refs https://github.com/TryGhost/Ghost/issues/12402
- Describes different types of jobs that could be executed depending on the nature of the jobs.
- Lays down ground rules on how to design scheduled jobs
no issue
- When providing a crontab schedule expression it should always contain 6 elements first one of them being a "seconds" schedule description . For example: '0/5 * * * * *' - meaning to run every 5 seconds
no issue
- When jobs are performing CPU intensive tasks they block main process'
event loop. They also can cause memory leaks or unexpected crashes
effectively crashing the parent proccess. To address these issues jobs need to be performed off of main
process. Worker Threads (https://nodejs.org/dist/latest-v12.x/docs/api/worker_threads.html)
are the best candidate for such work.
- These changes introduce an integration on top of bree
(https://github.com/breejs/bree/) which allows to run recurring
jobs in worker thereads. It falls back to child process execution for
Node v10 running without `--experimental-worker` flag.
- bree was chosen not only because it gives a polyfill for older Node
versions. It has support for some of the future use-cases Ghost is looking to
implement, like scheduled jobs.
- This changeset also includes a complete example of job running on an
interval with a possibility for graceful shutdown
no issue
- This is a quick implementation change to prevent from queue stalling and never becoming idle in case there's an error thrown from within the job function/module
- More robust error handling should be designed soon!
no issue
- Jobs should not always be functions, one of the standard practices is having a job defined in a module as a self contained executable function
- First parameter of `addJob` function now also handles path to modules which it imports and executes
no issue
- Accepting the schedule or a data when scheduled job should be run would follow a signature used in other established frameworks: (1) https://github.com/mperham/sidekiq/wiki/Ent-Periodic-Jobs#definition
- Another reason to put scheduling parameter first is this would allow leaving an optional "data" parameter as last
no issue
- CRON format is the most common one used for job scheduling and is well known to most developers
- This will become one of supported formats for job scheduling
