XSLoader - Dynamically load C libraries into Perl code
Version 0.32
package YourPackage;require XSLoader;XSLoader::load(__PACKAGE__, $VERSION);This module defines a standardsimplified 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, seeDynaLoader. Many (most) features ofDynaLoader are not implemented inXSLoader, like for example thedl_load_flags, not honored byXSLoader.
DynaLoaderA typical module usingDynaLoader 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__, $VERSION);In other words: replacerequire DynaLoader byuse XSLoader, removeDynaLoader from@ISA, changebootstrap byXSLoader::load. Do not forget to quote the name of your package on theXSLoader::load line, and add comma (,) before the arguments ($VERSION above).
Of course, if@ISA contained onlyDynaLoader, there is no need to have the@ISA assignment at all; moreover, if instead ofour 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 thebootstrap line, the last line becomes
XSLoader::load(__PACKAGE__);in which case it can be further simplified to
XSLoader::load();asload will usecaller 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 aboutXSLoader::load() arguments are needed since we replaceduse XSLoader byrequire, so the compiler does not know that a functionXSLoader::load() is present.
This boilerplate uses the low-overheadXSLoader if present; if used with an antique Perl which has noXSLoader, it falls back to usingDynaLoader.
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 aBOOT: section in your XS file (see"The BOOT: Keyword" in perlxs). What is described here is equally applicable to theDynaLoader interface.
A sufficiently complicated module using XS would have both Perl code (defined inYourPackage.pm) and XS code (defined inYourPackage.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 toXSLoader::load() (orbootstrap()) calls the module's bootstrap code. For modules build byxsubpp (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 // $VERSION (in the module's namespace)
the XSUBs are made accessible from Perl
if aBOOT: section was present in the.xs file, the code there is called.
Consequently, if the code in the.pm file makes calls to these XSUBs, it is convenient to have XSUBs installed before the Perl code is defined; for example, this makes prototypes for XSUBs visible to this Perl code. Alternatively, if theBOOT: section makes calls to Perl functions (or uses Perl variables) defined in the.pm file, they must be defined prior to the call toXSLoader::load() (orbootstrap()).
The first situation being much more frequent, it makes sense to rewrite the boilerplate as
package YourPackage;use XSLoader;our ($VERSION, @ISA);BEGIN { @ISA = qw( OnePackage OtherPackage ); $VERSION = '0.01'; # Put Perl code used in the BOOT: section here XSLoader::load(__PACKAGE__, $VERSION);}# Put Perl code making calls into XSUBs hereIf the interdependence of yourBOOT: section and Perl code is more complicated than this (e.g., theBOOT: section makes calls to Perl functions which make calls to XSUBs with prototypes), get rid of theBOOT: section altogether. Replace it with a functiononBOOT(), and call it like this:
package YourPackage;use XSLoader;our ($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 hereCan'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.
To reduce the overhead as much as possible, only one possible location is checked to find the extension DLL (this location is wheremake install would put the DLL). If not found, the search for the DLL is transparently delegated toDynaLoader, 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 aftermake install.
The new simpler way to callXSLoader::load() with no arguments at all does not work on Perl 5.8.4 and 5.8.5.
Please report any bugs or feature requests via the perlbug(1) utility.
Ilya Zakharevich originally extractedXSLoader fromDynaLoader.
CPAN version is currently maintained by Sébastien Aperghis-Tramoni <sebastien@aperghis.net>.
Previous maintainer was Michael G Schwern <schwern@pobox.com>.
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