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: [email protected] [mailto:mpi3-rma- [email protected]] 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: [email protected] [[email protected] forum.org] on behalf of Jim Dinan [[email protected]] Sent: Tuesday, September 04, 2012 5:10 PM To: [email protected] 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.
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