+ U32 refcount;
+} vmg_vtable;
+
+STATIC vmg_vtable *vmg_vtable_alloc(pTHX) {
+#define vmg_vtable_alloc() vmg_vtable_alloc(aTHX)
+ vmg_vtable *t;
+
+ t = VOID2(vmg_vtable *, PerlMemShared_malloc(sizeof *t));
+
+ t->vtbl = VOID2(MGVTBL *, PerlMemShared_malloc(sizeof *t->vtbl));
+ t->refcount = 1;
+
+ return t;
+}
+
+#define vmg_vtable_vtbl(T) (T)->vtbl
+
+STATIC perl_mutex vmg_vtable_refcount_mutex;
+
+STATIC vmg_vtable *vmg_vtable_dup(pTHX_ vmg_vtable *t) {
+#define vmg_vtable_dup(T) vmg_vtable_dup(aTHX_ (T))
+ VMG_LOCK(&vmg_vtable_refcount_mutex);
+ ++t->refcount;
+ VMG_UNLOCK(&vmg_vtable_refcount_mutex);
+
+ return t;
+}
+
+STATIC void vmg_vtable_free(pTHX_ vmg_vtable *t) {
+#define vmg_vtable_free(T) vmg_vtable_free(aTHX_ (T))
+ U32 refcount;
+
+ VMG_LOCK(&vmg_vtable_refcount_mutex);
+ refcount = --t->refcount;
+ VMG_UNLOCK(&vmg_vtable_refcount_mutex);
+
+ if (!refcount) {
+ PerlMemShared_free(t->vtbl);
+ PerlMemShared_free(t);
+ }
+}
+
+#else /* VMG_THREADSAFE */
+
+typedef MGVTBL vmg_vtable;
+
+STATIC vmg_vtable *vmg_vtable_alloc(pTHX) {
+#define vmg_vtable_alloc() vmg_vtable_alloc(aTHX)
+ vmg_vtable *t;
+
+ Newx(t, 1, vmg_vtable);
+
+ return t;
+}
+
+#define vmg_vtable_vtbl(T) ((MGVTBL *) (T))
+
+#define vmg_vtable_free(T) Safefree(T)
+
+#endif /* !VMG_THREADSAFE */
+
+/* --- <vmg_wizard> structure ---------------------------------------------- */
+
+typedef struct {
+ vmg_vtable *vtable;