public class SemaphoreDemo {private static volatile int count = 0 ;private static final Semaphore full = new Semaphore(5);private static final Semaphore empty = new Semaphore(0);private static final Semaphore mutex = new Semaphore(1);public static void main(String[] args) {ExecutorService threadPool = Executors.newFixedThreadPool(10);threadPool.execute(() -> {while(true){try {full.acquire();mutex.acquire();count++;System.out.println("生产了1个资源, 目前还有" + count + "个资源");Thread.sleep(1000);} catch (InterruptedException e) {e.printStackTrace();} finally {mutex.release();empty.release();}}});threadPool.execute(() -> {while(true){try {empty.acquire();mutex.acquire();count--;System.out.println("消费了1个资源, 目前还有" + count + "个资源");Thread.sleep(1000);} catch (InterruptedException e) {e.printStackTrace();} finally {mutex.release();full.release();}}});}
}

CountDownLatch

public class CountDownLatchDemo {public static void main(String[] args) throws InterruptedException {CountDownLatch latch = new CountDownLatch(6);ExecutorService executor = Executors.newFixedThreadPool(10);for(int i = 0; i < 5; i++){executor.execute(() -> {System.out.println("First batch has executed!");latch.countDown();});}for(int i = 0; i < 5; i++){executor.execute(() -> {try {latch.await();System.out.println("Second batch has executed!");} catch (InterruptedException e) {e.printStackTrace();}});}while(latch.getCount() != 1){Thread.sleep(1000);}latch.countDown();System.out.println("Wait for first batch finish!");}
}

public class CyclicBarrierDemo {public static void main(String[] args) {//final CyclicBarrier cyclicBarrier = new CyclicBarrier(5, () -> new Thread(() -> System.out.println("Wait for batch finish!")).start());final CyclicBarrier cyclicBarrier = new CyclicBarrier(5, () -> System.out.println("Wait for batch finish!"));for(int i = 0; i < 10; i++){new Thread(() -> {try {System.out.println("The batch has executed!");cyclicBarrier.await();} catch (InterruptedException | BrokenBarrierException e) {e.printStackTrace();}}).start();}}
}

CountDownLatch和CyclicBarrier的区别：

CountDownLatch是不可以重置的，所以无法重用;而CyclicBarrier则没有这种限制，可以重用。 CountDownLatch的基本操作组合是countDown/await。调用await的线程等待countDown直到足够的次数，不管是在一个线程还是多个线程里countDown。

CyclicBarrier的基本操作是await，当所有的线程都调用了await，才会继续进行任务，并自动进行重置。注意，正常情况下，CyclicBarrier的重置都是自动发生的，如果我们调用reset方法，但还有线程在等待，就会导致等待线程被打扰，抛出BrokenBarrierException异常。