java 多线程-信号量 Semaphore

public class Test{
	public static void main(String[] arg){
		Semaphore semaphore = new Semaphore(3);//定义信号量
		//SecurityManager sm = System.getSecurityManager();
		//ThreadGroup group = sm == null ? Thread.currentThread().getThreadGroup() : sm.getThreadGroup();
		ThreadGroup group = new ThreadGroup("semaphore");//自定义线程组
		AtomicInteger num = new AtomicInteger(0);

		ThreadPoolExecutor pool = new ThreadPoolExecutor(
				5, 
				8, 
				1000, 
				TimeUnit.SECONDS, 
				new LinkedBlockingDeque<Runnable>(20), new ThreadFactory() {//线程池工厂
					@Override
					public Thread newThread(Runnable r) {//生产新的线程
						Thread thread = new Thread(group, r, group.getName()+"-thread-"+num.getAndIncrement());
						thread.setUncaughtExceptionHandler(new UncaughtExceptionHandler() {
							@Override
							public void uncaughtException(Thread t, Throwable e) {
								System.out.println(t.getName()+"发生异常："+e.getMessage());
							}
						});
						return thread;
					}
				},new RejectedExecutionHandler() {//线程池的拒绝策略
					@Override
					public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
						throw new RuntimeException("任务队列已满，任务被拒绝");
					}
				});

		//定义任务
		Runnable task = ()->{
			try {
				semaphore.acquire();
				System.out.println(Thread.currentThread().getName()+"已获得信号量许可，正在运行");
				Thread.sleep(3000);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}finally {
				semaphore.release();
			}
		};

		for(int i = 0; i < 10; i++){//循环运行10个任务
			pool.execute(task);
		}

		if(Thread.activeCount() > 1){
			Thread.yield();
		}
		pool.shutdown();
	}
}

信号量就像是一个资源控制器，在任意时刻，只有获得信号量资源的线程才会运行