Extract GoodJob::Capsule

[bensheldon]

Extracts the duplicated instantiation of Scheduler, Poller, CronManager, etc that existed in both the Async Adapter and CLI into a single object.

• Name inspired by Sidekiq: https://ruby.social/@bensheldon/109722709921698011
• Extracted from ProcessManager refactoring, but also tried doing something similar in e4c5cfc (archived in Create Manager class #858) last year
• Extracting the thread executors out of the Adapter was long intended after Deprecate Adapter configuration of job execution/cron #558

Observations and Risks

• This creates a global GoodJob.capsule that holds the Scheduler (thread executor). It was previously easily possible to create multiple async Adapters, and thus end up with multiple Schedulers. This PR creates a better distinction and symmetry between the Adapter which enqueues, and the Capsule, which dequeues/executes. I think that subtly changes the meaning of the Adapters Async mode, but not a lot:
  • Old: Async Adapter executes in the same process
  • New: Async Adapter will enqueue and attempt to execute the job in an existing Capsule/Scheduler that may be running in the current process. (That’s a mouthful)
• As always, Rails boot/startup has some risky async orchestration.
• Where it's going: The future destination is having a stronger guarantee around the Process record: that the Process record must be present before jobs are executed, the Process record must be present until after the Schedulers are shut down, and Schedulers must not execute jobs if the Process record does not exist or is in a bad state. This makes it easier to get to Proposal: convert from session-based Advisory Locks to locked_at/locked_by columns #831. That also means that eventually “Process Record” will really be “Capsule (Process) Record” but that likely won’t be noticed