The Great and Terrible implementation of MPI-2

function index


Begins a nonblocking send
int MPI_Isend(
  void *buf,
  int count,
  MPI_Datatype datatype,
  int dest,
  int tag,
  MPI_Comm comm,
  MPI_Request *request


[in] initial address of send buffer (choice)
[in] number of elements in send buffer (integer)
[in] datatype of each send buffer element (handle)
[in] rank of destination (integer)
[in] message tag (integer)
[in] communicator (handle)
[out] communication request (handle)


Start a standard mode, nonblocking send.

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.

No error; MPI routine completed successfully.
Invalid communicator. A common error is to use a null communicator in a call (not even allowed in MPI_Comm_rank).
Invalid count argument. Count arguments must be non-negative; a count of zero is often valid.
Invalid datatype argument. May be an uncommitted MPI_Datatype (see MPI_Type_commit).
Invalid tag argument. Tags must be non-negative; tags in a receive (MPI_Recv, MPI_Irecv, MPI_Sendrecv, etc.) may also be MPI_ANY_TAG. The largest tag value is available through the the attribute MPI_TAG_UB.
Invalid source or destination rank. Ranks must be between zero and the size of the communicator minus one; ranks in a receive (MPI_Recv, MPI_Irecv, MPI_Sendrecv, etc.) may also be MPI_ANY_SOURCE.
This error is returned when some part of the MPICH implementation is unable to acquire memory.

Example Code

The following sample code illustrates MPI_Isend.

#include "mpi.h"
#include <stdio.h>
int main(int argc, char *argv[])
    int myid, numprocs, left, right;
    int buffer[10], buffer2[10];
    MPI_Request request, request2;
    MPI_Status status;

    MPI_Comm_size(MPI_COMM_WORLD, &numprocs);
    MPI_Comm_rank(MPI_COMM_WORLD, &myid);
    right = (myid + 1) % numprocs;
    left = myid - 1;
if (left < 0)
        left = numprocs - 1;
    MPI_Irecv(buffer, 10, MPI_INT, left, 123, MPI_COMM_WORLD, &request);
    MPI_Isend(buffer2, 10, MPI_INT, right, 123, MPI_COMM_WORLD, &request2);
    MPI_Wait(&request, &status);
    MPI_Wait(&request2, &status);
return 0;