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 */ 017package org.apache.commons.io; 018 019import java.io.File; 020import java.lang.ref.PhantomReference; 021import java.lang.ref.ReferenceQueue; 022import java.util.ArrayList; 023import java.util.Collection; 024import java.util.Collections; 025import java.util.HashSet; 026import java.util.List; 027 028/** 029 * Keeps track of files awaiting deletion, and deletes them when an associated 030 * marker object is reclaimed by the garbage collector. 031 * <p> 032 * This utility creates a background thread to handle file deletion. 033 * Each file to be deleted is registered with a handler object. 034 * When the handler object is garbage collected, the file is deleted. 035 * <p> 036 * In an environment with multiple class loaders (a servlet container, for 037 * example), you should consider stopping the background thread if it is no 038 * longer needed. This is done by invoking the method 039 * {@link #exitWhenFinished}, typically in 040 * {@code javax.servlet.ServletContextListener.contextDestroyed(javax.servlet.ServletContextEvent)} or similar. 041 * 042 */ 043public class FileCleaningTracker { 044 045 // Note: fields are package protected to allow use by test cases 046 047 /** 048 * Queue of <code>Tracker</code> instances being watched. 049 */ 050 ReferenceQueue<Object> q = new ReferenceQueue<>(); 051 /** 052 * Collection of <code>Tracker</code> instances in existence. 053 */ 054 final Collection<Tracker> trackers = Collections.synchronizedSet(new HashSet<Tracker>()); // synchronized 055 /** 056 * Collection of File paths that failed to delete. 057 */ 058 final List<String> deleteFailures = Collections.synchronizedList(new ArrayList<String>()); 059 /** 060 * Whether to terminate the thread when the tracking is complete. 061 */ 062 volatile boolean exitWhenFinished = false; 063 /** 064 * The thread that will clean up registered files. 065 */ 066 Thread reaper; 067 068 //----------------------------------------------------------------------- 069 /** 070 * Track the specified file, using the provided marker, deleting the file 071 * when the marker instance is garbage collected. 072 * The {@link FileDeleteStrategy#NORMAL normal} deletion strategy will be used. 073 * 074 * @param file the file to be tracked, not null 075 * @param marker the marker object used to track the file, not null 076 * @throws NullPointerException if the file is null 077 */ 078 public void track(final File file, final Object marker) { 079 track(file, marker, null); 080 } 081 082 /** 083 * Track the specified file, using the provided marker, deleting the file 084 * when the marker instance is garbage collected. 085 * The specified deletion strategy is used. 086 * 087 * @param file the file to be tracked, not null 088 * @param marker the marker object used to track the file, not null 089 * @param deleteStrategy the strategy to delete the file, null means normal 090 * @throws NullPointerException if the file is null 091 */ 092 public void track(final File file, final Object marker, final FileDeleteStrategy deleteStrategy) { 093 if (file == null) { 094 throw new NullPointerException("The file must not be null"); 095 } 096 addTracker(file.getPath(), marker, deleteStrategy); 097 } 098 099 /** 100 * Track the specified file, using the provided marker, deleting the file 101 * when the marker instance is garbage collected. 102 * The {@link FileDeleteStrategy#NORMAL normal} deletion strategy will be used. 103 * 104 * @param path the full path to the file to be tracked, not null 105 * @param marker the marker object used to track the file, not null 106 * @throws NullPointerException if the path is null 107 */ 108 public void track(final String path, final Object marker) { 109 track(path, marker, null); 110 } 111 112 /** 113 * Track the specified file, using the provided marker, deleting the file 114 * when the marker instance is garbage collected. 115 * The specified deletion strategy is used. 116 * 117 * @param path the full path to the file to be tracked, not null 118 * @param marker the marker object used to track the file, not null 119 * @param deleteStrategy the strategy to delete the file, null means normal 120 * @throws NullPointerException if the path is null 121 */ 122 public void track(final String path, final Object marker, final FileDeleteStrategy deleteStrategy) { 123 if (path == null) { 124 throw new NullPointerException("The path must not be null"); 125 } 126 addTracker(path, marker, deleteStrategy); 127 } 128 129 /** 130 * Adds a tracker to the list of trackers. 131 * 132 * @param path the full path to the file to be tracked, not null 133 * @param marker the marker object used to track the file, not null 134 * @param deleteStrategy the strategy to delete the file, null means normal 135 */ 136 private synchronized void addTracker(final String path, final Object marker, final FileDeleteStrategy 137 deleteStrategy) { 138 // synchronized block protects reaper 139 if (exitWhenFinished) { 140 throw new IllegalStateException("No new trackers can be added once exitWhenFinished() is called"); 141 } 142 if (reaper == null) { 143 reaper = new Reaper(); 144 reaper.start(); 145 } 146 trackers.add(new Tracker(path, deleteStrategy, marker, q)); 147 } 148 149 //----------------------------------------------------------------------- 150 /** 151 * Retrieve the number of files currently being tracked, and therefore 152 * awaiting deletion. 153 * 154 * @return the number of files being tracked 155 */ 156 public int getTrackCount() { 157 return trackers.size(); 158 } 159 160 /** 161 * Return the file paths that failed to delete. 162 * 163 * @return the file paths that failed to delete 164 * @since 2.0 165 */ 166 public List<String> getDeleteFailures() { 167 return deleteFailures; 168 } 169 170 /** 171 * Call this method to cause the file cleaner thread to terminate when 172 * there are no more objects being tracked for deletion. 173 * <p> 174 * In a simple environment, you don't need this method as the file cleaner 175 * thread will simply exit when the JVM exits. In a more complex environment, 176 * with multiple class loaders (such as an application server), you should be 177 * aware that the file cleaner thread will continue running even if the class 178 * loader it was started from terminates. This can constitute a memory leak. 179 * <p> 180 * For example, suppose that you have developed a web application, which 181 * contains the commons-io jar file in your WEB-INF/lib directory. In other 182 * words, the FileCleaner class is loaded through the class loader of your 183 * web application. If the web application is terminated, but the servlet 184 * container is still running, then the file cleaner thread will still exist, 185 * posing a memory leak. 186 * <p> 187 * This method allows the thread to be terminated. Simply call this method 188 * in the resource cleanup code, such as 189 * {@code javax.servlet.ServletContextListener.contextDestroyed(javax.servlet.ServletContextEvent)}. 190 * Once called, no new objects can be tracked by the file cleaner. 191 */ 192 public synchronized void exitWhenFinished() { 193 // synchronized block protects reaper 194 exitWhenFinished = true; 195 if (reaper != null) { 196 synchronized (reaper) { 197 reaper.interrupt(); 198 } 199 } 200 } 201 202 //----------------------------------------------------------------------- 203 /** 204 * The reaper thread. 205 */ 206 private final class Reaper extends Thread { 207 /** Construct a new Reaper */ 208 Reaper() { 209 super("File Reaper"); 210 setPriority(Thread.MAX_PRIORITY); 211 setDaemon(true); 212 } 213 214 /** 215 * Run the reaper thread that will delete files as their associated 216 * marker objects are reclaimed by the garbage collector. 217 */ 218 @Override 219 public void run() { 220 // thread exits when exitWhenFinished is true and there are no more tracked objects 221 while (exitWhenFinished == false || trackers.size() > 0) { 222 try { 223 // Wait for a tracker to remove. 224 final Tracker tracker = (Tracker) q.remove(); // cannot return null 225 trackers.remove(tracker); 226 if (!tracker.delete()) { 227 deleteFailures.add(tracker.getPath()); 228 } 229 tracker.clear(); 230 } catch (final InterruptedException e) { 231 continue; 232 } 233 } 234 } 235 } 236 237 //----------------------------------------------------------------------- 238 /** 239 * Inner class which acts as the reference for a file pending deletion. 240 */ 241 private static final class Tracker extends PhantomReference<Object> { 242 243 /** 244 * The full path to the file being tracked. 245 */ 246 private final String path; 247 /** 248 * The strategy for deleting files. 249 */ 250 private final FileDeleteStrategy deleteStrategy; 251 252 /** 253 * Constructs an instance of this class from the supplied parameters. 254 * 255 * @param path the full path to the file to be tracked, not null 256 * @param deleteStrategy the strategy to delete the file, null means normal 257 * @param marker the marker object used to track the file, not null 258 * @param queue the queue on to which the tracker will be pushed, not null 259 */ 260 Tracker(final String path, final FileDeleteStrategy deleteStrategy, final Object marker, 261 final ReferenceQueue<? super Object> queue) { 262 super(marker, queue); 263 this.path = path; 264 this.deleteStrategy = deleteStrategy == null ? FileDeleteStrategy.NORMAL : deleteStrategy; 265 } 266 267 /** 268 * Return the path. 269 * 270 * @return the path 271 */ 272 public String getPath() { 273 return path; 274 } 275 276 /** 277 * Deletes the file associated with this tracker instance. 278 * 279 * @return {@code true} if the file was deleted successfully; 280 * {@code false} otherwise. 281 */ 282 public boolean delete() { 283 return deleteStrategy.deleteQuietly(new File(path)); 284 } 285 } 286 287}