feat(concurrency): use parking_lot for the default backend#1541
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Adds `parking_lot` as the production backend behind the
`parking_lot` feature, and turns that feature on by default.
`parking_lot::{Mutex, RwLock}` already match the surface this crate
presents -- naked guards, no poison, fast contention path -- so the
default backend now pays no wrapping cost. Production builds get
the perf path; `--no-default-features` falls back to the
`std_backend` poison-as-panic wrapper from the previous PR.
* `concurrency::sync::parking_lot_backend` re-exports
`parking_lot::{Mutex, RwLock, ...Guard}` and the
`parking_lot`-shaped surface for `RwLockUpgradableReadGuard`
(`upgrade()` / `try_upgrade()` are inherited directly). Other
std-only types (`Arc`, `Weak`, `atomic`, `mpsc`, `Once`,
`OnceLock`, `Barrier`, `Condvar`) come straight from `std::sync`.
* `concurrency/src/sync/mod.rs` routes: `parking_lot` feature on
(default) -> parking_lot backend; `parking_lot` feature off ->
`std_backend`; loom / shuttle features keep their raw re-exports.
Workspace `Cargo.toml` adds `tokio/parking_lot` as a documented
exception to the "no workspace-wide features" rule. Without it,
tokio's runtime picks a different lock implementation than the
rest of the dataplane, which is divergence we don't want between
test binaries and the real dataplane process.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Signed-off-by: Daniel Noland <daniel@githedgehog.com>
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Summary
parking_lotCargo feature (enabled by default) and aconcurrency/src/sync/parking_lot_backend.rsthat is a zero-cost re-export ofparking_lot::{Mutex, RwLock}plus the std re-exports for everythingparking_lotdoesn't ship (Arc,Weak, atomics,Condvar, ...).concurrency/src/sync/mod.rspicksparking_lot_backendwhenfeature = "parking_lot"is on, falls back tostd_backendotherwise._strict_provenancefeature overridesparking_lotand routes throughstd_backend:parking_lot_core::word_lockuses integer-to-pointer casts that-Zmiri-strict-provenancerejects, and the CI miri job (--features=_strict_provenance) exercises the fallback slot, which needsstd::syncunderneath.Cargo.tomlgets atokioparking_lot override entry so thetokioparking_lot feature is enabled workspace-wide.PR 3 of 6. Depends on #1540 — facade-std. The next PR sweeps the workspace data-path crates to consume the facade.