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 "")
 155 #define FUNC_NAME s_scm_make_guardian
 156 {
 157   SCM cclo = scm_makcclo (guard1, 2L);
 158   guardian_t *g = SCM_MUST_MALLOC_TYPE(guardian_t);
 159   SCM z1 = scm_cons (SCM_BOOL_F, SCM_BOOL_F);
 160   SCM z2 = scm_cons (SCM_BOOL_F, SCM_BOOL_F);
 161   SCM z;
 162   /* A tconc starts out with one tail pair. */
 163   g->live.head = g->live.tail = z1;
 164   g->zombies.head = g->zombies.tail = z2;
 165
 166   SCM_NEWSMOB (z, scm_tc16_guardian, g);
 167
 168   CCLO_G (cclo) = z;
 169
 170   return cclo;
 171 }
 172 #undef FUNC_NAME
 173
 174 void
 175 scm_guardian_gc_init()
 176 {
 177   current_link_field = &first_live_guardian;
 178   first_live_guardian = NULL;
 179 }
 180
 181 void
 182 scm_guardian_zombify ()
 183 {
 184   guardian_t *g;
 185
 186   /* Note that new guardians may be stuck on the end of the live
 187      guardian list as we run this loop.  As we move unmarked objects
 188      to the zombie list and mark them, we may find some guarded
 189      guardians.  The guardian mark function will stick them on the end
 190      of this list, so they'll be processed properly.  */
 191   for (g = first_live_guardian; g; g = g->next)
 192     {
 193       /* Scan the live list for unmarked objects, and move them to the
 194          zombies tconc.  */
 195       SCM tconc_tail = g->live.tail;
 196       SCM *prev_ptr = &g->live.head;
 197       SCM pair = g->live.head;
 198
 199       while (pair != tconc_tail)
 200         {
 201           SCM next_pair = SCM_CDR (pair);
 202
 203           if (SCM_NMARKEDP (SCM_CAR (pair)))
 204             {
 205               /* got you, zombie! */
 206
 207               /* out of the live list! */
 208               *prev_ptr = next_pair;
 209
 210               /* to the zombie list! */
 211               TCONC_IN (g->zombies, SCM_CAR (pair), pair);
 212             }
 213           else
 214             prev_ptr = SCM_CDRLOC (pair);
 215
 216           pair = next_pair;
 217         }
 218
 219       /* Mark the cells of the live list.  */
 220       for (pair = g->live.head; SCM_NIMP (pair); pair = SCM_GCCDR (pair))
 221         SCM_SETGCMARK (pair);
 222
 223       /* Bring the zombies back from the dead.  */
 224       scm_gc_mark (g->zombies.head);
 225     }
 226 }
 227
 228 void
 229 scm_guard (SCM guardian, SCM obj)
 230 {
 231   SCM g = CCLO_G (guardian);
 232
 233   if (SCM_NIMP (obj))
 234     {
 235       SCM z;
 236
 237       SCM_NEWCELL (z);
 238
 239       /* This critical section barrier will be replaced by a mutex. */
 240       SCM_DEFER_INTS;
 241       TCONC_IN (GUARDIAN_LIVE (g), obj, z);
 242       SCM_ALLOW_INTS;
 243     }
 244 }
 245
 246 SCM
 247 scm_get_one_zombie (SCM guardian)
 248 {
 249   SCM g = CCLO_G (guardian);
 250   SCM res = SCM_BOOL_F;
 251
 252   /* This critical section barrier will be replaced by a mutex. */
 253   SCM_DEFER_INTS;
 254   if (!TCONC_EMPTYP (GUARDIAN_ZOMBIES (g)))
 255     TCONC_OUT (GUARDIAN_ZOMBIES (g), res);
 256   SCM_ALLOW_INTS;
 257
 258   return res;
 259 }
 260
 261 void
 262 scm_init_guardian()
 263 {
 264   scm_tc16_guardian = scm_make_smob_type_mfpe ("guardian", sizeof (guardian_t),
 265                                               g_mark, NULL, g_print, NULL);
 266   guard1 = scm_make_subr_opt ("guardian", scm_tc7_subr_2o, guard, 0);
 267
 268 #include "guardians.x"
 269 }