IRIX Base Documentation 2001 May/SGI IRIX Base Documentation 2001 May.iso/usr/share/catman/p_man/cat3/perl5/DynaLoader.z/DynaLoader

Text File | 1998-10-30 | 17.7 KB | 529 lines

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     DynaLoader - Dynamically load C libraries into Perl code

     _d_l__e_r_r_o_r(), _d_l__f_i_n_d_f_i_l_e(), _d_l__e_x_p_a_n_d_s_p_e_c(), _d_l__l_o_a_d__f_i_l_e(),
     _d_l__f_i_n_d__s_y_m_b_o_l(), _d_l__f_i_n_d__s_y_m_b_o_l__a_n_y_w_h_e_r_e(), _d_l__u_n_d_e_f__s_y_m_b_o_l_s(),
     _d_l__i_n_s_t_a_l_l__x_s_u_b(), _d_l__l_o_a_d__f_l_a_g_s(), _b_o_o_t_s_t_r_a_p() - routines used by
     DynaLoader modules

SSSSYYYYNNNNOOOOPPPPSSSSIIIISSSS
         package YourPackage;
         require DynaLoader;
         @ISA = qw(... DynaLoader ...);
         bootstrap YourPackage;

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


DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN
     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 ExtUtils::DynaLib module is
     available from CPAN sites which performs that function for some common
     system types.

     DynaLoader Interface Summary













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       @dl_library_path
       @dl_resolve_using
       @dl_require_symbols
       $dl_debug
       @dl_librefs
       @dl_modules
                                                       Implemented in:
       bootstrap($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
       $symref  = dl_find_symbol($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 _d_l__f_i_n_d_f_i_l_e() 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 CCCCoooonnnnffffiiiigggguuuurrrreeee
         ($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, LD_LIBRARYN32_PATH for IRIX -n32
         binaries).

         After initialisation @dl_library_path can be manipulated by an
         application using push and unshift before calling _d_l__f_i_n_d_f_i_l_e().
         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 _d_l__l_o_a_d__f_i_l_e() calls may require an absolute
         pathname.  The _d_l__f_i_n_d_f_i_l_e() 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 _l_o_a_d__f_i_l_e().

         This is only required on some platforms which do not handle dependent
         libraries automatically.  For example the Socket Perl extension



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         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
         _d_l__l_o_a_d__f_i_l_e(), made by bootstrap, in the order in which they were
         loaded.  Can be used with _d_l__f_i_n_d__s_y_m_b_o_l() 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_error()
         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., _d_l_e_r_r_o_r()).

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



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     dl_findfile()
         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 ----llllnnnnaaaammmmeeee 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 ----LLLLddddiiiirrrr.  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));


     dl_expandspec()
         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 _d_l__e_x_p_a_n_d_s_p_e_c() function can be
         implemented either in the _d_l_*._x_s file or code can be added to the
         autoloadable _d_l__e_x_p_a_n_d_s_p_e_c() 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 for more information.

     dl_load_file()
         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.



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         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($filename)
             NeXT:  rld_load($filename, @dl_resolve_using)
             VMS:   lib$find_image_symbol($filename,$dl_require_symbols[0])

         (The _d_l_o_p_e_n() 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.)

     dl_loadflags()
         Syntax:

             $flags = dl_loadflags $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
         _d_l__l_o_a_d__f_i_l_e().

     dl_find_symbol()
         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 _d_l__f_i_n_d__s_y_m_b_o_l() 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, _d_l__i_n_s_t_a_l_l__x_s_u_b().







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


     dl_find_symbol_anywhere()
         Syntax:

             $symref = dl_find_symbol_anywhere($symbol)

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

     dl_undef_symbols()
         Example

             @symbols = dl_undef_symbols()

         Return a list of symbol names which remain undefined after
         _l_o_a_d__f_i_l_e().  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.

     dl_install_xsub()
         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 _n_e_w_X_S_U_B().  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 _d_i_e(), _c_a_l_l_e_r() or the debugger.  If
         $filename is not defined then "DynaLoader" will be used.

     bootstrap()
         Syntax:

         _b_o_o_t_s_t_r_a_p($module)

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

         It performs the following actions:

     +o           locates an auto/$module directory by searching @INC






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     +o           uses _d_l__f_i_n_d_f_i_l_e() to determine the filename to load

     +o           sets @dl_require_symbols to ("boot_$module")

     +o           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)

     +o           calls _d_l__l_o_a_d__f_l_a_g_s() to determine how to load the file.

     +o           calls _d_l__l_o_a_d__f_i_l_e() to load the file

     +o           calls _d_l__u_n_d_e_f__s_y_m_b_o_l_s() and warns if any symbols are
                 undefined

     +o           calls _d_l__f_i_n_d__s_y_m_b_o_l() for "boot_$module"

     +o           calls _d_l__i_n_s_t_a_l_l__x_s_u_b() to install it as
                 "${module}::bootstrap"

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

AAAAUUUUTTTTHHHHOOOORRRR
     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.



















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