001/**
002The contents of this file are subject to the Mozilla Public License Version 1.1 
003(the "License"); you may not use this file except in compliance with the License. 
004You may obtain a copy of the License at http://www.mozilla.org/MPL/ 
005Software distributed under the License is distributed on an "AS IS" basis, 
006WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License for the 
007specific language governing rights and limitations under the License. 
008
009The Original Code is "ManagedRunnable.java".  Description: 
010"Base class for a unified management of threads with a defined lifecycle." 
011
012The Initial Developer of the Original Code is University Health Network. Copyright (C) 
0132001.  All Rights Reserved. 
014
015Contributor(s): ______________________________________. 
016
017Alternatively, the contents of this file may be used under the terms of the 
018GNU General Public License (the  "GPL"), in which case the provisions of the GPL are 
019applicable instead of those above.  If you wish to allow use of your version of this 
020file only under the terms of the GPL and not to allow others to use your version 
021of this file under the MPL, indicate your decision by deleting  the provisions above 
022and replace  them with the notice and other provisions required by the GPL License.  
023If you do not delete the provisions above, a recipient may use your version of 
024this file under either the MPL or the GPL. 
025 */
026package ca.uhn.hl7v2.concurrent;
027
028import java.util.concurrent.ExecutionException;
029import java.util.concurrent.ExecutorService;
030import java.util.concurrent.Future;
031import java.util.concurrent.TimeUnit;
032import java.util.concurrent.TimeoutException;
033
034import org.slf4j.Logger;
035import org.slf4j.LoggerFactory;
036
037/**
038 * Base class for a unified management of threads with a defined lifecycle. It
039 * uses a {@link #keepRunning} flag to regularly terminate a thread. Classes
040 * implementing this class must implement {@link #handle()} to do the main
041 * processing. {@link #afterStartup()} and {@link #afterTermination()} can be
042 * overridden to acquire and release resources required for processing.
043 */
044public abstract class Service implements Runnable {
045
046        private static final Logger log = LoggerFactory
047                        .getLogger(Service.class);
048        private volatile boolean keepRunning;
049        private long shutdownTimeout = 3000L;
050        private final String name;
051        private final ExecutorService executorService;
052        private Future<?> thread;
053        private Throwable serviceExitedWithException;
054
055        public Service(String name, ExecutorService executorService) {
056                super();
057                this.name = name;
058                this.executorService = executorService;
059        }
060
061        /**
062         * @return Returns <code>true</code> if the server has been started, and has
063         *         not yet been stopped.
064         */
065        public boolean isRunning() {
066                return keepRunning;
067        }
068
069        public ExecutorService getExecutorService() {
070                return executorService;
071        }
072
073        /**
074         * Sets the time in milliseconds how long {@link #stopAndWait()} should wait
075         * for the thread to terminate. Defaults to 3000ms.
076         * 
077         * @param shutdownTimeout
078         */
079        public void setShutdownTimeout(long shutdownTimeout) {
080                this.shutdownTimeout = shutdownTimeout;
081        }
082
083        /**
084         * Starts the server listening for connections in a new thread. This
085         * continues until <code>stop()</code> is called.
086         */
087        public void start() {
088                log.debug("Starting service {}", name);
089                keepRunning = true;
090                thread = getExecutorService().submit(this);
091        }
092
093        /**
094         * Prepare any resources before entering the main thread.
095         * 
096         * @throws RuntimeException
097         *             if resources could not acquired. In this case, the thread
098         *             will shutdown. Note that {@link #afterTermination()} is
099         *             called before.
100         */
101        protected void afterStartup() {
102        }
103
104        /**
105         * The main task of the thread, called in a loop as long as
106         * {@link #isRunning()} returns true. Overridden methods are responsible for
107         * yielding or pausing the thread when it's idle. The method must also not
108         * block indefinitely so that a call to {@link #stop()} is able to
109         * gracefully terminate the thread.
110         * 
111         * @throws Throwable
112         *             any exception thrown will terminate the thread.
113         */
114        protected abstract void handle();
115
116        /**
117         * Advises the thread to leave its main loop. {@link #beforeTermination()} is
118         * called before this method returns. {@link #afterTermination()} is
119         * called after the thread has left its main loop.
120         */
121        public void stop() {
122                if (isRunning()) {
123                        prepareTermination();
124                }
125        }
126
127        public void waitForTermination() {
128                if (!thread.isDone())
129                        try {
130                                thread.get(shutdownTimeout, TimeUnit.MILLISECONDS);
131                        } catch (ExecutionException ee) {
132                        } catch (TimeoutException te) {
133                                log.warn(
134                                                "Thread did not stop after {} milliseconds. Now cancelling.",
135                                                shutdownTimeout);
136                                thread.cancel(true);
137                        } catch (InterruptedException e) {
138                        }
139        }
140
141        /**
142         * Stops the thread by leaving its main loop. {@link #afterTermination()} is
143         * called before the thread is terminated. The method waits until the thread
144         * has stopped.
145         * 
146         * @throws Exception
147         *             if the thread has not finished within shutdownTimeout
148         */
149        public final void stopAndWait() {
150                stop();
151                waitForTermination();
152        }
153
154        /**
155         * Clean up any resources initialized in {@link #afterStartup()}.
156         */
157        protected void afterTermination() {
158        };
159        
160        /**
161         * Prepare thread to leave its main loop. By default sets {@link #keepRunning}
162         * to false, but some implementations may need to do additional stuff.
163         */
164        protected void prepareTermination() {
165                log.debug("Prepare to stop thread {}", name);
166                keepRunning = false;
167        };      
168
169        /**
170         * Runs the thread.
171         * 
172         * @see java.lang.Runnable#run()
173         */
174        public final void run() {
175                try {
176                        afterStartup();
177                        log.debug("Thread {} entering main loop", name);
178                        while (isRunning()) {
179                                handle();
180                        }
181                        log.debug("Thread {} leaving main loop", name);
182                } catch (RuntimeException t) {
183                        serviceExitedWithException = t.getCause();
184                        log.warn("Thread exiting main loop due to exception:", t.getCause());
185                } catch (Throwable t) {
186                        serviceExitedWithException = t;
187                        log.warn("Thread exiting main loop due to exception:", t);
188                } finally {
189                        afterTermination();
190                }
191
192        }
193
194        /**
195         * Provide the exception which caused this service to fail
196         */
197        protected void setServiceExitedWithException(Throwable theThreadExitedWithException) {
198                serviceExitedWithException = theThreadExitedWithException;
199        }
200
201
202        /**
203         * If this service exited with an exception, ths method returns that exception. This is useful for
204         * detecting if the service failed unexpectedly
205         */
206        public Throwable getServiceExitedWithException() {
207                return serviceExitedWithException;
208        }
209
210}