Struct UndoLog 

pub struct UndoLog { /* private fields */ }

ST-036: the per-thread undo/reverse log — see this module’s top doc comment for why it is a plain, caller-owned value (like ()) rather than a StateEngine-owned field. Implements PreWriteHook: every commit_write(cell, new, &mut log) call appends (cell, old, at) here before the store happens (Task 8/ST-091’s own ordering guarantee), giving that hook its first real body.

Implementations

impl UndoLog

pub fn new() -> Self

pub fn checkpoint_marker(&self) -> RollbackMark

ST-036: an opaque marker for the log’s current length — “current” meaning the absolute count of entries ever appended so far (already including any Self::fossil_collect has trimmed), so a mark taken before a trim and a mark taken after it are still comparable on the same absolute scale.

pub fn rollback_to( &mut self, engine: &mut StateEngine, mark: RollbackMark, ) -> Result<(), RewindError>

ST-036: pops entries back to mark, replaying each popped entry’s old value into engine via StateEngine::commit_write_no_hook (a second, hook-free write primitive, so unwinding the log never re-appends to the very log it’s unwinding) in reverse order — Vec:: pop naturally visits the most-recently-appended entry first, which is what makes a cell written twice since mark end up back at its original (not its intermediate) value.

Err(RewindError::PastFossilHorizon) — never a silent under-rollback — when mark refers to a position at or before entries Self::fossil_collect has already, irreversibly discarded; the log is left completely untouched in that case (checked before any entry is popped).

pub fn fossil_collect(&mut self, gvt: SimTime)

Trims every entry with at <= gvt from the front of the log (append-only, so the front holds the oldest entries) — “at or before gvt, never past it”: the scan stops at the first entry whose at is strictly after gvt, so nothing newer is ever removed even if a later entry happened to compare <= some other way.

Trait Implementations

impl Default for UndoLog

fn default() -> Self

Returns the “default value” for a type.

impl PreWriteHook for UndoLog

fn before_write( &mut self, cell: StateCellId, _loc: SlotLocation, old: &FourStateValue, _new_incoming: &FourStateValue, at: SimTime, )