CyclicBarrier和CountDownLatch的区别

1. 字面意思

CyclicBarrier ： 循环的屏障

CountDownLatch : 向下计数锁

2. 用途

CyclicBarrier ： 让指定的线程等待，直到所有线程达到同一执行点全部继续执行

CountDownLatch : 让线程等待，直到CountDownLatch计数到0，继续执行该线程。

3. 主要方法：

CyclicBarrier :

await() : 一直等待，直到所有线程都执行到await代码处，所有线程同时继续执行。

CountDownLatch:

countDown : 计数-1

await() : 线程等待，直到计数到0才继续执行

4. 实例：

CyclicBarrier:

public class CyclicBarrierTest {public static void main(String[] args) {CyclicBarrier cyclicBarrier = new CyclicBarrier(10);for(int i = 0; i < 10;i++) {Thread t = new Thread(new ThreadTest2(cyclicBarrier, i * 1000L));t.start();}}}class ThreadTest2 implements Runnable {CyclicBarrier cyclicBarrier;long s = 0;public ThreadTest2(CyclicBarrier cyclicBarrier, long s) {this.cyclicBarrier = cyclicBarrier;this.s = s;}@Overridepublic void run() {System.out.println("start current thread name : " + Thread.currentThread().getName());try {Thread.sleep(s);} catch (InterruptedException e) {e.printStackTrace();}System.out.println("current thread name : " + Thread.currentThread().getName() + "end sleep");try {cyclicBarrier.await();} catch (InterruptedException e1) {e1.printStackTrace();} catch (BrokenBarrierException e1) {e1.printStackTrace();}System.out.println("end current thread name : " + Thread.currentThread().getName());}}

结果：

start current thread name : Thread-3

start current thread name : Thread-2

start current thread name : Thread-0

start current thread name : Thread-1

start current thread name : Thread-5

start current thread name : Thread-4

start current thread name : Thread-6

start current thread name : Thread-7

start current thread name : Thread-8

current thread name : Thread-0end sleep

start current thread name : Thread-9

current thread name : Thread-1end sleep

current thread name : Thread-2end sleep

current thread name : Thread-3end sleep

current thread name : Thread-4end sleep

current thread name : Thread-5end sleep

current thread name : Thread-6end sleep

current thread name : Thread-7end sleep

current thread name : Thread-8end sleep

current thread name : Thread-9end sleep

end current thread name : Thread-9

end current thread name : Thread-8

end current thread name : Thread-7

end current thread name : Thread-6

end current thread name : Thread-5

end current thread name : Thread-0

end current thread name : Thread-4

end current thread name : Thread-3

end current thread name : Thread-2

end current thread name : Thread-1

分析：

main线程中启动10个子线程，并传入CyclicBarrier对象，子线程立即打印start current name,

随后执行睡眠(sleep),结束睡眠后打印end sleep ,虽然不同的子线程睡眠时间不一样，但由于调用 了

cyclicBarrier.await()方法，所有子线程都等待其它线程都执行到该代码处才继续执行打印end current name

CountDownLatch:

public class CountDownLatchTest {public static void main(String[] args) throws InterruptedException {System.out.println("main thread start");CountDownLatch latch = new CountDownLatch(10);for(int i = 0; i < 10; i++) {ThreadTest t = new ThreadTest(latch);Thread thread = new Thread(t);thread.start();}latch.await();System.out.println("main thread end");}}class ThreadTest implements Runnable {CountDownLatch latch;public ThreadTest(CountDownLatch latch) {this.latch = latch;}@Overridepublic void run() {System.out.println("start current thread name : " + Thread.currentThread().getName());latch.countDown();try {Thread.sleep(5000);} catch (InterruptedException e) {e.printStackTrace();}System.out.println("end current thread name : " + Thread.currentThread().getName());}}

结果：

main thread start

start current thread name : Thread-3

start current thread name : Thread-1

start current thread name : Thread-0

start current thread name : Thread-2

start current thread name : Thread-4

start current thread name : Thread-5

start current thread name : Thread-6

start current thread name : Thread-7

start current thread name : Thread-8

start current thread name : Thread-9

main thread end

分析：

main线程打印main thread start，随后启动10个子线程，启动完线程后由于调用了latch.await()方法，所以并没有立既继续执行main thread end，而是等待子线程调用latch.countDown()方法使计数到0后才继续执行main thread end