SemaphoreTest.java

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Semaphore;
import java.util.concurrent.TimeUnit;
import java.util.stream.IntStream;

final class Task implements Runnable
{
	private int taskId;
	private Semaphore semaphore;
	
	public Task(int taskId, Semaphore semaphore)
	{
		this.taskId=taskId;
		this.semaphore=semaphore;
	}
	
	@Override
	public void run() {
		System.out.println("Running a thread with name :"+Thread.currentThread().getName()+", for task id:"+this.taskId);	
		try {
			semaphore.acquire();
			//call slow service
			slowService();
			semaphore.release();
		}
		catch(InterruptedException e){}
	}	
	
	public void slowService() throws InterruptedException
	{
		Thread.sleep(100);
	}
}

public class SemaphoreTest {

	public static void main(String[] args) {
		try {
			//5 is the number of Permits
			Semaphore semaphore= new Semaphore(5);
			
			ExecutorService exeService=Executors.newFixedThreadPool(50);
			//IntStream.of(1000).forEach(i->exeService.submit(new Task(i, semaphore)));
			for (int i=0; i<100;i++){
				exeService.submit(new Task(i, semaphore));
			}
			
			exeService.shutdown();
			exeService.awaitTermination(1, TimeUnit.MINUTES);
		}
		catch(InterruptedException e){}
	}
}