libguile/weaks.c

   1 /* Copyright (C) 1995, 1996, 1998, 2000, 2001, 2003, 2006, 2008, 2009, 2010,
   2  *   2011, 2012 Free Software Foundation, Inc.
   3  *
   4  * This library is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU Lesser General Public License
   6  * as published by the Free Software Foundation; either version 3 of
   7  * the License, or (at your option) any later version.
   8  *
   9  * This library is distributed in the hope that it will be useful, but
  10  * WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12  * Lesser General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU Lesser General Public
  15  * License along with this library; if not, write to the Free Software
  16  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  17  * 02110-1301 USA
  18  */
  19
  20
  21 \f
  22 #ifdef HAVE_CONFIG_H
  23 # include <config.h>
  24 #endif
  25
  26 #include <stdio.h>
  27
  28 #include "libguile/_scm.h"
  29 #include "libguile/vectors.h"
  30 #include "libguile/hashtab.h"
  31
  32 #include "libguile/validate.h"
  33 #include "libguile/weaks.h"
  34
  35 #include "libguile/bdw-gc.h"
  36 #include <gc/gc_typed.h>
  37
  38
  39 \f
  40 /* Weak pairs for use in weak alist vectors and weak hash tables.
  41
  42    We have weal-car pairs, weak-cdr pairs, and doubly weak pairs.  In weak
  43    pairs, the weak component(s) are not scanned for pointers and are
  44    registered as disapperaring links; therefore, the weak component may be
  45    set to NULL by the garbage collector when no other reference to that word
  46    exist.  Thus, users should only access weak pairs via the
  47    `SCM_WEAK_PAIR_C[AD]R ()' macros.  See also `scm_fixup_weak_alist ()' in
  48    `hashtab.c'.  */
  49
  50 /* Type descriptors for weak-c[ad]r pairs.  */
  51 static GC_descr wcar_pair_descr, wcdr_pair_descr;
  52
  53
  54 SCM
  55 scm_weak_car_pair (SCM car, SCM cdr)
  56 {
  57   scm_t_cell *cell;
  58
  59   cell = (scm_t_cell *)GC_malloc_explicitly_typed (sizeof (*cell),
  60                                                    wcar_pair_descr);
  61
  62   cell->word_0 = car;
  63   cell->word_1 = cdr;
  64
  65   if (SCM_NIMP (car))
  66     /* Weak car cells make sense iff the car is non-immediate.  */
  67     SCM_I_REGISTER_DISAPPEARING_LINK ((void **) &cell->word_0, SCM2PTR (car));
  68
  69   return (SCM_PACK (cell));
  70 }
  71
  72 SCM
  73 scm_weak_cdr_pair (SCM car, SCM cdr)
  74 {
  75   scm_t_cell *cell;
  76
  77   cell = (scm_t_cell *)GC_malloc_explicitly_typed (sizeof (*cell),
  78                                                    wcdr_pair_descr);
  79
  80   cell->word_0 = car;
  81   cell->word_1 = cdr;
  82
  83   if (SCM_NIMP (cdr))
  84     /* Weak cdr cells make sense iff the cdr is non-immediate.  */
  85     SCM_I_REGISTER_DISAPPEARING_LINK ((void **) &cell->word_1, SCM2PTR (cdr));
  86
  87   return (SCM_PACK (cell));
  88 }
  89
  90 SCM
  91 scm_doubly_weak_pair (SCM car, SCM cdr)
  92 {
  93   /* Doubly weak cells shall not be scanned at all for pointers.  */
  94   scm_t_cell *cell = (scm_t_cell *)scm_gc_malloc_pointerless (sizeof (*cell),
  95                                                               "weak cell");
  96
  97   cell->word_0 = car;
  98   cell->word_1 = cdr;
  99
 100   if (SCM_NIMP (car))
 101     SCM_I_REGISTER_DISAPPEARING_LINK ((void **) &cell->word_0, SCM2PTR (car));
 102   if (SCM_NIMP (cdr))
 103     SCM_I_REGISTER_DISAPPEARING_LINK ((void **) &cell->word_1, SCM2PTR (cdr));
 104
 105   return (SCM_PACK (cell));
 106 }
 107
 108
 109 \f
 110
 111 /* 1. The current hash table implementation in hashtab.c uses weak alist
 112  *    vectors (formerly called weak hash tables) internally.
 113  *
 114  * 2. All hash table operations still work on alist vectors.
 115  *
 116  * 3. The weak vector and alist vector Scheme API is accessed through
 117  *    the module (ice-9 weak-vector).
 118  */
 119
 120
 121 /* {Weak Vectors}
 122  */
 123
 124
 125 SCM_DEFINE (scm_make_weak_vector, "make-weak-vector", 1, 1, 0,
 126             (SCM size, SCM fill),
 127             "Return a weak vector with @var{size} elements. If the optional\n"
 128             "argument @var{fill} is given, all entries in the vector will be\n"
 129             "set to @var{fill}. The default value for @var{fill} is the\n"
 130             "empty list.")
 131 #define FUNC_NAME s_scm_make_weak_vector
 132 {
 133   return scm_i_make_weak_vector (0, size, fill);
 134 }
 135 #undef FUNC_NAME
 136
 137
 138 SCM_REGISTER_PROC(s_list_to_weak_vector, "list->weak-vector", 1, 0, 0, scm_weak_vector);
 139
 140 SCM_DEFINE (scm_weak_vector, "weak-vector", 0, 0, 1,
 141            (SCM l),
 142             "@deffnx {Scheme Procedure} list->weak-vector l\n"
 143             "Construct a weak vector from a list: @code{weak-vector} uses\n"
 144             "the list of its arguments while @code{list->weak-vector} uses\n"
 145             "its only argument @var{l} (a list) to construct a weak vector\n"
 146             "the same way @code{list->vector} would.")
 147 #define FUNC_NAME s_scm_weak_vector
 148 {
 149   return scm_i_make_weak_vector_from_list (0, l);
 150 }
 151 #undef FUNC_NAME
 152
 153
 154 SCM_DEFINE (scm_weak_vector_p, "weak-vector?", 1, 0, 0,
 155             (SCM obj),
 156             "Return @code{#t} if @var{obj} is a weak vector. Note that all\n"
 157             "weak hashes are also weak vectors.")
 158 #define FUNC_NAME s_scm_weak_vector_p
 159 {
 160   return scm_from_bool (SCM_I_WVECTP (obj) && !SCM_IS_WHVEC (obj));
 161 }
 162 #undef FUNC_NAME
 163
 164 \f
 165 /* Weak alist vectors, i.e., vectors of alists.
 166
 167    The alist vector themselves are _not_ weak.  The `car' (or `cdr', or both)
 168    of the pairs within it are weak.  See `hashtab.c' for details.  */
 169
 170
 171 /* FIXME: We used to have two implementations of weak hash tables: the one in
 172    here and the one in `hashtab.c'.  The difference is that weak alist
 173    vectors could be used as vectors while (weak) hash tables can't.  We need
 174    to unify that.  */
 175
 176 SCM_DEFINE (scm_make_weak_key_alist_vector, "make-weak-key-alist-vector", 0, 1, 0,
 177             (SCM size),
 178             "@deffnx {Scheme Procedure} make-weak-value-alist-vector size\n"
 179             "@deffnx {Scheme Procedure} make-doubly-weak-alist-vector size\n"
 180             "Return a weak hash table with @var{size} buckets. As with any\n"
 181             "hash table, choosing a good size for the table requires some\n"
 182             "caution.\n"
 183             "\n"
 184             "You can modify weak hash tables in exactly the same way you\n"
 185             "would modify regular hash tables. (@pxref{Hash Tables})")
 186 #define FUNC_NAME s_scm_make_weak_key_alist_vector
 187 {
 188   return scm_make_weak_key_hash_table (size);
 189 }
 190 #undef FUNC_NAME
 191
 192
 193 SCM_DEFINE (scm_make_weak_value_alist_vector, "make-weak-value-alist-vector", 0, 1, 0,
 194             (SCM size),
 195             "Return a hash table with weak values with @var{size} buckets.\n"
 196             "(@pxref{Hash Tables})")
 197 #define FUNC_NAME s_scm_make_weak_value_alist_vector
 198 {
 199   return scm_make_weak_value_hash_table (size);
 200 }
 201 #undef FUNC_NAME
 202
 203
 204 SCM_DEFINE (scm_make_doubly_weak_alist_vector, "make-doubly-weak-alist-vector", 1, 0, 0,
 205             (SCM size),
 206             "Return a hash table with weak keys and values with @var{size}\n"
 207             "buckets.  (@pxref{Hash Tables})")
 208 #define FUNC_NAME s_scm_make_doubly_weak_alist_vector
 209 {
 210   return scm_make_doubly_weak_hash_table (size);
 211 }
 212 #undef FUNC_NAME
 213
 214
 215 SCM_DEFINE (scm_weak_key_alist_vector_p, "weak-key-alist-vector?", 1, 0, 0,
 216            (SCM obj),
 217             "@deffnx {Scheme Procedure} weak-value-alist-vector? obj\n"
 218             "@deffnx {Scheme Procedure} doubly-weak-alist-vector? obj\n"
 219             "Return @code{#t} if @var{obj} is the specified weak hash\n"
 220             "table. Note that a doubly weak hash table is neither a weak key\n"
 221             "nor a weak value hash table.")
 222 #define FUNC_NAME s_scm_weak_key_alist_vector_p
 223 {
 224   return scm_from_bool (SCM_I_WVECTP (obj) && SCM_IS_WHVEC (obj));
 225 }
 226 #undef FUNC_NAME
 227
 228
 229 SCM_DEFINE (scm_weak_value_alist_vector_p, "weak-value-alist-vector?", 1, 0, 0,
 230             (SCM obj),
 231             "Return @code{#t} if @var{obj} is a weak value hash table.")
 232 #define FUNC_NAME s_scm_weak_value_alist_vector_p
 233 {
 234   return scm_from_bool (SCM_I_WVECTP (obj) && SCM_IS_WHVEC_V (obj));
 235 }
 236 #undef FUNC_NAME
 237
 238
 239 SCM_DEFINE (scm_doubly_weak_alist_vector_p, "doubly-weak-alist-vector?", 1, 0, 0,
 240             (SCM obj),
 241             "Return @code{#t} if @var{obj} is a doubly weak hash table.")
 242 #define FUNC_NAME s_scm_doubly_weak_alist_vector_p
 243 {
 244   return scm_from_bool (SCM_I_WVECTP (obj) && SCM_IS_WHVEC_B (obj));
 245 }
 246 #undef FUNC_NAME
 247
 248
 249
 250 \f
 251 SCM
 252 scm_init_weaks_builtins ()
 253 {
 254 #include "libguile/weaks.x"
 255   return SCM_UNSPECIFIED;
 256 }
 257
 258 void
 259 scm_weaks_prehistory ()
 260 {
 261   /* Initialize weak pairs.  */
 262   GC_word wcar_pair_bitmap[GC_BITMAP_SIZE (scm_t_cell)] = { 0 };
 263   GC_word wcdr_pair_bitmap[GC_BITMAP_SIZE (scm_t_cell)] = { 0 };
 264
 265   /* In a weak-car pair, only the second word must be scanned for
 266      pointers.  */
 267   GC_set_bit (wcar_pair_bitmap, GC_WORD_OFFSET (scm_t_cell, word_1));
 268   wcar_pair_descr = GC_make_descriptor (wcar_pair_bitmap,
 269                                         GC_WORD_LEN (scm_t_cell));
 270
 271   /* Conversely, in a weak-cdr pair, only the first word must be scanned for
 272      pointers.  */
 273   GC_set_bit (wcdr_pair_bitmap, GC_WORD_OFFSET (scm_t_cell, word_0));
 274   wcdr_pair_descr = GC_make_descriptor (wcdr_pair_bitmap,
 275                                         GC_WORD_LEN (scm_t_cell));
 276
 277 }
 278
 279 void
 280 scm_init_weaks ()
 281 {
 282   scm_c_define_gsubr ("%init-weaks-builtins", 0, 0, 0,
 283                       scm_init_weaks_builtins);
 284 }
 285
 286
 287 /*
 288   Local Variables:
 289   c-file-style: "gnu"
 290   End:
 291 */