dynaloader.3

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.\" ========================================================================
.\"
.IX Title "DynaLoader 3"
.TH DynaLoader 3 "2008-01-23" "perl v5.10.0" "Perl Programmers Reference Guide"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
DynaLoader \- Dynamically load C libraries into Perl code
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 4
\&    package YourPackage;
\&    require DynaLoader;
\&    @ISA = qw(... DynaLoader ...);
\&    bootstrap YourPackage;
\&
\&    # optional method for \*(Aqglobal\*(Aq loading
\&    sub dl_load_flags { 0x01 }
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
This document defines a standard generic interface to the dynamic
linking mechanisms available on many platforms.  Its primary purpose is
to implement automatic dynamic loading of Perl modules.
.PP
This document serves as both a specification for anyone wishing to
implement the DynaLoader for a new platform and as a guide for
anyone wishing to use the DynaLoader directly in an application.
.PP
The DynaLoader is designed to be a very simple high-level
interface that is sufficiently general to cover the requirements
of SunOS, HP-UX, NeXT, Linux, \s-1VMS\s0 and other platforms.
.PP
It is also hoped that the interface will cover the needs of \s-1OS/2\s0, \s-1NT\s0
etc and also allow pseudo-dynamic linking (using \f(CW\*(C`ld \-A\*(C'\fR at runtime).
.PP
It must be stressed that the DynaLoader, by itself, is practically
useless for accessing non-Perl libraries because it provides almost no
Perl-to-C 'glue'.  There is, for example, no mechanism for calling a C
library function or supplying arguments.  A C::DynaLib module
is available from \s-1CPAN\s0 sites which performs that function for some
common system types.  And since the year 2000, there's also Inline::C,
a module that allows you to write Perl subroutines in C.  Also available
from your local \s-1CPAN\s0 site.
.PP
DynaLoader Interface Summary
.PP
.Vb 12
\&  @dl_library_path
\&  @dl_resolve_using
\&  @dl_require_symbols
\&  $dl_debug
\&  @dl_librefs
\&  @dl_modules
\&  @dl_shared_objects
\&                                                  Implemented in:
\&  bootstrap($modulename)                               Perl
\&  @filepaths = dl_findfile(@names)                     Perl
\&  $flags = $modulename\->dl_load_flags                  Perl
\&  $symref  = dl_find_symbol_anywhere($symbol)          Perl
\&
\&  $libref  = dl_load_file($filename, $flags)           C
\&  $status  = dl_unload_file($libref)                   C
\&  $symref  = dl_find_symbol($libref, $symbol)          C
\&  @symbols = dl_undef_symbols()                        C
\&  dl_install_xsub($name, $symref [, $filename])        C
\&  $message = dl_error                                  C
.Ve
.ie n .IP "@dl_library_path" 4
.el .IP "\f(CW@dl_library_path\fR" 4
.IX Item "@dl_library_path"
The standard/default list of directories in which \fIdl_findfile()\fR will
search for libraries etc.  Directories are searched in order:
\&\f(CW$dl_library_path\fR[0], [1], ... etc
.Sp
\&\f(CW@dl_library_path\fR is initialised to hold the list of 'normal' directories
(\fI/usr/lib\fR, etc) determined by \fBConfigure\fR (\f(CW$Config{\*(Aqlibpth\*(Aq}\fR).  This should
ensure portability across a wide range of platforms.
.Sp
\&\f(CW@dl_library_path\fR should also be initialised with any other directories
that can be determined from the environment at runtime (such as
\&\s-1LD_LIBRARY_PATH\s0 for SunOS).
.Sp
After initialisation \f(CW@dl_library_path\fR can be manipulated by an
application using push and unshift before calling \fIdl_findfile()\fR.
Unshift can be used to add directories to the front of the search order
either to save search time or to override libraries with the same name
in the 'normal' directories.
.Sp
The load function that \fIdl_load_file()\fR calls may require an absolute
pathname.  The \fIdl_findfile()\fR function and \f(CW@dl_library_path\fR can be
used to search for and return the absolute pathname for the
library/object that you wish to load.
.ie n .IP "@dl_resolve_using" 4
.el .IP "\f(CW@dl_resolve_using\fR" 4
.IX Item "@dl_resolve_using"
A list of additional libraries or other shared objects which can be
used to resolve any undefined symbols that might be generated by a
later call to \fIload_file()\fR.
.Sp
This is only required on some platforms which do not handle dependent
libraries automatically.  For example the Socket Perl extension
library (\fIauto/Socket/Socket.so\fR) contains references to many socket
functions which need to be resolved when it's loaded.  Most platforms
will automatically know where to find the 'dependent' library (e.g.,
\&\fI/usr/lib/libsocket.so\fR).  A few platforms need to be told the
location of the dependent library explicitly.  Use \f(CW@dl_resolve_using\fR
for this.
.Sp
Example usage:
.Sp
.Vb 1
\&    @dl_resolve_using = dl_findfile(\*(Aq\-lsocket\*(Aq);
.Ve
.ie n .IP "@dl_require_symbols" 4
.el .IP "\f(CW@dl_require_symbols\fR" 4
.IX Item "@dl_require_symbols"
A list of one or more symbol names that are in the library/object file
to be dynamically loaded.  This is only required on some platforms.
.ie n .IP "@dl_librefs" 4
.el .IP "\f(CW@dl_librefs\fR" 4
.IX Item "@dl_librefs"
An array of the handles returned by successful calls to \fIdl_load_file()\fR,
made by bootstrap, in the order in which they were loaded.
Can be used with \fIdl_find_symbol()\fR to look for a symbol in any of
the loaded files.
.ie n .IP "@dl_modules" 4
.el .IP "\f(CW@dl_modules\fR" 4
.IX Item "@dl_modules"
An array of module (package) names that have been bootstrap'ed.
.ie n .IP "@dl_shared_objects" 4
.el .IP "\f(CW@dl_shared_objects\fR" 4
.IX Item "@dl_shared_objects"
An array of file names for the shared objects that were loaded.
.IP "\fIdl_error()\fR" 4
.IX Item "dl_error()"
Syntax:
.Sp
.Vb 1
\&    $message = dl_error();
.Ve
.Sp