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分布式锁实现--基于zookeeper和redis的两种方案

分类: 文章 • 2024-11-22 09:05:57

前言：

 最近项目中需要一个定时任务,由于是集群环境,自然而然想到需要通过分布式锁来保证单台执行。查阅相关资料总结了一下实现分布式锁的两种实现方案。


分布式锁的由来：

在程序开发过程中不得不考虑的就是并发问题。在java中对于同一个jvm而言，jdk已经提供了lock和同步等。但是在分布式情况下，往往存在多个进程对一些资源产生竞争关系，而这些进程往往在不同的机器上，这个时候jdk中提供的已经不能满足。分布式锁顾明思议就是可以满足分布式情况下的并发锁。

方案一：基于zookeeper实现分布式锁

基于ZooKeeper分布式锁的流程

  • 在zookeeper指定节点（locks）下创建临时顺序节点node_n
  • 获取locks下所有子节点children
  • 对子节点按节点自增序号从小到大排序
  • 判断本节点是不是第一个子节点，若是，则获取锁；若不是，则监听比该节点小的那个节点的删除事件
  • 若监听事件生效，则回到第二步重新进行判断，直到获取到锁

流程图：

分布式锁实现--基于zookeeper和redis的两种方案


具体实现

下面就具体使用java和zookeeper实现分布式锁，操作zookeeper使用的是apache提供的zookeeper的包。

  • 通过实现Watch接口，实现process(WatchedEvent event)方法来实施监控，使CountDownLatch来完成监控，在等待锁的时候使用CountDownLatch来计数，等到后进行countDown，停止等待，继续运行。
  • 以下整体流程基本与上述描述流程一致，只是在监听的时候使用的是CountDownLatch来监听前一个节点
实现代码：

public class DistributedLock implements Lock, Watcher {
    private ZooKeeper zk = null;
    // 根节点 private 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;
    private int sessionTimeout = 30000;
    private List<Exception> exceptionList = new ArrayList<Exception>();

    /** * 配置分布式锁 * @param config 连接的url * @param lockName 竞争资源 */ public DistributedLock(String config, String lockName) {
        this.lockName = lockName;
        try {
            // 连接zookeeper zk = new ZooKeeper(config, sessionTimeout, this);
            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();
        }
    }

    // 节点监视器 @Override public void process(WatchedEvent event) {
        if (this.countDownLatch != null) {
            this.countDownLatch.countDown();
        }
    }

    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) {
        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 {
        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("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() {
        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);
        }
    }
}

方案二：基于redis实现分布式锁

话不多说了直接上例子吧！

mport org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.core.ValueOperations;

import java.io.Serializable;
import java.util.concurrent.TimeUnit;

/**
 * @author yekeping
 * @Title: ${file_name}
 * @Package ${package_name}
 * @Description: ${todo}
 * @date 2018/7/59:25
 */
public class DistributedLock{
    private String regionName;
    private Long expire = 0l;

    protected RedisTemplate<Serializable, Serializable> redisTemplate;

    private Serializable key(Serializable key) {
        if(regionName != null && regionName.length() > 0){
            return regionName + "." + String.valueOf(key);
        }
        return key;
    }

    private ValueOperations<Serializable, Serializable> opsForValue(){
        return redisTemplate.opsForValue();
    }


    public void set(Serializable key, Serializable value) {
        if (expire != null && expire > 0) {
            opsForValue().set(key(key), value, expire, TimeUnit.SECONDS);
        } else {
            opsForValue().set(key(key), value);
        }
    }


    public void set(Serializable key, Serializable value, Long _expire, TimeUnit expireTimeUnit) {
        if (_expire == null || _expire <= 0) {
            set(key, value);
        } else {
            redisTemplate.opsForValue().set(key(key), value, _expire, expireTimeUnit);
        }
    }


    public Serializable get(Serializable key) {
        return redisTemplate.opsForValue().get(key(key));
    }


    public void delete(Serializable key) {
        redisTemplate.delete(key(key));
    }


    public Serializable getAndSet(Serializable key, Serializable newValue) {
        return opsForValue().getAndSet(key(key), newValue);
    }


    public boolean setNotExist(Serializable key, Serializable value) {
        return opsForValue().setIfAbsent(key(key), value);
    }


    public boolean lock(Serializable lockKey, Long expireTimeOut, TimeUnit expireTimeUnit, Long lockTimeOut,TimeUnit lockTimeUnit) {
        long start = System.currentTimeMillis();
        long timeout = lockTimeUnit.toMillis(lockTimeOut); // if !useTimeout,
        boolean useTimeout = timeout > 0;
        while (useTimeout ? isTimeout(start, timeout) : true) {
            Serializable lockExpireTime = System.currentTimeMillis() + expireTimeUnit.toMillis(expireTimeOut) + 1;// 锁超时时间
            if (setNotExist(lockKey, lockExpireTime)) { // 获取到锁
                return true;
            }
            Serializable value = get(lockKey);
            if (value != null && timeExpired(value)) {
                // 假设多个线程(非单jvm)同时走到这里
                Serializable oldValue = getAndSet(lockKey, lockExpireTime);// 获取并设置新值，此操作是原子性的
                // 但是走到这里时每个线程拿到的oldValue肯定不可能一样(因为getset是原子性的)
                // 加入拿到的oldValue依然是expired的，那么就说明拿到锁了
                if (oldValue != null && timeExpired(oldValue)) {
                    return true;
                }
            }
        }
        return false;
    }


    public boolean tryLock(Serializable lockKey, Long expireTimeOut, TimeUnit expireTimeUnit) {
        long lockExpireTime = System.currentTimeMillis() + expireTimeUnit.toMillis(expireTimeOut) + 1;// 锁超时时间
        if (setNotExist(lockKey, lockExpireTime)) { // 获取到锁
            return true;
        }
        if (timeExpired(get(lockKey))) { // lock is expired
            // 假设多个线程(非单jvm)同时走到这里
            Serializable oldValue = getAndSet(lockKey, lockExpireTime); //getAndSet是原子性的
            // 但是走到这里时每个线程拿到的oldValue肯定不可能一样(因为getAndSet是原子性的)
            // 加入拿到的oldValue依然是expired的，那么就说明拿到锁了
            if (oldValue != null && timeExpired(oldValue)) {
                return true;
            }
        }
        return false;
    }


    public void unlock(Serializable lockKey) {
        delete(lockKey);
    }

    private boolean timeExpired(Serializable value) {
        return Long.parseLong(String.valueOf(value)) < System.currentTimeMillis();
    }

    private boolean isTimeout(long start, long timeout) {
        return start + timeout > System.currentTimeMillis();
    }

    public void setRedisTemplate(RedisTemplate<Serializable, Serializable> redisTemplate) {
        this.redisTemplate = redisTemplate;
    }

    public void setRegionName(String regionName) {
        this.regionName = regionName;
    }

    public void setExpire(Long expire) {
        this.expire = expire;
    }

}

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