Java分布式锁三种实现方案

96
蓝汀华韶
0.5 2016.10.09 15:09* 字数 1302
方案一:数据库乐观锁

乐观锁通常实现基于数据版本(version)的记录机制实现的,比如有一张红包表(t_bonus),有一个字段(left_count)记录礼物的剩余个数,用户每领取一个奖品,对应的left_count减1,在并发的情况下如何要保证left_count不为负数,乐观锁的实现方式为在红包表上添加一个版本号字段(version),默认为0。

异常实现流程
-- 可能会发生的异常情况
-- 线程1查询,当前left_count为1,则有记录
select * from t_bonus where id = 10001 and left_count > 0

-- 线程2查询,当前left_count为1,也有记录
select * from t_bonus where id = 10001 and left_count > 0

-- 线程1完成领取记录,修改left_count为0,
update t_bonus set left_count = left_count - 1 where id = 10001

-- 线程2完成领取记录,修改left_count为-1,产生脏数据
update t_bonus set left_count = left_count - 1 where id = 10001
通过乐观锁实现

-- 添加版本号控制字段
ALTER TABLE table ADD COLUMN version INT DEFAULT '0' NOT NULL AFTER t_bonus;

-- 线程1查询,当前left_count为1,则有记录,当前版本号为1234
select left_count, version from t_bonus where id = 10001 and left_count > 0

-- 线程2查询,当前left_count为1,有记录,当前版本号为1234
select left_count, version from t_bonus where id = 10001 and left_count > 0

-- 线程1,更新完成后当前的version为1235,update状态为1,更新成功
update t_bonus set version = 1235, left_count = left_count-1 where id = 10001 and version = 1234

-- 线程2,更新由于当前的version为1235,udpate状态为0,更新失败,再针对相关业务做异常处理
update t_bonus set version = 1235, left_count = left_count-1 where id = 10001 and version = 1234
方案二:基于Redis的分布式锁

SETNX命令(SET if Not eXists)
语法:SETNX key value
功能:原子性操作,当且仅当 key 不存在,将 key 的值设为 value ,并返回1;若给定的 key 已经存在,则 SETNX 不做任何动作,并返回0。
Expire命令
语法:expire(key, expireTime)
功能:key设置过期时间
GETSET命令
语法:GETSET key value
功能:将给定 key 的值设为 value ,并返回 key 的旧值 (old value),当 key 存在但不是字符串类型时,返回一个错误,当key不存在时,返回nil。
GET命令
语法:GET key
功能:返回 key 所关联的字符串值,如果 key 不存在那么返回特殊值 nil 。
DEL命令
语法:DEL key [KEY …]
功能:删除给定的一个或多个 key ,不存在的 key 会被忽略。

第一种:使用redis的setnx()、expire()方法,用于分布式锁
  1. setnx(lockkey, 1) 如果返回0,则说明占位失败;如果返回1,则说明占位成功
  2. expire()命令对lockkey设置超时时间,为的是避免死锁问题。
  3. 执行完业务代码后,可以通过delete命令删除key。

这个方案其实是可以解决日常工作中的需求的,但从技术方案的探讨上来说,可能还有一些可以完善的地方。比如,如果在第一步setnx执行成功后,在expire()命令执行成功前,发生了宕机的现象,那么就依然会出现死锁的问题

第二种:使用redis的setnx()、get()、getset()方法,用于分布式锁,解决死锁问题
  1. setnx(lockkey, 当前时间+过期超时时间) ,如果返回1,则获取锁成功;如果返回0则没有获取到锁,转向2。
  2. get(lockkey)获取值oldExpireTime ,并将这个value值与当前的系统时间进行比较,如果小于当前系统时间,则认为这个锁已经超时,可以允许别的请求重新获取,转向3。
  3. 计算newExpireTime=当前时间+过期超时时间,然后getset(lockkey, newExpireTime) 会返回当前lockkey的值currentExpireTime。
  4. 判断currentExpireTime与oldExpireTime 是否相等,如果相等,说明当前getset设置成功,获取到了锁。如果不相等,说明这个锁又被别的请求获取走了,那么当前请求可以直接返回失败,或者继续重试。
  5. 在获取到锁之后,当前线程可以开始自己的业务处理,当处理完毕后,比较自己的处理时间和对于锁设置的超时时间,如果小于锁设置的超时时间,则直接执行delete释放锁;如果大于锁设置的超时时间,则不需要再锁进行处理。

import cn.com.tpig.cache.redis.RedisService;
import cn.com.tpig.utils.SpringUtils;

/**
 * Created by IDEA
 * User: shma1664
 * Date: 2016-08-16 14:01
 * Desc: redis分布式锁
 */
public final class RedisLockUtil {

    private static final int defaultExpire = 60;

    private RedisLockUtil() {
        //
    }

    /**
     * 加锁
     * @param key redis key
     * @param expire 过期时间,单位秒
     * @return true:加锁成功,false,加锁失败
     */
    public static boolean lock(String key, int expire) {

        RedisService redisService = SpringUtils.getBean(RedisService.class);
        long status = redisService.setnx(key, "1");

        if(status == 1) {
            redisService.expire(key, expire);
            return true;
        }

        return false;
    }

    public static boolean lock(String key) {
        return lock2(key, defaultExpire);
    }

    /**
     * 加锁
     * @param key redis key
     * @param expire 过期时间,单位秒
     * @return true:加锁成功,false,加锁失败
     */
    public static boolean lock2(String key, int expire) {

        RedisService redisService = SpringUtils.getBean(RedisService.class);

        long value = System.currentTimeMillis() + expire;
        long status = redisService.setnx(key, String.valueOf(value));

        if(status == 1) {
            return true;
        }
        long oldExpireTime = Long.parseLong(redisService.get(key, "0"));
        if(oldExpireTime < System.currentTimeMillis()) {
            //超时
            long newExpireTime = System.currentTimeMillis() + expire;
            long currentExpireTime = Long.parseLong(redisService.getSet(key, String.valueOf(newExpireTime)));
            if(currentExpireTime == oldExpireTime) {
                return true;
            }
        }
        return false;
    }

    public static void unLock1(String key) {
        RedisService redisService = SpringUtils.getBean(RedisService.class);
        redisService.del(key);
    }

    public static void unLock2(String key) {    
        RedisService redisService = SpringUtils.getBean(RedisService.class);    
        long oldExpireTime = Long.parseLong(redisService.get(key, "0"));   
        if(oldExpireTime > System.currentTimeMillis()) {        
            redisService.del(key);    
        }
   }

}

public void drawRedPacket(long userId) {
    String key = "draw.redpacket.userid:" + userId;

    boolean lock = RedisLockUtil.lock2(key, 60);
    if(lock) {
        try {
            //领取操作
        } finally {
            //释放锁
            RedisLockUtil.unLock(key);
        }
    } else {
        new RuntimeException("重复领取奖励");
    }
}
Spring AOP基于注解方式和SpEL实现开箱即用的redis分布式锁策略
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * RUNTIME
 * 定义注解
 * 编译器将把注释记录在类文件中,在运行时 VM 将保留注释,因此可以反射性地读取。
 * @author shma1664
 *
 */
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface RedisLockable {


    String[] key() default "";

    long expiration() default 60;
}
import javax.annotation.Resource;

import java.lang.reflect.Method;

import com.autohome.api.dealer.util.cache.RedisClient;
import com.google.common.base.Joiner;
import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.Signature;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Pointcut;
import org.aspectj.lang.reflect.MethodSignature;
import org.springframework.expression.EvaluationContext;
import org.springframework.expression.Expression;
import org.springframework.expression.ExpressionParser;
import org.springframework.expression.spel.standard.SpelExpressionParser;
import org.springframework.expression.spel.support.StandardEvaluationContext;
import org.springframework.stereotype.Component;

/**
 * Created by IDEA
 * User: mashaohua
 * Date: 2016-09-28 18:08
 * Desc:
 */
@Aspect
@Component
public class RedisLockAop {

    @Resource
    private RedisClient redisClient;

    @Pointcut("execution(* com.autohome.api.dealer.tuan.service.*.*(..))")
    public void pointcut(){}

    @Around("pointcut()")
    public Object doAround(ProceedingJoinPoint point) throws Throwable{
        Signature signature = point.getSignature();
        MethodSignature methodSignature = (MethodSignature) signature;
        Method method = methodSignature.getMethod();
        String targetName = point.getTarget().getClass().getName();
        String methodName = point.getSignature().getName();
        Object[] arguments = point.getArgs();

        if (method != null && method.isAnnotationPresent(RedisLockable.class)) {
            RedisLockable redisLock = method.getAnnotation(RedisLockable.class);
            long expire = redisLock.expiration();
            String redisKey = getLockKey(targetName, methodName, redisLock.key(), arguments);
            boolean isLock = RedisLockUtil.lock2(redisKey, expire);
            if(!isLock) {
                try {
                    return point.proceed();
                } finally {
                    unLock2(redisKey);
                }
            } else {
                throw new RuntimeException("您的操作太频繁,请稍后再试");
            }
        }

        return point.proceed();
    }

    private String getLockKey(String targetName, String methodName, String[] keys, Object[] arguments) {

        StringBuilder sb = new StringBuilder();
        sb.append("lock.").append(targetName).append(".").append(methodName);

        if(keys != null) {
            String keyStr = Joiner.on(".").skipNulls().join(keys);
            String[] parameters = ReflectParamNames.getNames(targetName, methodName);
            ExpressionParser parser = new SpelExpressionParser();
            Expression expression = parser.parseExpression(keyStr);
            EvaluationContext context = new StandardEvaluationContext();
            int length = parameters.length;
            if (length > 0) {
                for (int i = 0; i < length; i++) {
                    context.setVariable(parameters[i], arguments[i]);
                }
            }
            String keysValue = expression.getValue(context, String.class);
            sb.append("#").append(keysValue);
        }
        return sb.toString();
    }

<!-- https://mvnrepository.com/artifact/javassist/javassist -->
<dependency>
    <groupId>org.javassist</groupId>
    <artifactId>javassist</artifactId>
    <version>3.18.1-GA</version>
</dependency>
import javassist.*;
import javassist.bytecode.CodeAttribute;
import javassist.bytecode.LocalVariableAttribute;
import javassist.bytecode.MethodInfo;
import org.apache.log4j.Logger;

/**
 * Created by IDEA
 * User: mashaohua
 * Date: 2016-09-28 18:39
 * Desc:
 */
public class ReflectParamNames {
    private static Logger log = Logger.getLogger(ReflectParamNames.class);
    private  static ClassPool pool = ClassPool.getDefault();

    static{
        ClassClassPath classPath = new ClassClassPath(ReflectParamNames.class);
        pool.insertClassPath(classPath);
    }

    public static String[] getNames(String className,String methodName) {
        CtClass cc = null;
        try {
            cc = pool.get(className);
            CtMethod cm = cc.getDeclaredMethod(methodName);
            // 使用javaassist的反射方法获取方法的参数名
            MethodInfo methodInfo = cm.getMethodInfo();
            CodeAttribute codeAttribute = methodInfo.getCodeAttribute();
            LocalVariableAttribute attr = (LocalVariableAttribute) codeAttribute.getAttribute(LocalVariableAttribute.tag);
            if (attr == null) return new String[0];

            int begin = 0;

            String[] paramNames = new String[cm.getParameterTypes().length];
            int count = 0;
            int pos = Modifier.isStatic(cm.getModifiers()) ? 0 : 1;

            for (int i = 0; i < attr.tableLength(); i++){
                //  为什么 加这个判断,发现在windows 跟linux执行时,参数顺序不一致,通过观察,实际的参数是从this后面开始的
                if (attr.variableName(i).equals("this")){
                    begin = i;
                    break;
                }
            }

            for (int i = begin+1; i <= begin+paramNames.length; i++){
                paramNames[count] = attr.variableName(i);
                count++;
            }
            return paramNames;
        } catch (Exception e) {
            e.printStackTrace();
        }finally{
            try {
                if(cc != null) cc.detach();
            } catch (Exception e2) {
                log.error(e2.getMessage());
            }


        }
        return new String[0];
    }
}
在需要使用分布式锁的地方添加注解
/**
 * 抽奖接口
 * 添加redis分布式锁保证一个订单只有一个请求处理,防止用户刷礼物,支持SpEL表达式
 * redisLockKey:lock.com.autohome.api.dealer.tuan.service.impl.drawBonus#orderId
 * @param orderId 订单id
 * @return 抽中的奖品信息
 */
@RedisLockable(key = {"#orderId"}, expiration = 120)
@Override
public BonusConvertBean drawBonus(Integer orderId) throws BonusException{
    // 业务逻辑
}
第三种方案:基于Zookeeper的分布式锁
利用节点名称的唯一性来实现独占锁

ZooKeeper机制规定同一个目录下只能有一个唯一的文件名,zookeeper上的一个znode看作是一把锁,通过createznode的方式来实现。所有客户端都去创建/lock/${lock_name}_lock节点,最终成功创建的那个客户端也即拥有了这把锁,创建失败的可以选择监听继续等待,还是放弃抛出异常实现独占锁。

package com.shma.example.zookeeper.lock;

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

/**
 * Created by IDEA
 * User: mashaohua
 * Date: 2016-09-30 16:09
 * Desc:
 */
public class ZookeeperLock implements Lock, Watcher {
    private ZooKeeper zk;
    private String root = "/locks";//根
    private String lockName;//竞争资源的标志
    private String myZnode;//当前锁
    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 ZookeeperLock(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);
        }
    }

    @Override
    public void lock() {
        if(exception.size() > 0){
            throw new LockException(exception.get(0));
        }
        if(!tryLock()) {
            throw new LockException("您的操作太频繁,请稍后再试");
        }
    }

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

    @Override
    public boolean tryLock() {
        try {
            myZnode = zk.create(root + "/" + lockName, new byte[0], ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
            return true;
        } catch (KeeperException e) {
            e.printStackTrace();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        return false;
    }

    @Override
    public boolean tryLock(long time, TimeUnit unit) throws InterruptedException {
        return tryLock();
    }

    @Override
    public void unlock() {
        try {
            zk.delete(myZnode, -1);
            myZnode = null;
            zk.close();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (KeeperException e) {
            e.printStackTrace();
        }
    }

    @Override
    public Condition newCondition() {
        return null;
    }

    @Override
    public void process(WatchedEvent watchedEvent) {
        //
    }

}

ZookeeperLock lock = null;
try {
    lock = new ZookeeperLock("127.0.0.1:2182","test1");
    lock.lock();
    //业务逻辑处理
} catch (LockException e) {
    throw e;
} finally {
    if(lock != null)
        lock.unlock();
}
利用临时顺序节点控制时序实现

/lock已经预先存在,所有客户端在它下面创建临时顺序编号目录节点,和选master一样,编号最小的获得锁,用完删除,依次方便。
算法思路:对于加锁操作,可以让所有客户端都去/lock目录下创建临时顺序节点,如果创建的客户端发现自身创建节点序列号是/lock/目录下最小的节点,则获得锁。否则,监视比自己创建节点的序列号小的节点(比自己创建的节点小的最大节点),进入等待。
对于解锁操作,只需要将自身创建的节点删除即可。

package com.shma.example.zookeeper.lock;

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;

/**
 * Created by IDEA
 * User: mashaohua
 * Date: 2016-09-30 16:09
 * Desc:
 */
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);
        }
    }

}

https://github.com/shawntime/shawn-common-utils/tree/master/src/main/java/com/shawntime/common/lock

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