java中CyclicBarrier和CountDownLatch的异同
CountDownLatch只能使用一次，cyclicBarrier可以重复使用，同时还提供barrierAction。 在功能上，cyclicBarrier可以完全替代countdownlatch， 但是性能上，如果同时工作的线程在几百数量级，则两者性能差不多，但是在千/万数量级的线程时，countdownlatch性能远远高于cyclicbarrier。
下面是测试代码，改变count值，观察输出结果：
public class Test2{CyclicBarrierbarrier;CountDownLatchlatch;intcount;longbeginTime;public static void main(String... args){final Test2 t = new Test2();t.count = 5000;t.beginTime = System.currentTimeMillis();t.barrier = new CyclicBarrier(t.count, new Runnable() {@Overridepublic void run(){System.out.println("cyclic barrier time consumed: " + (System.currentTimeMillis() - t.beginTime));}});t.latch = new CountDownLatch(t.count);// t.test();// tatal: 5177344, free: 3357624, used: 1819720 cyclic barrier time consumed: 766// t.test2();// tatal: 5177344, free: 4454904, used: 722440 countdown latch time consumed: 516// long total = Runtime.getRuntime().totalMemory();// long free = Runtime.getRuntime().freeMemory();// System.out.println("tatal: "+ total + ", free: "+ free +", used: "+ (total-free));}/** * cyclic barrier */private void test(){for (int i = 0; i < count; i++){new TestThread().start();}}/** * countdown latch */private void test2(){for (int i = 0; i < count; i++){new TestThread2().start();}try{latch.await();}catch (InterruptedException e){e.printStackTrace();}System.out.println("countdown latch time consumed: " + (System.currentTimeMillis() - beginTime));}class TestThread extends Thread{@Overridepublic void run(){try{Thread.sleep(100);barrier.await();}catch (InterruptedException e){e.printStackTrace();}catch (BrokenBarrierException e){e.printStackTrace();}}}class TestThread2 extends Thread{@Overridepublic void run(){try{Thread.sleep(100);latch.countDown();}catch (InterruptedException e){e.printStackTrace();}}}}