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<?php
declare(strict_types=1);
/**
* @copyright Copyright (c) 2016, ownCloud, Inc.
*
* @author Christoph Wurst <christoph@winzerhof-wurst.at>
* @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/>
*
*/
namespace OC\Lock;
use OCP\IMemcache;
use OCP\IMemcacheTTL;
use OCP\Lock\LockedException;
class MemcacheLockingProvider extends AbstractLockingProvider {
/**
* @var \OCP\IMemcache
*/
private $memcache;
/**
* @param \OCP\IMemcache $memcache
* @param int $ttl
*/
public function __construct(IMemcache $memcache, int $ttl = 3600) {
$this->memcache = $memcache;
$this->ttl = $ttl;
}
private function setTTL(string $path) {
if ($this->memcache instanceof IMemcacheTTL) {
$this->memcache->setTTL($path, $this->ttl);
}
}
/**
* @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) {
return $lockValue > 0;
} elseif ($type === self::LOCK_EXCLUSIVE) {
return $lockValue === 'exclusive';
} else {
return false;
}
}
/**
* @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 $readablePath = null) {
if ($type === self::LOCK_SHARED) {
if (!$this->memcache->inc($path)) {
throw new LockedException($path, null, $this->getExistingLockForException($path), $readablePath);
}
} else {
$this->memcache->add($path, 0);
if (!$this->memcache->cas($path, 0, 'exclusive')) {
throw new LockedException($path, null, $this->getExistingLockForException($path), $readablePath);
}
}
$this->setTTL($path);
$this->markAcquire($path, $type);
}
/**
* @param string $path
* @param int $type self::LOCK_SHARED or self::LOCK_EXCLUSIVE
*/
public function releaseLock(string $path, int $type) {
if ($type === self::LOCK_SHARED) {
$ownSharedLockCount = $this->getOwnSharedLockCount($path);
$newValue = 0;
if ($ownSharedLockCount === 0) { // if we are not holding the lock, don't try to release it
return;
}
if ($ownSharedLockCount === 1) {
$removed = $this->memcache->cad($path, 1); // if we're the only one having a shared lock we can remove it in one go
if (!$removed) { //someone else also has a shared lock, decrease only
$newValue = $this->memcache->dec($path);
}
} else {
// if we own more than one lock ourselves just decrease
$newValue = $this->memcache->dec($path);
}
// if we somehow release more locks then exists, reset the lock
if ($newValue < 0) {
$this->memcache->cad($path, $newValue);
}
} elseif ($type === self::LOCK_EXCLUSIVE) {
$this->memcache->cad($path, 'exclusive');
}
$this->markRelease($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 $targetType) {
if ($targetType === self::LOCK_SHARED) {
if (!$this->memcache->cas($path, 'exclusive', 1)) {
throw new LockedException($path, null, $this->getExistingLockForException($path));
}
} 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($path, 1, 'exclusive')) {
throw new LockedException($path, null, $this->getExistingLockForException($path));
}
}
$this->setTTL($path);
$this->markChange($path, $targetType);
}
private function getExistingLockForException($path) {
$existing = $this->memcache->get($path);
if (!$existing) {
return 'none';
} elseif ($existing === 'exclusive') {
return $existing;
} else {
return $existing . ' shared locks';
}
}
}
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