Redis+IDEA极速了解和实现单机锁和分布式锁

女爷i 2024-03-17 17:37 42阅读 0赞

## 单机下： ##

![64ae214c14174743b0507cf4f87a91bd.png][]

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

![079445e4facb4e73b1d0077910d19665.png][]

#### 1.SETNX ####

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

*  `EX` *seconds* – 设置键key的过期时间，单位时秒
 *  `PX` *milliseconds* – 设置键key的过期时间，单位时毫秒
 *  `NX` – 只有键key不存在的时候才会设置key的值
 *  `XX` – 只有键key存在的时候才会设置key的值

**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][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

![c49bf97062c9453a80c0d6b5402e84b9.png][]

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`RedLock`的`Redisson`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);
        }
    }

[64ae214c14174743b0507cf4f87a91bd.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/15/180cafafcab048c9839e6236c80b58af.png
[079445e4facb4e73b1d0077910d19665.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/15/d4ab231ad4bd452e8c3c94c86d02b15a.png
[http_t.csdn.cn_jvZFx]: http://t.csdn.cn/jvZFx
[c49bf97062c9453a80c0d6b5402e84b9.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/15/2fac2f71c661462bab4cbde31010d406.png