# use MCE;

Discussion in 'Perl Misc' started by gamo, Oct 31, 2013.

1. ### gamoGuest

Hello

I usually do a lot of simulations and heuristics in a linear funcional
way. Now I want to send random candidates to the cores or process, get
the results for each one and when the acceptable result is reached,
rerun the calculus, print a report and exit.

I take a look on the modules Parallel::* (Simple, ForkManager and Loops)
but none is both easy and could do the things well. Then I see MCE, wich
sure could do that things, but is complex and the MCE::Examples provided
don't cover a simple simulation scenario.

Are there somebody wich could guide me in the parallelization of
something like

\$var = 1;
\$foo = 2;
\$bar = 3;

while (1) {

\$r = rand();

\$result = \$r * (\$var+\$foo+\$bar);

\$anothervar = sqrt(\$var+\$foo+\$bar);

last if (\$result < \$anothervar+0.001 && \$result > \$anothervar-0.001);

}

print "\$r -> \$result\n";

exit ;

gamo, Oct 31, 2013

2. ### Rainer WeikusatGuest

[...]
It is somewhat unclear what is supposed to be parallelized how here, eg,
are the \$(bar|foo|var) really compile-time constant and if they're not,
how often to they change? And what's the point of this algorithm,
anyway? From the above, it follows that

\$r == sqrt(\$var + \$foo + bar) / (\$var + \$foo + \$bar)

means

\$result == \$another_var

in general and that the solution for your specific case is

[rw@sable]~#perl -e 'print sqrt(6)/6, "\n";'
0.408248290463863

Rainer Weikusat, Nov 4, 2013

3. ### gamoGuest

El 04/11/13 13:37, Rainer Weikusat escribiÃ³:
It's only an example. Suppose I have common variables (\$var, \$foo, \$bar)
to be used in an algorithm. The algorithm takes these and a
random input (\$r), and knows when to stop its calculations (comparison
with \$anothervar). Then it has a result (\$result).

What I want to do is parallelize the algorithm (could be a sub), and
to share input vars is difficult. AFAIK the most independent the
algorithm is, the easyest parallelization could be done.

I tought in threads, too, but there are limitations: a random is not
thread-safe or the creation of each thread need to be by hand via
create, as is by hand the finish of a thread. Last but not least after
all I want to reach better performance, in speed or precision.

gamo, Nov 4, 2013
4. ### marioeroyGuest

Below, you will find the simulation performed in parallel using MCE.

use MCE::Loop;

## Callback functions.

my (\$r, \$result);

sub get_rand {
return if defined \$result;
return rand();
}

sub recv_result {
return if defined \$result;
(\$r, \$result) = @_;
return;
}

## Configure MCE and common variables.

MCE::Loop::init {
chunk_size => 1, max_workers => 8,
input_data => \&get_rand,
gather => \&recv_result
};

my \$var = 1;
my \$foo = 2;
my \$bar = 3;

## Compute in parallel.

mce_loop {
# my (\$mce, \$chunk_ref, \$chunk_id) = @_;
my \$r = \$_;

my \$result = \$r * (\$var+\$foo+\$bar);
my \$anothervar = sqrt(\$var+\$foo+\$bar);

if (\$result < \$anothervar+0.001 && \$result > \$anothervar-0.001) {
MCE->gather(\$r, \$result); MCE->abort();
}

return;
};

print "\$r -> \$result\n";

- mario

marioeroy, Feb 2, 2014
5. ### marioeroyGuest

marioeroy, Feb 2, 2014
6. ### MarioGuest

Mario, Feb 3, 2014
7. ### gamoGuest

El 03/02/14 15:51, Mario escribiÃ³:
Thank you very much for replying, Mario.
I'm very interested in paralellyzing scripts, and that's is only an
example to figure out how to do it. It's not trivial how to.
If you are interested, I could post more real small examples in which
I wish to do the job using all the cpu resources.

Thanks

gamo, Feb 3, 2014
8. ### MarioGuest

Mario, Feb 6, 2014