[mpich-discuss] Advice on thread support

[Nicolas Rosner]

Hello all,

I'm considering a threads-based approach to solve a problem in my C++
MPI design.  I do know what threads are, and have written a few
programs that use multiple threads in languages like Java or Python,
but I don't have any experience with POSIX threads, or any other
flavor of a threads lib in C++, let alone mixing threads with MPI
code.  Furthermore, my idea would need different threads (well, at
least two of them) to be able to call MPI primitives independently,
thus requiring MPI_THREAD_MULTIPLE mode.

Since some of the documents I've been reading about this matter seem
to contradict each other (perhaps because some of them are older than
others, or because my interpretation of them was incorrect due to
ignorance of some details, or all of the above), I thought I'd ask you
a few questions:

- Does the current version of MPICH2 support threads in MULTIPLE mode?
 Is said support stable/reliable?

- What about MPICH2 1.0.7?  (The two clusters I'm currently using for
test and production purposes are still at that version, and their
maintenance is beyond my control; I guess I could install 1.0.8 in
user space, and use that instead, but it would be nice to know if that
will be necessary or 1.0.7 is recent enough.)

- What about MVAPICH?  (We intend to run experiments on a cluster with
an InfiniBand switch next month.)

- What about other MPI implementations?  Generally speaking, would you
say such support is reasonably widespread?

Not that I'm planning to move away from MPICH anytime soon -- I'm very
satisfied with it so far, and it's what most systems down here seem to
be using anyway.  But our original decision to use MPI was driven by
portability; in particular, we're still trying to gain access to some
newer, more powerful clusters, and would like our program to be able
to run on them with few or no modifications.

(Actually, small changes wouldn't be a major concern, since deployment
on a new cluster is by no means a frequent event. But it would be a
problem if we decided to add MPI_THREAD_MULTIPLE support as a strict
requirement, only to end up realizing, later on, that too many
potential clusters don't provide it at all.)

Thanks in advance for your opinion and any comments that might be of help.

Regards (and happy 2009!),

Nicolás Rosner
Universidad de Buenos Aires
Argentina