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variable / @typed/fx

Fx.drainLayer

Runs an Fx stream as a Layer. The stream is forked in the background when the layer is acquired.

Package version
2.0.0-beta.7
Category
Running effects
Since
1.0.0
Member of
Fx

Follow one execution

Acquire a Layer that drains values in a background fiber; closing the Layer Scope interrupts it.

Fx timelinedrainLayer(source)drainLayer
OperatordrainLayer(source)
Read this diagram

Follow each lane from left to right. Events stacked vertically share a tick; the green cursor marks the current time across every lane.

  • A value
    The text inside the pill is the emitted value.
  • Work starts
    The raised chevron starts an inner run (^ in the source).
  • The run returns
    The vertical bar ends this lane’s run.
  • A cause is delivered
    The exclamation mark belongs to this lane.
  • Work is interrupted
    The cross marks cancellation of this run.
  • Current time
    The line and diamond move together across all lanes.
  • Happening now
    A highlighted event is at the current tick.
  • Still ahead
    Muted, dashed values have not happened yet.
  • Time continues
    The lane’s arrow is not a return marker. An empty stretch can be quiet work that is still running.

Illustrated ticks start at 0. At 1×, one illustrated tick takes one second; captions specify real durations when timing matters. A cause or interruption belongs to its lane, and other work may continue. Scroll horizontally to inspect the rest of a long timeline.

Building the Layer starts drain(fx) with forkScoped. Acquisition succeeds after the fiber is registered; it does not wait for that fiber. The Layer scope interrupts the fiber on release. A source failure is stored in the discarded child Fiber exit: it does not fail Layer acquisition and this API exposes no handle for awaiting it. Recover, report, or otherwise observe failures inside fx before calling drainLayer, or use fork when the caller needs the Fiber exit. The annotated E channel remains in the public Layer type even though the background exit is not propagated by this implementation. Scope is supplied by the Layer.

Source implementation · Learn the surrounding model

Compare all Fx timelines →

Import

import { Fx } from "@typed/fx";

Access Fx.drainLayer through the imported Fx export. Its declaration below describes the member.

This public exposure is a re-export. Its import path is supported; declaration documentation is shared with the other public exposures below.

Signatures

export declare const drainLayer: <A, E, R>(fx: Fx<A, E, R>) => Layer<never, E, Exclude<R, Scope>>;

Why

A background producer can share the same acquisition and shutdown boundary as an application’s Effect Layer graph even when it provides no service itself.

Ownership and lifetime

Building the Layer starts drain(fx) with forkScoped. Acquisition succeeds after the fiber is registered; it does not wait for that fiber. The Layer scope interrupts the fiber on release. A source failure is stored in the discarded child Fiber exit: it does not fail Layer acquisition and this API exposes no handle for awaiting it. Recover, report, or otherwise observe failures inside fx before calling drainLayer, or use fork when the caller needs the Fiber exit. The annotated E channel remains in the public Layer type even though the background exit is not propagated by this implementation. Scope is supplied by the Layer.

Examples

import { Effect } from "effect"
import { Fx } from "@typed/fx"

const reported = Fx.fail("offline").pipe(
  Fx.catch((error) => Fx.fromEffect(Effect.logError(error)))
)
const Background = Fx.drainLayer(reported)
const program = Effect.void.pipe(Effect.provide(Background))

Other public imports

These import paths expose the same declaration. Each page retains its own public name and signature.

Source