基於zk「臨時順序節點「的分佈式鎖

import org.apache.zookeeper.*;
import org.apache.zookeeper.data.Stat;

import java.io.IOException;
import java.util.List;
import java.util.concurrent.CountDownLatch;

/**
 * Created by zzq on 2019/6/25.
 */
public class ZKLock implements Watcher {
    private ZooKeeper zk;
    //當前鎖
    private String currentLock;
    //資源名稱
    private String lockName;
    //鎖根節點
    private String ROOT_LOCK = "/root_lock";
    //鎖的各個資源根節點
    private String tmpRootLock;
    //因爲zookeeper監聽節點狀態會當即返回，因此須要使用CountDownLatch(也可以使用信號量等其餘機制)
    private CountDownLatch latch;

    public ZKLock(String zkAddress, String lockName) {
        this.lockName = "" + System.nanoTime();
        try {
            zk = new ZooKeeper(zkAddress, 30000, this);
            createZNode(ROOT_LOCK, CreateMode.PERSISTENT);
            tmpRootLock = ROOT_LOCK + "/" + lockName;
            createZNode(tmpRootLock, CreateMode.PERSISTENT);//****zk臨時節點下不能建立臨時順序節點
        } catch (IOException e) {
            e.printStackTrace();
        } catch (KeeperException e) {
            e.printStackTrace();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    private void createZNode(String node, CreateMode mode) throws KeeperException, InterruptedException {
        //獲取根節點狀態
        Stat stat = zk.exists(node, false);
        //若是根節點不存在，則建立根節點，根節點類型爲永久節點
        if (stat == null) {
            zk.create(node, new byte[0], ZooDefs.Ids.OPEN_ACL_UNSAFE, mode);
        }
    }

    public void lock() {
        try {
            //在根節點下建立臨時順序節點，返回值爲建立的節點路徑
            currentLock = zk.create(tmpRootLock + "/" + lockName, new byte[0],
                    ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);
            //獲取根節點下的全部臨時順序節點，不設置監視器
            List<String> children = zk.getChildren(tmpRootLock, false);
            //對根節點下的全部臨時順序節點進行從小到大排序
            children.sort(null);
            //判斷當前節點是否爲最小節點，若是是則獲取鎖，若不是，則找到本身的前一個節點，監聽其存在狀態
            int curIndex = children.indexOf(currentLock.substring(currentLock.lastIndexOf("/") + 1));
            if (curIndex != 0) {
                //獲取當前節點前一個節點的路徑
                String prev = children.get(curIndex - 1);
                //監聽當前節點的前一個節點的狀態，null則節點不存在
                Stat stat = zk.exists(tmpRootLock + "/" + prev, true);
                //此處再次判斷該節點是否存在
                if (stat != null) {
                    latch = new CountDownLatch(1);
                    //進入等待鎖狀態
                    latch.await();
                    latch = null;
                }
            }
        } catch (KeeperException e) {
            e.printStackTrace();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    //釋放鎖
    public void unlock() {
        try {
            //刪除建立的節點
            zk.delete(currentLock, -1);
            List<String> children = zk.getChildren(tmpRootLock, false);
            if (children.size() == 0) {
                zk.delete(tmpRootLock, -1);
                //關閉zookeeper鏈接
                zk.close();
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (KeeperException e) {
            e.printStackTrace();
        }
        currentLock = null;
    }

    @Override
    public void process(WatchedEvent event) {
        if (this.latch != null) {
            latch.countDown();
        }
    }

    public static void main(String[] args) throws Exception {
        for (int i = 0; i < 7; i++) {
//            new Thread(new Runnable() {
//                @Override
//                public void run() {
//                    ZKLock lock = new ZKLock("10.10.210.123:2181", "lock");
//                    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
//                    lock.lock();
//                }
//            }).start();
        }
        ZKLock lock = new ZKLock("10.10.210.123:2181", "L1");
        lock.lock();

        ZKLock lock1 = new ZKLock("10.10.210.123:2181", "L2");
        lock1.lock();
        lock1.unlock();

        lock.unlock();
        String uu = "";
    }
}