PHP分布式锁与应用场景

PHP分布式锁与应用场景

分布式锁在多个进程同时操作共享资源时很有用。Redis是实现分布式锁的常用工具。今天说说PHP中分布式锁的实现。

Redis的SET NX实现锁。

```php
class RedisDistributedLock
{
private Redis $redis;
private string $prefix = 'lock:';
private int $defaultTimeout = 10;

public function __construct(Redis $redis)
{
$this->redis = $redis;
}

public function acquire(string $key, int $timeout = null): ?string
{
$timeout = $timeout ?? $this->defaultTimeout;
$lockKey = $this->prefix . $key;
$token = bin2hex(random_bytes(16));

$result = $this->redis->set($lockKey, $token, ['NX', 'EX' => $timeout]);
return $result ? $token : null;
}

public function release(string $key, string $token): bool
{
$lockKey = $this->prefix . $key;

$script = '
if redis.call("GET", KEYS[1]) == ARGV[1] then
return redis.call("DEL", KEYS[1])
else
return 0
end
';

return (bool)$this->redis->eval($script, [$lockKey, $token], 1);
}

public function synchronized(string $key, callable $callback, int $timeout = null): mixed
{
$token = $this->acquire($key, $timeout);
if ($token === null) {
throw new RuntimeException("无法获取锁: $key");
}

try {
return $callback();
} finally {
$this->release($key, $token);
}
}
}

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

try {
$lock->synchronized('order:123', function () {
echo "处理订单123\n";
sleep(1);
});
} catch (RuntimeException $e) {
echo "获取锁失败: {$e->getMessage()}\n";
}
?>

数据库实现乐观锁。

```php
class OptimisticLock
{
private PDO $pdo;

public function __construct(PDO $pdo)
{
$this->pdo = $pdo;
}

public function updateWithLock(int $id, array $data, callable $updateFn): bool
{
$maxAttempts = 3;

for ($i = 0; $i < $maxAttempts; $i++) {
$stmt = $this->pdo->prepare("SELECT * FROM products WHERE id = ?");
$stmt->execute([$id]);
$product = $stmt->fetch();

if (!$product) throw new RuntimeException("商品不存在");

$newData = $updateFn($product);

$stmt = $this->pdo->prepare("
UPDATE products SET stock = ?, version = version + 1
WHERE id = ? AND version = ?
");
$stmt->execute([$newData['stock'], $id, $product['version']]);

if ($stmt->rowCount() > 0) return true;
usleep(100000);
}

throw new RuntimeException("更新失败，数据已被其他进程修改");
}
}
?>

分布式锁的应用场景。

```php
// 防止重复下单
function placeOrder(PDO $pdo, Redis $redis, int $userId, int $productId): void
{
$lockKey = "order:{$userId}:{$productId}";
$lock = new RedisDistributedLock($redis);

$lock->synchronized($lockKey, function () use ($pdo, $userId, $productId) {
$stmt = $pdo->prepare("SELECT COUNT(*) FROM orders WHERE user_id = ? AND product_id = ? AND created_at > DATE_SUB(NOW(), INTERVAL 1 MINUTE)");
$stmt->execute([$userId, $productId]);
if ($stmt->fetchColumn() > 0) {
throw new RuntimeException("请勿重复下单");
}
$pdo->prepare("INSERT INTO orders (user_id, product_id) VALUES (?, ?)")->execute([$userId, $productId]);
});
}

// 定时任务防重复执行
function runUniqueTask(string $taskName, callable $task): void
{
$redis = new Redis();
$redis->connect('127.0.0.1', 6379);
$lock = new RedisDistributedLock($redis);

try {
$lock->synchronized("task:{$taskName}", $task, 3600);
} catch (RuntimeException $e) {
echo "任务已在其他进程执行\n";
}
}
?>

分布式锁在需要互斥访问共享资源的场景中很有用。Redis锁实现简单性能好，但要处理锁超时和释放的问题。乐观锁通过版本号解决冲突，适合读多写少的场景。