Gathers into specified locations from all processes in a group in a nonblocking way


int MPI_Igatherv(const void *sendbuf, int sendcount, MPI_Datatype sendtype, void *recvbuf,
                 const int recvcounts[], const int displs[], MPI_Datatype recvtype, int root,
                 MPI_Comm comm, MPI_Request *request)

Input Parameters

starting address of the send buffer (choice)
number of elements in send buffer (non-negative integer)
data type of send buffer elements (handle)
non-negative integer array (of length group size) containing the number of elements that are received from each process (significant only at root)
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)
data type of receive buffer elements (significant only at root) (handle)
rank of receiving process (integer)
communicator (handle)

Output Parameters

starting address of the receive buffer (significant only at root) (choice)
communication request (handle)

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.


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 guarentee that an MPI program can continue past an error; however, MPI implementations will attempt to continue whenever possible.