001 /* 002 * Licensed to the Apache Software Foundation (ASF) under one or more 003 * contributor license agreements. See the NOTICE file distributed with 004 * this work for additional information regarding copyright ownership. 005 * The ASF licenses this file to You under the Apache License, Version 2.0 006 * (the "License"); you may not use this file except in compliance with 007 * the License. You may obtain a copy of the License at 008 * 009 * http://www.apache.org/licenses/LICENSE-2.0 010 * 011 * Unless required by applicable law or agreed to in writing, software 012 * distributed under the License is distributed on an "AS IS" BASIS, 013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 014 * See the License for the specific language governing permissions and 015 * limitations under the License. 016 */ 017 package org.apache.commons.io; 018 019 import java.io.File; 020 import java.lang.ref.PhantomReference; 021 import java.lang.ref.ReferenceQueue; 022 import java.util.Collection; 023 import java.util.Vector; 024 025 /** 026 * Keeps track of files awaiting deletion, and deletes them when an associated 027 * marker object is reclaimed by the garbage collector. 028 * <p> 029 * This utility creates a background thread to handle file deletion. 030 * Each file to be deleted is registered with a handler object. 031 * When the handler object is garbage collected, the file is deleted. 032 * <p> 033 * In an environment with multiple class loaders (a servlet container, for 034 * example), you should consider stopping the background thread if it is no 035 * longer needed. This is done by invoking the method 036 * {@link #exitWhenFinished}, typically in 037 * {@link javax.servlet.ServletContextListener#contextDestroyed} or similar. 038 * 039 * @author Noel Bergman 040 * @author Martin Cooper 041 * @version $Id: FileCleaner.java 490987 2006-12-29 12:11:48Z scolebourne $ 042 */ 043 public class FileCleaningTracker { 044 /** 045 * Queue of <code>Tracker</code> instances being watched. 046 */ 047 ReferenceQueue /* Tracker */ q = new ReferenceQueue(); 048 /** 049 * Collection of <code>Tracker</code> instances in existence. 050 */ 051 final Collection /* Tracker */ trackers = new Vector(); // synchronized 052 /** 053 * Whether to terminate the thread when the tracking is complete. 054 */ 055 volatile boolean exitWhenFinished = false; 056 /** 057 * The thread that will clean up registered files. 058 */ 059 Thread reaper; 060 061 //----------------------------------------------------------------------- 062 /** 063 * Track the specified file, using the provided marker, deleting the file 064 * when the marker instance is garbage collected. 065 * The {@link FileDeleteStrategy#NORMAL normal} deletion strategy will be used. 066 * 067 * @param file the file to be tracked, not null 068 * @param marker the marker object used to track the file, not null 069 * @throws NullPointerException if the file is null 070 */ 071 public void track(File file, Object marker) { 072 track(file, marker, (FileDeleteStrategy) null); 073 } 074 075 /** 076 * Track the specified file, using the provided marker, deleting the file 077 * when the marker instance is garbage collected. 078 * The speified deletion strategy is used. 079 * 080 * @param file the file to be tracked, not null 081 * @param marker the marker object used to track the file, not null 082 * @param deleteStrategy the strategy to delete the file, null means normal 083 * @throws NullPointerException if the file is null 084 */ 085 public void track(File file, Object marker, FileDeleteStrategy deleteStrategy) { 086 if (file == null) { 087 throw new NullPointerException("The file must not be null"); 088 } 089 addTracker(file.getPath(), marker, deleteStrategy); 090 } 091 092 /** 093 * Track the specified file, using the provided marker, deleting the file 094 * when the marker instance is garbage collected. 095 * The {@link FileDeleteStrategy#NORMAL normal} deletion strategy will be used. 096 * 097 * @param path the full path to the file to be tracked, not null 098 * @param marker the marker object used to track the file, not null 099 * @throws NullPointerException if the path is null 100 */ 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 */ 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 */ 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 */ 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 */ 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 */ 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 public void run() { 200 // thread exits when exitWhenFinished is true and there are no more tracked objects 201 while (exitWhenFinished == false || trackers.size() > 0) { 202 Tracker tracker = null; 203 try { 204 // Wait for a tracker to remove. 205 tracker = (Tracker) q.remove(); 206 } catch (Exception e) { 207 continue; 208 } 209 if (tracker != null) { 210 tracker.delete(); 211 tracker.clear(); 212 trackers.remove(tracker); 213 } 214 } 215 } 216 } 217 218 //----------------------------------------------------------------------- 219 /** 220 * Inner class which acts as the reference for a file pending deletion. 221 */ 222 private static final class Tracker extends PhantomReference { 223 224 /** 225 * The full path to the file being tracked. 226 */ 227 private final String path; 228 /** 229 * The strategy for deleting files. 230 */ 231 private final FileDeleteStrategy deleteStrategy; 232 233 /** 234 * Constructs an instance of this class from the supplied parameters. 235 * 236 * @param path the full path to the file to be tracked, not null 237 * @param deleteStrategy the strategy to delete the file, null means normal 238 * @param marker the marker object used to track the file, not null 239 * @param queue the queue on to which the tracker will be pushed, not null 240 */ 241 Tracker(String path, FileDeleteStrategy deleteStrategy, Object marker, ReferenceQueue queue) { 242 super(marker, queue); 243 this.path = path; 244 this.deleteStrategy = (deleteStrategy == null ? FileDeleteStrategy.NORMAL : deleteStrategy); 245 } 246 247 /** 248 * Deletes the file associated with this tracker instance. 249 * 250 * @return <code>true</code> if the file was deleted successfully; 251 * <code>false</code> otherwise. 252 */ 253 public boolean delete() { 254 return deleteStrategy.deleteQuietly(new File(path)); 255 } 256 } 257 258 }