Threads.java

/*
 * Copyright (c) 2004-2013 Tada AB and other contributors, as listed below.
 *
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the The BSD 3-Clause License
 * which accompanies this distribution, and is available at
 * http://opensource.org/licenses/BSD-3-Clause
 *
 * Contributors:
 *   Tada AB
 */
package org.postgresql.pljava.example;

import java.util.logging.Level;
import java.util.logging.Logger;

/**
 * This class contains thread related methods.
 * 
 * @author Thomas Hallgren
 */
public class Threads {
	static class Locker extends Thread {
		private final String m_name;
		private final String m_first;
		private final String m_second;

		Locker(String name, String first, String second) {
			m_name = name;
			m_first = first;
			m_second = second;
		}

		@Override
		public void run() {
			Logger log = Logger.getAnonymousLogger();
			try {
				log.info("Thread " + m_name + " wants " + m_first);
				synchronized (m_first) {
					log.info("Thread " + m_name + " got " + m_first);
					Thread.sleep(100);
					log.info("Thread " + m_name + " wants " + m_second);
					synchronized (m_second) {
						log.info("Thread " + m_name + " got " + m_second);
					}
				}
			} catch (Exception e) {
				log.log(Level.INFO, "Thread " + m_name + " got exception: ", e);
			}
		}
	}

	private final static String s_lockOne = "lock number one";

	private final static String s_lockTwo = "lock number two";

	public static void forceDeadlock() {
		// Cause a deadlock.
		//
		Locker x = new Locker("x", s_lockOne, s_lockTwo);
		Locker y = new Locker("y", s_lockTwo, s_lockOne);
		x.start();
		y.start();

		// Sleep for a while. The logger will fail if trying to access the
		// backend when it is not in a Java call.
		//
		try {
			Logger.getAnonymousLogger().log(Level.INFO,
					"Main thread sleeps a while");
			Thread.sleep(1000);
		} catch (Exception e) {
			Logger.getAnonymousLogger().log(Level.INFO,
					"Main thread interrupted while sleeping: ", e);
		}
	}
}