/**
* 基于zookeeper特性实现分布式锁
*
* @author huangwu
*
*/
public class DistributedLock implements Lock, Watcher {
private ZooKeeper zk = null;
// 根节点
private final String ROOT_LOCK = "/locks";
// 竞争的资源
private String lockName;
// 等待的前一个锁
private String WAIT_LOCK;
// 当前锁
private String CURRENT_LOCK;
// 计数器
private CountDownLatch countDownLatch;
//连接锁
private CountDownLatch keepLatch = new CountDownLatch(1);
private int sessionTimeout = 30000;
private List<Exception> exceptionList = new ArrayList<Exception>();
/**
* 配置分布式锁
*
* @param config:zookeeper连接
* @param lockName 竞争锁的名称
*/
public DistributedLock(String config, String lockName) {
this.lockName = lockName;
try {
// 连接zookeeper
zk = new ZooKeeper(config, sessionTimeout, this);
keepLatch.await();
Stat stat = zk.exists(ROOT_LOCK, false);
if (stat == null) {
// 如果根节点不存在,则创建根节点
zk.create(ROOT_LOCK, new byte[0], ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
}
} catch (IOException e) {
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (KeeperException e) {
e.printStackTrace();
}
}
public void process(WatchedEvent event) {
if(event.getState() == KeeperState.SyncConnected) {
keepLatch.countDown();
}
if(event.getType()==EventType.NodeDeleted){
this.countDownLatch.countDown();
}
/*if (this.countDownLatch != null) {
System.out.println("目前状态是:"+event.getType());
}*/
}
public void lock() {
if (exceptionList.size() > 0) {
throw new LockException(exceptionList.get(0));
}
try {
if (this.tryLock()) {
System.out.println(Thread.currentThread().getName() + " " + lockName + "获得了锁");
return;
} else {
// 等待锁
waitForLock(WAIT_LOCK, sessionTimeout);
}
} catch (InterruptedException e) {
e.printStackTrace();
} catch (KeeperException e) {
e.printStackTrace();
}
}
public boolean tryLock() {
try {
String splitStr = "_lock_";
if (lockName.contains(splitStr)) {
throw new LockException("锁名有误");
}
// 创建临时有序节点
CURRENT_LOCK = zk.create(ROOT_LOCK + "/" + lockName + splitStr, new byte[0], ZooDefs.Ids.OPEN_ACL_UNSAFE,
CreateMode.EPHEMERAL_SEQUENTIAL);
System.out.println(CURRENT_LOCK + " 已经创建");
// 取所有子节点
List<String> subNodes = zk.getChildren(ROOT_LOCK, false);
// 取出所有lockName的锁
List<String> lockObjects = new ArrayList<String>();
for (String node : subNodes) {
String _node = node.split(splitStr)[0];
if (_node.equals(lockName)) {
lockObjects.add(node);
}
}
Collections.sort(lockObjects);
System.out.println(Thread.currentThread().getName() + " 的锁是 " + CURRENT_LOCK);
// 若当前节点为最小节点,则获取锁成功
if (CURRENT_LOCK.equals(ROOT_LOCK + "/" + lockObjects.get(0))) {
return true;
}
// 若不是最小节点,则找到自己的前一个节点
String prevNode = CURRENT_LOCK.substring(CURRENT_LOCK.lastIndexOf("/") + 1);
WAIT_LOCK = lockObjects.get(Collections.binarySearch(lockObjects, prevNode) - 1);
} catch (InterruptedException e) {
e.printStackTrace();
} catch (KeeperException e) {
e.printStackTrace();
}
return false;
}
public boolean tryLock(long timeout, TimeUnit unit) throws InterruptedException {
try {
if (this.tryLock()) {
return true;
}
return waitForLock(WAIT_LOCK, timeout);
} catch (Exception e) {
e.printStackTrace();
}
return false;
}
// 等待锁
private boolean waitForLock(String prev, long waitTime) throws KeeperException, InterruptedException {
//注册watch事件
Stat stat = zk.exists(ROOT_LOCK + "/" + prev, true);
if (stat != null) {
System.out.println(Thread.currentThread().getName() + "等待锁 " + ROOT_LOCK + "/" + prev);
this.countDownLatch = new CountDownLatch(1);
// 计数等待,若等到前一个节点消失,则precess中进行countDown,停止等待,获取锁
this.countDownLatch.await(waitTime, TimeUnit.MILLISECONDS);
this.countDownLatch = null;
System.out.println(Thread.currentThread().getName() + " 等到了锁");
}
return true;
}
public void unlock() {
try {
System.out.println(Thread.currentThread().getName() + " 释放锁 " + CURRENT_LOCK);
zk.delete(CURRENT_LOCK, -1);
CURRENT_LOCK = null;
zk.close();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (KeeperException e) {
e.printStackTrace();
}
}
public Condition newCondition() {
// TODO Auto-generated method stub
return null;
}
public void lockInterruptibly() throws InterruptedException {
this.lock();
}
public class LockException extends RuntimeException {
private static final long serialVersionUID = 1L;
public LockException(String e) {
super(e);
}
public LockException(Exception e) {
super(e);
}
}
}