Java多线程——其他工具类CyclicBarrier、CountDownLatch和Exchange

CyclicBarrier

适用于：创建一组任务，它们并行地执行任务，然后在进行下一个步骤之前等待，直至所有任务完成。它使得所有的并行任务都将在栅栏处列队，因此可以一致地向前移动。

表示大家彼此等待，大家集合好后才开始出发，分散活动后又在指定地点集合碰面，这就好比整个公司的人员利用周末时间集体郊游一样，先各自从家出发到公司集合后，再同时出发到公园游玩，在指定地点集合后再同时开始就餐…

package java_thread;
import java.util.concurrent.CyclicBarrier;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class CyclicBarrierTest {

	public static void main(String[] args) {
		ExecutorService service = Executors.newCachedThreadPool();
		final  CyclicBarrier cb = new CyclicBarrier(3);
		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();

						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();
	}
}

CountDownLatch

犹如倒计时计数器，调用CountDownLatch对象的countDown方法就将计数器减1，当计数到达0时，则所有等待者或单个等待者开始执行。这直接通过代码来说明CountDownLatch的作用，这样学员的理解效果更直接。 可以实现一个人（也可以是多个人）等待其他所有人都来通知他，这犹如一个计划需要多个领导都签字后才能继续向下实施。还可以实现一个人通知多个人的效果，类似裁判一声口令，运动员同时开始奔跑。用这个功能做百米赛跑的游戏程序不错哦！

package java_thread;
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();			//等待计数器归零
						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();		//减小主线程计数值
					} catch (Exception e) {
						e.printStackTrace();
					}
				}
			};
			service.execute(runnable);
		}
		try {			//主线程
			Thread.sleep((long)(Math.random()*10000));

			System.out.println("线程" + Thread.currentThread().getName() +
					"即将发布命令");
			cdOrder.countDown();		//减小计数值
			System.out.println("线程" + Thread.currentThread().getName() +
			"已发送命令，正在等待结果");
			cdAnswer.await();					//等待计数器归零
			System.out.println("线程" + Thread.currentThread().getName() +
			"已收到所有响应结果");
		} catch (Exception e) {
			e.printStackTrace();
		}
		service.shutdown();

	}
}

Exchanger

用于实现两个人之间的数据交换，每个人在完成一定的事务后想与对方交换数据，第一个先拿出数据的人将一直等待第二个人拿着数据到来时，才能彼此交换数据。

package java_thread;
import java.util.concurrent.Exchanger;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class ExchangerTest {

	public static void main(String[] args) {
		ExecutorService service = Executors.newCachedThreadPool();
		final Exchanger exchanger = new Exchanger();
		service.execute(new Runnable(){
			public void run() {
				try {				

					String data1 = "zxx";
					System.out.println("线程" + Thread.currentThread().getName() +
					"正在把数据" + data1 +"换出去");
					Thread.sleep((long)(Math.random()*10000));
					String data2 = (String)exchanger.exchange(data1);
					System.out.println("线程" + Thread.currentThread().getName() +
					"换回的数据为" + data2);
				}catch(Exception e){

				}
			}
		});
		service.execute(new Runnable(){
			public void run() {
				try {				

					String data1 = "lhm";
					System.out.println("线程" + Thread.currentThread().getName() +
					"正在把数据" + data1 +"换出去");
					Thread.sleep((long)(Math.random()*10000));
					String data2 = (String)exchanger.exchange(data1);
					System.out.println("线程" + Thread.currentThread().getName() +
					"换回的数据为" + data2);
				}catch(Exception e){

				}
			}
		});
	}
}