in multi core cpython project. 
when use  multi sub interpreters, Type is not safe. Type shared by interpreters.
but isolate type may cause python abi/api change. python 4.0?

temporary solution:
1. add a type lock to guarantee type object safe in multi subinterpreters.
2. some thing like pycmethod object and descr in pytype, set their refcount to INT MAX.It is guaranteed that these objects will not be released. and not cause memory leaks, only one type exist in memory.