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