[MPI3 Fortran] ASYNC attribute

[Jeff Squyres]

1. How does the MPI_Wait know that it can have no code motion with  
respect to buf?

2. Yes, the MPI_Request argument to MPI_Wait is inout.


On May 5, 2009, at 7:45 PM, Craig Rasmussen wrote:

> I'm at the WG5 Fortran standards meeting and I think we've made
> significant advances regarding the MPI-3 Fortran API.  We are
> discussing adding a new variable attribute, ASYNC.  I'd like to get
> feedback from the MPI-3 Fortran working group on these possible  
> changes.
>
> ASYNC implies that a variable is potentially active in asynchronous
> operations outside of Fortran.  The use of this new attribute should
> give the compiler enough information to inhibit optimizations similar
> to inhibitions involved in Fortran asynchronous I/O, specifically
> copyin/copyout and code motion.  The compiler will likely have to
> inhibit code motion regarding any use of a variable with the ASYNC
> attribute and procedures other than intrinsics.  The affect is similar
> to the use of the volatile attribute (but not regarding loads and
> stores).
>
> Usage is outlined below:
>
> ----------------
>
> real, ASYNC_EXTERNAL :: buf(100,100)
> type(MPI_Request) :: request
>
> ! initiate data transfer of boundary
> CALL MPI_IRecv(buf(:,1),...,request,...)  ! no copyin/copyout will
> happen
>
> ! do work on interior of the buffer while transfer is in progress
> CALL UPDATE_INTERIOR(buf)  ! dummy arg should have ASYNC attribute
>
> ! wait for the communication to finish
> CALL MPI_Wait(request,...)   ! no code motion allowed with respect to
> buf
>
> ! finish work on buffer boundaries
> CALL UPDATE_BOUNDARIES(buf)  ! should copyin/copyout be allowed here?
>
> ----------------
>
> So how does this look?  Anything we've left out?  I'm also including
> the interface definition.
>
> - craig
>
> ----------------
>
> interface
>
> SUBROUTINE MPI_Irecv(buf, count, datatype, source, tag, comm, request,
> err) BIND(C, name="MPI_Irecv")
>     import MPI_Datatype, MPI_Comm, MPI_Request
>     TYPE(*), DIMENSION(..), ASYNC   :: buf
>     integer, value,     intent(in)  :: count
>     type(MPI_Datatype), intent(in)  :: datatype
>     integer, value,     intent(in)  :: source
>     integer, value,     intent(in)  :: tag
>     type(MPI_Comm),     intent(in)  :: comm
>     type(MPI_Request),  intent(out) :: request
>     integer,            intent(out) :: err
> END SUBROUTINE MPI_Irecv
>
> SUBROUTINE MPI_Isend(buf, count, datatype, dest, tag, comm, request,
> err) BIND(C, name="MPI_Isend")
>     import MPI_Datatype, MPI_Comm, MPI_Request
>     TYPE(*), DIMENSION(..), ASYNC   :: buf
>     integer, value,     intent(in)  :: count
>     type(MPI_Datatype), intent(in)  :: datatype
>     integer, value,     intent(in)  :: dest
>     integer, value,     intent(in)  :: tag
>     type(MPI_Comm),     intent(in)  :: comm
>     type(MPI_Request),  intent(out) :: request
>     integer,            intent(out) :: err
> END SUBROUTINE MPI_Isend
>
> SUBROUTINE MPI_Wait(request, status, err) BIND(C, name="MPI_Wait")
>     import MPI_Request, MPI_Status
>     type(MPI_Request), intent(in)  :: request  !        inout?
>     type(MPI_Status),  intent(out) :: status
>     integer,           intent(out) :: err
> END SUBROUTINE MPI_Wait
>
> end interface
>
>
>
>
>
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-- 
Jeff Squyres
Cisco Systems