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<?php |
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namespace Elgg\Database; |
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/** |
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* WARNING: API IN FLUX. DO NOT USE DIRECTLY. |
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* |
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* Provides database mutex that can be used to prevent race conditions |
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* between two processes that affect the same data. |
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* |
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* @access private |
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* @since 2.1.0 |
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*/ |
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class Mutex { |
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/** |
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* @var \Elgg\Database |
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*/ |
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private $db; |
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/** |
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* @var \Elgg\Logger |
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*/ |
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private $logger; |
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/** |
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* Constructor |
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* |
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* @param \Elgg\Database $db Database |
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* @param \Elgg\Logger $logger Logger |
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*/ |
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public function __construct(\Elgg\Database $db, \Elgg\Logger $logger) { |
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$this->db = $db; |
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$this->logger = $logger; |
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} |
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/** |
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* Creates a table {prefix}{$namespace}_lock that is used as a mutex. |
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* |
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* @param string $namespace Allows having separate locks for separate processes |
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* @return bool |
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*/ |
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public function lock($namespace) { |
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$this->assertNamespace($namespace); |
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if (!$this->isLocked($namespace)) { |
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// Lock it |
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$this->db->insertData("CREATE TABLE {$this->db->prefix}{$namespace}_lock (id INT)"); |
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$this->logger->info("Locked mutex for $namespace"); |
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return true; |
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} |
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$this->logger->warn("Cannot lock mutex for {$namespace}: already locked."); |
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return false; |
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} |
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/** |
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* Unlocks mutex |
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* |
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* @param string $namespace Namespace to use for the database table |
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* @return void |
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*/ |
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public function unlock($namespace) { |
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$this->assertNamespace($namespace); |
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$this->db->deleteData("DROP TABLE {$this->db->prefix}{$namespace}_lock"); |
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$this->logger->notice("Mutex unlocked for $namespace."); |
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} |
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/** |
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* Checks if mutex is locked |
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* |
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* @param string $namespace Namespace to use for the database table |
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* @return bool |
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*/ |
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public function isLocked($namespace) { |
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$this->assertNamespace($namespace); |
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return (bool) count($this->db->getData("SHOW TABLES LIKE '{$this->db->prefix}{$namespace}_lock'")); |
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} |
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/** |
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* Assert that the namespace contains only characters [A-Za-z] |
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* |
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* @param string $namespace Namespace to use for the database table |
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* @throws InvalidParameterException |
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* @return void |
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*/ |
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private function assertNamespace($namespace) { |
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if (!ctype_alpha($namespace)) { |
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throw new InvalidParameterException("Mutex namespace can only have characters [A-Za-z]."); |
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} |
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} |
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} |
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