XSLoader(3p) Perl Programmers Reference Guide XSLoader(3p)
XSLoader - Dynamically load C libraries into Perl code
Version 0.06
package YourPackage;
use XSLoader;
XSLoader::load 'YourPackage', $YourPackage::VERSION;
This module defines a standard simplified interface to the
dynamic linking mechanisms available on many platforms. Its
primary purpose is to implement cheap automatic dynamic
loading of Perl modules.
For a more complicated interface, see DynaLoader. Many
(most) features of "DynaLoader" are not implemented in
"XSLoader", like for example the "dl_load_flags", not
honored by "XSLoader".
Migration from "DynaLoader"
A typical module using DynaLoader starts like this:
package YourPackage;
require DynaLoader;
our @ISA = qw( OnePackage OtherPackage DynaLoader );
our $VERSION = '0.01';
bootstrap YourPackage $VERSION;
Change this to
package YourPackage;
use XSLoader;
our @ISA = qw( OnePackage OtherPackage );
our $VERSION = '0.01';
XSLoader::load 'YourPackage', $VERSION;
In other words: replace "require DynaLoader" by "use
XSLoader", remove "DynaLoader" from @ISA, change "bootstrap"
by "XSLoader::load". Do not forget to quote the name of
your package on the "XSLoader::load" line, and add comma
(",") before the arguments ($VERSION above).
Of course, if @ISA contained only "DynaLoader", there is no
need to have the @ISA assignment at all; moreover, if
instead of "our" one uses the more backward-compatible
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use vars qw($VERSION @ISA);
one can remove this reference to @ISA together with the @ISA
assignment.
If no $VERSION was specified on the "bootstrap" line, the
last line becomes
XSLoader::load 'YourPackage';
Backward compatible boilerplate
If you want to have your cake and eat it too, you need a
more complicated boilerplate.
package YourPackage;
use vars qw($VERSION @ISA);
@ISA = qw( OnePackage OtherPackage );
$VERSION = '0.01';
eval {
require XSLoader;
XSLoader::load('YourPackage', $VERSION);
1;
} or do {
require DynaLoader;
push @ISA, 'DynaLoader';
bootstrap YourPackage $VERSION;
};
The parentheses about "XSLoader::load()" arguments are
needed since we replaced "use XSLoader" by "require", so the
compiler does not know that a function "XSLoader::load()" is
present.
This boilerplate uses the low-overhead "XSLoader" if
present; if used with an antic Perl which has no "XSLoader",
it falls back to using "DynaLoader".
Order of initialization: early load()
Skip this section if the XSUB functions are supposed to be
called from other modules only; read it only if you call
your XSUBs from the code in your module, or have a "BOOT:"
section in your XS file (see "The BOOT: Keyword" in perlxs).
What is described here is equally applicable to the
DynaLoader interface.
A sufficiently complicated module using XS would have both
Perl code (defined in YourPackage.pm) and XS code (defined
in YourPackage.xs). If this Perl code makes calls into this
XS code, and/or this XS code makes calls to the Perl code,
one should be careful with the order of initialization.
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The call to "XSLoader::load()" (or "bootstrap()") has three
side effects:
+ if $VERSION was specified, a sanity check is done to
ensure that the versions of the .pm and the (compiled)
.xs parts are compatible;
+ the XSUBs are made accessible from Perl;
+ if a "BOOT:" section was present in the .xs file, the
code there is called.
Consequently, if the code in the .pm file makes calls to
these XSUBs, it is convenient to have XSUBs installed before
the Perl code is defined; for example, this makes prototypes
for XSUBs visible to this Perl code. Alternatively, if the
"BOOT:" section makes calls to Perl functions (or uses Perl
variables) defined in the .pm file, they must be defined
prior to the call to "XSLoader::load()" (or "bootstrap()").
The first situation being much more frequent, it makes sense
to rewrite the boilerplate as
package YourPackage;
use XSLoader;
use vars qw($VERSION @ISA);
BEGIN {
@ISA = qw( OnePackage OtherPackage );
$VERSION = '0.01';
# Put Perl code used in the BOOT: section here
XSLoader::load 'YourPackage', $VERSION;
}
# Put Perl code making calls into XSUBs here
The most hairy case
If the interdependence of your "BOOT:" section and Perl code
is more complicated than this (e.g., the "BOOT:" section
makes calls to Perl functions which make calls to XSUBs with
prototypes), get rid of the "BOOT:" section altogether.
Replace it with a function "onBOOT()", and call it like
this:
package YourPackage;
use XSLoader;
use vars qw($VERSION @ISA);
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BEGIN {
@ISA = qw( OnePackage OtherPackage );
$VERSION = '0.01';
XSLoader::load 'YourPackage', $VERSION;
}
# Put Perl code used in onBOOT() function here; calls to XSUBs are
# prototype-checked.
onBOOT;
# Put Perl initialization code assuming that XS is initialized here
Can't find '%s' symbol in %s
(F) The bootstrap symbol could not be found in the
extension module.
Can't load '%s' for module %s: %s
(F) The loading or initialisation of the extension
module failed. The detailed error follows.
Undefined symbols present after loading %s: %s
(W) As the message says, some symbols stay undefined
although the extension module was correctly loaded and
initialised. The list of undefined symbols follows.
XSLoader::load('Your::Module', $Your::Module::VERSION)
(F) You tried to invoke "load()" without any argument.
You must supply a module name, and optionally its ver-
sion.
To reduce the overhead as much as possible, only one possi-
ble location is checked to find the extension DLL (this
location is where "make install" would put the DLL). If not
found, the search for the DLL is transparently delegated to
"DynaLoader", which looks for the DLL along the @INC list.
In particular, this is applicable to the structure of @INC
used for testing not-yet-installed extensions. This means
that running uninstalled extensions may have much more over-
head than running the same extensions after "make install".
Please report any bugs or feature requests via the perl-
bug(1) utility.
DynaLoader
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Ilya Zakharevich originally extracted "XSLoader" from
"DynaLoader".
CPAN version is currently maintained by Sebastien Aperghis-
Tramoni <sebastien@aperghis.net>
Previous maintainer was Michael G Schwern
<schwern@pobox.com>
This program is free software; you can redistribute it
and/or modify it under the same terms as Perl itself.
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