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https://github.com/perlalien/alien-role-dino
Experimental support for dynamic share Alien install
https://github.com/perlalien/alien-role-dino
alien dynamic-library perl
Last synced: 15 days ago
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Experimental support for dynamic share Alien install
- Host: GitHub
- URL: https://github.com/perlalien/alien-role-dino
- Owner: PerlAlien
- Created: 2017-07-24T17:18:24.000Z (over 7 years ago)
- Default Branch: main
- Last Pushed: 2022-08-30T07:11:51.000Z (over 2 years ago)
- Last Synced: 2024-11-21T16:37:29.541Z (3 months ago)
- Topics: alien, dynamic-library, perl
- Language: Shell
- Homepage:
- Size: 410 KB
- Stars: 0
- Watchers: 2
- Forks: 1
- Open Issues: 2
-
Metadata Files:
- Readme: README.md
- Changelog: Changes
Awesome Lists containing this project
README
# Alien::Role::Dino  
Experimental support for dynamic share Alien install
# SYNOPSIS
In your [alienfile](https://metacpan.org/pod/alienfile):
```perl
use alienfile;
share {
...
plugin 'Gather::Dino';
}
```
Apply [Alien::Role::Dino](https://metacpan.org/pod/Alien::Role::Dino) to your [Alien::Base](https://metacpan.org/pod/Alien::Base) subclass:
```perl
package Alien::libfoo;
use base qw( Alien::Base );
use Role::Tiny::With qw( with );
with 'Alien::Role::Dino';
1;
```
And finally from the .pm side of your XS module:
```perl
package Foo::XS;
use Alien::libfoo;
our $VERSION = '1.00';
# Note caveat: your Alien is now a run-time
# dependency of your XS module.
Alien::libfoo->xs_load(__PACKAGE__, $VERSION);
1;
```
# DESCRIPTION
Every now and then someone will ask me why thus and such [Alien](https://metacpan.org/pod/Alien) thing
doesn't work with a dynamic library error. My usual response is can you
make it work with static libraries? The reason for this is that
**building** dynamic libraries for an [Alien](https://metacpan.org/pod/Alien) **share** install introduce
a number of challenges, and honestly I don't see the point of using
them, if you can avoid it. So far I haven't actually seen a situation
where it couldn't be avoided. Just to be clear: dynamic libraries are
fine for Alien, and in fact desirable when you are using the system
provided libraries. You get the patches and security fixes supplied by
your operating system.
Okay, so why not build a dynamic library for a **share** install?
For this discussion, say you have an alienized library `Alien::libfoo`
and an XS module that uses it called `Foo::XS` (as illustrated in the
synopsis above).
- Your Alien becomes a run-time dependency.
When you link your `Foo::XS` module with a static library from
`Alien::libfoo` it gets added into the DLL or `.so` file that the Perl
toolchain produces. That means when you later use it, it doesn't need
anything else. When you try to do the same thing with a dynamic
library, you need that dynamic library, which is stored in a share
directory of `Alien::libfoo`.
For people who install out of CPAN this is probably not a big deal, but
for operating system vendors (the people who integrate Perl modules into
their operating system), it is a hassle because now you need this big
build tool [Alien::Build](https://metacpan.org/pod/Alien::Build) and the alien `Alien::libfoo` with extra
dependencies during runtime. Normally you wouldn't need those packages
installed for end-user use.
- Upgrades can and will break your XS module.
Again, when `Alien::libfoo` builds a static library and it gets linked
into a DLL or `.so` for `Foo::XS`, it doesn't need the original
library anymore. If you are using a dynamic library and you do the same
thing it maybe works today, but say tomorrow you upgrade
`Alien::libfoo` and it replaces the DLL or `.so` file with an
incompatible API or ABI? Now your `Foo::XS` module has stopped
working!
- Dynamic libraries are not portable
Dynamic libraries are widely supported on most modern operating systems,
but each system provides a different interface. For example, Linux,
Windows and OS X all have an environment variable that allows you to
alter the search path for finding dynamic libraries, but all three have
different extensions for dynamic libraries (OS X even has two!), the
environment variables are called something different, and WHEN you can
change them is different.
The Perl core has code for loading dynamic libraries as part of its XS
system on all platforms where you can build XS extensions dynamically.
Unfortunately that code isn't quite reusable for use by Alien. Alien
developers have limited time and access to many platforms, which means
that many platforms will probably never get Alien support.
Static libraries on the other hand pretty much work the same on all
platforms. Even on Windows which likes to be different, static
libraries are essentially the same as on Unix.
So all that said, why have I written this module, which provides support
for dynamic libraries? Well, maybe I am wrong, maybe it isn't that
hard. Also, maybe you don't have a choice, maybe you have found a
library that can ONLY be built using a dynamic library.
What about you? Should you use this module? It has the worked
**Experimental** in the description. The experimental aspect of this
module should not worry you, because in the situation that your Alien
finds the library from the system, nothing is different from the core
[Alien::Build](https://metacpan.org/pod/Alien::Build). The only place it is different is if you have to do a
share install, and hopefully you are only using it because you really
can't build a static library. Thus you haven't really lost anything in
stability, and at worst your Alien may work in places where it wouldn't
otherwise.
So in summary, the experimental aspect shouldn't worry you, the caveats
above should!
# HOW
How does it work? Use the bundled [alienfile](https://metacpan.org/pod/alienfile) plugin
[Alien::Build::Plugin::Gather::Dino](https://metacpan.org/pod/Alien::Build::Plugin::Gather::Dino). That will find any dynamic
library paths in your share directory in case they are needed at
runtime. Then apply this role to you [Alien::Base](https://metacpan.org/pod/Alien::Base) subclass using
[Role::Tiny::With](https://metacpan.org/pod/Role::Tiny::With). Instead of using [XSLoader](https://metacpan.org/pod/XSLoader) or [DynaLoader](https://metacpan.org/pod/DynaLoader)
to load your XS module, use the `xs_load` from your [Alien](https://metacpan.org/pod/Alien).
Hopefully the synopsis above makes it clear.
# ETYMOLOGY
This module is named **Dino** being short for Dinosaur. I really like
Dinosaurs (also friendly crocodiles and [platypuses](https://metacpan.org/pod/FFI::Platypus) in
case you hadn't noticed). "Dino" also has a similar sound to "Dyna"
which is frequently used as a short name or prefix meaning "dynamic". I
didn't want to call it "Dyna" or "Dynamic" since it is only building a
dynamic library for share installs. I didn't want to call it DynaShare
because that was getting a bit wordy. So Dino.
# METHODS
## rpath
```perl
my @dirs = $alien->rpath;
```
Returns the list of directories that have non-system dynamic libraries
in them. On some systems this is needed at compile time, on others
it is needed at run time.
## xs\_load
```
$alien->xs_load($package, $version);
$alien->xs_load($package, $version, @other_dino_aliens);
```
# CAVEATS
Lots. In summary:
- Your Alien is a run-time dependency and you will annoy system integrators
- Your XS can be broken by upgrades to your Alien
- Your platform may not be supported
Also, this module should start with the caveat section and then go from
there. Most modules I write are not like that.
These platforms seem to work: Linux, OS X, Windows, Cygwin, FreeBSD,
NetBSD, OpenBSD, Debian kFreeBSD.
Currently has [Alien::Autotools](https://metacpan.org/pod/Alien::Autotools) as a prerequisite. I hope to remove that prereq
asap.
# SEE ALSO
- [alienfile](https://metacpan.org/pod/alienfile)
- [Alien::Base](https://metacpan.org/pod/Alien::Base)
- [Alien::Build](https://metacpan.org/pod/Alien::Build)
- [Alien::Build::Plugin::Gather::Dino](https://metacpan.org/pod/Alien::Build::Plugin::Gather::Dino)
# AUTHOR
Graham Ollis
# COPYRIGHT AND LICENSE
This software is copyright (c) 2017-2022 by Graham Ollis.
This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.