typedef std::tuple</*sender*/ int, /* reciever */ int, /* tag */int> req_key_t;
typedef std::unordered_map<req_key_t, MPI_Request, hash_tuple::hash<std::tuple<int,int,int>>> req_storage_t;
typedef std::tuple</*sender*/ int, /* reciever */ int, /* tag */int> req_key_t;
typedef std::unordered_map<req_key_t, MPI_Request, hash_tuple::hash<std::tuple<int,int,int>>> req_storage_t;