With_thread_id.Fieldsval thread_id :
([< `Read | `Set_and_create ], 'a t, int) Fieldslib.Field.t_with_permval result :
([< `Read | `Set_and_create ], 'result t, 'result)
Fieldslib.Field.t_with_permval create : result:'a -> thread_id:int -> 'a t