# MPI_Waitany

Waits for any specified send or receive to complete

## Synopsis

    #include "mpi.h"
    int MPI_Waitany(
            int count,
            MPI_Request array_of_requests[],
            int *index,
            MPI_Status *status )

## Input Parameters

| count | list length (integer)
| array_of_requests | array of requests (array of handles)

## Output Parameters

| index | index of handle for operation that completed (integer). In the range `0` to `count-1`. In Fortran, the range is `1` to `count`.
| status | status object (Status)

## Notes

If all of the requests are `MPI_REQUEST_NULL`, then `index` is returned as `MPI_UNDEFINED`, and `status` is returned as an empty status.

## Note on status for send operations

For send operations, the only use of status is for MPI_Test_cancelled or in the case that there is an error, in which case the MPI_ERROR field of status will be set.

## 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_Errhandler_set`; 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.

MPI_SUCCESS
  No error; MPI routine completed successfully.

MPI_ERR_REQUEST
  Invalid `MPI_Request`. Either null or, in the case of a `MPI_Start` or `MPI_Startall`, not a persistent request.

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

Location:waitany.c