Mutex.php

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<?php

namespace Elgg\Database;

use Elgg\Database;
use Elgg\Exceptions\InvalidArgumentException;
use Elgg\Traits\Loggable;

class Mutex {

    use Loggable;

    public function __construct(protected Database $db) {
    }

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

        if (!$this->isLocked($namespace)) {
            // Lock it
            $this->db->getConnection('write')->executeStatement("CREATE TABLE {$this->db->prefix}{$namespace}_lock (id INT)");

            $this->getLogger()->info("Locked mutex for {$namespace}");
            return true;
        }

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

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

        $this->db->getConnection('write')->executeStatement("DROP TABLE {$this->db->prefix}{$namespace}_lock");

        $this->getLogger()->notice("Mutex unlocked for {$namespace}.");
    }

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

        $result = $this->db->getConnection('read')->executeQuery("SHOW TABLES LIKE '{$this->db->prefix}{$namespace}_lock'");
        return $result->rowCount() > 0;
    }

    protected function assertNamespace(string $namespace): void {
        if (!ctype_alpha($namespace)) {
            throw new InvalidArgumentException('Mutex namespace can only have characters [A-Za-z].');
        }
    }
}