:ref:`MPI_Waitany` - Waits for any specified send or receive to complete.
#include <mpi.h>
int MPI_Waitany(int count, MPI_Request array_of_requests[],
int *index, MPI_Status *status)
USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_WAITANY(COUNT, ARRAY_OF_REQUESTS, INDEX, STATUS, IERROR)
INTEGER COUNT, ARRAY_OF_REQUESTS(*), INDEX
INTEGER STATUS(MPI_STATUS_SIZE), IERROR
USE mpi_f08
MPI_Waitany(count, array_of_requests, index, status, ierror)
INTEGER, INTENT(IN) :: count
TYPE(MPI_Request), INTENT(INOUT) :: array_of_requests(count)
INTEGER, INTENT(OUT) :: index
TYPE(MPI_Status) :: status
INTEGER, OPTIONAL, INTENT(OUT) :: ierror
count
: List length (integer).array_of_requests
: Array of requests (array of handles).
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).ierror
: Fortran only: Error status (integer).
A call to :ref:`MPI_Waitany` can be used to wait for the completion of one out of several requests.
The array_of_requests list may contain null or inactive handles. If the
list contains no active handles (list has length zero or all entries are
null or inactive), then the call returns immediately with index =
MPI_UNDEFINED
, and an empty status.
The execution of MPI_Waitany(count, array_of_requests, index, status)
has the same effect as the execution of MPI_Wait(&array_of_requests[i], status)
,
where i is the value returned by index (unless the value of
index is MPI_UNDEFINED
). :ref:`MPI_Waitany` with an array containing one active
entry is equivalent to :ref:`MPI_Wait`.
If your application does not need to examine the status field, you can
save resources by using the predefined constant MPI_STATUS_IGNORE
as a
special value for the status argument.
Example: Client-server code (starvation can occur).
CALL MPI_COMM_SIZE(comm, size, ierr)
CALL MPI_COMM_RANK(comm, rank, ierr)
IF(rank > 0) THEN ! client code
DO
CALL MPI_ISEND(a, n, MPI_REAL, 0, tag, comm, request, ierr)
CALL MPI_WAIT(request, status, ierr)
END DO
ELSE ! rank=0 -- server code
DO i=1, size-1
CALL MPI_IRECV(a(1,i), n, MPI_REAL, i tag, &
comm, request_list(i), ierr)
END DO
DO
CALL MPI_WAITANY(size-1, request_list, index, status, ierr)
CALL DO_SERVICE(a(1,index)) ! handle one message
CALL MPI_IRECV(a(1, index), n, MPI_REAL, index, tag, &
comm, request_list(index), ierr)
END DO
END IF
Note that per MPI-1 section 3.2.5, MPI errors on requests passed to
:ref:`MPI_WAITANY` do not set the status.MPI_ERROR
field in the returned
status. The error code is passed to the back-end error handler and may
be passed back to the caller through the return value of :ref:`MPI_WAITANY` if
the back-end error handler returns it. The pre-defined MPI error handler
MPI_ERRORS_RETURN
exhibits this behavior, for example.
.. seealso::
* :ref:`MPI_Comm_set_errhandler`
* :ref:`MPI_File_set_errhandler`
* :ref:`MPI_Test`
* :ref:`MPI_Testall`
* :ref:`MPI_Testany`
* :ref:`MPI_Testsome`
* :ref:`MPI_Wait`
* :ref:`MPI_Waitall`
* :ref:`MPI_Waitsome`
* :ref:`MPI_Win_set_errhandler`