Some hosting providers have a requirement to prevent users making
modifications to the configuration of scheduled tasks as doing so may have
a negative impact not only on their own site, but also on the performance
of other sites (depending on host configuration). For example, if the
statistics or automated backup tasks were run every minute, this could have
a negative impact for other users).
Centralise management of all types of cron tasks with registration, scheduling,
parallel task conflicts(blocking) and running once off tasks, all using an
administration screen.
This is a combination of several issues:
MDL-25502: Added "black magic" task allocator for cron
MDL-25503: Add step to cron to run all scheduled tasks
MDL-25504 cron: Refactor to use scheduler
MDL-25505: Add an admin interface to schedule tasks via cron.
MDL-25507: Add support for adhoc tasks.
