libguile/weaks.c

   1 /* Copyright (C) 1995,1996,1998,2000,2001, 2003, 2006, 2008, 2009 Free Software Foundation, Inc.
   2  *
   3  * This library is free software; you can redistribute it and/or
   4  * modify it under the terms of the GNU Lesser General Public
   5  * License as published by the Free Software Foundation; either
   6  * version 2.1 of the License, or (at your option) any later version.
   7  *
   8  * This library 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 GNU
  11  * Lesser General Public License for more details.
  12  *
  13  * You should have received a copy of the GNU Lesser General Public
  14  * License along with this library; if not, write to the Free Software
  15  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  16  */
  17
  18
  19 \f
  20 #ifdef HAVE_CONFIG_H
  21 # include <config.h>
  22 #endif
  23
  24 #include <stdio.h>
  25
  26 #include "libguile/_scm.h"
  27 #include "libguile/vectors.h"
  28 #include "libguile/lang.h"
  29 #include "libguile/hashtab.h"
  30
  31 #include "libguile/validate.h"
  32 #include "libguile/weaks.h"
  33
  34 #include "libguile/boehm-gc.h"
  35 #include <gc/gc_typed.h>
  36
  37
  38 \f
  39 /* Weak pairs for use in weak alist vectors and weak hash tables.
  40
  41    We have weal-car pairs, weak-cdr pairs, and doubly weak pairs.  In weak
  42    pairs, the weak component(s) are not scanned for pointers and are
  43    registered as disapperaring links; therefore, the weak component may be
  44    set to NULL by the garbage collector when no other reference to that word
  45    exist.  Thus, users should only access weak pairs via the
  46    `SCM_WEAK_PAIR_C[AD]R ()' macros.  See also `scm_fixup_weak_alist ()' in
  47    `hashtab.c'.  */
  48
  49 /* Type descriptors for weak-c[ad]r pairs.  */
  50 static GC_descr wcar_pair_descr, wcdr_pair_descr;
  51
  52
  53 SCM
  54 scm_weak_car_pair (SCM car, SCM cdr)
  55 {
  56   scm_t_cell *cell;
  57
  58   cell = (scm_t_cell *)GC_malloc_explicitly_typed (sizeof (*cell),
  59                                                    wcar_pair_descr);
  60
  61   cell->word_0 = car;
  62   cell->word_1 = cdr;
  63
  64   if (SCM_NIMP (car))
  65     {
  66       /* Weak car cells make sense iff the car is non-immediate.  */
  67       SCM_I_REGISTER_DISAPPEARING_LINK ((GC_PTR) &cell->word_0,
  68                                         (GC_PTR) SCM_UNPACK (car));
  69     }
  70
  71   return (SCM_PACK (cell));
  72 }
  73
  74 SCM
  75 scm_weak_cdr_pair (SCM car, SCM cdr)
  76 {
  77   scm_t_cell *cell;
  78
  79   cell = (scm_t_cell *)GC_malloc_explicitly_typed (sizeof (*cell),
  80                                                    wcdr_pair_descr);
  81
  82   cell->word_0 = car;
  83   cell->word_1 = cdr;
  84
  85   if (SCM_NIMP (cdr))
  86     {
  87       /* Weak cdr cells make sense iff the cdr is non-immediate.  */
  88       SCM_I_REGISTER_DISAPPEARING_LINK ((GC_PTR) &cell->word_1,
  89                                         (GC_PTR) SCM_UNPACK (cdr));
  90     }
  91
  92   return (SCM_PACK (cell));
  93 }
  94
  95 SCM
  96 scm_doubly_weak_pair (SCM car, SCM cdr)
  97 {
  98   /* Doubly weak cells shall not be scanned at all for pointers.  */
  99   scm_t_cell *cell = (scm_t_cell *)scm_gc_malloc_pointerless (sizeof (*cell),
 100                                                               "weak cell");
 101
 102   cell->word_0 = car;
 103   cell->word_1 = cdr;
 104
 105   if (SCM_NIMP (car))
 106     {
 107       SCM_I_REGISTER_DISAPPEARING_LINK ((GC_PTR) &cell->word_0,
 108                                         (GC_PTR) SCM_UNPACK (car));
 109     }
 110   if (SCM_NIMP (cdr))
 111     {
 112       SCM_I_REGISTER_DISAPPEARING_LINK ((GC_PTR) &cell->word_1,
 113                                         (GC_PTR) SCM_UNPACK (cdr));
 114     }
 115
 116   return (SCM_PACK (cell));
 117 }
 118
 119
 120 \f
 121
 122 /* 1. The current hash table implementation in hashtab.c uses weak alist
 123  *    vectors (formerly called weak hash tables) internally.
 124  *
 125  * 2. All hash table operations still work on alist vectors.
 126  *
 127  * 3. The weak vector and alist vector Scheme API is accessed through
 128  *    the module (ice-9 weak-vector).
 129  */
 130
 131
 132 /* {Weak Vectors}
 133  */
 134
 135
 136 SCM_DEFINE (scm_make_weak_vector, "make-weak-vector", 1, 1, 0,
 137             (SCM size, SCM fill),
 138             "Return a weak vector with @var{size} elements. If the optional\n"
 139             "argument @var{fill} is given, all entries in the vector will be\n"
 140             "set to @var{fill}. The default value for @var{fill} is the\n"
 141             "empty list.")
 142 #define FUNC_NAME s_scm_make_weak_vector
 143 {
 144   return scm_i_make_weak_vector (0, size, fill);
 145 }
 146 #undef FUNC_NAME
 147
 148
 149 SCM_REGISTER_PROC(s_list_to_weak_vector, "list->weak-vector", 1, 0, 0, scm_weak_vector);
 150
 151 SCM_DEFINE (scm_weak_vector, "weak-vector", 0, 0, 1,
 152            (SCM l),
 153             "@deffnx {Scheme Procedure} list->weak-vector l\n"
 154             "Construct a weak vector from a list: @code{weak-vector} uses\n"
 155             "the list of its arguments while @code{list->weak-vector} uses\n"
 156             "its only argument @var{l} (a list) to construct a weak vector\n"
 157             "the same way @code{list->vector} would.")
 158 #define FUNC_NAME s_scm_weak_vector
 159 {
 160   return scm_i_make_weak_vector_from_list (0, l);
 161 }
 162 #undef FUNC_NAME
 163
 164
 165 SCM_DEFINE (scm_weak_vector_p, "weak-vector?", 1, 0, 0,
 166             (SCM obj),
 167             "Return @code{#t} if @var{obj} is a weak vector. Note that all\n"
 168             "weak hashes are also weak vectors.")
 169 #define FUNC_NAME s_scm_weak_vector_p
 170 {
 171   return scm_from_bool (SCM_I_WVECTP (obj) && !SCM_IS_WHVEC (obj));
 172 }
 173 #undef FUNC_NAME
 174
 175 \f
 176 /* Weak alist vectors, i.e., vectors of alists.
 177
 178    The alist vector themselves are _not_ weak.  The `car' (or `cdr', or both)
 179    of the pairs within it are weak.  See `hashtab.c' for details.  */
 180
 181
 182 /* FIXME: We used to have two implementations of weak hash tables: the one in
 183    here and the one in `hashtab.c'.  The difference is that weak alist
 184    vectors could be used as vectors while (weak) hash tables can't.  We need
 185    to unify that.  */
 186
 187 SCM_DEFINE (scm_make_weak_key_alist_vector, "make-weak-key-alist-vector", 0, 1, 0,
 188             (SCM size),
 189             "@deffnx {Scheme Procedure} make-weak-value-alist-vector size\n"
 190             "@deffnx {Scheme Procedure} make-doubly-weak-alist-vector size\n"
 191             "Return a weak hash table with @var{size} buckets. As with any\n"
 192             "hash table, choosing a good size for the table requires some\n"
 193             "caution.\n"
 194             "\n"
 195             "You can modify weak hash tables in exactly the same way you\n"
 196             "would modify regular hash tables. (@pxref{Hash Tables})")
 197 #define FUNC_NAME s_scm_make_weak_key_alist_vector
 198 {
 199   return scm_make_weak_key_hash_table (size);
 200 }
 201 #undef FUNC_NAME
 202
 203
 204 SCM_DEFINE (scm_make_weak_value_alist_vector, "make-weak-value-alist-vector", 0, 1, 0,
 205             (SCM size),
 206             "Return a hash table with weak values with @var{size} buckets.\n"
 207             "(@pxref{Hash Tables})")
 208 #define FUNC_NAME s_scm_make_weak_value_alist_vector
 209 {
 210   return scm_make_weak_value_hash_table (size);
 211 }
 212 #undef FUNC_NAME
 213
 214
 215 SCM_DEFINE (scm_make_doubly_weak_alist_vector, "make-doubly-weak-alist-vector", 1, 0, 0,
 216             (SCM size),
 217             "Return a hash table with weak keys and values with @var{size}\n"
 218             "buckets.  (@pxref{Hash Tables})")
 219 #define FUNC_NAME s_scm_make_doubly_weak_alist_vector
 220 {
 221   return scm_make_doubly_weak_hash_table (size);
 222 }
 223 #undef FUNC_NAME
 224
 225
 226 SCM_DEFINE (scm_weak_key_alist_vector_p, "weak-key-alist-vector?", 1, 0, 0,
 227            (SCM obj),
 228             "@deffnx {Scheme Procedure} weak-value-alist-vector? obj\n"
 229             "@deffnx {Scheme Procedure} doubly-weak-alist-vector? obj\n"
 230             "Return @code{#t} if @var{obj} is the specified weak hash\n"
 231             "table. Note that a doubly weak hash table is neither a weak key\n"
 232             "nor a weak value hash table.")
 233 #define FUNC_NAME s_scm_weak_key_alist_vector_p
 234 {
 235   return scm_from_bool (SCM_I_WVECTP (obj) && SCM_IS_WHVEC (obj));
 236 }
 237 #undef FUNC_NAME
 238
 239
 240 SCM_DEFINE (scm_weak_value_alist_vector_p, "weak-value-alist-vector?", 1, 0, 0,
 241             (SCM obj),
 242             "Return @code{#t} if @var{obj} is a weak value hash table.")
 243 #define FUNC_NAME s_scm_weak_value_alist_vector_p
 244 {
 245   return scm_from_bool (SCM_I_WVECTP (obj) && SCM_IS_WHVEC_V (obj));
 246 }
 247 #undef FUNC_NAME
 248
 249
 250 SCM_DEFINE (scm_doubly_weak_alist_vector_p, "doubly-weak-alist-vector?", 1, 0, 0,
 251             (SCM obj),
 252             "Return @code{#t} if @var{obj} is a doubly weak hash table.")
 253 #define FUNC_NAME s_scm_doubly_weak_alist_vector_p
 254 {
 255   return scm_from_bool (SCM_I_WVECTP (obj) && SCM_IS_WHVEC_B (obj));
 256 }
 257 #undef FUNC_NAME
 258
 259
 260
 261 \f
 262 SCM
 263 scm_init_weaks_builtins ()
 264 {
 265 #include "libguile/weaks.x"
 266   return SCM_UNSPECIFIED;
 267 }
 268
 269 void
 270 scm_weaks_prehistory ()
 271 {
 272   /* Initialize weak pairs.  */
 273   GC_word wcar_pair_bitmap[GC_BITMAP_SIZE (scm_t_cell)] = { 0 };
 274   GC_word wcdr_pair_bitmap[GC_BITMAP_SIZE (scm_t_cell)] = { 0 };
 275
 276   /* In a weak-car pair, only the second word must be scanned for
 277      pointers.  */
 278   GC_set_bit (wcar_pair_bitmap, GC_WORD_OFFSET (scm_t_cell, word_1));
 279   wcar_pair_descr = GC_make_descriptor (wcar_pair_bitmap,
 280                                         GC_WORD_LEN (scm_t_cell));
 281
 282   /* Conversely, in a weak-cdr pair, only the first word must be scanned for
 283      pointers.  */
 284   GC_set_bit (wcdr_pair_bitmap, GC_WORD_OFFSET (scm_t_cell, word_0));
 285   wcdr_pair_descr = GC_make_descriptor (wcdr_pair_bitmap,
 286                                         GC_WORD_LEN (scm_t_cell));
 287
 288 }
 289
 290 void
 291 scm_init_weaks ()
 292 {
 293   scm_c_define_gsubr ("%init-weaks-builtins", 0, 0, 0,
 294                       scm_init_weaks_builtins);
 295 }
 296
 297
 298 /*
 299   Local Variables:
 300   c-file-style: "gnu"
 301   End:
 302 */