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Design Goal

  • No delay job. Next schedule for a particular job shall not be delayed for its processing time. For example: Every(1).Minute() ensures tasks run at 10:01, 10:02, 10:03, but not 10:01+processing.
  • Every(second,minute,hour,day,week).At(hh:mm)

Design Specs

CRON

An ADT that maintains a sequence of chronologically sorted entries. Cron keeps track of any number of entries, invoking the associated func as specified by the schedule. It may also be started, stopped and the entries may be inspected.

  • Start(). Signals 'start' to get cron instant up & running.
  • Add(schedule, job). Signals add to add entry(schedule, job) to cron instant.
  • Stop(). Signals stop to halt cron instant's processing. Bear in mind that (child go-routines) running jobs will be halted as well.
  • StopAfterJobDone. Signals stop after job done to halt cron processing. Different to stop signal, running child go-routines would finish normally before cron stop.
  • Clear(). Clear all entries from queue.
  • run(). Core functionality, run indefinitely(go-routine), forking out child go-routine: one for each job, multiplexing different channels/signals.

SCHEDULE

An interface which wraps Next(time) method.

  • Next(time). Deduces next occurring schedule w.r.t time instant t.

JOB

An interface which wraps Run method.

  • Run(wg *sync.WaitGroup). To execute the underlying func.

ENTRY

An ADT consists of a schedule and job to be run on that schedule. Also known as wrapper to schedule and job.

It keep tracks on the following states: schedule, job, next, prev.

Detailed Design

Cron: run() -- core

  1. Sort entries chronologically.
  2. Earliest entry be taken as the next triggering point.
  3. Multiplexing of blocking channels/signals, that includes:
    • ready. earliest entry is ready to be run, in which subsequent entries will be measured, for which time is up and ready, it will be run as well.
    • add. add to entries.
    • stop.
  4. Repeat 1. until stop is signaled.

Entry: Sorted entry-slice

Entry slice implements sort package, chronologically.

Schedule: periodicSchedule

A periodic schedule which occurs periodically: t + period

  • Every(period). Returns a periodicSchedule instant.

Testing

Given a queue of scheduled entries. Test that:

  • order of execution. add entries in reverse order, after one run, expects all entries are sorted accordingly.
  • execution. ensure all entries are being executed.
  • test concurrency adding.