XSLoader(3perl) Perl Programmers Reference Guide XSLoader(3perl)
NAME
XSLoader - Dynamically load C libraries into Perl code
VERSION
Version 0.32
SYNOPSIS
package YourPackage;
require XSLoader;
XSLoader::load(__PACKAGE__, $VERSION);
DESCRIPTION
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 $VERSION = '0.01';
__PACKAGE__->bootstrap($VERSION);
Change this to
package YourPackage;
use XSLoader;
our @ISA = qw( OnePackage OtherPackage );
our $VERSION = '0.01';
XSLoader::load(__PACKAGE__, $VERSION);
In other words: replace "require DynaLoader" by "use XSLoader", remove
"DynaLoader" from @ISA, change "bootstrap" by "XSLoader::load". Do not
forget to quote the name of your package on the "XSLoader::load" line,
and add comma (",") before the arguments ($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
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(__PACKAGE__);
in which case it can be further simplified to
XSLoader::load();
as "load" will use "caller" to determine the package.
Backward compatible boilerplate
If you want to have your cake and eat it too, you need a more
complicated boilerplate.
package YourPackage;
our @ISA = qw( OnePackage OtherPackage );
our $VERSION = '0.01';
eval {
require XSLoader;
XSLoader::load(__PACKAGE__, $VERSION);
1;
} or do {
require DynaLoader;
push @ISA, 'DynaLoader';
__PACKAGE__->bootstrap($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 antique 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.
The call to XSLoader::load() (or bootstrap()) calls the module's
bootstrap code. For modules build by xsubpp (nearly all modules) this
has three side effects:
• A sanity check is done to ensure that the versions of the .pm and
the (compiled) .xs parts are compatible. If $VERSION was specified,
this is used for the check. If not specified, it defaults to
"$XS_VERSION // $VERSION" (in the module's namespace)
• the XSUBs are made accessible from Perl
• if a "BOOT:" section was present in the .xs file, the code there is
called.
Consequently, if the code in the .pm file makes calls to these XSUBs, it
is convenient to have XSUBs installed before the Perl code is defined;
for example, this makes prototypes for XSUBs visible to this Perl code.
Alternatively, if the "BOOT:" section makes calls to Perl functions (or
uses Perl variables) defined in the .pm file, they must be defined prior
to the call to XSLoader::load() (or bootstrap()).
The first situation being much more frequent, it makes sense to rewrite
the boilerplate as
package YourPackage;
use XSLoader;
our ($VERSION, @ISA);
BEGIN {
@ISA = qw( OnePackage OtherPackage );
$VERSION = '0.01';
# Put Perl code used in the BOOT: section here
XSLoader::load(__PACKAGE__, $VERSION);
}
# Put Perl code making calls into XSUBs here
The most hairy case
If the interdependence of your "BOOT:" section and Perl code is more
complicated than this (e.g., the "BOOT:" section makes calls to Perl
functions which make calls to XSUBs with prototypes), get rid of the
"BOOT:" section altogether. Replace it with a function onBOOT(), and
call it like this:
package YourPackage;
use XSLoader;
our ($VERSION, @ISA);
BEGIN {
@ISA = qw( OnePackage OtherPackage );
$VERSION = '0.01';
XSLoader::load(__PACKAGE__, $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
DIAGNOSTICS
"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.
LIMITATIONS
To reduce the overhead as much as possible, only one possible 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 overhead than running the same
extensions after "make install".
KNOWN BUGS
The new simpler way to call XSLoader::load() with no arguments at all
does not work on Perl 5.8.4 and 5.8.5.
BUGS
Please report any bugs or feature requests via the perlbug(1) utility.
SEE ALSO
DynaLoader
AUTHORS
Ilya Zakharevich originally extracted "XSLoader" from "DynaLoader".
CPAN version is currently maintained by Sébastien Aperghis-Tramoni
<sebastien@aperghis.net>.
Previous maintainer was Michael G Schwern <schwern@pobox.com>.
COPYRIGHT & LICENSE
Copyright (C) 1990-2011 by Larry Wall and others.
This program is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
perl v5.40.1 2026-08-30 XSLoader(3perl)
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