/*
 * Copyright (c) 2001 Matthew Feldt. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided the copyright notice above is
 * retained.
 *
 * THIS SOFTWARE IS PROVIDED ''AS IS'' AND WITHOUT ANY EXPRESSED OR
 * IMPLIED WARRANTIES.
 */

/**
 * Deadlock.java
 *
 * Java Examples In A Nutshell Copyright (c) 2000 David Flanagan
 * Exercise 4-2:
 * Example 4-3 demonstrates how deadlock acan occur when two threads each
 * attempt to obtain a lock held by the other. Modify the example to create
 * deadlock among three threads, where each thread is trying to acquire a lock
 * held by one of the other threads.
 *
 * @author Matthew Feldt <developer@feldt.com>
 * @version 1.0, 02/15/2001 16:37
 */

package com.feldt.examples.thread;

public class Deadlock {
	public static void main(String[] args) {
		// resource objects to locks on
		final Object resource1 = "resource1";
		final Object resource2 = "resource2";
		final Object resource3 = "resource3";

		// first thread -  it tries to lock resource1 then resource2
		Thread t1 = new Thread() {
			public void run() {
				// lock resource1
				synchronized(resource1) {
					System.out.println("Thread 1: locked resource 1");

					// pause...
					try { Thread.sleep(50); }
					catch (InterruptedException e) {}

					// attempt to lock resource2
					System.out.println("Thread 1: wants resource 2");
					synchronized(resource2) {
						System.out.println("Thread 1: locked resource 2");
					}
				}
			}
		};

		// second thread - it tries to lock resource2 then resource3
		Thread t2 = new Thread() {
			public void run() {
				// lock resource2
				synchronized(resource2) {
					System.out.println("Thread 2: locked resource 2");

					// pause...
					try { Thread.sleep(50); }
					catch (InterruptedException e) {}

					System.out.println("Thread 2: wants resource 3");
					synchronized(resource3) {
						System.out.println("Thread 2: locked resource 3");
					}
				}
			}
		};

		// third thread - it tries to lock resource3 then resource1
		Thread t3 = new Thread() {
			public void run() {
				// lock resource3
				synchronized(resource3) {
					System.out.println("Thread 3: locked resource 3");

					// pause...
					try { Thread.sleep(50); }
					catch (InterruptedException e) {}

					System.out.println("Thread 3: wants resource 1");
					synchronized(resource1) {
						System.out.println("Thread 3: locked resource 1");
					}
				}
			}
		};

		// start all three threads - should deadlock and program will never exit
		t1.start();
		t2.start();
		t3.start();
	}
}