FA-90830 / Garbage collector invariants / Member archive

Heap resizing: shrinking goes below the minimum heap · case 05

Nearly empty heaps shrink below the configured minimum.

Member previewVariant 5 · 3 implementations · 7 checks per implementation

Case contract

After each full collection with live bytes L and capacity C: if the free share (C - L) / C is below min_free percent, grow to the smallest capacity whose free share is at least min_free, i.e. ceil(L * 100 / (100 - min_free)), never shrinking and never above max_heap; if the free share exceeds max_free percent, compute ceil(L * 100 / (100 - max_free)) floored at min_heap and move shrink_pct percent of the way from C toward it (integer arithmetic). Otherwise keep C. Return the capacity after each collection.

Why this case matters

Heap sizing policies decide footprint and GC frequency; rounding and clamping errors oscillate or overshoot.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
regression: grow, hold and shrink	`[250, 250, 234, 151]`	`[250, 250, 234, 167]`	Failed

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