Use Redis to implement distributed locks to ensure data security

With the continuous development of Internet technology, distributed systems are becoming more and more common in development, especially in high-concurrency processing and large-scale data processing scenarios. Distributed systems can improve the system scalability and improve system performance and concurrency capabilities. However, in a distributed system, because data is scattered across multiple machines, it is easy to have problems such as data inconsistency or repeated operations. In order to solve these problems, we often need to use distributed locks.

Distributed lock is a lock mechanism proposed to maintain data consistency in distributed systems. It is mainly used to avoid problems such as data competition and data inconsistency in distributed systems. In the traditional stand-alone lock mechanism, it is generally implemented using synchronized or ReentrantLock. However, in a distributed system, the lock implementation solution needs to consider issues such as network delay and concurrency, which requires the use of special distributed lock technology.

Redis, as a high-performance key-value storage database, is often used to implement the locking mechanism of distributed systems. Redis provides a variety of distributed lock implementation methods, such as locks based on SETNX commands, locks based on the Redlock algorithm, and locks based on Lua scripts. Next, we will introduce to you the distributed lock implementation solution of Redis based on the SETNX command.

Redis distributed lock implementation principle

The SETNX command of Redis is used to set the value of a certain key in Redis. If the key does not exist, the setting is successful and 1 is returned. Otherwise, the setting is Fails and returns 0. We can use this feature to implement distributed locks.

When we need to lock a certain data, we use the SETNX command to try to set the value of a certain key to 1. If the setting is successful, it means that no other client currently holds the lock, and the locking is successful; if the setting fails, it means that other clients currently hold the lock, and the locking fails. When unlocking, we only need to delete the key corresponding to the lock.

Redis distributed lock implementation steps

Below we will introduce how to implement distributed locks through Redis to ensure data security. The following steps are only examples and need to be adjusted according to specific conditions in actual applications.

1.Introducing the Redis client

In Java, we can use either Jedis or Lettuce, the two Redis client toolkits, to perform Redis related operations. Here we use Jedis For example. You can add the following dependencies in the pom.xml file:

<dependency>
  <groupId>redis.clients</groupId>
  <artifactId>jedis</artifactId>
  <version>3.0.1</version>
</dependency>

2. Create a Redis connection

Before using Redis, you need to create a connection with the Redis service. You can use the JedisPool object provided by Jedis. The maxTotal parameter specifies the maximum number of connections in the connection pool, the maxIdle parameter specifies the maximum number of idle connections in the connection pool, and the timeout is set to 5000 milliseconds.

JedisPool jedisPool = new JedisPool(new GenericObjectPoolConfig(),
        "localhost",
        6379, 
        5000, 
        "password");

3. Locking operation

We implement locking and unlocking logic by encapsulating a LockUtil class. In the locking operation, we try to use the SetNx command to set the value of a certain key to 1. If the setting is successful, true is returned; if the setting fails, it means that the lock has been occupied by other threads, and false is returned. It should be noted that after successful locking, a timeout must be set to avoid deadlock due to some reasons.

public class LockUtil {

    private static final String LOCK_KEY_PREFIX = "lock:";

    public static boolean lock(String key, int timeout) {
        Jedis jedis = null;
        try {
            jedis = jedisPool.getResource();
            String lockKey = LOCK_KEY_PREFIX + key;
            long start = System.currentTimeMillis();
            while (true) {
                // 使用SETNX命令来设置key的值为1
                long result = jedis.setnx(lockKey, "1");
                // 设置成功
                if (result == 1) {
                    jedis.expire(lockKey, timeout);
                    return true;
                }
                // 设置失败
                else {
                    // 检查是否超时
                    long end = System.currentTimeMillis();
                    if (end - start > timeout) {
                        return false;
                    }
                }
                Thread.sleep(1000);
            }
        } catch (Exception e) {
            return false;
        } finally {
            if (jedis != null) {
                jedis.close();
            }
        }
    }
}

4. Unlocking operation

In the unlocking operation, we use the del command to delete the key and release the resources.

public class LockUtil {
    
    public static boolean unlock(String key) {
        Jedis jedis = null;
        try {
            jedis = jedisPool.getResource();
            String lockKey = LOCK_KEY_PREFIX + key;
            jedis.del(lockKey);
            return true;
        } catch (Exception e) {
            return false;
        } finally {
            if (jedis != null) {
                jedis.close();
            }
        }
    }
}

5. Test

Finally, use a simple test to verify whether our distributed lock can work properly, as shown below:

@Test
public void testLock() throws InterruptedException {
    ExecutorService executorService = Executors.newFixedThreadPool(10);
    for (int i = 0; i < 10; i++) {
        executorService.submit(new Runnable() {
            @Override
            public void run() {
                boolean lockResult = LockUtil.lock("test", 5000);
                if (lockResult) {
                    System.out.println(Thread.currentThread().getName() + " get lock");
                    try {
                        // 处理业务
                        Thread.sleep(5000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    } finally {
                        LockUtil.unlock("test");
                    }
                } else {
                    System.out.println(Thread.currentThread().getName() + " fail to get lock");
                }
            }
        });
    }
    sleep(100000);
}

The above code will Create 10 threads, each thread tries to acquire the lock of the same key, performs some business operations, and releases the lock resource after 5 seconds. If the distributed lock is implemented successfully, each thread can successfully acquire the lock and complete business processing.

Through the above examples, we can see that using the SETNX command of Redis, a simple and efficient distributed lock mechanism can be implemented to effectively ensure the security of data in the distributed system. In the actual application process, we need to adjust and optimize the lock implementation plan based on actual business scenarios and needs.

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