Bulk register obj_free candidataes and PPPs

-   Buffer obj_free candidates and PPPs and send to mmtk-ruby in bulk.
-   Ensure those buffers are flushed for all threads when GC is
    triggered.
-   Ensure buffers are flushed when thread exits.
-   Ensure buffered candidates have their `obj_free` called on exit.
-   T_SYMBOL is no longer a PPP candidate.

gc.c

@@ -2560,63 +2560,7 @@ gc_event_hook_body(rb_execution_context_t *ec, rb_objspace_t *objspace, const rb
 #define gc_event_hook(objspace, event, data) gc_event_hook_prep(objspace, event, data, (void)0)
 
 #if USE_MMTK
-static inline void
-maybe_register_finalizable(VALUE obj) {
- // Any object that has non-trivial cleaning-up code in `obj_free`
- // should be registered as "finalizable" to MMTk.
- switch (RB_BUILTIN_TYPE(obj)) {
- case T_OBJECT:
- // FIXME: Ordinary objects can be non-embedded, too,
- // but there are just too many such objects,
- // and few of them have large buffers.
- // Just let them leak for now.
- // We'll prioritize eliminating the underlying buffer of ordinary objects.
- break;
- case T_MODULE:
- case T_CLASS:
- case T_STRING:
- case T_ARRAY:
- case T_HASH:
- case T_REGEXP:
- case T_DATA:
- case T_MATCH:
- case T_FILE:
- case T_ICLASS:
- case T_BIGNUM:
- case T_STRUCT:
- case T_SYMBOL:
- case T_IMEMO:
- mmtk_add_obj_free_candidate((MMTk_ObjectReference)obj);
- RUBY_DEBUG_LOG("Object registered for obj_free: %p: %s %s",
- (MMTk_ObjectReference)obj,
- rb_type_str(RB_BUILTIN_TYPE(obj)),
- RB_BUILTIN_TYPE(obj) == T_IMEMO ? rb_imemo_name(imemo_type(obj)) :
- rb_obj_class(obj) == 0 ? "(null klass)" :
- rb_class2name(rb_obj_class(obj))
- );
- break;
- case T_RATIONAL:
- case T_COMPLEX:
- case T_FLOAT:
- // There are only counters increments for these types in `obj_free`
- break;
- case T_NIL:
- case T_FIXNUM:
- case T_TRUE:
- case T_FALSE:
- // These are non-heap value types.
- case T_MOVED:
- // Should not see this when object is just created.
- case T_NODE:
- // GC doesn't handle T_NODE.
- rb_bug("maybe_register_finalizable: unexpected data type 0x%x(%p) 0x%"PRIxVALUE,
- BUILTIN_TYPE(obj), (void*)obj, RBASIC(obj)->flags);
- break;
- default:
- rb_bug("maybe_register_finalizable: unknown data type 0x%x(%p) 0x%"PRIxVALUE,
- BUILTIN_TYPE(obj), (void*)obj, RBASIC(obj)->flags);
- }
-}
+
 #endif
 
 static inline VALUE
@@ -2634,7 +2578,7 @@ newobj_init(VALUE klass, VALUE flags, int wb_protected, rb_objspace_t *objspace,
 
 #if USE_MMTK
  if (rb_mmtk_enabled_p()) {
- maybe_register_finalizable(obj);
+ rb_mmtk_maybe_register_obj_free_candidate(obj);
  rb_mmtk_maybe_register_ppp(obj);
  }
 #endif
@@ -7626,6 +7570,11 @@ gc_mark_children(rb_objspace_t *objspace, VALUE obj)
  case T_SYMBOL:
  /* Not immediates, but does not have references and singleton
  * class */
+
+#if USE_MMTK
+ // Note: When using MMTk, RSYMBOL(obj)->fstr is a reference field.
+ // It will be scanned in gc_update_object_references.
+#endif
  return;
 
  case T_NIL:
@@ -12656,7 +12605,8 @@ objspace_malloc_increase_body(rb_objspace_t *objspace, void *mem, size_t new_siz
 #if USE_MMTK
  if (rb_mmtk_enabled_p()) {
  // This will trigger user-requested GC.
- // After GC finishes, obj_free will be invoked on resurrected objects.
+ // `obj_free` is called during GC for dead objects.
+ // It will free underlying xmalloc-ed buffers for them.
  mmtk_handle_user_collection_request((MMTk_VMMutatorThread)GET_THREAD());
 
  gc_reset_malloc_info(objspace, true);

internal/mmtk.h

@@ -166,12 +166,16 @@ MMTk_Address mmtk_last_heap_address(void);
 
 void mmtk_add_obj_free_candidate(MMTk_ObjectReference object);
 
+void mmtk_add_obj_free_candidates(const MMTk_ObjectReference *objects, size_t len);
+
 struct MMTk_RawVecOfObjRef mmtk_get_all_obj_free_candidates(void);
 
 void mmtk_free_raw_vec_of_obj_ref(struct MMTk_RawVecOfObjRef raw_vec);
 
 void mmtk_register_ppp(MMTk_ObjectReference object);
 
+void mmtk_register_ppps(const MMTk_ObjectReference *objects, size_t len);
+
 void *mmtk_get_givtbl(MMTk_ObjectReference object);
 
 size_t mmtk_get_vo_bit_log_region_size(void);

internal/mmtk_support.h

@@ -17,9 +17,13 @@ bool rb_mmtk_enabled_p(void);
 
 // Initialization
 void rb_gc_init_collection(void);
-void* rb_mmtk_bind_mutator(MMTk_VMMutatorThread cur_thread);
+void rb_mmtk_bind_mutator(MMTk_VMMutatorThread cur_thread);
 void rb_mmtk_main_thread_init(void);
 
+// Flushing and de-initialization
+void rb_mmtk_flush_mutator_local_buffers(MMTk_VMMutatorThread thread);
+void rb_mmtk_destroy_mutator(MMTk_VMMutatorThread cur_thread);
+
 // Object layout
 size_t rb_mmtk_prefix_size(void);
 size_t rb_mmtk_suffix_size(void);
@@ -38,6 +42,7 @@ VALUE rb_mmtk_maybe_forward(VALUE object);
 void rb_mmtk_maybe_register_ppp(VALUE obj);
 
 // Finalization and exiting
+void rb_mmtk_maybe_register_obj_free_candidate(VALUE obj);
 int rb_mmtk_run_finalizers_immediately(st_data_t key, st_data_t value, st_data_t data);
 void rb_mmtk_call_obj_free_on_exit(void);