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/*
Copyright (C) 2013 Red Hat, Inc.
This file is part of IcedTea.
IcedTea is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License as published by
the Free Software Foundation, version 2.
IcedTea is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
You should have received a copy of the GNU General Public License
along with IcedTea; see the file COPYING. If not, write to
the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
02110-1301 USA.
Linking this library statically or dynamically with other modules is
making a combined work based on this library. Thus, the terms and
conditions of the GNU General Public License cover the whole
combination.
As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
modules, and to copy and distribute the resulting executable under
terms of your choice, provided that you also meet, for each linked
independent module, the terms and conditions of the license of that
module. An independent module is a module which is not derived from
or based on this library. If you modify this library, you may extend
this exception to your version of the library, but you are not
obligated to do so. If you do not wish to do so, delete this
exception statement from your version.
*/
package net.sourceforge.jnlp.util.lockingfile;
import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.channels.FileChannel;
import java.nio.channels.FileLock;
import java.util.Map;
import java.util.WeakHashMap;
import java.util.concurrent.locks.ReentrantLock;
import net.sourceforge.jnlp.runtime.JNLPRuntime;
/*
* Process & thread locked access to a file. Creates file if it does not already exist.
*/
public class LockedFile {
// The file for access
private RandomAccessFile randomAccessFile;
private FileChannel fileChannel;
private File file;
// A file lock will protect against locks for multiple
// processes, while a thread lock is still needed within a single JVM.
private FileLock processLock = null;
private ReentrantLock threadLock = new ReentrantLock();
private boolean readOnly;
private LockedFile(File file) {
this.file = file;
try {
//just try to create
this.file.createNewFile();
} catch (Exception ex) {
//intentionaly silent
}
if (!this.file.isFile() && file.getParentFile() != null && !file.getParentFile().canWrite()) {
readOnly = true;
} else {
this.readOnly = !file.canWrite();
if (!readOnly && file.getParentFile() != null && !file.getParentFile().canWrite()) {
readOnly = true;
}
}
}
public boolean isReadOnly() {
return readOnly;
}
// Provide shared access to LockedFile's via weak map
static private final Map<File, LockedFile> instanceCache = new WeakHashMap<File, LockedFile>();
/**
* Get a LockedFile for a given File. Ensures that we share the same
* instance for all threads
*
* @param file the file to lock
* @return a LockedFile instance
*/
synchronized public static LockedFile getInstance(File file) {
if (!instanceCache.containsKey(file)) {
instanceCache.put(file, new LockedFile(file));
}
return instanceCache.get(file);
}
/**
* Get the file being locked.
*
* @return the file
*/
public File getFile() {
return file;
}
/**
* Lock access to the file. Lock is reentrant.
*/
public void lock() throws IOException {
if (JNLPRuntime.isWindows()) {
return;
}
// Create if does not already exist, cannot lock non-existing file
if (!isReadOnly()) {
this.file.createNewFile();
}
this.threadLock.lock();
if (this.processLock != null) {
return;
}
if (this.file.exists()) {
this.randomAccessFile = new RandomAccessFile(this.file, isReadOnly() ? "r" : "rws");
this.fileChannel = randomAccessFile.getChannel();
if (!isReadOnly()){
this.processLock = this.fileChannel.lock();
}
}
}
/**
* Unlock access to the file. Lock is reentrant.
*/
public void unlock() throws IOException {
if (JNLPRuntime.isWindows()) {
return;
}
boolean releaseProcessLock = (this.threadLock.getHoldCount() == 1);
try {
if (releaseProcessLock) {
if (this.processLock != null){
this.processLock.release();
}
this.processLock = null;
//necessary for read only file
if (this.randomAccessFile != null){
this.randomAccessFile.close();
}
//necessary for not existing parent direcotry
if (this.fileChannel != null){
this.fileChannel.close();
}
}
} finally {
this.threadLock.unlock();
}
}
}
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