/ 
Alien-Base-0.009_04
River stage zero No dependents
/ Alien::Base::Authoring

NAME

Alien::Base::Authoring - Authoring an Alien:: module

DESCRIPTION

Congratulations! You have made the decision to help the Perl community by providing a C library via CPAN. The Alien namespace has been instrumental in providing C libraries for many years, but authoring those modules has been a commitment that most authors weren't willing to take on. Alien::Base tries to ease that pain by providing most of the needed functionality; usually authors should only need a little boilerplate and configuration!

STATUS

Alien::Base is under active development and is currently beta release. The author hopes that the API has stabilized, but will not promise that it has. Please resist the temptation to use it for production code until the warning is removed. Of course you are welcomed, and in fact encouraged, to test it with for your favorite library; if you do, you are more than welcome to share your experience with me.

ECOSYSTEM

The Alien::Base ecosystem is made up of several elements. Some of these elements are the base classes in the distribution itself. Of course, no ecosystem is complete without inhabitants, therefore, it is also important to consider the users of these base classes. This documentation will assume that you are writing Alien::MyLibrary which provides libmylibrary.so. Further it will assume that you or someone else is going to use this module/library to write Some::Module::MyLibrary. Finally an end user might use that module to write myscript.pl.

Alien::Base::ModuleBuild

Alien::Base::ModuleBuild provides a base class, utility methods and configuration handling for the build/install phase of the library. It is itself a subclass of Module::Build, which is what supports the building and installing of the surrouning Alien:: module. Alien::MyLibrary's Build.PL file will use Alien::Base::ModuleBuild to create its builder object.

# file: Alien-MyLibrary/Build.PL
use Alien::Base::ModuleBuild;
my $builder = Alien::Base::ModuleBuild->new(...);
$builder->create_build_script;

This is just like you would do for Module::Build, except that there will be a few additional configuration parameters (see Alien::Base::ModuleBuild::API).

Alien::Base::ModuleBuild adds the additional build actions alien_code and alien_install. These actions need never be run directly, the usual build action (usually seen as ./Build) and install (./Build install) will call them for you. The alien_code action is responsible for finding, downloading, extracting and building the external libary (the commands specified in builder parameter alien_build_commands). The alien_install action is responsible for installing the library into its final destination.

The ./Build test command will invoke any library tests specified in alien_test_commands, though none are defined by default. Finally ./Build install will invoke whatever alien_install_commands were specified.

Alien::Base

Alien::Base is the base class of Alien::MyLibrary. In this context, Alien::Base has two distinct uses. First it is used by Alien::MyLibrary to provide the build information/flags for building Some::Module::MyLibrary. Secondly it is used (again through Alien::MyLibrary) to provide run-time access to libmylibrary.so to Some::Module::MyLibrary.

Alien::Base for Building

Alien::MyLibrary is called by Some::Library::MyLibrary's build script, either Build.PL or Makefile.PL. Most of the functionality can be utilized through class method calls, though creating an object can save a few keystrokes.

# file: Some-Module-MyLibrary/Build.PL
use Module::Build;
use Alien::MyLibrary;

my $alien = Alien::MyLibrary->new;
my $builder = Module::Build->new(
  ...
  extra_compiler_flags => $alien->cflags(),
  extra_linker_flags   => $alien->libs(),
);
$builder->create_build_script;

Additional information can be gotten from the config method.

Alien::Base for Run-Time Provision

Alien::MyLibrary must be a subclass of Alien::Base. This provides the import method, which does the run-time provisioning so that when the XS file is loaded, it can find libmylibrary.so. The import method does this by pre-loading the library via DynaLoader::dl_load_file which is a platform-independent wrapper for dlopen or your system's equivalent. It no longer appends to $ENV{LD_RUN_PATH}.

# file: Alien-MyLibrary/lib/Alien/MyLibrary.pm
package Alien::MyLibrary;

use parent 'Alien::Base';

1;

Finally, Alien::MyLibrary must also be called by Some::Library::MyLibrary before DynaLoader::bootstrap or XSLoader::load. The use directive is recommended, however if you must use require then be sure to call the import method too. Without this import call, the loader doesn't know where to find libmylibrary.so.

# file: Some-Module-MyLibrary/lib/Some/Module/MyLibrary.pm
package Some::Module::MyLibrary;

use Alien::MyLibrary;
our $VERSION = '0.54';

require XSLoader;
XSLoader::load('Some::Module::MyLibrary', $VERSION);

# your code

EXAMPLES

The example code that was housed in this distribution during alpha phase has been moved to two different CPAN distributions. Those are:

  • Acme::Alien::DontPanic -- An example Alien:: module which provides libdontpanic.so. It provides the C function answer which is simply:

    int answer () { return 42 }

  • Acme::Ford::Prefect -- An XS module which provides the Perl-level access to answer. It relies on libdontpanic.so and uses Acme::Alien::DontPanic to locate/load it.

Additionally, there exists in-production Alien:: distributions that serve as de-facto tests of Alien::Base's networking components:

  • Alien::LibYAML -- Builds and installs libyaml, acquiring the library archive from its hosted location via Alien::Base::Repository::HTTP.

Also, the author intends to convert Alien::GSL to use this system as soon as it is production ready, so that Alien:: authors can see another "Code in the Wild" example. Until then, a pre-release version of this module is provided in the examples directory as well.

AUTHOR

Joel Berger <joel.a.berger@gmail.com>

SEE ALSO

SOURCE REPOSITORY

http://github.com/Perl5-Alien/Alien-Base

AUTHOR

Original author: Joel Berger, <joel.a.berger@gmail.com>

Current maintainer: Graham Ollis <plicease@cpan.org> and the Alien::Base team

COPYRIGHT AND LICENSE

Copyright (C) 2012-2015 by Joel Berger

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.