MixedSchedulerProvides a scheduler implementation that batches queued tasks and dispatches them by priority.
When to use
Use when you need the default runtime scheduler directly, including a scheduler that batches queued work by priority and preserves FIFO order within each priority.
Details
MixedScheduler supports synchronous and asynchronous execution modes, uses
operation counts to decide when fibers should yield, and is the default
scheduler implementation.
export class class MixedSchedulerclass MixedScheduler {
executionMode: "sync" | "async";
setImmediate: (f: () => void) => () => void;
shouldYield: (fiber: Fiber.Fiber<unknown, unknown>) => boolean;
makeDispatcher: () => MixedSchedulerDispatcher;
}
Provides a scheduler implementation that batches queued tasks and dispatches them by
priority.
When to use
Use when you need the default runtime scheduler directly, including a
scheduler that batches queued work by priority and preserves FIFO order within
each priority.
Details
MixedScheduler supports synchronous and asynchronous execution modes, uses
operation counts to decide when fibers should yield, and is the default
scheduler implementation.
MixedScheduler implements Scheduler {
readonly MixedScheduler.executionMode: "sync" | "async"executionMode: "sync" | "async"
readonly MixedScheduler.setImmediate: (f: () => void) => () => voidsetImmediate: (f: () => voidf: () => void) => () => void
constructor(
executionMode: "sync" | "async"executionMode: "sync" | "async" = "async",
setImmediateFn: (f: () => void) => () => voidsetImmediateFn: (f: () => voidf: () => void) => () => void = const setImmediate: (
f: () => void
) => () => void
MixedScheduler.executionMode: "sync" | "async"executionMode = executionMode: "sync" | "async"executionMode
this.MixedScheduler.setImmediate: (f: () => void) => () => voidsetImmediate = setImmediateFn: (f: () => void) => () => voidsetImmediateFn
}
/**
* Returns whether the fiber has reached its operation budget and should yield.
*
* **When to use**
*
* Use to decide whether a fiber should yield after consuming its current
* operation budget.
*
* @since 2.0.0
*/
MixedScheduler.shouldYield(fiber: Fiber.Fiber<unknown, unknown>): booleanReturns whether the fiber has reached its operation budget and should yield.
When to use
Use to decide whether a fiber should yield after consuming its current
operation budget.
shouldYield(fiber: Fiber.Fiber<unknown, unknown>(parameter) fiber: {
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; <…;
}
import FiberFiber.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<unknown, unknown>) {
return fiber: Fiber.Fiber<unknown, unknown>(parameter) fiber: {
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; <…;
}
Fiber<out A, out E = never>.currentOpCount: numbercurrentOpCount >= fiber: Fiber.Fiber<unknown, unknown>(parameter) fiber: {
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; <…;
}
Fiber<out A, out E = never>.maxOpsBeforeYield: numbermaxOpsBeforeYield
}
/**
* Creates a dispatcher that schedules work through this scheduler.
*
* **When to use**
*
* Use when you need a standalone dispatcher from a scheduler instance, for
* example in tests that enqueue tasks and then flush them deterministically.
*
* @since 4.0.0
*/
MixedScheduler.makeDispatcher(): MixedSchedulerDispatcherCreates a dispatcher that schedules work through this scheduler.
When to use
Use when you need a standalone dispatcher from a scheduler instance, for
example in tests that enqueue tasks and then flush them deterministically.
makeDispatcher() {
return new constructor MixedSchedulerDispatcher(setImmediateFn?: (f: () => void) => () => void): MixedSchedulerDispatcherMixedSchedulerDispatcher(this.MixedScheduler.setImmediate: (f: () => void) => () => voidsetImmediate)
}
}