zookeeper实现共享锁

共享锁（Shared Locks，简称S锁），又称为读锁。

如果事务T1对数据对象O1加上了共享锁，那么T1只能对O1进行读操作，其他事务也能同时对O1加共享锁（不能是排他锁），直到O1上的所有共享锁都释放后O1才能被加排他锁。

public class ZookeeperShareLock implements Watcher {
	private ZooKeeper zk;
	String root = "/ty";
	private String path;
	private String currentNode;
	private String waitNode;
	CountDownLatch latch;
	private CountDownLatch cl2 = new CountDownLatch(1);

	public ZookeeperShareLock(String host, String path) {
		this.path = path;
		try {
			zk = new ZooKeeper(host, 50000, this);
			cl2.await();
			System.err.println("开始执行");
		} catch (Exception e) {
			e.printStackTrace();
		}
		try {
			Stat sta = zk.exists(root, false);
			if (null == sta) {
				zk.create(root, new byte[0], ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
			}

		} catch (Exception e) {
			e.printStackTrace();
		}

	}

	public void lock() {
		try {
			currentNode = zk.create(root + "/" + path, new byte[0], ZooDefs.Ids.OPEN_ACL_UNSAFE,
					CreateMode.EPHEMERAL_SEQUENTIAL);
		} catch (Exception e) {
			e.printStackTrace();
		}
		try {
			List<String> lockObjNodes = zk.getChildren(root, false);
			Collections.sort(lockObjNodes); // 排序 //最小的那个 0 1 2 3 4
			if (currentNode.equals(root + "/" + lockObjNodes.get(0))) {
				return;
			} else {
				// lock_0001
				String childZnode = currentNode.substring(currentNode.lastIndexOf("/") + 1);// 获取当前节点
				int num = Collections.binarySearch(lockObjNodes, childZnode);// 当前节点去找下
				// 看看在什么问题
				if (num == 0) {
					num = 1;
				}
				waitNode = lockObjNodes.get(num - 1);
				Stat stat = zk.exists(root + "/" + waitNode, true);
				if (null != stat) {
					latch = new CountDownLatch(1);
					this.latch.await(5000, TimeUnit.MILLISECONDS);
				}
			}

		} catch (Exception e) {
			e.printStackTrace();
		}

	}

	public void unLock() {
		try {
			zk.delete(currentNode, -1);
			currentNode = null;
			// zk.close();
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

	@Override
	public void process(WatchedEvent event) {
		System.out.println("进入 process 。。。。。event = " + event);
		try {
			Thread.sleep(200);
		} catch (InterruptedException e) {
			e.printStackTrace();
		}

		if (event == null) {
			return;
		}

		// 连接状态
		KeeperState keeperState = event.getState();
		// 事件类型
		EventType eventType = event.getType();
		// 受影响的path
		String path = event.getPath();

		String logPrefix = "";
		System.out.println(logPrefix + "收到Watcher通知");
		System.out.println(logPrefix + "连接状态:\t" + keeperState.toString());
		System.out.println(logPrefix + "事件类型:\t" + eventType.toString());

		if (KeeperState.SyncConnected == keeperState) {
			// 成功连接上ZK服务器
			if (EventType.None == eventType) {
				System.out.println("成功连接上ZK服务器");
				cl2.countDown();
			}
			// 删除节点
			else if (EventType.NodeDeleted == eventType) {
				if (null != latch) {
					latch.countDown();
				}
			} else
				;
		} else if (KeeperState.Disconnected == keeperState) {
			System.out.println(logPrefix + "与ZK服务器断开连接");
		} else if (KeeperState.AuthFailed == keeperState) {
			System.out.println(logPrefix + "权限检查失败");
		} else if (KeeperState.Expired == keeperState) {
			System.out.println(logPrefix + "会话失效");
		} else
			;

		System.out.println("--------------------------------------------");

	}
}