import java.util.concurrent.Executor;

import java.util.concurrent.ExecutorService;

import java.util.concurrent.Executors;

import java.util.concurrent.Semaphore;

/**

* @author lastwhisper

*/

public class SemapDemo implements Runnable {

final Semaphore semaphore = new Semaphore(5);

@Override

public void run() {

try {

semaphore.acquire();

Thread.sleep(2000);

System.out.println(Thread.currentThread().getId()+": done");

} catch (InterruptedException e) {

e.printStackTrace();

}finally {

semaphore.release();

}

}

public static void main(String[] args){

ExecutorService executorService = Executors.newFixedThreadPool(20);

SemapDemo semapDemo = new SemapDemo();

for (int i = 0; i < 20; i++) {

executorService.submit(semapDemo);

}

}

}