构建zookeeper分布式锁

代码展示：

//定义接口
public interface ZKLock {

    boolean lock(String lockpath);
    boolean unlock(String lockpath);
}

//实现分布式锁
@Slf4j
public class ZKLockImpl implements ZKLock,InitializingBean {

    private final static String LOCK_ROOT_PATH = "/ZkLock";
    private Map<String,CountDownLatch> concurrentMap = new ConcurrentHashMap<>();
    private ReentrantLock lock = new ReentrantLock();
    @Autowired
    private CuratorFramework curatorFramework;

    @Override
    public boolean lock(String lockpath) {
        boolean result = false;
        String keyPath = LOCK_ROOT_PATH + lockpath;
        try {
            curatorFramework
                    .create()
                    .creatingParentsIfNeeded()
                    .withMode(CreateMode.EPHEMERAL)
                    .withACL(ZooDefs.Ids.OPEN_ACL_UNSAFE)
                    .forPath(keyPath);
            result = true;
            log.info("success to acquire mutex lock for path:{}",keyPath);
        } catch (Exception e) {
            log.info("Thread:{};failed to acquire mutex lock for path:{}",Thread.currentThread().getName(),keyPath);
            if(!concurrentMap.containsKey(lockpath)){
                try {
                    /*
                     * 这里考虑到高并发场景,必须保证对同一个节点加锁的线程失败后是落在同一个countdown对象上
                     * ,否则有的线程永远没有办法唤醒了
                     */
                    lock.lock();
                    //双重校验,考虑高并发问题
                    if(!concurrentMap.containsKey(lockpath)){
                        concurrentMap.put(lockpath,new CountDownLatch(1));
                    }
                } finally {
                    lock.unlock();
                }
            }
            try {
                CountDownLatch countDownLatch = concurrentMap.get(lockpath);
                //这里为什么要判断呢？大家可以思考一下,高并发场景
                if(countDownLatch != null){
                    countDownLatch.await();
                }
            } catch (InterruptedException e1) {
                log.info("InterruptedException message:{}",e1.getMessage());
            }
        }
        return result;
    }

    @Override
    public boolean unlock(String lockpath) {
        String keyPath = LOCK_ROOT_PATH + lockpath;
        try {
            if(curatorFramework.checkExists().forPath(keyPath) != null){
                curatorFramework.delete().forPath(keyPath);
            }
        } catch (Exception e) {
            log.error("failed to release mutex lock");
            return false;
        }
        return true;
    }

    /**
     * 监听节点事件
     * @param lockPath
     *       加锁的路径
     */
    private void addWatcher(String lockPath) throws Exception {
        String keyPath;
        if(LOCK_ROOT_PATH.equals(lockPath)){
            keyPath = lockPath;
        }else{
            keyPath = LOCK_ROOT_PATH + lockPath;
        }

        final PathChildrenCache cache = new PathChildrenCache(curatorFramework,keyPath,false);
        cache.start(PathChildrenCache.StartMode.POST_INITIALIZED_EVENT);

        /*
         * 添加监听器
         */
        cache.getListenable().addListener((client,event) -> {
            if(event.getType().equals(PathChildrenCacheEvent.Type.CHILD_REMOVED)){
                String oldPath = event.getData().getPath();
                log.info("oldPath delete:{},redis缓存已经更新！",oldPath);
                if(oldPath.contains(lockPath)){
                    //TODO 释放计数器，释放锁
                    CountDownLatch countDownLatch = concurrentMap.remove(oldPath);
                    if(countDownLatch != null){//有可能没有竞争,countdown不存在
                        countDownLatch.countDown();
                    }
                }
            }
        });
    }

    @Override
    public void afterPropertiesSet() {
        curatorFramework = curatorFramework.usingNamespace("zklock-namespace");
        //zk锁的根路径 不存在则创建
        try {
            if(curatorFramework.checkExists().forPath(LOCK_ROOT_PATH) == null){
                curatorFramework
                        .create()
                        .creatingParentsIfNeeded()
                        .withMode(CreateMode.PERSISTENT)
                        .withACL(ZooDefs.Ids.OPEN_ACL_UNSAFE)
                        .forPath(LOCK_ROOT_PATH);
            }
            //启动监听器
            addWatcher(LOCK_ROOT_PATH);
        } catch (Exception e) {
            log.error("connect zookeeper failed:{}",e.getMessage(),e);
        }
    }
}