Cluster.Singleton reference

Singleton

Source: packages/effect-cluster/src/Singleton.ts

A Singleton on an Effect Cluster: one fiber, running on exactly one of its pool. If that runner stops, another starts it.

Declare it by name, with its implementation: an Effect that resolves bindings once per runner and returns the fiber, which only the runner that owns the singleton runs. Providing a pool Layer to the implementation is what deploys it. Or declare it bare and implement it with .make(props, impl), as a Layer.

Singleton: Declaring a singleton

A loop that runs once across the cluster

src/Reaper.ts

export default class Reaper extends Cluster.Singleton<Reaper>()(
  "Reaper",
  { main: import.meta.url },
  Effect.gen(function* () {
    const counters = yield* Counter;
    return Effect.gen(function* () {
      const counter = yield* counters.getByName("reaped");
      yield* counter.Increment({ amount: 1 });
    }).pipe(Effect.repeat(Schedule.spaced("1 minute")), Effect.orDie);
  }).pipe(Effect.provide(Default)),
) {}

Declared bare, and implemented as a Layer

src/Reaper.ts

export class Reaper extends Cluster.Singleton<Reaper>()("Reaper") {}

// src/ReaperLive.ts
export default Reaper.make(
  { main: import.meta.url },
  Effect.gen(function* () {
    const counters = yield* Counter;
    return Effect.gen(function* () {
      const counter = yield* counters.getByName("reaped");
      yield* counter.Increment({ amount: 1 });
    }).pipe(Effect.repeat(Schedule.spaced("1 minute")), Effect.orDie);
  }).pipe(Effect.provide(Default)),
);