//One Thread method that a supervisor thread may use to monitor another thread is .isAlive(). This method returns true if the thread is still running, and false if it has terminated. A supervisor might continuously poll this value (check it at a fixed interval) until it changes, and then notify the user that the thread has changed state.

import java.time.Instant;
import java.time.Duration;
 
public class Factorial {
 public int compute(int n) {
   // the existing method to compute factorials
 }
 
 // utility method to create a supervisor thread
 public static Thread createSupervisor(Thread t) {
   Thread supervisor = new Thread(() -> {
     Instant startTime = Instant.now();
     // supervisor is polling for t's status
     while (t.isAlive()) {
       System.out.println(Thread.currentThread().getName() + " - Computation still running...");
       Thread.sleep(1000);
     }
   });
 
   // setting a custom name for the supervisor thread
   supervisor.setName("supervisor");
   return supervisor;
 
 }
 
 public static void main(String[] args) {
   Factorial f = new Factorial();
 
   Thread t1 = new Thread(() -> {
     System.out.println("25 factorial is...");
     System.out.println(f.compute(25));
   });
 
 
   Thread supervisor = createSupervisor(t1);
 
   t1.start();
   supervisor.start();
 
   System.out.println("Supervisor " + supervisor.getName() + " watching worker " + t1.getName());
 }
}