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

NAME

       XSLoader - Dynamically load C libraries into Perl code

VERSION

       Version 0.16

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

AUTHORS

       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>.

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 v5.18.2							    2017-10-07							     XSLoader(3pm)