Fiber stack initial size and cap

Platform spec ADR

Fiber stack initial size and cap

Back to Fiber scheduler and stacks ◎ Open feature in platform map

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

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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

Context

Fiber stacks must balance memory use against deep call chains from generated code and corelib. GC needs precise stack maps at safepoints on every fiber stack.

Decision

Parameter	Value
Initial size	64 KiB per fiber
Growth	Growable until cap
Maximum	8 MiB cap per fiber
Overflow	FiberError::StackOverflow at Join — no undefined behavior
Switching	Callee stacks ABI-aligned; callee-saved registers saved per platform ABI
GC	All fiber stacks enumerable at safepoints via compiler stack maps

Consequences

Documentation and corelib must cite these limits. Stack switching may use manual swap techniques documented in design model.

Verification anchors

Scheduler stack allocator; fiber spawn/join integration tests.