semaphore信号灯

public static void t2() {
ExecutorService service = Executors.newCachedThreadPool();
final Semaphore semaphore=new Semaphore(3,true);
for(int i=0;i<10;i++){
Runnable runnable=new Runnable(){
public void run(){
try {
semaphore.acquire();
System.out.println(Thread.currentThread().getName()+"进入,并发数为："+(3-semaphore.availablePermits()));
Thread.sleep((long)(Math.random()*10000)+1000);
semaphore.release();
System.out.println(Thread.currentThread().getName()+"离开****,并发数为："+(3-semaphore.availablePermits()));
} catch (InterruptedException e) {
e.printStackTrace();
}
}
};
service.execute(runnable);
}
service.shutdown();
}