MPI_Waitany(3)                     Open MPI                     MPI_Waitany(3)



NAME
       MPI_Waitany - Waits for any specified send or receive to complete.


SYNTAX
C Syntax
       #include <mpi.h>
       int MPI_Waitany(int count, MPI_Request *array_of_requests,
            int *index, MPI_Status *status)


Fortran Syntax
       INCLUDE 'mpif.h'
       MPI_WAITANY(COUNT, ARRAY_OF_REQUESTS, INDEX, STATUS, IERROR)
            INTEGER   COUNT, ARRAY_OF_REQUESTS(*), INDEX
            INTEGER   STATUS(MPI_STATUS_SIZE), IERROR


C++ Syntax
       #include <mpi.h>
       static int Request::Waitany(int count, Request
            array_of_requests[], Status& status)

       static int Request::Waitany(int count, Request array_of_requests[])


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).


       IERROR    Fortran only: Error status (integer).


DESCRIPTION
       A call to 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). MPI_Waitany with an array containing one
       active entry is equivalent to 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 .GT 0) THEN         ! client code
               DO WHILE(.TRUE.)
                  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 WHILE(.TRUE.)
                     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



ERRORS
       Almost all MPI routines return an error value; C routines as the value
       of the function and Fortran routines in the last argument. C++
       functions do not return errors. If the default error handler is set to
       MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception mechanism
       will be used to throw an MPI::Exception object.

       Before the error value is returned, the current MPI error handler is
       called. By default, this error handler aborts the MPI job, except for
       I/O function errors. The error handler may be changed with
       MPI_Comm_set_errhandler, MPI_File_set_errhandler, or
       MPI_Win_set_errhandler (depending on the type of MPI handle that
       generated the request); 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.

       Note that per MPI-1 section 3.2.5, MPI exceptions on requests passed to
       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 MPI_WAITANY if
       the back-end error handler returns it.  The pre-defined MPI error
       handler MPI_ERRORS_RETURN exhibits this behavior, for example.


SEE ALSO
       MPI_Comm_set_errhandler
       MPI_File_set_errhandler
       MPI_Test
       MPI_Testall
       MPI_Testany
       MPI_Testsome
       MPI_Wait
       MPI_Waitall
       MPI_Waitsome
       MPI_Win_set_errhandler




1.4.1                            Jan 14, 2010                   MPI_Waitany(3)
