guile/libguile/extensions.c

/* extensions.c - registering and loading extensions.
 *
 * Copyright (C) 2001 Free Software Foundation, Inc.
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2, or (at your option)
 * any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this software; see the file COPYING.  If not, write to
 * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
 * Boston, MA 02110-1301 USA
 *
 * As a special exception, the Free Software Foundation gives permission
 * for additional uses of the text contained in its release of GUILE.
 *
 * The exception is that, if you link the GUILE library with other files
 * to produce an executable, this does not by itself cause the
 * resulting executable to be covered by the GNU General Public License.
 * Your use of that executable is in no way restricted on account of
 * linking the GUILE library code into it.
 *
 * This exception does not however invalidate any other reasons why
 * the executable file might be covered by the GNU General Public License.
 *
 * This exception applies only to the code released by the
 * Free Software Foundation under the name GUILE.  If you copy
 * code from other Free Software Foundation releases into a copy of
 * GUILE, as the General Public License permits, the exception does
 * not apply to the code that you add in this way.  To avoid misleading
 * anyone as to the status of such modified files, you must delete
 * this exception notice from them.
 *
 * If you write modifications of your own for GUILE, it is your choice
 * whether to permit this exception to apply to your modifications.
 * If you do not wish that, delete this exception notice.  */

#include <string.h>

#include "libguile/_scm.h"
#include "libguile/strings.h"
#include "libguile/gc.h"
#include "libguile/dynl.h"

#include "libguile/extensions.h"

typedef struct extension_t
{
  struct extension_t *next;
  const char *lib;
  const char *init;
  void (*func)(void *);
  void *data;
} extension_t;

static extension_t *registered_extensions;

/* Register a LIB/INIT pair for use by `scm_load_extension'.  LIB is
   allowed to be NULL and then only INIT is used to identify the
   registered entry.  This is useful when you don't know the library
   name (which isn't really relevant anyway in a completely linked
   program) and you are sure that INIT is unique (which it must be for
   static linking).  Hmm, given this reasoning, what use is LIB
   anyway?
*/

void
scm_c_register_extension (const char *lib, const char *init,
			  void (*func) (void *), void *data)
{
  extension_t *ext = scm_must_malloc (sizeof(extension_t),
					   "scm_register_extension");
  if (lib)
    ext->lib = scm_must_strdup (lib);
  else
    ext->lib = NULL;
  ext->init = scm_must_strdup (init);
  ext->func = func;
  ext->data = data;

  ext->next = registered_extensions;
  registered_extensions = ext;
}

static void
load_extension (SCM lib, SCM init)
{
  /* Search the registry. */
  {
    extension_t *ext;

    for (ext = registered_extensions; ext; ext = ext->next)
      if ((ext->lib == NULL || !strcmp (ext->lib, SCM_STRING_CHARS (lib)))
	  && !strcmp (ext->init, SCM_STRING_CHARS (init)))
	{
	  ext->func (ext->data);
	  return;
	}
  }

  /* Dynamically link the library. */

  scm_dynamic_call (init, scm_dynamic_link (lib));
}

void
scm_c_load_extension (const char *lib, const char *init)
{
  load_extension (scm_makfrom0str (lib), scm_makfrom0str (init));
}

SCM_DEFINE (scm_load_extension, "load-extension", 2, 0, 0,
	    (SCM lib, SCM init),
	    "Load and initialize the extension designated by LIB and INIT.\n"
	    "When there is no pre-registered function for LIB/INIT, this is\n"
	    "equivalent to\n"
	    "\n"
	    "@lisp\n"
	    "(dynamic-call INIT (dynamic-link LIB))\n"
	    "@end lisp\n"
	    "\n"
	    "When there is a pre-registered function, that function is called\n"
	    "instead.\n"
	    "\n"
	    "Normally, there is no pre-registered function.  This option exists\n"
	    "only for situations where dynamic linking is unavailable or unwanted.\n"
	    "In that case, you would statically link your program with the desired\n"
	    "library, and register its init function right after Guile has been\n"
	    "initialized.\n"
	    "\n"
	    "LIB should be a string denoting a shared library without any file type\n"
	    "suffix such as \".so\".  The suffix is provided automatically.  It\n"
	    "should also not contain any directory components.  Libraries that\n"
	    "implement Guile Extensions should be put into the normal locations for\n"
	    "shared libraries.  We recommend to use the naming convention\n"
	    "libguile-bla-blum for a extension related to a module `(bla blum)'.\n"
	    "\n"
	    "The normal way for a extension to be used is to write a small Scheme\n"
	    "file that defines a module, and to load the extension into this\n"
	    "module.  When the module is auto-loaded, the extension is loaded as\n"
	    "well.  For example,\n"
	    "\n"
	    "@lisp\n"
	    "(define-module (bla blum))\n"
	    "\n"
	    "(load-extension \"libguile-bla-blum\" \"bla_init_blum\")\n"
	    "@end lisp")
#define FUNC_NAME s_scm_load_extension
{
  SCM_VALIDATE_STRING (1, lib);
  SCM_VALIDATE_STRING (2, init);
  load_extension (lib, init);
  return SCM_UNSPECIFIED;
}
#undef FUNC_NAME

void
scm_init_extensions ()
{
  registered_extensions = NULL;
#include "libguile/extensions.x"
}

/*
  Local Variables:
  c-file-style: "gnu"
  End:
*/