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AspectJ tools most notably contains the AspectJ compiler (AJC). AJC applies aspects to Java classes during compilation, fully replacing Javac for plain Java classes and also compiling native AspectJ or annotation-based @AspectJ syntax. Furthermore, AJC can weave aspects into existing class files in a post-compile binary weaving step. This library is a superset of AspectJ weaver and hence also of AspectJ runtime.

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/*******************************************************************************
 * Copyright (c) 2004, 2012 IBM Corporation and others.
 *
 * This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.osgi.internal.location;

import java.io.*;

/**
 * Internal class.
 */
public class Locker_JavaIo implements Locker {
	private File lockFile;
	private RandomAccessFile lockRAF;

	public Locker_JavaIo(File lockFile) {
		this.lockFile = lockFile;
	}

	@Override
	public synchronized boolean lock() throws IOException {
		//if the lock file already exists, try to delete,
		//assume failure means another eclipse has it open
		if (lockFile.exists())
			lockFile.delete();
		if (lockFile.exists())
			return false;

		//open the lock file so other instances can't co-exist
		lockRAF = new RandomAccessFile(lockFile, "rw"); //$NON-NLS-1$
		try {
			lockRAF.writeByte(0);
		} catch (IOException e) {
			lockRAF.close();
			lockRAF = null;
			throw e;
		}

		return true;
	}

	@Override
	public synchronized void release() {
		try {
			if (lockRAF != null) {
				lockRAF.close();
				lockRAF = null;
			}
		} catch (IOException e) {
			//don't complain, we're making a best effort to clean up
		}
		if (lockFile != null)
			lockFile.delete();
	}

	@Override
	public synchronized boolean isLocked() throws IOException {
		if (lockRAF != null)
			return true;
		try {
			return !lock();
		} finally {
			release();
		}
	}
}