[mpich-discuss] MPI_Get on the same memory location

[Boisvert, Sebastien]

> ________________________________________
> From: Nick Radcliffe [nradclif at cray.com]
> Sent: Thursday, August 21, 2014 8:42 PM
> To: discuss at mpich.org
> Subject: Re: [mpich-discuss] MPI_Get on the same memory location
> > If buffers overlap, use memmov and not memcpy:
> Good point, you would have to use memmov in general for overlapping source and target buffers. I was thinking of the special case where the source and target buffers are identical.

Identical buffers overlap, right ?

So MPICH should not be calling memcpy with those operands, or the user should not do that in the
first place maybe.

> > I don’t think so.  It’s an incorrect program to get from a buffer to itself.  MPICH is being helpful is catching this user error.
> Do you know where in the standard this is specified? I'm having trouble finding it.
> -Nick
> ________________________________________
> From: Boisvert, Sebastien [boisvert at anl.gov]
> Sent: Thursday, August 21, 2014 7:30 PM
> To: discuss at mpich.org
> Subject: Re: [mpich-discuss] MPI_Get on the same memory location
> > ________________________________________
> > From: Nick Radcliffe [nradclif at cray.com]
> > Sent: Thursday, August 21, 2014 5:47 PM
> > To: discuss at mpich.org
> > Subject: Re: [mpich-discuss] MPI_Get on the same memory location
> > > MPIR_Localcopy(357): memcpy arguments alias each other, dst=0x19a5f40
> > src=0x19a5f40 len=4
> > It looks like memcpy is doing a check to make sure the source and destination buffers don't overlap. This seems like a bug to me -- when doing an MPI_Get from a buffer to itself, the implementation should probably just do nothing and return.
> I disagree.
> If buffers overlap, use memmov and not memcpy:
> " If copying takes place between objects that overlap, the behavior is undefined."
> --source: http://pubs.opengroup.org/onlinepubs/009695399/functions/memcpy.html
> Also:
> http://stackoverflow.com/questions/1960991/which-one-to-use-memmove-or-memcpy-when-buffers-dont-overlap
> 
> > -Nick
> > ________________________________________
> > From: alessandro.fanfarillo at gmail.com [alessandro.fanfarillo at gmail.com] on behalf of Alessandro Fanfarillo [fanfarillo at ing.uniroma2.it]
> > Sent: Thursday, August 21, 2014 5:25 PM
> > To: discuss at mpich.org
> > Subject: [mpich-discuss] MPI_Get on the same memory location
> > Dear all,
> > I'm having the following error:
> > Fatal error in MPI_Get: Internal MPI error!, error stack:
> > MPI_Get(156).......: MPI_Get(origin_addr=0x19a5f40, origin_count=4,
> > MPI_BYTE, target_rank=0, target_disp=0, target_count=4, MPI_BYTE,
> > win=0xa0000000) failed
> > MPIDI_Get(247).....:
> > MPIR_Localcopy(357): memcpy arguments alias each other, dst=0x19a5f40
> > src=0x19a5f40 len=4
> > if I try to execute MPI_Get on the same memory location on a shared
> > memory machine (my laptop).
> > I cannot find anything in the standard that denies it for the one-sided.
> > Running with OpenMPI everything works fine.
> > Is it a bug or I missed something in the standard?
> > Thanks.
> > Alessandro
> > --
> > Alessandro Fanfarillo
> > Dip. di Ingegneria Civile ed Ingegneria Informatica
> > Università di Roma "Tor Vergata"
> > NCAR Office: +1 (303) 497-2442
> > Tel: +39-06-7259 7719
> > _______________________________________________
> > discuss mailing list     discuss at mpich.org
> > To manage subscription options or unsubscribe:
> > https://lists.mpich.org/mailman/listinfo/discuss
> > _______________________________________________
> > discuss mailing list     discuss at mpich.org
> > To manage subscription options or unsubscribe:
> > https://lists.mpich.org/mailman/listinfo/discuss
> _______________________________________________
> discuss mailing list     discuss at mpich.org
> To manage subscription options or unsubscribe:
> https://lists.mpich.org/mailman/listinfo/discuss
> _______________________________________________
> discuss mailing list     discuss at mpich.org
> To manage subscription options or unsubscribe:
> https://lists.mpich.org/mailman/listinfo/discuss