1 /*
2  * Licensed to the Apache Software Foundation (ASF) under one or more
3  * contributor license agreements.  See the NOTICE file distributed with
4  * this work for additional information regarding copyright ownership.
5  * The ASF licenses this file to You under the Apache License, Version 2.0
6  * (the "License"); you may not use this file except in compliance with
7  * the License.  You may obtain a copy of the License at
8  *
9  *      http://www.apache.org/licenses/LICENSE-2.0
10  *
11  * Unless required by applicable law or agreed to in writing, software
12  * distributed under the License is distributed on an "AS IS" BASIS,
13  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14  * See the License for the specific language governing permissions and
15  * limitations under the License.
16  */
17 package org.apache.commons.io;
18 
19 import java.io.File;
20 import java.lang.ref.PhantomReference;
21 import java.lang.ref.ReferenceQueue;
22 import java.util.Collection;
23 import java.util.Vector;
24 
25 /**
26  * Keeps track of files awaiting deletion, and deletes them when an associated
27  * marker object is reclaimed by the garbage collector.
28  * <p>
29  * This utility creates a background thread to handle file deletion.
30  * Each file to be deleted is registered with a handler object.
31  * When the handler object is garbage collected, the file is deleted.
32  * <p>
33  * In an environment with multiple class loaders (a servlet container, for
34  * example), you should consider stopping the background thread if it is no
35  * longer needed. This is done by invoking the method
36  * {@link #exitWhenFinished}, typically in
37  * {@link javax.servlet.ServletContextListener#contextDestroyed} or similar.
38  *
39  * @author Noel Bergman
40  * @author Martin Cooper
41  * @version $Id: FileCleaner.java 490987 2006-12-29 12:11:48Z scolebourne $
42  */
43 public class FileCleaningTracker {
44     /**
45      * Queue of <code>Tracker</code> instances being watched.
46      */
47     ReferenceQueue<Object> /* Tracker */ q = new ReferenceQueue<Object>();
48     /**
49      * Collection of <code>Tracker</code> instances in existence.
50      */
51     final Collection<Tracker> /* Tracker */ trackers = new Vector<Tracker>();  // synchronized
52     /**
53      * Whether to terminate the thread when the tracking is complete.
54      */
55     volatile boolean exitWhenFinished = false;
56     /**
57      * The thread that will clean up registered files.
58      */
59     Thread reaper;
60 
61     //-----------------------------------------------------------------------
62     /**
63      * Track the specified file, using the provided marker, deleting the file
64      * when the marker instance is garbage collected.
65      * The {@link FileDeleteStrategy#NORMAL normal} deletion strategy will be used.
66      *
67      * @param file  the file to be tracked, not null
68      * @param marker  the marker object used to track the file, not null
69      * @throws NullPointerException if the file is null
70      */
track(File file, Object marker)71     public void track(File file, Object marker) {
72         track(file, marker, (FileDeleteStrategy) null);
73     }
74 
75     /**
76      * Track the specified file, using the provided marker, deleting the file
77      * when the marker instance is garbage collected.
78      * The speified deletion strategy is used.
79      *
80      * @param file  the file to be tracked, not null
81      * @param marker  the marker object used to track the file, not null
82      * @param deleteStrategy  the strategy to delete the file, null means normal
83      * @throws NullPointerException if the file is null
84      */
track(File file, Object marker, FileDeleteStrategy deleteStrategy)85     public void track(File file, Object marker, FileDeleteStrategy deleteStrategy) {
86         if (file == null) {
87             throw new NullPointerException("The file must not be null");
88         }
89         addTracker(file.getPath(), marker, deleteStrategy);
90     }
91 
92     /**
93      * Track the specified file, using the provided marker, deleting the file
94      * when the marker instance is garbage collected.
95      * The {@link FileDeleteStrategy#NORMAL normal} deletion strategy will be used.
96      *
97      * @param path  the full path to the file to be tracked, not null
98      * @param marker  the marker object used to track the file, not null
99      * @throws NullPointerException if the path is null
100      */
track(String path, Object marker)101     public void track(String path, Object marker) {
102         track(path, marker, (FileDeleteStrategy) null);
103     }
104 
105     /**
106      * Track the specified file, using the provided marker, deleting the file
107      * when the marker instance is garbage collected.
108      * The speified deletion strategy is used.
109      *
110      * @param path  the full path to the file to be tracked, not null
111      * @param marker  the marker object used to track the file, not null
112      * @param deleteStrategy  the strategy to delete the file, null means normal
113      * @throws NullPointerException if the path is null
114      */
track(String path, Object marker, FileDeleteStrategy deleteStrategy)115     public void track(String path, Object marker, FileDeleteStrategy deleteStrategy) {
116         if (path == null) {
117             throw new NullPointerException("The path must not be null");
118         }
119         addTracker(path, marker, deleteStrategy);
120     }
121 
122     /**
123      * Adds a tracker to the list of trackers.
124      *
125      * @param path  the full path to the file to be tracked, not null
126      * @param marker  the marker object used to track the file, not null
127      * @param deleteStrategy  the strategy to delete the file, null means normal
128      */
addTracker(String path, Object marker, FileDeleteStrategy deleteStrategy)129     private synchronized void addTracker(String path, Object marker, FileDeleteStrategy deleteStrategy) {
130         // synchronized block protects reaper
131         if (exitWhenFinished) {
132             throw new IllegalStateException("No new trackers can be added once exitWhenFinished() is called");
133         }
134         if (reaper == null) {
135             reaper = new Reaper();
136             reaper.start();
137         }
138         trackers.add(new Tracker(path, deleteStrategy, marker, q));
139     }
140 
141     //-----------------------------------------------------------------------
142     /**
143      * Retrieve the number of files currently being tracked, and therefore
144      * awaiting deletion.
145      *
146      * @return the number of files being tracked
147      */
getTrackCount()148     public int getTrackCount() {
149         return trackers.size();
150     }
151 
152     /**
153      * Call this method to cause the file cleaner thread to terminate when
154      * there are no more objects being tracked for deletion.
155      * <p>
156      * In a simple environment, you don't need this method as the file cleaner
157      * thread will simply exit when the JVM exits. In a more complex environment,
158      * with multiple class loaders (such as an application server), you should be
159      * aware that the file cleaner thread will continue running even if the class
160      * loader it was started from terminates. This can consitute a memory leak.
161      * <p>
162      * For example, suppose that you have developed a web application, which
163      * contains the commons-io jar file in your WEB-INF/lib directory. In other
164      * words, the FileCleaner class is loaded through the class loader of your
165      * web application. If the web application is terminated, but the servlet
166      * container is still running, then the file cleaner thread will still exist,
167      * posing a memory leak.
168      * <p>
169      * This method allows the thread to be terminated. Simply call this method
170      * in the resource cleanup code, such as {@link javax.servlet.ServletContextListener#contextDestroyed}.
171      * One called, no new objects can be tracked by the file cleaner.
172      */
exitWhenFinished()173     public synchronized void exitWhenFinished() {
174         // synchronized block protects reaper
175         exitWhenFinished = true;
176         if (reaper != null) {
177             synchronized (reaper) {
178                 reaper.interrupt();
179             }
180         }
181     }
182 
183     //-----------------------------------------------------------------------
184     /**
185      * The reaper thread.
186      */
187     private final class Reaper extends Thread {
188         /** Construct a new Reaper */
Reaper()189         Reaper() {
190             super("File Reaper");
191             setPriority(Thread.MAX_PRIORITY);
192             setDaemon(true);
193         }
194 
195         /**
196          * Run the reaper thread that will delete files as their associated
197          * marker objects are reclaimed by the garbage collector.
198          */
199         @Override
run()200         public void run() {
201             // thread exits when exitWhenFinished is true and there are no more tracked objects
202             while (exitWhenFinished == false || trackers.size() > 0) {
203                 Tracker tracker = null;
204                 try {
205                     // Wait for a tracker to remove.
206                     tracker = (Tracker) q.remove();
207                 } catch (Exception e) {
208                     continue;
209                 }
210                 if (tracker != null) {
211                     tracker.delete();
212                     tracker.clear();
213                     trackers.remove(tracker);
214                 }
215             }
216         }
217     }
218 
219     //-----------------------------------------------------------------------
220     /**
221      * Inner class which acts as the reference for a file pending deletion.
222      */
223     private static final class Tracker extends PhantomReference<Object> {
224 
225         /**
226          * The full path to the file being tracked.
227          */
228         private final String path;
229         /**
230          * The strategy for deleting files.
231          */
232         private final FileDeleteStrategy deleteStrategy;
233 
234         /**
235          * Constructs an instance of this class from the supplied parameters.
236          *
237          * @param path  the full path to the file to be tracked, not null
238          * @param deleteStrategy  the strategy to delete the file, null means normal
239          * @param marker  the marker object used to track the file, not null
240          * @param queue  the queue on to which the tracker will be pushed, not null
241          */
Tracker(String path, FileDeleteStrategy deleteStrategy, Object marker, ReferenceQueue<Object> queue)242         Tracker(String path, FileDeleteStrategy deleteStrategy, Object marker, ReferenceQueue<Object> queue) {
243             super(marker, queue);
244             this.path = path;
245             this.deleteStrategy = (deleteStrategy == null ? FileDeleteStrategy.NORMAL : deleteStrategy);
246         }
247 
248         /**
249          * Deletes the file associated with this tracker instance.
250          *
251          * @return <code>true</code> if the file was deleted successfully;
252          *         <code>false</code> otherwise.
253          */
delete()254         public boolean delete() {
255             return deleteStrategy.deleteQuietly(new File(path));
256         }
257     }
258 
259 }
260