Ctypes.Rootval create : 'a -> unit ptrcreate v allocates storage for the address of the OCaml value v, registers the storage as a root, and returns its address.
val get : unit ptr -> 'aget p retrieves the OCaml value whose address is stored at p.
val set : unit ptr -> 'a -> unitset p v updates the OCaml value stored as a root at p.
val release : unit ptr -> unitrelease p unregsiters the root p.