Thread Resource Example

package com.j256.resource;

/**
 * Little example of thread resource contention.
 */
public class Person implements Runnable {
    private final int id;
    private final String resourceName;
    private final Resource resource;

    long enjoyCount;

    public static void main(String[] args) {
        Resource resource = new Resource();

        Thread t1 = new Thread(new Person(1, "paper", resource));
        Thread t2 = new Thread(new Person(2, "toy", resource));
        Thread t3 = new Thread(new Person(3, "food", resource));

        t1.start();
        t2.start();
        t3.start();
    }

    public Person(int id, String resourceName, Resource resource) {
        this.id = id;
        this.resourceName = resourceName;
        this.resource = resource;
    }

    public void enjoys() {
        try {
            Thread.sleep(1);
            enjoyCount++;
            if (enjoyCount % 1000 == 0) {
                System.out.println("Person " + id + " enjoyed " + enjoyCount);
            }
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
            return;
        }
    }

    public void run() {
        while (true) {
            try {
                // this sleep makes it a little bit far otherwise the thread that called notify tends to reacquire
                // the lock immediately
                Thread.sleep(1);
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
                return;
            }
            resource.takesResource(this);
            enjoys();
            resource.signal(this);
        }
    }

    public static class Resource {
        boolean paper;
        boolean toy;
        boolean food;

        public synchronized void takesResource(Person person) {

            if ("paper".equals(person.resourceName)) {
                while (toy || food) {
                    try {
                        wait();
                    } catch (InterruptedException e) {
                        Thread.currentThread().interrupt();
                        return;
                    }
                }
                toy = true;
                food = true;
            } else if ("toy".equals(person.resourceName)) {
                while (food || paper) {
                    try {
                        wait();
                    } catch (InterruptedException e) {
                        Thread.currentThread().interrupt();
                        return;
                    }
                }
                food = true;
                paper = true;
            } else if ("food".equals(person.resourceName)) {
                while (paper || toy) {
                    try {
                        wait();
                    } catch (InterruptedException e) {
                        Thread.currentThread().interrupt();
                        return;
                    }
                }
                paper = true;
                toy = true;
            } else {
                System.exit(1);
            }
        }

        public synchronized void signal(Person person) {
            if ("paper".equals(person.resourceName)) {
                toy = false;
                food = false;
            } else if ("toy".equals(person.resourceName)) {
                food = false;
                paper = false;
            } else if ("food".equals(person.resourceName)) {
                paper = false;
                toy = false;
            } else {
                System.exit(1);
            }
            notifyAll();
        }
    }
}