[mpiwg-languages] static datatypes lifetimes

[Jeff Hammond]

Attributes on ops, datatypes and files is critical for multiple use cases. It’s ridiculous we don’t have them. The standard is inconsistent without. 

Jeff

Sent from my iPhone

> On 27. Apr 2025, at 5.51, Joseph Schuchart via mpiwg-languages <mpiwg-languages at lists.mpi-forum.org> wrote:
> 
> 
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> Unfortunately, there is a catch: MPI_COMM_SELF is only 
> relevant/available/valid in the World Process Model (WPM), i.e., if 
> using `MPI_Init`/`MPI_Finalize`. In the Sessions process model, 
> predefined communicators are not available.
> 
> The life-time of datatypes is a known quirk and I think it was 
> discovered after Sessions became part of the standard. They are not 
> bound to any other MPI object and can survive complete shutdown of all 
> sessions / the WPM. IIRC in Open MPI (but have to check), datatypes 
> retain a reference on the internal MPI instance and it is the 
> application's responsibility to free all MPI objects before shutdown. 
> Once the last datatype/session/wpm is gone we release the instance.
> 
> I don't like the state of things there and it is problematic. For 
> starters, it prevents complete session isolation (and the benefits that 
> come with it, such as different threading levels). It's not clear to me 
> how that can be rectified and I think the Forum is not clear on that 
> either, which is why we ended up with this weird zombie state. If 
> someone wants to open a ticket to start a discussion on this I'm happy 
> to participate.
> 
> For the problem at hand though (as I understand it), maybe it's 
> sufficient to add attributes to datatypes? I don't see why that would be 
> a problem and if it helps with language adoption we have a good argument 
> for it.
> 
> Cheers
> Joseph
> 
> On 4/25/25 17:24, Alfredo Correa via mpiwg-languages wrote:
> > Hi Sayan, On Fri, Apr 25, 2025 at 2: 03 PM Ghosh, Sayan 
> > <sayan. ghosh@ pnnl. gov> wrote: Consider finalize-delete-callback 
> > (this is what Alfredo is alluding to perhaps w. r. t 
> > datatype-attached-to-environment) – that seems to rely on MPI_COMM_SELF
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> > Hi Sayan,
> >
> > On Fri, Apr 25, 2025 at 2:03 PM Ghosh, Sayan <sayan.ghosh at pnnl.gov> wrote:
> >
> >       * Consider finalize-delete-callback (this is what Alfredo is
> >         alluding to perhaps w.r.t datatype-attached-to-environment) –
> >         that seems to rely on MPI_COMM_SELF callback (freeing
> >         comm-self triggers callback)
> >
> >
> >
> > That is a good point. At first glance, attaching things to 
> > MPI_COMM_WORLD or MPI_COMM_SELF would have a similar effect to 
> > attaching stuff to the environment.
> > I didn't think about this because I was reluctant to modify (in any 
> > way) either of these special communicators, in particular MPI_COMM_WORLD.
> > But MPI_COMM_SELF might still be a good candidate; others can point 
> > out if there is a catch.
> >
> > Thanks,
> > Alfredo
> > _
> > _
> >
> >
> 
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