsException
043 */
044 public abstract <T> T register(String name, String desc, T source);
045
046 /**
047 * Register a metrics source (deriving name and description from the object)
048 * @param <T> the actual type of the source object
049 * @param source object to register
050 * @return the source object
051 * @exception MetricsException
052 */
053 public <T> T register(T source) {
054 return register(null, null, source);
055 }
056
057 /**
058 * @param name of the metrics source
059 * @return the metrics source (potentially wrapped) object
060 */
061 @InterfaceAudience.Private
062 public abstract MetricsSource getSource(String name);
063
064 /**
065 * Register a metrics sink
066 * @param <T> the type of the sink
067 * @param sink to register
068 * @param name of the sink. Must be unique.
069 * @param desc the description of the sink
070 * @return the sink
071 * @exception MetricsException
072 */
073 public abstract <T extends MetricsSink>
074 T register(String name, String desc, T sink);
075
076 /**
077 * Register a callback interface for JMX events
078 * @param callback the callback object implementing the MBean interface.
079 */
080 public abstract void register(Callback callback);
081
082 /**
083 * Shutdown the metrics system completely (usually during server shutdown.)
084 * The MetricsSystemMXBean will be unregistered.
085 * @return true if shutdown completed
086 */
087 public abstract boolean shutdown();
088
089 /**
090 * The metrics system callback interface (needed for proxies.)
091 */
092 public interface Callback {
093 /**
094 * Called before start()
095 */
096 void preStart();
097
098 /**
099 * Called after start()
100 */
101 void postStart();
102
103 /**
104 * Called before stop()
105 */
106 void preStop();
107
108 /**
109 * Called after stop()
110 */
111 void postStop();
112 }
113
114 /**
115 * Convenient abstract class for implementing callback interface
116 */
117 public static abstract class AbstractCallback implements Callback {
118 @Override public void preStart() {}
119 @Override public void postStart() {}
120 @Override public void preStop() {}
121 @Override public void postStop() {}
122 }
123 }