feat(runtime): phase 3 — pluggable run queue (rq-mutex / rq-mpmc / rq-striped)
src/run_queue.rs: the run queue extracted behind a compile-time-selected type alias; mutually-exclusive cargo features with compile_error! guards (zero or >1 selected). No runtime dispatch. All variants compile in every build so their unit tests always run; the feature only picks the alias. - rq-mutex (default): Mutex<VecDeque>, the control/baseline. - rq-mpmc: hand-rolled Vyukov bounded MPMC ring, per-cell sequence numbers, padded enqueue/dequeue counters. Strict FIFO, lock-free. - rq-striped: M Vyukov rings (M = thread_count rounded up to pow2), fetch-add ticket distribution, probe-from-home on push. Relaxed FIFO with stripe-bounded skew; Σcapacity ≈ 2×max_actors so the probe terminates. Capacity soundness: occupancy ≤ max_actors by the at-most-once-enqueued invariant + slab cap, rings sized ≥ that bound, so push is infallible; a full ring panics as a double-enqueue invariant violation rather than spin. Two contracts the extraction made explicit (documented + debug-asserted): - Queue ops require preemption disabled: a producer suspended between claiming a cell and publishing its sequence stalls every consumer behind it — livelock, since the suspended actor's own resume entry is behind the hole. Structurally guaranteed since the phase-2 with_runtime NoPreempt fix. - pop()==None is a snapshot, not a fence. Termination is counter-first: every queue entry's target stays Queued (hence live) until that entry is popped, so live==0 alone implies nothing actionable is or can be queued; argument rewritten at the schedule_loop site. SharedState and with_shared are deleted — nothing global is mutex-guarded on the run path under the ring variants. Validated: 22 suites green per variant (release for all three; debug with live asserts for all three), ring unit tests (FIFO, lap wraparound, 4p/4c exactly-once, skewed drain) in every build, both compile_error! guards verified to fire.
This commit is contained in:
Claude
@@ -5,7 +5,13 @@ edition = "2021"
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rust-version = "1.95"
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[features]
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default = ["rq-mutex"]
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smarm-trace = []
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# Run-queue selection: exactly one, compile-time (see src/run_queue.rs).
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# Non-default variants need --no-default-features (features are additive).
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rq-mutex = []
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rq-mpmc = []
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rq-striped = []
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[dependencies]
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libc = "0.2"
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+17
-8
@@ -63,19 +63,28 @@ Make slot lookup lock-free and per-slot state independently mutable.
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&& queue empty && live == 0; decrement-last ordering documented as the
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correctness crux at the site.
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## Phase 3 — Pluggable run queue + bench shootout
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- [ ] Extract `RunQueue` behind a `type RunQueue = ...` alias selected at
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compile time by mutually-exclusive features, with a `compile_error!`
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guard if zero or >1 is set. No runtime dispatch.
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## Phase 3 — Pluggable run queue ✅ DONE (shootout = phase 4 harness)
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- [x] `RunQueue` alias in `src/run_queue.rs`, compile-time selected,
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`compile_error!` guards for zero / >1 features. No runtime dispatch.
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All variants compile in every build (unit tests always run); the
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feature only picks the alias. Non-default variants:
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`--no-default-features --features rq-…`.
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- `rq-mutex` — `Mutex<VecDeque>`, the control/baseline.
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- `rq-mpmc` — single hand-rolled Vyukov bounded MPMC ring
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(per-cell seq numbers). Strict FIFO; "one hot cache line".
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- `rq-striped` — M Vyukov rings, fetch-add ticket distribution. Relaxed
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FIFO, reordering bounded by ~M. Predicted winner @20c.
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- [ ] Bounded rings are sound because the slab cap + at-most-once-enqueued
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invariant bound occupancy ≤ `max_actors`; size Σcapacity > `max_actors`
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so push is infallible (probe next stripe when full; terminates).
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- [ ] All hand-rolled, dependency-free (portability incl. possible embedded).
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- [x] Bounded rings sound via slab cap + at-most-once-enqueued (occupancy ≤
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`max_actors`); mpmc capacity = next_pow2(max_actors), striped
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Σcapacity ≈ 2×max_actors with probe-from-home-stripe. A full ring
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panics as an invariant violation (double enqueue), never spins.
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- [x] All hand-rolled, dependency-free.
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- [x] Two contracts surfaced by the extraction, documented + debug-asserted
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in `run_queue.rs`: queue ops require preemption disabled (a producer
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suspended mid-publish stalls every consumer behind its cell — livelock);
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and pop-None is a snapshot, not a fence — termination is counter-first
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(`live == 0` alone implies the queue holds nothing actionable; argument
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rewritten at the `schedule_loop` site).
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## Phase 4 — Bench harness
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- [ ] Raw-structure microbench: N threads, push/pop throughput vs thread count,
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@@ -27,6 +27,7 @@ pub mod link;
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pub mod gen_server;
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pub mod runtime;
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pub(crate) mod raw_mutex;
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pub(crate) mod run_queue;
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pub mod trace;
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// ---------------------------------------------------------------------------
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+4
-3
@@ -27,9 +27,10 @@
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//!
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//! Lock-order position: slot cold locks, the free list, and the stack pool
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//! are all `RawMutex`es and all *leaves among themselves* — never hold two at
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//! once. Holding a `RawMutex` while taking the run-queue mutex (`with_shared`)
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//! is permitted (e.g. unpark from inside a cold section); the reverse —
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//! taking any `RawMutex` from inside `with_shared` — is forbidden.
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//! once. Holding a `RawMutex` while pushing to the run queue is permitted
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//! (e.g. unpark from inside a cold section); the reverse — taking any
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//! `RawMutex` from inside a run-queue op — cannot arise (queue ops call
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//! nothing).
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use std::cell::UnsafeCell;
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use std::ops::{Deref, DerefMut};
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@@ -0,0 +1,467 @@
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//! The run queue, selected at COMPILE TIME by mutually-exclusive cargo
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//! features (no runtime dispatch — the scheduler's pop loop is the hottest
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//! code in the runtime):
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//!
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//! - `rq-mutex` (default) — `Mutex<VecDeque>`. The control/baseline:
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//! strictly FIFO, trivially correct, one global lock.
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//! - `rq-mpmc` — a single hand-rolled Vyukov bounded MPMC ring (per-cell
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//! sequence numbers). Strict FIFO, lock-free, one hot
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//! enqueue/dequeue cache-line pair.
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//! - `rq-striped` — M Vyukov rings with fetch-add ticket distribution.
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//! *Relaxed* FIFO: ordering across stripes is bounded-skewed
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//! (≈ one ring's worth of reordering per stripe), in exchange
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//! for spreading the hot line M ways. Predicted winner at
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//! high core counts; phase 4's shootout decides.
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//!
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//! Select non-default variants with `--no-default-features --features rq-…`
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//! (cargo features are additive, so the default must be switched off).
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//!
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//! All variants are compiled unconditionally (so every build runs every
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//! variant's unit tests); the feature only picks which one the runtime uses
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//! via the [`RunQueue`] alias.
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//!
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//! # Contract (shared by all variants)
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//!
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//! - **Occupancy is bounded by `max_actors`.** A pid is in the queue at most
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//! once (pushes pair 1:1 with transitions into `Queued`; only the
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//! scheduler transitions `Queued → Running` — see the state-machine docs
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//! in `runtime.rs`), and at most `max_actors` actors exist. The bounded
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//! rings are sized ≥ `max_actors`, so **`push` is infallible**; a full
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//! ring is an invariant violation and panics loudly rather than spinning.
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//! - **Preemption must be disabled around every push/pop** (debug-asserted).
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//! For the mutex variant this is the usual no-switch/no-unwind-under-lock
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//! rule. For the rings it is *load-bearing in a sharper way*: a producer
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//! suspended between claiming a cell and publishing its sequence number
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//! stalls every consumer behind that cell — on a busy runtime that is a
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//! livelock, since the suspended actor's own resume entry sits behind the
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//! hole. Callers get this for free: every queue op happens inside
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//! `with_runtime`/`try_with_runtime` (NoPreempt for their span since
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//! phase 2) or on a scheduler thread between resumes (preemption off).
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//! - **`pop() == None` is a snapshot, not a fence.** A push that is mid-
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//! publish (or in a stripe the probe already passed) may be missed; the
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//! caller's idle path sleeps ≤ 100µs and retries, so the cost is a bounded
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//! latency blip, never a lost entry. Termination does not lean on this:
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//! the all-clear is `live_actors == 0` (+ io quiescent), and `live == 0`
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//! already implies the queue holds nothing actionable — see the argument
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//! in `schedule_loop`.
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//! - `len()` is approximate (stats only).
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use crate::pid::Pid;
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use std::cell::UnsafeCell;
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use std::mem::MaybeUninit;
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use std::sync::atomic::{AtomicUsize, Ordering};
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// ---------------------------------------------------------------------------
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// Feature selection
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// ---------------------------------------------------------------------------
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#[cfg(not(any(feature = "rq-mutex", feature = "rq-mpmc", feature = "rq-striped")))]
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compile_error!(
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"smarm: no run queue selected. Enable exactly one of the features \
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`rq-mutex` (default), `rq-mpmc`, `rq-striped`."
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);
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#[cfg(all(feature = "rq-mutex", feature = "rq-mpmc"))]
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compile_error!(
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"smarm: features `rq-mutex` and `rq-mpmc` are mutually exclusive \
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(use --no-default-features to drop the default `rq-mutex`)."
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);
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#[cfg(all(feature = "rq-mutex", feature = "rq-striped"))]
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compile_error!(
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"smarm: features `rq-mutex` and `rq-striped` are mutually exclusive \
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(use --no-default-features to drop the default `rq-mutex`)."
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);
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#[cfg(all(feature = "rq-mpmc", feature = "rq-striped"))]
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compile_error!("smarm: features `rq-mpmc` and `rq-striped` are mutually exclusive.");
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#[cfg(feature = "rq-mutex")]
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pub(crate) type RunQueue = MutexQueue;
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#[cfg(feature = "rq-mpmc")]
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pub(crate) type RunQueue = MpmcRing;
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#[cfg(feature = "rq-striped")]
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pub(crate) type RunQueue = StripedRing;
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#[inline]
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fn assert_no_preempt() {
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debug_assert!(
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!crate::preempt::PREEMPTION_ENABLED.with(|c| c.get()),
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"run-queue op with preemption enabled — a switch mid-op stalls or \
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corrupts the queue; route through with_runtime or scheduler context"
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);
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}
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// ---------------------------------------------------------------------------
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// rq-mutex — the baseline
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// ---------------------------------------------------------------------------
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#[allow(dead_code)]
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pub(crate) struct MutexQueue {
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q: std::sync::Mutex<std::collections::VecDeque<Pid>>,
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}
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#[allow(dead_code)]
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impl MutexQueue {
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pub(crate) fn new(_threads: usize, max_actors: usize) -> Self {
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Self {
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// Pre-size: the queue can never outgrow the slab, and one
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// allocation at init beats reallocating under the lock later.
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q: std::sync::Mutex::new(std::collections::VecDeque::with_capacity(max_actors)),
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}
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}
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pub(crate) fn push(&self, pid: Pid) {
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assert_no_preempt();
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self.q.lock().unwrap().push_back(pid);
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}
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pub(crate) fn pop(&self) -> Option<Pid> {
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assert_no_preempt();
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self.q.lock().unwrap().pop_front()
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}
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pub(crate) fn len(&self) -> u64 {
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self.q.lock().unwrap().len() as u64
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}
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}
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// ---------------------------------------------------------------------------
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// rq-mpmc — Vyukov bounded MPMC ring
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// ---------------------------------------------------------------------------
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//
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// Dmitry Vyukov's bounded MPMC queue: each cell carries a sequence number.
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// A producer may write cell `i` when `seq == pos` (its turn); it publishes
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// with `seq = pos + 1`. A consumer may read when `seq == pos + 1`; it
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// releases the cell to the next lap with `seq = pos + capacity`. Producers
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// and consumers each contend on one counter; cell handoff is a per-cell
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// Acquire/Release pair, so unrelated push/pop pairs don't serialize.
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/// Pad to a cache-line pair so the producer and consumer counters (and the
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/// cells) don't false-share.
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#[repr(align(128))]
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struct CachePadded<T>(T);
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struct Cell {
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seq: AtomicUsize,
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pid: UnsafeCell<MaybeUninit<Pid>>,
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}
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#[allow(dead_code)]
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pub(crate) struct MpmcRing {
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buf: Box<[Cell]>,
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mask: usize,
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enqueue_pos: CachePadded<AtomicUsize>,
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dequeue_pos: CachePadded<AtomicUsize>,
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}
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// SAFETY: cells are handed off between threads via the per-cell seq
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// (Release on publish, Acquire on claim); Pid is Copy + Send.
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unsafe impl Send for MpmcRing {}
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unsafe impl Sync for MpmcRing {}
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#[allow(dead_code)]
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impl MpmcRing {
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pub(crate) fn new(_threads: usize, max_actors: usize) -> Self {
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Self::with_capacity(max_actors)
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}
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fn with_capacity(min_cap: usize) -> Self {
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// Occupancy ≤ max_actors (queue contract), so capacity = the next
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// power of two ≥ max_actors can never overflow. (≥ 2 so mask works.)
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let cap = min_cap.next_power_of_two().max(2);
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let buf: Box<[Cell]> = (0..cap)
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.map(|i| Cell {
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seq: AtomicUsize::new(i),
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pid: UnsafeCell::new(MaybeUninit::uninit()),
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})
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.collect();
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Self {
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buf,
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mask: cap - 1,
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enqueue_pos: CachePadded(AtomicUsize::new(0)),
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dequeue_pos: CachePadded(AtomicUsize::new(0)),
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}
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}
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pub(crate) fn push(&self, pid: Pid) {
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assert_no_preempt();
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assert!(
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self.try_push(pid),
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"smarm: run queue overflow — occupancy exceeded the slab bound, \
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which the at-most-once-enqueued invariant forbids. This is a \
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runtime bug (double enqueue), not a capacity tuning problem."
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);
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}
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/// One full claim attempt; `false` only if the ring is full.
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fn try_push(&self, pid: Pid) -> bool {
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let mut pos = self.enqueue_pos.0.load(Ordering::Relaxed);
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loop {
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let cell = &self.buf[pos & self.mask];
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let seq = cell.seq.load(Ordering::Acquire);
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let diff = seq as isize - pos as isize;
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if diff == 0 {
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// Our turn: claim the position.
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match self.enqueue_pos.0.compare_exchange_weak(
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pos, pos + 1, Ordering::Relaxed, Ordering::Relaxed,
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) {
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Ok(_) => {
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// SAFETY: the claim gives us exclusive write access
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// to this cell until we publish below.
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unsafe { (*cell.pid.get()).write(pid) };
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cell.seq.store(pos + 1, Ordering::Release);
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return true;
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}
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Err(actual) => pos = actual,
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}
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} else if diff < 0 {
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return false; // full — a whole lap behind
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} else {
|
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pos = self.enqueue_pos.0.load(Ordering::Relaxed);
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}
|
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}
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}
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pub(crate) fn pop(&self) -> Option<Pid> {
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assert_no_preempt();
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let mut pos = self.dequeue_pos.0.load(Ordering::Relaxed);
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loop {
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let cell = &self.buf[pos & self.mask];
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let seq = cell.seq.load(Ordering::Acquire);
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let diff = seq as isize - (pos + 1) as isize;
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if diff == 0 {
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match self.dequeue_pos.0.compare_exchange_weak(
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pos, pos + 1, Ordering::Relaxed, Ordering::Relaxed,
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) {
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Ok(_) => {
|
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// SAFETY: the claim gives us exclusive read access;
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// the producer's Release publish made `pid` visible
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// to our Acquire load of `seq`.
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let pid = unsafe { (*cell.pid.get()).assume_init_read() };
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// Release the cell for the next lap.
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cell.seq.store(pos + self.mask + 1, Ordering::Release);
|
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return Some(pid);
|
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}
|
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Err(actual) => pos = actual,
|
||||
}
|
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} else if diff < 0 {
|
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// Empty (or the producer at this cell hasn't published yet —
|
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// a snapshot miss the caller's idle-retry loop absorbs).
|
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return None;
|
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} else {
|
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pos = self.dequeue_pos.0.load(Ordering::Relaxed);
|
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}
|
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}
|
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}
|
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|
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pub(crate) fn len(&self) -> u64 {
|
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let e = self.enqueue_pos.0.load(Ordering::Relaxed);
|
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let d = self.dequeue_pos.0.load(Ordering::Relaxed);
|
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e.saturating_sub(d) as u64
|
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}
|
||||
}
|
||||
|
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// ---------------------------------------------------------------------------
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// rq-striped — M Vyukov rings, ticket-distributed
|
||||
// ---------------------------------------------------------------------------
|
||||
//
|
||||
// Producers fetch-add a ticket and start probing at stripe `ticket % M`;
|
||||
// consumers do the same with their own ticket. Under symmetric load the
|
||||
// tickets spread producers and consumers uniformly, so each stripe sees
|
||||
// ~1/M of the traffic and the single hot cache-line pair becomes M cooler
|
||||
// ones. FIFO is relaxed: two pushes that land in different stripes can be
|
||||
// popped in either order, with skew bounded by stripe occupancy imbalance.
|
||||
//
|
||||
// Push probes forward from its home stripe until a `try_push` succeeds.
|
||||
// Σ stripe capacity ≥ 2 × max_actors while occupancy ≤ max_actors, so at
|
||||
// every instant at least half the total capacity is free and the probe
|
||||
// terminates (in practice on the first stripe).
|
||||
|
||||
#[allow(dead_code)]
|
||||
pub(crate) struct StripedRing {
|
||||
stripes: Box<[MpmcRing]>,
|
||||
/// Stripe count minus one (count is a power of two).
|
||||
stripe_mask: usize,
|
||||
push_ticket: CachePadded<AtomicUsize>,
|
||||
pop_ticket: CachePadded<AtomicUsize>,
|
||||
}
|
||||
|
||||
#[allow(dead_code)]
|
||||
impl StripedRing {
|
||||
pub(crate) fn new(threads: usize, max_actors: usize) -> Self {
|
||||
// One stripe per scheduler thread, rounded up to a power of two —
|
||||
// more stripes than threads buys nothing (at most `threads` ops are
|
||||
// in flight) and costs pop-probe latency when mostly empty.
|
||||
let n = threads.max(1).next_power_of_two();
|
||||
// Per-stripe capacity: 2 × max_actors / n in total, and never below
|
||||
// a floor that keeps degenerate configs (tiny slab, many threads)
|
||||
// trivially correct.
|
||||
let per = ((2 * max_actors) / n).next_power_of_two().max(8);
|
||||
let stripes: Box<[MpmcRing]> = (0..n).map(|_| MpmcRing::with_capacity(per)).collect();
|
||||
Self {
|
||||
stripes,
|
||||
stripe_mask: n - 1,
|
||||
push_ticket: CachePadded(AtomicUsize::new(0)),
|
||||
pop_ticket: CachePadded(AtomicUsize::new(0)),
|
||||
}
|
||||
}
|
||||
|
||||
pub(crate) fn push(&self, pid: Pid) {
|
||||
assert_no_preempt();
|
||||
let home = self.push_ticket.0.fetch_add(1, Ordering::Relaxed);
|
||||
// Probe from the home stripe; capacity headroom (Σ ≥ 2×occupancy)
|
||||
// guarantees a free stripe exists, so the outer loop terminates.
|
||||
// The retry-from-home lap handles the racy case where every stripe
|
||||
// momentarily refused us.
|
||||
loop {
|
||||
for i in 0..=self.stripe_mask {
|
||||
let s = &self.stripes[(home + i) & self.stripe_mask];
|
||||
if s.try_push(pid) {
|
||||
return;
|
||||
}
|
||||
}
|
||||
std::hint::spin_loop();
|
||||
}
|
||||
}
|
||||
|
||||
pub(crate) fn pop(&self) -> Option<Pid> {
|
||||
assert_no_preempt();
|
||||
let home = self.pop_ticket.0.fetch_add(1, Ordering::Relaxed);
|
||||
for i in 0..=self.stripe_mask {
|
||||
if let Some(pid) = self.stripes[(home + i) & self.stripe_mask].pop() {
|
||||
return Some(pid);
|
||||
}
|
||||
}
|
||||
None // snapshot miss possible across stripes; idle-retry absorbs it
|
||||
}
|
||||
|
||||
pub(crate) fn len(&self) -> u64 {
|
||||
self.stripes.iter().map(|s| s.len()).sum()
|
||||
}
|
||||
}
|
||||
|
||||
// ---------------------------------------------------------------------------
|
||||
// Tests — all variants, in every build (the feature only picks the alias)
|
||||
// ---------------------------------------------------------------------------
|
||||
|
||||
#[cfg(test)]
|
||||
mod tests {
|
||||
use super::*;
|
||||
use std::collections::HashSet;
|
||||
use std::sync::Arc;
|
||||
|
||||
fn pid(i: u32) -> Pid {
|
||||
Pid::new(i, 0)
|
||||
}
|
||||
|
||||
fn fifo_smoke<Q>(q: &Q, push: impl Fn(&Q, Pid), pop: impl Fn(&Q) -> Option<Pid>) {
|
||||
for i in 0..100 {
|
||||
push(q, pid(i));
|
||||
}
|
||||
for i in 0..100 {
|
||||
assert_eq!(pop(q), Some(pid(i)));
|
||||
}
|
||||
assert_eq!(pop(q), None);
|
||||
}
|
||||
|
||||
#[test]
|
||||
fn mutex_fifo() {
|
||||
let q = MutexQueue::new(1, 1024);
|
||||
fifo_smoke(&q, |q, p| q.push(p), |q| q.pop());
|
||||
}
|
||||
|
||||
#[test]
|
||||
fn mpmc_fifo_single_thread() {
|
||||
let q = MpmcRing::new(1, 1024);
|
||||
fifo_smoke(&q, |q, p| q.push(p), |q| q.pop());
|
||||
}
|
||||
|
||||
#[test]
|
||||
fn mpmc_wraps_many_laps() {
|
||||
let q = MpmcRing::with_capacity(8);
|
||||
for lap in 0..1000u32 {
|
||||
for i in 0..8 {
|
||||
q.push(pid(lap * 8 + i));
|
||||
}
|
||||
for i in 0..8 {
|
||||
assert_eq!(q.pop(), Some(pid(lap * 8 + i)));
|
||||
}
|
||||
}
|
||||
assert_eq!(q.pop(), None);
|
||||
}
|
||||
|
||||
/// N producers, M consumers, every element exactly once. Run on plain OS
|
||||
/// threads (PREEMPTION_ENABLED defaults false, satisfying the contract).
|
||||
fn exactly_once<Q: Send + Sync + 'static>(
|
||||
q: Q,
|
||||
push: fn(&Q, Pid),
|
||||
pop: fn(&Q) -> Option<Pid>,
|
||||
producers: u32,
|
||||
consumers: u32,
|
||||
per_producer: u32,
|
||||
) {
|
||||
let q = Arc::new(q);
|
||||
let total = (producers * per_producer) as usize;
|
||||
let popped = Arc::new(std::sync::Mutex::new(Vec::with_capacity(total)));
|
||||
let remaining = Arc::new(AtomicUsize::new(total));
|
||||
|
||||
let mut hs = Vec::new();
|
||||
for p in 0..producers {
|
||||
let q = q.clone();
|
||||
hs.push(std::thread::spawn(move || {
|
||||
for i in 0..per_producer {
|
||||
push(&q, pid(p * per_producer + i));
|
||||
}
|
||||
}));
|
||||
}
|
||||
for _ in 0..consumers {
|
||||
let q = q.clone();
|
||||
let popped = popped.clone();
|
||||
let remaining = remaining.clone();
|
||||
hs.push(std::thread::spawn(move || {
|
||||
let mut local = Vec::new();
|
||||
while remaining.load(Ordering::Relaxed) > 0 {
|
||||
if let Some(pid) = pop(&q) {
|
||||
remaining.fetch_sub(1, Ordering::Relaxed);
|
||||
local.push(pid);
|
||||
} else {
|
||||
std::hint::spin_loop();
|
||||
}
|
||||
}
|
||||
popped.lock().unwrap().extend(local);
|
||||
}));
|
||||
}
|
||||
for h in hs {
|
||||
h.join().unwrap();
|
||||
}
|
||||
|
||||
let popped = popped.lock().unwrap();
|
||||
assert_eq!(popped.len(), total, "count mismatch");
|
||||
let set: HashSet<u64> = popped.iter().map(|p| ((p.index() as u64) << 32) | p.generation() as u64).collect();
|
||||
assert_eq!(set.len(), total, "duplicate or lost element");
|
||||
assert_eq!(pop(&q), None);
|
||||
}
|
||||
|
||||
#[test]
|
||||
fn mpmc_exactly_once_contended() {
|
||||
exactly_once(MpmcRing::new(8, 4096), |q, p| q.push(p), |q| q.pop(), 4, 4, 1000);
|
||||
}
|
||||
|
||||
#[test]
|
||||
fn striped_exactly_once_contended() {
|
||||
exactly_once(StripedRing::new(8, 4096), |q, p| q.push(p), |q| q.pop(), 4, 4, 1000);
|
||||
}
|
||||
|
||||
#[test]
|
||||
fn striped_drains_after_skewed_load() {
|
||||
// Hammer pushes from one thread (all tickets walk the stripes in
|
||||
// order) and verify a single consumer sees every element.
|
||||
let q = StripedRing::new(4, 64);
|
||||
let mut seen = HashSet::new();
|
||||
for i in 0..64 {
|
||||
q.push(pid(i));
|
||||
}
|
||||
while let Some(p) = q.pop() {
|
||||
assert!(seen.insert(p.index()));
|
||||
}
|
||||
assert_eq!(seen.len(), 64);
|
||||
}
|
||||
}
|
||||
+43
-62
@@ -9,7 +9,7 @@
|
||||
//! RuntimeInner {
|
||||
//! slots: Box<[Slot]> ← FIXED slab, max_actors entries, lock-free lookup
|
||||
//! free: RawMutex<Vec<u32>> ← vacant slot indices
|
||||
//! shared: Mutex<SharedState> ← the run queue (and nothing else)
|
||||
//! run_queue: RunQueue ← compile-time selected (src/run_queue.rs)
|
||||
//! timers: Mutex<Timers>
|
||||
//! io: Mutex<Option<IoThread>>
|
||||
//! live_actors: AtomicU32 ← spawned-but-not-finalized count (termination)
|
||||
@@ -62,15 +62,17 @@
|
||||
//!
|
||||
//! # Locks and ordering
|
||||
//!
|
||||
//! - `shared` now guards **only the run queue**. It is the innermost lock:
|
||||
//! nothing else is ever acquired while holding it.
|
||||
//! - The run queue is its own module (`run_queue.rs`), selected at compile
|
||||
//! time (`rq-mutex` / `rq-mpmc` / `rq-striped`). Queue ops require
|
||||
//! preemption disabled (debug-asserted there); when the mutex variant is in
|
||||
//! play it is the innermost lock — nothing else is acquired under it.
|
||||
//! - Per-slot `cold` locks ([`RawMutex`], non-poisoning, guard enters
|
||||
//! `NoPreempt`) guard the lifecycle collections. **Leaf rule: never hold
|
||||
//! two cold locks at once** — `finalize_actor`'s link cascade and `link()`
|
||||
//! lock peers one at a time (correctness arguments at the call sites).
|
||||
//! Holding a cold lock while pushing to the run queue is permitted.
|
||||
//! - Lock order overall: `io` → (slot `cold` | `free` | `stack_pool`,
|
||||
//! mutually leaf) → `shared`/run-queue. `timers` is independent (never
|
||||
//! mutually leaf) → run queue (innermost). `timers` is independent (never
|
||||
//! nested with any of the above on either side).
|
||||
//!
|
||||
//! # Termination (counter-based)
|
||||
@@ -106,7 +108,6 @@ use crate::supervisor::Signal;
|
||||
use crate::timer::Timers;
|
||||
use crate::context::{get_actor_sp, set_actor_sp, switch_to_actor};
|
||||
|
||||
use std::collections::VecDeque;
|
||||
use std::sync::atomic::{
|
||||
AtomicBool, AtomicPtr, AtomicU32, AtomicU64, AtomicUsize, Ordering,
|
||||
};
|
||||
@@ -487,28 +488,15 @@ impl Slot {
|
||||
}
|
||||
}
|
||||
|
||||
// ---------------------------------------------------------------------------
|
||||
// Shared state (behind Mutex<>) — now: the run queue, nothing else
|
||||
// ---------------------------------------------------------------------------
|
||||
|
||||
pub(crate) struct SharedState {
|
||||
pub(crate) run_queue: VecDeque<Pid>,
|
||||
}
|
||||
|
||||
impl SharedState {
|
||||
fn new() -> Self {
|
||||
Self { run_queue: VecDeque::new() }
|
||||
}
|
||||
}
|
||||
|
||||
// ---------------------------------------------------------------------------
|
||||
// RuntimeInner — the shared core behind an Arc
|
||||
// ---------------------------------------------------------------------------
|
||||
|
||||
pub(crate) struct RuntimeInner {
|
||||
/// The run queue. Innermost lock: nothing else is acquired under it.
|
||||
/// Phase 3 swaps this for the compile-time-selected `RunQueue`.
|
||||
pub(crate) shared: Mutex<SharedState>,
|
||||
/// The run queue, compile-time selected (see `run_queue.rs` for the
|
||||
/// contract: ops require preemption disabled, push is infallible,
|
||||
/// pop-None is a snapshot).
|
||||
pub(crate) run_queue: crate::run_queue::RunQueue,
|
||||
/// The fixed actor slot table. Allocated once; slots never move.
|
||||
pub(crate) slots: Box<[Slot]>,
|
||||
/// Vacant slot indices. RawMutex leaf; never held with a cold lock.
|
||||
@@ -552,7 +540,7 @@ impl RuntimeInner {
|
||||
// Low indices on top of the stack so early spawns get low pids.
|
||||
let free: Vec<u32> = (0..max_actors as u32).rev().collect();
|
||||
Arc::new(Self {
|
||||
shared: Mutex::new(SharedState::new()),
|
||||
run_queue: crate::run_queue::RunQueue::new(thread_count, max_actors),
|
||||
slots,
|
||||
free: RawMutex::new(free),
|
||||
live_actors: AtomicU32::new(0),
|
||||
@@ -570,17 +558,6 @@ impl RuntimeInner {
|
||||
})
|
||||
}
|
||||
|
||||
pub(crate) fn with_shared<R>(&self, f: impl FnOnce(&mut SharedState) -> R) -> R {
|
||||
// Preemption must be off while we hold the queue mutex: a
|
||||
// preemption-driven context switch under it would carry the lock off
|
||||
// to a suspended actor and stall every scheduler thread. (The stop
|
||||
// sentinel shares the gate, so nothing can unwind in here either.)
|
||||
let prev = crate::preempt::PREEMPTION_ENABLED.with(|c| c.replace(false));
|
||||
let result = f(&mut self.shared.lock().unwrap());
|
||||
crate::preempt::PREEMPTION_ENABLED.with(|c| c.set(prev));
|
||||
result
|
||||
}
|
||||
|
||||
/// Slot lookup by index only — bounds-checked, NOT generation-checked.
|
||||
/// `ROOT_PID` (index `u32::MAX`) is out of bounds by construction and
|
||||
/// resolves to `None`. Callers verify the generation atomically: either
|
||||
@@ -594,7 +571,7 @@ impl RuntimeInner {
|
||||
/// into `Queued` (spawn's publish, the unpark protocol, or the
|
||||
/// scheduler's yield/notified-park return paths).
|
||||
pub(crate) fn enqueue(&self, pid: Pid) {
|
||||
self.with_shared(|s| s.run_queue.push_back(pid));
|
||||
self.run_queue.push(pid);
|
||||
crate::te!(crate::trace::Event::Enqueue(pid));
|
||||
}
|
||||
|
||||
@@ -694,14 +671,14 @@ impl Runtime {
|
||||
crate::trace::open();
|
||||
|
||||
// Re-initialise shared state for this run.
|
||||
{
|
||||
let s = self.inner.shared.lock().unwrap();
|
||||
assert!(s.run_queue.is_empty(), "run() called while previous run still active");
|
||||
debug_assert_eq!(
|
||||
self.inner.live_actors.load(Ordering::Acquire), 0,
|
||||
"run() called while previous run still active"
|
||||
);
|
||||
}
|
||||
assert_eq!(
|
||||
self.inner.run_queue.len(), 0,
|
||||
"run() called while previous run still active"
|
||||
);
|
||||
debug_assert_eq!(
|
||||
self.inner.live_actors.load(Ordering::Acquire), 0,
|
||||
"run() called while previous run still active"
|
||||
);
|
||||
*self.inner.io.lock().unwrap() = Some(IoThread::start().expect("failed to start IO thread"));
|
||||
|
||||
// Spawn the initial actor through the public spawn path (which
|
||||
@@ -1113,27 +1090,31 @@ fn schedule_loop(inner: &Arc<RuntimeInner>, slot_idx: usize) {
|
||||
None => (0, None),
|
||||
};
|
||||
|
||||
let pop = inner.with_shared(|s| {
|
||||
let len = s.run_queue.len() as u64;
|
||||
stats.run_queue_len.store(len, Ordering::Relaxed);
|
||||
match s.run_queue.pop_front() {
|
||||
Some(pid) => Pop::Got(pid),
|
||||
None => {
|
||||
// live_actors is read under the queue lock. If it is 0,
|
||||
// every finalize fully completed — including its wakeup
|
||||
// enqueues, which happen-before the decrement — so with
|
||||
// the queue also empty, nothing can produce work again
|
||||
// (any enqueue targets a live actor; a spawner is itself
|
||||
// live). io_out was read before the lock per phase 1.
|
||||
let live = inner.live_actors.load(Ordering::Acquire);
|
||||
if live == 0 && io_out == 0 {
|
||||
Pop::AllDone
|
||||
} else {
|
||||
Pop::Idle { io_outstanding: io_out, wake_fd: io_fd }
|
||||
}
|
||||
stats.run_queue_len.store(inner.run_queue.len(), Ordering::Relaxed);
|
||||
let pop = match inner.run_queue.pop() {
|
||||
Some(pid) => Pop::Got(pid),
|
||||
None => {
|
||||
// Termination does not lean on pop-None being a fence (with
|
||||
// the ring queues it is only a snapshot). The argument is
|
||||
// counter-first: every queue entry's target stays `Queued` —
|
||||
// hence un-finalized, hence counted live — until that very
|
||||
// entry is popped. So `live == 0` (Acquire, pairing with
|
||||
// finalize's Release decrement, which strictly follows all
|
||||
// wakeup enqueues) by itself implies no entry is in, or can
|
||||
// ever again enter, the queue: enqueues only target live
|
||||
// actors, and a spawner is itself live. The pop-None above
|
||||
// is then just the cheap fast-path filter; io_out was read
|
||||
// before it per the phase-1 ordering. `live == 0` is also
|
||||
// final — no spawn can resurrect the count — so every
|
||||
// scheduler thread independently reaches this same verdict.
|
||||
let live = inner.live_actors.load(Ordering::Acquire);
|
||||
if live == 0 && io_out == 0 {
|
||||
Pop::AllDone
|
||||
} else {
|
||||
Pop::Idle { io_outstanding: io_out, wake_fd: io_fd }
|
||||
}
|
||||
}
|
||||
});
|
||||
};
|
||||
|
||||
let pid = match pop {
|
||||
Pop::Got(pid) => pid,
|
||||
|
||||
Reference in New Issue
Block a user