sv_sim_sim/sched/

ops.rs

//! SCHED::OPS — the blocking-assignment commit path and the `SchedulerOps`
//! mock surface a compiled process body calls into during `resume()`
//! (scheduler.md §4/"Public Interfaces"; ARCHITECTURE §6.3; ledger SC-043,
//! SC-044, SC-070).
//!
//! [`commit_blocking_write`] mirrors Task 7's [`crate::sched::commit_nba`]
//! cell-write path but synchronous/single-cell: applies immediately, and iff
//! the write actually changed the stored value, calls
//! [`ValueChangeSink::notify_change`] tagged `Region::Active` — this crate's
//! second (and last) sanctioned production `.notify_change(` call site
//! (SC-042; the other is `commit_nba`; Task 22's crate-wide scan is the
//! proof that exactly these two exist). The function's own signature is the
//! SC-043 evidence: it takes an opaque [`StateCellId`] and an edge-classified
//! [`FourStateValue`] transition and nothing else — no parameter, branch, or
//! call anywhere in this module distinguishes how a cell's value is sourced
//! or resolved; that distinction belongs entirely to another subsystem.

use crate::sched::{SchedTime, infer_edge};
use crate::state::{ChangeDelta, FourStateValue, SignalAccess, StateCellId, ValueChangeSink};
use sv_sim_abi::Region;

/// Commits a blocking (`=`) assignment synchronously, inside the caller's own
/// `resume()` call: writes `value` to `cell` via `arena.write`, and iff that
/// write actually changed the stored value, classifies the transition and
/// calls `sink.notify_change(..)` tagged `Region::Active` before returning.
/// Any concrete `SchedulerOps::commit_blocking_write` implementation must
/// call this function (SC-044) rather than applying the write some other
/// way.
pub fn commit_blocking_write(
    cell: StateCellId,
    value: FourStateValue,
    arena: &mut dyn SignalAccess,
    at: SchedTime,
    sink: &mut dyn ValueChangeSink,
) -> bool {
    let old = arena.read(cell);
    let new_for_edge = value.clone();
    let changed = arena.write(cell, value);
    if changed {
        if sink.wants_delta(cell) {
            sink.note_delta(cell, ChangeDelta::between(&old, &new_for_edge));
        }
        notify_blocking_change(cell, infer_edge(&old, &new_for_edge), at, sink);
    }
    notify_alias_changes(arena, at, sink);
    changed
}

/// Announces the changes of other names for the storage a write just
/// touched (window aliases of ref ports, `state::alias`).
pub fn notify_alias_changes(
    arena: &mut dyn SignalAccess,
    at: SchedTime,
    sink: &mut dyn ValueChangeSink,
) {
    for change in arena.take_alias_changes() {
        let edge = if change.no_edge {
            crate::state::EdgeKind::None
        } else {
            infer_edge(&change.old, &change.new)
        };
        notify_blocking_change(change.cell, edge, at, sink);
    }
}

/// The notification half of [`commit_blocking_write`], for a blocking write
/// the caller already committed through another STATE path that
/// `SignalAccess::write` cannot express -- one row of a memory
/// (`sched::kernel_adapter::real_sv_set_mem_word`). Call only when that
/// write actually changed the stored value.
pub fn notify_blocking_change(
    cell: StateCellId,
    edge: crate::state::EdgeKind,
    at: SchedTime,
    sink: &mut dyn ValueChangeSink,
) {
    sink.notify_change(cell, edge, at.to_abi_display(0), Region::Active);
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::sched::{DeferredIoCallback, NbaLog, ProcessId, SchedulerOps};
    use crate::state::{EdgeKind, ListenerRole};
    use std::cell::RefCell;
    use std::collections::HashMap;
    use std::rc::Rc;
    use sv_sim_abi::SimTime;

    // `FakeArena`, independently declared per this plan's established
    // pattern (see Task 21's own note: `notify.rs`'s `FakeArena` is private
    // to that module's test block and unreachable here) — same shape as
    // `notify::tests::FakeArena`: one shared piece of state backing both a
    // `SignalAccess` view and a `ValueChangeSink` view, split into two thin
    // handles sharing one `Rc<RefCell<..>>` because `commit_blocking_write`
    // takes `arena: &mut dyn SignalAccess` and `sink: &mut dyn
    // ValueChangeSink` as two simultaneous `&mut` parameters.
    struct FakeArenaState {
        cells: HashMap<StateCellId, FourStateValue>,
        notifications: Vec<(StateCellId, EdgeKind, SimTime, Region)>,
    }

    #[derive(Clone)]
    struct FakeArena(Rc<RefCell<FakeArenaState>>);

    struct ArenaHandle(Rc<RefCell<FakeArenaState>>);
    struct SinkHandle(Rc<RefCell<FakeArenaState>>);

    fn four_state_eq(a: &FourStateValue, b: &FourStateValue) -> bool {
        match (a, b) {
            (FourStateValue::Narrow(x), FourStateValue::Narrow(y)) => x == y,
            (
                FourStateValue::Wide { aval: a1, bval: b1 },
                FourStateValue::Wide { aval: a2, bval: b2 },
            ) => a1 == a2 && b1 == b2,
            _ => false,
        }
    }

    impl FakeArena {
        fn new() -> Self {
            Self(Rc::new(RefCell::new(FakeArenaState {
                cells: HashMap::new(),
                notifications: Vec::new(),
            })))
        }

        fn seed(&self, cell: StateCellId, value: FourStateValue) {
            self.0.borrow_mut().cells.insert(cell, value);
        }

        fn notifications(&self) -> Vec<(StateCellId, EdgeKind, SimTime, Region)> {
            self.0.borrow().notifications.clone()
        }

        fn arena_handle(&self) -> ArenaHandle {
            ArenaHandle(self.0.clone())
        }

        fn sink_handle(&self) -> SinkHandle {
            SinkHandle(self.0.clone())
        }
    }

    impl SignalAccess for ArenaHandle {
        fn read(&self, cell: StateCellId) -> FourStateValue {
            self.0
                .borrow()
                .cells
                .get(&cell)
                .cloned()
                .unwrap_or(FourStateValue::Narrow(0))
        }

        fn write(&mut self, cell: StateCellId, value: FourStateValue) -> bool {
            let mut state = self.0.borrow_mut();
            let changed = match state.cells.get(&cell) {
                Some(existing) => !four_state_eq(existing, &value),
                None => true,
            };
            state.cells.insert(cell, value);
            changed
        }

        fn subscribe(
            &mut self,
            _cell: StateCellId,
            _role: ListenerRole,
            _sink: Box<dyn ValueChangeSink + Send>,
        ) {
            // Not exercised by this task's tests — Task 9 owns
            // SensitivityTable wiring.
        }
    }

    impl ValueChangeSink for SinkHandle {
        fn notify_change(
            &mut self,
            cell: StateCellId,
            edge: EdgeKind,
            at: SimTime,
            region: Region,
        ) {
            self.0
                .borrow_mut()
                .notifications
                .push((cell, edge, at, region));
        }
    }

    const PROC_A: ProcessId = 1;

    // --- commit_blocking_write (SC-044) ---

    #[test]
    fn commit_blocking_write_is_visible_immediately_same_activation() {
        let fake = FakeArena::new();
        let cell = StateCellId(1);
        fake.seed(cell, FourStateValue::Narrow(0));
        let mut arena = fake.arena_handle();
        let mut sink = fake.sink_handle();

        let changed = commit_blocking_write(
            cell,
            FourStateValue::Narrow(1),
            &mut arena,
            SchedTime { ticks: 0 },
            &mut sink,
        );

        assert!(changed);
        // Read back through the very same handle, in the same test scope,
        // before any region/timestep advance — simulating "within one
        // resume() call". Fails if the write were staged instead of applied
        // synchronously.
        assert!(matches!(arena.read(cell), FourStateValue::Narrow(1)));
    }

    #[test]
    fn commit_blocking_write_triggers_notify_within_the_same_active_pass() {
        let fake = FakeArena::new();
        let cell = StateCellId(2);
        fake.seed(cell, FourStateValue::Narrow(0));
        let mut arena = fake.arena_handle();
        let mut sink = fake.sink_handle();

        commit_blocking_write(
            cell,
            FourStateValue::Narrow(1),
            &mut arena,
            SchedTime { ticks: 5 },
            &mut sink,
        );

        let notes = fake.notifications();
        assert_eq!(
            notes.len(),
            1,
            "exactly one notify_change call, with no deferral to a later region"
        );
        assert_eq!(notes[0].0, cell);
        assert_eq!(
            notes[0].3,
            Region::Active,
            "commit_blocking_write must tag its notify_change call Region::Active"
        );
    }

    /// Mutation-test kill: an implementation that calls `sink.notify_change`
    /// unconditionally (moving the call outside the `if changed` guard)
    /// passes every other test in this file, since they only ever write a
    /// value that actually differs from the seeded one. Writing the cell's
    /// *already-current* value must report `changed == false` and must not
    /// call `notify_change` at all (SC-040/SC-041's "never for a write whose
    /// resolved value equals the cell's current one").
    #[test]
    fn commit_blocking_write_does_not_notify_when_the_value_is_unchanged() {
        let fake = FakeArena::new();
        let cell = StateCellId(9);
        fake.seed(cell, FourStateValue::Narrow(5));
        let mut arena = fake.arena_handle();
        let mut sink = fake.sink_handle();

        let changed = commit_blocking_write(
            cell,
            FourStateValue::Narrow(5),
            &mut arena,
            SchedTime { ticks: 0 },
            &mut sink,
        );

        assert!(
            !changed,
            "writing the cell's own current value must report no change"
        );
        assert!(
            fake.notifications().is_empty(),
            "a write that does not change the stored value must never call notify_change"
        );
    }

    #[test]
    fn commit_blocking_write_behaves_identically_for_a_net_backed_or_var_backed_cell() {
        // "net"/"var" label these two cells purely for the human reader —
        // commit_blocking_write's own signature (above) has no parameter
        // that could carry such a distinction. That absence, not this
        // comment, is the actual proof; this test only checks the
        // consequence: both calls, given equivalent value transitions,
        // produce structurally identical (bool, notify-log-entry) outcomes.
        let net_labeled_cell = StateCellId(10);
        let var_labeled_cell = StateCellId(11);

        let fake = FakeArena::new();
        fake.seed(net_labeled_cell, FourStateValue::Narrow(0));
        fake.seed(var_labeled_cell, FourStateValue::Narrow(0));
        let mut arena = fake.arena_handle();
        let mut sink = fake.sink_handle();

        let changed_a = commit_blocking_write(
            net_labeled_cell,
            FourStateValue::Narrow(1),
            &mut arena,
            SchedTime { ticks: 0 },
            &mut sink,
        );
        let changed_b = commit_blocking_write(
            var_labeled_cell,
            FourStateValue::Narrow(1),
            &mut arena,
            SchedTime { ticks: 0 },
            &mut sink,
        );

        assert_eq!(changed_a, changed_b);
        let notes = fake.notifications();
        assert_eq!(notes.len(), 2);
        assert_eq!(
            notes[0].1, notes[1].1,
            "both transitions must classify to the same edge"
        );
        assert_eq!(
            notes[0].3, notes[1].3,
            "both calls must tag the same region"
        );
    }

    /// Reviewer-facing negative for SC-043: scans this file's own
    /// *production* source (via `determinism::scan_support::
    /// strip_cfg_test_blocks`, the same technique Task 3's DT-006 test
    /// uses, so this test's own use of the scanned-for words above never
    /// trips itself) for the case-insensitive substrings a net-vs-variable
    /// distinction would need, and asserts none appear. A future
    /// implementation that adds any such branch — even one that still
    /// passes the behavioral test above by coincidence — fails this test.
    #[test]
    fn ops_rs_production_code_has_no_signal_origin_vocabulary() {
        let path = std::path::Path::new(env!("CARGO_MANIFEST_DIR")).join("src/sched/ops.rs");
        let src = std::fs::read_to_string(&path)
            .expect("read sched/ops.rs for the SC-043 source-text scan");
        let production_only = crate::determinism::scan_support::strip_cfg_test_blocks(&src);
        let lower = production_only.to_lowercase();
        let banned = ["net", "strength", "driver"];
        let found: Vec<&str> = banned
            .iter()
            .copied()
            .filter(|needle| lower.contains(needle))
            .collect();
        assert!(
            found.is_empty(),
            "sched/ops.rs production code must draw no net-vs-variable \
             distinction (SC-043), but found banned substring(s) {found:?}"
        );
    }

    // --- SchedulerOps / MockSchedulerOps (SC-070) ---

    #[derive(Clone, Copy, PartialEq, Eq, Debug)]
    enum MockOpsCall {
        Now,
        CurrentRegion,
        StageNba,
        CommitBlockingWrite,
        RequestFinish,
        DeferIo,
        RegisterRegionCallback,
    }

    /// The in-crate test double standing in for a compiled kernel's view of
    /// the scheduler (no codegen exists yet). Records one [`MockOpsCall`]
    /// variant per call, and for `stage_nba`/`commit_blocking_write` also
    /// actually calls through to [`NbaLog::stage`]/[`commit_blocking_write`]
    /// so the mock is behaviorally real, not just a spy.
    struct MockSchedulerOps {
        arena: RefCell<FakeArena>,
        // Not in the plan's illustrative field list, but required for
        // `stage_nba` to genuinely "call through to `NbaLog::stage`" as the
        // task brief specifies rather than only recording the call —
        // documented as a deviation (field list is additive, not narrowing).
        nba: RefCell<NbaLog>,
        calls: RefCell<Vec<MockOpsCall>>,
        region: Region,
        now: SchedTime,
    }

    impl MockSchedulerOps {
        fn new(arena: FakeArena, region: Region, now: SchedTime) -> Self {
            Self {
                arena: RefCell::new(arena),
                nba: RefCell::new(NbaLog::new()),
                calls: RefCell::new(Vec::new()),
                region,
                now,
            }
        }
    }

    impl SchedulerOps for MockSchedulerOps {
        fn now(&self) -> SchedTime {
            self.calls.borrow_mut().push(MockOpsCall::Now);
            self.now
        }

        fn current_region(&self) -> Region {
            self.calls.borrow_mut().push(MockOpsCall::CurrentRegion);
            self.region
        }

        fn stage_nba(&self, cell: StateCellId, value: FourStateValue, source: ProcessId) {
            self.calls.borrow_mut().push(MockOpsCall::StageNba);
            self.nba.borrow_mut().stage(cell, value, source);
        }

        fn commit_blocking_write(&self, cell: StateCellId, value: FourStateValue) {
            self.calls
                .borrow_mut()
                .push(MockOpsCall::CommitBlockingWrite);
            let fake = self.arena.borrow();
            let mut arena_handle = fake.arena_handle();
            let mut sink_handle = fake.sink_handle();
            super::commit_blocking_write(
                cell,
                value,
                &mut arena_handle,
                self.now,
                &mut sink_handle,
            );
        }

        fn request_finish(&self, _code: i32) {
            self.calls.borrow_mut().push(MockOpsCall::RequestFinish);
        }

        fn defer_io(&self, _at: SchedTime, _region: Region, _cb: DeferredIoCallback) {
            self.calls.borrow_mut().push(MockOpsCall::DeferIo);
        }

        fn register_region_callback(
            &self,
            _region: Region,
            _at: SchedTime,
            _cb: Box<dyn crate::sched::RegionCallback>,
        ) {
            self.calls
                .borrow_mut()
                .push(MockOpsCall::RegisterRegionCallback);
        }
    }

    /// A no-op [`crate::sched::RegionCallback`] double for the exhaustive
    /// `SchedulerOps` method-count test below — this test never invokes it,
    /// only proves `MockSchedulerOps::register_region_callback` itself was
    /// called.
    struct NoopRegionCallback;
    impl crate::sched::RegionCallback for NoopRegionCallback {
        fn invoke(&mut self, _ctx: &dyn crate::sched::SchedulerCtx) {}
    }

    #[test]
    fn mock_scheduler_ops_exercises_all_seven_methods() {
        let fake = FakeArena::new();
        let cell = StateCellId(20);
        fake.seed(cell, FourStateValue::Narrow(0));
        let ops = MockSchedulerOps::new(fake, Region::Active, SchedTime { ticks: 0 });

        // Drives the mock through all seven methods from inside a closure
        // standing in for a compiled kernel's resume() body, in this order.
        let resume_body = |ops: &MockSchedulerOps| {
            let _ = ops.now();
            let _ = ops.current_region();
            ops.stage_nba(cell, FourStateValue::Narrow(1), PROC_A);
            ops.commit_blocking_write(cell, FourStateValue::Narrow(2));
            ops.request_finish(0);
            ops.defer_io(SchedTime { ticks: 0 }, Region::Active, Box::new(|_ctx| {}));
            ops.register_region_callback(
                Region::Postponed,
                SchedTime { ticks: 0 },
                Box::new(NoopRegionCallback),
            );
        };
        resume_body(&ops);

        let calls = ops.calls.borrow();
        assert_eq!(calls.len(), 7, "the trait has exactly seven methods");
        assert_eq!(
            *calls,
            vec![
                MockOpsCall::Now,
                MockOpsCall::CurrentRegion,
                MockOpsCall::StageNba,
                MockOpsCall::CommitBlockingWrite,
                MockOpsCall::RequestFinish,
                MockOpsCall::DeferIo,
                MockOpsCall::RegisterRegionCallback,
            ],
            "each of the seven methods must appear exactly once, in call order"
        );
    }
}