Zookeeper典型应用场景分布式锁的实现（五）

r囧r小猫 2024-04-17 05:53 63阅读 0赞

## 1、分布式锁的概述 ##

可以保证在分布式部署的应用集群中，同一个方法在同一时间只能被一台机器-上的一个线程执行。  
避免死锁  
获取锁和释放锁的性能要好

## 2、NoSafeDemo ##

public class NoSafe {
    
        private static CountDownLatch countDownLatch = new CountDownLatch(1);
    
        private static Integer number = 0;
    
        public static void main(String[] args) {
            for (int i = 1; i <= 50; i++) {
                new Thread(() -> {
                    for (int j = 1; j <= 100; j++) {
                        number++;
                    }
                    System.out.println(Thread.currentThread().getName() + "->" + number);
                }, "t" + i).start();
            }
    
            try {
                countDownLatch.await();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
    
        }
    }

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM0MTI1OTk5_size_16_color_FFFFFF_t_70]

## 3、zookeeper实现分布式锁 ##

大体思路：在锁的根节点下创建临时有序节点。获取锁的根节点下所有节点，如果当前节点是根节点的头节点，那么获取成功。如果不是，监听当前节点的前一个节点，监听事件为删除事件。

3.1、zkLock

public interface ZkLock {
        //加锁
        void lock();
        //解锁
        void unlock();
    }

3.2、AbstractZkLock

public abstract class AbstractZkLock implements ZkLock {
    
        public void lock() {
            if (tryLock()) {
                System.out.println(Thread.currentThread().getName()+"获取该锁，执行任务");
            } else {
                //等待
                watiLock();
                //重新获取该锁
                lock();
            }
        }
    
        protected abstract boolean tryLock();
    
    
        public abstract void watiLock();
    }

3.3、ZKLockImpl

public class ZKLockImpl extends AbstractZkLock {
    
        //等待
        private CountDownLatch countDownLatch = null;
        //前一个节点路径
        private String beforeNodePath;
        //当前节点路径
        private String currentNodePath;
        //zkClient
        private ZkClient zkClient = new ZkClient(ZkCommonConsts.ZOOKEEPER_ADDRESS, Integer.MAX_VALUE);
    
        private String BASE_PATH = "/lock";
    
        private String LOCK_PATH = "/lock";
    
        /**
         * 功能描述  尝试获取锁
         *
         * @date 2019/8/24
         */
        @Override
        protected boolean tryLock() {
            //1、判读BASE_PATH是否存在，如果不存在则建立
            if (!zkClient.exists(BASE_PATH)) {
                zkClient.createPersistent(BASE_PATH);
            }
            //2、排号
            if (StringUtils.isBlank(currentNodePath)) {
                currentNodePath = zkClient.createEphemeralSequential(BASE_PATH + LOCK_PATH, "lock");
            }
            //2、获取所有临时节点
            List<String> childrens = zkClient.getChildren(BASE_PATH);
            //3、如果当前锁的路径是列表头，认为得到了锁
            if (currentNodePath.equals(BASE_PATH + "/" + childrens.get(0))) {
                return true;
            }
            //4、如果当前节点不是排名第一，那么记住它前面的值
            else {
                int index = -1;
                for (int i = 0; i < childrens.size(); i++) {
                    if (currentNodePath.equals(BASE_PATH + "/" + childrens.get(i))) {
                        index = i;
                        break;
                    }
                }
                beforeNodePath = BASE_PATH + "/" + childrens.get(index - 1);
                return false;
            }
        }
    
        /**
         * 功能描述 等待锁
         *
         * @author Zrs
         * @date 2019/8/24
         */
        @Override
        public void watiLock() {
            //1、创建一个监听器，监听delete事件
            IZkDataListener listener = new IZkDataListener() {
                @Override
                public void handleDataChange(String s, Object o) throws Exception {
                }
    
                @Override
                public void handleDataDeleted(String s) throws Exception {
                    if (countDownLatch != null) {
                        countDownLatch.countDown();
                    }
                }
            };
            //2、在前一个节点添加wathch事件
            zkClient.subscribeDataChanges(beforeNodePath, listener);
            //3、判读前一个节点是否存在，如果存在那么就等待
            if (zkClient.exists(beforeNodePath)) {
                countDownLatch = new CountDownLatch(1);
                try {
                    countDownLatch.await();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            //4、清除监听事件
            zkClient.unsubscribeDataChanges(beforeNodePath, listener);
        }
    
        /***
         *功能描述 解锁
         */
        @Override
        public void unlock() {
            //删除当前节点
            zkClient.delete(currentNodePath);
            //关闭客户端
            zkClient.close();
        }
    }

3.4、测试

public class TestLock {
    
        private static CountDownLatch countDownLatch = new CountDownLatch(1);
    
        private static Integer number = 0;
    
        public static void main(String[] args) {
            for (int i = 1; i <= 50; i++) {
                new Thread(() -> {
                    ZkLock lock = new ZKLockImpl();
                    try {
                        lock.lock();
                        for (int j = 1; j <= 100; j++) {
                            number++;
                        }
                        System.out.println(Thread.currentThread().getName() + "->" + number);
                    } catch (Exception e) {
                        e.printStackTrace();
                    } finally {
                        lock.unlock();
                    }
                }, "t" + i).start();
            }
    
            try {
                countDownLatch.await();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
    
        }
    }

3.5、结果  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM0MTI1OTk5_size_16_color_FFFFFF_t_70 1]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM0MTI1OTk5_size_16_color_FFFFFF_t_70]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/11/fad63448fb86491da7570980b836c2de.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM0MTI1OTk5_size_16_color_FFFFFF_t_70 1]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/11/ac4316b634614fc2b7bf43cf69dd4956.png