Module marker 

Tri-color mark phase for the GC.

Colors:

• White: Unmarked, potentially reclaimable after marking completes.
• Gray: Reachable, but children not yet scanned.
• Black: Reachable, all children scanned.

Algorithm:

1. All objects start white.
2. Root objects are colored gray and pushed to the worklist.
3. Process gray objects: for each, trace children (color white->gray), color self black.
4. After worklist is empty, all white objects are garbage.

Incremental marking

Instead of processing the entire gray worklist in one STW pause, the marker exposes mark_step(budget) which processes a bounded number of objects per mutator safepoint. An SATB write barrier (see barrier.rs) records references overwritten by the mutator during marking. Mark termination is a short STW pause that drains the SATB buffers and re-processes any new grays until convergence.

Structs

Marker

The marker manages the gray worklist and tri-color state.

Enums

MarkPhase

Marker phase state.