[Mpi-22] Ticket #46: Add const Keywordto the Cbindings-implementation

[Barrett, Brian W]

I believe the procedural arguments are the most worrying thing, and they
haven't been commented on, which is a bit worrying.

Nor has the fact that the proposal, even with *TWO* corrections which are
separate proposals, still isn't complete (in that user callbacks which
should be const aren't because we're rushing this through 2.2 instead of
working in the 3.0 framework, where we could make minor user code changes
like correcting const in the callbacks.

But in response to your question, Open MPI does have a test suite, and we
can use the ANL and Intel test suites.  However, none of them test that
we're handing const correctly.  They test that the behavior according to
MPI-2.1 is correct.  They don't check that there are const keywords in the
right place.  Such a change would be fairly large (to the test suite, that
is), which only adds to the "largeness" of this patch.

We're not ignoring your statement of 2.5 hours.  But I don't think that's a
realistic metric for doing the implementation, updating/developing test
cases, and properly testing on a variety of compilers.

Both Jeff and I have asked essentially the same question, without a
reasonable answer.  Why are we pushing a proposal with known procedural
issues and possibly oversized implementation into 2.2 when it can easily be
pushed to 3.0?  What's the rush - let's do this completely and correctly the
first time, rather than looking like fools in two months when it turns out
we did something wrong.

Brian

On 3/19/09 9:50 , "Erez Haba" <erezh_at_[hidden]> wrote:

> Jeff, I don't understand why you ignore all the work that has been done with
> this ticket and suggest your own metric. Was the information I provided
> unreliable or untrue?
> 
> As I said, it took me about 2.5h to implement the entire change on the MSMPI
> code base; yes there were many internal functions that had const in it, but
> also many that did not. I don't think that by any measure this is a
> significant work for any implementer.
> 
> More than that, this interface change was tested using the ANL test suite and
> the Intel complete test suite, without a single compile or runtime error over
> multiple platforms and compilers. Again, this was not a significant work item;
> and I believe that OpenMPI has a regression suite that crosses platform and
> compilers which is easy to run (as you described to me many times).
> 
> 
> With this information that I have already provided before, I don't understand
> your claims; unless you think that they are biased and unreliable.
> 
> Hence this ticket completely meets MPI 2.2 requirements in scope and backward
> compatibility.
> 
> Thanks,
> .Erez
> 
> -----Original Message-----
> From: mpi-22-bounces_at_[hidden]
> [mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Jeff Squyres
> Sent: Thursday, March 19, 2009 5:20 AM
> To: Bronis R. de Supinski; MPI 2.2
> Subject: Re: [Mpi-22] Ticket #46: Add const Keywordto the
> Cbindings-implementation
> 
> On Mar 19, 2009, at 12:03 AM, Bronis R. de Supinski wrote:
> 
>> I have been quiet on this debate but I am to the point
>> that I feel a need to speak up. I think the "significant
>> changes" reason is a canard (I think Brian and Jeff
>> believe it but it is still a red herring for the most
>> part). The changes to support it are not significant.
>> You can implement it by casting it away early.
>> 
> 
> 
> The changes *are* significant.  I count 90 top-level MPI API functions
> that are affected by this proposal.
> 
> The bar for 2.2 is "trivial" implementation efforts, no?  This is not
> trivial.  The MPICH diff was ~10,000 lines.  Apparently, they chose to
> go above and beyond the requirement and propagate const to lower
> layers (vs. casting it away immediately), but still -- if a 2.2 change
> can inspire a 10,000 line diff, that just seems like it doesn't meet
> the spirit of the "trivial" implementation requirement.
> 
> Indeed, in doing the "simple" cast-it-away-immediately approach
> implementation, editing and testing each of the 90 functions will
> require a good amount of effort.  Sure, the first-wave addition of
> "const" across all of the affected functions is probably relatively
> easy -- one code monkey and several hours.  But how long will it take
> you to find the one place where you put "const" in the wrong
> location?  How long will it take you to write new tests to verify the
> const-ness in all the right places?  To be clear: it's a "not
> significant" change to a code monkey.  But try to tell your QA guys
> that this is not significant -- they'll freak out.
> 
> Hence, if you take the overall scope of both the change and the
> additional testing to validate this change, this is a large scale
> implementation effort.  I just don't see what the rush is to get this
> into 2.2.
> 
> I think Brian makes several good arguments, one of which is: those who
> want const can put it in today.  It hypothetically shouldn't break any
> existing user codes (this is the code monkey in me talking, not the QA
> rep), and those implementors who want it for stronger contracts can
> have it.
> 
> --
> Jeff Squyres
> Cisco Systems
> 
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--
   Brian W. Barrett
   Dept. 1423: Scalable System Software
   Sandia National Laboratories