Redis利用原子操作(INCR,DECR)实现分布式计数器

import redis

# 连接到 Redis
r = redis.Redis(host='localhost', port=6379, db=0, decode_responses=True)

def get_post_views(post_id: int) -> int:
    """获取文章的阅读量"""
    key = f"post:{post_id}:views"
    view_count = r.get(key)
    return int(view_count) if view_count else 0

def increment_post_views(post_id: int) -> int:
    """增加文章的阅读量"""
    key = f"post:{post_id}:views"
    # INCR 是原子操作，返回增加后的值
    return r.incr(key)

# --- 使用示例 ---
post_id = 123
print(f"文章 {post_id} 的初始阅读量: {get_post_views(post_id)}")

# 模拟10次并发的阅读请求
for _ in range(10):
    new_views = increment_post_views(post_id)
    print(f"阅读量已增加至: {new_views}")

print(f"文章 {post_id} 的最终阅读量: {get_post_views(post_id)}")

import redis.clients.jedis.Jedis;

public class DistributedCounter {

    private final Jedis jedis;

    public DistributedCounter(String host, int port) {
        this.jedis = new Jedis(host, port);
    }

    public long increment(String key) {
        // incr 是原子操作
        return jedis.incr(key);
    }

    public long decrement(String key) {
        // decr 是原子操作
        return jedis.decr(key);
    }

    public long getCount(String key) {
        String value = jedis.get(key);
        return value != null ? Long.parseLong(value) : 0;
    }

    public static void main(String[] args) {
        DistributedCounter counter = new DistributedCounter("localhost", 6379);
        String counterKey = "online_users";

        System.out.println("初始在线人数: " + counter.getCount(counterKey));

        // 模拟用户登录
        long user1_login = counter.increment(counterKey);
        System.out.println("用户1登录，当前在线人数: " + user1_login);

        long user2_login = counter.increment(counterKey);
        System.out.println("用户2登录，当前在线人数: " + user2_login);

        // 模拟用户登出
        long user1_logout = counter.decrement(counterKey);
        System.out.println("用户1登出，当前在线人数: " + user1_logout);

        System.out.println("最终在线人数: " + counter.getCount(counterKey));
    }
}

-- increment_with_ttl.lua
local key = KEYS[1]
local ttl = ARGV[1]

local count = redis.call("INCR", key)

-- 如果是第一次增加（即增加后的值为1），则设置过期时间
if count == 1 then
    redis.call("EXPIRE", key, ttl)
end

return count