方法实现junit junitRELEASE org.apache.logging.log4j log4j-core2.8.2 org.apache.zookeeper zookeeper3.5.7
import org.apache.zookeeper.*; import org.apache.zookeeper.data.Stat; import java.io.IOException; import java.util.Collections; import java.util.List; import java.util.concurrent.CountDownLatch; public class DistributedLock { // zookeeper server 列表 private String connectString = "hadoop102:2181,hadoop103:2181,hadoop104:2181"; // 超时时间 private int sessionTimeout = 2000; private ZooKeeper zk; private String rootNode = "locks"; private String subNode = "seq-"; // 当前client 等待的子节点 private String waitPath; //ZooKeeper 连接 private CountDownLatch connectLatch = new CountDownLatch(1); //ZooKeeper 节点等待 private CountDownLatch waitLatch = new CountDownLatch(1); // 当前client 创建的子节点 private String currentNode; // 和zk 服务建立连接,并创建根节点 public DistributedLock() throws IOException, InterruptedException, KeeperException { zk = new ZooKeeper(connectString, sessionTimeout, new Watcher() { @Override public void process(WatchedEvent event) { // 连接建立时, 打开latch, 唤醒wait 在该latch 上的线程 if (event.getState() == Event.KeeperState.SyncConnected) { connectLatch.countDown(); } // 发生了waitPath 的删除事件 if (event.getType() == Event.EventType.NodeDeleted && event.getPath().equals(waitPath)) { waitLatch.countDown(); } } }); // 等待连接建立 connectLatch.await(); //获取根节点状态 Stat stat = zk.exists("/" + rootNode, false); //如果根节点不存在,则创建根节点,根节点类型为永久节点 if (stat == null) { System.out.println("根节点不存在"); zk.create("/" + rootNode, new byte[0], ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT); } } // 加锁方法 public void zkLock() { try { //在根节点下创建临时顺序节点,返回值为创建的节点路径 currentNode = zk.create("/" + rootNode + "/" + subNode, null, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL); // wait 一小会, 让结果更清晰一些 Thread.sleep(10); // 注意, 没有必要监听"/locks"的子节点的变化情况 List测试childrenNodes = zk.getChildren("/" + rootNode, false); // 列表中只有一个子节点, 那肯定就是 currentNode , 说明 client 获得锁 if (childrenNodes.size() == 1) { return; } else { //对根节点下的所有临时顺序节点进行从小到大排序 Collections.sort(childrenNodes); //当前节点名称 String thisNode = currentNode.substring(("/" + rootNode + "/").length()); //获取当前节点的位置 int index = childrenNodes.indexOf(thisNode); if (index == -1) { System.out.println("数据异常"); } else if (index == 0) { // index == 0, 说明 thisNode 在列表中最小, 当前 client 获得锁 return; } else { // 获得排名比currentNode 前1 位的节点 this.waitPath = "/" + rootNode + "/" + childrenNodes.get(index - 1); // 在 waitPath 上注册监听器, 当 waitPath 被删除时, zookeeper 会回调监听器的process 方法 zk.getData(waitPath, true, new Stat()); //进入等待锁状态 waitLatch.await(); return; } } } catch (KeeperException e) { e.printStackTrace(); } catch (InterruptedException e) { e.printStackTrace(); } } // 解锁方法 public void zkUnlock() { try { zk.delete(this.currentNode, -1); } catch (InterruptedException | KeeperException e) { e.printStackTrace(); } } }
import org.apache.zookeeper.KeeperException; import java.io.IOException; public class DistributedLockTest { public static void main(String[] args) throws InterruptedException, IOException, KeeperException { // 创建分布式锁1 final DistributedLock lock1 = new DistributedLock(); // 创建分布式锁2 final DistributedLock lock2 = new DistributedLock(); new Thread(new Runnable() { @Override public void run() { // 获取锁对象 try { lock1.zkLock(); System.out.println("线程1 获取锁"); Thread.sleep(5 * 1000); lock1.zkUnlock(); System.out.println("线程1 释放锁"); } catch (Exception e) { e.printStackTrace(); } } }).start(); new Thread(new Runnable() { @Override public void run() { // 获取锁对象 try { lock2.zkLock(); System.out.println("线程2 获取锁"); Thread.sleep(5 * 1000); lock2.zkUnlock(); System.out.println("线程2 释放锁"); } catch (Exception e) { e.printStackTrace(); } } }).start(); } }方法讲解
当线程获取到zookeeper得节点创建一个临时节点,作为锁标志,并获取当前节点在zookeeper得位置,如果不为0,会监听这个节点得前置节点,并进入等待状态,直到获取锁。如果为-1 则出现错误,其他状态会等待锁。当方法完成之后会进行删除当前线程持有的节点,以达到释放锁的目的。
通过Curator 框架实现分布式锁导入依赖原生的Java API 开发存在的问题
(1)会话连接是异步的,需要自己去处理。比如使用CountDownLatch
(2)Watch 需要重复注册,不然就不能生效
(3)开发的复杂性还是比较高的
(4)不支持多节点删除和创建。需要自己去递归
org.apache.curator curator-framework4.3.0 org.apache.curator curator-recipes4.3.0 org.apache.curator curator-client4.3.0
代码演示
import org.apache.curator.RetryPolicy; import org.apache.curator.framework.Curatorframework; import org.apache.curator.framework.CuratorframeworkFactory; import org.apache.curator.framework.recipes.locks.InterProcessLock; import org.apache.curator.framework.recipes.locks.InterProcessMutex; import org.apache.curator.retry.ExponentialBackoffRetry; public class CuratorLockTest { private String rootNode = "/locks"; // zookeeper server 列表 private String connectString = "hadoop102:2181,hadoop103:2181,hadoop104:2181"; // connection 超时时间 private int connectionTimeout = 2000; // session 超时时间 private int sessionTimeout = 2000; public static void main(String[] args) { new CuratorLockTest().test(); } // 测试 private void test() { // 创建分布式锁1 final InterProcessLock lock1 = new InterProcessMutex(getCuratorframework(), rootNode); // 创建分布式锁2 final InterProcessLock lock2 = new InterProcessMutex(getCuratorframework(), rootNode); new Thread(new Runnable() { @Override public void run() { // 获取锁对象 try { lock1.acquire(); System.out.println("线程1 获取锁"); // 测试锁重入 lock1.acquire(); System.out.println("线程1 再次获取锁"); Thread.sleep(5 * 1000); lock1.release(); System.out.println("线程1 释放锁"); lock1.release(); System.out.println("线程1 再次释放锁"); } catch (Exception e) { e.printStackTrace(); } } }).start(); new Thread(new Runnable() { @Override public void run() { // 获取锁对象 try { lock2.acquire(); System.out.println("线程2 获取锁"); // 测试锁重入 lock2.acquire(); System.out.println("线程2 再次获取锁"); Thread.sleep(5 * 1000); lock2.release(); System.out.println("线程2 释放锁"); lock2.release(); System.out.println("线程2 再次释放锁"); } catch (Exception e) { e.printStackTrace(); } } }).start(); } // 分布式锁初始化 public Curatorframework getCuratorframework (){ //重试策略,初试时间3 秒,重试3 次 RetryPolicy policy = new ExponentialBackoffRetry(3000, 3); //通过工厂创建Curator Curatorframework client = CuratorframeworkFactory.builder() .connectString(connectString) .connectionTimeoutMs(connectionTimeout) .sessionTimeoutMs(sessionTimeout) .retryPolicy(policy).build(); //开启连接 client.start(); System.out.println("zookeeper 初始化完成..."); return client; } }
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