libguile/guardians.c

   1 /*      Copyright (C) 1998, 1999 Free Software Foundation, Inc.
   2  *
   3  * This program is free software; you can redistribute it and/or modify
   4  * it under the terms of the GNU General Public License as published by
   5  * the Free Software Foundation; either version 2, or (at your option)
   6  * any later version.
   7  *
   8  * This program is distributed in the hope that it will be useful,
   9  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  11  * GNU General Public License for more details.
  12  *
  13  * You should have received a copy of the GNU General Public License
  14  * along with this software; see the file COPYING.  If not, write to
  15  * the Free Software Foundation, Inc., 59 Temple Place, Suite 330,
  16  * Boston, MA 02111-1307 USA
  17  *
  18  * As a special exception, the Free Software Foundation gives permission
  19  * for additional uses of the text contained in its release of GUILE.
  20  *
  21  * The exception is that, if you link the GUILE library with other files
  22  * to produce an executable, this does not by itself cause the
  23  * resulting executable to be covered by the GNU General Public License.
  24  * Your use of that executable is in no way restricted on account of
  25  * linking the GUILE library code into it.
  26  *
  27  * This exception does not however invalidate any other reasons why
  28  * the executable file might be covered by the GNU General Public License.
  29  *
  30  * This exception applies only to the code released by the
  31  * Free Software Foundation under the name GUILE.  If you copy
  32  * code from other Free Software Foundation releases into a copy of
  33  * GUILE, as the General Public License permits, the exception does
  34  * not apply to the code that you add in this way.  To avoid misleading
  35  * anyone as to the status of such modified files, you must delete
  36  * this exception notice from them.
  37  *
  38  * If you write modifications of your own for GUILE, it is your choice
  39  * whether to permit this exception to apply to your modifications.
  40  * If you do not wish that, delete this exception notice.  */
  41
  42 /* Software engineering face-lift by Greg J. Badros, 11-Dec-1999,
  43    gjb@cs.washington.edu, http://www.cs.washington.edu/homes/gjb */
  44
  45 \f
  46
  47 /* This is an implementation of guardians as described in
  48  * R. Kent Dybvig, Carl Bruggeman, and David Eby (1993) "Guardians in
  49  * a Generation-Based Garbage Collector" ACM SIGPLAN Conference on
  50  * Programming Language Design and Implementation, June 1993
  51  * ftp://ftp.cs.indiana.edu/pub/scheme-repository/doc/pubs/guardians.ps.gz
  52  *
  53  * Author:      Michael N. Livshin
  54  * Modified by: Mikael Djurfeldt
  55  */
  56
  57 #include <stdio.h>
  58 #include <assert.h>
  59
  60 #include "_scm.h"
  61 #include "print.h"
  62 #include "smob.h"
  63 #include "genio.h"
  64
  65 #include "scm_validate.h"
  66 #include "guardians.h"
  67
  68 static long scm_tc16_guardian;
  69
  70 /* The live and zombies FIFOs are implemented as tconcs as described
  71    in Dybvig's paper.  This decouples addition and removal of elements
  72    so that no synchronization between these needs to take place.
  73 */
  74 #define TCONC_IN(tc, obj, pair) \
  75 do { \
  76   SCM_SETCAR ((tc).tail, obj); \
  77   SCM_SETCAR (pair, SCM_BOOL_F); \
  78   SCM_SETCDR (pair, SCM_BOOL_F); \
  79   SCM_SETCDR ((tc).tail, pair); \
  80   (tc).tail = pair; \
  81 } while (0)
  82
  83 #define TCONC_OUT(tc, res) \
  84 do { \
  85   (res) = SCM_CAR ((tc).head); \
  86   (tc).head = SCM_CDR ((tc).head); \
  87 } while (0)
  88
  89 #define TCONC_EMPTYP(tc) ((tc).head == (tc).tail)
  90
  91 typedef struct tconc_t
  92 {
  93   SCM head;
  94   SCM tail;
  95 } tconc_t;
  96
  97 typedef struct guardian_t
  98 {
  99   tconc_t live;
 100   tconc_t zombies;
 101   struct guardian_t *next;
 102 } guardian_t;
 103
 104 #define GUARDIAN(x) ((guardian_t *) SCM_CDR (x))
 105 #define GUARDIAN_LIVE(x) (GUARDIAN (x)->live)
 106 #define GUARDIAN_ZOMBIES(x) (GUARDIAN (x)->zombies)
 107 #define GUARDIAN_NEXT(x) (GUARDIAN (x)->next)
 108
 109 static guardian_t *first_live_guardian = NULL;
 110 static guardian_t **current_link_field = NULL;
 111
 112 static SCM
 113 g_mark (SCM ptr)
 114 {
 115   *current_link_field = GUARDIAN (ptr);
 116   current_link_field = &GUARDIAN_NEXT (ptr);
 117   GUARDIAN_NEXT (ptr) = NULL;
 118
 119   /* Can't mark zombies here since they can refer to objects which are
 120      living dead, thereby preventing them to join the zombies. */
 121   return SCM_BOOL_F;
 122 }
 123
 124 static int
 125 g_print (SCM exp, SCM port, scm_print_state *pstate)
 126 {
 127   char buf[256];
 128   sprintf (buf, "#<guardian live objs: %lu zombies: %lu>",
 129            scm_ilength (SCM_CDR (GUARDIAN_LIVE (exp).head)),
 130            scm_ilength (SCM_CDR (GUARDIAN_ZOMBIES (exp).head)));
 131   scm_puts (buf, port);
 132
 133   return 1;
 134 }
 135
 136 #define CCLO_G(cclo) (SCM_VELTS (cclo)[1])
 137
 138 static SCM
 139 guard (SCM cclo, SCM arg)
 140 {
 141   if (!SCM_UNBNDP (arg))
 142     {
 143       scm_guard (cclo, arg);
 144       return SCM_UNSPECIFIED;
 145     }
 146   else
 147     return scm_get_one_zombie (cclo);
 148 }
 149
 150 static SCM guard1;
 151
 152 SCM_DEFINE (scm_make_guardian, "make-guardian", 0, 0, 0,
 153             (),
 154             "Return a new guardian object.\n"
 155             "A guardian allows dynamically allocated objects to be\n"
 156             "saved from deallocation by the garbage collector so that\n"
 157             "clean up or other actions can be performed using the data\n"
 158             "stored within the objects.\n"
 159             "See R. Kent Dybvig, Carl Bruggeman, and David Eby (1993)\n"
 160             "\"Guardians in a Generation-Based Garbage Collector\".\n"
 161             "ACM SIGPLAN Conference on Programming Language Design\n"
 162             "and Implementation, June 1993\n.")
 163 #define FUNC_NAME s_scm_make_guardian
 164 {
 165   SCM cclo = scm_makcclo (guard1, 2L);
 166   guardian_t *g = SCM_MUST_MALLOC_TYPE(guardian_t);
 167   SCM z1 = scm_cons (SCM_BOOL_F, SCM_BOOL_F);
 168   SCM z2 = scm_cons (SCM_BOOL_F, SCM_BOOL_F);
 169   SCM z;
 170   /* A tconc starts out with one tail pair. */
 171   g->live.head = g->live.tail = z1;
 172   g->zombies.head = g->zombies.tail = z2;
 173
 174   SCM_NEWSMOB (z, scm_tc16_guardian, g);
 175
 176   CCLO_G (cclo) = z;
 177
 178   return cclo;
 179 }
 180 #undef FUNC_NAME
 181
 182 void
 183 scm_guardian_gc_init()
 184 {
 185   current_link_field = &first_live_guardian;
 186   first_live_guardian = NULL;
 187 }
 188
 189 void
 190 scm_guardian_zombify ()
 191 {
 192   guardian_t *g;
 193
 194   /* Note that new guardians may be stuck on the end of the live
 195      guardian list as we run this loop.  As we move unmarked objects
 196      to the zombie list and mark them, we may find some guarded
 197      guardians.  The guardian mark function will stick them on the end
 198      of this list, so they'll be processed properly.  */
 199   for (g = first_live_guardian; g; g = g->next)
 200     {
 201       /* Scan the live list for unmarked objects, and move them to the
 202          zombies tconc.  */
 203       SCM tconc_tail = g->live.tail;
 204       SCM *prev_ptr = &g->live.head;
 205       SCM pair = g->live.head;
 206
 207       while (pair != tconc_tail)
 208         {
 209           SCM next_pair = SCM_CDR (pair);
 210
 211           if (SCM_NMARKEDP (SCM_CAR (pair)))
 212             {
 213               /* got you, zombie! */
 214
 215               /* out of the live list! */
 216               *prev_ptr = next_pair;
 217
 218               /* to the zombie list! */
 219               TCONC_IN (g->zombies, SCM_CAR (pair), pair);
 220             }
 221           else
 222             prev_ptr = SCM_CDRLOC (pair);
 223
 224           pair = next_pair;
 225         }
 226
 227       /* Mark the cells of the live list.  */
 228       for (pair = g->live.head; SCM_NIMP (pair); pair = SCM_GCCDR (pair))
 229         SCM_SETGCMARK (pair);
 230
 231       /* Bring the zombies back from the dead.  */
 232       scm_gc_mark (g->zombies.head);
 233     }
 234 }
 235
 236 void
 237 scm_guard (SCM guardian, SCM obj)
 238 {
 239   SCM g = CCLO_G (guardian);
 240
 241   if (SCM_NIMP (obj))
 242     {
 243       SCM z;
 244
 245       SCM_NEWCELL (z);
 246
 247       /* This critical section barrier will be replaced by a mutex. */
 248       SCM_DEFER_INTS;
 249       TCONC_IN (GUARDIAN_LIVE (g), obj, z);
 250       SCM_ALLOW_INTS;
 251     }
 252 }
 253
 254 SCM
 255 scm_get_one_zombie (SCM guardian)
 256 {
 257   SCM g = CCLO_G (guardian);
 258   SCM res = SCM_BOOL_F;
 259
 260   /* This critical section barrier will be replaced by a mutex. */
 261   SCM_DEFER_INTS;
 262   if (!TCONC_EMPTYP (GUARDIAN_ZOMBIES (g)))
 263     TCONC_OUT (GUARDIAN_ZOMBIES (g), res);
 264   SCM_ALLOW_INTS;
 265
 266   return res;
 267 }
 268
 269 void
 270 scm_init_guardian()
 271 {
 272   scm_tc16_guardian = scm_make_smob_type_mfpe ("guardian", sizeof (guardian_t),
 273                                               g_mark, NULL, g_print, NULL);
 274   guard1 = scm_make_subr_opt ("guardian", scm_tc7_subr_2o, guard, 0);
 275
 276 #include "guardians.x"
 277 }