[Mpi3-bwcompat] MPI_Count mixing with int...

[Rajeev Thakur]

Yes, that is a long standing problem -- that datatypes use MPI_Aint
(wherever they do), but they really need to use the larger of MPI_Aint
or MPI_Offset.

Rajeev
 

> -----Original Message-----
> From: mpi3-bwcompat-bounces_at_[hidden] 
> [mailto:mpi3-bwcompat-bounces_at_[hidden]] On Behalf Of Fab Tillier
> Sent: Thursday, July 08, 2010 11:20 PM
> To: MPI-3 backwards compatability WG
> Subject: Re: [Mpi3-bwcompat] MPI_Count mixing with int...
> 
> Rajeev Thakur wrote on Thu, 8 Jul 2010 at 18:24:16
> 
> > You can define a filetype that is many Gbytes and read only a small 
> > part of it. The filetype is specified in MPI_File_set_view 
> and is not 
> > passed in the read/write calls. The datatype passed in the 
> read/write 
> > calls refers to the buffer passed to that call.
> 
> Perfect, thanks for the example!  Does this imply that 
> MPI_Type_get_extent, which returns an MPI_Aint, might 
> overflow the extent parameter on a 32-bit platform on which a 
> user defines a many Gbyte filetype?  How should we address 
> this (there are probably other APIs affected similarly)?
> 
> -Fab 
> 
> >> -----Original Message-----
> >> From: Fab Tillier
> >> Sent: Thursday, July 08, 2010 3:32 PM
> >> 
> >> Rajeev Thakur wrote on Thu, 8 Jul 2010 at 12:52:58
> >> 
> >>>> As an aside, can count ever be larger than size_t?
> >>> 
> >>> Probably not in the communication or I/O functions since count 
> >>> refers to the number of items in the memory buffer, but 
> it could be 
> >>> for the datatype constructor functions since datatypes can
> >> represent file layout.
> >> 
> >> How would you use a datatype that is larger than your 
> address space?  
> >> You can't read or write it, you can't send or receive it, 
> you can't 
> >> pack/unpack it...
> >> 
> >> Am I missing something and a datatype like this would be useful?
> >> 
> >> -Fab
> 
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