<A, E>(self: Fiber<A, E>): Effect<A, E>Joins a fiber, blocking until it completes. If the fiber succeeds, returns its value. If it fails, the error is propagated.
When to use
Use when you need a forked fiber's failure to fail the current Effect because that fiber is part of the current workflow.
Gotchas
Joining a failed fiber propagates the fiber's Cause. Use await when
you need to inspect the Exit instead of failing.
Example (Joining a fiber)
import { Effect, Fiber } from "effect"
const program = Effect.gen(function*() {
const fiber = yield* Effect.forkChild(Effect.succeed(42))
const result = yield* Fiber.join(fiber)
console.log(result) // 42
})export const const join: <A, E>(
self: Fiber<A, E>
) => Effect<A, E>
Joins a fiber, blocking until it completes. If the fiber succeeds,
returns its value. If it fails, the error is propagated.
When to use
Use when you need a forked fiber's failure to fail the current Effect because
that fiber is part of the current workflow.
Gotchas
Joining a failed fiber propagates the fiber's Cause. Use
await
when
you need to inspect the Exit instead of failing.
Example (Joining a fiber)
import { Effect, Fiber } from "effect"
const program = Effect.gen(function*() {
const fiber = yield* Effect.forkChild(Effect.succeed(42))
const result = yield* Fiber.join(fiber)
console.log(result) // 42
})
join: <function (type parameter) A in <A, E>(self: Fiber<A, E>): Effect<A, E>A, function (type parameter) E in <A, E>(self: Fiber<A, E>): Effect<A, E>E>(self: Fiber<A, E>(parameter) self: {
id: number;
currentOpCount: number;
getRef: <A>(ref: Context.Reference<A>) => A;
context: Context.Context<never>;
setContext: (context: Context.Context<never>) => void;
currentScheduler: Scheduler;
currentDispatcher: SchedulerDispatcher;
currentSpan: AnySpan | undefined;
currentLogLevel: LogLevel;
minimumLogLevel: LogLevel;
currentStackFrame: StackFrame | undefined;
maxOpsBeforeYield: number;
currentPreventYield: boolean;
addObserver: (cb: (exit: Exit<A, E>) => void) => () => void;
interruptUnsafe: (fiberId?: number | undefined, annotations?: Context.Context<never> | undefined) => void;
pollUnsafe: () => Exit<A, E> | undefined;
pipe: { <A>(this: A): A; <A, B = never>(this: A, ab: (_: A) => B): B; <A, B = never, C = never>(this: A, ab: (_: A) => B, bc: (_: B) => C): C; <A, B = never, C = never, D = never>(this: A, ab: (_: A) => B, bc: (_: B) => C, cd: (_: C) => D): D; <…;
}
interface Fiber<out A, out E = never>A runtime fiber is a lightweight thread that executes Effects. Fibers are
the unit of concurrency in Effect. They provide a way to run multiple
Effects concurrently while maintaining structured concurrency and
cancellation safety.
When to use
Use to observe, join, interrupt, or coordinate work that has already been
forked.
Details
A fiber exposes both safe Effect-based operations, such as
await
,
join
, and
interrupt
, and low-level runtime fields used by
the scheduler and runtime internals.
Gotchas
Prefer the exported functions in this module over calling interruptUnsafe
or pollUnsafe directly. The unsafe methods are immediate runtime hooks and
do not provide the same Effect-based sequencing guarantees.
Example (Awaiting a forked fiber)
import { Effect, Fiber } from "effect"
const program = Effect.gen(function*() {
// Fork an effect to run in a new fiber
const fiber = yield* Effect.forkChild(Effect.succeed(42))
// Wait for the fiber to complete and get its result
const result = yield* Fiber.await(fiber)
console.log(result) // Exit.succeed(42)
return result
})
The Fiber namespace contains utility types and functions for working with fibers.
It provides type-level utilities for fiber operations and variance encoding.
When to use
Use to reference type-level helpers associated with Fiber.
Details
The namespace currently exposes type-level support used by the Fiber
interface. Runtime operations are exported as module-level functions.
Example (Working with fiber types)
import { Effect, Fiber } from "effect"
const program = Effect.gen(function*() {
// Create a fiber
const fiber = yield* Effect.forkChild(Effect.succeed(42))
// Use namespace types for variance
const typedFiber: Fiber.Fiber<number, never> = fiber
// Access fiber properties
console.log(`Fiber ID: ${fiber.id}`)
// Join the fiber
const result = yield* Fiber.join(fiber)
return result // 42
})
Fiber<function (type parameter) A in <A, E>(self: Fiber<A, E>): Effect<A, E>A, function (type parameter) E in <A, E>(self: Fiber<A, E>): Effect<A, E>E>) => import EffectEffect<function (type parameter) A in <A, E>(self: Fiber<A, E>): Effect<A, E>A, function (type parameter) E in <A, E>(self: Fiber<A, E>): Effect<A, E>E> = import effecteffect.const fiberJoin: <A, E>(
self: Fiber.Fiber<A, E>
) => Effect.Effect<A, E>