001package org.apache.commons.jcs.auxiliary; 002 003/* 004 * Licensed to the Apache Software Foundation (ASF) under one 005 * or more contributor license agreements. See the NOTICE file 006 * distributed with this work for additional information 007 * regarding copyright ownership. The ASF licenses this file 008 * to you under the Apache License, Version 2.0 (the 009 * "License"); you may not use this file except in compliance 010 * with the License. You may obtain a copy of the License at 011 * 012 * http://www.apache.org/licenses/LICENSE-2.0 013 * 014 * Unless required by applicable law or agreed to in writing, 015 * software distributed under the License is distributed on an 016 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY 017 * KIND, either express or implied. See the License for the 018 * specific language governing permissions and limitations 019 * under the License. 020 */ 021 022import java.util.concurrent.atomic.AtomicBoolean; 023import java.util.concurrent.locks.Condition; 024import java.util.concurrent.locks.Lock; 025import java.util.concurrent.locks.ReentrantLock; 026 027import org.apache.commons.logging.Log; 028import org.apache.commons.logging.LogFactory; 029 030/** 031 * Used to monitor and repair any failed connection for the lateral cache service. By default the 032 * monitor operates in a failure driven mode. That is, it goes into a wait state until there is an 033 * error. Upon the notification of a connection error, the monitor changes to operate in a time 034 * driven mode. That is, it attempts to recover the connections on a periodic basis. When all failed 035 * connections are restored, it changes back to the failure driven mode. 036 */ 037public abstract class AbstractAuxiliaryCacheMonitor extends Thread 038{ 039 /** The logger */ 040 protected final Log log = LogFactory.getLog( this.getClass() ); 041 042 /** How long to wait between runs */ 043 protected static long idlePeriod = 20 * 1000; 044 045 /** 046 * Must make sure AbstractAuxiliaryCacheMonitor is started before any error can be detected! 047 */ 048 protected AtomicBoolean allright = new AtomicBoolean(true); 049 050 /** 051 * shutdown flag 052 */ 053 private AtomicBoolean shutdown = new AtomicBoolean(false); 054 055 /** Synchronization helper lock */ 056 private Lock lock = new ReentrantLock(); 057 058 /** Synchronization helper condition */ 059 private Condition trigger = lock.newCondition(); 060 061 /** 062 * Constructor 063 * 064 * @param name the thread name 065 */ 066 public AbstractAuxiliaryCacheMonitor(String name) 067 { 068 super(name); 069 } 070 071 /** 072 * Configures the idle period between repairs. 073 * <p> 074 * @param idlePeriod The new idlePeriod value 075 */ 076 public static void setIdlePeriod( long idlePeriod ) 077 { 078 if ( idlePeriod > AbstractAuxiliaryCacheMonitor.idlePeriod ) 079 { 080 AbstractAuxiliaryCacheMonitor.idlePeriod = idlePeriod; 081 } 082 } 083 084 /** 085 * Notifies the cache monitor that an error occurred, and kicks off the error recovery process. 086 */ 087 public void notifyError() 088 { 089 if (allright.compareAndSet(true, false)) 090 { 091 signalTrigger(); 092 } 093 } 094 095 /** 096 * Notifies the cache monitor that the service shall shut down 097 */ 098 public void notifyShutdown() 099 { 100 if (shutdown.compareAndSet(false, true)) 101 { 102 signalTrigger(); 103 } 104 } 105 106 // Trigger continuation of loop 107 private void signalTrigger() 108 { 109 try 110 { 111 lock.lock(); 112 trigger.signal(); 113 } 114 finally 115 { 116 lock.unlock(); 117 } 118 } 119 120 /** 121 * Clean up all resources before shutdown 122 */ 123 protected abstract void dispose(); 124 125 /** 126 * do actual work 127 */ 128 protected abstract void doWork(); 129 130 /** 131 * Main processing method for the AbstractAuxiliaryCacheMonitor object 132 */ 133 @Override 134 public void run() 135 { 136 do 137 { 138 if ( log.isDebugEnabled() ) 139 { 140 if ( allright.get() ) 141 { 142 log.debug( "ERROR DRIVEN MODE: allright = true, cache monitor will wait for an error." ); 143 } 144 else 145 { 146 log.debug( "ERROR DRIVEN MODE: allright = false cache monitor running." ); 147 } 148 } 149 150 if ( allright.get() ) 151 { 152 // Failure driven mode. 153 try 154 { 155 lock.lock(); 156 trigger.await(); 157 // wake up only if there is an error. 158 } 159 catch ( InterruptedException ignore ) 160 { 161 //no op, this is expected 162 } 163 finally 164 { 165 lock.unlock(); 166 } 167 } 168 169 // check for requested shutdown 170 if ( shutdown.get() ) 171 { 172 log.info( "Shutting down cache monitor" ); 173 dispose(); 174 return; 175 } 176 177 // The "allright" flag must be false here. 178 // Simply presume we can fix all the errors until proven otherwise. 179 allright.set(true); 180 181 if ( log.isDebugEnabled() ) 182 { 183 log.debug( "Cache monitor running." ); 184 } 185 186 doWork(); 187 188 try 189 { 190 // don't want to sleep after waking from an error 191 // run immediately and sleep here. 192 if ( log.isDebugEnabled() ) 193 { 194 log.debug( "Cache monitor sleeping for " + idlePeriod + " between runs." ); 195 } 196 197 Thread.sleep( idlePeriod ); 198 } 199 catch ( InterruptedException ex ) 200 { 201 // ignore; 202 } 203 } 204 while ( true ); 205 } 206}