[Mpi3-rma] Target displacement sign issue

[Jim Dinan]

This is true, but we've relied on a correspondence between Aints and 
pointers in a variety use cases for dynamic windows, e.g. the linked 
list example.

  ~Jim.

On 9/5/12 9:15 AM, Pavan Balaji wrote:
>
> FYI, casting back MPI_Aint to a pointer was never safe (even in
> MPI-2.2), since MPI_Aint can be larger than void *.
>
>   -- Pavan
>
> On 09/05/2012 09:13 AM, Jim Dinan wrote:
>> Hi Hubert,
>>
>> If I understand this correctly, then one would no longer be able to cast
>> an MPI_Aint back to a pointer.  We would have to add another routine,
>> MPI_Get_pointer_dynamic() to do this conversion.
>>
>>    ~Jim.
>>
>> On 9/4/12 6:25 PM, Hubert Ritzdorf wrote:
>>>
>>> Hi,
>>>
>>> Possibly another solution:
>>>
>>> (*) Let MPI_AINT_MAX the maximal value of MPI_Aint variable
>>> (*) Let the window_base of a window created by MPI_WIN_CREATE_DYNAMIC
>>>       be MPI_AINT_MAX + 1
>>> (*) Define a new function MPI_Get_address_dynamic returning the
>>>       address of a location relative to MPI_AINT_MAX + 1
>>> (*) Remove the non-negative qualification in the description
>>>       of target_disp in MPI_{Put/Get/Accumulate/...).
>>>
>>> Hubert
>>>
>>>> -----Original Message-----
>>>> From: mpi3-rma-bounces at lists.mpi-forum.org [mailto:mpi3-rma-
>>>> bounces at lists.mpi-forum.org] On Behalf Of Hubert Ritzdorf
>>>> Sent: Tuesday, September 04, 2012 7:23 PM
>>>> To: MPI 3.0 Remote Memory Access working group
>>>> Subject: Re: [Mpi3-rma] Target displacement sign issue
>>>>
>>>> Hi,
>>>>
>>>> MPI_Get_address returns an MPI_Aint which is signed.(integer).
>>>>
>>>> C:
>>>> MPI_Aint's may be used in Reduce Operations with Min/Max
>>>> or the application can internally use min/max computations.
>>>> Can anybody guarantee that applications don't perform
>>>> min/max operations on these displacements (which results in different
>>>> results for unsigned and signed variables) or use derived values of
>>>> these
>>>> displacements in other signed/unsigned significant cases.
>>>>
>>>> Fortran:
>>>> MPI_BOTTOM is a variable in a common block/module. Thus,
>>>> MPI_Get_address might really return a signed integer (depending on the
>>>> compiler).
>>>> Fortran doesn't have unsigned integers and cannot handle them.
>>>> Thus, the non-negative integer specification for target_disp in
>>>> MPI_{Put/Get/Accumulate/...)
>>>> might be incorrect for Fortran and MPI_Win_Create_dynamic().
>>>>
>>>> Hubert
>>>> ________________________________________
>>>> From: mpi3-rma-bounces at lists.mpi-forum.org [mpi3-rma-bounces at lists.mpi-
>>>> forum.org] on behalf of Jim Dinan [dinan at mcs.anl.gov]
>>>> Sent: Tuesday, September 04, 2012 5:10 PM
>>>> To: mpi3-rma at lists.mpi-forum.org
>>>> Subject: Re: [Mpi3-rma] Target displacement sign issue
>>>>
>>>> Hi All,
>>>>
>>>> This is an important issue that we need to resolve before releasing the
>>>> 3.0 spec.  Please take a look and send feedback.
>>>>
>>>> Dave has voiced a concern that the implicit type conversion in my
>>>> proposed text below may not be portable.  If anyone has more experience
>>>> with this aspect (signed->unsigned conversion) of C/Fortran/etc type
>>>> systems, please chime in.
>>>>
>>>>     ~Jim.
>>>>
>>>> On 8/28/12 2:29 PM, Jim Dinan wrote:
>>>>> Hi All,
>>>>>
>>>>> Here is the suggested change to address this issue.  In the
>>>>> paragraph on
>>>>> page 425, line 1, add the bracketed sentence:
>>>>>
>>>>> In the case of a window created with MPI_WIN_CREATE_DYNAMIC, the
>>>>> target_disp for all RMA functions is the address at the target; i.e.,
>>>>> the effective window_base is MPI_BOTTOM and the disp_unit is one.
>>>>> [Thus,
>>>>> for dynamic windows, the target_disp argument to all RMA functions in
>>>>> interpreted as unsigned.] Users should use MPI_GET_ADDRESS at the
>>>>> target
>>>>> process to determine the address of a target memory location and
>>>>> communicate this address to the origin process.
>>>>>
>>>>>      ~Jim.
>>>>>
>>>>> On 8/28/12 9:46 AM, Jim Dinan wrote:
>>>>>> Hi All,
>>>>>>
>>>>>> Currently, target displacements in put/get/acc/etc are defined to be
>>>>>> non-negative integers of type, MPI_Aint.  MPI_Aint is defined to be a
>>>>>> signed integer.  However, displacements associated with dynamic
>>>>>> windows
>>>>>> are addresses (unsigned) and can range into the space of negative
>>>>>> integers.
>>>>>>
>>>>>> It seems like the least impact change would be to add a special case
>>>>>> that the displacement argument will be interpreted as unsigned for
>>>>>> dynamic windows.  Changing the interface to take an 'unsigned
>>>>>> MPI_Aint'
>>>>>> would be the most clear (and preserve the existing and intended new
>>>>>> semantics), but would break backward compatibility.
>>>>>>
>>>>>> Interested to hear your thoughts.
>>>>>>
>>>>>>     ~Jim.
>>>> _______________________________________________
>>>> mpi3-rma mailing list
>>>> mpi3-rma at lists.mpi-forum.org
>>>> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi3-rma
>>>>
>>>>
>>>>    Click
>>>> https://www.mailcontrol.com/sr/O6SiJI5AP4bTndxI!oX7Up2F0f+S6NySj!qlvEoKFyZ
>>>>
>>>> NTFyVkk9WjRzJbmnfHdyw83VGVWKbSfC8ewgPpp7kgg==  to report this email as
>>>> spam.
>>>>
>>>> _______________________________________________
>>>> mpi3-rma mailing list
>>>> mpi3-rma at lists.mpi-forum.org
>>>> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi3-rma
>>>
>>> _______________________________________________
>>> mpi3-rma mailing list
>>> mpi3-rma at lists.mpi-forum.org
>>> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi3-rma
>>>
>> _______________________________________________
>> mpi3-rma mailing list
>> mpi3-rma at lists.mpi-forum.org
>> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi3-rma
>>
>