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XSLoader(3pm) Perl Programmers Reference Guide XSLoader(3pm)
NAME
XSLoader - Dynamically load C libraries into Perl code
VERSION
Version 0.15
SYNOPSIS
package YourPackage;
require XSLoader;
XSLoader::load();
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';
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
use vars qw($VERSION @ISA);
one can remove this reference to @ISA together with the @ISA assignment.
If no $VERSION was specified on the "bootstrap" line, the last line becomes
XSLoader::load 'YourPackage';
If the call to "load" is from the YourPackage, then that can be further simplified to
XSLoader::load();
as "load" will use "caller" to determine the package.
Backward compatible boilerplate
If you want to have your cake and eat it too, you need a more complicated boilerplate.
package YourPackage;
use vars qw($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.
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:
o 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 // $VERSION" (in the module's namespace)
o the XSUBs are made accessible from Perl
o if a "BOOT:" section was present in the .xs file, the code there is called.
Consequently, if the code in the .pm file makes calls to these XSUBs, it is convenient to
have XSUBs installed before the Perl code is defined; for example, this makes prototypes
for XSUBs visible to this Perl code. Alternatively, if the "BOOT:" section makes calls to
Perl functions (or uses Perl variables) defined in the .pm file, they must be defined
prior to the call to "XSLoader::load()" (or "bootstrap()").
The first situation being much more frequent, it makes sense to rewrite the boilerplate as
package YourPackage;
use XSLoader;
use vars qw($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);
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
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 Sebastien Aperghis-Tramoni
<sebastien AT aperghis.net>.
Previous maintainer was Michael G Schwern <schwern AT 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 v5.16.3 2021-02-02 XSLoader(3pm)
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