How does Ruby ensure correctness when objects move during GC compaction?

Ruby updates all references to moved objects using forwarding pointers and full heap traversal updates.

During compaction, objects are physically moved to eliminate fragmentation. Each moved object leaves a forwarding address so references can be updated. GC then scans root sets and heap references to rewrite pointers. This ensures no stale references remain. The process requires stop-the-world pauses for correctness, as concurrent mutation would invalidate pointer consistency.