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<?php |
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namespace TH\RedisLock; |
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use Exception; |
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use Predis\Client; |
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use Predis\Response\Status; |
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use Psr\Log\LoggerInterface; |
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use Psr\Log\NullLogger; |
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use TH\Lock\Lock; |
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class RedisSimpleLock implements Lock |
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{ |
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private $identifier; |
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private $client; |
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private $ttl; |
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private $logger; |
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private $id; |
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/** |
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* Create new RedisSimpleLock |
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* |
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* @param string $identifier the redis lock key |
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* @param Client $client the Predis client |
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* @param integer $ttl lock time-to-live in milliseconds |
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* @param LoggerInterface|null $logger |
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*/ |
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public function __construct($identifier, Client $client, $ttl = 10000, LoggerInterface $logger = null) |
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{ |
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$this->identifier = $identifier; |
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$this->client = $client; |
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$this->ttl = $ttl; |
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$this->logger = $logger ?: new NullLogger; |
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$this->id = mt_rand(); |
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register_shutdown_function($this->releaseClosure()); |
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} |
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public function acquire() |
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{ |
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$log_data = ["identifier" => $this->identifier]; |
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$response = $this->client->set($this->identifier, $this->id, "PX", $this->ttl, "NX"); |
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if (!$response instanceof Status || $response->getPayload() !== "OK") { |
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$this->logger->debug("could not acquire lock on {identifier}", $log_data); |
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throw new Exception("Could not acquire lock on " . $this->identifier); |
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} |
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$this->logger->debug("lock acquired on {identifier}", $log_data); |
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} |
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public function release() |
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{ |
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$closure = $this->releaseClosure(); |
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$closure(); |
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} |
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public function __destruct() |
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{ |
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$this->release(); |
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} |
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private function releaseClosure() |
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{ |
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$client = $this->client; |
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$id = $this->id; |
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$identifier = $this->$identifier; |
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$logger = $this->logger; |
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$closure = function () use ($client, $identifier, $id, $logger) { |
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$script = <<<LUA |
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if redis.call("get", KEYS[1]) == ARGV[1] then |
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return redis.call("del", KEYS[1]) |
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end |
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LUA; |
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if ($this->client->eval($script, 1, $this->identifier, $this->id)) { |
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$this->logger->debug("lock released on {identifier}", ["identifier" => $this->identifier]); |
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} |
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}; |
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return $closure->bindTo(null); |
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} |
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} |
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texthtml /
php-lock-redis
This error can happen if you refactor code and forget to move the variable initialization.
Let’s take a look at a simple example:
The above code is perfectly fine. Now imagine that we re-order the statements:
In that case,
$xwould be read before it is initialized. This was a very basic example, however the principle is the same for the found issue.