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<?php
// This file is part of Moodle - http://moodle.org/
//
// Moodle is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// Moodle is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.

/**
 * Class representing a lock
 *
 * The methods available for a specific lock type are only known by it's factory.
 *
 * @package    core
 * @copyright  Damyon Wiese 2013
 * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */

namespace core\lock;

defined('MOODLE_INTERNAL') || die();

/**
 * Class representing a lock
 *
 * The methods available for a specific lock type are only known by it's factory.
 *
 * @package   core
 * @category  lock
 * @copyright Damyon Wiese 2013
 * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */
class lock {

/** @var string|int $key A unique key representing a held lock */
    protected $key = '';

/** @var lock_factory $factory The factory that generated this lock */
    protected $factory;

/** @var bool $released Has this lock been released? If a lock falls out of scope without being released - show a warning. */
    protected $released;

/** @var string $caller Where was this called from? Stored for when a warning is shown */
    protected $caller = 'unknown';

/**
     * Construct a lock containing the unique key required to release it.
     * @param mixed $key - The lock key. The type of this is up to the lock_factory being used.
     *      For file locks this is a file handle. For MySQL this is a string.
     * @param lock_factory $factory - The factory that generated this lock.
     */
    public function __construct($key, $factory) {
        $this->factory = $factory;
        $this->key = $key;
        $this->released = false;
        $caller = debug_backtrace(true, 2)[1];
        if ($caller && array_key_exists('file', $caller ) ) {
            $this->caller = $caller['file'] . ' on line ' . $caller['line'];
        } else if ($caller && array_key_exists('class', $caller)) {
            $this->caller = $caller['class'] . $caller['type'] . $caller['function'];
        }
    }

/**
     * Return the unique key representing this lock.
     * @return string|int lock key.
     */
    public function get_key() {
        return $this->key;
    }

/**
     * Extend the lifetime of this lock. Not supported by all factories.
     * @param int $maxlifetime - the new lifetime for the lock (in seconds).
     * @return bool
     */
    public function extend($maxlifetime = 86400) {
        if ($this->factory) {
            return $this->factory->extend_lock($this, $maxlifetime);
        }
        return false;
    }

/**
     * Release this lock
     * @return bool
     */
    public function release() {
        $this->released = true;
        if (empty($this->factory)) {
            return false;
        }
        $result = $this->factory->release_lock($this);
        // Release any held references to the factory.
        unset($this->factory);
        $this->factory = null;
        $this->key = '';
        return $result;
    }

/**
     * Print debugging if this lock falls out of scope before being released.
     */
    public function __destruct() {
        if (!$this->released && defined('PHPUNIT_TEST')) {
            $key = $this->key;
            $this->release();
            throw new \coding_exception("A lock was created but not released at:\n" .
                                        $this->caller . "\n\n" .
                                        " Code should look like:\n\n" .
                                        " \$factory = \core\lock\lock_config::get_lock_factory('type');\n" .
                                        " \$lock = \$factory->get_lock($key);\n" .
                                        " \$lock->release();  // Locks must ALWAYS be released like this.\n\n");
        }
    }

}