Mutex.php

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<?php

namespace Elgg\Database;

class Mutex {

    private $db;

    private $logger;

    public function __construct(\Elgg\Database $db, \Elgg\Logger $logger) {
        $this->db = $db;
        $this->logger = $logger;
    }

    public function lock($namespace) {
        $this->assertNamespace($namespace);

        if (!$this->isLocked($namespace)) {
            // Lock it
            $this->db->insertData("CREATE TABLE {$this->db->prefix}{$namespace}_lock (id INT)");
            $this->logger->info("Locked mutex for $namespace");
            return true;
        }

        $this->logger->warn("Cannot lock mutex for {$namespace}: already locked.");
        return false;
    }

    public function unlock($namespace) {
        $this->assertNamespace($namespace);

        $this->db->deleteData("DROP TABLE {$this->db->prefix}{$namespace}_lock");
        $this->logger->notice("Mutex unlocked for $namespace.");
    }

    public function isLocked($namespace) {
        $this->assertNamespace($namespace);

        return (bool) count($this->db->getData("SHOW TABLES LIKE '{$this->db->prefix}{$namespace}_lock'"));
    }

    private function assertNamespace($namespace) {
        if (!ctype_alpha($namespace)) {
            throw new InvalidParameterException("Mutex namespace can only have characters [A-Za-z].");
        }
    }
}