java并发之同步辅助类CyclicBarrier和CountDownLatch

CyclicBarrier 的字面意思是可循环使用（Cyclic）的屏障（Barrier）。它要做的事情是，让一组线程到达一个屏障（也可以叫同步点）时被阻塞，直到最后一个线程到达屏障时，屏障才会开门，所有被屏障拦截的线程才会继续干活。CyclicBarrier默认的构造方法是

CyclicBarrier(int parties)，其参数表示屏障拦截的线程数量，每个线程调用await方法告诉CyclicBarrier我已经到达了屏障，然后当前线程被阻塞。

cBarrierTest {public static void main(String[] args) {ExecutorService service = Executors.newCachedThreadPool();final CyclicBarrier cb = new CyclicBarrier(3);//约定三个人同时到达for (int i = 0; i < 3; i++) {Runnable runnable = new Runnable() {public void run() {try {Thread.sleep((long) (Math.random() * 10000));System.out.println("线程" + Thread.currentThread().getName() +"即将到达集合地点1，当前已有" + (cb.getNumberWaiting() + 1) + "个已经到达，" + (cb.getNumberWaiting() == 2 ? "都到齐了，继续走啊" : "正在等候"));cb.await();//三个同时线程的时候才往下走
Thread.sleep((long) (Math.random() * 10000));System.out.println("线程" + Thread.currentThread().getName() +"即将到达集合地点2，当前已有" + (cb.getNumberWaiting() + 1) + "个已经到达，" + (cb.getNumberWaiting() == 2 ? "都到齐了，继续走啊" : "正在等候"));cb.await();Thread.sleep((long) (Math.random() * 10000));System.out.println("线程" + Thread.currentThread().getName() +"即将到达集合地点3，当前已有" + (cb.getNumberWaiting() + 1) + "个已经到达，" + (cb.getNumberWaiting() == 2 ? "都到齐了，继续走啊" : "正在等候"));cb.await();} catch (Exception e) {e.printStackTrace();}}};service.execute(runnable);}service.shutdown();}
}

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.CyclicBarrier;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;public class CountdownLatchTest {public static void main(String[] args) {ExecutorService service = Executors.newCachedThreadPool();final CountDownLatch cdOrder = new CountDownLatch(1);final CountDownLatch cdAnswer = new CountDownLatch(3);for (int i = 0; i < 3; i++) {Runnable runnable = new Runnable() {public void run() {try {System.out.println("线程" + Thread.currentThread().getName() +"正准备接受命令");cdOrder.await();//三个线程同时进来接受命令//调用await()方法的线程会被挂起，它会等待直到count值为0才继续执行System.out.println("线程" + Thread.currentThread().getName() +"已接受命令");Thread.sleep((long) (Math.random() * 10000));System.out.println("线程" + Thread.currentThread().getName() +"回应命令处理结果");cdAnswer.countDown();} catch (Exception e) {e.printStackTrace();}}};service.execute(runnable);}try {Thread.sleep((long) (Math.random() * 10000));System.out.println("线程" + Thread.currentThread().getName() +"即将发布命令");cdOrder.countDown();//这里等于0之后触发了wait事件让其往下执行System.out.println("线程" + Thread.currentThread().getName() +"已发送命令，正在等待结果");cdAnswer.await();//调用await()方法的线程会被挂起，它会等待直到count值为0才继续执行
System.out.println("线程" + Thread.currentThread().getName() +"已收到所有响应结果");} catch (Exception e) {e.printStackTrace();}service.shutdown();}
}