[boost] [Review][MPI] Boost.MPI Review

From: Dean Michael Berris (mikhailberis_at_[hidden])
Date: 2006-09-06 17:10:53

Hi Everyone,

I have been lurking a while already, and I'm doing my first review of
a Boost library being proposed for inclusion. I would like to say that
I'm pretty new at this review thing, and I'm trying to learn about the
way it's being done as fast as I can. I certainly hope this review
brings out a few points that may make sense, and I also hope the
library authors (Doug Gregor and Matthias Troyer) would take the time
to consider the points in this message. So here goes the review:

Explicitly State My View: YES, I think it should be accepted into
Boost. Details and suggestions below.

- What is your evaluation of the design?

The design is pretty straightforward, and easy to understand even for
the novice C++ developer -- which is a welcome characteristic IMO. I
certainly appreciate the relatively few headers, and "fat classes"
that group together the related methods and data -- citing the
Communicator and the Environment classes.

- What is your evaluation of the implementation?

Given the very well-thought out and straightforward design, I have
some reservations about the interface specifically with the
Communicator class. Having been reading up on type-safe interfaces,
the main issue I see is the relative ease in confusing the order of
the fields/types in communicator::send/receive/isend/ireceive
arguments:

template <typename T> void send(int, int, const T &) const ;

The above line doesn't say anything about what the first int is, and
what the second int is -- and it's fairly easy to confuse which one is
the rank and which one is the tag. A suggestion I would make is either
to utilize Boost.Parameter to come up with something like:

mpi::communicator c;
std::string str("Hello, World!");
c.send(tag=0, rank=1, value=str);
c.send(rank=1, tag=0, value=str);
c.send(value=str, rank=1, tag=0);

Or if that introduces too many issues regarding performance (I'm not
sure), then perhaps using some wrappers and overloads for type safety
will be useful to allow the following:

mpi::communicator c;
std::string str("Hello, World!");
c.send(mpi::tag(0), mpi::rank(1), mpi::value(str));
c.send(mpi::rank(1), mpi::tag(0), mpi::value(str));
c.send(mpi::value(str), mpi::tag(0), mpi::rank(1));

The two approaches above would IMO make the library more "idiot-proof"
or "newbie-friendly" and certainly (though more tideous to use)
considerably type-safe and verbose.

- What is your evaluation of the documentation?

The web documentation contains certain characters marked and displayed
as question marks not present in the PDF version. There are also a
handful of typographical errors, though nothing a quick copy-editing
would not be able to fix.

There is also a need to revise the introduction, and move the in-depth
details in a separate section. The Introduction section already talks
about a lot of the specifics, when a user reading the documentation
would be more concerned really just about what Boost.MPI is rather
than the details of how it implemented certain things.

I can elaborate in a separate email, which I think I should probably do.

- What is your evaluation of the potential usefulness of the library?

I think this library will be very useful indeed having been exposed to
the mess that is the C implementation of the MPI standard. I've
personally tried to tackle with issues like sending and receiving
strings and user created data structures (C structs) and the MPI
methods are not very helpful nor intuitive in their current form (even
MPI 2.0).

Being able to introduce an object oriented view of the parallel
computing application by encapsulating in objects the MPI interface
and adding terse yet expressive interfaces will definitely be helpful
in the field. In my experience with academic use of parallel computers
(though how very little exposure I have here in the Philippines of
that), the biggest barrier to entry is the programming interface. The
MPI API's require a lot of patience from even the most experienced C
or C++ programmers, and the Boost.MPI interface is a welcome
implementation on the change to making it make more sense. Since most
of the people I've talked to are in the academe, it would be easier to
1) teach MPI programming with Boost.MPI 2) use the MPI especially for
non-computer scientists (Physicists, Mathematicians, Engineers) that
might not have the same exposure to C or C++.

Since the Boost.MPI interface makes the programs considerably more
readable, it should allow for lowering the barrier to entry into
parallel and high-performance computing.

- Did you try to use the library?

No, since I don't have the required libraries and tools (Boost CVS,
LAM/MPI 7 for Windows) set up yet. However, I intend to use this
library in its current form most probably post-review regardless of
the review outcome, and even try to contribute in any way I can (docs,
patches, etc.)

- How much effort did you put into your evaluation?

I have read the documentation, and looked at the design primarily of
the library -- and focused on the interface provided. Since I have not
had the time nor means for testing the library at the moment, I cannot
comment on the implementation especially in terms of the effects in
runtime performance and the compile time characteristics. Because of
this, I have reserved my comments until the time I can scrutinize the
implementation and how it relates to the MPI implementation I shall
use.

- Are you knowledgable about the problem domain?

I have used the MPI C API (LAM/MPI Implementation) in more than one
instance in an academic setting (translation: school project on a
prallel genetic algorithm implementation for finding the optimal tour
in a 100 city travelling salesman problem, thesis on adaptive dynamic
allocation algorithm in heterogeneous non-dedicated computing
clusters). I would like to think I am knowledgable about the problem
domain with ample exposure to the MPI C API (though with MPI 2.0).

-- 
Dean Michael C. Berris
C++ Software Architect
Orange and Bronze Software Labs, Ltd. Co.
web: http://software.orangeandbronze.com/
email: dean_at_[hidden]
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phone: [phone]
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blogs: http://mikhailberis.blogspot.com http://3w-agility.blogspot.com
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