260 lines
10 KiB
Java
260 lines
10 KiB
Java
/*
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership.
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* The ASF licenses this file to You under the Apache License, Version 2.0
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* (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package org.apache.commons.io;
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import java.io.File;
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import java.lang.ref.PhantomReference;
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import java.lang.ref.ReferenceQueue;
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import java.util.Collection;
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import java.util.Vector;
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/**
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* Keeps track of files awaiting deletion, and deletes them when an associated
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* marker object is reclaimed by the garbage collector.
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* <p>
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* This utility creates a background thread to handle file deletion.
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* Each file to be deleted is registered with a handler object.
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* When the handler object is garbage collected, the file is deleted.
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* <p>
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* In an environment with multiple class loaders (a servlet container, for
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* example), you should consider stopping the background thread if it is no
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* longer needed. This is done by invoking the method
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* {@link #exitWhenFinished}, typically in
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* {@link javax.servlet.ServletContextListener#contextDestroyed} or similar.
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*
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* @author Noel Bergman
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* @author Martin Cooper
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* @version $Id: FileCleaner.java 490987 2006-12-29 12:11:48Z scolebourne $
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*/
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public class FileCleaningTracker {
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/**
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* Queue of <code>Tracker</code> instances being watched.
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*/
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ReferenceQueue<Object> /* Tracker */ q = new ReferenceQueue<Object>();
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/**
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* Collection of <code>Tracker</code> instances in existence.
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*/
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final Collection<Tracker> /* Tracker */ trackers = new Vector<Tracker>(); // synchronized
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/**
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* Whether to terminate the thread when the tracking is complete.
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*/
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volatile boolean exitWhenFinished = false;
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/**
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* The thread that will clean up registered files.
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*/
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Thread reaper;
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//-----------------------------------------------------------------------
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/**
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* Track the specified file, using the provided marker, deleting the file
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* when the marker instance is garbage collected.
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* The {@link FileDeleteStrategy#NORMAL normal} deletion strategy will be used.
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*
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* @param file the file to be tracked, not null
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* @param marker the marker object used to track the file, not null
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* @throws NullPointerException if the file is null
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*/
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public void track(File file, Object marker) {
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track(file, marker, (FileDeleteStrategy) null);
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}
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/**
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* Track the specified file, using the provided marker, deleting the file
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* when the marker instance is garbage collected.
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* The speified deletion strategy is used.
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*
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* @param file the file to be tracked, not null
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* @param marker the marker object used to track the file, not null
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* @param deleteStrategy the strategy to delete the file, null means normal
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* @throws NullPointerException if the file is null
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*/
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public void track(File file, Object marker, FileDeleteStrategy deleteStrategy) {
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if (file == null) {
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throw new NullPointerException("The file must not be null");
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}
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addTracker(file.getPath(), marker, deleteStrategy);
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}
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/**
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* Track the specified file, using the provided marker, deleting the file
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* when the marker instance is garbage collected.
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* The {@link FileDeleteStrategy#NORMAL normal} deletion strategy will be used.
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*
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* @param path the full path to the file to be tracked, not null
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* @param marker the marker object used to track the file, not null
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* @throws NullPointerException if the path is null
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*/
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public void track(String path, Object marker) {
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track(path, marker, (FileDeleteStrategy) null);
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}
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/**
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* Track the specified file, using the provided marker, deleting the file
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* when the marker instance is garbage collected.
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* The speified deletion strategy is used.
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*
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* @param path the full path to the file to be tracked, not null
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* @param marker the marker object used to track the file, not null
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* @param deleteStrategy the strategy to delete the file, null means normal
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* @throws NullPointerException if the path is null
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*/
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public void track(String path, Object marker, FileDeleteStrategy deleteStrategy) {
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if (path == null) {
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throw new NullPointerException("The path must not be null");
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}
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addTracker(path, marker, deleteStrategy);
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}
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/**
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* Adds a tracker to the list of trackers.
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*
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* @param path the full path to the file to be tracked, not null
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* @param marker the marker object used to track the file, not null
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* @param deleteStrategy the strategy to delete the file, null means normal
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*/
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private synchronized void addTracker(String path, Object marker, FileDeleteStrategy deleteStrategy) {
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// synchronized block protects reaper
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if (exitWhenFinished) {
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throw new IllegalStateException("No new trackers can be added once exitWhenFinished() is called");
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}
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if (reaper == null) {
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reaper = new Reaper();
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reaper.start();
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}
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trackers.add(new Tracker(path, deleteStrategy, marker, q));
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}
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//-----------------------------------------------------------------------
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/**
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* Retrieve the number of files currently being tracked, and therefore
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* awaiting deletion.
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*
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* @return the number of files being tracked
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*/
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public int getTrackCount() {
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return trackers.size();
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}
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/**
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* Call this method to cause the file cleaner thread to terminate when
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* there are no more objects being tracked for deletion.
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* <p>
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* In a simple environment, you don't need this method as the file cleaner
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* thread will simply exit when the JVM exits. In a more complex environment,
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* with multiple class loaders (such as an application server), you should be
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* aware that the file cleaner thread will continue running even if the class
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* loader it was started from terminates. This can consitute a memory leak.
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* <p>
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* For example, suppose that you have developed a web application, which
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* contains the commons-io jar file in your WEB-INF/lib directory. In other
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* words, the FileCleaner class is loaded through the class loader of your
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* web application. If the web application is terminated, but the servlet
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* container is still running, then the file cleaner thread will still exist,
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* posing a memory leak.
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* <p>
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* This method allows the thread to be terminated. Simply call this method
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* in the resource cleanup code, such as {@link javax.servlet.ServletContextListener#contextDestroyed}.
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* One called, no new objects can be tracked by the file cleaner.
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*/
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public synchronized void exitWhenFinished() {
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// synchronized block protects reaper
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exitWhenFinished = true;
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if (reaper != null) {
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synchronized (reaper) {
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reaper.interrupt();
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}
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}
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}
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//-----------------------------------------------------------------------
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/**
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* The reaper thread.
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*/
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private final class Reaper extends Thread {
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/** Construct a new Reaper */
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Reaper() {
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super("File Reaper");
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setPriority(Thread.MAX_PRIORITY);
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setDaemon(true);
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}
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/**
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* Run the reaper thread that will delete files as their associated
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* marker objects are reclaimed by the garbage collector.
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*/
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@Override
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public void run() {
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// thread exits when exitWhenFinished is true and there are no more tracked objects
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while (exitWhenFinished == false || trackers.size() > 0) {
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Tracker tracker = null;
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try {
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// Wait for a tracker to remove.
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tracker = (Tracker) q.remove();
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} catch (Exception e) {
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continue;
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}
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if (tracker != null) {
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tracker.delete();
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tracker.clear();
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trackers.remove(tracker);
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}
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}
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}
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}
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//-----------------------------------------------------------------------
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/**
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* Inner class which acts as the reference for a file pending deletion.
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*/
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private static final class Tracker extends PhantomReference<Object> {
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/**
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* The full path to the file being tracked.
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*/
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private final String path;
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/**
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* The strategy for deleting files.
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*/
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private final FileDeleteStrategy deleteStrategy;
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/**
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* Constructs an instance of this class from the supplied parameters.
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*
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* @param path the full path to the file to be tracked, not null
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* @param deleteStrategy the strategy to delete the file, null means normal
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* @param marker the marker object used to track the file, not null
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* @param queue the queue on to which the tracker will be pushed, not null
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*/
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Tracker(String path, FileDeleteStrategy deleteStrategy, Object marker, ReferenceQueue<Object> queue) {
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super(marker, queue);
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this.path = path;
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this.deleteStrategy = (deleteStrategy == null ? FileDeleteStrategy.NORMAL : deleteStrategy);
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}
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/**
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* Deletes the file associated with this tracker instance.
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*
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* @return <code>true</code> if the file was deleted successfully;
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* <code>false</code> otherwise.
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*/
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public boolean delete() {
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return deleteStrategy.deleteQuietly(new File(path));
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}
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}
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}
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