XSLoader - Dynamically load C libraries into Perl code
Version 0.32
package YourPackage;
require XSLoader;
XSLoader::load(__PACKAGE__, $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 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.
DynaLoaderA 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.
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.
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:
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 // $VERSION (in the module's namespace)
the XSUBs are made accessible from Perl
if a BOOT: section was present in the .xs file, the code there is called.
Consequently, if the code in the .pm file makes calls to these XSUBs, it is convenient to have XSUBs installed before the Perl code is defined; for example, this makes prototypes for XSUBs visible to this Perl code. Alternatively, if the BOOT: section makes calls to Perl functions (or uses Perl variables) defined in the .pm file, they must be defined prior to the call to XSLoader::load() (or bootstrap()).
The first situation being much more frequent, it makes sense to rewrite the boilerplate as
package YourPackage;
use XSLoader;
our ($VERSION, @ISA);
BEGIN {
@ISA = qw( OnePackage OtherPackage );
$VERSION = '0.01';
# Put Perl code used in the BOOT: section here
XSLoader::load(__PACKAGE__, $VERSION);
}
# Put Perl code making calls into XSUBs hereIf the interdependence of your BOOT: section and Perl code is more complicated than this (e.g., the BOOT: section makes calls to Perl functions which make calls to XSUBs with prototypes), get rid of the BOOT: section altogether. Replace it with a function onBOOT(), and call it like this:
package YourPackage;
use XSLoader;
our ($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