Question

Java programming

Exercise 32.11 Write a program that uses explicit locks (or semaphores) to cause a deadlock. Do not use the synchronized keyword. Repeatedly try to lock and unlock the locks and print messages to indicate when a lock is locked or unlocked to give some indication of what the program is doing. Using Thread.sleep) might be helpful to make a deadlock more likely.

Answer 1

import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class DeadlockUsingSemaphore {
  
final static Lock lock1 = new ReentrantLock();
final static Lock lock2 = new ReentrantLock();
  
public static void main(String[]args)
{
Thread t1 = new Thread(new Runnable3());
t1.setName("First Thread");
t1.start();
  
Thread t2 = new Thread(new Runnable4());
t2.setName("Second Thread");
t2.start();
}
  
static class Runnable3 implements Runnable
{
public void run()
{
DeadlockUsingSemaphore.lock1.lock();
try
{
System.out.println(Thread.currentThread().getName() + ": acquired lock1. Trying for lock2...");
try
{
Thread.sleep(500);
}catch(InterruptedException e){ e.printStackTrace(); }
  
DeadlockUsingSemaphore.lock2.lock();
try
{
System.out.println(Thread.currentThread().getName() + ": acquired lock2.");
} finally {
DeadlockUsingSemaphore.lock2.unlock();
}
}finally{
DeadlockUsingSemaphore.lock1.lock();
}
}
}
  
static class Runnable4 implements Runnable
{
public void run()
{
DeadlockUsingSemaphore.lock2.lock();
try
{
System.out.println(Thread.currentThread().getName() + ": acquired lock2. Trying for lock1...");
try
{
Thread.sleep(500);
}catch(InterruptedException e){ e.printStackTrace(); }
DeadlockUsingSemaphore.lock1.lock();
try
{
System.out.println(Thread.currentThread().getName() + ": acquired lock1.");
}finally{
DeadlockUsingSemaphore.lock1.unlock();
}
}finally{
DeadlockUsingSemaphore.lock2.unlock();
}
}
}
}

****************************************************************** SCREENSHOT *********************************************************

run: First Thread: acquired lock1. Trying for lock2... Second Thread: acquired lock2. Trying for lock1.