M:N cooperative fiber scheduler

Platform spec ADR

M:N cooperative fiber scheduler

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Spec standingStandard

Owner

Piotr Mikstacki pmikstacki@cybernomad.it

Submitter

Piotr Mikstacki pmikstacki@cybernomad.it

Current document

Articles

• Fiber scheduler and stacks - Design model Scheduler loops, parking, and stack switching implementation expectations. article Standard Reviewed Wed May 20
• Fiber scheduler and stacks - Verification and traceability Tests and ABI anchors for fiber scheduler work. article Standard Reviewed Wed May 20

History

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Completeness

OKfeature · 9 SpecSection(s) · 1 H2 heading(s)

Section id	Required	Found
what-this-feature-specifies	yes	yes
implementation-anchors	yes	yes

Full tree: run pnpm verify:platform-spec-layout (writes src/generated/platform-spec-layout-report.json).

Related spec docs

• Feature
  Fiber scheduler and stacks

  Parent feature hub

• Feature
  Fibers and spawn

  spawn lowering

Context

Beskid rejects Rust-style async/await state machines at the language level (D-INC-0008). The runtime must provide cooperative concurrency primitives consumed by corelib_concurrency.

Decision

Rule	Detail
Model	M:N — many fibers on a pool of OS worker threads
API surface	fiber_* builtins back `Fiber<T>`; no async lowering in compiler
Preemption	User fibers are cooperative; preemptive parallelism uses System.Threading (OS threads)
Work stealing	Per-worker run queues; work-stealing permitted
Parking	Fibers park on channel ops, join, cancel, and blocking syscalls

Consequences

Scheduler modules live under beskid_runtime/src/scheduler/. Deprecated rt_yield (sched feature) is superseded by fiber_yield.

Verification anchors

compiler/crates/beskid_runtime/tests/concurrency.rs; corelib concurrency tests; git: 12ee673, 76a58f5.