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<?php
declare(strict_types=1);
/**
* SPDX-FileCopyrightText: 2022 Nextcloud GmbH and Nextcloud contributors
* SPDX-License-Identifier: AGPL-3.0-or-later
*/
namespace OCP\AppFramework\Db;
use OC\DB\Exceptions\DbalException;
use OCP\DB\Exception;
use OCP\IDBConnection;
use Throwable;
use function OCP\Log\logger;
/**
* Helper trait for transactional operations
*
* @since 24.0.0
*/
trait TTransactional {
/**
* Run an atomic database operation
*
* - Commit if no exceptions are thrown, return the callable result
* - Revert otherwise and rethrows the exception
*
* @template T
* @param callable $fn
* @psalm-param callable():T $fn
* @param IDBConnection $db
*
* @return mixed the result of the passed callable
* @psalm-return T
*
* @throws Exception for possible errors of commit or rollback or the custom operations within the closure
* @throws Throwable any other error caused by the closure
*
* @since 24.0.0
* @see https://docs.nextcloud.com/server/latest/developer_manual/basics/storage/database.html#transactions
*/
protected function atomic(callable $fn, IDBConnection $db) {
$db->beginTransaction();
try {
$result = $fn();
$db->commit();
return $result;
} catch (Throwable $e) {
$db->rollBack();
throw $e;
}
}
/**
* Wrapper around atomic() to retry after a retryable exception occurred
*
* Certain transactions might need to be retried. This is especially useful
* in highly concurrent requests where a deadlocks is thrown by the database
* without waiting for the lock to be freed (e.g. due to MySQL/MariaDB deadlock
* detection)
*
* @template T
* @param callable $fn
* @psalm-param callable():T $fn
* @param IDBConnection $db
* @param int $maxRetries
*
* @return mixed the result of the passed callable
* @psalm-return T
*
* @throws Exception for possible errors of commit or rollback or the custom operations within the closure
* @throws Throwable any other error caused by the closure
*
* @since 27.0.0
*/
protected function atomicRetry(callable $fn, IDBConnection $db, int $maxRetries = 3): mixed {
for ($i = 0; $i < $maxRetries; $i++) {
try {
return $this->atomic($fn, $db);
} catch (DbalException $e) {
if (!$e->isRetryable() || $i === ($maxRetries - 1)) {
throw $e;
}
logger('core')->warning('Retrying operation after retryable exception.', [ 'exception' => $e ]);
}
}
}
}
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