package javacore.threading;

import java.util.concurrent.Semaphore;

public class SemaphoreExample {
	private static final int DEFAULT_PERMITS = 2;
    private static final int NO_OF_THREADS = 4;
    private Semaphore semaphore = new Semaphore(DEFAULT_PERMITS);


    private class SemaphoreTestThread implements Runnable {
        @Override
        public void run() {
            try {
                for(int i=0;i<NO_OF_THREADS;i++) {
                	//Acquiring  context here
                    semaphore.acquire();
                    System.out.println("Semaphore acquired: "+ Thread.currentThread().getName());

                    // only ever two threads here
                    Thread.sleep(1000);
                    //Releasing context here
                    semaphore.release();
                    System.out.println("Semaphore released: "+ Thread.currentThread().getName());
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    private void init() {
        for(int i=0; i<NO_OF_THREADS; ++i) {
            Thread th = new Thread(new SemaphoreTestThread());
            th.start();
        }
    }

    public static void main(String[] args) {
    	new SemaphoreExample().init();
	}
}