Source Code Cross Referenced for InaccurateTimeoutWatchdog.java in  » Web-Mail » james-2.3.1 » org » apache » james » util » watchdog » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » Web Mail » james 2.3.1 » org.apache.james.util.watchdog 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


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,   *
013:         * software distributed under the License is distributed on an  *
014:         * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY       *
015:         * KIND, either express or implied.  See the License for the    *
016:         * specific language governing permissions and limitations      *
017:         * under the License.                                           *
018:         ****************************************************************/package org.apache.james.util.watchdog;
019:
020:        import org.apache.excalibur.thread.ThreadPool;
021:        import org.apache.avalon.framework.activity.Disposable;
022:        import org.apache.avalon.framework.container.ContainerUtil;
023:        import org.apache.avalon.framework.logger.AbstractLogEnabled;
024:
025:        /**
026:         * This class represents an watchdog process that serves to
027:         * monitor a situation and triggers an action after a certain time has
028:         * passed.  This implementation is deliberately inaccurate, trading
029:         * accuracy for minimal impact on reset.  This should be used when
030:         * the time of the Watchdog trigger is not critical, and a high number
031:         * of resets are expected.
032:         *
033:         */
034:        public class InaccurateTimeoutWatchdog extends AbstractLogEnabled
035:                implements  Watchdog, Runnable, Disposable {
036:
037:            /**
038:             * Whether the watchdog is currently checking the trigger condition
039:             */
040:            private volatile boolean isChecking = false;
041:
042:            /**
043:             * Whether the watchdog has been reset since the thread slept.
044:             */
045:            private volatile boolean isReset = false;
046:
047:            /**
048:             * The number of milliseconds until the watchdog times out.
049:             */
050:            private final long timeout;
051:
052:            /**
053:             * The last time the internal timer was reset, as measured in milliseconds since
054:             * January 1, 1970 00:00:00.000 GMT.
055:             */
056:            private volatile long lastReset;
057:
058:            /**
059:             * The WatchdogTarget whose execute() method will be called upon triggering
060:             * of the condition.
061:             */
062:            private WatchdogTarget triggerTarget;
063:
064:            /**
065:             * The thread that runs the watchdog.
066:             */
067:            private Thread watchdogThread;
068:
069:            /**
070:             * The thread pool used to generate InaccurateTimeoutWatchdogs
071:             */
072:            private ThreadPool myThreadPool;
073:
074:            /**
075:             * The sole constructor for the InaccurateTimeoutWatchdog
076:             *
077:             * @param timeout the time (in msec) that it will take the Watchdog to timeout
078:             * @param target the WatchdogTarget to be executed when this Watchdog expires
079:             * @param threadPool the thread pool used to generate threads for this implementation.
080:             */
081:            public InaccurateTimeoutWatchdog(long timeout,
082:                    WatchdogTarget target, ThreadPool threadPool) {
083:                if (target == null) {
084:                    throw new IllegalArgumentException(
085:                            "The WatchdogTarget for this TimeoutWatchdog cannot be null.");
086:                }
087:                if (threadPool == null) {
088:                    throw new IllegalArgumentException(
089:                            "The thread pool for this TimeoutWatchdog cannot be null.");
090:                }
091:                this .timeout = timeout;
092:                triggerTarget = target;
093:                myThreadPool = threadPool;
094:            }
095:
096:            /**
097:             * Start this Watchdog, causing it to begin checking.
098:             */
099:            public void start() {
100:                getLogger().debug("Calling start()");
101:                lastReset = System.currentTimeMillis();
102:                isChecking = true;
103:                synchronized (this ) {
104:                    if (watchdogThread == null) {
105:                        myThreadPool.execute(this );
106:                    }
107:                }
108:            }
109:
110:            /**
111:             * Reset this Watchdog.  Tells the Watchdog thread to reset
112:             * the timer when it next awakens.
113:             */
114:            public void reset() {
115:                if (watchdogThread != null) {
116:                    getLogger().debug(
117:                            "Calling reset() " + watchdogThread.getName());
118:                } else {
119:                    getLogger().debug("Calling reset() for inactive watchdog");
120:                }
121:                isReset = true;
122:            }
123:
124:            /**
125:             * Stop this Watchdog, causing the Watchdog to stop checking the trigger
126:             * condition.  The monitor can be restarted with a call to startWatchdog.
127:             */
128:            public void stop() {
129:                if (watchdogThread != null) {
130:                    getLogger().debug(
131:                            "Calling stop() " + watchdogThread.getName());
132:                } else {
133:                    getLogger().debug("Calling stop() for inactive watchdog");
134:                }
135:                isChecking = false;
136:            }
137:
138:            /**
139:             * Execute the body of the Watchdog, triggering as appropriate.
140:             */
141:            public void run() {
142:
143:                try {
144:                    watchdogThread = Thread.currentThread();
145:
146:                    while ((!(Thread.currentThread().interrupted()))
147:                            && (watchdogThread != null)) {
148:                        try {
149:                            if (!isChecking) {
150:                                if (getLogger().isDebugEnabled()) {
151:                                    getLogger()
152:                                            .debug(
153:                                                    "Watchdog "
154:                                                            + Thread
155:                                                                    .currentThread()
156:                                                                    .getName()
157:                                                            + " is not active - going to exit.");
158:                                }
159:                                synchronized (this ) {
160:                                    if (!isChecking) {
161:                                        watchdogThread = null;
162:                                    }
163:                                    continue;
164:                                }
165:                            } else {
166:                                long currentTime = System.currentTimeMillis();
167:                                if (isReset) {
168:                                    isReset = false;
169:                                    lastReset = currentTime;
170:                                }
171:                                long timeToSleep = lastReset + timeout
172:                                        - currentTime;
173:                                if (watchdogThread != null) {
174:                                    getLogger().debug(
175:                                            "Watchdog "
176:                                                    + watchdogThread.getName()
177:                                                    + " has time to sleep "
178:                                                    + timeToSleep);
179:                                } else {
180:                                    getLogger().debug(
181:                                            "Watchdog has time to sleep "
182:                                                    + timeToSleep);
183:                                }
184:                                if (timeToSleep <= 0) {
185:                                    try {
186:                                        synchronized (this ) {
187:                                            if ((isChecking)
188:                                                    && (triggerTarget != null)) {
189:                                                triggerTarget.execute();
190:                                            }
191:                                            watchdogThread = null;
192:                                        }
193:                                    } catch (Throwable t) {
194:                                        getLogger()
195:                                                .error(
196:                                                        "Encountered error while executing Watchdog target.",
197:                                                        t);
198:                                    }
199:                                    isChecking = false;
200:                                    continue;
201:                                } else {
202:                                    synchronized (this ) {
203:                                        wait(timeToSleep);
204:                                    }
205:                                }
206:                            }
207:                        } catch (InterruptedException ie) {
208:                        }
209:                    }
210:
211:                    synchronized (this ) {
212:                        watchdogThread = null;
213:                    }
214:                } finally {
215:                    // Ensure that the thread is in a non-interrupted state when it gets returned
216:                    // to the pool.
217:                    Thread.currentThread().interrupted();
218:                }
219:                getLogger().debug(
220:                        "Watchdog " + Thread.currentThread().getName()
221:                                + " is exiting run().");
222:            }
223:
224:            /**
225:             * @see org.apache.avalon.framework.activity.Disposable#dispose()
226:             */
227:            public void dispose() {
228:                synchronized (this ) {
229:                    isChecking = false;
230:                    if (watchdogThread != null) {
231:                        getLogger().debug(
232:                                "Calling disposeWatchdog() "
233:                                        + watchdogThread.getName());
234:                    } else {
235:                        getLogger()
236:                                .debug(
237:                                        "Calling disposeWatchdog() for inactive watchdog");
238:                    }
239:                    if (watchdogThread != null) {
240:                        watchdogThread = null;
241:                        notifyAll();
242:                    }
243:                    ContainerUtil.dispose(triggerTarget);
244:                    triggerTarget = null;
245:                }
246:            }
247:        }
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