Issues in this module:
- \App\Cron\Main::getCronjobObj creates a new object everytime
- the Mutex/Lock has a bug where 2 processes checking the same lock will signal one of them as being locked, so I have no other option but to re-check the lock a few times until I'm sure the lock is really locked. This slows down checking
    - another lock mecanism should be found
        - it needs to be process-depended, if the process crashes for some reason, it should automatically unlock
        - flock() should be ok, but it doesn't properly support isLocked()
        - pid-based should be ok, unless we get to reuse pid's. This assumes we have pnctl functions available though
        - https://www.php.net/manual/en/intro.sync.php should work, unless the php process crashes. This assumes this pecl extension is installed
        - also @see https://stackoverflow.com/questions/2921469/php-mutual-exclusion-mutex
            - short answer: it's complicated and it depends
        - also @see https://github.com/php-lock/lock
            - complicated
