libguile/gc.c

   1 /* Copyright (C) 1995,1996,1997,1998,1999,2000,2001, 2002, 2003, 2006, 2008 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 /* #define DEBUGINFO */
  19
  20 #ifdef HAVE_CONFIG_H
  21 #  include <config.h>
  22 #endif
  23
  24 #include "libguile/gen-scmconfig.h"
  25
  26 #include <stdio.h>
  27 #include <errno.h>
  28 #include <string.h>
  29 #include <assert.h>
  30
  31 #ifdef __ia64__
  32 #include <ucontext.h>
  33 extern unsigned long * __libc_ia64_register_backing_store_base;
  34 #endif
  35
  36 #include "libguile/_scm.h"
  37 #include "libguile/eval.h"
  38 #include "libguile/stime.h"
  39 #include "libguile/stackchk.h"
  40 #include "libguile/struct.h"
  41 #include "libguile/smob.h"
  42 #include "libguile/unif.h"
  43 #include "libguile/async.h"
  44 #include "libguile/ports.h"
  45 #include "libguile/root.h"
  46 #include "libguile/strings.h"
  47 #include "libguile/vectors.h"
  48 #include "libguile/weaks.h"
  49 #include "libguile/hashtab.h"
  50 #include "libguile/tags.h"
  51
  52 #include "libguile/private-gc.h"
  53 #include "libguile/validate.h"
  54 #include "libguile/deprecation.h"
  55 #include "libguile/gc.h"
  56 #include "libguile/dynwind.h"
  57
  58 #include "libguile/boehm-gc.h"
  59
  60 #ifdef GUILE_DEBUG_MALLOC
  61 #include "libguile/debug-malloc.h"
  62 #endif
  63
  64 #ifdef HAVE_MALLOC_H
  65 #include <malloc.h>
  66 #endif
  67
  68 #ifdef HAVE_UNISTD_H
  69 #include <unistd.h>
  70 #endif
  71
  72 /* Lock this mutex before doing lazy sweeping.
  73  */
  74 scm_i_pthread_mutex_t scm_i_sweep_mutex = SCM_I_PTHREAD_MUTEX_INITIALIZER;
  75
  76 /* Set this to != 0 if every cell that is accessed shall be checked:
  77  */
  78 int scm_debug_cell_accesses_p = 0;
  79 int scm_expensive_debug_cell_accesses_p = 0;
  80
  81 /* Set this to 0 if no additional gc's shall be performed, otherwise set it to
  82  * the number of cell accesses after which a gc shall be called.
  83  */
  84 int scm_debug_cells_gc_interval = 0;
  85
  86 /*
  87   Global variable, so you can switch it off at runtime by setting
  88   scm_i_cell_validation_already_running.
  89  */
  90 int scm_i_cell_validation_already_running ;
  91
  92 #if (SCM_DEBUG_CELL_ACCESSES == 1)
  93
  94
  95 /*
  96
  97   Assert that the given object is a valid reference to a valid cell.  This
  98   test involves to determine whether the object is a cell pointer, whether
  99   this pointer actually points into a heap segment and whether the cell
 100   pointed to is not a free cell.  Further, additional garbage collections may
 101   get executed after a user defined number of cell accesses.  This helps to
 102   find places in the C code where references are dropped for extremely short
 103   periods.
 104
 105 */
 106 void
 107 scm_i_expensive_validation_check (SCM cell)
 108 {
 109   if (!scm_in_heap_p (cell))
 110     {
 111       fprintf (stderr, "scm_assert_cell_valid: this object does not live in the heap: %lux\n",
 112                (unsigned long) SCM_UNPACK (cell));
 113       abort ();
 114     }
 115
 116   /* If desired, perform additional garbage collections after a user
 117    * defined number of cell accesses.
 118    */
 119   if (scm_debug_cells_gc_interval)
 120     {
 121       static unsigned int counter = 0;
 122
 123       if (counter != 0)
 124         {
 125           --counter;
 126         }
 127       else
 128         {
 129           counter = scm_debug_cells_gc_interval;
 130           scm_gc ();
 131         }
 132     }
 133 }
 134
 135 void
 136 scm_assert_cell_valid (SCM cell)
 137 {
 138   if (!scm_i_cell_validation_already_running && scm_debug_cell_accesses_p)
 139     {
 140       scm_i_cell_validation_already_running = 1;  /* set to avoid recursion */
 141
 142       /*
 143         During GC, no user-code should be run, and the guile core
 144         should use non-protected accessors.
 145       */
 146       if (scm_gc_running_p)
 147         return;
 148
 149       /*
 150         Only scm_in_heap_p and rescanning the heap is wildly
 151         expensive.
 152       */
 153       if (scm_expensive_debug_cell_accesses_p)
 154         scm_i_expensive_validation_check (cell);
 155 #if (SCM_DEBUG_MARKING_API == 0)
 156       if (!SCM_GC_MARK_P (cell))
 157         {
 158           fprintf (stderr,
 159                    "scm_assert_cell_valid: this object is unmarked. \n"
 160                    "It has been garbage-collected in the last GC run: "
 161                    "%lux\n",
 162                    (unsigned long) SCM_UNPACK (cell));
 163           abort ();
 164         }
 165 #endif /* SCM_DEBUG_MARKING_API */
 166
 167       scm_i_cell_validation_already_running = 0;  /* re-enable */
 168     }
 169 }
 170
 171
 172
 173 SCM_DEFINE (scm_set_debug_cell_accesses_x, "set-debug-cell-accesses!", 1, 0, 0,
 174             (SCM flag),
 175             "If @var{flag} is @code{#f}, cell access checking is disabled.\n"
 176             "If @var{flag} is @code{#t}, cheap cell access checking is enabled,\n"
 177             "but no additional calls to garbage collection are issued.\n"
 178             "If @var{flag} is a number, strict cell access checking is enabled,\n"
 179             "with an additional garbage collection after the given\n"
 180             "number of cell accesses.\n"
 181             "This procedure only exists when the compile-time flag\n"
 182             "@code{SCM_DEBUG_CELL_ACCESSES} was set to 1.")
 183 #define FUNC_NAME s_scm_set_debug_cell_accesses_x
 184 {
 185   if (scm_is_false (flag))
 186     {
 187       scm_debug_cell_accesses_p = 0;
 188     }
 189   else if (scm_is_eq (flag, SCM_BOOL_T))
 190     {
 191       scm_debug_cells_gc_interval = 0;
 192       scm_debug_cell_accesses_p = 1;
 193       scm_expensive_debug_cell_accesses_p = 0;
 194     }
 195   else
 196     {
 197       scm_debug_cells_gc_interval = scm_to_signed_integer (flag, 0, INT_MAX);
 198       scm_debug_cell_accesses_p = 1;
 199       scm_expensive_debug_cell_accesses_p = 1;
 200     }
 201   return SCM_UNSPECIFIED;
 202 }
 203 #undef FUNC_NAME
 204
 205
 206 #endif  /* SCM_DEBUG_CELL_ACCESSES == 1 */
 207
 208 \f
 209 /* Hooks.  */
 210 scm_t_c_hook scm_before_gc_c_hook;
 211 scm_t_c_hook scm_before_mark_c_hook;
 212 scm_t_c_hook scm_before_sweep_c_hook;
 213 scm_t_c_hook scm_after_sweep_c_hook;
 214 scm_t_c_hook scm_after_gc_c_hook;
 215
 216
 217 /* scm_mtrigger
 218  * is the number of bytes of malloc allocation needed to trigger gc.
 219  */
 220 unsigned long scm_mtrigger;
 221
 222 /* GC Statistics Keeping
 223  */
 224 unsigned long scm_mallocated = 0;
 225 unsigned long scm_gc_ports_collected = 0;
 226
 227
 228 static unsigned long protected_obj_count = 0;
 229
 230
 231 SCM_SYMBOL (sym_cells_allocated, "cells-allocated");
 232 SCM_SYMBOL (sym_heap_size, "heap-size");
 233 SCM_SYMBOL (sym_heap_free_size, "heap-free-size");
 234 SCM_SYMBOL (sym_heap_total_allocated, "heap-total-allocated");
 235 SCM_SYMBOL (sym_mallocated, "bytes-malloced");
 236 SCM_SYMBOL (sym_mtrigger, "gc-malloc-threshold");
 237 SCM_SYMBOL (sym_heap_segments, "cell-heap-segments");
 238 SCM_SYMBOL (sym_gc_time_taken, "gc-time-taken");
 239 SCM_SYMBOL (sym_gc_mark_time_taken, "gc-mark-time-taken");
 240 SCM_SYMBOL (sym_times, "gc-times");
 241 SCM_SYMBOL (sym_cells_marked, "cells-marked");
 242 SCM_SYMBOL (sym_cells_marked_conservatively, "cells-marked-conservatively");
 243 SCM_SYMBOL (sym_cells_swept, "cells-swept");
 244 SCM_SYMBOL (sym_malloc_yield, "malloc-yield");
 245 SCM_SYMBOL (sym_cell_yield, "cell-yield");
 246 SCM_SYMBOL (sym_protected_objects, "protected-objects");
 247 SCM_SYMBOL (sym_total_cells_allocated, "total-cells-allocated");
 248
 249
 250 /* Number of calls to SCM_NEWCELL since startup.  */
 251 unsigned scm_newcell_count;
 252 unsigned scm_newcell2_count;
 253
 254
 255 /* {Scheme Interface to GC}
 256  */
 257 static SCM
 258 tag_table_to_type_alist (void *closure, SCM key, SCM val, SCM acc)
 259 {
 260   if (scm_is_integer (key))
 261     {
 262       int c_tag = scm_to_int (key);
 263
 264       char const * name = scm_i_tag_name (c_tag);
 265       if (name != NULL)
 266         {
 267           key = scm_from_locale_string (name);
 268         }
 269       else
 270         {
 271           char s[100];
 272           sprintf (s, "tag %d", c_tag);
 273           key = scm_from_locale_string (s);
 274         }
 275     }
 276
 277   return scm_cons (scm_cons (key, val), acc);
 278 }
 279
 280 SCM_DEFINE (scm_gc_live_object_stats, "gc-live-object-stats", 0, 0, 0,
 281             (),
 282             "Return an alist of statistics of the current live objects. ")
 283 #define FUNC_NAME s_scm_gc_live_object_stats
 284 {
 285   SCM tab = scm_make_hash_table (scm_from_int (57));
 286   SCM alist;
 287
 288   alist
 289     = scm_internal_hash_fold (&tag_table_to_type_alist, NULL, SCM_EOL, tab);
 290
 291   return alist;
 292 }
 293 #undef FUNC_NAME
 294
 295 extern int scm_gc_malloc_yield_percentage;
 296 SCM_DEFINE (scm_gc_stats, "gc-stats", 0, 0, 0,
 297             (),
 298             "Return an association list of statistics about Guile's current\n"
 299             "use of storage.\n")
 300 #define FUNC_NAME s_scm_gc_stats
 301 {
 302   SCM answer;
 303   size_t heap_size, free_bytes, bytes_since_gc, total_bytes;
 304   size_t gc_times;
 305
 306   heap_size      = GC_get_heap_size ();
 307   free_bytes     = GC_get_free_bytes ();
 308   bytes_since_gc = GC_get_bytes_since_gc ();
 309   total_bytes    = GC_get_total_bytes ();
 310   gc_times       = GC_gc_no;
 311
 312   /* njrev: can any of these scm_cons's or scm_list_n signal a memory
 313      error?  If so we need a frame here. */
 314   answer =
 315     scm_list_n (scm_cons (sym_gc_time_taken, SCM_INUM0),
 316 #if 0
 317                 scm_cons (sym_cells_allocated,
 318                           scm_from_ulong (local_scm_cells_allocated)),
 319                 scm_cons (sym_mallocated,
 320                           scm_from_ulong (local_scm_mallocated)),
 321                 scm_cons (sym_mtrigger,
 322                           scm_from_ulong (local_scm_mtrigger)),
 323                 scm_cons (sym_gc_mark_time_taken,
 324                           scm_from_ulong (local_scm_gc_mark_time_taken)),
 325                 scm_cons (sym_cells_marked,
 326                           scm_from_double (local_scm_gc_cells_marked)),
 327                 scm_cons (sym_cells_swept,
 328                           scm_from_double (local_scm_gc_cells_swept)),
 329                 scm_cons (sym_malloc_yield,
 330                           scm_from_long (local_scm_gc_malloc_yield_percentage)),
 331                 scm_cons (sym_cell_yield,
 332                           scm_from_long (local_scm_gc_cell_yield_percentage)),
 333                 scm_cons (sym_heap_segments, heap_segs),
 334 #endif
 335                 scm_cons (sym_heap_size, scm_from_size_t (heap_size)),
 336                 scm_cons (sym_heap_free_size, scm_from_size_t (free_bytes)),
 337                 scm_cons (sym_heap_total_allocated,
 338                           scm_from_size_t (total_bytes)),
 339                 scm_cons (sym_protected_objects,
 340                           scm_from_ulong (protected_obj_count)),
 341                 scm_cons (sym_times, scm_from_size_t (gc_times)),
 342                 SCM_UNDEFINED);
 343
 344   return answer;
 345 }
 346 #undef FUNC_NAME
 347
 348
 349
 350 SCM_DEFINE (scm_object_address, "object-address", 1, 0, 0,
 351             (SCM obj),
 352             "Return an integer that for the lifetime of @var{obj} is uniquely\n"
 353             "returned by this function for @var{obj}")
 354 #define FUNC_NAME s_scm_object_address
 355 {
 356   return scm_from_ulong (SCM_UNPACK (obj));
 357 }
 358 #undef FUNC_NAME
 359
 360
 361 SCM_DEFINE (scm_gc_disable, "gc-disable", 0, 0, 0,
 362             (),
 363             "Disables the garbage collector.  Nested calls are permitted.  "
 364             "GC is re-enabled once @code{gc-enable} has been called the "
 365             "same number of times @code{gc-disable} was called.")
 366 #define FUNC_NAME s_scm_gc_disable
 367 {
 368   GC_disable ();
 369   return SCM_UNSPECIFIED;
 370 }
 371 #undef FUNC_NAME
 372
 373 SCM_DEFINE (scm_gc_enable, "gc-enable", 0, 0, 0,
 374             (),
 375             "Enables the garbage collector.")
 376 #define FUNC_NAME s_scm_gc_enable
 377 {
 378   GC_enable ();
 379   return SCM_UNSPECIFIED;
 380 }
 381 #undef FUNC_NAME
 382
 383
 384 SCM_DEFINE (scm_gc, "gc", 0, 0, 0,
 385            (),
 386             "Scans all of SCM objects and reclaims for further use those that are\n"
 387             "no longer accessible.")
 388 #define FUNC_NAME s_scm_gc
 389 {
 390   scm_i_scm_pthread_mutex_lock (&scm_i_sweep_mutex);
 391   scm_gc_running_p = 1;
 392   scm_i_gc ("call");
 393   /* njrev: It looks as though other places, e.g. scm_realloc,
 394      can call scm_i_gc without acquiring the sweep mutex.  Does this
 395      matter?  Also scm_i_gc (or its descendants) touch the
 396      scm_sys_protects, which are protected in some cases
 397      (e.g. scm_permobjs above in scm_gc_stats) by a critical section,
 398      not by the sweep mutex.  Shouldn't all the GC-relevant objects be
 399      protected in the same way? */
 400   scm_gc_running_p = 0;
 401   scm_i_pthread_mutex_unlock (&scm_i_sweep_mutex);
 402   scm_c_hook_run (&scm_after_gc_c_hook, 0);
 403   return SCM_UNSPECIFIED;
 404 }
 405 #undef FUNC_NAME
 406
 407 void
 408 scm_i_gc (const char *what)
 409 {
 410   GC_gcollect ();
 411 }
 412
 413
 414 \f
 415 /* {GC Protection Helper Functions}
 416  */
 417
 418
 419 /*
 420  * If within a function you need to protect one or more scheme objects from
 421  * garbage collection, pass them as parameters to one of the
 422  * scm_remember_upto_here* functions below.  These functions don't do
 423  * anything, but since the compiler does not know that they are actually
 424  * no-ops, it will generate code that calls these functions with the given
 425  * parameters.  Therefore, you can be sure that the compiler will keep those
 426  * scheme values alive (on the stack or in a register) up to the point where
 427  * scm_remember_upto_here* is called.  In other words, place the call to
 428  * scm_remember_upto_here* _behind_ the last code in your function, that
 429  * depends on the scheme object to exist.
 430  *
 431  * Example: We want to make sure that the string object str does not get
 432  * garbage collected during the execution of 'some_function' in the code
 433  * below, because otherwise the characters belonging to str would be freed and
 434  * 'some_function' might access freed memory.  To make sure that the compiler
 435  * keeps str alive on the stack or in a register such that it is visible to
 436  * the conservative gc we add the call to scm_remember_upto_here_1 _after_ the
 437  * call to 'some_function'.  Note that this would not be necessary if str was
 438  * used anyway after the call to 'some_function'.
 439  *   char *chars = scm_i_string_chars (str);
 440  *   some_function (chars);
 441  *   scm_remember_upto_here_1 (str);  // str will be alive up to this point.
 442  */
 443
 444 /* Remove any macro versions of these while defining the functions.
 445    Functions are always included in the library, for upward binary
 446    compatibility and in case combinations of GCC and non-GCC are used.  */
 447 #undef scm_remember_upto_here_1
 448 #undef scm_remember_upto_here_2
 449
 450 void
 451 scm_remember_upto_here_1 (SCM obj SCM_UNUSED)
 452 {
 453   /* Empty.  Protects a single object from garbage collection. */
 454 }
 455
 456 void
 457 scm_remember_upto_here_2 (SCM obj1 SCM_UNUSED, SCM obj2 SCM_UNUSED)
 458 {
 459   /* Empty.  Protects two objects from garbage collection. */
 460 }
 461
 462 void
 463 scm_remember_upto_here (SCM obj SCM_UNUSED, ...)
 464 {
 465   /* Empty.  Protects any number of objects from garbage collection. */
 466 }
 467
 468 /*
 469   These crazy functions prevent garbage collection
 470   of arguments after the first argument by
 471   ensuring they remain live throughout the
 472   function because they are used in the last
 473   line of the code block.
 474   It'd be better to have a nice compiler hint to
 475   aid the conservative stack-scanning GC. --03/09/00 gjb */
 476 SCM
 477 scm_return_first (SCM elt, ...)
 478 {
 479   return elt;
 480 }
 481
 482 int
 483 scm_return_first_int (int i, ...)
 484 {
 485   return i;
 486 }
 487
 488
 489 SCM
 490 scm_permanent_object (SCM obj)
 491 {
 492   return (scm_gc_protect_object (obj));
 493 }
 494
 495
 496 /* Protect OBJ from the garbage collector.  OBJ will not be freed, even if all
 497    other references are dropped, until the object is unprotected by calling
 498    scm_gc_unprotect_object (OBJ).  Calls to scm_gc_protect/unprotect_object nest,
 499    i. e. it is possible to protect the same object several times, but it is
 500    necessary to unprotect the object the same number of times to actually get
 501    the object unprotected.  It is an error to unprotect an object more often
 502    than it has been protected before.  The function scm_protect_object returns
 503    OBJ.
 504 */
 505
 506 /* Implementation note:  For every object X, there is a counter which
 507    scm_gc_protect_object (X) increments and scm_gc_unprotect_object (X) decrements.
 508 */
 509
 510
 511
 512 SCM
 513 scm_gc_protect_object (SCM obj)
 514 {
 515   SCM handle;
 516
 517   /* This critical section barrier will be replaced by a mutex. */
 518   /* njrev: Indeed; if my comment above is correct, there is the same
 519      critsec/mutex inconsistency here. */
 520   SCM_CRITICAL_SECTION_START;
 521
 522   handle = scm_hashq_create_handle_x (scm_protects, obj, scm_from_int (0));
 523   SCM_SETCDR (handle, scm_sum (SCM_CDR (handle), scm_from_int (1)));
 524
 525   protected_obj_count ++;
 526
 527   SCM_CRITICAL_SECTION_END;
 528
 529   return obj;
 530 }
 531
 532
 533 /* Remove any protection for OBJ established by a prior call to
 534    scm_protect_object.  This function returns OBJ.
 535
 536    See scm_protect_object for more information.  */
 537 SCM
 538 scm_gc_unprotect_object (SCM obj)
 539 {
 540   SCM handle;
 541
 542   /* This critical section barrier will be replaced by a mutex. */
 543   /* njrev: and again. */
 544   SCM_CRITICAL_SECTION_START;
 545
 546   if (scm_gc_running_p)
 547     {
 548       fprintf (stderr, "scm_unprotect_object called during GC.\n");
 549       abort ();
 550     }
 551
 552   handle = scm_hashq_get_handle (scm_protects, obj);
 553
 554   if (scm_is_false (handle))
 555     {
 556       fprintf (stderr, "scm_unprotect_object called on unprotected object\n");
 557       abort ();
 558     }
 559   else
 560     {
 561       SCM count = scm_difference (SCM_CDR (handle), scm_from_int (1));
 562       if (scm_is_eq (count, scm_from_int (0)))
 563         scm_hashq_remove_x (scm_protects, obj);
 564       else
 565         SCM_SETCDR (handle, count);
 566     }
 567   protected_obj_count --;
 568
 569   SCM_CRITICAL_SECTION_END;
 570
 571   return obj;
 572 }
 573
 574 void
 575 scm_gc_register_root (SCM *p)
 576 {
 577   /* Nothing.  */
 578 }
 579
 580 void
 581 scm_gc_unregister_root (SCM *p)
 582 {
 583   /* Nothing.  */
 584 }
 585
 586 void
 587 scm_gc_register_roots (SCM *b, unsigned long n)
 588 {
 589   SCM *p = b;
 590   for (; p < b + n; ++p)
 591     scm_gc_register_root (p);
 592 }
 593
 594 void
 595 scm_gc_unregister_roots (SCM *b, unsigned long n)
 596 {
 597   SCM *p = b;
 598   for (; p < b + n; ++p)
 599     scm_gc_unregister_root (p);
 600 }
 601
 602 int scm_i_terminating;
 603
 604 \f
 605
 606
 607 /*
 608   MOVE THIS FUNCTION. IT DOES NOT HAVE ANYTHING TODO WITH GC.
 609  */
 610
 611 /* Get an integer from an environment variable.  */
 612 int
 613 scm_getenv_int (const char *var, int def)
 614 {
 615   char *end = 0;
 616   char *val = getenv (var);
 617   long res = def;
 618   if (!val)
 619     return def;
 620   res = strtol (val, &end, 10);
 621   if (end == val)
 622     return def;
 623   return res;
 624 }
 625
 626 void
 627 scm_storage_prehistory ()
 628 {
 629   GC_all_interior_pointers = 0;
 630
 631   GC_INIT ();
 632
 633 #if (! ((defined GC_VERSION_MAJOR) && (GC_VERSION_MAJOR >= 7))) \
 634     && (defined SCM_I_GSC_USE_PTHREAD_THREADS)
 635   /* When using GC 6.8, this call is required to initialize thread-local
 636      freelists (shouldn't be necessary with GC 7.0).  */
 637   GC_init ();
 638 #endif
 639
 640   GC_expand_hp (SCM_DEFAULT_INIT_HEAP_SIZE_2);
 641
 642   /* We only need to register a displacement for those types for which the
 643      higher bits of the type tag are used to store a pointer (that is, a
 644      pointer to an 8-octet aligned region).  For `scm_tc3_struct', this is
 645      handled in `scm_alloc_struct ()'.  */
 646   GC_REGISTER_DISPLACEMENT (scm_tc3_cons);
 647   GC_REGISTER_DISPLACEMENT (scm_tc3_closure);
 648
 649   /* Sanity check.  */
 650   if (!GC_is_visible (scm_sys_protects))
 651     abort ();
 652
 653   scm_c_hook_init (&scm_before_gc_c_hook, 0, SCM_C_HOOK_NORMAL);
 654   scm_c_hook_init (&scm_before_mark_c_hook, 0, SCM_C_HOOK_NORMAL);
 655   scm_c_hook_init (&scm_before_sweep_c_hook, 0, SCM_C_HOOK_NORMAL);
 656   scm_c_hook_init (&scm_after_sweep_c_hook, 0, SCM_C_HOOK_NORMAL);
 657   scm_c_hook_init (&scm_after_gc_c_hook, 0, SCM_C_HOOK_NORMAL);
 658 }
 659
 660 scm_i_pthread_mutex_t scm_i_gc_admin_mutex = SCM_I_PTHREAD_MUTEX_INITIALIZER;
 661
 662 int
 663 scm_init_storage ()
 664 {
 665   size_t j;
 666
 667   j = SCM_NUM_PROTECTS;
 668   while (j)
 669     scm_sys_protects[--j] = SCM_BOOL_F;
 670
 671   j = SCM_HEAP_SEG_SIZE;
 672
 673 #if 0
 674   /* We can't have a cleanup handler since we have no thread to run it
 675      in. */
 676
 677 #ifdef HAVE_ATEXIT
 678   atexit (cleanup);
 679 #else
 680 #ifdef HAVE_ON_EXIT
 681   on_exit (cleanup, 0);
 682 #endif
 683 #endif
 684
 685 #endif
 686
 687   scm_stand_in_procs = scm_make_weak_key_hash_table (scm_from_int (257));
 688   scm_protects = scm_c_make_hash_table (31);
 689
 690   return 0;
 691 }
 692
 693 \f
 694
 695 SCM scm_after_gc_hook;
 696
 697 static SCM gc_async;
 698
 699 /* The function gc_async_thunk causes the execution of the after-gc-hook.  It
 700  * is run after the gc, as soon as the asynchronous events are handled by the
 701  * evaluator.
 702  */
 703 static SCM
 704 gc_async_thunk (void)
 705 {
 706   scm_c_run_hook (scm_after_gc_hook, SCM_EOL);
 707   return SCM_UNSPECIFIED;
 708 }
 709
 710
 711 /* The function mark_gc_async is run by the scm_after_gc_c_hook at the end of
 712  * the garbage collection.  The only purpose of this function is to mark the
 713  * gc_async (which will eventually lead to the execution of the
 714  * gc_async_thunk).
 715  */
 716 static void *
 717 mark_gc_async (void * hook_data SCM_UNUSED,
 718                void *fn_data SCM_UNUSED,
 719                void *data SCM_UNUSED)
 720 {
 721   /* If cell access debugging is enabled, the user may choose to perform
 722    * additional garbage collections after an arbitrary number of cell
 723    * accesses.  We don't want the scheme level after-gc-hook to be performed
 724    * for each of these garbage collections for the following reason: The
 725    * execution of the after-gc-hook causes cell accesses itself.  Thus, if the
 726    * after-gc-hook was performed with every gc, and if the gc was performed
 727    * after a very small number of cell accesses, then the number of cell
 728    * accesses during the execution of the after-gc-hook will suffice to cause
 729    * the execution of the next gc.  Then, guile would keep executing the
 730    * after-gc-hook over and over again, and would never come to do other
 731    * things.
 732    *
 733    * To overcome this problem, if cell access debugging with additional
 734    * garbage collections is enabled, the after-gc-hook is never run by the
 735    * garbage collecter.  When running guile with cell access debugging and the
 736    * execution of the after-gc-hook is desired, then it is necessary to run
 737    * the hook explicitly from the user code.  This has the effect, that from
 738    * the scheme level point of view it seems that garbage collection is
 739    * performed with a much lower frequency than it actually is.  Obviously,
 740    * this will not work for code that depends on a fixed one to one
 741    * relationship between the execution counts of the C level garbage
 742    * collection hooks and the execution count of the scheme level
 743    * after-gc-hook.
 744    */
 745
 746 #if (SCM_DEBUG_CELL_ACCESSES == 1)
 747   if (scm_debug_cells_gc_interval == 0)
 748     scm_system_async_mark (gc_async);
 749 #else
 750   scm_system_async_mark (gc_async);
 751 #endif
 752
 753   return NULL;
 754 }
 755
 756 char const *
 757 scm_i_tag_name (scm_t_bits tag)
 758 {
 759   if (tag >= 255)
 760     {
 761       if (tag == scm_tc_free_cell)
 762         return "free cell";
 763
 764       {
 765         int k = 0xff & (tag >> 8);
 766         return (scm_smobs[k].name);
 767       }
 768     }
 769
 770   switch (tag) /* 7 bits */
 771     {
 772     case scm_tcs_struct:
 773       return "struct";
 774     case scm_tcs_cons_imcar:
 775       return "cons (immediate car)";
 776     case scm_tcs_cons_nimcar:
 777       return "cons (non-immediate car)";
 778     case scm_tcs_closures:
 779       return "closures";
 780     case scm_tc7_pws:
 781       return "pws";
 782     case scm_tc7_wvect:
 783       return "weak vector";
 784     case scm_tc7_vector:
 785       return "vector";
 786 #ifdef CCLO
 787     case scm_tc7_cclo:
 788       return "compiled closure";
 789 #endif
 790     case scm_tc7_number:
 791       switch (tag)
 792         {
 793         case scm_tc16_real:
 794           return "real";
 795           break;
 796         case scm_tc16_big:
 797           return "bignum";
 798           break;
 799         case scm_tc16_complex:
 800           return "complex number";
 801           break;
 802         case scm_tc16_fraction:
 803           return "fraction";
 804           break;
 805         }
 806       break;
 807     case scm_tc7_string:
 808       return "string";
 809       break;
 810     case scm_tc7_stringbuf:
 811       return "string buffer";
 812       break;
 813     case scm_tc7_symbol:
 814       return "symbol";
 815       break;
 816     case scm_tc7_variable:
 817       return "variable";
 818       break;
 819     case scm_tcs_subrs:
 820       return "subrs";
 821       break;
 822     case scm_tc7_port:
 823       return "port";
 824       break;
 825     case scm_tc7_smob:
 826       return "smob";            /* should not occur. */
 827       break;
 828     }
 829
 830   return NULL;
 831 }
 832
 833
 834
 835 \f
 836 void
 837 scm_init_gc ()
 838 {
 839   /* `GC_INIT ()' was invoked in `scm_storage_prehistory ()'.  */
 840
 841   scm_after_gc_hook = scm_permanent_object (scm_make_hook (SCM_INUM0));
 842   scm_c_define ("after-gc-hook", scm_after_gc_hook);
 843
 844   gc_async = scm_c_make_subr ("%gc-thunk", scm_tc7_subr_0,
 845                               gc_async_thunk);
 846
 847   scm_c_hook_add (&scm_after_gc_c_hook, mark_gc_async, NULL, 0);
 848
 849 #include "libguile/gc.x"
 850 }
 851
 852
 853 void
 854 scm_gc_sweep (void)
 855 #define FUNC_NAME "scm_gc_sweep"
 856 {
 857   /* FIXME */
 858   fprintf (stderr, "%s: doing nothing\n", __FUNCTION__);
 859 }
 860
 861 #undef FUNC_NAME
 862
 863
 864
 865 /*
 866   Local Variables:
 867   c-file-style: "gnu"
 868   End:
 869 */