The Finite-Source Cookie Jar Problem

Question: A cookie jar is being shared by two sisters, Tina and Judy, using the following rule: Judy can get a cookie from the jar only after Tina (being the older sister) gets a cookie in at least two separate occasions, whereas Tina gets a cookie from the jar whenever she wants to. The mother is alerted by Judy or Tina whenever they want to eat a cookie and the jar is empty, in which case the mother fills the jar up (from a hidden source), and the kids go on eating. Treating Tina, Judy and the mother as three independently executing processes and the Cookie Jar as a shared resource, develop a concurrent algorithm to solve the Finite-Source Cookie Jar Problem.

Solution:

package cookiejar.finitesource;

import java.util.Random;

public class CookieJar {

static Object o = new Object();
static Object mother = new Object();
static Object children = new Object();

static int tinaCount = 0;
static int cookieCount = 25;
static Random random = new Random();

public static void main(String... args) {
new Thread(new Mother()).start();
new Thread(new Tina()).start();
new Thread(new Judy()).start();
}

private static void checkCookieCount() {
if (cookieCount == 0) {
synchronized (mother) {
System.out.println("Oops! no cookie mother!!! Please help.");
mother.notifyAll();
}
try {
System.out
.println("We are hungry mother. Where are other cookies? We are waiting.");
synchronized (children) {
children.wait();
}
} catch (InterruptedException e) {
}

}

}

private static void randomWait() {
int millisecs = random.nextInt(100);
try {
Thread.sleep(millisecs);
} catch (InterruptedException e) {
}
}

static class Tina implements Runnable {

@Override
public void run() {
while (true) {
randomWait();
boolean empty = false;
synchronized (o) {
if (cookieCount == 0) {
empty = true;
synchronized (mother) {
System.out
.println("Oops! no cookie mother!!! Please help.");
mother.notifyAll();
}
}
}
if (empty) {
try {
System.out
.println("We are hungry mother. Where are other cookies? We are waiting.");
synchronized (children) {
children.wait();
}
} catch (InterruptedException e) {
}
}
synchronized (o) {

cookieCount--;
tinaCount++;
System.out.println("TinaCount = " + tinaCount);
o.notify();
}
System.out.println("Tina is eating cookie.");
}

}

}

static class Judy implements Runnable {

@Override
public void run() {
while (true) {
randomWait();
boolean empty = false;
synchronized (o) {
System.out.println("Judy tries to get a cookie.");

while (tinaCount < 2) {
System.out
.println("Judy is waiting since Tina has not eaten 2 times.");
try {
o.wait();
System.out
.println("Judy is now awake and again checking for tinaCount.");
} catch (InterruptedException e) {
}
}
// start of method

if (cookieCount == 0) {
empty = true;
synchronized (mother) {
System.out
.println("Oops! no cookie mother!!! Please help.");
mother.notify();
}
}
}

if (empty) {
try {
System.out
.println("We are hungry mother. Where are other cookies? We are waiting.");
synchronized (children) {
children.wait();
}
} catch (InterruptedException e) {
}
}
// end of method
synchronized (o) {

}
System.out.println("Judy is eating cookie.");
synchronized (o) {
cookieCount--;
tinaCount = 0;
System.out.println("Judy has now reset the tinaCount.");
}
}

}

}

static class Mother implements Runnable {

@Override
public void run() {
while (true) {
synchronized (mother) {
try {
System.out
.println("Mother is sleeping children. Wake me up when you finish your cookies.");
mother.wait();
} catch (InterruptedException e) {
}
}
synchronized (o) {
cookieCount = 25;
System.out
.println("Mother has filled the cookie jar with good cookies.");
}
synchronized (children) {
System.out
.println("Get the cookies dear! I've filled up the jar.");
children.notifyAll();
}
}

}

}

}