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Subject: Re: [OMPI users] Parallel I/O with MPI-1
From: Neil Storer (Neil.Storer_at_[hidden])
Date: 2008-07-23 08:28:53


Jeff,

In general NFS servers run a file-locking daemon that should enable
clients to lock files.

However, in Unix, there are two flavours of file locking, flock() from
BSD and lockf() from System V. It varies from system to system which of
these mechanisms work with NFS. In Solaris lockf() works with NFS, and
flock() is implemented via lockf(). On other systems, the results are
less consistent. For example, on some systems, lockf() is not
implemented at all, and flock() does not support NFS; while on other
systems, lockf() supports NFS but flock() does not.

Unless you have a parallel filesystem, such as GPFS, which is
well-defined and does support file-locking, I would suggest writing to
different files, or doing I/O via a single MPI task, or via MPI-IO.

Regards
       Neil

Jeff Squyres wrote:
> On Jul 23, 2008, at 6:35 AM, Gabriele Fatigati wrote:
>
>> >There is a whole chapter in the MPI standard about file I/O
>> operations. I'm quite confident you will find whatever you're looking
>> for there :)
>>
>> Hi George, i know this chapter :) But i'm using MPI-1, not MPI-2. I
>> would like to know methods for I/O with MPI-1.
>
> Open MPI builds ROMIO by default; there's no real distinction between
> MPI-1 features and MPI-2 features in the Open MPI code base.
>
> You could always effect your own parallel IO (e.g., use MPI sends and
> receives to coordinate parallel reads and writes), but why? It's
> already done in the MPI-IO implementation.
>
> FWIW: I do not believe that flock() is guaranteed to be safe across
> network filesystems such as NFS.
>

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