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org.apache.jcs.auxiliary.remote.RemoteCacheMonitor |
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1 | package org.apache.jcs.auxiliary.remote; |
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2 | ||
3 | /* |
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4 | * Licensed to the Apache Software Foundation (ASF) under one |
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5 | * or more contributor license agreements. See the NOTICE file |
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6 | * distributed with this work for additional information |
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7 | * regarding copyright ownership. The ASF licenses this file |
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8 | * to you under the Apache License, Version 2.0 (the |
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9 | * "License"); you may not use this file except in compliance |
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10 | * with the License. You may obtain a copy of the License at |
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11 | * |
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12 | * http://www.apache.org/licenses/LICENSE-2.0 |
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13 | * |
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14 | * Unless required by applicable law or agreed to in writing, |
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15 | * software distributed under the License is distributed on an |
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16 | * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY |
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17 | * KIND, either express or implied. See the License for the |
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18 | * specific language governing permissions and limitations |
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19 | * under the License. |
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20 | */ |
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21 | ||
22 | import java.util.Iterator; |
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23 | ||
24 | import org.apache.jcs.engine.CacheConstants; |
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25 | ||
26 | import org.apache.commons.logging.Log; |
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27 | import org.apache.commons.logging.LogFactory; |
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28 | ||
29 | /** |
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30 | * Used to monitor and repair any failed connection for the remote cache |
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31 | * service. By default the monitor operates in a failure driven mode. That is, |
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32 | * it goes into a wait state until there is an error. TODO consider moving this |
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33 | * into an active monitoring mode. Upon the notification of a connection error, |
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34 | * the monitor changes to operate in a time driven mode. That is, it attempts to |
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35 | * recover the connections on a periodic basis. When all failed connections are |
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36 | * restored, it changes back to the failure driven mode. |
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37 | * |
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38 | */ |
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39 | public class RemoteCacheMonitor |
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40 | implements Runnable |
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41 | { |
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42 | /** The logger */ |
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43 | 14 | private final static Log log = LogFactory.getLog( RemoteCacheMonitor.class ); |
44 | ||
45 | /** The remote cache that we are monitoring */ |
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46 | private static RemoteCacheMonitor instance; |
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47 | ||
48 | /** Time between checks */ |
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49 | 7 | private static long idlePeriod = 30 * 1000; |
50 | ||
51 | // minimum 30 seconds. |
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52 | //private static long idlePeriod = 3*1000; // for debugging. |
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53 | ||
54 | /** Must make sure RemoteCacheMonitor is started before any remote error can |
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55 | * be detected! */ |
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56 | 7 | private boolean alright = true; |
57 | ||
58 | /** Time driven mode */ |
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59 | final static int TIME = 0; |
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60 | ||
61 | /** Error driven mode -- only check on health if there is an error */ |
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62 | final static int ERROR = 1; |
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63 | ||
64 | /** The mode to use */ |
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65 | 7 | static int mode = ERROR; |
66 | ||
67 | /** |
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68 | * Configures the idle period between repairs. |
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69 | * |
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70 | * @param idlePeriod |
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71 | * The new idlePeriod value |
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72 | */ |
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73 | public static void setIdlePeriod( long idlePeriod ) |
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74 | { |
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75 | 0 | if ( idlePeriod > RemoteCacheMonitor.idlePeriod ) |
76 | { |
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77 | 0 | RemoteCacheMonitor.idlePeriod = idlePeriod; |
78 | } |
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79 | 0 | } |
80 | ||
81 | /** Constructor for the RemoteCacheMonitor object */ |
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82 | private RemoteCacheMonitor() |
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83 | { |
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84 | 7 | super(); |
85 | 7 | } |
86 | ||
87 | /** |
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88 | * Returns the singleton instance; |
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89 | * |
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90 | * @return The instance value |
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91 | */ |
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92 | static RemoteCacheMonitor getInstance() |
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93 | { |
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94 | 7 | synchronized ( RemoteCacheMonitor.class ) |
95 | { |
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96 | 7 | if ( instance == null ) |
97 | { |
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98 | 7 | return instance = new RemoteCacheMonitor(); |
99 | } |
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100 | 0 | } |
101 | 0 | return instance; |
102 | } |
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103 | ||
104 | /** |
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105 | * Notifies the cache monitor that an error occurred, and kicks off the |
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106 | * error recovery process. |
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107 | */ |
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108 | public void notifyError() |
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109 | { |
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110 | 0 | log.debug( "Notified of an error." ); |
111 | 0 | bad(); |
112 | 0 | synchronized ( this ) |
113 | { |
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114 | 0 | notify(); |
115 | 0 | } |
116 | 0 | } |
117 | ||
118 | // Run forever. |
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119 | ||
120 | // Avoid the use of any synchronization in the process of monitoring for |
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121 | // performance reason. |
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122 | // If exception is thrown owing to synchronization, |
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123 | // just skip the monitoring until the next round. |
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124 | /** Main processing method for the RemoteCacheMonitor object */ |
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125 | public void run() |
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126 | { |
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127 | 7 | log.debug( "Monitoring daemon started" ); |
128 | do |
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129 | { |
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130 | 7 | if ( mode == ERROR ) |
131 | { |
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132 | 7 | synchronized ( this ) |
133 | { |
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134 | 7 | if ( alright ) |
135 | { |
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136 | // make this configurable, comment out wait to enter |
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137 | // time driven mode |
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138 | // Failure driven mode. |
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139 | try |
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140 | { |
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141 | 7 | if ( log.isDebugEnabled() ) |
142 | { |
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143 | 0 | log.debug( "FAILURE DRIVEN MODE: cache monitor waiting for error" ); |
144 | } |
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145 | 7 | wait(); |
146 | // wake up only if there is an error. |
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147 | } |
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148 | 0 | catch ( InterruptedException ignore ) |
149 | { |
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150 | // swallow |
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151 | 0 | } |
152 | } |
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153 | 0 | } |
154 | 0 | } |
155 | else |
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156 | { |
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157 | 0 | if ( log.isDebugEnabled() ) |
158 | { |
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159 | 0 | log.debug( "TIME DRIVEN MODE: cache monitor sleeping for " + idlePeriod ); |
160 | } |
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161 | // Time driven mode: sleep between each round of recovery |
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162 | // attempt. |
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163 | // will need to test not just check status |
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164 | } |
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165 | ||
166 | try |
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167 | { |
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168 | 0 | Thread.sleep( idlePeriod ); |
169 | } |
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170 | 0 | catch ( InterruptedException ex ) |
171 | { |
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172 | // ignore; |
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173 | 0 | } |
174 | ||
175 | // The "alright" flag must be false here. |
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176 | // Simply presume we can fix all the errors until proven otherwise. |
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177 | 0 | synchronized ( this ) |
178 | { |
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179 | 0 | alright = true; |
180 | 0 | } |
181 | //p("cache monitor running."); |
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182 | // Monitor each RemoteCacheManager instance one after the other. |
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183 | // Each RemoteCacheManager corresponds to one remote connection. |
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184 | 0 | for ( Iterator itr = RemoteCacheManager.instances.values().iterator(); itr.hasNext(); ) |
185 | { |
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186 | 0 | RemoteCacheManager mgr = (RemoteCacheManager) itr.next(); |
187 | try |
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188 | { |
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189 | // If any cache is in error, it strongly suggests all caches |
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190 | // managed by the |
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191 | // same RmicCacheManager instance are in error. So we fix |
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192 | // them once and for all. |
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193 | 0 | for ( Iterator itr2 = mgr.caches.values().iterator(); itr2.hasNext(); ) |
194 | { |
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195 | 0 | if ( itr2.hasNext() ) |
196 | { |
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197 | 0 | RemoteCacheNoWait c = (RemoteCacheNoWait) itr2.next(); |
198 | 0 | if ( c.getStatus() == CacheConstants.STATUS_ERROR ) |
199 | { |
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200 | 0 | RemoteCacheRestore repairer = new RemoteCacheRestore( mgr ); |
201 | // If we can't fix them, just skip and re-try in |
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202 | // the next round. |
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203 | 0 | if ( repairer.canFix() ) |
204 | { |
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205 | 0 | repairer.fix(); |
206 | 0 | } |
207 | else |
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208 | { |
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209 | 0 | bad(); |
210 | } |
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211 | 0 | break; |
212 | } |
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213 | 0 | } |
214 | } |
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215 | } |
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216 | 0 | catch ( Exception ex ) |
217 | { |
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218 | 0 | bad(); |
219 | // Problem encountered in fixing the caches managed by a |
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220 | // RemoteCacheManager instance. |
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221 | // Soldier on to the next RemoteCacheManager instance. |
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222 | 0 | log.error( ex ); |
223 | 0 | } |
224 | 0 | } |
225 | } |
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226 | 0 | while ( true ); |
227 | } |
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228 | ||
229 | /** Sets the "alright" flag to false in a critial section. */ |
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230 | private synchronized void bad() |
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231 | { |
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232 | 0 | alright = false; |
233 | 0 | } |
234 | } |
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