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.metrics2; 020 021import org.apache.hadoop.classification.InterfaceAudience; 022import org.apache.hadoop.classification.InterfaceStability; 023 024/** 025 * The metrics system interface 026 */ 027@InterfaceAudience.Public 028@InterfaceStability.Evolving 029public 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}