File.php

<?php
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */

namespace Magento\Framework\Simplexml\Config\Cache;

/**
 * File based cache for configuration
 */
class File extends \Magento\Framework\Simplexml\Config\Cache\AbstractCache
{
    /**
     * Initialize variables that depend on the cache key
     *
     * @param string $key
     * @return string
     */
    public function setKey($key)
    {
        $this->setData('key', $key);

        $file = $this->getDir() . '/' . $this->getKey();
        $this->setFileName($file . '.xml');
        $this->setStatFileName($file . '.stat');

        return $this;
    }

    /**
     * Try to load configuration cache from file
     *
     * @return boolean
     */
    public function load()
    {
        $this->setIsLoaded(false);

        // try to read stats
        if (!($stats = @file_get_contents($this->getStatFileName()))) {
            return false;
        }

        // try to validate stats
        if (!$this->validateComponents(unserialize($stats))) {
            return false;
        }

        // try to read cache file
        if (!($cache = @file_get_contents($this->getFileName()))) {
            return false;
        }

        // try to process cache file
        if (!($data = $this->getConfig()->processFileData($cache))) {
            return false;
        }

        $xml = $this->getConfig()->loadString($data);
        $this->getConfig()->setXml($xml);
        $this->setIsLoaded(true);

        return true;
    }

    /**
     * Try to save configuration cache to file
     *
     * @return boolean
     */
    public function save()
    {
        if (!$this->getIsAllowedToSave()) {
            return false;
        }

        // save stats
        @file_put_contents($this->getStatFileName(), serialize($this->getComponents()));

        // save cache
        @file_put_contents($this->getFileName(), $this->getConfig()->getNode()->asNiceXml());

        return true;
    }
}