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Subject: Re: [OMPI users] OpenMPI runtime-specific environment variable?
From: Reuti (reuti_at_[hidden])
Date: 2008-10-21 18:40:17

Am 22.10.2008 um 00:08 schrieb Adams, Brian M:

>> -----Original Message-----
>> From: users-bounces_at_[hidden]
>> [mailto:users-bounces_at_[hidden]] On Behalf Of Reuti
>> Sent: Tuesday, October 21, 2008 11:36 AM
>> To: Open MPI Users
>> Subject: Re: [OMPI users] OpenMPI runtime-specific
>> environment variable?
>> Hi,
>> Am 21.10.2008 um 18:52 schrieb Ralph Castain:
>>> On Oct 21, 2008, at 10:37 AM, Adams, Brian M wrote:
>>>> Doug is right that we could use an additional command line flag to
>>>> indicate MPI runs, but at this point, we're trying to hide
>> that from
>>>> the user, such that all they have to do is run the binary vs.
>>>> orterun/mpirun the binary and we detect whether it's a serial or
>>>> parallel run.
>> And when you have this information you decide for your user,
>> whether to use mpirun (and the correct version to use) or
>> just the plain binary?
> I might have created some confusion here too. The goal is to build
> an MPI-enabled binary 'foo' which a user may invoke as
> (1) ./foo
> -OR-
> (2) mpirun -np 4 ./foo

Okay, now I see. Why not just call MPI_Comm_size(MPI_COMM_WORLD,
&nprocs) When nprocs is 1, it's a serial run. It can also be executed
when not running within mpirun AFAICS.

-- Reuti

> The binary foo then determines at run-time whether it is to run in
> (1) serial, where MPI_Init will never be called; or (2) parallel,
> calling MPI_Init and so on. This is a historical behavior which we
> need to preserve, at least for our present software release.
>> You are making something like "strings the_binary" and grep
>> for indications of the compilation type? For the standard
>> Open MPI with shared libraries a "ldd the_binary" might
>> reveal some information.
> Hadn't thought to do that actually, since it addresses a slightly
> different problem than I propose above. Thanks for the
> suggestion. This is another possibility if instead of doing this
> detection directly in our binary, we decide to change to a wrapper
> script approach.
> In any case, I appreciate all the discussion -- I believe I have a
> reasonable path forward using a combination of pre-processor
> defines that the OMPI wrappers and headers make with the runtime
> environment variables Ralph suggested (I'll just check for both the
> <1.3 and >= 1.3 environment cases).
> Brian
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