MPI_Gatherv

MPI_Gatherv - Gathers into specified locations from all processes in a group

SYNOPSIS

int MPI_Gatherv(const void *sendbuf, int sendcount, MPI_Datatype sendtype,
void *recvbuf, const int *recvcounts, const int *displs,
MPI_Datatype recvtype, int root, MPI_Comm comm)

INPUT PARAMETERS

sendbuf

  • starting address of send buffer (choice)

sendcount

  • number of elements in send buffer (integer)

sendtype

  • data type of send buffer elements (handle)

recvcounts

  • integer array (of length group size) containing the number of

elements that are received from each process (significant only at root )

displs

  • integer array (of length group size). Entry i specifies the

displacement relative to recvbuf at which to place the incoming data from process i (significant only at root)

recvtype

  • data type of recv buffer elements (significant only at root )

(handle)

root

  • rank of receiving process (integer)

comm

  • communicator (handle)

OUTPUT PARAMETERS

recvbuf

  • address of receive buffer (choice, significant only at root )

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 malloc or 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. ierr is 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 INTEGER in 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_TYPE

  • Invalid datatype argument. Additionally, this error can occur if an

uncommitted MPI_Datatype (see MPI_Type_commit ) is used in a communication call.

MPI_ERR_BUFFER

  • Invalid buffer pointer. Usually a null buffer where one is not

valid.