XSLoader
XSLoader(3) Perl Programmers Reference Guide XSLoader(3)
NAME
XSLoader - Dynamically load C libraries into Perl code
SYNOPSIS
package YourPackage;
use XSLoader;
XSLoader::load 'YourPackage', $YourPackage::VERSION;
DESCRIPTION
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 honored 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', $VERSION;
In other words: replace "require DynaLoader" by "use XSLoader", remove
"DynaLoader" from @ISA, change "bootstrap" by "XSLoader::load". Do not
forget to quote the name of your package on the "XSLoader::load" line,
and add comma (",") before the arguments ($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
backward-compatible
use vars qw($VERSION @ISA);
one can remove this reference to @ISA together with the @ISA assignment
If no $VERSION was specified on the "bootstrap" line, the last line
becomes
XSLoader::load 'YourPackage';
Backward compatible boilerplate
If you want to have your cake and eat it too, you need a more compli-
cated boilerplate.
package YourPackage;
use vars qw($VERSION @ISA);
@ISA = qw( OnePackage OtherPackage );
$VERSION = '0.01';
eval {
require XSLoader;
XSLoader::load('YourPackage', $VERSION);
1;
} 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 present; 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 perlxs). What is described here is equally applica-
ble 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
initialization.
The call to XSLoader::load() (or bootstrap()) has three side effects:
o if $VERSION was specified, a sanity check is done to insure that
the versions of the .pm and the (compiled) .xs parts are compati-
ble;
o The XSUBs are made accessible from Perl;
o If the "BOOT:" section was present in .xs file, the code there is
called.
Consequently, if the code in .pm file makes calls to these XSUBs, it is
convenient to have XSUBs installed before the Perl code is defined; for
example, this makes prototypes for XSUBs visible to this Perl code.
Alternatively, if the "BOOT:" section makes calls to Perl functions (or
uses Perl variables) defined in .pm file, they must be defined prior to
the call to XSLoader::load() (or bootstrap()).
The first situation being much more frequent, it makes sense to rewrite
the boilerplate as
package YourPackage;
use XSLoader;
use vars qw($VERSION @ISA);
BEGIN {
@ISA = qw( OnePackage OtherPackage );
$VERSION = '0.01';
# Put Perl code used in the BOOT: section here
XSLoader::load 'YourPackage', $VERSION;
}
# Put Perl code making calls into XSUBs here
The most hairy case
If the interdependence of your "BOOT:" section and Perl code is more
complicated than this (e.g., the "BOOT:" section makes calls to Perl
functions which make calls to XSUBs with prototypes), get rid of the
"BOOT:" section altogether. Replace it with a function onBOOT(), and
call it like this:
package YourPackage;
use XSLoader;
use vars qw($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
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 the overhead of
running uninstalled extension may be much more than running the same
extension after "make install".
AUTHOR
Ilya Zakharevich: extraction from DynaLoader.
perl v5.8.6 2001-09-21 XSLoader(3)
