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.\" ========================================================================
.\"
.IX Title "XSLoader 3"
.TH XSLoader 3 "2001-09-21" "perl v5.8.6" "Perl Programmers Reference Guide"
.SH "NAME"
XSLoader \- Dynamically load C libraries into Perl code
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 2
\& package YourPackage;
\& use XSLoader;
.Ve
.PP
.Vb 1
\& XSLoader::load 'YourPackage', $YourPackage::VERSION;
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
This module defines a standard \fIsimplified\fR interface to the dynamic
linking mechanisms available on many platforms. Its primary purpose is
to implement cheap automatic dynamic loading of Perl modules.
.PP
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.
.ie n .Sh "Migration from ""DynaLoader"""
.el .Sh "Migration from \f(CWDynaLoader\fP"
.IX Subsection "Migration from DynaLoader"
A typical module using DynaLoader starts like this:
.PP
.Vb 2
\& package YourPackage;
\& require DynaLoader;
.Ve
.PP
.Vb 3
\& our @ISA = qw( OnePackage OtherPackage DynaLoader );
\& our $VERSION = '0.01';
\& bootstrap YourPackage $VERSION;
.Ve
.PP
Change this to
.PP
.Vb 2
\& package YourPackage;
\& use XSLoader;
.Ve
.PP
.Vb 3
\& our @ISA = qw( OnePackage OtherPackage );
\& our $VERSION = '0.01';
\& XSLoader::load 'YourPackage', $VERSION;
.Ve
.PP
In other words: replace \f(CW\*(C`require DynaLoader\*(C'\fR by \f(CW\*(C`use XSLoader\*(C'\fR, remove
\&\f(CW\*(C`DynaLoader\*(C'\fR from \f(CW@ISA\fR, change \f(CW\*(C`bootstrap\*(C'\fR by \f(CW\*(C`XSLoader::load\*(C'\fR. Do not
forget to quote the name of your package on the \f(CW\*(C`XSLoader::load\*(C'\fR line,
and add comma (\f(CW\*(C`,\*(C'\fR) before the arguments ($VERSION above).
.PP
Of course, if \f(CW@ISA\fR contained only \f(CW\*(C`DynaLoader\*(C'\fR, there is no need to have the
\&\f(CW@ISA\fR assignment at all; moreover, if instead of \f(CW\*(C`our\*(C'\fR one uses
backward-compatible
.PP
.Vb 1
\& use vars qw($VERSION @ISA);
.Ve
.PP
one can remove this reference to \f(CW@ISA\fR together with the \f(CW@ISA\fR assignment
.PP
If no \f(CW$VERSION\fR was specified on the \f(CW\*(C`bootstrap\*(C'\fR line, the last line becomes
.PP
.Vb 1
\& XSLoader::load 'YourPackage';
.Ve
.Sh "Backward compatible boilerplate"
.IX Subsection "Backward compatible boilerplate"
If you want to have your cake and eat it too, you need a more complicated
boilerplate.
.PP
.Vb 2
\& package YourPackage;
\& use vars qw($VERSION @ISA);
.Ve
.PP
.Vb 11
\& @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;
\& };
.Ve
.PP
The parentheses about \fIXSLoader::load()\fR arguments are needed since we replaced
\&\f(CW\*(C`use XSLoader\*(C'\fR by \f(CW\*(C`require\*(C'\fR, so the compiler does not know that a function
\&\fIXSLoader::load()\fR is present.
.PP
This boilerplate uses the low-overhead \f(CW\*(C`XSLoader\*(C'\fR if present; if used with
an antic Perl which has no \f(CW\*(C`XSLoader\*(C'\fR, it falls back to using \f(CW\*(C`DynaLoader\*(C'\fR.
.SH "Order of initialization: early \fIload()\fP"
.IX Header "Order of initialization: early load()"
\&\fISkip this section if the \s-1XSUB\s0 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 \f(CI\*(C`BOOT:\*(C'\fI section in your \s-1XS\s0 file (see \*(L"The \s-1BOOT:\s0 Keyword\*(R" in perlxs).
What is described here is equally applicable to DynaLoader
interface.\fR
.PP
A sufficiently complicated module using \s-1XS\s0 would have both Perl code (defined
in \fIYourPackage.pm\fR) and \s-1XS\s0 code (defined in \fIYourPackage.xs\fR). If this
Perl code makes calls into this \s-1XS\s0 code, and/or this \s-1XS\s0 code makes calls to
the Perl code, one should be careful with the order of initialization.
.PP
The call to \fIXSLoader::load()\fR (or \fIbootstrap()\fR) has three side effects:
.IP "\(bu" 4
if \f(CW$VERSION\fR was specified, a sanity check is done to insure that the versions
of the \fI.pm\fR and the (compiled) \fI.xs\fR parts are compatible;
.IP "\(bu" 4
The XSUBs are made accessible from Perl;
.IP "\(bu" 4
If the \f(CW\*(C`BOOT:\*(C'\fR section was present in \fI.xs\fR file, the code there is called.
.PP
Consequently, if the code in \fI.pm\fR 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 \f(CW\*(C`BOOT:\*(C'\fR section makes calls to Perl functions (or
uses Perl variables) defined in \fI.pm\fR file, they must be defined prior to
the call to \fIXSLoader::load()\fR (or \fIbootstrap()\fR).
.PP
The first situation being much more frequent, it makes sense to rewrite the
boilerplate as
.PP
.Vb 3
\& package YourPackage;
\& use XSLoader;
\& use vars qw($VERSION @ISA);
.Ve
.PP
.Vb 3
\& BEGIN {
\& @ISA = qw( OnePackage OtherPackage );
\& $VERSION = '0.01';
.Ve
.PP
.Vb 1
\& # Put Perl code used in the BOOT: section here
.Ve
.PP
.Vb 2
\& XSLoader::load 'YourPackage', $VERSION;
\& }
.Ve
.PP
.Vb 1
\& # Put Perl code making calls into XSUBs here
.Ve
.Sh "The most hairy case"
.IX Subsection "The most hairy case"
If the interdependence of your \f(CW\*(C`BOOT:\*(C'\fR section and Perl code is
more complicated than this (e.g., the \f(CW\*(C`BOOT:\*(C'\fR section makes calls to Perl
functions which make calls to XSUBs with prototypes), get rid of the \f(CW\*(C`BOOT:\*(C'\fR
section altogether. Replace it with a function \fIonBOOT()\fR, and call it like
this:
.PP
.Vb 3
\& package YourPackage;
\& use XSLoader;
\& use vars qw($VERSION @ISA);
.Ve
.PP
.Vb 5
\& BEGIN {
\& @ISA = qw( OnePackage OtherPackage );
\& $VERSION = '0.01';
\& XSLoader::load 'YourPackage', $VERSION;
\& }
.Ve
.PP
.Vb 2
\& # Put Perl code used in onBOOT() function here; calls to XSUBs are
\& # prototype-checked.
.Ve
.PP
.Vb 1
\& onBOOT;
.Ve
.PP
.Vb 1
\& # Put Perl initialization code assuming that XS is initialized here
.Ve
.SH "LIMITATIONS"
.IX Header "LIMITATIONS"
To reduce the overhead as much as possible, only one possible location
is checked to find the extension \s-1DLL\s0 (this location is where \f(CW\*(C`make install\*(C'\fR
would put the \s-1DLL\s0). If not found, the search for the \s-1DLL\s0 is transparently
delegated to \f(CW\*(C`DynaLoader\*(C'\fR, which looks for the \s-1DLL\s0 along the \f(CW@INC\fR list.
.PP
In particular, this is applicable to the structure of \f(CW@INC\fR 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
\&\f(CW\*(C`make install\*(C'\fR.
.SH "AUTHOR"
.IX Header "AUTHOR"
Ilya Zakharevich: extraction from DynaLoader.
www.fiveanddime.net
