Zookeeper学习笔记(六)分布式Barrier

当我们需要多个线程同时启动时，我们可以使用jdk自带的CycliBarrier。先来看看它的常用用法：

package com.my.CuratorTest;import java.util.concurrent.BrokenBarrierException;import java.util.concurrent.CyclicBarrier;/** * Title: <br/> * Intention: <br/> * <p> * Class Name: com.my.CuratorTest.CycliBarrierTest<br/> * Create Date: 2017/8/26 11:18 <br/> * Project Name: MyTest <br/> * Company:  All Rights Reserved. <br/> * Copyright © 2017 <br/> * </p> * <p> * author: GaoWei <br/> * 1st_examiner: <br/> * 2nd_examiner: <br/> * </p> * * @version 1.0 * @since JDK 1.7 */public class CycliBarrierTest {public static void main(String[] args) {CyclicBarrier barrier = new CyclicBarrier(5);for (int i = 0; i < 5; i++) {new Thread(new Runnable() {@Overridepublic void run() {System.out.println(Thread.currentThread().getName()+", 等待...");try {barrier.await();System.out.println(Thread.currentThread().getName()+ ", " + System.currentTimeMillis() + ", 开始工作");} catch (InterruptedException e) {e.printStackTrace();} catch (BrokenBarrierException e) {e.printStackTrace();}}}).start();}}}

运行结果：

Thread-3, 等待...Thread-1, 等待...Thread-0, 等待...Thread-2, 等待...Thread-4, 等待...Thread-4, 1503736464892, 开始工作Thread-3, 1503736464892, 开始工作Thread-0, 1503736464892, 开始工作Thread-1, 1503736464892, 开始工作Thread-2, 1503736464892, 开始工作

那么，在分布式环境下如何解决多个线程同时启动的问题呢？Curator为我们提供了DistributedBarrier（主线程触发barrier释放） 和 DistributedDoubleBarrier（线程自发触发barrier释放）。

DistributedBarrier的使用如下，拷贝书上代码：

package com.my.CuratorTest;import org.apache.curator.framework.CuratorFramework;import org.apache.curator.framework.CuratorFrameworkFactory;import org.apache.curator.framework.recipes.barriers.DistributedBarrier;import org.apache.curator.retry.ExponentialBackoffRetry;/** * Title: <br/> * Intention: <br/> * <p> * Class Name: com.my.CuratorTest.RecipesBarrier<br/> * Create Date: 2017/8/26 11:07 <br/> * Project Name: MyTest <br/> * Company:  All Rights Reserved. <br/> * Copyright © 2017 <br/> * </p> * <p> * author: GaoWei <br/> * 1st_examiner: <br/> * 2nd_examiner: <br/> * </p> * * @version 1.0 * @since JDK 1.7 */public class RecipesBarrier {static String barrierPath = "/curator_recipes_barrier_path";static DistributedBarrier barrier;public static void main(String[] args) throws Exception {for(int i=0;i<5;i++) {new Thread(new Runnable() {@Overridepublic void run() {CuratorFramework client = CuratorFrameworkFactory.builder().connectString("127.0.0.1:2181").retryPolicy(new ExponentialBackoffRetry(1000, 8)).build();client.start();barrier = new DistributedBarrier(client, barrierPath);System.out.println(Thread.currentThread().getName() + "号barrier设置");try {barrier.setBarrier();barrier.waitOnBarrier();System.err.println(Thread.currentThread().getName() + " 启动...");} catch (Exception e) {e.printStackTrace();}}}).start();}Thread.sleep(2000);barrier.removeBarrier();}}

运行结果：

Thread-4号barrier设置Thread-2号barrier设置Thread-3号barrier设置Thread-0号barrier设置Thread-1号barrier设置Thread-3 启动...Thread-4 启动...Thread-2 启动...Thread-0 启动...Thread-1 启动...

DistributedDoubleBarrier的使用如下：

package com.my.CuratorTest;import org.apache.curator.framework.CuratorFramework;import org.apache.curator.framework.CuratorFrameworkFactory;import org.apache.curator.framework.recipes.barriers.DistributedDoubleBarrier;import org.apache.curator.retry.ExponentialBackoffRetry;/** * Title: <br/> * Intention: <br/> * <p> * Class Name: com.my.CuratorTest.RecipesBarrier2<br/> * Create Date: 2017/8/26 16:05 <br/> * Project Name: MyTest <br/> * Company:  All Rights Reserved. <br/> * Copyright © 2017 <br/> * </p> * <p> * author: GaoWei <br/> * 1st_examiner: <br/> * 2nd_examiner: <br/> * </p> * * @version 1.0 * @since JDK 1.7 */public class RecipesBarrier2 {static String barrierPath = "/curator_recipes_barrier_path";public static void main(String[] args) {for (int i = 0; i < 5; i ++) {new Thread(new Runnable() {@Overridepublic void run() {try {CuratorFramework client = CuratorFrameworkFactory.builder().connectString("127.0.0.1:2181").retryPolicy(new ExponentialBackoffRetry(1000, 3)).build();client.start();DistributedDoubleBarrier barrier = new DistributedDoubleBarrier(client, barrierPath, 5);Thread.sleep(Math.round(Math.random() * 3000));System.out.println(Thread.currentThread().getName() +" 号进入barrier");barrier.enter();System.out.println(Thread.currentThread().getName() +" 启动...");Thread.sleep(Math.round(Math.random() * 3000));barrier.leave();System.out.println(Thread.currentThread().getName() +" 退出...");} catch (InterruptedException e) {e.printStackTrace();} catch (Exception e) {e.printStackTrace();}}}).start();}}}

运行结果：

Thread-2 号进入barrierThread-1 号进入barrierThread-4 号进入barrierThread-0 号进入barrierThread-3 号进入barrierThread-3 启动...Thread-4 启动...Thread-1 启动...Thread-0 启动...Thread-2 启动...Thread-2 退出...Thread-4 退出...Thread-0 退出...Thread-1 退出...Thread-3 退出...