custom-backend.php

<?php

class SomeClass implements Flushable {

    protected static $cache_key = 'my_cache_key';

    protected static function init()
    {
        if (!self::$initialized) {
            $cacheDir = BASE_PATH . DIRECTORY_SEPARATOR . 'localcache' . DIRECTORY_SEPARATOR . self::$cache_key;
            if(!@is_writable($cacheDir)){
                $oldUmask = umask();
                umask(0);
                mkdir($cacheDir, 0777);
                umask($oldUmask);
            }
            SS_Cache::add_backend(self::$cache_key, 'File', ['cache_dir' => $cacheDir]);
            SS_Cache::set_cache_lifetime(self::$cache_key, (4 * 60 * 60), 10);
            SS_Cache::pick_backend(self::$cache_key, self::$cache_key, 10);
            self::$initialized = true;
        }

    }
    
    public static function flush(){
      self::init();
      $cache = SS_Cache::factory(self::$cache_key);
      $cache->save('some value', 'some_key');
    }
}