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