Redis

关注公众号 jb51net

关闭
首页 > 数据库 > Redis > Redis单机锁和分布式锁

Redis+IDEA实现单机锁和分布式锁的过程

作者:kkoneone11

这篇文章主要介绍了Redis+IDEA实现单机锁和分布式锁的过程,本文通过示例代码给大家介绍的非常详细,对大家的学习或工作具有一定的参考借鉴价值,需要的朋友可以参考下

单机下:

只适用于单机环境下(单个JVM),多个客户端访问同一个服务器

1.synchronized

package com.cloud.SR.controller;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import javax.annotation.Resource;
@RestController
public class TestConrtoller1 {
    @Value("${server.port}")
    private String serverPort;
    @Resource
    private StringRedisTemplate stringRedisTemplate;
    @GetMapping("/buy1")
    public String shopping(){
        synchronized (this){
            String result = stringRedisTemplate.opsForValue().get("goods:001");
            int total = result == null? 0 :Integer.parseInt(s);
            if(total > 0){
                int realTotal = total - 1;
                stringRedisTemplate.opsForValue().set("goods:001",String.valueOf(realCount ));
                System.out.println("剩余商品为:"+realCount +",提供服务的端口号:"+serverPort);
                return "剩余商品为:"+realTotal +",提供服务的端口号:"+serverPort;
            }else{
                System.out.println("购买商品失败!");
            }
            return "购买商品失败!";
        }
    }
}
 

2.ReentrantLock

@RestController
public class TestConrtoller2 {
    @Value("${server.port}")
    private String serverPort;
    // 使用ReentrantLock锁解决单体应用的并发问题
    Lock lock = new ReentrantLock();
    @Autowired
    StringRedisTemplate stringRedisTemplate;
    @RequestMapping("/buy2")
    public String index() {
        lock.lock();
        try {
            String result = stringRedisTemplate.opsForValue().get("goods:001");
            int total = result == null ? 0 : Integer.parseInt(result);
            if (total > 0) {
                int realTotal = total - 1;
                stringRedisTemplate.opsForValue().set("goods:001", String.valueOf(realTotal));
                System.out.println("购买商品成功,库存还剩:" + realTotal + ",服务端口为:"+serverPort);
                return "购买商品成功,库存还剩:" + realTotal + ",服务端口为:"+serverPort;
            } else {
                System.out.println("购买商品失败!");
            }
        } catch (Exception e) {
            lock.unlock();
        } finally {
            lock.unlock();
        }
        return "购买商品失败!";
    }
}

分布式下:

而在服务器分布式集群下,,单个服务器的synchronized和ReentrantLock

1.SETNX

SET key value [EX seconds] [PX milliseconds] [NX|XX]

例子:

1.set lock01 01 NX :意思就是说只要谁把key为lock01的值设置为01且key不存在的时候就能拿到锁

2. set lock01 01 NX EX 30 :在例1的基础上把锁设置的时间设置为30秒后过期。避免有服务挂了而没有释放锁的情况、或者业务处理完但一直拿着锁不释放导致死锁。

项目中使用SETNX:

template.opsForValue().setIfAbsent()

测试的话就得本机模拟集群,当然有虚拟机的也可以用两台虚拟机,但此处用两台JVM即可完成简易集群本机实现集群的可以看这篇文章:http://t.csdn.cn/jvZFx

 先让集群跑起来,然后启动Nginx,再通过Jmeter实现高并发的秒杀环节

 用template.opsForValue().setIfAbsent()命令进行加锁。加上了过期时间后就解决了key无法删除的问题,但如果key设置的时间太短,当业务处理的时间长于key设置的时间,key过期后其他请求就可以设置这个key而当这个线程再回来处理这个程序的时候就会把人家设置的key给删除了,因此我们规定谁设置的锁只能由谁删除。

finally {
            // 谁加的锁,谁才能删除
            if(template.opsForValue().get(REDIS_LOCK).equals(value)){
                template.delete(REDIS_LOCK);
            }

而新的问题就是finally块的判断和del删除操作不是原子操作,并发的时候也会出问题。因此采用lua(原子性)来进行删除

finally {
            // 谁加的锁,谁才能删除,使用Lua脚本,进行锁的删除
            Jedis jedis = null;
            try{
                jedis = RedisUtils.getJedis();
                String script = "if redis.call('get',KEYS[1]) == ARGV[1] " +
                        "then " +
                        "return redis.call('del',KEYS[1]) " +
                        "else " +
                        "   return 0 " +
                        "end";
                Object eval = jedis.eval(script, Collections.singletonList(REDIS_LOCK), Collections.singletonList(value));
                if("1".equals(eval.toString())){
                    System.out.println("-----del redis lock ok....");
                }else{
                    System.out.println("-----del redis lock error ....");
                }
            }catch (Exception e){
            }finally {
                if(null != jedis){
                    jedis.close();
                }
            }

总的代码: 

@RestController
public class TestConrtoller3 {
    @Value("${server.port}")
    private String serverPort;
    public static final String REDIS_LOCK = "good_lock";
    @Autowired
    StringRedisTemplate stringtemplate;
    @RequestMapping("/buy3")
    public String shopping(){
        // 每个人进来先要进行加锁,key值为"good_lock",且用UUID保证每个人的锁不同
        String value = UUID.randomUUID().toString().replace("-","");
        try{
            // 为key加一个过期时间
            Boolean flag = stringtemplate.opsForValue().setIfAbsent(REDIS_LOCK, value,10L,TimeUnit.SECONDS);
            // 加锁失败
            if(!flag){
                return "抢锁失败!";
            }
            System.out.println( value+ " 抢锁成功");
            String result = stringtemplate.opsForValue().get("goods:001");
            int total = result == null ? 0 : Integer.parseInt(result);
            if (total > 0) {
                // 如果在此处需要调用其他微服务,处理时间较长。。。
                int realTotal = total - 1;
                stringtemplate.opsForValue().set("goods:001", String.valueOf(realTotal));
                System.out.println("购买商品成功,库存还剩:" + realTotal + ",服务端口为"+serverPort);
                return "购买商品成功,库存还剩:" + realTotal + "服务端口为"+serverPort;
            } else {
                System.out.println("购买商品失败");
            }
            return "购买商品失败!";
        }finally {
            // 谁加的锁,谁才能删除,使用Lua脚本,进行锁的删除
            Jedis jedis = null;
            try{
                jedis = RedisUtils.getJedis();
                String script = "if redis.call('get',KEYS[1]) == ARGV[1] " +
                        "then " +
                        "return redis.call('del',KEYS[1]) " +
                        "else " +
                        "   return 0 " +
                        "end";
                Object eval = jedis.eval(script, Collections.singletonList(REDIS_LOCK), Collections.singletonList(value));
                if("1".equals(eval.toString())){
                    System.out.println("-----del redis lock ok....");
                }else{
                    System.out.println("-----del redis lock error ....");
                }
            }catch (Exception e){
            }finally {
                if(null != jedis){
                    jedis.close();
                }
            }
        }
    }
}

2.Redisson(推荐)

考虑缓存续命,以及Redis集群部署下,异步复制造成的锁丢失:主节点没来得及把刚刚set进来这条数据给从节点,就挂了。所以直接上RedLockRedisson落地实现

@RestController
public class TestConrtoller4 {
    @Value("${server.port}")
    private String serverPort;
    public static final String REDIS_LOCK = "good_lock";
    @Autowired
    StringRedisTemplate stringtemplate;
    @Autowired
    Redisson redisson;
    @RequestMapping("/buy4")
    public String shopping(){
        RLock lock = redisson.getLock(REDIS_LOCK);
        lock.lock();
        // 每个人进来先要进行加锁,key值为"good_lock"
        String value = UUID.randomUUID().toString().replace("-","");
        try{
            String result = stringtemplate.opsForValue().get("goods:001");
            int total = result == null ? 0 : Integer.parseInt(result);
            if (total > 0) {
                // 如果在此处需要调用其他微服务,处理时间较长
                int realTotal = total - 1;
                stringtemplate.opsForValue().set("goods:001", String.valueOf(realTotal));
                System.out.println("购买商品成功,库存还剩:" + realTotal + "件, 服务端口为"+serverPort);
                return "购买商品成功,库存还剩:" + realTotal + "件, 服务端口为"+serverPort;
            } else {
                System.out.println("购买商品失败");
            }
            return "购买商品失败";
        }finally {
            if(lock.isLocked() && lock.isHeldByCurrentThread()){
                lock.unlock();
            }
        }
    }
}

Redis工具类

 
import com.myfutech.common.util.constant.RedisPrefix;
import lombok.extern.slf4j.Slf4j;
import org.springframework.data.redis.connection.RedisStringCommands;
import org.springframework.data.redis.connection.ReturnType;
import org.springframework.data.redis.core.RedisCallback;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.core.types.Expiration;
import java.nio.charset.StandardCharsets;
import java.util.UUID;
/**
 * 基于redis分布式锁
 */
@Slf4j
public class RedisLockUtils {
    /**
     * 默认轮休获取锁间隔时间, 单位:毫秒
     */
    private static final int DEFAULT_ACQUIRE_RESOLUTION_MILLIS = 100;
    private static final String UNLOCK_LUA;
    static {
        StringBuilder sb = new StringBuilder();
        sb.append("if redis.call(\"get\",KEYS[1]) == ARGV[1] ");
        sb.append("then ");
        sb.append("    return redis.call(\"del\",KEYS[1]) ");
        sb.append("else ");
        sb.append("    return 0 ");
        sb.append("end ");
        UNLOCK_LUA = sb.toString();
    }
    /**
     * 获取锁,没有获取到则一直等待,异常情况则返回null
     *
     * @param redisTemplate     redis连接
     * @param key               redis key
     * @param expire            锁过期时间, 单位 秒
     * @return                  当前锁唯一id,如果没有获取到,返回 null
     */
    public static String lock(RedisTemplate redisTemplate, final String key, long expire){
        return lock(redisTemplate, key, expire, -1);
    }
    /**
     * 获取锁,acquireTimeout时间内没有获取到,则返回null,异常情况返回null
     *
     * @param redisTemplate     redis连接
     * @param key               redis key
     * @param expire            锁过期时间, 单位 秒
     * @param acquireTimeout    获取锁超时时间, -1代表永不超时, 单位 秒
     * @return                  当前锁唯一id,如果没有获取到,返回 null
     */
    public static String lock(RedisTemplate redisTemplate, final String key, long expire, long acquireTimeout){
        try {
            return acquireLock(redisTemplate, key, expire, acquireTimeout);
        } catch (Exception e) {
            log.error("acquire lock exception", e);
        }
        return null;
    }
    /**
     * 获取锁,没有获取到则一直等待,没有获取到则抛出异常
     *
     * @param redisTemplate     redis连接
     * @param key               redis key
     * @param expire            锁过期时间, 单位 秒
     * @return                  当前锁唯一id,如果没有获取到,返回 null
     */
    public static String lockFailThrowException(RedisTemplate redisTemplate, final String key, long expire){
        return lockFailThrowException(redisTemplate, key, expire, -1);
    }
    /**
     * 获取锁,到达超时时间时没有获取到,则抛出异常
     *
     * @param redisTemplate     redis连接
     * @param key               redis key
     * @param expire            锁过期时间, 单位 秒
     * @param acquireTimeout    获取锁超时时间, -1代表永不超时, 单位 秒
     * @return                  当前锁唯一id,如果没有获取到,返回 null
     */
    public static String lockFailThrowException(RedisTemplate redisTemplate, final String key, long expire, long acquireTimeout){
        try {
            String lockId = acquireLock(redisTemplate, key, expire, acquireTimeout);
            if (lockId != null) {
                return lockId;
            }
            throw new RuntimeException("acquire lock fail");
        } catch (Exception e) {
            throw new RuntimeException("acquire lock exception", e);
        }
    }
    private static String acquireLock(RedisTemplate redisTemplate, String key, long expire, long acquireTimeout) throws InterruptedException {
        long acquireTime = -1;
        if (acquireTimeout != -1) {
            acquireTime = acquireTimeout * 1000 + System.currentTimeMillis();
        }
        synchronized (key) {
            String lockId = UUID.randomUUID().toString();
            while (true) {
                if (acquireTime != -1 && acquireTime < System.currentTimeMillis()) {
                    break;
                }
                //调用tryLock
                boolean hasLock = tryLock(redisTemplate, key, expire, lockId);
                //获取锁成功
                if (hasLock) {
                    return lockId;
                }
                Thread.sleep(DEFAULT_ACQUIRE_RESOLUTION_MILLIS);
            }
        }
        return null;
    }
    /**
     *  释放锁
     *
     * @param redisTemplate     redis连接
     * @param key               redis key
     * @param lockId            当前锁唯一id
     */
    public static void unlock(RedisTemplate redisTemplate, String key, String lockId) {
        try {
            RedisCallback<Boolean> callback = (connection) ->
                    connection.eval(UNLOCK_LUA.getBytes(StandardCharsets.UTF_8),ReturnType.BOOLEAN, 1,
                            (RedisPrefix.LOCK_REDIS_PREFIX + key).getBytes(StandardCharsets.UTF_8), lockId.getBytes(StandardCharsets.UTF_8));
            redisTemplate.execute(callback);
        } catch (Exception e) {
            log.error("release lock exception", e);
        }
    }
    /**
     * 获取当前锁的id
     *
     * @param key       redis key
     * @return          当前锁唯一id
     */
    public static String get(RedisTemplate redisTemplate, String key) {
        try {
            RedisCallback<String> callback = (connection) -> {
                byte[] bytes = connection.get((RedisPrefix.LOCK_REDIS_PREFIX + key).getBytes(StandardCharsets.UTF_8));
                if (bytes != null){
                    return new String(bytes, StandardCharsets.UTF_8);
                }
                return null;
            };
            return (String)redisTemplate.execute(callback);
        } catch (Exception e) {
            log.error("get lock id exception", e);
        }
        return null;
    }
    private static boolean tryLock(RedisTemplate redisTemplate, String key, long expire, String lockId) {
        RedisCallback<Boolean> callback = (connection) ->
        connection.set((RedisPrefix.LOCK_REDIS_PREFIX + key).getBytes(StandardCharsets.UTF_8),
                lockId.getBytes(StandardCharsets.UTF_8), Expiration.seconds(expire), RedisStringCommands.SetOption.SET_IF_ABSENT);
        return (Boolean)redisTemplate.execute(callback);
    }
}

到此这篇关于Redis+IDEA极速了解和实现单机锁和分布式锁的文章就介绍到这了,更多相关Redis单机锁和分布式锁内容请搜索脚本之家以前的文章或继续浏览下面的相关文章希望大家以后多多支持脚本之家!

您可能感兴趣的文章:
阅读全文