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XSLoader(3)


NAME

  XSLoader - Dynamically load C libraries into Perl code


VERSION

  Version 0.06


SYNOPSIS

      package YourPackage;
      use XSLoader;

      XSLoader::load 'YourPackage', $YourPackage::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';
      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';

  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()") has three side effects:

  ·   if $VERSION was specified, a sanity check is done to ensure that the
      versions of the .pm and the (compiled) .xs parts are compatible;

  ·   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 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.

  XSLoader::load('Your::Module', $Your::Module::VERSION)
      (F) You tried to invoke "load()" without any argument. You must supply
      a module name, and optionally its version.


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".


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

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

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