FA-90554 / Garbage collector invariants / Member archive

Ephemerons: single pass over the ephemeron list · case 04

Values whose keys become reachable only through later-listed ephemerons are dropped.

Member previewVariant 4 · 3 implementations · 7 checks per implementation

Case contract

Ephemeron entries [table, key, value]: the value is traced only when both the table and the key are reachable; values may make further keys reachable, so iterate to a fixpoint. Keys and tables are never retained by an entry. Return the sorted live set and the [table, key] entries of live tables whose key died (to be cleared).

Why this case matters

WeakMap-style tables need fixpoint ephemeron marking or they leak or lose entries.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
regression: ephemeron chain listed in reverse	`{"cleared": [["T4", "V2_4"]], "live": ["K1_4", "T4", "V1_4", "V7_4", "root"]}`	`{"cleared": [], "live": ["K1_4", "T4", "V1_4", "V2_4", "V3_4", "V7_4", "root"]}`	Failed

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