NAME

Alien::OpenMP - Encapsulate system info for OpenMP

SYNOPSIS

    use Alien::OpenMP;
    say Alien::OpenMP->cflags;       # e.g. '-fopenmp' if gcc
    say Alien::OpenMP->lddlflags;    # e.g. '-fopenmp' if gcc
    say Alien::OpenMP->auto_include; # e.g. '#include <omp.h>' if gcc

DESCRIPTION

This module encapsulates the knowledge required to compile OpenMP programs $Config{ccname}. C, Fortran, and C++ programs annotated with declarative OpenMP pragmas will still compile if the compiler (and linker if this is a separate process) is not passed the appropriate flag to enable OpenMP support. This is because all pragmas are hidden behind full line comments (with the addition of OpenMP specific sentinels, as they are called).

All compilers require OpenMP to be explicitly activated during compilation; for example, GCC's implementation, GOMP, is invoked by the -fopenmp flag.

Most major compilers support OpenMP, including: GCC, Intel, IBM, Portland Group, NAG, and those compilers created using LLVM. GCC's OpenMP implementation, GOMP, is available in all modern versions. Unfortunately, while OpenMP is a well supported standard; compilers are not required to use the same commandline switch to activate support. All compilers that support OpenMP use slightly different ways of invoking it.

Compilers Supported by this module

At this time, the following compilers are supported:

gcc

-fopenmp enables OpenMP support in via compiler and linker:

    gcc -fopenmp ./my-openmp.c -o my-openmp.x

clang EXPERIMENTAL

-fopenmp enables OpenMP support via compiler and linker in recent versions of clang. MacOS shipped versions are missing the library which needs installing either with Homebrew or Macports.

Note On Compiler Support

If used for an unsupported compiler, ExtUtils::MakeMaker::os_unsupported is invoked, which results an exception propagating from this method being raised with the value of qq{OS unsupported\n} (note the new line).

This module assumes that the compiler in question is the same one used to build perl. Since the vast majority of perls are building using gcc, initial support is targeting it. However, like perl, many other compilers may be used.

Adding support for a new compiler should be straightforward; please section on contributing, below.

Contributing

The biggest need is to support additional compilers. OpenMP is a well established standard across compilers, but there is no guarantee that all compilers will use the same flags, library names, or header files. It should also be easy to contribute a patch to add this information, which is effectively its purpose. At the very least, please create an issue at the official issue tracker to request this support, and be sure to include the relevant information. Chances are the maintainers of this module do not have access to an unsupported compiler.

METHODS

cflags

Returns flag used by a supported compiler to enable OpenMP. If not support, an empty string is provided since by definition all OpenMP programs must compile because OpenMP pragmas are annotations hidden behind source code comments.

Example, GCC uses, -fopenmp.

lddlflags

Returns the flag used by the linker to enable OpenMP. This is usually the same as what is returned by cflags.

Example, GCC uses, -fopenmp, for this as well.

Inline

Used in support of Inline::C's with method (inherited from Inline). This method is not called directly, but used when compiling OpenMP programs with Inline::C:

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

The nice, compact form above replaces this mess:

    use Alien::OpenMP; use Inline (
        C             => 'DATA',
        ccflagsex     => Alien::OpenMP->cflags(),
        lddlflags     => join( q{ }, $Config::Config{lddlflags}, Alien::OpenMP::lddlflags() ),
        auto_include => Alien::OpenMP->auto_include(),
    );

It also means that the standard include for OpenMP is not required in the C code, i.e., #include <omp.h>.

AUTHOR

OODLER 577 <oodler@cpan.org>

COPYRIGHT AND LICENSE

Copyright (C) 2021 by oodler577

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.30.0 or, at your option, any later version of Perl 5 you may have available.

SEE ALSO

PDL, OpenMP::Environment, https://gcc.gnu.org/onlinedocs/libgomp/index.html.