php高并发防止重复读取_讲解在高并发环境下如何防止数据重复读取

// 开启事务
mysqli_begin_transaction($connection);
<p>// 加锁读取库存
$sql = "SELECT stock FROM products WHERE id = ? FOR UPDATE";
$stmt = mysqli_prepare($connection, $sql);
mysqli_stmt_bind_param($stmt, 'i', $product_id);
mysqli_stmt_execute($stmt);
$result = mysqli_stmt_get_result($stmt);
$row = mysqli_fetch_assoc($result);</p><p>if ($row['stock'] > 0) {
// 扣减库存
$update_sql = "UPDATE products SET stock = stock - 1 WHERE id = ?";
$update_stmt = mysqli_prepare($connection, $update_sql);
mysqli_stmt_bind_param($update_stmt, 'i', $product_id);
mysqli_stmt_execute($update_stmt);
}</p><p>// 提交事务释放锁
mysqli_commit($connection);

ALTER TABLE user_coupon ADD UNIQUE KEY uk_user_coupon (user_id, coupon_id);

$redis = new Redis();
$redis->connect('127.0.0.1', 6379);
<p>$lock_key = "lock:coupon:" . $user_id;
$expire_time = 5; // 锁过期时间（秒）</p><p>// 尝试加锁
$is_lock = $redis->set($lock_key, 1, ['NX', 'EX' => $expire_time]);
if (!$is_lock) {
echo "操作过于频繁，请稍后再试";
exit;
}</p><p>try {
// 检查是否已领取（查库）
// 执行领取逻辑（写库）
} finally {
// 释放锁
$redis->del($lock_key);
}

UPDATE products 
SET stock = stock - 1, version = version + 1 
WHERE id = ? AND version = ?

$affected = mysqli_affected_rows($connection);
if ($affected == 0) {
    // 更新失败，可能已被其他请求处理
    echo "库存扣减失败，请重试";
}