97 lines
2.9 KiB
Java
97 lines
2.9 KiB
Java
// SPDX-FileCopyrightText: 2022 Paul Schaub <vanitasvitae@fsfe.org>
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//
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// SPDX-License-Identifier: Apache-2.0
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package pgp.cert_d;
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import java.io.File;
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import java.io.FileNotFoundException;
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import java.io.IOException;
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import java.io.RandomAccessFile;
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import java.nio.channels.FileLock;
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import java.nio.channels.OverlappingFileLockException;
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public class FileLockingMechanism implements LockingMechanism {
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private final File lockFile;
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private RandomAccessFile randomAccessFile;
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private FileLock fileLock;
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public FileLockingMechanism(File lockFile) {
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this.lockFile = lockFile;
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}
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public static FileLockingMechanism defaultDirectoryFileLock(File baseDirectory) {
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return new FileLockingMechanism(new File(baseDirectory, "writelock"));
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}
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@Override
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public synchronized void lockDirectory() throws IOException, InterruptedException {
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if (randomAccessFile != null) {
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// we own the lock already. Let's wait...
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this.wait();
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}
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try {
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randomAccessFile = new RandomAccessFile(lockFile, "rw");
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} catch (FileNotFoundException e) {
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lockFile.createNewFile();
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randomAccessFile = new RandomAccessFile(lockFile, "rw");
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}
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fileLock = randomAccessFile.getChannel().lock();
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}
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@Override
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public synchronized boolean tryLockDirectory() throws IOException {
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if (randomAccessFile != null) {
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// We already locked the directory for another write operation.
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// We fail, since we have not yet released the lock from the other operation.
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return false;
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}
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try {
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randomAccessFile = new RandomAccessFile(lockFile, "rw");
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} catch (FileNotFoundException e) {
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lockFile.createNewFile();
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randomAccessFile = new RandomAccessFile(lockFile, "rw");
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}
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try {
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fileLock = randomAccessFile.getChannel().tryLock();
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if (fileLock == null) {
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// try-lock failed, file is locked by another process.
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randomAccessFile.close();
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randomAccessFile = null;
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return false;
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}
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} catch (OverlappingFileLockException e) {
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// Some other object is holding the lock.
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randomAccessFile.close();
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randomAccessFile = null;
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return false;
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}
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return true;
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}
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@Override
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public synchronized void releaseDirectory() throws IOException {
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// unlock file
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if (fileLock != null) {
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fileLock.release();
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fileLock = null;
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}
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// close file
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if (randomAccessFile != null) {
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randomAccessFile.close();
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randomAccessFile = null;
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}
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// delete file
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if (lockFile.exists()) {
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lockFile.delete();
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}
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// notify waiters
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this.notify();
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}
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}
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