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<?php |
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/** |
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* This file is part of ninja-mutex. |
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* |
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* (C) Kamil Dziedzic <[email protected]> |
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* |
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* For the full copyright and license information, please view the LICENSE |
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* file that was distributed with this source code. |
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*/ |
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namespace NinjaMutex\Lock; |
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use Predis; |
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/** |
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* Lock implementor using Predis (client library for Redis) |
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* |
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* @author Kamil Dziedzic <[email protected]> |
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*/ |
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class PredisRedisLock extends LockAbstract implements LockExpirationInterface |
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{ |
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/** |
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* Predis connection |
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* |
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* @var Predis\Client |
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*/ |
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protected $client; |
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/** |
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* @var int Expiration time of the lock in seconds |
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*/ |
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protected $expiration = 0; |
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/** |
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* @param $client Predis\Client |
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*/ |
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public function __construct(Predis\Client $client) |
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{ |
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parent::__construct(); |
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$this->client = $client; |
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} |
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/** |
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* @param int $expiration Expiration time of the lock in seconds |
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*/ |
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public function setExpiration($expiration) |
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{ |
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$this->expiration = $expiration; |
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// Regenerate the lock information |
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$this->lockInformation = $this->generateLockInformation(); |
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} |
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/** |
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* @inheritDoc |
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*/ |
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protected function generateLockInformation() |
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{ |
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$params = parent::generateLockInformation(); |
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if ($this->expiration) { |
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$params[] = time() + $this->expiration; |
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} |
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return $params; |
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} |
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/** |
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* @param string $name |
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* @param bool $blocking |
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* @return bool |
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*/ |
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protected function getLock($name, $blocking) |
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{ |
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/** |
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* Perform the process recommended by Redis for acquiring a lock, from here: https://redis.io/commands/setnx |
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* We are "C4" in this example... |
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* |
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* 1. C4 sends SETNX lock.foo in order to acquire the lock (sets the value if it does not already exist). |
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* 2. The crashed client C3 still holds it, so Redis will reply with 0 to C4. |
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* 3. C4 sends GET lock.foo to check if the lock expired. |
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* If it is not, it will sleep for some time and retry from the start. |
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* 4. Instead, if the lock is expired because the Unix time at lock.foo is older than the current Unix time, |
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* C4 tries to perform: |
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* GETSET lock.foo <current Unix timestamp + lock timeout + 1> |
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* Because of the GETSET semantic, C4 can check if the old value stored at key is still an expired timestamp |
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* If it is, the lock was acquired. |
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* 5. If another client, for instance C5, was faster than C4 and acquired the lock with the GETSET operation, |
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* the C4 GETSET operation will return a non expired timestamp. |
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* C4 will simply restart from the first step. Note that even if C4 wrote they key and set the expiry time |
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* a few seconds in the future this is not a problem. C5's timeout will just be a few seconds later. |
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*/ |
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$lockValue = serialize($this->getLockInformation()); |
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if ($this->client->setnx($name, $lockValue)) { |
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return true; |
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} |
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// Check if the existing lock has an expiry time. If it does and it has expired, delete the lock. |
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if ($existingValue = $this->client->get($name)) { |
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$existingValue = unserialize($existingValue); |
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if (!empty($existingValue[3]) && $existingValue[3] <= time()) { |
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// The existing lock has expired. We can delete it and take over. |
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$newExistingValue = unserialize($this->client->getset($name, $lockValue)); |
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// GETSET atomically sets key to value and returns the old value that was stored at key. |
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// If the old value from getset does not still contain an expired timestamp |
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// another probably acquired the lock in the meantime. |
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if ($newExistingValue[3] > time()) { |
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return false; |
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} |
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// Got him. |
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return true; |
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} |
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} |
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return false; |
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} |
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/** |
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* Release lock |
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* |
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* @param string $name name of lock |
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* @return bool |
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*/ |
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public function releaseLock($name) |
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{ |
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if (isset($this->locks[$name]) && $this->client->del([$name])) { |
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unset($this->locks[$name]); |
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return true; |
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} |
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return false; |
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} |
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/** |
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* Check if lock is locked |
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* |
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* @param string $name name of lock |
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* @return bool |
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*/ |
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public function isLocked($name) |
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{ |
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return null !== $this->client->get($name); |
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} |
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/** |
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* Clear lock without releasing it |
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* Do not use this method unless you know what you do |
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* |
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* @param string $name name of lock |
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* @return bool |
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*/ |
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public function clearLock($name) |
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{ |
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if (!isset($this->locks[$name])) { |
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return false; |
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} |
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unset($this->locks[$name]); |
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return true; |
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} |
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} |
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arvenil /
ninja-mutex
