FA-90503 / Garbage collector invariants / Member archive

Heap pacing: percentage change based on current live bytes · case 03

Changing the percentage mid-cycle uses a live size the collector has not measured.

Member previewVariant 3 · 3 implementations · 7 checks per implementation

Case contract

GOGC-style pacing starting at 100 percent with goal = min_heap. alloc b adds b to the heap and to live bytes and triggers a collection when collection is enabled (percentage >= 0) and heap >= goal: the heap shrinks to the live bytes, which become the marked size, and goal = max(marked + marked * pct // 100, min_heap). drop b turns b live bytes into garbage. setgc p changes the percentage (-1 disables) and, unless disabled, recomputes the goal from the last marked size. Return the heap sizes at which collections triggered, the final goal and heap.

Why this case matters

Collector pacing decides when collections run; off-by-one or base errors change memory footprint.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
goal recomputed from last marked heap	`{"gcs": [260, 660], "goal": 1590, "heap": 660}`	`{"gcs": [260, 790], "goal": 1980, "heap": 660}`	Failed

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