diff options
Diffstat (limited to 'lib/private/Lock/MemcacheLockingProvider.php')
| -rw-r--r-- | lib/private/Lock/MemcacheLockingProvider.php | 148 |
1 files changed, 87 insertions, 61 deletions
diff --git a/lib/private/Lock/MemcacheLockingProvider.php b/lib/private/Lock/MemcacheLockingProvider.php index 008a7875d7e..8cc0c27bbf9 100644 --- a/lib/private/Lock/MemcacheLockingProvider.php +++ b/lib/private/Lock/MemcacheLockingProvider.php @@ -1,62 +1,52 @@ <?php declare(strict_types=1); - /** - * @copyright Copyright (c) 2016, ownCloud, Inc. - * - * @author Christoph Wurst <christoph@winzerhof-wurst.at> - * @author Jaakko Salo <jaakkos@gmail.com> - * @author Robin Appelman <robin@icewind.nl> - * @author Roeland Jago Douma <roeland@famdouma.nl> - * - * @license AGPL-3.0 - * - * This code is free software: you can redistribute it and/or modify - * it under the terms of the GNU Affero General Public License, version 3, - * as published by the Free Software Foundation. - * - * 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, version 3, - * along with this program. If not, see <http://www.gnu.org/licenses/> - * + * SPDX-FileCopyrightText: 2016-2024 Nextcloud GmbH and Nextcloud contributors + * SPDX-FileCopyrightText: 2016 ownCloud, Inc. + * SPDX-License-Identifier: AGPL-3.0-only */ namespace OC\Lock; +use OCP\AppFramework\Utility\ITimeFactory; use OCP\IMemcache; use OCP\IMemcacheTTL; use OCP\Lock\LockedException; class MemcacheLockingProvider extends AbstractLockingProvider { - /** - * @var \OCP\IMemcache - */ - private $memcache; + /** @var array<string, array{time: int, ttl: int}> */ + private array $oldTTLs = []; - /** - * @param \OCP\IMemcache $memcache - * @param int $ttl - */ - public function __construct(IMemcache $memcache, int $ttl = 3600) { - $this->memcache = $memcache; - $this->ttl = $ttl; + public function __construct( + private IMemcache $memcache, + private ITimeFactory $timeFactory, + int $ttl = 3600, + ) { + parent::__construct($ttl); } - private function setTTL(string $path) { + private function setTTL(string $path, ?int $ttl = null, mixed $compare = null): void { + if (is_null($ttl)) { + $ttl = $this->ttl; + } if ($this->memcache instanceof IMemcacheTTL) { - $this->memcache->setTTL($path, $this->ttl); + if ($compare !== null) { + $this->memcache->compareSetTTL($path, $compare, $ttl); + } else { + $this->memcache->setTTL($path, $ttl); + } + } + } + + private function getTTL(string $path): int { + if ($this->memcache instanceof IMemcacheTTL) { + $ttl = $this->memcache->getTTL($path); + return $ttl === false ? -1 : $ttl; + } else { + return -1; } } - /** - * @param string $path - * @param int $type self::LOCK_SHARED or self::LOCK_EXCLUSIVE - * @return bool - */ public function isLocked(string $path, int $type): bool { $lockValue = $this->memcache->get($path); if ($type === self::LOCK_SHARED) { @@ -68,32 +58,30 @@ class MemcacheLockingProvider extends AbstractLockingProvider { } } - /** - * @param string $path - * @param int $type self::LOCK_SHARED or self::LOCK_EXCLUSIVE - * @param string $readablePath human readable path to use in error messages - * @throws \OCP\Lock\LockedException - */ - public function acquireLock(string $path, int $type, string $readablePath = null) { + public function acquireLock(string $path, int $type, ?string $readablePath = null): void { if ($type === self::LOCK_SHARED) { + // save the old TTL to for `restoreTTL` + $this->oldTTLs[$path] = [ + 'ttl' => $this->getTTL($path), + 'time' => $this->timeFactory->getTime() + ]; if (!$this->memcache->inc($path)) { throw new LockedException($path, null, $this->getExistingLockForException($path), $readablePath); } } else { + // when getting exclusive locks, we know there are no old TTLs to restore $this->memcache->add($path, 0); + // ttl is updated automatically when the `set` succeeds if (!$this->memcache->cas($path, 0, 'exclusive')) { throw new LockedException($path, null, $this->getExistingLockForException($path), $readablePath); } + unset($this->oldTTLs[$path]); } $this->setTTL($path); $this->markAcquire($path, $type); } - /** - * @param string $path - * @param int $type self::LOCK_SHARED or self::LOCK_EXCLUSIVE - */ - public function releaseLock(string $path, int $type) { + public function releaseLock(string $path, int $type): void { if ($type === self::LOCK_SHARED) { $ownSharedLockCount = $this->getOwnSharedLockCount($path); $newValue = 0; @@ -110,6 +98,12 @@ class MemcacheLockingProvider extends AbstractLockingProvider { $newValue = $this->memcache->dec($path); } + if ($newValue > 0) { + $this->restoreTTL($path); + } else { + unset($this->oldTTLs[$path]); + } + // if we somehow release more locks then exists, reset the lock if ($newValue < 0) { $this->memcache->cad($path, $newValue); @@ -120,14 +114,7 @@ class MemcacheLockingProvider extends AbstractLockingProvider { $this->markRelease($path, $type); } - /** - * Change the type of an existing lock - * - * @param string $path - * @param int $targetType self::LOCK_SHARED or self::LOCK_EXCLUSIVE - * @throws \OCP\Lock\LockedException - */ - public function changeLock(string $path, int $targetType) { + public function changeLock(string $path, int $targetType): void { if ($targetType === self::LOCK_SHARED) { if (!$this->memcache->cas($path, 'exclusive', 1)) { throw new LockedException($path, null, $this->getExistingLockForException($path)); @@ -135,14 +122,53 @@ class MemcacheLockingProvider extends AbstractLockingProvider { } elseif ($targetType === self::LOCK_EXCLUSIVE) { // we can only change a shared lock to an exclusive if there's only a single owner of the shared lock if (!$this->memcache->cas($path, 1, 'exclusive')) { + $this->restoreTTL($path); throw new LockedException($path, null, $this->getExistingLockForException($path)); } + unset($this->oldTTLs[$path]); } $this->setTTL($path); $this->markChange($path, $targetType); } - private function getExistingLockForException($path) { + /** + * With shared locks, each time the lock is acquired, the ttl for the path is reset. + * + * Due to this "ttl extension" when a shared lock isn't freed correctly for any reason + * the lock won't expire until no shared locks are required for the path for 1h. + * This can lead to a client repeatedly trying to upload a file, and failing forever + * because the lock never gets the opportunity to expire. + * + * To help the lock expire in this case, we lower the TTL back to what it was before we + * took the shared lock *only* if nobody else got a shared lock after we did. + * + * This doesn't handle all cases where multiple requests are acquiring shared locks + * but it should handle some of the more common ones and not hurt things further + */ + private function restoreTTL(string $path): void { + if (isset($this->oldTTLs[$path])) { + $saved = $this->oldTTLs[$path]; + $elapsed = $this->timeFactory->getTime() - $saved['time']; + + // old value to compare to when setting ttl in case someone else changes the lock in the middle of this function + $value = $this->memcache->get($path); + + $currentTtl = $this->getTTL($path); + + // what the old ttl would be given the time elapsed since we acquired the lock + // note that if this gets negative the key will be expired directly when we set the ttl + $remainingOldTtl = $saved['ttl'] - $elapsed; + // what the currently ttl would be if nobody else acquired a lock since we did (+1 to cover rounding errors) + $expectedTtl = $this->ttl - $elapsed + 1; + + // check if another request has acquired a lock (and didn't release it yet) + if ($currentTtl <= $expectedTtl) { + $this->setTTL($path, $remainingOldTtl, $value); + } + } + } + + private function getExistingLockForException(string $path): string { $existing = $this->memcache->get($path); if (!$existing) { return 'none'; |