@prelude/supervisor · v1.0.1

Supervisor module

Restart strategies and restart limits for @prelude/actor, in the spirit of Erlang/OTP supervisors.

one-for-one restarts the failing child; all-for-one restarts every child; rest-for-one restarts the failing child and those started after it.
Restarts happen in place (Actor.restart): mailboxes and references survive.
More than maxRestarts restarts within window ms makes the supervisor give up: it escalates to its own supervisor if it has one, otherwise it kills the remaining children and fails with a SupervisorError.
Supervisors nest: a supervisor is itself a supervisable child.

Usage

npm i -E @prelude/supervisor

import * as Supervisor from '@prelude/supervisor'

const supervisor = Supervisor.of({ strategy: 'one-for-one', maxRestarts: 3, window: 5000 })

const worker = supervisor.spawn({
  name: 'worker',
  init: () => ({ processed: 0 }),
  receive: (job: Job, state) => {
    state.processed += 1
    return process(job)          // a throw here restarts the worker with fresh state
  }
})

supervisor.supervise(existingActor)     // adopt an actor created elsewhere

await supervisor.stop()                 // stops children in reverse start order

Children escalate to the supervisor through their failure policy — the default 'escalate' directive — so a child with a local onError that returns 'resume' never reaches it.

Nesting

const root = Supervisor.of({ strategy: 'one-for-one', maxRestarts: 1 })
const workers = root.supervise(Supervisor.of({ strategy: 'all-for-one', maxRestarts: 5 }))
workers.spawn(…)

When workers exhausts its restart budget it asks root; a 'restart' from root restarts every worker and resets the budget, a 'stop' kills the workers and fails workers, which in turn counts against root's budget.

Deterministic tests

Pass now to control the restart window:

let time = 0
const supervisor = Supervisor.of({ maxRestarts: 2, window: 1000, now: () => time })

License

This package is dedicated to the public domain under CC0 1.0.