SemapDemo.java

package ch3.s1;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Semaphore;

public class SemapDemo implements Runnable {
    //5个一组输出
    final Semaphore semp = new Semaphore(5);

    public void run() {
        try {
            semp.acquire();
            Thread.sleep(2000);
            System.out.println(Thread.currentThread().getId() + " done!");
            semp.release();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    public static void main(String []args){
        ExecutorService exec = Executors.newFixedThreadPool(20);
        final SemapDemo demo = new SemapDemo();
        for(int i=0;i<20;i++){
            exec.submit(demo);
        }
    }
}