FA-90618 / Garbage collector invariants / Member archive

Adaptive tenuring: reaching the desired size lowers the threshold · case 03

Survivor populations exactly at the target size are promoted a cycle early.

Member previewVariant 3 · 3 implementations · 7 checks per implementation

Case contract

Survivors are [id, age, size] after a minor collection. desired = capacity * ratio // 100. Walking ages 1..max_threshold, accumulate sizes; the first age at which the running total exceeds desired becomes the tenuring threshold (max_threshold if never exceeded). Objects with age >= threshold are promoted; the rest are placed youngest first (ties by id) into the survivor space of the given capacity, and any that do not fit overflow into promotion. Return threshold, promoted ids, kept ids and bytes used.

Why this case matters

Tenuring policy controls premature promotion and survivor overflow in generational collectors.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
cumulative size exactly at the desired size	`{"kept": [1], "promoted": [2, 3], "threshold": 2, "used": 30}`	`{"kept": [1, 2], "promoted": [3], "threshold": 3, "used": 50}`	Failed

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