使用Zookeeper实现分布式共享锁

分布式系统中经常需要协调多进程，多个jvm，或者多台机器之间的同步问题，得益于zookeeper，实现了一个分布式的共享锁，方便在多台服务器之间竞争资源时，来协调各系统之间的协作和同步。

package com.concurrent;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;

import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooDefs;
import org.apache.zookeeper.ZooKeeper;
import org.apache.zookeeper.data.Stat;

/**
   DistributedLock lock = null;
 try {
  lock = new DistributedLock("127.0.0.1:2182","test");
  lock.lock();
  //do something...
 } catch (Exception e) {
  e.printStackTrace();
 }
 finally {
  if(lock != null)
   lock.unlock();
 }
 * @author xueliang
 *
 */
public class DistributedLock implements Lock, Watcher{
 private ZooKeeper zk;
 private String root = "/locks";//根
 private String lockName;//竞争资源的标志
 private String waitNode;//等待前一个锁
 private String myZnode;//当前锁
 private CountDownLatch latch;//计数器
 private int sessionTimeout = 30000;
 private List<Exception> exception = new ArrayList<Exception>();
 
 /**
  * 创建分布式锁,使用前请确认config配置的zookeeper服务可用
  * @param config 127.0.0.1:2181
  * @param lockName 竞争资源标志,lockName中不能包含单词lock
  */
 public DistributedLock(String config, String lockName){
  this.lockName = lockName;
  // 创建一个与服务器的连接
  try {
   zk = new ZooKeeper(config, sessionTimeout, this);
   Stat stat = zk.exists(root, false);
   if(stat == null){
    // 创建根节点
    zk.create(root, new byte[0], ZooDefs.Ids.OPEN_ACL_UNSAFE,CreateMode.PERSISTENT);
   }
  } catch (IOException e) {
   exception.add(e);
  } catch (KeeperException e) {
   exception.add(e);
  } catch (InterruptedException e) {
   exception.add(e);
  }
 }

 /**
  * zookeeper节点的监视器
  */
 public void process(WatchedEvent event) {
  if(this.latch != null) { 
            this.latch.countDown(); 
        }
 }
 
 public void lock() {
  if(exception.size() > 0){
   throw new LockException(exception.get(0));
  }
  try {
   if(this.tryLock()){
    System.out.println("Thread " + Thread.currentThread().getId() + " " +myZnode + " get lock true");
    return;
   }
   else{
    waitForLock(waitNode, sessionTimeout);//等待锁
   }
  } catch (KeeperException e) {
   throw new LockException(e);
  } catch (InterruptedException e) {
   throw new LockException(e);
  }
 }

 public boolean tryLock() {
  try {
   String splitStr = "_lock_";
   if(lockName.contains(splitStr))
    throw new LockException("lockName can not contains \\u000B");
   //创建临时子节点
   myZnode = zk.create(root + "/" + lockName + splitStr, new byte[0], ZooDefs.Ids.OPEN_ACL_UNSAFE,CreateMode.EPHEMERAL_SEQUENTIAL);
   System.out.println(myZnode + " is created ");
   //取出所有子节点
   List<String> subNodes = zk.getChildren(root, false);
   //取出所有lockName的锁
   List<String> lockObjNodes = new ArrayList<String>();
   for (String node : subNodes) {
    String _node = node.split(splitStr)[0];
    if(_node.equals(lockName)){
     lockObjNodes.add(node);
    }
   }
   Collections.sort(lockObjNodes);
   System.out.println(myZnode + "==" + lockObjNodes.get(0));
   if(myZnode.equals(root+"/"+lockObjNodes.get(0))){
    //如果是最小的节点,则表示取得锁
            return true;
        }
   //如果不是最小的节点，找到比自己小1的节点
   String subMyZnode = myZnode.substring(myZnode.lastIndexOf("/") + 1);
   waitNode = lockObjNodes.get(Collections.binarySearch(lockObjNodes, subMyZnode) - 1);
  } catch (KeeperException e) {
   throw new LockException(e);
  } catch (InterruptedException e) {
   throw new LockException(e);
  }
  return false;
 }

 public boolean tryLock(long time, TimeUnit unit) {
  try {
   if(this.tryLock()){
    return true;
   }
        return waitForLock(waitNode,time);
  } catch (Exception e) {
   e.printStackTrace();
  }
  return false;
 }

 private boolean waitForLock(String lower, long waitTime) throws InterruptedException, KeeperException {
        Stat stat = zk.exists(root + "/" + lower,true);
        //判断比自己小一个数的节点是否存在,如果不存在则无需等待锁,同时注册监听
        if(stat != null){
         System.out.println("Thread " + Thread.currentThread().getId() + " waiting for " + root + "/" + lower);
         this.latch = new CountDownLatch(1);
         this.latch.await(waitTime, TimeUnit.MILLISECONDS);
         this.latch = null;
        }
        return true;
    }

 public void unlock() {
  try {
   System.out.println("unlock " + myZnode);
   zk.delete(myZnode,-1);
   myZnode = null;
   zk.close();
  } catch (InterruptedException e) {
   e.printStackTrace();
  } catch (KeeperException e) {
   e.printStackTrace();
  }
 }

 public void lockInterruptibly() throws InterruptedException {
  this.lock();
 }

 public Condition newCondition() {
  return null;
 }
 
 public class LockException extends RuntimeException {
  private static final long serialVersionUID = 1L;
  public LockException(String e){
   super(e);
  }
  public LockException(Exception e){
   super(e);
  }
 }

 }