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MAN page from Fedora 29 perl-libs-5.26.3-415.module_2543+eed510a0.x86_64.rpm

XSLoader

Section: Perl Programmers Reference Guide (3pm)
Updated: 2018-12-05
Index 

NAME

XSLoader - Dynamically load C libraries into Perl code 

VERSION

Version 0.24 

SYNOPSIS

    package YourPackage;    require XSLoader;    XSLoader::load();
 

DESCRIPTION

This module defines a standard simplified interface to the dynamiclinking mechanisms available on many platforms. Its primary purpose isto 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 forexample 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 notforget 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 havethe @ISA assignment at all; moreover, if instead of "our" one uses themore 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 "YourPackage", then that can be furthersimplified 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 complicatedboilerplate.

    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 withan 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 othermodules 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 DynaLoaderinterface.

A sufficiently complicated module using XS would have both Perl code (definedin YourPackage.pm) and XS code (defined in YourPackage.xs). If thisPerl code makes calls into this XS code, and/or this XS code makes calls tothe Perl code, one should be careful with the order of initialization.

The call to "XSLoader::load()" (or "bootstrap()") calls the module'sbootstrap code. For modules build by xsubpp (nearly all modules) thishas three side effects:

*
A sanity check is done to ensure that the versions of the .pm and the(compiled) .xs parts are compatible. If $VERSION was specified, thisis used for the check. If not specified, it defaults to"$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 isconvenient to have XSUBs installed before the Perl code is defined; forexample, this makes prototypes for XSUBs visible to this Perl code.Alternatively, if the "BOOT:" section makes calls to Perl functions (oruses Perl variables) defined in the .pm file, they must be defined prior tothe call to "XSLoader::load()" (or "bootstrap()").

The first situation being much more frequent, it makes sense to rewrite theboilerplate 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 ismore complicated than this (e.g., the "BOOT:" section makes calls to Perlfunctions which make calls to XSUBs with prototypes), get rid of the "BOOT:"section altogether. Replace it with a function "onBOOT()", and call it likethis:

    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 theextension module was correctly loaded and initialised. The list of undefinedsymbols follows.
 

LIMITATIONS

To reduce the overhead as much as possible, only one possible locationis 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 transparentlydelegated to "DynaLoader", which looks for the DLL along the @INC list.

In particular, this is applicable to the structure of @INC used for testingnot-yet-installed extensions. This means that running uninstalled extensionsmay 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 alldoes 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<sebastienAATTaperghis.net>.

Previous maintainer was Michael G Schwern <schwernAATTpobox.com>. 

COPYRIGHT & LICENSE

Copyright (C) 1990-2011 by Larry Wall and others.

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


 

Index

NAME
VERSION
SYNOPSIS
DESCRIPTION
Migration from DynaLoader
Backward compatible boilerplate
Order of initialization: early load()
The most hairy case
DIAGNOSTICS
LIMITATIONS
KNOWN BUGS
BUGS
SEE ALSO
AUTHORS
COPYRIGHT & LICENSE

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