Key points of distributed lock design in PHP instant killing system

Key points of distributed lock design in PHP flash sale system

With the development of the Internet, rush buying activities on e-commerce platforms are becoming more and more common. In high-concurrency scenarios, the implementation of flash sale activities faces many challenges. One of them is how to ensure that each user can only purchase once before the product is sold out. To solve this problem, distributed locks have become a common solution. In PHP development, we can implement distributed locks through the following design points.
1. Select appropriate storage media and technology
Before choosing a distributed lock implementation solution, we need to select appropriate storage media and technology based on the actual situation. Generally speaking, the implementation of distributed locks can be based on database, cache, shared storage and other methods. Common choices include MySQL, Redis, Memcached, etc. Based on actual scenarios and needs, it is very important to choose appropriate storage media and technology.

2. Use optimistic locking
In a distributed environment, when multiple users request to purchase the same product at the same time, concurrency conflicts will occur. To solve this problem, optimistic locking can be used. The basic idea of ​​optimistic locking is to read the data version number before updating the data. If the version numbers are inconsistent, it means that the data has been modified by other users, and the request can be returned as failed. By using optimistic locking, the problem of concurrency conflicts can be effectively solved.

The following is a code example of using optimistic locking to implement a distributed flash sale system:

<?php

function buyGoods($goodsId, $userId)
{
    $key = "goods:{$goodsId}"; // 商品的唯一标识符，作为锁的key
    $timeout = 10; // 超时时间，避免死锁
    
    // 加锁
    $redis = new Redis();
    $redis->connect('127.0.0.1', 6379); // 连接Redis
    $lock = $redis->set($key, $userId, ['NX', 'EX' => $timeout]);
    
    // 检查是否成功加锁
    if (!$lock) {
        echo "Failed to acquire lock";
        return;
    }
    
    // 进行秒杀操作
    $goods = $redis->hgetall($key);
    if (empty($goods) || $goods['stock'] <= 0) {
        echo "Goods sold out";
    } else {
        $goods['stock'] -= 1;
        $redis->hmset($key, $goods);
        echo "Buy goods successfully";
    }
    
    // 释放锁
    $redis->del($key);
}

$goodsId = 1;
$userId = "user1";
buyGoods($goodsId, $userId);

In the above example, we used Redis as the storage medium and set the NX parameters to ensure that there is only one user Able to successfully lock. Before the flash sale operation, first obtain the lock based on the unique identifier of the product. If the acquisition is successful, the flash sale will be performed, otherwise a failure will be returned. After completing the flash kill operation, release the lock.

Summary:
Distributed locks are a very important part of the flash sale system. Choosing appropriate storage media and technology and using optimistic locking to resolve concurrency conflicts can effectively ensure that each user can only purchase once. Through reasonable design and implementation, it can better cope with rush buying activities in high concurrency scenarios.

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