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 "ports.h"
  62 #include "print.h"
  63 #include "smob.h"
  64 #include "vectors.h"
  65
  66 #include "validate.h"
  67 #include "guardians.h"
  68
  69 static long scm_tc16_guardian;
  70
  71 /* The live and zombies FIFOs are implemented as tconcs as described
  72    in Dybvig's paper.  This decouples addition and removal of elements
  73    so that no synchronization between these needs to take place.
  74 */
  75 #define TCONC_IN(tc, obj, pair) \
  76 do { \
  77   SCM_SETCAR ((tc).tail, obj); \
  78   SCM_SETCAR (pair, SCM_BOOL_F); \
  79   SCM_SETCDR (pair, SCM_BOOL_F); \
  80   SCM_SETCDR ((tc).tail, pair); \
  81   (tc).tail = pair; \
  82 } while (0)
  83
  84 #define TCONC_OUT(tc, res) \
  85 do { \
  86   (res) = SCM_CAR ((tc).head); \
  87   (tc).head = SCM_CDR ((tc).head); \
  88 } while (0)
  89
  90 #define TCONC_EMPTYP(tc) ((tc).head == (tc).tail)
  91
  92 typedef struct tconc_t
  93 {
  94   SCM head;
  95   SCM tail;
  96 } tconc_t;
  97
  98 typedef struct guardian_t
  99 {
 100   tconc_t live;
 101   tconc_t zombies;
 102   struct guardian_t *next;
 103 } guardian_t;
 104
 105 #define GUARDIAN(x) ((guardian_t *) SCM_CDR (x))
 106 #define GUARDIAN_LIVE(x) (GUARDIAN (x)->live)
 107 #define GUARDIAN_ZOMBIES(x) (GUARDIAN (x)->zombies)
 108 #define GUARDIAN_NEXT(x) (GUARDIAN (x)->next)
 109
 110 static guardian_t *first_live_guardian = NULL;
 111 static guardian_t **current_link_field = NULL;
 112
 113 static SCM
 114 g_mark (SCM ptr)
 115 {
 116   *current_link_field = GUARDIAN (ptr);
 117   current_link_field = &GUARDIAN_NEXT (ptr);
 118   GUARDIAN_NEXT (ptr) = NULL;
 119
 120   /* Can't mark zombies here since they can refer to objects which are
 121      living dead, thereby preventing them to join the zombies. */
 122   return SCM_BOOL_F;
 123 }
 124
 125 static int
 126 g_print (SCM exp, SCM port, scm_print_state *pstate)
 127 {
 128   char buf[256];
 129   sprintf (buf, "#<guardian live objs: %lu zombies: %lu>",
 130            scm_ilength (SCM_CDR (GUARDIAN_LIVE (exp).head)),
 131            scm_ilength (SCM_CDR (GUARDIAN_ZOMBIES (exp).head)));
 132   scm_puts (buf, port);
 133
 134   return 1;
 135 }
 136
 137 #define CCLO_G(cclo) (SCM_VELTS (cclo)[1])
 138
 139 static SCM
 140 guard (SCM cclo, SCM arg)
 141 {
 142   if (!SCM_UNBNDP (arg))
 143     {
 144       scm_guard (cclo, arg);
 145       return SCM_UNSPECIFIED;
 146     }
 147   else
 148     return scm_get_one_zombie (cclo);
 149 }
 150
 151 static SCM guard1;
 152
 153 SCM_DEFINE (scm_make_guardian, "make-guardian", 0, 0, 0,
 154             (),
 155             "Return a new guardian object.\n"
 156             "A guardian allows dynamically allocated objects to be\n"
 157             "saved from deallocation by the garbage collector so that\n"
 158             "clean up or other actions can be performed using the data\n"
 159             "stored within the objects.\n"
 160             "See R. Kent Dybvig, Carl Bruggeman, and David Eby (1993)\n"
 161             "\"Guardians in a Generation-Based Garbage Collector\".\n"
 162             "ACM SIGPLAN Conference on Programming Language Design\n"
 163             "and Implementation, June 1993\n.")
 164 #define FUNC_NAME s_scm_make_guardian
 165 {
 166   SCM cclo = scm_makcclo (guard1, 2L);
 167   guardian_t *g = SCM_MUST_MALLOC_TYPE(guardian_t);
 168   SCM z1 = scm_cons (SCM_BOOL_F, SCM_BOOL_F);
 169   SCM z2 = scm_cons (SCM_BOOL_F, SCM_BOOL_F);
 170   SCM z;
 171   /* A tconc starts out with one tail pair. */
 172   g->live.head = g->live.tail = z1;
 173   g->zombies.head = g->zombies.tail = z2;
 174
 175   SCM_NEWSMOB (z, scm_tc16_guardian, g);
 176
 177   CCLO_G (cclo) = z;
 178
 179   return cclo;
 180 }
 181 #undef FUNC_NAME
 182
 183 void
 184 scm_guardian_gc_init()
 185 {
 186   current_link_field = &first_live_guardian;
 187   first_live_guardian = NULL;
 188 }
 189
 190 void
 191 scm_guardian_zombify ()
 192 {
 193   guardian_t *g;
 194
 195   /* Note that new guardians may be stuck on the end of the live
 196      guardian list as we run this loop.  As we move unmarked objects
 197      to the zombie list and mark them, we may find some guarded
 198      guardians.  The guardian mark function will stick them on the end
 199      of this list, so they'll be processed properly.  */
 200   for (g = first_live_guardian; g; g = g->next)
 201     {
 202       /* Scan the live list for unmarked objects, and move them to the
 203          zombies tconc.  */
 204       SCM tconc_tail = g->live.tail;
 205       SCM *prev_ptr = &g->live.head;
 206       SCM pair = g->live.head;
 207
 208       while (pair != tconc_tail)
 209         {
 210           SCM next_pair = SCM_CDR (pair);
 211
 212           if (SCM_NMARKEDP (SCM_CAR (pair)))
 213             {
 214               /* got you, zombie! */
 215
 216               /* out of the live list! */
 217               *prev_ptr = next_pair;
 218
 219               /* to the zombie list! */
 220               TCONC_IN (g->zombies, SCM_CAR (pair), pair);
 221             }
 222           else
 223             prev_ptr = SCM_CDRLOC (pair);
 224
 225           pair = next_pair;
 226         }
 227
 228       /* Mark the cells of the live list.  */
 229       for (pair = g->live.head; SCM_NIMP (pair); pair = SCM_GCCDR (pair))
 230         SCM_SETGCMARK (pair);
 231
 232       /* Bring the zombies back from the dead.  */
 233       scm_gc_mark (g->zombies.head);
 234     }
 235 }
 236
 237 void
 238 scm_guard (SCM guardian, SCM obj)
 239 {
 240   SCM g = CCLO_G (guardian);
 241
 242   if (SCM_NIMP (obj))
 243     {
 244       SCM z;
 245
 246       SCM_NEWCELL (z);
 247
 248       /* This critical section barrier will be replaced by a mutex. */
 249       SCM_DEFER_INTS;
 250       TCONC_IN (GUARDIAN_LIVE (g), obj, z);
 251       SCM_ALLOW_INTS;
 252     }
 253 }
 254
 255 SCM
 256 scm_get_one_zombie (SCM guardian)
 257 {
 258   SCM g = CCLO_G (guardian);
 259   SCM res = SCM_BOOL_F;
 260
 261   /* This critical section barrier will be replaced by a mutex. */
 262   SCM_DEFER_INTS;
 263   if (!TCONC_EMPTYP (GUARDIAN_ZOMBIES (g)))
 264     TCONC_OUT (GUARDIAN_ZOMBIES (g), res);
 265   SCM_ALLOW_INTS;
 266
 267   return res;
 268 }
 269
 270 void
 271 scm_init_guardian()
 272 {
 273   scm_tc16_guardian = scm_make_smob_type_mfpe ("guardian", sizeof (guardian_t),
 274                                               g_mark, NULL, g_print, NULL);
 275   guard1 = scm_make_subr_opt ("guardian", scm_tc7_subr_2o, guard, 0);
 276
 277 #include "guardians.x"
 278 }