From: Jeff Squyres Date: January 19, 2008 1:16:55 PM CST To: mpi-21@XXXXXXXXXXXXX Cc: "mpi-21@cs.uiuc.edu" Subject: Re: [mpi-21] const C++ MPI handles (take 2) Reply-To: mpi-21@XXXXXXXXXXXXX Well, we pretty much have so far. :-) The const was removed in ballot 2, but I wonder how many people actually noticed (I didn't, until a few days ago). On Jan 19, 2008, at 1:21 PM, Erez Haba wrote: > I agree, const is the better way to implement. The question is: do > you want to *force* the optimized implementation? > > -----Original Message----- > From: owner-mpi-21@mpi-forum.org [mailto:owner-mpi-21@mpi- > forum.org] On Behalf Of Jeff Squyres > Sent: Friday, January 18, 2008 5:49 PM > To: mpi-21@mpi-forum.org > Cc: mpi-21@XXXXXXXXXXX > Subject: Re: [mpi-21] const C++ MPI handles (take 2) > > 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 point of why we originally made the C++ handles be const was on the 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@mpi-forum.org [mailto:owner-mpi-21@mpi-forum.org] >> On Behalf Of Jeff Squyres >> Sent: Friday, January 18, 2008 11:14 AM >> To: mpi-21@mpi-forum.org >> Cc: mpi-21@XXXXXXXXXXX >> 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 > -- Jeff Squyres Cisco Systems