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prometeu-runtime/discussion/workflow/plans/PLN-0113-implement-thread-safe-latest-wins-handoff.md

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id ticket title status created completed ref_decisions tags
PLN-0113 real-render-worker-establishment Implement Thread-Safe Latest-Wins Handoff open 2026-06-15
DEC-0033
runtime
renderer
worker
concurrency
handoff

Briefing

DEC-0033 requires a thread-safe single-slot latest-wins handoff. The producer must replace pending work without waiting for rasterization or present, and the consumer must take ownership of the latest pending submission.

Decisions de Origem

  • DEC-0033: Real Render Worker Contract.

Alvo

Add the real worker handoff primitive in prometeu-system, using explicit synchronization and deterministic tests.

Escopo

  • Implement a single-slot pending submission structure.
  • Use Mutex<Option<RenderSubmission>> + Condvar or an equivalent explicit structure.
  • Add producer publish/replace behavior and consumer wait/take behavior.
  • Track replacement/drop telemetry.

Fora de Escopo

  • No worker thread controller lifecycle.
  • No backend rendering.
  • No host integration.
  • No stale epoch publish behavior beyond storing ownership data already present in submissions.

Plano de Execucao

Step 1 - Add handoff module

What: Create the worker handoff primitive. How: Add a module under crates/console/prometeu-system/src/services/vm_runtime/, for example render_worker_handoff.rs. File(s): new system module, mod.rs exports.

Step 2 - Implement publish replacement

What: Producer publishes owned RenderSubmission. How: Lock the slot, replace any pending submission, increment replacement/drop counters when applicable, notify the condvar, and return immediately. File(s): handoff module.

Step 3 - Implement consumer wait/take

What: Consumer waits for work or shutdown signal. How: Add wait/take APIs that block only the consumer side and return owned submissions. File(s): handoff module.

Step 4 - Add deterministic tests

What: Prove latest-wins and blocking boundaries. How: Use threads, barriers, and condvars to prove producer replacement and consumer wake behavior without sleeps. File(s): handoff module tests or async_render_contract_tests.rs.

Criterios de Aceite

  • Producer publish does not wait for consumer rasterization.
  • Multiple pending publishes leave only the newest submission available.
  • Replacements increment telemetry.
  • Consumer can wait for work and is woken by publish.
  • Tests do not use sleep as their primary synchronization proof.

Tests / Validacao

  • cargo test -p prometeu-system render_worker_handoff
  • cargo test -p prometeu-system

Riscos

  • Holding the mutex while doing heavy work would violate non-blocking producer behavior.
  • Condvar wait loops must handle spurious wakeups.