Question

[Java] [Threads] The following class implements a model of a student dining hall serving pizzas to students. 10 pizzas are baked, then served to 20 students.

Students are numbered between 0 and 19 in the order they are served.

A message is printed indicating whether a student starved or was served a pizza.

(a.) Rewrite the DiningHall class so that after the makePizza( ) method is called 10 times,

the servePizza( ) method is called once each from 20 different threads.

(b.) Insert synchronization to eliminate data races in your code, if any exist.

(c.) Describe what data races may occur in your multithreaded code without synchronization.

public class DiningHall {

static int pizzaNum;
static int studentID;

public void makePizza() {
pizzaNum++;
}

public void servePizza() {
String result;
if (pizzaNum > 0) {
result = "Served ";
pizzaNum--;
} else {
result = "Starved ";
}
System.out.println(result + studentID);
studentID++;
}

public static void main(String[] args) {
DiningHall d = new DiningHall();
for (int i = 0; i < 10; i++) {
d.makePizza();
}
for (int i = 0; i < 20; i++) {
d.servePizza();
}
}
}

Answer 1

Answer: Program: public class DiningHall extends Thread static int pizzaNum; static int studentID public void makePizza ) pizzaNumt+; public synchronized void run () String result; if (pizzaNum > 0) result"Served "; iz zaNum--. else result"Starved " if (student ID<20 ) System.out.println (result + studentID) studentID++ DubL ic static void main (String L args) DiningHall d - new DiningHall for (int h= 0; < 10; Ả++) d makePizza) for (int j- 0; 0; j 20; j++) ne DiningHal10).start);

Sample Output: Before synchronizations: sh-4.3 java DiningHall Served e Served e Served 0 Starved 3 Starved 3 Starved 5 Starved 6 Starved 7 Starved 8 Starved 9 Starved 10 Starved 11 Starved 12 Starved 13 Starved 14 Starved 15 Starved 16 Starved 17 Starved 18 Starved 19 Starved 20 Starved 21 Starved 21 Starved 23 Starved 23 Starved 25 Starved 27 Starved 28

After synchronizations: sh-4.3s java DiningHall Served e Starved 1 Starved 2 Starved 3 Starved 4 Starved 4 Starved 6 Starved 7 Starved 8 Starved 9 Starved 10 Starved 11 Starved 12 Starved 13 Starved 14 Starved 15 Starved 15 Starved 17 Served 18 Starved 19 sh-4.3$ Conclusions: Without synchronizations it is incrementing more than 19 also, but by using synchronizations this issue can be solved.

Copyable Code:

public class DiningHall extends Thread
{
static int pizzaNum;
static int studentID;
public void makePizza()
{
pizzaNum++;
}
public synchronized void run()
{
String result;
if (pizzaNum > 0)
{
result = "Served ";
pizzaNum--;
}
else
{
result = "Starved ";
}
if(studentID<20)
System.out.println(result + studentID);
studentID++;
}
public static void main(String[] args)
{
DiningHall d = new DiningHall();
for (int i = 0; i < 10; i++)
{
d.makePizza();
for (int j = 0; j < 20; j++)
{
new DiningHall().start();
}
}
}
}