【2020.07.11】Springboot redis 分布式锁，分别使用 setnx 和 redisson 实现

╰+攻爆jí腚メ 2023-02-25 03:40 149阅读 0赞

1、线程不安全，使用synchronized 单体程序可以保证线程安全，但分布式下也是线程不安全的

@Autowired
    private RedisTemplate redisTemplate;
    
    @GetMapping("/lock")
    public Result lock() { 
        Integer stock = (Integer) redisTemplate.opsForValue().get("stock");
        if (stock > 0) { 
            stock = stock - 1;
            redisTemplate.opsForValue().set("stock", stock);
            System.out.println("剩余库存: " + stock);
        } else { 
            System.out.println("扣减失败" + stock);
        }
        return Result.success("操作成功");
    }

2、分布式锁、redis setnx

*  setnx
    
     *  key 不存在，设置 key
     *  key 存在，不做任何动作
 *  redisTemplate.opsForValue().setIfAbsent
    
     *  Key 不存在，设置成功。返回 true
     *  Key 不存在，不操作。返回 false

@Autowired
    private RedisTemplate redisTemplate;
    
    @GetMapping("/lock")
    public Result lock() { 
        Boolean result = redisTemplate.opsForValue().setIfAbsent(LOCKKEY, "paulson");
        if (!result) { 
            return Result.fail("分布式锁占用中");
        }
    
    
        Integer stock = (Integer) redisTemplate.opsForValue().get("stock");
        if (stock > 0) { 
            stock = stock - 1;
            redisTemplate.opsForValue().set("stock", stock);
            System.out.println("剩余库存: " + stock);
        } else { 
            System.out.println("扣减失败" + stock);
        }
    
    
        redisTemplate.delete(LOCKKEY);
        return Result.success("操作成功");
    }

注意：1、业务异常，没有删除 key 导致死锁  
解决方案： try finally

3、分布式锁

@Autowired
    private RedisTemplate redisTemplate;
    
    @GetMapping("/lock")
    public Result lock() { 
        try { 
            Boolean result = redisTemplate.opsForValue().setIfAbsent(LOCKKEY, "paulson");
            if (!result) { 
                return Result.fail("分布式锁占用中");
            }
    
    
            Integer stock = (Integer) redisTemplate.opsForValue().get("stock");
            if (stock > 0) { 
                stock = stock - 1;
                redisTemplate.opsForValue().set("stock", stock);
                System.out.println("剩余库存: " + stock);
            } else { 
                System.out.println("扣减失败" + stock);
            }
        } finally{ 
            // 释放分布式锁
            redisTemplate.delete(LOCKKEY);
        }
        return Result.success("操作成功");
    }

注意：服务器挂掉，重启，导致没有执行delete  
解决方案：设置锁的生效时间

4、分布式锁

@Autowired
    private RedisTemplate redisTemplate;
    @GetMapping("/lock")
    public Result lock() { 
        try { 
            Boolean result = redisTemplate.opsForValue().setIfAbsent(LOCKKEY, "paulson", 10, TimeUnit.SECONDS);
            if (!result) { 
                return Result.fail("分布式锁占用中");
            }
    
    
            Integer stock = (Integer) redisTemplate.opsForValue().get("stock");
            if (stock > 0) { 
                stock = stock - 1;
                redisTemplate.opsForValue().set("stock", stock);
                System.out.println("剩余库存: " + stock);
            } else { 
                System.out.println("扣减失败" + stock);
            }
        } finally  { 
            // 释放分布式锁
            redisTemplate.delete(LOCKKEY);
        }
        return Result.success("操作成功");
    }

注意：超时时间应该设置多久，还是执行结束就释放掉了  
解决方案：只释放自己加的锁

5、分布式锁

@Autowired
     private RedisTemplate redisTemplate;
    
     @Autowired
     private IdWorker idWorker;
    
    @GetMapping("/lock")
    public Result lock() { 
        String clientId = idWorker.nextId() + "";
        try { 
            Boolean result = redisTemplate.opsForValue().setIfAbsent(LOCKKEY, clientId, 10, TimeUnit.SECONDS);
            if (!result) { 
                return Result.fail("分布式锁占用中");
            }
    
    
            Integer stock = (Integer) redisTemplate.opsForValue().get("stock");
            if (stock > 0) { 
                stock = stock - 1;
                redisTemplate.opsForValue().set("stock", stock);
                System.out.println("剩余库存: " + stock);
            } else { 
                System.out.println("扣减失败" + stock);
            }
        } finally { 
            // 释放分布式锁,只释放自己创建的锁
            if (clientId.equals(redisTemplate.opsForValue().get(LOCKKEY))) { 
                redisTemplate.delete(LOCKKEY);
            }
        }
        return Result.success("操作成功");
    }

6、使用 redisson

*  Maven

<dependency>
       <groupId>org.redisson</groupId>
       <artifactId>redisson</artifactId>
       <version>3.13.2</version>
    </dependency>

*  Gradle

compile 'org.redisson:redisson:3.13.2'

*  注入 Bean

@Bean
        public Redisson redisson() { 
            // 单机模式
            Config config = new Config();
            config.useSingleServer().setAddress("redis://10.179.229.187:6379").setDatabase(1);
            return (Redisson) Redisson.create(config);
        }

@Autowired
    private Redisson redisson;
    
    @GetMapping("/deduct_lock2")
    public Result redissonLock() { 
        RLock lock = redisson.getLock(LOCKKEY);
        try { 
            lock.tryLock(30, TimeUnit.SECONDS);
            Integer stock = (Integer) redisTemplate.opsForValue().get("stock");
            if (stock > 0) { 
                stock = stock - 1;
                redisTemplate.opsForValue().set("stock", stock);
                System.out.println("剩余库存: " + stock);
            } else { 
                System.out.println("扣减失败" + stock);
            }
        } catch (InterruptedException e) { 
            e.printStackTrace();
        } finally { 
            // 释放分布式锁,只释放自己创建的锁
            lock.unlock();
        }
        return Result.success("操作成功");
    }