save and restore arena index to prevent arena overflow.

src/class.c

@@ -1069,8 +1069,10 @@ mrb_mod_attr_reader(mrb_state *mrb, mrb_value mod)
   struct RClass *c = mrb_class_ptr(mod);
   mrb_value *argv;
   mrb_int argc, i;
+  int ai;
 
   mrb_get_args(mrb, "*", &argv, &argc);
+  ai = mrb_gc_arena_save(mrb);
   for (i=0; i<argc; i++) {
     mrb_value name, str;
     mrb_sym method, sym;
@@ -1085,6 +1087,7 @@ mrb_mod_attr_reader(mrb_state *mrb, mrb_value mod)
     name = mrb_symbol_value(sym);
     mrb_define_method_raw(mrb, c, method,
                           mrb_proc_new_cfunc_with_env(mrb, attr_reader, 1, &name));
+    mrb_gc_arena_restore(mrb, ai);
   }
   return mrb_nil_value();
 }
@@ -1106,8 +1109,10 @@ mrb_mod_attr_writer(mrb_state *mrb, mrb_value mod)
   struct RClass *c = mrb_class_ptr(mod);
   mrb_value *argv;
   mrb_int argc, i;
+  int ai;
 
   mrb_get_args(mrb, "*", &argv, &argc);
+  ai = mrb_gc_arena_save(mrb);
   for (i=0; i<argc; i++) {
     mrb_value name, str, attr;
     mrb_sym method, sym;
@@ -1131,6 +1136,7 @@ mrb_mod_attr_writer(mrb_state *mrb, mrb_value mod)
 
     mrb_define_method_raw(mrb, c, method,
                           mrb_proc_new_cfunc_with_env(mrb, attr_writer, 1, &attr));
+    mrb_gc_arena_restore(mrb, ai);
   }
   return mrb_nil_value();
 }