Temporarily push object seen through the GC API

This is definitely a bad idea, but we need it for now to make the ractor
move stuff work as intended.

With address based hashing I don't think this will be necessary, but
we're not there yet

Author: eightbitraptor

gc.c

@@ -681,6 +681,7 @@ typedef struct gc_function_map {
     const char *(*active_gc_name)(void);
     // Miscellaneous
     struct rb_gc_object_metadata_entry *(*object_metadata)(void *objspace_ptr, VALUE obj);
+    void (*set_object_seen)(VALUE obj, bool seen);
     bool (*pointer_to_heap_p)(void *objspace_ptr, const void *ptr);
     bool (*garbage_object_p)(void *objspace_ptr, VALUE obj);
     void (*set_event_hook)(void *objspace_ptr, const rb_event_flag_t event);
@@ -945,6 +946,7 @@ ruby_modular_gc_init(void)
 # define rb_gc_impl_active_gc_name rb_gc_functions.active_gc_name
 // Miscellaneous
 # define rb_gc_impl_object_metadata rb_gc_functions.object_metadata
+# define rb_gc_impl_set_object_seen rb_gc_functions.set_object_seen
 # define rb_gc_impl_pointer_to_heap_p rb_gc_functions.pointer_to_heap_p
 # define rb_gc_impl_garbage_object_p rb_gc_functions.garbage_object_p
 # define rb_gc_impl_set_event_hook rb_gc_functions.set_event_hook
@@ -2972,6 +2974,12 @@ rb_gc_object_metadata(VALUE obj)
     return rb_gc_impl_object_metadata(rb_gc_get_objspace(), obj);
 }
 
+void
+rb_gc_set_object_seen(VALUE obj, bool seen)
+{
+   rb_gc_impl_set_object_seen(obj, seen);
+}
+
 /* GC */
 
 void *

gc/default/default.c

@@ -6251,6 +6251,12 @@ rb_gc_impl_object_metadata(void *objspace_ptr, VALUE obj)
     return object_metadata_entries;
 }
 
+void
+rb_gc_impl_set_object_seen(VALUE obj, bool seen)
+{
+    RVALUE_METADATA(obj)->seen_obj_id = seen;
+}
+
 bool
 rb_gc_impl_has_finalizer(VALUE obj)
 {

gc/gc_impl.h

@@ -117,6 +117,7 @@ GC_IMPL_FN VALUE rb_gc_impl_stat_heap(void *objspace_ptr, VALUE heap_name, VALUE
 GC_IMPL_FN const char *rb_gc_impl_active_gc_name(void);
 // Miscellaneous
 GC_IMPL_FN struct rb_gc_object_metadata_entry *rb_gc_impl_object_metadata(void *objspace_ptr, VALUE obj);
+GC_IMPL_FN void rb_gc_impl_set_object_seen(VALUE obj, bool seen);
 GC_IMPL_FN bool rb_gc_impl_pointer_to_heap_p(void *objspace_ptr, const void *ptr);
 GC_IMPL_FN bool rb_gc_impl_garbage_object_p(void *objspace_ptr, VALUE obj);
 GC_IMPL_FN void rb_gc_impl_set_event_hook(void *objspace_ptr, const rb_event_flag_t event);

internal/gc.h

@@ -250,6 +250,7 @@ const char *rb_objspace_data_type_name(VALUE obj);
 VALUE rb_wb_protected_newobj_of(struct rb_execution_context_struct *, VALUE, VALUE, size_t);
 VALUE rb_wb_unprotected_newobj_of(VALUE, VALUE, size_t);
 size_t rb_obj_memsize_of(VALUE);
+void rb_gc_set_object_seen(VALUE obj, bool seen);
 struct rb_gc_object_metadata_entry *rb_gc_object_metadata(VALUE obj);
 bool rb_obj_id_seen_p(VALUE obj);
 void rb_gc_mark_values(long n, const VALUE *values);

ractor.c

@@ -3573,7 +3573,7 @@ move_leave(VALUE obj, struct obj_traverse_replace_data *data)
 {
     size_t size = rb_gc_obj_slot_size(obj);
     memcpy((void *)data->replacement, (void *)obj, size);
-    FL_UNSET_RAW(data->replacement, FL_SEEN_OBJ_ID);
+    rb_gc_set_object_seen(data->replacement, false);
 
     void rb_replace_generic_ivar(VALUE clone, VALUE obj); // variable.c
 
@@ -3584,7 +3584,7 @@ move_leave(VALUE obj, struct obj_traverse_replace_data *data)
     // Avoid mutations using bind_call, etc.
     // We keep FL_SEEN_OBJ_ID so GC later clean the obj_id_table.
     MEMZERO((char *)obj + sizeof(struct RBasic), char, size - sizeof(struct RBasic));
-    RBASIC(obj)->flags = T_OBJECT | FL_FREEZE | (RBASIC(obj)->flags & FL_SEEN_OBJ_ID);
+    RBASIC(obj)->flags = T_OBJECT | FL_FREEZE;
     RBASIC_SET_CLASS_RAW(obj, rb_cRactorMovedObject);
     return traverse_cont;
 }