NAME

OpenMP::Simple - Wrapper around Alien::OpenMP that provides helpful C MACROs and runtime functions

SYNOPSIS

use strict;
use warnings;

use OpenMP::Simple;
use OpenMP::Environment;

use Inline (
    C    => 'DATA',
    with => qw/OpenMP::Simple/,
);

my $env = OpenMP::Environment->new;

for my $want_num_threads ( 1 .. 8 ) {
    $env->omp_num_threads($want_num_threads);

    $env->assert_omp_environment; # (optional) validates %ENV

    # call parallelized C function
    my $got_num_threads = _check_num_threads();

    printf "%0d threads spawned in ".
            "the OpenMP runtime, expecting %0d\n",
              $got_num_threads, $want_num_threads;
}

__DATA__
__C__

int _check_num_threads() {
  PerlOMP_GETENV_BASIC
  int ret = 0;
  #pragma omp parallel
  {
    #pragma omp single
    ret = omp_get_num_threads();
  }
  return ret;
}

See the ./t directory for many more examples. It should be obvious, but Test::More is not required; it's just for show and convenience here.

DESCRIPTION

This module is a wrapper that provides a custom ".h" file, which is injected into Alien::OpenMP via Inline:C's AUTO_INCLUDE hook. This header file constains C MACROs for reading OpenMP relavent environmental variables via %ENV (set preferably using OpenMP::Environment) and by calling the standard OpenMP runtime functions to set them (e.g., OMP_NUM_THREADS / set_omp_num_threads).

OpenMP::Simple is meant to work directly with OpenMP::Environment in a way that provides the same runtime control experience that OpenMP's environmental variables provides.

The most common use case is updating the number of OpenMP threads that are defined via OMP_NUM_THREADS.

Experimental Parts

There is some attempt at helping to deal with getting data structures that are very common in the computational domains into and out of these Inline::C'd routines that are parallized via OpenMP. We are currently investigating what is actually needed in this regard. It is possible that a lot of this is unnecessariy and it is likely that a large number of read-only scenerios involving Perl internal data structures and OpenMP threads are actually thread-safe. This does not address the potential knowledge gap for those who are more experienced with C and OpenMP than they are with the Perl C API for accessing internal Perl data structures inside of C code.

PROVIDED MACROS

Updating Runtime with Environmental Variables

All MACROS have at least 1 test in the suite. Please look at these in the Github repository to get an idea of how to use OpenMP::Simple's macros with OpenMP::Environment.

PerlOMP_GETENV_BASIC

Equivalent of using,

PerlOMP_UPDATE_WITH_ENV__NUM_THREADS
PerlOMP_UPDATE_WITH_ENV__NUM_SCHEDULE

The purpose of this bundled approach is to make it easier to get started quickly. This list may be updated between versions. This is the recommended one to use when starting with this module. See the SYNOPSIS example.

PerlOMP_GETENV_ALL

Equivalent of using,

PerlOMP_UPDATE_WITH_ENV__DEFAULT_DEVICE
PerlOMP_UPDATE_WITH_ENV__TEAMS_THREAD_LIMIT
PerlOMP_UPDATE_WITH_ENV__NUM_TEAMS
PerlOMP_UPDATE_WITH_ENV__MAX_ACTIVE_LEVELS
PerlOMP_UPDATE_WITH_ENV__NUM_THREADS
PerlOMP_UPDATE_WITH_ENV__DYNAMIC
PerlOMP_UPDATE_WITH_ENV__NESTED
PerlOMP_UPDATE_WITH_ENV__SCHEDULE

PerlOMP_UPDATE_WITH_ENV__NUM_THREADS

Updates the OpenMP runtime with the value of the environmental variable, $ENV{OMP_NUM_THREADS}, which is managed via OpenMP::Environment->omp_num_threads[int numThreads]);.

PerlOMP_UPDATE_WITH_ENV__DEFAULT_DEVICE

Updates the OpenMP runtime with the value of the environmental variable, $ENV{OMP_DEFAULT_DEVICE}, which is managed via OpenMP::Environment->omp_default_device([int deviceNo]);.

PerlOMP_UPDATE_WITH_ENV__MAX_ACTIVE_LEVELS

Updates the OpenMP runtime with the value of the environmental variable, $ENV{OMP_MAX_ACTIVE_LEVELS}, which is managed via OpenMP::Environment->omp_max_active_levels([int maxLevel]);.

PerlOMP_UPDATE_WITH_ENV__DYNAMIC

Updates the OpenMP runtime with the value of the environmental variable, $ENV{OMP_DYNAMIC}, which is managed via OpenMP::Environment->omp_dynamic(['true'|'false']);.

PerlOMP_UPDATE_WITH_ENV__NESTED

Updates the OpenMP runtime with the value of the environmental variable, $ENV{OMP_NESTED}, which is managed via OpenMP::Environment->omp_nested(['true'|'false']);.

PerlOMP_UPDATE_WITH_ENV__SCHEDULE

Updates the OpenMP runtime with the value of the environmental variable, $ENV{OMP_SCHEDULE}, which is managed via OpenMP::Environment->omp_schedule(...);.

Note: The schedule syntax is of the form schedule[;chunkSize].

PerlOMP_UPDATE_WITH_ENV__TEAMS_THREAD_LIMIT

Updates the OpenMP runtime with the value of the environmental variable, $ENV{OMP_TEAMS_THREAD_LIMIT}, which is managed via OpenMP::Environment->omp_([int limit]);.

Note: OMP_TEAMS_THREAD_LIMIT is not supported until GCC 12.3.0

PerlOMP_UPDATE_WITH_ENV__NUM_TEAMS

Updates the OpenMP runtime with the value of the environmental variable, $ENV{OMP_NUM_TEAMS}, which is managed via OpenMP::Environment->omp_([int num]);.

Note: OMP_NUM_TEAMS is not supported until GCC 12.3.0

PerlOMP_RET_ARRAY_REF_ret

(may not be needed) - creates a new AV* and sets it mortal (doesn't survive outside of the current scope). Used when wanting to return an array reference that's been populated via av_push.

PROVIDED PERL TO C CONVERSION FUNCTIONS

Note: Work is currently focused on finding the true limits of the Perl C API. It is likely that in a lot of cases, elements in Perl Arrays (AV) and Perl Hashes (HV) maybe accessed safely without first transferring the entire data structures into its pure C equivalent.

PerlOMP_2D_AoA_TO_2D_FLOAT_ARRAY(AoA, num_nodes, dims, nodes)

Used to extract the contents of a 2D rectangular Perl array reference that has been used to represent a 2D matrix.

float nodes[num_nodes][dims];
PerlOMP_2D_AoA_TO_2D_FLOAT_ARRAY(AoA, num_nodes, dims, nodes);

SEE ALSO

This is a module that aims at making it easier to bootstrap Perl+OpenMP programs. It is designed to work together with OpenMP::Environment.

This module heavily favors the GOMP implementation of the OpenMP specification within gcc. In fact, it has not been tested with any other implementations because Alien::OpenMP doesn't support anything other than GCC at the time of this writing due to lack of anyone asking for it.

https://gcc.gnu.org/onlinedocs/libgomp/index.html

Please also see the rperl project for a glimpse into the potential future of Perl+OpenMP, particularly in regards to thread-safe data structures.

https://www.rperl.org

AUTHOR

Brett Estrade <oodler@cpan.org>

LICENSE & COPYRIGHT

Same as Perl.