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Redesign AsyncioWaker around caller-context-independent state transitions

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Valutazione

Difficoltà
5/5
Tempo stimato
Più di una settimana
Idoneità per principianti
25/100
Tipo di issue
Refactoring
Chiarezza
Da chiarire
Stato di attività
Attiva
Stack tecnologico
rust
Ambito
backend, testing-qa

Direzione di ricerca

Start with src/future/asyncio/waker.rs and the runtime attachment check in src/utils.rs, then run the subprocess regressions in python/tests/test_deadlocks.py. Agree on the state-machine design before implementation; done means the listed wake, callback, shutdown, finalization, and subprocess tests define correct behavior without public Python API changes.

Scritto dal modello di indicizzazione a partire dal testo della issue.

Descrizione

enhancement

Problem and proposed change

AsyncioWaker connects Rust future wakeups to an asyncio.Future. A mutex-protected slot records whether the coroutine is idle, was woken before parking, or is parked on a Python future.

A Rust future can wake:

  • synchronously while Python is polling it; or
  • later from a detached Tokio worker.

The standard Wake trait does not report which context called it. Current code therefore detects attachment at runtime. Parking also invokes Python event-loop methods while holding the slot mutex. These assumptions make lock ordering, shutdown, and interpreter finalization difficult to reason about.

Redesign the state machine so the mutex protects only short state transitions and ownership moves. Release the mutex before calling Python or destroying Python-owned values. Make wake_by_ref work without detecting caller attachment.

Agree on the design first, then implement it separately.

Context

Current slot states and parking path:

https://github.com/scylladb/python-rs-driver/blob/ef53b6c01f174add44c87c184740a02eadf51d7f/src/future/asyncio/waker.rs#L39-L110

Current explicit wake methods and mixed-context Wake implementation:

https://github.com/scylladb/python-rs-driver/blob/ef53b6c01f174add44c87c184740a02eadf51d7f/src/future/asyncio/waker.rs#L113-L172

Current runtime attachment check:

https://github.com/scylladb/python-rs-driver/blob/ef53b6c01f174add44c87c184740a02eadf51d7f/src/utils.rs#L308-L323

Existing subprocess regressions:

https://github.com/scylladb/python-rs-driver/blob/ef53b6c01f174add44c87c184740a02eadf51d7f/python/tests/test_deadlocks.py#L27-L132

The same-thread re-entry report #212 was closed as not planned. This proposal is broader structural hardening, not an automatic reopening:

https://github.com/scylladb/python-rs-driver/issues/212

An unconditional Python attachment on every worker wake could hurt performance. Related investigation:

https://github.com/scylladb/python-rs-driver/issues/179

Acceptance criteria

  • The slot guard protects only state transitions and ownership moves.
  • Python calls and Python-owned-value destruction occur after unlocking.
  • wake_by_ref does not need to detect caller attachment.
  • Wake before, during, and after parking remains correct.
  • Tests cover synchronous self-wake and detached worker wake.
  • Tests cover callback completion, close, cancel, and exception delivery.
  • Task destruction and runtime shutdown behavior are defined.
  • Interpreter-finalization behavior is defined if any fallback attaches.
  • Potential hangs run in subprocesses with external watchdogs.
  • Tests detect lost and duplicate wakeups.
  • The worker fast path does not gain unconditional Python attachment without an explicit performance decision.
  • No public Python API changes.
Lingua principale
Rust
Stelle
6
Fork
8
Merge medio
5g 18h
PR unite (30g)
13

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