[mpi-21] const C++ MPI handles (take 2)

Jeff Squyres jsquyres at [hidden]
Fri Jan 18 19:48:52 CST 2008

Yes, that's the way the original C++ bindings were implemented.  But  
it's not required or necessary to do that; that C errhandler could  
easily be cached somewhere else.

More specifically, isn't it better to have a const object to allow for  
compiler optimizations?  (I'm not a compiler guru, but I thought the  
point of why we originally made the C++ handles be const was on the  
argument for potential compiler optimizations)

On Jan 18, 2008, at 8:35 PM, Erez Haba wrote:

> For example an implementation might choose to cache the error  
> handler for MPI::COMM_WORD (in the MPI::Comm object) and call it  
> itself on error so it can pass in the right object to the error  
> handler.
> Thus requiring MPI::COMM_WORLD not to be const.
> -----Original Message-----
> From: owner-mpi-21_at_[hidden] [mailto:owner-mpi-21_at_[hidden]]  
> On Behalf Of Jeff Squyres
> Sent: Friday, January 18, 2008 11:14 AM
> To: mpi-21_at_[hidden]
> Cc: mpi-21_at_[hidden]
> Subject: [mpi-21] const C++ MPI handles (take 2)
> On Jan 18, 2008, at 2:02 PM, Erez Haba wrote:
>> Okay; about one issue at a time.
> Changing mail subject to reflect the discussion...
>> *For this sentence* it does not matter what's a common usage for C++
>> global variables. Some MPI implementations would need to have non-
>> const qualified global objects.
> Why?  As I understand it, most (all?) MPI C++ implementations
> currently only require some objects to be non-const because of the
> standard-related issue that was already raised (Set_attr(),
> Set_name(), Set_errhandler() methods not having const variants).  Is
> there a reason that an implementation would *need* MPI handles to be
> non-const?
> Per my prior mail, I believe that the standard should specify that
> some of the methods on these classes should have const and non-const
> variants, and then it should be fine to require that the predefined
> handles be const.
> So the question is still open: what's common practice in the C++
> community regarding const/non-const global variable specification?
> This question will be moot if you can demonstrate that an
> implementation would need non-const C++ MPI predefined handles.
> --
> Jeff Squyres
> Cisco Systems

Jeff Squyres
Cisco Systems

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