1 files changed, 40 insertions, 22 deletions

diff --git a/lib/public/AppFramework/Db/TTransactional.php b/lib/public/AppFramework/Db/TTransactional.php
index 59f4a346386..8dd275e5420 100644
--- a/lib/public/AppFramework/Db/TTransactional.php
+++ b/lib/public/AppFramework/Db/TTransactional.php
@@ -1,33 +1,17 @@
 <?php
 
 declare(strict_types=1);
-
-/*
- * @copyright 2022 Christoph Wurst <christoph@winzerhof-wurst.at>
- *
- * @author 2022 Christoph Wurst <christoph@winzerhof-wurst.at>
- *
- * @license GNU AGPL version 3 or any later version
- *
- * This program is free software: you can redistribute it and/or modify
- * it under the terms of the GNU Affero General Public License as
- * published by the Free Software Foundation, either version 3 of the
- * License, or (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU Affero General Public License for more details.
- *
- * You should have received a copy of the GNU Affero General Public License
- * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+/**
+ * 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
@@ -35,7 +19,6 @@ use Throwable;
  * @since 24.0.0
  */
 trait TTransactional {
-
 	/**
 	 * Run an atomic database operation
 	 *
@@ -67,4 +50,39 @@ trait TTransactional {
 			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 ]);
+			}
+		}
+	}
 }