Crate shape_gc

Expand description

shape-gc: Zero-pause hardware-assisted garbage collector for the Shape VM.

Replaces Arc refcounting with a concurrent mark-relocate GC using hardware pointer masking (ARM TBI / x86-64 LAM) for zero-pause collection.

Bump allocation with thread-local allocation buffers (TLABs) for ~1 cycle alloc
Tri-color marking (white/gray/black) with incremental mark steps
Hardware pointer masking to store GC metadata in upper pointer bits
Concurrent relocation with forwarding table + SIGSEGV trap handler
Generational collection with card table write barriers

Modules§

allocator: Bump allocator with thread-local allocation buffers (TLABs).
barrier: SATB (Snapshot At The Beginning) write barrier for incremental marking.
fixup: Pointer fixup after relocation.
generations: Generational collection with card table write barriers.
header: GC object header — 8 bytes prepended to every GC-managed allocation.
marker: Tri-color mark phase for the GC.
platform: Hardware pointer masking platform detection and operations.
ptr: GcPtr — typed pointer to a GC-managed object.
region: Memory regions — 2MB mmap’d chunks for GC allocation.
relocator: Concurrent relocation with forwarding table.
roots: Root scanning infrastructure for the GC.
safepoint: Safepoint coordination between mutator threads and GC.
scheduler: Adaptive GC scheduling — decides WHEN and WHAT to collect.
trap_handler: SIGSEGV trap handler for concurrent relocation.

GcHeap: Main GC heap — owns all regions, allocator, marker, and relocation state.
GcHeapStats: Collection statistics.
SweepStats: Statistics from a sweep phase.

set_thread_gc_heap^⚠: Set the thread-local GC heap pointer. Called by VM before execution.
thread_gc_heap: Get the thread-local GC heap, panicking if not set.