DynaLoader - Dynamically load C libraries into Perl code
package YourPackage;
require DynaLoader;
@ISA = qw(... DynaLoader ...);
bootstrap YourPackage;
# optional method for 'global' loading
sub dl_load_flags { 0x01 } 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.
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.
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, VMS and other platforms.
It is also hoped that the interface will cover the needs of OS/2, NT etc and also allow pseudo-dynamic linking (using ld -A at runtime).
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 CPAN 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 CPAN site.
DynaLoader Interface Summary
@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 CThe standard/default list of directories in which dl_findfile() will search for libraries etc. Directories are searched in order: $dl_library_path[0], [1], ... etc
@dl_library_path is initialised to hold the list of 'normal' directories (/usr/lib, etc) determined by Configure ($Config{'libpth'}). This should ensure portability across a wide range of platforms.
@dl_library_path should also be initialised with any other directories that can be determined from the environment at runtime (such as LD_LIBRARY_PATH for SunOS).
After initialisation @dl_library_path can be manipulated by an application using push and unshift before calling dl_findfile(). 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.
The load function that dl_load_file() calls may require an absolute pathname. The dl_findfile() function and @dl_library_path can be used to search for and return the absolute pathname for the library/object that you wish to load.
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 load_file().
This is only required on some platforms which do not handle dependent libraries automatically. For example the Socket Perl extension library (auto/Socket/Socket.so) 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., /usr/lib/libsocket.so). A few platforms need to be told the location of the dependent library explicitly. Use @dl_resolve_using for this.
Example usage:
@dl_resolve_using = dl_findfile('-lsocket');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.
An array of the handles returned by successful calls to dl_load_file(), made by bootstrap, in the order in which they were loaded. Can be used with dl_find_symbol() to look for a symbol in any of the loaded files.
An array of module (package) names that have been bootstrap'ed.
An array of file names for the shared objects that were loaded.
Syntax:
$message = dl_error();Error message text from the last failed DynaLoader function. Note that, similar to errno in unix, a successful function call does not reset this message.
Implementations should detect the error as soon as it occurs in any of the other functions and save the corresponding message for later retrieval. This will avoid problems on some platforms (such as SunOS) where the error message is very temporary (e.g., dlerror()).
Internal debugging messages are enabled when $dl_debug is set true. Currently setting $dl_debug only affects the Perl side of the DynaLoader. These messages should help an application developer to resolve any DynaLoader usage problems.
$dl_debug is set to $ENV{'PERL_DL_DEBUG'} if defined.
For the DynaLoader developer/porter there is a similar debugging variable added to the C code (see dlutils.c) and enabled if Perl was built with the -DDEBUGGING flag. This can also be set via the PERL_DL_DEBUG environment variable. Set to 1 for minimal information or higher for more.
Syntax:
@filepaths = dl_findfile(@names)Determine the full paths (including file suffix) of one or more loadable files given their generic names and optionally one or more directories. Searches directories in @dl_library_path by default and returns an empty list if no files were found.
Names can be specified in a variety of platform independent forms. Any names in the form -lname are converted into libname.*, where .* is an appropriate suffix for the platform.
If a name does not already have a suitable prefix and/or suffix then the corresponding file will be searched for by trying combinations of prefix and suffix appropriate to the platform: "$name.o", "lib$name.*" and "$name".
If any directories are included in @names they are searched before @dl_library_path. Directories may be specified as -Ldir. Any other names are treated as filenames to be searched for.
Using arguments of the form -Ldir and -lname is recommended.
Example:
@dl_resolve_using = dl_findfile(qw(-L/usr/5lib -lposix));Syntax:
$filepath = dl_expandspec($spec)Some unusual systems, such as VMS, require special filename handling in order to deal with symbolic names for files (i.e., VMS's Logical Names).
To support these systems a dl_expandspec() function can be implemented either in the dl_*.xs file or code can be added to the dl_expandspec() function in DynaLoader.pm. See DynaLoader_pm.PL for more information.