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       XSLoader - Dynamically load C libraries into Perl code

           package YourPackage;
           use XSLoader;

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

       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 more complicated interface see DynaLoader.  Many
       (most) features of DynaLoader are not implemented in
       XSLoader, like for example the dl_load_flags is not hon-
       ored 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 "boot-
       strap" 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 backward-compatible

           use vars qw($VERSION @ISA);

       one can remove this reference to @ISA together with the
       @ISA assignment

perl v5.8.5                 2002-11-06                          1


       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);
           } 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 pre-
       sent; 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 per-
       lxs).  What is described here is equally applicable to
       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 initializa-

       The call to XSLoader::load() (or bootstrap()) has three
       side effects:

       o   if $VERSION was specified, a sanity check is done to
           insure that the versions of the .pm and the (compiled)

perl v5.8.5                 2002-11-06                          2


           .xs parts are compatible;

       o   The XSUBs are made accessible from Perl;

       o   If the "BOOT:" section was present in .xs file, the
           code there is called.

       Consequently, if the code in .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 .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:" sec-
       tion 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.

perl v5.8.5                 2002-11-06                          3



           # Put Perl initialization code assuming that XS is initialized here

       To reduce the overhead as much as possible, only one pos-
       sible 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 dele-
       gated 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 the overhead of running uninstalled extension may be
       much more than running the same extension after "make

       Ilya Zakharevich: extraction from DynaLoader.

perl v5.8.5                 2002-11-06                          4