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

NAME
       XSLoader	- Dynamically load C libraries into Perl code

VERSION
       Version 0.30

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:

       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;
	   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 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 v5.28.3			  2021-03-01			   XSLoader(3)

NAME | VERSION | SYNOPSIS | DESCRIPTION | Order of initialization: early load() | DIAGNOSTICS | LIMITATIONS | KNOWN BUGS | BUGS | SEE ALSO | AUTHORS | COPYRIGHT & LICENSE

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