PEGO
A240: Stream VM Stack Cleanup
Popping a VM value stack can leave references beyond its active length. Stream cleanup clears that inactive suffix when completed elements no longer need it.
Mechanism and Invariants
Cleanup waits for VM completion of an element and the same prune-batched 1,024-position boundary. It clears only the inactive stack region, preserving live operands and published results. Capacity remains reusable. This is distinct from the cleared stack retained by a Document across reparses.
Scope and State
Default recursive and iterative VM streaming only. Closure has no VM operand stack; generated Go/TypeScript have no streaming API.
Reference Control
Build tag pego_reference_stream_stack restores the former inactive-reference
behavior. The combined storage tag also changes undo/prefix policy.
Evidence and Implementation
Record 089 measures the storage controls and their combined retained-heap reduction. It does not establish an independent universal stack-cleanup speedup or immediate release at every commit.
Evidence records: 089.
Source owners: inactive VM value cleanup,
vmMachine.ClearInactive, prune-batched commit cleanup.
The comparison policy distinguishes same-source controls, historical changes and full checkpoints.