boehm-gc/gc.h

   1 /*
   2  * Copyright 1988, 1989 Hans-J. Boehm, Alan J. Demers
   3  * Copyright (c) 1991-1995 by Xerox Corporation.  All rights reserved.
   4  * Copyright 1996 by Silicon Graphics.  All rights reserved.
   5  *
   6  * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
   7  * OR IMPLIED.  ANY USE IS AT YOUR OWN RISK.
   8  *
   9  * Permission is hereby granted to use or copy this program
  10  * for any purpose,  provided the above notices are retained on all copies.
  11  * Permission to modify the code and to distribute modified code is granted,
  12  * provided the above notices are retained, and a notice that the code was
  13  * modified is included with the above copyright notice.
  14  */
  15
  16 /*
  17  * Note that this defines a large number of tuning hooks, which can
  18  * safely be ignored in nearly all cases.  For normal use it suffices
  19  * to call only GC_MALLOC and perhaps GC_REALLOC.
  20  * For better performance, also look at GC_MALLOC_ATOMIC, and
  21  * GC_enable_incremental.  If you need an action to be performed
  22  * immediately before an object is collected, look at GC_register_finalizer.
  23  * If you are using Solaris threads, look at the end of this file.
  24  * Everything else is best ignored unless you encounter performance
  25  * problems.
  26  */
  27
  28 #ifndef _GC_H
  29
  30 # define _GC_H
  31 # define __GC
  32 # include <stddef.h>
  33
  34 #if defined(__CYGWIN32__) && defined(GC_USE_DLL)
  35 #include "libgc_globals.h"
  36 #endif
  37
  38 #if defined(_MSC_VER) && defined(_DLL)
  39 # ifdef GC_BUILD
  40 #   define GC_API __declspec(dllexport)
  41 # else
  42 #   define GC_API __declspec(dllimport)
  43 # endif
  44 #endif
  45
  46 #if defined(__WATCOMC__) && defined(GC_DLL)
  47 # ifdef GC_BUILD
  48 #   define GC_API extern __declspec(dllexport)
  49 # else
  50 #   define GC_API extern __declspec(dllimport)
  51 # endif
  52 #endif
  53
  54 #ifndef GC_API
  55 #define GC_API extern
  56 #endif
  57
  58 # if defined(__STDC__) || defined(__cplusplus)
  59 #   define GC_PROTO(args) args
  60     typedef void * GC_PTR;
  61 #   define GC_CONST const
  62 # else
  63 #   define GC_PROTO(args) ()
  64     typedef char * GC_PTR;
  65 #   define GC_CONST
  66 #  endif
  67
  68 # ifdef __cplusplus
  69     extern "C" {
  70 # endif
  71
  72
  73 /* Define word and signed_word to be unsigned and signed types of the   */
  74 /* size as char * or void *.  There seems to be no way to do this       */
  75 /* even semi-portably.  The following is probably no better/worse       */
  76 /* than almost anything else.                                           */
  77 /* The ANSI standard suggests that size_t and ptr_diff_t might be       */
  78 /* better choices.  But those appear to have incorrect definitions      */
  79 /* on may systems.  Notably "typedef int size_t" seems to be both       */
  80 /* frequent and WRONG.                                                  */
  81 typedef unsigned long GC_word;
  82 typedef long GC_signed_word;
  83
  84 /* Public read-only variables */
  85
  86 GC_API GC_word GC_gc_no;/* Counter incremented per collection.          */
  87                         /* Includes empty GCs at startup.               */
  88
  89
  90 /* Public R/W variables */
  91
  92 GC_API GC_PTR (*GC_oom_fn) GC_PROTO((size_t bytes_requested));
  93                         /* When there is insufficient memory to satisfy */
  94                         /* an allocation request, we return             */
  95                         /* (*GC_oom_fn)().  By default this just        */
  96                         /* returns 0.                                   */
  97                         /* If it returns, it must return 0 or a valid   */
  98                         /* pointer to a previously allocated heap       */
  99                         /* object.                                      */
 100
 101 GC_API int GC_find_leak;
 102                         /* Do not actually garbage collect, but simply  */
 103                         /* report inaccessible memory that was not      */
 104                         /* deallocated with GC_free.  Initial value     */
 105                         /* is determined by FIND_LEAK macro.            */
 106
 107 GC_API int GC_quiet;    /* Disable statistics output.  Only matters if  */
 108                         /* collector has been compiled with statistics  */
 109                         /* enabled.  This involves a performance cost,  */
 110                         /* and is thus not the default.                 */
 111
 112 GC_API int GC_finalize_on_demand;
 113                         /* If nonzero, finalizers will only be run in   */
 114                         /* response to an eplit GC_invoke_finalizers    */
 115                         /* call.  The default is determined by whether  */
 116                         /* the FINALIZE_ON_DEMAND macro is defined      */
 117                         /* when the collector is built.                 */
 118
 119 GC_API int GC_java_finalization;
 120                         /* Mark objects reachable from finalizable      */
 121                         /* objects in a separate postpass.  This makes  */
 122                         /* it a bit safer to use non-topologically-     */
 123                         /* ordered finalization.  Default value is      */
 124                         /* determined by JAVA_FINALIZATION macro.       */
 125
 126 GC_API int GC_dont_gc;  /* Dont collect unless explicitly requested, e.g. */
 127                         /* because it's not safe.                         */
 128
 129 GC_API int GC_dont_expand;
 130                         /* Dont expand heap unless explicitly requested */
 131                         /* or forced to.                                */
 132
 133 GC_API int GC_full_freq;    /* Number of partial collections between    */
 134                             /* full collections.  Matters only if       */
 135                             /* GC_incremental is set.                   */
 136                             /* Full collections are also triggered if   */
 137                             /* the collector detects a substantial      */
 138                             /* increase in the number of in-use heap    */
 139                             /* blocks.  Values in the tens are now      */
 140                             /* perfectly reasonable, unlike for         */
 141                             /* earlier GC versions.                     */
 142
 143 GC_API GC_word GC_non_gc_bytes;
 144                         /* Bytes not considered candidates for collection. */
 145                         /* Used only to control scheduling of collections. */
 146
 147 GC_API GC_word GC_free_space_divisor;
 148                         /* We try to make sure that we allocate at      */
 149                         /* least N/GC_free_space_divisor bytes between  */
 150                         /* collections, where N is the heap size plus   */
 151                         /* a rough estimate of the root set size.       */
 152                         /* Initially, GC_free_space_divisor = 4.        */
 153                         /* Increasing its value will use less space     */
 154                         /* but more collection time.  Decreasing it     */
 155                         /* will appreciably decrease collection time    */
 156                         /* at the expense of space.                     */
 157                         /* GC_free_space_divisor = 1 will effectively   */
 158                         /* disable collections.                         */
 159
 160 GC_API GC_word GC_max_retries;
 161                         /* The maximum number of GCs attempted before   */
 162                         /* reporting out of memory after heap           */
 163                         /* expansion fails.  Initially 0.               */
 164
 165
 166 GC_API char *GC_stackbottom;    /* Cool end of user stack.              */
 167                                 /* May be set in the client prior to    */
 168                                 /* calling any GC_ routines.  This      */
 169                                 /* avoids some overhead, and            */
 170                                 /* potentially some signals that can    */
 171                                 /* confuse debuggers.  Otherwise the    */
 172                                 /* collector attempts to set it         */
 173                                 /* automatically.                       */
 174                                 /* For multithreaded code, this is the  */
 175                                 /* cold end of the stack for the        */
 176                                 /* primordial thread.                   */
 177
 178 /* Public procedures */
 179 /*
 180  * general purpose allocation routines, with roughly malloc calling conv.
 181  * The atomic versions promise that no relevant pointers are contained
 182  * in the object.  The nonatomic versions guarantee that the new object
 183  * is cleared.  GC_malloc_stubborn promises that no changes to the object
 184  * will occur after GC_end_stubborn_change has been called on the
 185  * result of GC_malloc_stubborn. GC_malloc_uncollectable allocates an object
 186  * that is scanned for pointers to collectable objects, but is not itself
 187  * collectable.  GC_malloc_uncollectable and GC_free called on the resulting
 188  * object implicitly update GC_non_gc_bytes appropriately.
 189  */
 190 GC_API GC_PTR GC_malloc GC_PROTO((size_t size_in_bytes));
 191 GC_API GC_PTR GC_malloc_atomic GC_PROTO((size_t size_in_bytes));
 192 GC_API GC_PTR GC_malloc_uncollectable GC_PROTO((size_t size_in_bytes));
 193 GC_API GC_PTR GC_malloc_stubborn GC_PROTO((size_t size_in_bytes));
 194
 195 /* The following is only defined if the library has been suitably       */
 196 /* compiled:                                                            */
 197 GC_API GC_PTR GC_malloc_atomic_uncollectable GC_PROTO((size_t size_in_bytes));
 198
 199 /* Explicitly deallocate an object.  Dangerous if used incorrectly.     */
 200 /* Requires a pointer to the base of an object.                         */
 201 /* If the argument is stubborn, it should not be changeable when freed. */
 202 /* An object should not be enable for finalization when it is           */
 203 /* explicitly deallocated.                                              */
 204 /* GC_free(0) is a no-op, as required by ANSI C for free.               */
 205 GC_API void GC_free GC_PROTO((GC_PTR object_addr));
 206
 207 /*
 208  * Stubborn objects may be changed only if the collector is explicitly informed.
 209  * The collector is implicitly informed of coming change when such
 210  * an object is first allocated.  The following routines inform the
 211  * collector that an object will no longer be changed, or that it will
 212  * once again be changed.  Only nonNIL pointer stores into the object
 213  * are considered to be changes.  The argument to GC_end_stubborn_change
 214  * must be exacly the value returned by GC_malloc_stubborn or passed to
 215  * GC_change_stubborn.  (In the second case it may be an interior pointer
 216  * within 512 bytes of the beginning of the objects.)
 217  * There is a performance penalty for allowing more than
 218  * one stubborn object to be changed at once, but it is acceptable to
 219  * do so.  The same applies to dropping stubborn objects that are still
 220  * changeable.
 221  */
 222 GC_API void GC_change_stubborn GC_PROTO((GC_PTR));
 223 GC_API void GC_end_stubborn_change GC_PROTO((GC_PTR));
 224
 225 /* Return a pointer to the base (lowest address) of an object given     */
 226 /* a pointer to a location within the object.                           */
 227 /* Return 0 if displaced_pointer doesn't point to within a valid        */
 228 /* object.                                                              */
 229 GC_API GC_PTR GC_base GC_PROTO((GC_PTR displaced_pointer));
 230
 231 /* Given a pointer to the base of an object, return its size in bytes.  */
 232 /* The returned size may be slightly larger than what was originally    */
 233 /* requested.                                                           */
 234 GC_API size_t GC_size GC_PROTO((GC_PTR object_addr));
 235
 236 /* For compatibility with C library.  This is occasionally faster than  */
 237 /* a malloc followed by a bcopy.  But if you rely on that, either here  */
 238 /* or with the standard C library, your code is broken.  In my          */
 239 /* opinion, it shouldn't have been invented, but now we're stuck. -HB   */
 240 /* The resulting object has the same kind as the original.              */
 241 /* If the argument is stubborn, the result will have changes enabled.   */
 242 /* It is an error to have changes enabled for the original object.      */
 243 /* Follows ANSI comventions for NULL old_object.                        */
 244 GC_API GC_PTR GC_realloc
 245         GC_PROTO((GC_PTR old_object, size_t new_size_in_bytes));
 246
 247 /* Explicitly increase the heap size.   */
 248 /* Returns 0 on failure, 1 on success.  */
 249 GC_API int GC_expand_hp GC_PROTO((size_t number_of_bytes));
 250
 251 /* Limit the heap size to n bytes.  Useful when you're debugging,       */
 252 /* especially on systems that don't handle running out of memory well.  */
 253 /* n == 0 ==> unbounded.  This is the default.                          */
 254 GC_API void GC_set_max_heap_size GC_PROTO((GC_word n));
 255
 256 /* Inform the collector that a certain section of statically allocated  */
 257 /* memory contains no pointers to garbage collected memory.  Thus it    */
 258 /* need not be scanned.  This is sometimes important if the application */
 259 /* maps large read/write files into the address space, which could be   */
 260 /* mistaken for dynamic library data segments on some systems.          */
 261 GC_API void GC_exclude_static_roots GC_PROTO((GC_PTR start, GC_PTR finish));
 262
 263 /* Clear the set of root segments.  Wizards only. */
 264 GC_API void GC_clear_roots GC_PROTO((void));
 265
 266 /* Add a root segment.  Wizards only. */
 267 GC_API void GC_add_roots GC_PROTO((char * low_address,
 268                                    char * high_address_plus_1));
 269
 270 /* Add a displacement to the set of those considered valid by the       */
 271 /* collector.  GC_register_displacement(n) means that if p was returned */
 272 /* by GC_malloc, then (char *)p + n will be considered to be a valid    */
 273 /* pointer to n.  N must be small and less than the size of p.          */
 274 /* (All pointers to the interior of objects from the stack are          */
 275 /* considered valid in any case.  This applies to heap objects and      */
 276 /* static data.)                                                        */
 277 /* Preferably, this should be called before any other GC procedures.    */
 278 /* Calling it later adds to the probability of excess memory            */
 279 /* retention.                                                           */
 280 /* This is a no-op if the collector was compiled with recognition of    */
 281 /* arbitrary interior pointers enabled, which is now the default.       */
 282 GC_API void GC_register_displacement GC_PROTO((GC_word n));
 283
 284 /* The following version should be used if any debugging allocation is  */
 285 /* being done.                                                          */
 286 GC_API void GC_debug_register_displacement GC_PROTO((GC_word n));
 287
 288 /* Explicitly trigger a full, world-stop collection.    */
 289 GC_API void GC_gcollect GC_PROTO((void));
 290
 291 /* Trigger a full world-stopped collection.  Abort the collection if    */
 292 /* and when stop_func returns a nonzero value.  Stop_func will be       */
 293 /* called frequently, and should be reasonably fast.  This works even   */
 294 /* if virtual dirty bits, and hence incremental collection is not       */
 295 /* available for this architecture.  Collections can be aborted faster  */
 296 /* than normal pause times for incremental collection.  However,        */
 297 /* aborted collections do no useful work; the next collection needs     */
 298 /* to start from the beginning.                                         */
 299 /* Return 0 if the collection was aborted, 1 if it succeeded.           */
 300 typedef int (* GC_stop_func) GC_PROTO((void));
 301 GC_API int GC_try_to_collect GC_PROTO((GC_stop_func stop_func));
 302
 303 /* Return the number of bytes in the heap.  Excludes collector private  */
 304 /* data structures.  Includes empty blocks and fragmentation loss.      */
 305 /* Includes some pages that were allocated but never written.           */
 306 GC_API size_t GC_get_heap_size GC_PROTO((void));
 307
 308 /* Return a lower bound on the number of free bytes in the heap.        */
 309 GC_API size_t GC_get_free_bytes GC_PROTO((void));
 310
 311 /* Return the number of bytes allocated since the last collection.      */
 312 GC_API size_t GC_get_bytes_since_gc GC_PROTO((void));
 313
 314 /* Enable incremental/generational collection.  */
 315 /* Not advisable unless dirty bits are          */
 316 /* available or most heap objects are           */
 317 /* pointerfree(atomic) or immutable.            */
 318 /* Don't use in leak finding mode.              */
 319 /* Ignored if GC_dont_gc is true.               */
 320 GC_API void GC_enable_incremental GC_PROTO((void));
 321
 322 /* Perform some garbage collection work, if appropriate.        */
 323 /* Return 0 if there is no more work to be done.                */
 324 /* Typically performs an amount of work corresponding roughly   */
 325 /* to marking from one page.  May do more work if further       */
 326 /* progress requires it, e.g. if incremental collection is      */
 327 /* disabled.  It is reasonable to call this in a wait loop      */
 328 /* until it returns 0.                                          */
 329 GC_API int GC_collect_a_little GC_PROTO((void));
 330
 331 /* Allocate an object of size lb bytes.  The client guarantees that     */
 332 /* as long as the object is live, it will be referenced by a pointer    */
 333 /* that points to somewhere within the first 256 bytes of the object.   */
 334 /* (This should normally be declared volatile to prevent the compiler   */
 335 /* from invalidating this assertion.)  This routine is only useful      */
 336 /* if a large array is being allocated.  It reduces the chance of       */
 337 /* accidentally retaining such an array as a result of scanning an      */
 338 /* integer that happens to be an address inside the array.  (Actually,  */
 339 /* it reduces the chance of the allocator not finding space for such    */
 340 /* an array, since it will try hard to avoid introducing such a false   */
 341 /* reference.)  On a SunOS 4.X or MS Windows system this is recommended */
 342 /* for arrays likely to be larger than 100K or so.  For other systems,  */
 343 /* or if the collector is not configured to recognize all interior      */
 344 /* pointers, the threshold is normally much higher.                     */
 345 GC_API GC_PTR GC_malloc_ignore_off_page GC_PROTO((size_t lb));
 346 GC_API GC_PTR GC_malloc_atomic_ignore_off_page GC_PROTO((size_t lb));
 347
 348 #if defined(__sgi) && !defined(__GNUC__) && _COMPILER_VERSION >= 720
 349 #   define GC_ADD_CALLER
 350 #   define GC_RETURN_ADDR (GC_word)__return_address
 351 #endif
 352
 353 #ifdef GC_ADD_CALLER
 354 #  define GC_EXTRAS GC_RETURN_ADDR, __FILE__, __LINE__
 355 #  define GC_EXTRA_PARAMS GC_word ra, GC_CONST char * descr_string,
 356                           int descr_int
 357 #else
 358 #  define GC_EXTRAS __FILE__, __LINE__
 359 #  define GC_EXTRA_PARAMS GC_CONST char * descr_string, int descr_int
 360 #endif
 361
 362 /* Debugging (annotated) allocation.  GC_gcollect will check            */
 363 /* objects allocated in this way for overwrites, etc.                   */
 364 GC_API GC_PTR GC_debug_malloc
 365         GC_PROTO((size_t size_in_bytes, GC_EXTRA_PARAMS));
 366 GC_API GC_PTR GC_debug_malloc_atomic
 367         GC_PROTO((size_t size_in_bytes, GC_EXTRA_PARAMS));
 368 GC_API GC_PTR GC_debug_malloc_uncollectable
 369         GC_PROTO((size_t size_in_bytes, GC_EXTRA_PARAMS));
 370 GC_API GC_PTR GC_debug_malloc_stubborn
 371         GC_PROTO((size_t size_in_bytes, GC_EXTRA_PARAMS));
 372 GC_API void GC_debug_free GC_PROTO((GC_PTR object_addr));
 373 GC_API GC_PTR GC_debug_realloc
 374         GC_PROTO((GC_PTR old_object, size_t new_size_in_bytes,
 375                   GC_EXTRA_PARAMS));
 376
 377 GC_API void GC_debug_change_stubborn GC_PROTO((GC_PTR));
 378 GC_API void GC_debug_end_stubborn_change GC_PROTO((GC_PTR));
 379 # ifdef GC_DEBUG
 380 #   define GC_MALLOC(sz) GC_debug_malloc(sz, GC_EXTRAS)
 381 #   define GC_MALLOC_ATOMIC(sz) GC_debug_malloc_atomic(sz, GC_EXTRAS)
 382 #   define GC_MALLOC_UNCOLLECTABLE(sz) GC_debug_malloc_uncollectable(sz, \
 383                                                         GC_EXTRAS)
 384 #   define GC_REALLOC(old, sz) GC_debug_realloc(old, sz, GC_EXTRAS)
 385 #   define GC_FREE(p) GC_debug_free(p)
 386 #   define GC_REGISTER_FINALIZER(p, f, d, of, od) \
 387         GC_debug_register_finalizer(p, f, d, of, od)
 388 #   define GC_REGISTER_FINALIZER_IGNORE_SELF(p, f, d, of, od) \
 389         GC_debug_register_finalizer_ignore_self(p, f, d, of, od)
 390 #   define GC_REGISTER_FINALIZER_NO_ORDER(p, f, d, of, od) \
 391         GC_debug_register_finalizer_no_order(p, f, d, of, od)
 392 #   define GC_MALLOC_STUBBORN(sz) GC_debug_malloc_stubborn(sz, GC_EXTRAS);
 393 #   define GC_CHANGE_STUBBORN(p) GC_debug_change_stubborn(p)
 394 #   define GC_END_STUBBORN_CHANGE(p) GC_debug_end_stubborn_change(p)
 395 #   define GC_GENERAL_REGISTER_DISAPPEARING_LINK(link, obj) \
 396         GC_general_register_disappearing_link(link, GC_base(obj))
 397 #   define GC_REGISTER_DISPLACEMENT(n) GC_debug_register_displacement(n)
 398 # else
 399 #   define GC_MALLOC(sz) GC_malloc(sz)
 400 #   define GC_MALLOC_ATOMIC(sz) GC_malloc_atomic(sz)
 401 #   define GC_MALLOC_UNCOLLECTABLE(sz) GC_malloc_uncollectable(sz)
 402 #   define GC_REALLOC(old, sz) GC_realloc(old, sz)
 403 #   define GC_FREE(p) GC_free(p)
 404 #   define GC_REGISTER_FINALIZER(p, f, d, of, od) \
 405         GC_register_finalizer(p, f, d, of, od)
 406 #   define GC_REGISTER_FINALIZER_IGNORE_SELF(p, f, d, of, od) \
 407         GC_register_finalizer_ignore_self(p, f, d, of, od)
 408 #   define GC_REGISTER_FINALIZER_NO_ORDER(p, f, d, of, od) \
 409         GC_register_finalizer_no_order(p, f, d, of, od)
 410 #   define GC_MALLOC_STUBBORN(sz) GC_malloc_stubborn(sz)
 411 #   define GC_CHANGE_STUBBORN(p) GC_change_stubborn(p)
 412 #   define GC_END_STUBBORN_CHANGE(p) GC_end_stubborn_change(p)
 413 #   define GC_GENERAL_REGISTER_DISAPPEARING_LINK(link, obj) \
 414         GC_general_register_disappearing_link(link, obj)
 415 #   define GC_REGISTER_DISPLACEMENT(n) GC_register_displacement(n)
 416 # endif
 417 /* The following are included because they are often convenient, and    */
 418 /* reduce the chance for a misspecifed size argument.  But calls may    */
 419 /* expand to something syntactically incorrect if t is a complicated    */
 420 /* type expression.                                                     */
 421 # define GC_NEW(t) (t *)GC_MALLOC(sizeof (t))
 422 # define GC_NEW_ATOMIC(t) (t *)GC_MALLOC_ATOMIC(sizeof (t))
 423 # define GC_NEW_STUBBORN(t) (t *)GC_MALLOC_STUBBORN(sizeof (t))
 424 # define GC_NEW_UNCOLLECTABLE(t) (t *)GC_MALLOC_UNCOLLECTABLE(sizeof (t))
 425
 426 /* Finalization.  Some of these primitives are grossly unsafe.          */
 427 /* The idea is to make them both cheap, and sufficient to build         */
 428 /* a safer layer, closer to PCedar finalization.                        */
 429 /* The interface represents my conclusions from a long discussion       */
 430 /* with Alan Demers, Dan Greene, Carl Hauser, Barry Hayes,              */
 431 /* Christian Jacobi, and Russ Atkinson.  It's not perfect, and          */
 432 /* probably nobody else agrees with it.     Hans-J. Boehm  3/13/92      */
 433 typedef void (*GC_finalization_proc)
 434         GC_PROTO((GC_PTR obj, GC_PTR client_data));
 435
 436 GC_API void GC_register_finalizer
 437         GC_PROTO((GC_PTR obj, GC_finalization_proc fn, GC_PTR cd,
 438                   GC_finalization_proc *ofn, GC_PTR *ocd));
 439 GC_API void GC_debug_register_finalizer
 440         GC_PROTO((GC_PTR obj, GC_finalization_proc fn, GC_PTR cd,
 441                   GC_finalization_proc *ofn, GC_PTR *ocd));
 442         /* When obj is no longer accessible, invoke             */
 443         /* (*fn)(obj, cd).  If a and b are inaccessible, and    */
 444         /* a points to b (after disappearing links have been    */
 445         /* made to disappear), then only a will be              */
 446         /* finalized.  (If this does not create any new         */
 447         /* pointers to b, then b will be finalized after the    */
 448         /* next collection.)  Any finalizable object that       */
 449         /* is reachable from itself by following one or more    */
 450         /* pointers will not be finalized (or collected).       */
 451         /* Thus cycles involving finalizable objects should     */
 452         /* be avoided, or broken by disappearing links.         */
 453         /* All but the last finalizer registered for an object  */
 454         /* is ignored.                                          */
 455         /* Finalization may be removed by passing 0 as fn.      */
 456         /* Finalizers are implicitly unregistered just before   */
 457         /* they are invoked.                                    */
 458         /* The old finalizer and client data are stored in      */
 459         /* *ofn and *ocd.                                       */
 460         /* Fn is never invoked on an accessible object,         */
 461         /* provided hidden pointers are converted to real       */
 462         /* pointers only if the allocation lock is held, and    */
 463         /* such conversions are not performed by finalization   */
 464         /* routines.                                            */
 465         /* If GC_register_finalizer is aborted as a result of   */
 466         /* a signal, the object may be left with no             */
 467         /* finalization, even if neither the old nor new        */
 468         /* finalizer were NULL.                                 */
 469         /* Obj should be the nonNULL starting address of an     */
 470         /* object allocated by GC_malloc or friends.            */
 471         /* Note that any garbage collectable object referenced  */
 472         /* by cd will be considered accessible until the        */
 473         /* finalizer is invoked.                                */
 474
 475 /* Another versions of the above follow.  It ignores            */
 476 /* self-cycles, i.e. pointers from a finalizable object to      */
 477 /* itself.  There is a stylistic argument that this is wrong,   */
 478 /* but it's unavoidable for C++, since the compiler may         */
 479 /* silently introduce these.  It's also benign in that specific */
 480 /* case.                                                        */
 481 GC_API void GC_register_finalizer_ignore_self
 482         GC_PROTO((GC_PTR obj, GC_finalization_proc fn, GC_PTR cd,
 483                   GC_finalization_proc *ofn, GC_PTR *ocd));
 484 GC_API void GC_debug_register_finalizer_ignore_self
 485         GC_PROTO((GC_PTR obj, GC_finalization_proc fn, GC_PTR cd,
 486                   GC_finalization_proc *ofn, GC_PTR *ocd));
 487
 488 /* Another version of the above.  It ignores all cycles.        */
 489 /* It should probably only be used by Java implementations.      */
 490 GC_API void GC_register_finalizer_no_order
 491         GC_PROTO((GC_PTR obj, GC_finalization_proc fn, GC_PTR cd,
 492                   GC_finalization_proc *ofn, GC_PTR *ocd));
 493 GC_API void GC_debug_register_finalizer_no_order
 494         GC_PROTO((GC_PTR obj, GC_finalization_proc fn, GC_PTR cd,
 495                   GC_finalization_proc *ofn, GC_PTR *ocd));
 496
 497 /* The following routine may be used to break cycles between    */
 498 /* finalizable objects, thus causing cyclic finalizable         */
 499 /* objects to be finalized in the correct order.  Standard      */
 500 /* use involves calling GC_register_disappearing_link(&p),      */
 501 /* where p is a pointer that is not followed by finalization    */
 502 /* code, and should not be considered in determining            */
 503 /* finalization order.                                          */
 504 GC_API int GC_register_disappearing_link GC_PROTO((GC_PTR * /* link */));
 505         /* Link should point to a field of a heap allocated     */
 506         /* object obj.  *link will be cleared when obj is       */
 507         /* found to be inaccessible.  This happens BEFORE any   */
 508         /* finalization code is invoked, and BEFORE any         */
 509         /* decisions about finalization order are made.         */
 510         /* This is useful in telling the finalizer that         */
 511         /* some pointers are not essential for proper           */
 512         /* finalization.  This may avoid finalization cycles.   */
 513         /* Note that obj may be resurrected by another          */
 514         /* finalizer, and thus the clearing of *link may        */
 515         /* be visible to non-finalization code.                 */
 516         /* There's an argument that an arbitrary action should  */
 517         /* be allowed here, instead of just clearing a pointer. */
 518         /* But this causes problems if that action alters, or   */
 519         /* examines connectivity.                               */
 520         /* Returns 1 if link was already registered, 0          */
 521         /* otherwise.                                           */
 522         /* Only exists for backward compatibility.  See below:  */
 523
 524 GC_API int GC_general_register_disappearing_link
 525         GC_PROTO((GC_PTR * /* link */, GC_PTR obj));
 526         /* A slight generalization of the above. *link is       */
 527         /* cleared when obj first becomes inaccessible.  This   */
 528         /* can be used to implement weak pointers easily and    */
 529         /* safely. Typically link will point to a location      */
 530         /* holding a disguised pointer to obj.  (A pointer      */
 531         /* inside an "atomic" object is effectively             */
 532         /* disguised.)   In this way soft                       */
 533         /* pointers are broken before any object                */
 534         /* reachable from them are finalized.  Each link        */
 535         /* May be registered only once, i.e. with one obj       */
 536         /* value.  This was added after a long email discussion */
 537         /* with John Ellis.                                     */
 538         /* Obj must be a pointer to the first word of an object */
 539         /* we allocated.  It is unsafe to explicitly deallocate */
 540         /* the object containing link.  Explicitly deallocating */
 541         /* obj may or may not cause link to eventually be       */
 542         /* cleared.                                             */
 543 GC_API int GC_unregister_disappearing_link GC_PROTO((GC_PTR * /* link */));
 544         /* Returns 0 if link was not actually registered.       */
 545         /* Undoes a registration by either of the above two     */
 546         /* routines.                                            */
 547
 548 /* Auxiliary fns to make finalization work correctly with displaced     */
 549 /* pointers introduced by the debugging allocators.                     */
 550 GC_API GC_PTR GC_make_closure GC_PROTO((GC_finalization_proc fn, GC_PTR data));
 551 GC_API void GC_debug_invoke_finalizer GC_PROTO((GC_PTR obj, GC_PTR data));
 552
 553 GC_API int GC_invoke_finalizers GC_PROTO((void));
 554         /* Run finalizers for all objects that are ready to     */
 555         /* be finalized.  Return the number of finalizers       */
 556         /* that were run.  Normally this is also called         */
 557         /* implicitly during some allocations.  If              */
 558         /* GC-finalize_on_demand is nonzero, it must be called  */
 559         /* explicitly.                                          */
 560
 561 /* GC_set_warn_proc can be used to redirect or filter warning messages. */
 562 /* p may not be a NULL pointer.                                         */
 563 typedef void (*GC_warn_proc) GC_PROTO((char *msg, GC_word arg));
 564 GC_API GC_warn_proc GC_set_warn_proc GC_PROTO((GC_warn_proc p));
 565     /* Returns old warning procedure.   */
 566
 567 /* The following is intended to be used by a higher level       */
 568 /* (e.g. cedar-like) finalization facility.  It is expected     */
 569 /* that finalization code will arrange for hidden pointers to   */
 570 /* disappear.  Otherwise objects can be accessed after they     */
 571 /* have been collected.                                         */
 572 /* Note that putting pointers in atomic objects or in           */
 573 /* nonpointer slots of "typed" objects is equivalent to         */
 574 /* disguising them in this way, and may have other advantages.  */
 575 # if defined(I_HIDE_POINTERS) || defined(GC_I_HIDE_POINTERS)
 576     typedef GC_word GC_hidden_pointer;
 577 #   define HIDE_POINTER(p) (~(GC_hidden_pointer)(p))
 578 #   define REVEAL_POINTER(p) ((GC_PTR)(HIDE_POINTER(p)))
 579     /* Converting a hidden pointer to a real pointer requires verifying */
 580     /* that the object still exists.  This involves acquiring the       */
 581     /* allocator lock to avoid a race with the collector.               */
 582 # endif /* I_HIDE_POINTERS */
 583
 584 typedef GC_PTR (*GC_fn_type) GC_PROTO((GC_PTR client_data));
 585 GC_API GC_PTR GC_call_with_alloc_lock
 586                 GC_PROTO((GC_fn_type fn, GC_PTR client_data));
 587
 588 /* Check that p and q point to the same object.                 */
 589 /* Fail conspicuously if they don't.                            */
 590 /* Returns the first argument.                                  */
 591 /* Succeeds if neither p nor q points to the heap.              */
 592 /* May succeed if both p and q point to between heap objects.   */
 593 GC_API GC_PTR GC_same_obj GC_PROTO((GC_PTR p, GC_PTR q));
 594
 595 /* Checked pointer pre- and post- increment operations.  Note that      */
 596 /* the second argument is in units of bytes, not multiples of the       */
 597 /* object size.  This should either be invoked from a macro, or the     */
 598 /* call should be automatically generated.                              */
 599 GC_API GC_PTR GC_pre_incr GC_PROTO((GC_PTR *p, size_t how_much));
 600 GC_API GC_PTR GC_post_incr GC_PROTO((GC_PTR *p, size_t how_much));
 601
 602 /* Check that p is visible                                              */
 603 /* to the collector as a possibly pointer containing location.          */
 604 /* If it isn't fail conspicuously.                                      */
 605 /* Returns the argument in all cases.  May erroneously succeed          */
 606 /* in hard cases.  (This is intended for debugging use with             */
 607 /* untyped allocations.  The idea is that it should be possible, though */
 608 /* slow, to add such a call to all indirect pointer stores.)            */
 609 /* Currently useless for multithreaded worlds.                          */
 610 GC_API GC_PTR GC_is_visible GC_PROTO((GC_PTR p));
 611
 612 /* Check that if p is a pointer to a heap page, then it points to       */
 613 /* a valid displacement within a heap object.                           */
 614 /* Fail conspicuously if this property does not hold.                   */
 615 /* Uninteresting with ALL_INTERIOR_POINTERS.                            */
 616 /* Always returns its argument.                                         */
 617 GC_API GC_PTR GC_is_valid_displacement GC_PROTO((GC_PTR p));
 618
 619 /* Safer, but slow, pointer addition.  Probably useful mainly with      */
 620 /* a preprocessor.  Useful only for heap pointers.                      */
 621 #ifdef GC_DEBUG
 622 #   define GC_PTR_ADD3(x, n, type_of_result) \
 623         ((type_of_result)GC_same_obj((x)+(n), (x)))
 624 #   define GC_PRE_INCR3(x, n, type_of_result) \
 625         ((type_of_result)GC_pre_incr(&(x), (n)*sizeof(*x))
 626 #   define GC_POST_INCR2(x, type_of_result) \
 627         ((type_of_result)GC_post_incr(&(x), sizeof(*x))
 628 #   ifdef __GNUC__
 629 #       define GC_PTR_ADD(x, n) \
 630             GC_PTR_ADD3(x, n, typeof(x))
 631 #   define GC_PRE_INCR(x, n) \
 632             GC_PRE_INCR3(x, n, typeof(x))
 633 #   define GC_POST_INCR(x, n) \
 634             GC_POST_INCR3(x, typeof(x))
 635 #   else
 636         /* We can't do this right without typeof, which ANSI    */
 637         /* decided was not sufficiently useful.  Repeatedly     */
 638         /* mentioning the arguments seems too dangerous to be   */
 639         /* useful.  So does not casting the result.             */
 640 #       define GC_PTR_ADD(x, n) ((x)+(n))
 641 #   endif
 642 #else   /* !GC_DEBUG */
 643 #   define GC_PTR_ADD3(x, n, type_of_result) ((x)+(n))
 644 #   define GC_PTR_ADD(x, n) ((x)+(n))
 645 #   define GC_PRE_INCR3(x, n, type_of_result) ((x) += (n))
 646 #   define GC_PRE_INCR(x, n) ((x) += (n))
 647 #   define GC_POST_INCR2(x, n, type_of_result) ((x)++)
 648 #   define GC_POST_INCR(x, n) ((x)++)
 649 #endif
 650
 651 /* Safer assignment of a pointer to a nonstack location.        */
 652 #ifdef GC_DEBUG
 653 # ifdef __STDC__
 654 #   define GC_PTR_STORE(p, q) \
 655         (*(void **)GC_is_visible(p) = GC_is_valid_displacement(q))
 656 # else
 657 #   define GC_PTR_STORE(p, q) \
 658         (*(char **)GC_is_visible(p) = GC_is_valid_displacement(q))
 659 # endif
 660 #else /* !GC_DEBUG */
 661 #   define GC_PTR_STORE(p, q) *((p) = (q))
 662 #endif
 663
 664 /* Fynctions called to report pointer checking errors */
 665 GC_API void (*GC_same_obj_print_proc) GC_PROTO((GC_PTR p, GC_PTR q));
 666
 667 GC_API void (*GC_is_valid_displacement_print_proc)
 668         GC_PROTO((GC_PTR p));
 669
 670 GC_API void (*GC_is_visible_print_proc)
 671         GC_PROTO((GC_PTR p));
 672
 673 #if defined(_SOLARIS_PTHREADS) && !defined(SOLARIS_THREADS)
 674 #   define SOLARIS_THREADS
 675 #endif
 676
 677 #ifdef SOLARIS_THREADS
 678 /* We need to intercept calls to many of the threads primitives, so     */
 679 /* that we can locate thread stacks and stop the world.                 */
 680 /* Note also that the collector cannot see thread specific data.        */
 681 /* Thread specific data should generally consist of pointers to         */
 682 /* uncollectable objects, which are deallocated using the destructor    */
 683 /* facility in thr_keycreate.                                           */
 684 # include <thread.h>
 685 # include <signal.h>
 686   int GC_thr_create(void *stack_base, size_t stack_size,
 687                     void *(*start_routine)(void *), void *arg, long flags,
 688                     thread_t *new_thread);
 689   int GC_thr_join(thread_t wait_for, thread_t *departed, void **status);
 690   int GC_thr_suspend(thread_t target_thread);
 691   int GC_thr_continue(thread_t target_thread);
 692   void * GC_dlopen(const char *path, int mode);
 693
 694 # ifdef _SOLARIS_PTHREADS
 695 #   include <pthread.h>
 696     extern int GC_pthread_create(pthread_t *new_thread,
 697                                  const pthread_attr_t *attr,
 698                                  void * (*thread_execp)(void *), void *arg);
 699     extern int GC_pthread_join(pthread_t wait_for, void **status);
 700
 701 #   undef thread_t
 702
 703 #   define pthread_join GC_pthread_join
 704 #   define pthread_create GC_pthread_create
 705 #endif
 706
 707 # define thr_create GC_thr_create
 708 # define thr_join GC_thr_join
 709 # define thr_suspend GC_thr_suspend
 710 # define thr_continue GC_thr_continue
 711 # define dlopen GC_dlopen
 712
 713 # endif /* SOLARIS_THREADS */
 714
 715
 716 #if defined(IRIX_THREADS) || defined(LINUX_THREADS) || defined(HPUX_THREADS)
 717 /* We treat these similarly. */
 718 # include <pthread.h>
 719 # include <signal.h>
 720
 721   int GC_pthread_create(pthread_t *new_thread,
 722                         const pthread_attr_t *attr,
 723                         void *(*start_routine)(void *), void *arg);
 724   int GC_pthread_sigmask(int how, const sigset_t *set, sigset_t *oset);
 725   int GC_pthread_join(pthread_t thread, void **retval);
 726
 727 # define pthread_create GC_pthread_create
 728 # define pthread_sigmask GC_pthread_sigmask
 729 # define pthread_join GC_pthread_join
 730
 731 #endif /* IRIX_THREADS || LINUX_THREADS */
 732
 733 # if defined(PCR) || defined(SOLARIS_THREADS) || defined(WIN32_THREADS) || \
 734         defined(IRIX_THREADS) || defined(LINUX_THREADS) || \
 735         defined(IRIX_JDK_THREADS) || defined(HPUX_THREADS)
 736         /* Any flavor of threads except SRC_M3. */
 737 /* This returns a list of objects, linked through their first           */
 738 /* word.  Its use can greatly reduce lock contention problems, since    */
 739 /* the allocation lock can be acquired and released many fewer times.   */
 740 /* lb must be large enough to hold the pointer field.                   */
 741 GC_PTR GC_malloc_many(size_t lb);
 742 #define GC_NEXT(p) (*(GC_PTR *)(p))     /* Retrieve the next element    */
 743                                         /* in returned list.            */
 744 extern void GC_thr_init();      /* Needed for Solaris/X86       */
 745
 746 #endif /* THREADS && !SRC_M3 */
 747
 748 /*
 749  * If you are planning on putting
 750  * the collector in a SunOS 5 dynamic library, you need to call GC_INIT()
 751  * from the statically loaded program section.
 752  * This circumvents a Solaris 2.X (X<=4) linker bug.
 753  */
 754 #if defined(sparc) || defined(__sparc)
 755 #   define GC_INIT() { extern end, etext; \
 756                        GC_noop(&end, &etext); }
 757 #else
 758 # if defined(__CYGWIN32__) && defined(GC_USE_DLL)
 759     /*
 760      * Similarly gnu-win32 DLLs need explicit initialization
 761      */
 762 #   define GC_INIT() { GC_add_roots(DATASTART, DATAEND); }
 763 # else
 764 #   define GC_INIT()
 765 # endif
 766 #endif
 767
 768 #if (defined(_MSDOS) || defined(_MSC_VER)) && (_M_IX86 >= 300) \
 769      || defined(_WIN32)
 770   /* win32S may not free all resources on process exit.  */
 771   /* This explicitly deallocates the heap.               */
 772     GC_API void GC_win32_free_heap ();
 773 #endif
 774
 775 #ifdef __cplusplus
 776     }  /* end of extern "C" */
 777 #endif
 778
 779 #endif /* _GC_H */