FA-90668 / Garbage collector invariants / Member archive

Mark parity: new cycle starts with pages left unswept · case 03

Dead objects from the previous cycle are resurrected when the parity flips back to their stale mark.

Member previewVariant 3 · 3 implementations · 6 checks per implementation

Case contract

Mark bits flip meaning every cycle: an object is live when its mark equals epoch % 2. Initially every object has mark 0 at epoch 0. gc live_ids: finish sweeping every unswept page, advance the epoch, set the mark of each listed live object to the new parity, and mark all pages unswept. alloc id page: sweep the page first if it is unswept, then create the object with the current parity. finish sweeps the remaining pages. Sweeping a page removes objects whose mark differs from the current parity and logs [page, removed]. Return the sweep log and surviving objects per page.

Why this case matters

Flipping mark polarity avoids clearing mark bits but makes sweep ordering and allocation colour critical.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
second cycle with an unswept page	`{"log": [[1, ["b3", "c3"]], [1, ["x3"]], [2, ["d3"]]], "pages": {"1": ["a3"], "2": ["e3"]}}`	`{"log": [[1, ["b3", "c3"]], [2, ["e3"]], [1, ["x3"]], [2, ["d3"]]], "pages": {"1": ["a3"], "2": []}}`	Failed

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