Ractor: revert to moving object bytes, but size pool aware

Using `rb_obj_clone` introduce other problems, such as `initialize_*`
callbacks invocation in the context of the parent ractor.

So we can revert back to copy the content of the object slots,
but in a way that is aware of size pools.

Author: byroot

bootstraptest/test_ractor.rb

@@ -2101,3 +2101,24 @@ def ==(o)
     :fail
   end
 }
+
+# move objects inside frozen containers
+assert_equal 'ok', %q{
+  ractor = Ractor.new { Ractor.receive }
+  obj = Array.new(10, 42)
+  original = obj.dup
+  ractor.send([obj].freeze, move: true)
+  roundtripped_obj = ractor.take[0]
+  roundtripped_obj == original ? :ok : roundtripped_obj
+}
+
+# move object with generic ivar
+assert_equal 'ok', %q{
+  ractor = Ractor.new { Ractor.receive }
+  obj = Array.new(10, 42)
+  obj.instance_variable_set(:@array, [1])
+
+  ractor.send(obj, move: true)
+  roundtripped_obj = ractor.take
+  roundtripped_obj.instance_variable_get(:@array) == [1] ? :ok : roundtripped_obj
+}

gc.c

@@ -2658,14 +2658,6 @@ rb_gc_mark_roots(void *objspace, const char **categoryp)
 
 #define TYPED_DATA_REFS_OFFSET_LIST(d) (size_t *)(uintptr_t)RTYPEDDATA(d)->type->function.dmark
 
-void
-rb_gc_ractor_moved(VALUE dest, VALUE src)
-{
-    rb_gc_obj_free(rb_gc_get_objspace(), src);
-    MEMZERO((void *)src, char, rb_gc_obj_slot_size(src));
-    RBASIC(src)->flags = T_OBJECT | FL_FREEZE; // Avoid mutations using bind_call, etc.
-}
-
 void
 rb_gc_mark_children(void *objspace, VALUE obj)
 {

internal/gc.h

@@ -183,7 +183,6 @@ struct rb_gc_object_metadata_entry {
 /* gc.c */
 RUBY_ATTR_MALLOC void *ruby_mimmalloc(size_t size);
 RUBY_ATTR_MALLOC void *ruby_mimcalloc(size_t num, size_t size);
-void rb_gc_ractor_moved(VALUE dest, VALUE src);
 void ruby_mimfree(void *ptr);
 void rb_gc_prepare_heap(void);
 void rb_objspace_set_event_hook(const rb_event_flag_t event);

ractor.c

@@ -3539,6 +3539,19 @@ rb_obj_traverse_replace(VALUE obj,
     }
 }
 
+static const bool wb_protected_types[RUBY_T_MASK] = {
+    [T_OBJECT] = RGENGC_WB_PROTECTED_OBJECT,
+    [T_HASH] = RGENGC_WB_PROTECTED_HASH,
+    [T_ARRAY] = RGENGC_WB_PROTECTED_ARRAY,
+    [T_STRING] = RGENGC_WB_PROTECTED_STRING,
+    [T_STRUCT] = RGENGC_WB_PROTECTED_STRUCT,
+    [T_COMPLEX] = RGENGC_WB_PROTECTED_COMPLEX,
+    [T_REGEXP] = RGENGC_WB_PROTECTED_REGEXP,
+    [T_MATCH] = RGENGC_WB_PROTECTED_MATCH,
+    [T_FLOAT] = RGENGC_WB_PROTECTED_FLOAT,
+    [T_RATIONAL] = RGENGC_WB_PROTECTED_RATIONAL,
+};
+
 static enum obj_traverse_iterator_result
 move_enter(VALUE obj, struct obj_traverse_replace_data *data)
 {
@@ -3547,15 +3560,31 @@ move_enter(VALUE obj, struct obj_traverse_replace_data *data)
         return traverse_skip;
     }
     else {
-        data->replacement = rb_obj_clone(obj);
+        VALUE type = RB_BUILTIN_TYPE(obj);
+        type |= wb_protected_types[type] ? FL_WB_PROTECTED : 0;
+        NEWOBJ_OF(moved, struct RBasic, 0, type, rb_gc_obj_slot_size(obj), 0);
+        data->replacement = (VALUE)moved;
         return traverse_cont;
     }
 }
 
 static enum obj_traverse_iterator_result
 move_leave(VALUE obj, struct obj_traverse_replace_data *data)
 {
-    rb_gc_ractor_moved(data->replacement, obj);
+    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);
+
+    void rb_replace_generic_ivar(VALUE clone, VALUE obj); // variable.c
+
+    if (UNLIKELY(FL_TEST_RAW(obj, FL_EXIVAR))) {
+        rb_replace_generic_ivar(data->replacement, obj);
+    }
+
+    // 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_SET_CLASS_RAW(obj, rb_cRactorMovedObject);
     return traverse_cont;
 }

variable.c

@@ -2157,6 +2157,27 @@ rb_copy_generic_ivar(VALUE clone, VALUE obj)
     }
 }
 
+void
+rb_replace_generic_ivar(VALUE clone, VALUE obj)
+{
+    RUBY_ASSERT(FL_TEST(obj, FL_EXIVAR));
+
+    RB_VM_LOCK_ENTER();
+    {
+        st_data_t ivtbl, obj_data = (st_data_t)obj;
+        if (st_delete(generic_iv_tbl_, &obj_data, &ivtbl)) {
+            FL_UNSET_RAW(obj, FL_EXIVAR);
+
+            st_insert(generic_iv_tbl_, (st_data_t)clone, ivtbl);
+            FL_SET_RAW(clone, FL_EXIVAR);
+        }
+        else {
+            rb_bug("unreachable");
+        }
+    }
+    RB_VM_LOCK_LEAVE();
+}
+
 void
 rb_ivar_foreach(VALUE obj, rb_ivar_foreach_callback_func *func, st_data_t arg)
 {