MPI_Alltoallw

Generalized all-to-all communication allowing different datatypes, counts, and displacements for each partner

Synopsis

int MPI_Alltoallw(const void *sendbuf, const int sendcounts[],
                  const int sdispls[], const MPI_Datatype sendtypes[],
                  void *recvbuf, const int recvcounts[], const int rdispls[],
                  const MPI_Datatype recvtypes[], MPI_Comm comm)

Input Parameters

sendbuf: starting address of send buffer (choice)
sendcounts: integer array equal to the group size specifying the number of elements to send to each processor (integer)
sdispls: integer array (of length group size). Entry j specifies the displacement in bytes (relative to sendbuf) from which to take the outgoing data destined for process j
sendtypes: array of datatypes (of length group size). Entry j specifies the type of data to send to process j (handle)
recvcounts: integer array equal to the group size specifying the number of elements that can be received from each processor (integer)
rdispls: integer array (of length group size). Entry i specifies the displacement in bytes (relative to recvbuf) at which to place the incoming data from process i
recvtypes: array of datatypes (of length group size). Entry i specifies the type of data received from process i (handle)
comm: communicator (handle)

Output Parameters

recvbuf: address of receive buffer (choice)

Thread and Interrupt Safety

This routine is thread-safe. This means that this routine may be safely used by multiple threads without the need for any user-provided thread locks. However, the routine is not interrupt safe. Typically, this is due to the use of memory allocation routines such as mallocor other non-MPICH runtime routines that are themselves not interrupt-safe.

Notes for Fortran

All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK) have an additional argument ierr at the end of the argument list. ierris an integer and has the same meaning as the return value of the routine in C. In Fortran, MPI routines are subroutines, and are invoked with the call statement.

All MPI objects (e.g., MPI_Datatype, MPI_Comm) are of type INTEGERin Fortran.

Errors

All MPI routines (except MPI_Wtime and MPI_Wtick) return an error value; C routines as the value of the function and Fortran routines in the last argument. Before the value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job. The error handler may be changed with MPI_Comm_set_errhandler (for communicators), MPI_File_set_errhandler (for files), and MPI_Win_set_errhandler (for RMA windows). The MPI-1 routine MPI_Errhandler_set may be used but its use is deprecated. The predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarantee that an MPI program can continue past an error; however, MPI implementations will attempt to continue whenever possible.

MPI_SUCCESS: No error; MPI routine completed successfully.

MPI_ERR_COMM: Invalid communicator. A common error is to use a null communicator in a call (not even allowed in MPI_Comm_rank).

MPI_ERR_ARG: Invalid argument. Some argument is invalid and is not identified by a specific error class (e.g., MPI_ERR_RANK).

MPI_ERR_COUNT: Invalid count argument. Count arguments must be non-negative; a count of zero is often valid.

MPI_ERR_TYPE: Invalid datatype argument. Additionally, this error can occur if an uncommitted MPI_Datatype (see MPI_Type_commit) is used in a communication call.