线程同步之CyclicBarrier

我们之前分享了一个同步工具CountDonwLatch，它的作用是当一定线程执行完之后，才执行后面代码

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对CountDownLatch感兴趣的同学请点击达拉然传送门

而CyclicBarrier的功能是当指定的所有线程处于同一个状态时，同时执行后序代码，我们看下面的例子

public class CyclicBarrierDemo {public static void main(String[] args) {Runnable runnable1 = new Runnable() {Thread thread = Thread.currentThread();@Overridepublic void run() {System.out.println("thread:"+thread.currentThread().getName()+" start,state:"+thread.getState());try {Thread.sleep(200);} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}System.out.println("thread:"+thread.currentThread().getName()+" end,state:"+thread.getState());}};Runnable runnable2 = new Runnable() {Thread thread = Thread.currentThread();@Overridepublic void run() {System.out.println("thread:"+thread.currentThread().getName()+" start,state:"+thread.getState());try {Thread.sleep(2000);} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}System.out.println("thread:"+thread.currentThread().getName()+" end,state:"+thread.getState());}};Thread thread1 = new Thread(runnable1);Thread thread2 = new Thread(runnable2);Thread thread3 = new Thread(runnable1);thread1.start();thread2.start();thread3.start();}}

打印结果：

首先打印出

thread:Thread-0 start,state:TERMINATED

thread:Thread-2 start,state:TERMINATED

thread:Thread-1 start,state:TERMINATED

thread:Thread-2 end,state:TERMINATED

thread:Thread-0 end,state:TERMINATED

过了一会又打印出

thread:Thread-1 end,state:TERMINATED

这个结果大家可以试一下，那么现在我们要求3个线程要同时输出end语句，这就要用到了CyclicBarrier

我们看下面代码

public class CyclicBarrierDemo {public static void main(String[] args) {//构造cyclicBarrier，入参count为 触发后序代码的线程数CyclicBarrier cyclicBarrier = new CyclicBarrier(3);Runnable runnable1 = new Runnable() {Thread thread = Thread.currentThread();@Overridepublic void run() {System.out.println("thread:"+thread.currentThread().getName()+" start,state:"+thread.getState());try {Thread.sleep(200);} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}try {//在此等待其他线程cyclicBarrier.await();} catch (Exception e) {e.printStackTrace();} System.out.println("thread:"+thread.currentThread().getName()+" end,state:"+thread.getState());}};Runnable runnable2 = new Runnable() {Thread thread = Thread.currentThread();@Overridepublic void run() {System.out.println("thread:"+thread.currentThread().getName()+" start,state:"+thread.getState());try {Thread.sleep(2000);} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}try {//在此等待其他线程cyclicBarrier.await();} catch (Exception e) {e.printStackTrace();} System.out.println("thread:"+thread.currentThread().getName()+" end,state:"+thread.getState());}};Thread thread1 = new Thread(runnable1);Thread thread2 = new Thread(runnable2);Thread thread3 = new Thread(runnable1);thread1.start();thread2.start();thread3.start();}}

这次我们可以看到，所有end语句同时打印

这里要说明的是CyclicBarrier的构造方法还有一个是传入count 和 runnable的，如果选择此构造方法，在执行后序代码之前，先要执行传入的runnable的run方法代码