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