It’s not even a centralized task scheduler on its native UNIX: iI’s a centralized *userspace* task scheduler.
Mainframe and minicomputer operating systems support scheduling in the operating system itself, as part of their process/thread scheduler; their native queuing systems are built on top of the primitives their scheduler offers, for proper accounting and maximum resource utilization (including prioritization).
Only UNIX would just provide a way to run processes at a specified time or interval and call the job done.
Although you're right that Unix never really reached having the full three-level scheduling mechanisms of the mainframe operating systems, cron is not the actual Unix parallel of the high-level scheduler that keeps the running jobs list fed.
That is in fact batch (and atrun, although that's considered an implementation detail).
I was going to guess the author needed something that unified the task scheduling across a distributed system of computers. But that requirement is never mentioned in the article. And they still use cron to call their new scheduler... So unless I am missing something they did not replace cron al all, they just rewrote their scheduled jobs to use a common library and have more robust error handling.
It's lacking a convenient way to queue a task and inspect the task queue, but "at" (at/atq/atrm) provides exactly the "single cron job responsible for executing scheduled tasks that runs once every minute" that the author was looking for.
It’s not even a centralized task scheduler on its native UNIX: iI’s a centralized *userspace* task scheduler.
Mainframe and minicomputer operating systems support scheduling in the operating system itself, as part of their process/thread scheduler; their native queuing systems are built on top of the primitives their scheduler offers, for proper accounting and maximum resource utilization (including prioritization).
Only UNIX would just provide a way to run processes at a specified time or interval and call the job done.
Although you're right that Unix never really reached having the full three-level scheduling mechanisms of the mainframe operating systems, cron is not the actual Unix parallel of the high-level scheduler that keeps the running jobs list fed.
That is in fact batch (and atrun, although that's considered an implementation detail).
* https://pubs.opengroup.org/onlinepubs/9799919799/utilities/b...
Most implementations flesh out the "implementation-defined algorithms" stuff to be calculations based upon load averages, as on NetBSD.
* https://man.netbsd.org/batch.1
* https://man.netbsd.org/atrun.8
Or fairly primitive parallelism limits as on Illumos.
* https://illumos.org/man/1/batch
* https://illumos.org/man/5/queuedefs
Not quite JECL, is it? (-:
I was going to guess the author needed something that unified the task scheduling across a distributed system of computers. But that requirement is never mentioned in the article. And they still use cron to call their new scheduler... So unless I am missing something they did not replace cron al all, they just rewrote their scheduled jobs to use a common library and have more robust error handling.
It's lacking a convenient way to queue a task and inspect the task queue, but "at" (at/atq/atrm) provides exactly the "single cron job responsible for executing scheduled tasks that runs once every minute" that the author was looking for.
centralized for many computers.