every cron or cron-like service has some kind of polling behind. Beanstalk, redis-queue, you name it. Many open source redis based scheduler are all implemented

every cron or cron-like service has some kind of polling behind. Beanstalk, redis-queue, you name it. Many open source redis based scheduler are all implemented in a sleep(5) loop. Even the Unix cron is implemented with a sleep() call https://en.wikipedia.org/wiki/Cron#History https://en.wikipedia.org/wiki/Cron#History