DinningPhilosophers.java

package interview;

import java.util.Random;
import java.util.concurrent.Semaphore;

public class DinningPhilosophers {
  private static Random random = new Random(System.currentTimeMillis());

  private Semaphore[] forks = new Semaphore[5];
  private Semaphore maxDiners = new Semaphore(4);

  public DinningPhilosophers(){
    forks[0]=new Semaphore(1);
    forks[1]=new Semaphore(1);
    forks[2]=new Semaphore(1);
    forks[3]=new Semaphore(1);
    forks[4]=new Semaphore(1);
  }

  public void lifeCycleOfPhilosopher(int id) throws InterruptedException{
    while (true){
      contemplate();
      eat(id);
    }
  }

  void contemplate() throws InterruptedException{
    Thread.sleep(random.nextInt(50));
  }

  void eat(int id) throws InterruptedException{
    maxDiners.acquire();
    forks[id].acquire();
    forks[(id+1)%5].acquire();
    System.out.println("Philosopher "+id+" is eating");
    forks[(id+1)%5].release();
    forks[id].release();
    maxDiners.release();
  }

  static void startPhilosopher(DinningPhilosophers dp , int id){
    try{
      dp.lifeCycleOfPhilosopher(id);
    }catch (InterruptedException e){

    }
  }

  public static void runTest() throws InterruptedException{
    final DinningPhilosophers dp = new DinningPhilosophers();
    Thread p1 = new Thread(new Runnable() {
      @Override
      public void run() {
        startPhilosopher(dp,0);
      }
    });

    Thread p2 = new Thread(new Runnable() {
      @Override
      public void run() {
        startPhilosopher(dp,1);
      }
    });
    Thread p3 = new Thread(new Runnable() {
      @Override
      public void run() {
        startPhilosopher(dp,2);
      }
    });
    Thread p4 = new Thread(new Runnable() {
      @Override
      public void run() {
        startPhilosopher(dp,3);
      }
    });

    Thread p5 = new Thread(new Runnable() {
      @Override
      public void run() {
        startPhilosopher(dp,4);
      }
    });

    p1.start();
    p2.start();
    p3.start();
    p4.start();
    p5.start();

    p1.join();
    p2.join();
    p3.join();
    p4.join();
    p5.join();


  }

  public static void main(String[] args) throws Exception{
    DinningPhilosophers.runTest();
  }

}