[mpich-discuss] Specifying a timeout for MPI_Comm_Accept

[Balaji, Pavan]

Thanks, Matthieu.

  — Pavan

On Sep 8, 2014, at 3:17 AM, Matthieu Dorier <matthieu.dorier at irisa.fr> wrote:

> Hi Pavan,
> 
> With all the work on in situ analysis/visualization, non-blocking versions of MPI_Comm_accept/connect could become very useful in the future to easily couple simulations and visualization codes.
> 
> Here is an example: the VisIt software can use in situ, but right now the connection between VisIt and the simulation is done through a normal socket. The simulation will periodically call VisItDetectInput to check (in a non-blocking manner) if VisIt connected to the simulation.
> 
> I recently had to use VisIt with a master-worker type simulation, that is, the master has an MPI_Recv(MPI_ANY_SOURCE...) to wait for workers to finish pieces of work. When using VisIt, this simple MPI_Recv becomes a non-blocking receive an active loop alternating between an MPI_Testany and VisItDetectInput. If VisIt could leverage non-blocking accept/connect, this active loop could be replaced with an MPI_Waitany on a set of MPI_Requests, one of them being VisIt connecting (the result of an MPI_Comm_iaccept), the other being workers finishing some work.
> 
> I'm not a VisIt developer, though. This is just a thought.
> 
> Matthieu Dorier 
> PhD student at ENS Rennes 
> http://people.irisa.fr/Matthieu.Dorier 
> ----- Mail original -----
>> De: "Pavan Balaji" <balaji at anl.gov>
>> À: discuss at mpich.org
>> Envoyé: Dimanche 7 Septembre 2014 00:53:58
>> Objet: Re: [mpich-discuss] Specifying a timeout for MPI_Comm_Accept
>> 
>> Hirak,
>> 
>> The function definitions for MPI_Comm_accept, etc., are a part of the MPI
>> standard.  We cannot change them in MPICH without changing them in the MPI
>> standard first.  Changes to the MPI standard go through the MPI Forum, and
>> through a formal proposal and voting process before they get in.
>> 
>> FWIW, both a timeout model and a nonblocking connect/accept have been
>> proposed in the past, but they were both voted down.  The nonblocking
>> connect/accept proposal was originally done by Josh Hursey
>> (http://www.cs.uwlax.edu/~jjhursey/), but I’m planning to revive the ticket
>> but more broadly asking for nonblocking variants for many other operations
>> as well.  It’s unclear if/when this will get in, but we can try.
>> 
>> The timeout proposal was put together by Jeff Squyres @ Cisco and Fab Tillier
>> @ Microsoft (they are both on this list).  I personally thought it was a
>> very elegant proposal, but it was voted down because there was no use case
>> for it at the time, particularly given that there was no standardized fault
>> model in MPI.  Once the Fault Tolerance working group gets its proposal in,
>> there might be room to revisit this.  But you’ll need to talk to the above
>> mentioned guys to see if they are planning to revive it.
>> 
>> Hope that helps.
>> 
>>  — Pavan
>> 
>> On Sep 6, 2014, at 12:35 PM, Roy, Hirak <Hirak_Roy at mentor.com> wrote:
>> 
>>> Hi,
>>> 
>>> The thread at the end of my email, shows that there is no way we can
>>> specify a timeout in MPI_Comm_accept/connect.
>>> Since the thread is pretty old (2007), I would like to know if there is any
>>> development related to this or not?
>>> 
>>> If we still can not specify a timeout, is there any provision of
>>> non-blocking accept/connect ?
>>> 
>>> Thanks,
>>> Hirak
>>> 
>>> 
>>> https://lists.mcs.anl.gov/mailman/htdig/mpich-discuss/2007-April/002159.html
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>> 
>> --
>> Pavan Balaji  ✉️
>> http://www.mcs.anl.gov/~balaji
>> 
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--
Pavan Balaji  ✉️
http://www.mcs.anl.gov/~balaji