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 perlxs/``The BOOT: Keyword''). 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