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object serialization

From: Mikael Djurfeldt
Subject: object serialization
Date: Sun, 06 Feb 2005 11:46:57 +0100

[Resending to list as well.]

On Sat, 5 Feb 2005 11:40:36 -0600 (CST), Mario Storti
<address@hidden> wrote:
> I´m writing a parallel Finite Element
> ( program and I´m making some
> experiments with extending it with Guile.

That's very exciting!  I've written a neuron simulator which is
parallelized with MPI and extended with Guile.  (It's not publicly
available right now.  It's GPL:ed alright, but not in a releasable
state and doesn't have enough docs.)

> The program runs in parallel using Message Passing with the MPI Library
> ( I have wrapped some basic MPI
> functions (MPI_Comm_rank,MPI_Comm_size,MPI_Recv and MPI_Wend), and it
> seems to work fine, but I ask you people if someone knows of a port of
> MPI to Guile.

I've never seen one.  I don't think it exists.  However, I would welcome one!

> When running in parallel I had to compile myself the Guile interpreter
> since I need that all processes read and interpret the script. This
> prevents me to using the interpreter in interactive form (when running
> in parallel) because MPI does not broadcast the standard input to the
> other processes. I think that this can be fixed by modifiying the REPL,
> i.e. when running in interactive mode, in parallel, the REPL in the
> master node should be in charge of broadcasting the standard input to
> the nodes. Any ideas?

Maybe you should have a look at how to implement custom port objects. 
There should be some documentation in the reference manual and
guile-readline is one example. The idea would then be that you
interact with a master process with a custom standard input port. At
every newline, it sends data to another kind of custom standard input
port on the slaves.

Once you have figured out how to make the ports, you can simply
redirect input with:

(set-current-input-port MY-PORT)

> Also, i´m not very happy with the way I do the MPI initialization. I
> had to write my own guile interpreter because MPI needs to have accesss
> to the argc, argv arguments of main(), so that MPI initialization is
> done _always_. I would like rather to have a Scheme `mpi-init' function
> called by the user.

My view on this situation is that since the installed Guile
interpreter currently can't run any custom code before parsing its
arguments and since MPI *has to* parse the arguments before that,
there's no other choice but to write your own interpreter like you've

> But, on the other hand I can´t do the finalization
> in the `inner_main()´ because I receive a lot of `net_recv' errors
> _before_ reaching the MPI_Finalize().

But this should be due to some synchronization problem in your
program.  Maybe everybody hasn't received all data before senders
begin to finalize?  Have you tried to but a call to MPI_Barrier right
before MPI_Finalize?

Best regards,
Mikael D.

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