Implementing Distributed Locks with Redis in PHP to Prevent Overselling

In high‑concurrency environments, simultaneous purchase requests can cause overselling; using a Redis‑based distributed lock in PHP ensures that only one process accesses the critical section at a time.

Redis provides the setnx command, which attempts to create a key only if it does not already exist, making it suitable for implementing mutual exclusion across multiple PHP processes.

1. Initialize Redis connection

$redis = new Redis();
$redis->connect('127.0.0.1', 6379);

2. Acquire lock

$user_id = 1001; // ID
$goods_id = 2001; // 商品 ID
// Try to acquire the lock; a return value of 1 means success
if ($redis->setnx("lock_{$goods_id}", 1)) {
    // Lock acquired, proceed with purchase logic
} else {
    // Lock acquisition failed, purchase fails
    echo '购买失败';
}

3. Release lock

$redis->del("lock_{$goods_id}");

4. Full implementation example

$user_id = 1001; // 用户 ID
$goods_id = 2001; // 商品 ID
$redis = new Redis();
$redis->connect('127.0.0.1', 6379);
if ($redis->setnx("lock_{$goods_id}", 1)) {
    // Simulate inventory check
    $stock = 100;
    $sold = 50;
    if ($sold < $stock) {
        echo '购买成功';
    } else {
        echo '库存不足，购买失败';
    }
    $redis->del("lock_{$goods_id}"); // Release lock
} else {
    echo '购买失败'; // Could not acquire lock
}

The article also notes that production‑grade code should handle additional edge cases such as lock timeouts, failure to release, and performance tuning of Redis to maintain high concurrency.

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