:ref:`MPI_Neighbor_alltoallw`, :ref:`MPI_Ineighbor_alltoallw`, :ref:`MPI_Neighbor_alltoallw_init` - All processes send data of different types to, and receive data of different types from, all processes
#include <mpi.h>
int MPI_Neighbor_alltoallw(const void *sendbuf, const int sendcounts[],
const MPI_Aint sdispls[], const MPI_Datatype sendtypes[],
void *recvbuf, const int recvcounts[], const MPI_Aint rdispls[],
const MPI_Datatype recvtypes[], MPI_Comm comm)
int MPI_Ineighbor_alltoallw(const void *sendbuf, const int sendcounts[],
const MPI_Aint sdispls[], const MPI_Datatype sendtypes[],
void *recvbuf, const int recvcounts[], const MPI_Aint rdispls[],
const MPI_Datatype recvtypes[], MPI_Comm comm, MPI_Request *request)
int MPI_Neighbor_alltoallw_init(const void *sendbuf, const int sendcounts[],
const MPI_Aint sdispls[], const MPI_Datatype sendtypes[],
void *recvbuf, const int recvcounts[], const MPI_Aint rdispls[],
const MPI_Datatype recvtypes[], MPI_Comm comm, MPI_Info info, MPI_Request *request)USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_NEIGHBOR_ALLTOALLW(SENDBUF, SENDCOUNTS, SDISPLS, SENDTYPES,
RECVBUF, RECVCOUNTS, RDISPLS, RECVTYPES, COMM, IERROR)
<type> SENDBUF(*), RECVBUF(*)
INTEGER SENDCOUNTS(*), SENDTYPES(*)
INTEGER RECVCOUNTS(*), RECVTYPES(*)
INTEGER(KIND=MPI_ADDRESS_KIND) SDISPLS(*), RDISPLS(*)
INTEGER COMM, IERROR
MPI_INEIGHBOR_ALLTOALLW(SENDBUF, SENDCOUNTS, SDISPLS, SENDTYPES,
RECVBUF, RECVCOUNTS, RDISPLS, RECVTYPES, COMM, REQUEST, IERROR)
<type> SENDBUF(*), RECVBUF(*)
INTEGER SENDCOUNTS(*), SENDTYPES(*)
INTEGER RECVCOUNTS(*), RECVTYPES(*)
INTEGER(KIND=MPI_ADDRESS_KIND) SDISPLS(*), RDISPLS(*)
INTEGER COMM, REQUEST, IERROR
MPI_NEIGHBOR_ALLTOALLW_INIT(SENDBUF, SENDCOUNTS, SDISPLS, SENDTYPES,
RECVBUF, RECVCOUNTS, RDISPLS, RECVTYPES, COMM, INFO, REQUEST, IERROR)
<type> SENDBUF(*), RECVBUF(*)
INTEGER SENDCOUNTS(*), SENDTYPES(*)
INTEGER RECVCOUNTS(*), RECVTYPES(*)
INTEGER(KIND=MPI_ADDRESS_KIND) SDISPLS(*), RDISPLS(*)
INTEGER COMM, INFO, REQUEST, IERRORUSE mpi_f08
MPI_Neighbor_alltoallw(sendbuf, sendcounts, sdispls, sendtypes, recvbuf,
recvcounts, rdispls, recvtypes, comm, ierror)
TYPE(*), DIMENSION(..), INTENT(IN) :: sendbuf
TYPE(*), DIMENSION(..) :: recvbuf
INTEGER, INTENT(IN) :: sendcounts(*), recvcounts(*)
INTEGER(KIND=MPI_ADDRESS_KIND), INTENT(IN) :: sdispls(*), rdispls(*)
TYPE(MPI_Datatype), INTENT(IN) :: sendtypes(*), recvtypes(*)
TYPE(MPI_Comm), INTENT(IN) :: comm
INTEGER, OPTIONAL, INTENT(OUT) :: ierror
MPI_Ineighbor_alltoallw(sendbuf, sendcounts, sdispls, sendtypes, recvbuf,
recvcounts, rdispls, recvtypes, comm, request, ierror)
TYPE(*), DIMENSION(..), INTENT(IN), ASYNCHRONOUS :: sendbuf
TYPE(*), DIMENSION(..), ASYNCHRONOUS :: recvbuf
INTEGER, INTENT(IN), ASYNCHRONOUS :: sendcounts(*), recvcounts(*)
INTEGER(KIND=MPI_ADDRESS_KIND), INTENT(IN), ASYNCHRONOUS ::
sdispls(*), rdispls(*)
TYPE(MPI_Datatype), INTENT(IN), ASYNCHRONOUS :: sendtypes(*),
recvtypes(*)
TYPE(MPI_Comm), INTENT(IN) :: comm
TYPE(MPI_Request), INTENT(OUT) :: request
INTEGER, OPTIONAL, INTENT(OUT) :: ierror
MPI_Neighbor_alltoallw_init(sendbuf, sendcounts, sdispls, sendtypes, recvbuf,
recvcounts, rdispls, recvtypes, comm, info, request, ierror)
TYPE(*), DIMENSION(..), INTENT(IN), ASYNCHRONOUS :: sendbuf
TYPE(*), DIMENSION(..), ASYNCHRONOUS :: recvbuf
INTEGER, INTENT(IN), ASYNCHRONOUS :: sendcounts(*), recvcounts(*)
INTEGER(KIND=MPI_ADDRESS_KIND), INTENT(IN), ASYNCHRONOUS ::
sdispls(*), rdispls(*)
TYPE(MPI_Datatype), INTENT(IN), ASYNCHRONOUS :: sendtypes(*),
recvtypes(*)
TYPE(MPI_Comm), INTENT(IN) :: comm
TYPE(MPI_Info), INTENT(IN) :: info
TYPE(MPI_Request), INTENT(OUT) :: request
INTEGER, OPTIONAL, INTENT(OUT) :: ierrorsendbuf: Starting address of send buffer.sendcounts: Integer array, where entry i specifies the number of elements to send to neighbor i.sdispls: Integer array, where entry i specifies the displacement (in bytes, offset from sendbuf) from which to send data to neighbor i.sendtypes: Datatype array, where entry i specifies the datatype to use when sending data to neighbor i.recvcounts: Integer array, where entry j specifies the number of elements to receive from neighbor j.rdispls: Integer array, where entry j specifies the displacement (in bytes, offset from recvbuf) to which data from neighbor j should be written.recvtypes: Datatype array, where entry j specifies the datatype to use when receiving data from neighbor j.comm: Communicator over which data is to be exchanged.info: Info (handle, persistent only).
recvbuf: Address of receive buffer.request: Request (handle, non-blocking only).ierror: Fortran only: Error status.
:ref:`MPI_Neighbor_alltoallw` is a generalized collective operation in which all processes send data to and receive data from all neighbors. It adds flexibility to :ref:`MPI_Neighbor_alltoallv` by allowing the user to specify the datatype of individual data blocks (in addition to displacement and element count). Its operation can be thought of in the following way, where each process performs 2n (n being the number of neighbors in the topology of communicator comm) independent point-to-point communications. The neighbors and buffer layout are determined by the topology of comm.
MPI_Cart_get(comm, maxdims, dims, periods, coords);
for (dim = 0, i = 0 ; dim < dims ; ++dim) {
MPI_Cart_shift(comm, dim, 1, &r0, &r1);
MPI_Isend(sendbuf + sdispls[i] * extent(sendtype),
sendcount, sendtypes[i], r0, ..., comm, ...);
MPI_Irecv(recvbuf + rdispls[i] * extent(recvtype),
recvcount, recvtypes[i], r0, ..., comm, ...);
++i;
MPI_Isend(sendbuf + sdispls[i] * extent(sendtype),
sendcount, sendtypes[i], r1, ..., comm, &req[i]);
MPI_Irecv(recvbuf + rdispls[i] * extent(recvtype),
recvcount, recvtypes[i], r1, ..., comm, ...);
++i;
}
MPI_Wait_all (...);
MPI_Comm_size(comm, &n);
for (i = 0, i < n; i++)
MPI_Send(sendbuf + sdispls[i], sendcounts[i],
sendtypes[i], i, ..., comm);
for (i = 0, i < n; i++)
MPI_Recv(recvbuf + rdispls[i], recvcounts[i],
recvtypes[i], i, ..., comm);Process j sends the k-th block of its local sendbuf to neighbor k, which places the data in the j-th block of its local recvbuf.
When a pair of processes exchanges data, each may pass different element count and datatype arguments so long as the sender specifies the same amount of data to send (in bytes) as the receiver expects to receive.
Note that process i may send a different amount of data to process j than it receives from process j. Also, a process may send entirely different amounts and types of data to different processes in the communicator.
The MPI_IN_PLACE option for sendbuf is not meaningful for this operation
The specification of counts, types, and displacements should not cause any location to be written more than once.
All arguments on all processes are significant. The comm argument, in particular, must describe the same communicator on all processes.
The offsets of sdispls and rdispls are measured in bytes. Compare this to :ref:`MPI_Neighbor_alltoallv`, where these offsets are measured in units of sendtype and recvtype, respectively.
.. seealso::
* :ref:`MPI_Neighbor_alltoall`
* :ref:`MPI_Neighbor_alltoallv`
* :ref:`MPI_Cart_create`
* :ref:`MPI_Graph_create`
* :ref:`MPI_Dist_graph_create`