zookeeper应用场景练习（分布式锁）

 

 在平常的高并发的程序中，为了保证数据的一致性，因此都会用到锁，来对当前的线程进行锁定。在单机操作中，很好做到，比如可以采用Synchronized、Lock或者其他的读写多来锁定当前的线程。但是在分布式的系统中，就很难做到这一点。因此可以采用zookeeper中节点的特性来满足这一点。大致实现的思路如下。

 1.每个客户端都去zookeeper上创建临时的顺序节点

 2.客户端判断当前自己创建的节点是不是最小的

 3.如果是的话，就获得了执行当前任务的锁

 4.如果不是的话，就找到比自己小的节点，然后进行监听，如果被删除的话，就可以获得锁

 上面就是大致的实现思路，下面我们来通过代码来实现一下。

 

package com.test;import java.util.ArrayList;import java.util.Collections;import java.util.List;import java.util.concurrent.CountDownLatch;import org.apache.curator.framework.CuratorFramework;import org.apache.curator.framework.CuratorFrameworkFactory;import org.apache.curator.framework.api.CuratorWatcher;import org.apache.curator.framework.state.ConnectionState;import org.apache.curator.framework.state.ConnectionStateListener;import org.apache.curator.retry.RetryNTimes;import org.apache.zookeeper.CreateMode;import org.apache.zookeeper.WatchedEvent;import org.apache.zookeeper.Watcher.Event.EventType;import org.apache.zookeeper.data.Stat;import org.slf4j.Logger;import org.slf4j.LoggerFactory;public class DistributedLock {private String lockName;private final int timeOut = 3000;private final String root = "/locks";private String myZnode;// 代表当前节点信息private String waitZnode;private static Logger logger = LoggerFactory.getLogger(DistributedLock.class);private CuratorFramework client;private CountDownLatch latch = new CountDownLatch(1);public DistributedLock(String connectString, String lockName) {this.lockName = lockName;client = CuratorFrameworkFactory.builder().connectionTimeoutMs(timeOut).connectString(connectString).retryPolicy(new RetryNTimes(3, 3000)).build();ConnectionStateListener listener = new ConnectionStateListener() {public void stateChanged(CuratorFramework client,ConnectionState newState) {if (newState == ConnectionState.CONNECTED) {logger.info("连接成功了");latch.countDown();}}};client.getConnectionStateListenable().addListener(listener);client.start();try {latch.await();createRoot();} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}}/** * @Title: 创建根节点root * @Description: TODO * @param * @return void * @throws */private void createRoot() {try {Stat stat = client.checkExists().forPath(root);if (stat != null) {logger.info("root has already exists");} else {// 创建跟节点client.create().creatingParentsIfNeeded().forPath(root);}} catch (Exception e) {// TODO Auto-generated catch blocke.printStackTrace();}}public void getLocks() {try {myZnode = client.create().withMode(CreateMode.EPHEMERAL_SEQUENTIAL).forPath(root + "/" + lockName);logger.info(myZnode + "has created");// 取出所有的子节点，然后找出比自己小的节点，进行监听的设置List<String> subNodes = client.getChildren().forPath(root);// 取出所有带有lockname的节点信息List<String> lockObjNodes = new ArrayList<String>();for (String node : subNodes) {if (node.contains(lockName)) {lockObjNodes.add(node);}}// 对当前节点进行排序Collections.sort(lockObjNodes);// 判断当前的节点是不是最小的节点if (myZnode.equals(root + "/" + lockObjNodes.get(0))) {doAction();} else {// 找到比自己节点大一的节点进行监听String subMyZone = myZnode.substring(myZnode.lastIndexOf("/") + 1);waitZnode = lockObjNodes.get(Collections.binarySearch(lockObjNodes, subMyZone) - 1);// 对节点进行监听Stat stat = client.checkExists().usingWatcher(deleteNodeWatcher).forPath("/"+waitZnode);if (stat != null) {System.out.println(Thread.currentThread().getName()+ "处于等待状态");} else {doAction();}}} catch (Exception e) {logger.error(e.getMessage());}}// 删除节点的事件监听CuratorWatcher deleteNodeWatcher = new CuratorWatcher() {public void process(WatchedEvent event) throws Exception {if (event.getType() == EventType.NodeDeleted) {doAction();}}};private void doAction() {System.out.println(Thread.currentThread().getName() + "开始执行");client.close();}}

 下面来测试一下

 

/**      * @FileName: TestCurrentZk.java    * @Package:com.test    * @Description: TODO   * @author: LUCKY     * @date:2016年2月2日 下午11:36:04    * @version V1.0      */package com.test;/** * @ClassName: TestCurrentZk * @Description: TODO * @author: LUCKY * @date:2016年2月2日 下午11:36:04 */public class TestCurrentZk {public static void main(String[] args) throws Exception {Thread threads[] = new Thread[10];for (int i = 0; i < threads.length; i++) {threads[i] = new Thread(new Runnable() {public void run() {ClientTest clientTest = new ClientTest("100.66.162.36:2181", "locknametest");clientTest.getLocks();}});threads[i].start();}Thread.sleep(Integer.MAX_VALUE);}}