| XSLoader - Dynamically load C libraries into Perl code |
load()
XSLoader - Dynamically load C libraries into Perl code
Version 0.30
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 the DynaLoader manpage. 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.
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 the perlxs manpage).
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:
$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__, $VERSION);
}
# Put Perl code making calls into XSUBs here
If the interdependence of your BOOT: section and Perl code is
more complicated than this (e.g., the BOOT: section makes calls to Perl
functions which make calls to XSUBs with prototypes), get rid of the BOOT:
section altogether. Replace it with a function onBOOT(), and call it like
this:
package YourPackage;
use XSLoader;
our ($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
Can't find '%s' symbol in %sCan't load '%s' for module %s: %sUndefined symbols present after loading %s: %s
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.
The new simpler way to call XSLoader::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 extracted XSLoader from DynaLoader.
CPAN version is currently maintained by Sébastien Aperghis-Tramoni <sebastien@aperghis.net>.
Previous maintainer was Michael G Schwern <schwern@pobox.com>.
Copyright (C) 1990-2011 by Larry Wall and others.
This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
| XSLoader - Dynamically load C libraries into Perl code |