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XSLoader(3pm)          Perl Programmers Reference Guide          XSLoader(3pm)




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 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 "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 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:

       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(3)


AUTHORS

       Ilya Zakharevich originally extracted "XSLoader" from "DynaLoader".

       CPAN version is currently maintained by SA(C)bastien 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 v5.26.0                      2017-06-07                       XSLoader(3)

xsloader 0.240.0 - Generated Sun Nov 19 10:26:27 CST 2017
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