DynaLoader(3p) Perl Programmers Reference Guide DynaLoader(3p) #

DynaLoader(3p) Perl Programmers Reference Guide DynaLoader(3p)

NNAAMMEE #

 DynaLoader - Dynamically load C libraries into Perl code

SSYYNNOOPPSSIISS #

     package YourPackage;
     require DynaLoader;
     @ISA = qw(... DynaLoader ...);
     __PACKAGE__->bootstrap;

     # optional method for 'global' loading
     sub dl_load_flags { 0x01 }

DDEESSCCRRIIPPTTIIOONN #

 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, 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
   $dl_dlext
   @dl_librefs
   @dl_modules
   @dl_shared_objects
                                                   Implemented in:
   bootstrap($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

 @dl_library_path
     The standard/default list of directories in which ddll__ffiinnddffiillee(()) 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 (_/_u_s_r_/_l_i_b, etc) determined by CCoonnffiigguurree
     ($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 ddll__ffiinnddffiillee(()).
     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 ddll__llooaadd__ffiillee(()) calls may require an absolute
     pathname.  The ddll__ffiinnddffiillee(()) 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.

 @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 llooaadd__ffiillee(()).

     This is only required on some platforms which do not handle dependent
     libraries automatically.  For example the Socket Perl extension
     library (_a_u_t_o_/_S_o_c_k_e_t_/_S_o_c_k_e_t_._s_o) 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.,
     _/_u_s_r_/_l_i_b_/_l_i_b_s_o_c_k_e_t_._s_o).  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');

 @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.

 @dl_librefs
     An array of the handles returned by successful calls to
     ddll__llooaadd__ffiillee(()), made by bootstrap, in the order in which they were
     loaded.  Can be used with ddll__ffiinndd__ssyymmbbooll(()) to look for a symbol in
     any of the loaded files.

 @dl_modules
     An array of module (package) names that have been bootstrap'ed.

 @dl_shared_objects
     An array of file names for the shared objects that were loaded.

 ddll__eerrrroorr(())
     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., ddlleerrrroorr(())).

 $dl_debug
     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 --DDDDEEBBUUGGGGIINNGG flag.  This can also be set via the
     PERL_DL_DEBUG environment variable.  Set to 1 for minimal information
     or higher for more.

 $dl_dlext
     When specified (localised) in a module's _._p_m file, indicates the
     extension which the module's loadable object will have. For example:

         local $DynaLoader::dl_dlext = 'unusual_ext';

     would indicate that the module's loadable object has an extension of
     "unusual_ext" instead of the more usual $Config{dlext}.  NOTE: This
     also requires that the module's _M_a_k_e_f_i_l_e_._P_L specify (in
     "WriteMakefile()"):

         DLEXT => 'unusual_ext',

 ddll__ffiinnddffiillee(())
     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 --llnnaammee are converted into _l_i_b_n_a_m_e_._*, 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 --LLddiirr.  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));

 ddll__eexxppaannddssppeecc(())
     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 ddll__eexxppaannddssppeecc(()) function can be
     implemented either in the _d_l___*_._x_s file or code can be added to the
     ddll__eexxppaannddssppeecc(()) function in _D_y_n_a_L_o_a_d_e_r_._p_m.  See _D_y_n_a_L_o_a_d_e_r___p_m_._P_L for
     more information.

 ddll__llooaadd__ffiillee(())
     Syntax:

         $libref = dl_load_file($filename, $flags)

     Dynamically load $filename, which must be the path to a shared object
     or library.  An opaque 'library reference' is returned as a handle
     for the loaded object.  Returns undef on error.

     The $flags argument to alters dl_load_file behaviour.  Assigned bits:

      0x01  make symbols available for linking later dl_load_file's.
            (only known to work on Solaris 2 using dlopen(RTLD_GLOBAL))
            (ignored under VMS; this is a normal part of image linking)

     (On systems that provide a handle for the loaded object such as SunOS
     and HPUX, $libref will be that handle.  On other systems $libref will
     typically be $filename or a pointer to a buffer containing $filename.
     The application should not examine or alter $libref in any way.)

     This is the function that does the real work.  It should use the
     current values of @dl_require_symbols and @dl_resolve_using if
     required.

         SunOS: dlopen($filename)
         HP-UX: shl_load($filename)
         Linux: dld_create_reference(@dl_require_symbols); dld_link($filename)
         VMS:   lib$find_image_symbol($filename,$dl_require_symbols[0])

     (The ddllooppeenn(()) function is also used by Solaris and some versions of
     Linux, and is a common choice when providing a "wrapper" on other
     mechanisms as is done in the OS/2 port.)

 ddll__uunnllooaadd__ffiillee(())
     Syntax:

         $status = dl_unload_file($libref)

     Dynamically unload $libref, which must be an opaque 'library
     reference' as returned from dl_load_file.  Returns one on success and
     zero on failure.  This function is optional and may not necessarily
     be provided on all platforms.

     If it is defined and perl is compiled with the C macro
     "DL_UNLOAD_ALL_AT_EXIT" defined, then it is called automatically when
     the interpreter exits for every shared object or library loaded by
     DynaLoader::bootstrap.  All such library references are stored in
     @dl_librefs by DynaLoader::Bootstrap as it loads the libraries.  The
     files are unloaded in last-in, first-out order.

     This unloading is usually necessary when embedding a shared-object
     perl (e.g.  one configured with -Duseshrplib) within a larger
     application, and the perl interpreter is created and destroyed
     several times within the lifetime of the application.  In this case
     it is possible that the system dynamic linker will unload and then
     subsequently reload the shared libperl without relocating any
     references to it from any files DynaLoaded by the previous
     incarnation of the interpreter.  As a result, any shared objects
     opened by DynaLoader may point to a now invalid 'ghost' of the
     libperl shared object, causing apparently random memory corruption
     and crashes.  This behaviour is most commonly seen when using Apache
     and mod_perl built with the APXS mechanism.

         SunOS: dlclose($libref)

HP-UX: ??? #

         Linux: ???

VMS: ??? #

     (The ddllcclloossee(()) function is also used by Solaris and some versions of
     Linux, and is a common choice when providing a "wrapper" on other
     mechanisms as is done in the OS/2 port.)

 ddll__llooaadd__ffllaaggss(())
     Syntax:

         $flags = dl_load_flags $modulename;

     Designed to be a method call, and to be overridden by a derived class
     (i.e. a class which has DynaLoader in its @ISA).  The definition in
     DynaLoader itself returns 0, which produces standard behavior from
     ddll__llooaadd__ffiillee(()).

 ddll__ffiinndd__ssyymmbbooll(())
     Syntax:

         $symref = dl_find_symbol($libref, $symbol)

     Return the address of the symbol $symbol or "undef" if not found.  If
     the target system has separate functions to search for symbols of
     different types then ddll__ffiinndd__ssyymmbbooll(()) should search for function
     symbols first and then other types.

     The exact manner in which the address is returned in $symref is not
     currently defined.  The only initial requirement is that $symref can
     be passed to, and understood by, ddll__iinnssttaallll__xxssuubb(()).

         SunOS: dlsym($libref, $symbol)
         HP-UX: shl_findsym($libref, $symbol)
         Linux: dld_get_func($symbol) and/or dld_get_symbol($symbol)
         VMS:   lib$find_image_symbol($libref,$symbol)

 ddll__ffiinndd__ssyymmbbooll__aannyywwhheerree(())
     Syntax:

         $symref = dl_find_symbol_anywhere($symbol)

     Applies ddll__ffiinndd__ssyymmbbooll(()) to the members of @dl_librefs and returns
     the first match found.

 ddll__uunnddeeff__ssyymmbboollss(())
     Example

         @symbols = dl_undef_symbols()

     Return a list of symbol names which remain undefined after
     llooaadd__ffiillee(()).  Returns "()" if not known.  Don't worry if your
     platform does not provide a mechanism for this.  Most do not need it
     and hence do not provide it, they just return an empty list.

 ddll__iinnssttaallll__xxssuubb(())
     Syntax:

         dl_install_xsub($perl_name, $symref [, $filename])

     Create a new Perl external subroutine named $perl_name using $symref
     as a pointer to the function which implements the routine.  This is
     simply a direct call to nneewwXXSS(())/nneewwXXSS__ffllaaggss(()).  Returns a reference
     to the installed function.

     The $filename parameter is used by Perl to identify the source file
     for the function if required by ddiiee(()), ccaalllleerr(()) or the debugger.  If
     $filename is not defined then "DynaLoader" will be used.

 bboooottssttrraapp(())
     Syntax:

     bootstrap($module [...])

     This is the normal entry point for automatic dynamic loading in Perl.

     It performs the following actions:

     •       locates an auto/$module directory by searching @INC

     •       uses ddll__ffiinnddffiillee(()) to determine the filename to load

     •       sets @dl_require_symbols to "("boot_$module")"

     •       executes an _a_u_t_o_/_$_m_o_d_u_l_e_/_$_m_o_d_u_l_e_._b_s file if it exists
             (typically used to add to @dl_resolve_using any files which
             are required to load the module on the current platform)

     •       calls ddll__llooaadd__ffllaaggss(()) to determine how to load the file.

     •       calls ddll__llooaadd__ffiillee(()) to load the file

     •       calls ddll__uunnddeeff__ssyymmbboollss(()) and warns if any symbols are
             undefined

     •       calls ddll__ffiinndd__ssyymmbbooll(()) for "boot_$module"

     •       calls ddll__iinnssttaallll__xxssuubb(()) to install it as
             "${module}::bootstrap"

     •       calls &{"${module}::bootstrap"} to bootstrap the module
             (actually it uses the function reference returned by
             dl_install_xsub for speed)

     All arguments to bboooottssttrraapp(()) are passed to the module's bootstrap
     function.  The default code generated by _x_s_u_b_p_p expects $module [,
     $version] If the optional $version argument is not given, it defaults
     to "$XS_VERSION // $VERSION" in the module's symbol table. The
     default code compares the Perl-space version with the version of the
     compiled XS code, and croaks with an error if they do not match.

AAUUTTHHOORR #

 Tim Bunce, 11 August 1994.

 This interface is based on the work and comments of (in no particular
 order): Larry Wall, Robert Sanders, Dean Roehrich, Jeff Okamoto, Anno
 Siegel, Thomas Neumann, Paul Marquess, Charles Bailey, myself and others.

 Larry Wall designed the elegant inherited bootstrap mechanism and
 implemented the first Perl 5 dynamic loader using it.

 Solaris global loading added by Nick Ing-Simmons with design/coding
 assistance from Tim Bunce, January 1996.

perl v5.36.3 2024-03-20 DynaLoader(3p)