MMTk 0.6.0

GC Plans

• Added the Immix plan, an efficient mark-region garbage collector.
• Added a large code space for BasePlan (included by all the plans).

Allocators

• Added the Immix allocator.

Policies

• Added the Immix space, and related data structures.
• Added get_forwarded_object() and is_reachable() to the space function table (SFT).
• Improved the Malloc space (marksweep).
  • It now supports parallel sweeping.
  • It now uses side metadata for page and chunk bits.
  • It now supports bulk check for live objects if mark bits are side metadata.
• Fixed a bug that the side forwarding bits were not cleared for CopySpace.

API

• Refactored the metadata specs in the ObjectModel trait. Now each spec
  has a specific type (e.g. VMGlobalLogBitSpec), and provides a simpler constructor
  for binding implementers to create them.
• Added support for VM specific weak reference processing:
  • added an API function on_closure_end() to add a callback so the binding will
    be notified when a object transitive closure ends.
  • added vm_release() and process_weak_refs() to the Collection trait.

Misc

• Added a few new plan constraints.
  • needs_log_bit: indicates whether a plan will use the global log bit.
  • may_trace_duplicate_edges: indicates whether a plan may allow benign races and trace duplicate edges in a GC.
  • max_non_los_default_alloc_bytes: indicates the maximum object size (in bytes) that can be allocated with the
    default allocator for the plan. For objects that are larger than this, they should be allocated with AllocationSemantics.Los.
• Added utilities to measure process-wide perf events.
• Refactored the offset field for SideMetadataSpec with a union type SideMetadataOffset.
• Fixed a concurrency bug that may cause munprotect fail for the PageProtect plan.
• Fixed a few issues with the tutorial and documentation.