mono/sgen/sgen-fin-weak-hash.c

   1 /*
   2  * sgen-fin-weak-hash.c: Finalizers and weak links.
   3  *
   4  * Author:
   5  *      Paolo Molaro (lupus@ximian.com)
   6  *  Rodrigo Kumpera (kumpera@gmail.com)
   7  *
   8  * Copyright 2005-2011 Novell, Inc (http://www.novell.com)
   9  * Copyright 2011 Xamarin Inc (http://www.xamarin.com)
  10  * Copyright 2011 Xamarin, Inc.
  11  * Copyright (C) 2012 Xamarin Inc
  12  *
  13  * This library is free software; you can redistribute it and/or
  14  * modify it under the terms of the GNU Library General Public
  15  * License 2.0 as published by the Free Software Foundation;
  16  *
  17  * This library is distributed in the hope that it will be useful,
  18  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  19  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  20  * Library General Public License for more details.
  21  *
  22  * You should have received a copy of the GNU Library General Public
  23  * License 2.0 along with this library; if not, write to the Free
  24  * Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  25  */
  26
  27 #include "config.h"
  28 #ifdef HAVE_SGEN_GC
  29
  30 #include "mono/sgen/sgen-gc.h"
  31 #include "mono/sgen/sgen-gray.h"
  32 #include "mono/sgen/sgen-protocol.h"
  33 #include "mono/sgen/sgen-pointer-queue.h"
  34 #include "mono/sgen/sgen-client.h"
  35 #include "mono/utils/mono-membar.h"
  36
  37 #define ptr_in_nursery sgen_ptr_in_nursery
  38
  39 typedef SgenGrayQueue GrayQueue;
  40
  41 static int no_finalize = 0;
  42
  43 #define DISLINK_OBJECT(l)       (REVEAL_POINTER (*(void**)(l)))
  44 #define DISLINK_TRACK(l)        ((~(size_t)(*(void**)(l))) & 1)
  45
  46 /*
  47  * The finalizable hash has the object as the key, the
  48  * disappearing_link hash, has the link address as key.
  49  *
  50  * Copyright 2011 Xamarin Inc.
  51  */
  52
  53 #define TAG_MASK ((mword)0x1)
  54
  55 static inline GCObject*
  56 tagged_object_get_object (GCObject *object)
  57 {
  58         return (GCObject*)(((mword)object) & ~TAG_MASK);
  59 }
  60
  61 static inline int
  62 tagged_object_get_tag (GCObject *object)
  63 {
  64         return ((mword)object) & TAG_MASK;
  65 }
  66
  67 static inline GCObject*
  68 tagged_object_apply (void *object, int tag_bits)
  69 {
  70        return (GCObject*)((mword)object | (mword)tag_bits);
  71 }
  72
  73 static int
  74 tagged_object_hash (GCObject *o)
  75 {
  76         return sgen_aligned_addr_hash (tagged_object_get_object (o));
  77 }
  78
  79 static gboolean
  80 tagged_object_equals (GCObject *a, GCObject *b)
  81 {
  82         return tagged_object_get_object (a) == tagged_object_get_object (b);
  83 }
  84
  85 static SgenHashTable minor_finalizable_hash = SGEN_HASH_TABLE_INIT (INTERNAL_MEM_FIN_TABLE, INTERNAL_MEM_FINALIZE_ENTRY, 0, (GHashFunc)tagged_object_hash, (GEqualFunc)tagged_object_equals);
  86 static SgenHashTable major_finalizable_hash = SGEN_HASH_TABLE_INIT (INTERNAL_MEM_FIN_TABLE, INTERNAL_MEM_FINALIZE_ENTRY, 0, (GHashFunc)tagged_object_hash, (GEqualFunc)tagged_object_equals);
  87
  88 static SgenHashTable*
  89 get_finalize_entry_hash_table (int generation)
  90 {
  91         switch (generation) {
  92         case GENERATION_NURSERY: return &minor_finalizable_hash;
  93         case GENERATION_OLD: return &major_finalizable_hash;
  94         default: g_assert_not_reached ();
  95         }
  96 }
  97
  98 #define BRIDGE_OBJECT_MARKED 0x1
  99
 100 /* LOCKING: requires that the GC lock is held */
 101 void
 102 sgen_mark_bridge_object (GCObject *obj)
 103 {
 104         SgenHashTable *hash_table = get_finalize_entry_hash_table (ptr_in_nursery (obj) ? GENERATION_NURSERY : GENERATION_OLD);
 105
 106         sgen_hash_table_set_key (hash_table, obj, tagged_object_apply (obj, BRIDGE_OBJECT_MARKED));
 107 }
 108
 109 /* LOCKING: requires that the GC lock is held */
 110 void
 111 sgen_collect_bridge_objects (int generation, ScanCopyContext ctx)
 112 {
 113         CopyOrMarkObjectFunc copy_func = ctx.ops->copy_or_mark_object;
 114         GrayQueue *queue = ctx.queue;
 115         SgenHashTable *hash_table = get_finalize_entry_hash_table (generation);
 116         GCObject *object;
 117         gpointer dummy G_GNUC_UNUSED;
 118         char *copy;
 119         SgenPointerQueue moved_fin_objects;
 120
 121         sgen_pointer_queue_init (&moved_fin_objects, INTERNAL_MEM_TEMPORARY);
 122
 123         if (no_finalize)
 124                 return;
 125
 126         SGEN_HASH_TABLE_FOREACH (hash_table, object, dummy) {
 127                 int tag = tagged_object_get_tag (object);
 128                 object = tagged_object_get_object (object);
 129
 130                 /* Bridge code told us to ignore this one */
 131                 if (tag == BRIDGE_OBJECT_MARKED)
 132                         continue;
 133
 134                 /* Object is a bridge object and major heap says it's dead  */
 135                 if (major_collector.is_object_live ((char*)object))
 136                         continue;
 137
 138                 /* Nursery says the object is dead. */
 139                 if (!sgen_gc_is_object_ready_for_finalization (object))
 140                         continue;
 141
 142                 if (!sgen_client_bridge_is_bridge_object (object))
 143                         continue;
 144
 145                 copy = (char*)object;
 146                 copy_func ((void**)&copy, queue);
 147
 148                 sgen_client_bridge_register_finalized_object ((GCObject*)copy);
 149
 150                 if (hash_table == &minor_finalizable_hash && !ptr_in_nursery (copy)) {
 151                         /* remove from the list */
 152                         SGEN_HASH_TABLE_FOREACH_REMOVE (TRUE);
 153
 154                         /* insert it into the major hash */
 155                         sgen_hash_table_replace (&major_finalizable_hash, tagged_object_apply (copy, tag), NULL, NULL);
 156
 157                         SGEN_LOG (5, "Promoting finalization of object %p (%s) (was at %p) to major table", copy, sgen_client_vtable_get_name (SGEN_LOAD_VTABLE (copy)), object);
 158
 159                         continue;
 160                 } else if (copy != (char*)object) {
 161                         /* update pointer */
 162                         SGEN_HASH_TABLE_FOREACH_REMOVE (TRUE);
 163
 164                         /* register for reinsertion */
 165                         sgen_pointer_queue_add (&moved_fin_objects, tagged_object_apply (copy, tag));
 166
 167                         SGEN_LOG (5, "Updating object for finalization: %p (%s) (was at %p)", copy, sgen_client_vtable_get_name (SGEN_LOAD_VTABLE (copy)), object);
 168
 169                         continue;
 170                 }
 171         } SGEN_HASH_TABLE_FOREACH_END;
 172
 173         while (!sgen_pointer_queue_is_empty (&moved_fin_objects)) {
 174                 sgen_hash_table_replace (hash_table, sgen_pointer_queue_pop (&moved_fin_objects), NULL, NULL);
 175         }
 176
 177         sgen_pointer_queue_free (&moved_fin_objects);
 178 }
 179
 180
 181 /* LOCKING: requires that the GC lock is held */
 182 void
 183 sgen_finalize_in_range (int generation, ScanCopyContext ctx)
 184 {
 185         CopyOrMarkObjectFunc copy_func = ctx.ops->copy_or_mark_object;
 186         GrayQueue *queue = ctx.queue;
 187         SgenHashTable *hash_table = get_finalize_entry_hash_table (generation);
 188         GCObject *object;
 189         gpointer dummy G_GNUC_UNUSED;
 190         SgenPointerQueue moved_fin_objects;
 191
 192         sgen_pointer_queue_init (&moved_fin_objects, INTERNAL_MEM_TEMPORARY);
 193
 194         if (no_finalize)
 195                 return;
 196         SGEN_HASH_TABLE_FOREACH (hash_table, object, dummy) {
 197                 int tag = tagged_object_get_tag (object);
 198                 object = tagged_object_get_object (object);
 199                 if (!major_collector.is_object_live ((char*)object)) {
 200                         gboolean is_fin_ready = sgen_gc_is_object_ready_for_finalization (object);
 201                         GCObject *copy = object;
 202                         copy_func ((void**)&copy, queue);
 203                         if (is_fin_ready) {
 204                                 /* remove and put in fin_ready_list */
 205                                 SGEN_HASH_TABLE_FOREACH_REMOVE (TRUE);
 206                                 sgen_queue_finalization_entry (copy);
 207                                 /* Make it survive */
 208                                 SGEN_LOG (5, "Queueing object for finalization: %p (%s) (was at %p) (%d)", copy, sgen_client_vtable_get_name (SGEN_LOAD_VTABLE (copy)), object, sgen_hash_table_num_entries (hash_table));
 209                                 continue;
 210                         } else {
 211                                 if (hash_table == &minor_finalizable_hash && !ptr_in_nursery (copy)) {
 212                                         /* remove from the list */
 213                                         SGEN_HASH_TABLE_FOREACH_REMOVE (TRUE);
 214
 215                                         /* insert it into the major hash */
 216                                         sgen_hash_table_replace (&major_finalizable_hash, tagged_object_apply (copy, tag), NULL, NULL);
 217
 218                                         SGEN_LOG (5, "Promoting finalization of object %p (%s) (was at %p) to major table", copy, sgen_client_vtable_get_name (SGEN_LOAD_VTABLE (copy)), object);
 219
 220                                         continue;
 221                                 } else if (copy != object) {
 222                                         /* update pointer */
 223                                         SGEN_HASH_TABLE_FOREACH_REMOVE (TRUE);
 224
 225                                         /* register for reinsertion */
 226                                         sgen_pointer_queue_add (&moved_fin_objects, tagged_object_apply (copy, tag));
 227
 228                                         SGEN_LOG (5, "Updating object for finalization: %p (%s) (was at %p)", copy, sgen_client_vtable_get_name (SGEN_LOAD_VTABLE (copy)), object);
 229
 230                                         continue;
 231                                 }
 232                         }
 233                 }
 234         } SGEN_HASH_TABLE_FOREACH_END;
 235
 236         while (!sgen_pointer_queue_is_empty (&moved_fin_objects)) {
 237                 sgen_hash_table_replace (hash_table, sgen_pointer_queue_pop (&moved_fin_objects), NULL, NULL);
 238         }
 239
 240         sgen_pointer_queue_free (&moved_fin_objects);
 241 }
 242
 243 /* LOCKING: requires that the GC lock is held */
 244 static void
 245 register_for_finalization (GCObject *obj, void *user_data, int generation)
 246 {
 247         SgenHashTable *hash_table = get_finalize_entry_hash_table (generation);
 248
 249         if (no_finalize)
 250                 return;
 251
 252         if (user_data) {
 253                 if (sgen_hash_table_replace (hash_table, obj, NULL, NULL)) {
 254                         GCVTable *vt = SGEN_LOAD_VTABLE_UNCHECKED (obj);
 255                         SGEN_LOG (5, "Added finalizer for object: %p (%s) (%d) to %s table", obj, sgen_client_vtable_get_name (vt), hash_table->num_entries, sgen_generation_name (generation));
 256                 }
 257         } else {
 258                 if (sgen_hash_table_remove (hash_table, obj, NULL)) {
 259                         GCVTable *vt = SGEN_LOAD_VTABLE_UNCHECKED (obj);
 260                         SGEN_LOG (5, "Removed finalizer for object: %p (%s) (%d)", obj, sgen_client_vtable_get_name (vt), hash_table->num_entries);
 261                 }
 262         }
 263 }
 264
 265 /*
 266  * We're using (mostly) non-locking staging queues for finalizers and weak links to speed
 267  * up registering them.  Otherwise we'd have to take the GC lock.
 268  *
 269  * The queues are arrays of `StageEntry`, plus a `next_entry` index.  Threads add entries to
 270  * the queue via `add_stage_entry()` in a linear fashion until it fills up, in which case
 271  * `process_stage_entries()` is called to drain it.  A garbage collection will also drain
 272  * the queues via the same function.  That implies that `add_stage_entry()`, since it
 273  * doesn't take a lock, must be able to run concurrently with `process_stage_entries()`,
 274  * though it doesn't have to make progress while the queue is drained.  In fact, once it
 275  * detects that the queue is being drained, it blocks until the draining is done.
 276  *
 277  * The protocol must guarantee that entries in the queue are causally ordered, otherwise two
 278  * entries for the same location might get switched, resulting in the earlier one being
 279  * committed and the later one ignored.
 280  *
 281  * `next_entry` is the index of the next entry to be filled, or `-1` if the queue is
 282  * currently being drained.  Each entry has a state:
 283  *
 284  * `STAGE_ENTRY_FREE`: The entry is free.  Its data fields must be `NULL`.
 285  *
 286  * `STAGE_ENTRY_BUSY`: The entry is currently being filled in.
 287  *
 288  * `STAGE_ENTRY_USED`: The entry is completely filled in and must be processed in the next
 289  * draining round.
 290  *
 291  * `STAGE_ENTRY_INVALID`: The entry was busy during queue draining and therefore
 292  * invalidated.  Entries that are `BUSY` can obviously not be processed during a drain, but
 293  * we can't leave them in place because new entries might be inserted before them, including
 294  * from the same thread, violating causality.  An alternative would be not to reset
 295  * `next_entry` to `0` after a drain, but to the index of the last `BUSY` entry plus one,
 296  * but that can potentially waste the whole queue.
 297  *
 298  * State transitions:
 299  *
 300  * | from    | to      | filler? | drainer? |
 301  * +---------+---------+---------+----------+
 302  * | FREE    | BUSY    | X       |          |
 303  * | BUSY    | FREE    | X       |          |
 304  * | BUSY    | USED    | X       |          |
 305  * | BUSY    | INVALID |         | X        |
 306  * | USED    | FREE    |         | X        |
 307  * | INVALID | FREE    | X       |          |
 308  *
 309  * `next_entry` can be incremented either by the filler thread that set the corresponding
 310  * entry to `BUSY`, or by another filler thread that's trying to get a `FREE` slot.  If that
 311  * other thread wasn't allowed to increment, it would block on the first filler thread.
 312  *
 313  * An entry's state, once it's set from `FREE` to `BUSY` by a filler thread, can only be
 314  * changed by that same thread or by the drained.  The drainer can only set a `BUSY` thread
 315  * to `INVALID`, so it needs to be set to `FREE` again by the original filler thread.
 316  */
 317
 318 #define STAGE_ENTRY_FREE        0
 319 #define STAGE_ENTRY_BUSY        1
 320 #define STAGE_ENTRY_USED        2
 321 #define STAGE_ENTRY_INVALID     3
 322
 323 typedef struct {
 324         volatile gint32 state;
 325         GCObject *obj;
 326         void *user_data;
 327 } StageEntry;
 328
 329 #define NUM_FIN_STAGE_ENTRIES   1024
 330
 331 static volatile gint32 next_fin_stage_entry = 0;
 332 static StageEntry fin_stage_entries [NUM_FIN_STAGE_ENTRIES];
 333
 334 /*
 335  * This is used to lock the stage when processing is forced, i.e. when it's triggered by a
 336  * garbage collection.  In that case, the world is already stopped and there's only one
 337  * thread operating on the queue.
 338  */
 339 static void
 340 lock_stage_for_processing (volatile gint32 *next_entry)
 341 {
 342         *next_entry = -1;
 343 }
 344
 345 /*
 346  * When processing is triggered by an overflow, we don't want to take the GC lock
 347  * immediately, and then set `next_index` to `-1`, because another thread might have drained
 348  * the queue in the mean time.  Instead, we make sure the overflow is still there, we
 349  * atomically set `next_index`, and only once that happened do we take the GC lock.
 350  */
 351 static gboolean
 352 try_lock_stage_for_processing (int num_entries, volatile gint32 *next_entry)
 353 {
 354         gint32 old = *next_entry;
 355         if (old < num_entries)
 356                 return FALSE;
 357         return InterlockedCompareExchange (next_entry, -1, old) == old;
 358 }
 359
 360 /* LOCKING: requires that the GC lock is held */
 361 static void
 362 process_stage_entries (int num_entries, volatile gint32 *next_entry, StageEntry *entries, void (*process_func) (GCObject*, void*, int))
 363 {
 364         int i;
 365
 366         /*
 367          * This can happen if after setting `next_index` to `-1` in
 368          * `try_lock_stage_for_processing()`, a GC was triggered, which then drained the
 369          * queue and reset `next_entry`.
 370          *
 371          * We have the GC lock now, so if it's still `-1`, we can't be interrupted by a GC.
 372          */
 373         if (*next_entry != -1)
 374                 return;
 375
 376         for (i = 0; i < num_entries; ++i) {
 377                 gint32 state;
 378
 379         retry:
 380                 state = entries [i].state;
 381
 382                 switch (state) {
 383                 case STAGE_ENTRY_FREE:
 384                 case STAGE_ENTRY_INVALID:
 385                         continue;
 386                 case STAGE_ENTRY_BUSY:
 387                         /* BUSY -> INVALID */
 388                         /*
 389                          * This must be done atomically, because the filler thread can set
 390                          * the entry to `USED`, in which case we must process it, so we must
 391                          * detect that eventuality.
 392                          */
 393                         if (InterlockedCompareExchange (&entries [i].state, STAGE_ENTRY_INVALID, STAGE_ENTRY_BUSY) != STAGE_ENTRY_BUSY)
 394                                 goto retry;
 395                         continue;
 396                 case STAGE_ENTRY_USED:
 397                         break;
 398                 default:
 399                         SGEN_ASSERT (0, FALSE, "Invalid stage entry state");
 400                         break;
 401                 }
 402
 403                 /* state is USED */
 404
 405                 process_func (entries [i].obj, entries [i].user_data, i);
 406
 407                 entries [i].obj = NULL;
 408                 entries [i].user_data = NULL;
 409
 410                 mono_memory_write_barrier ();
 411
 412                 /* USED -> FREE */
 413                 /*
 414                  * This transition only happens here, so we don't have to do it atomically.
 415                  */
 416                 entries [i].state = STAGE_ENTRY_FREE;
 417         }
 418
 419         mono_memory_write_barrier ();
 420
 421         *next_entry = 0;
 422 }
 423
 424 #ifdef HEAVY_STATISTICS
 425 static guint64 stat_overflow_abort = 0;
 426 static guint64 stat_wait_for_processing = 0;
 427 static guint64 stat_increment_other_thread = 0;
 428 static guint64 stat_index_decremented = 0;
 429 static guint64 stat_entry_invalidated = 0;
 430 static guint64 stat_success = 0;
 431 #endif
 432
 433 static int
 434 add_stage_entry (int num_entries, volatile gint32 *next_entry, StageEntry *entries, GCObject *obj, void *user_data)
 435 {
 436         gint32 index, new_next_entry, old_next_entry;
 437         gint32 previous_state;
 438
 439  retry:
 440         for (;;) {
 441                 index = *next_entry;
 442                 if (index >= num_entries) {
 443                         HEAVY_STAT (++stat_overflow_abort);
 444                         return -1;
 445                 }
 446                 if (index < 0) {
 447                         /*
 448                          * Backed-off waiting is way more efficient than even using a
 449                          * dedicated lock for this.
 450                          */
 451                         while ((index = *next_entry) < 0) {
 452                                 /*
 453                                  * This seems like a good value.  Determined by timing
 454                                  * sgen-weakref-stress.exe.
 455                                  */
 456                                 g_usleep (200);
 457                                 HEAVY_STAT (++stat_wait_for_processing);
 458                         }
 459                         continue;
 460                 }
 461                 /* FREE -> BUSY */
 462                 if (entries [index].state != STAGE_ENTRY_FREE ||
 463                                 InterlockedCompareExchange (&entries [index].state, STAGE_ENTRY_BUSY, STAGE_ENTRY_FREE) != STAGE_ENTRY_FREE) {
 464                         /*
 465                          * If we can't get the entry it must be because another thread got
 466                          * it first.  We don't want to wait for that thread to increment
 467                          * `next_entry`, so we try to do it ourselves.  Whether we succeed
 468                          * or not, we start over.
 469                          */
 470                         if (*next_entry == index) {
 471                                 InterlockedCompareExchange (next_entry, index + 1, index);
 472                                 //g_print ("tried increment for other thread\n");
 473                                 HEAVY_STAT (++stat_increment_other_thread);
 474                         }
 475                         continue;
 476                 }
 477                 /* state is BUSY now */
 478                 mono_memory_write_barrier ();
 479                 /*
 480                  * Incrementing `next_entry` must happen after setting the state to `BUSY`.
 481                  * If it were the other way around, it would be possible that after a filler
 482                  * incremented the index, other threads fill up the queue, the queue is
 483                  * drained, the original filler finally fills in the slot, but `next_entry`
 484                  * ends up at the start of the queue, and new entries are written in the
 485                  * queue in front of, not behind, the original filler's entry.
 486                  *
 487                  * We don't actually require that the CAS succeeds, but we do require that
 488                  * the value of `next_entry` is not lower than our index.  Since the drainer
 489                  * sets it to `-1`, that also takes care of the case that the drainer is
 490                  * currently running.
 491                  */
 492                 old_next_entry = InterlockedCompareExchange (next_entry, index + 1, index);
 493                 if (old_next_entry < index) {
 494                         /* BUSY -> FREE */
 495                         /* INVALID -> FREE */
 496                         /*
 497                          * The state might still be `BUSY`, or the drainer could have set it
 498                          * to `INVALID`.  In either case, there's no point in CASing.  Set
 499                          * it to `FREE` and start over.
 500                          */
 501                         entries [index].state = STAGE_ENTRY_FREE;
 502                         HEAVY_STAT (++stat_index_decremented);
 503                         continue;
 504                 }
 505                 break;
 506         }
 507
 508         SGEN_ASSERT (0, index >= 0 && index < num_entries, "Invalid index");
 509
 510         entries [index].obj = obj;
 511         entries [index].user_data = user_data;
 512
 513         mono_memory_write_barrier ();
 514
 515         new_next_entry = *next_entry;
 516         mono_memory_read_barrier ();
 517         /* BUSY -> USED */
 518         /*
 519          * A `BUSY` entry will either still be `BUSY` or the drainer will have set it to
 520          * `INVALID`.  In the former case, we set it to `USED` and we're finished.  In the
 521          * latter case, we reset it to `FREE` and start over.
 522          */
 523         previous_state = InterlockedCompareExchange (&entries [index].state, STAGE_ENTRY_USED, STAGE_ENTRY_BUSY);
 524         if (previous_state == STAGE_ENTRY_BUSY) {
 525                 SGEN_ASSERT (0, new_next_entry >= index || new_next_entry < 0, "Invalid next entry index - as long as we're busy, other thread can only increment or invalidate it");
 526                 HEAVY_STAT (++stat_success);
 527                 return index;
 528         }
 529
 530         SGEN_ASSERT (0, previous_state == STAGE_ENTRY_INVALID, "Invalid state transition - other thread can only make busy state invalid");
 531         entries [index].obj = NULL;
 532         entries [index].user_data = NULL;
 533         mono_memory_write_barrier ();
 534         /* INVALID -> FREE */
 535         entries [index].state = STAGE_ENTRY_FREE;
 536
 537         HEAVY_STAT (++stat_entry_invalidated);
 538
 539         goto retry;
 540 }
 541
 542 /* LOCKING: requires that the GC lock is held */
 543 static void
 544 process_fin_stage_entry (GCObject *obj, void *user_data, int index)
 545 {
 546         if (ptr_in_nursery (obj))
 547                 register_for_finalization (obj, user_data, GENERATION_NURSERY);
 548         else
 549                 register_for_finalization (obj, user_data, GENERATION_OLD);
 550 }
 551
 552 /* LOCKING: requires that the GC lock is held */
 553 void
 554 sgen_process_fin_stage_entries (void)
 555 {
 556         lock_stage_for_processing (&next_fin_stage_entry);
 557         process_stage_entries (NUM_FIN_STAGE_ENTRIES, &next_fin_stage_entry, fin_stage_entries, process_fin_stage_entry);
 558 }
 559
 560 void
 561 sgen_object_register_for_finalization (GCObject *obj, void *user_data)
 562 {
 563         while (add_stage_entry (NUM_FIN_STAGE_ENTRIES, &next_fin_stage_entry, fin_stage_entries, obj, user_data) == -1) {
 564                 if (try_lock_stage_for_processing (NUM_FIN_STAGE_ENTRIES, &next_fin_stage_entry)) {
 565                         LOCK_GC;
 566                         process_stage_entries (NUM_FIN_STAGE_ENTRIES, &next_fin_stage_entry, fin_stage_entries, process_fin_stage_entry);
 567                         UNLOCK_GC;
 568                 }
 569         }
 570 }
 571
 572 /* LOCKING: requires that the GC lock is held */
 573 static int
 574 finalizers_with_predicate (SgenObjectPredicateFunc predicate, void *user_data, GCObject **out_array, int out_size, SgenHashTable *hash_table)
 575 {
 576         GCObject *object;
 577         gpointer dummy G_GNUC_UNUSED;
 578         int count;
 579
 580         if (no_finalize || !out_size || !out_array)
 581                 return 0;
 582         count = 0;
 583         SGEN_HASH_TABLE_FOREACH (hash_table, object, dummy) {
 584                 object = tagged_object_get_object (object);
 585
 586                 if (predicate (object, user_data)) {
 587                         /* remove and put in out_array */
 588                         SGEN_HASH_TABLE_FOREACH_REMOVE (TRUE);
 589                         out_array [count ++] = object;
 590                         SGEN_LOG (5, "Collecting object for finalization: %p (%s) (%d)", object, sgen_client_vtable_get_name (SGEN_LOAD_VTABLE (object)), sgen_hash_table_num_entries (hash_table));
 591                         if (count == out_size)
 592                                 return count;
 593                         continue;
 594                 }
 595         } SGEN_HASH_TABLE_FOREACH_END;
 596         return count;
 597 }
 598
 599 /**
 600  * sgen_gather_finalizers_if:
 601  * @predicate: predicate function
 602  * @user_data: predicate function data argument
 603  * @out_array: output array
 604  * @out_size: size of output array
 605  *
 606  * Store inside @out_array up to @out_size objects that match @predicate. Returns the number
 607  * of stored items. Can be called repeteadly until it returns 0.
 608  *
 609  * The items are removed from the finalizer data structure, so the caller is supposed
 610  * to finalize them.
 611  *
 612  * @out_array me be on the stack, or registered as a root, to allow the GC to know the
 613  * objects are still alive.
 614  */
 615 int
 616 sgen_gather_finalizers_if (SgenObjectPredicateFunc predicate, void *user_data, GCObject **out_array, int out_size)
 617 {
 618         int result;
 619
 620         LOCK_GC;
 621         sgen_process_fin_stage_entries ();
 622         result = finalizers_with_predicate (predicate, user_data, (GCObject**)out_array, out_size, &minor_finalizable_hash);
 623         if (result < out_size) {
 624                 result += finalizers_with_predicate (predicate, user_data, (GCObject**)out_array + result, out_size - result,
 625                         &major_finalizable_hash);
 626         }
 627         UNLOCK_GC;
 628
 629         return result;
 630 }
 631
 632 static SgenHashTable minor_disappearing_link_hash = SGEN_HASH_TABLE_INIT (INTERNAL_MEM_DISLINK_TABLE, INTERNAL_MEM_DISLINK, 0, sgen_aligned_addr_hash, NULL);
 633 static SgenHashTable major_disappearing_link_hash = SGEN_HASH_TABLE_INIT (INTERNAL_MEM_DISLINK_TABLE, INTERNAL_MEM_DISLINK, 0, sgen_aligned_addr_hash, NULL);
 634
 635 static SgenHashTable*
 636 get_dislink_hash_table (int generation)
 637 {
 638         switch (generation) {
 639         case GENERATION_NURSERY: return &minor_disappearing_link_hash;
 640         case GENERATION_OLD: return &major_disappearing_link_hash;
 641         default: g_assert_not_reached ();
 642         }
 643 }
 644
 645 /* LOCKING: assumes the GC lock is held */
 646 static void
 647 add_or_remove_disappearing_link (GCObject *obj, void **link, int generation)
 648 {
 649         SgenHashTable *hash_table = get_dislink_hash_table (generation);
 650
 651         if (!obj) {
 652                 if (sgen_hash_table_remove (hash_table, link, NULL)) {
 653                         SGEN_LOG (5, "Removed dislink %p (%d) from %s table",
 654                                         link, hash_table->num_entries, sgen_generation_name (generation));
 655                 }
 656                 return;
 657         }
 658
 659         sgen_hash_table_replace (hash_table, link, NULL, NULL);
 660         SGEN_LOG (5, "Added dislink for object: %p (%s) at %p to %s table",
 661                         obj, sgen_client_vtable_get_name (SGEN_LOAD_VTABLE_UNCHECKED (obj)), link, sgen_generation_name (generation));
 662 }
 663
 664 /* LOCKING: requires that the GC lock is held */
 665 void
 666 sgen_null_link_in_range (int generation, gboolean before_finalization, ScanCopyContext ctx)
 667 {
 668         CopyOrMarkObjectFunc copy_func = ctx.ops->copy_or_mark_object;
 669         GrayQueue *queue = ctx.queue;
 670         void **link;
 671         gpointer dummy G_GNUC_UNUSED;
 672         SgenHashTable *hash = get_dislink_hash_table (generation);
 673
 674         SGEN_HASH_TABLE_FOREACH (hash, link, dummy) {
 675                 char *object;
 676                 gboolean track;
 677
 678                 /*
 679                 We null a weak link before unregistering it, so it's possible that a thread is
 680                 suspended right in between setting the content to null and staging the unregister.
 681
 682                 The rest of this code cannot handle null links as DISLINK_OBJECT (NULL) produces an invalid address.
 683
 684                 We should simply skip the entry as the staged removal will take place during the next GC.
 685                 */
 686                 if (!*link) {
 687                         SGEN_LOG (5, "Dislink %p was externally nullified", link);
 688                         continue;
 689                 }
 690
 691                 track = DISLINK_TRACK (link);
 692                 /*
 693                  * Tracked references are processed after
 694                  * finalization handling whereas standard weak
 695                  * references are processed before.  If an
 696                  * object is still not marked after finalization
 697                  * handling it means that it either doesn't have
 698                  * a finalizer or the finalizer has already run,
 699                  * so we must null a tracking reference.
 700                  */
 701                 if (track != before_finalization) {
 702                         object = DISLINK_OBJECT (link);
 703                         /*
 704                         We should guard against a null object been hidden. This can sometimes happen.
 705                         */
 706                         if (!object) {
 707                                 SGEN_LOG (5, "Dislink %p with a hidden null object", link);
 708                                 continue;
 709                         }
 710
 711                         if (!major_collector.is_object_live (object)) {
 712                                 if (sgen_gc_is_object_ready_for_finalization (object)) {
 713                                         *link = NULL;
 714                                         binary_protocol_dislink_update (link, NULL, 0, 0);
 715                                         SGEN_LOG (5, "Dislink nullified at %p to GCed object %p", link, object);
 716                                         SGEN_HASH_TABLE_FOREACH_REMOVE (TRUE);
 717                                         continue;
 718                                 } else {
 719                                         char *copy = object;
 720                                         copy_func ((void**)&copy, queue);
 721
 722                                         /* Update pointer if it's moved.  If the object
 723                                          * has been moved out of the nursery, we need to
 724                                          * remove the link from the minor hash table to
 725                                          * the major one.
 726                                          *
 727                                          * FIXME: what if an object is moved earlier?
 728                                          */
 729
 730                                         if (hash == &minor_disappearing_link_hash && !ptr_in_nursery (copy)) {
 731                                                 SGEN_HASH_TABLE_FOREACH_REMOVE (TRUE);
 732
 733                                                 g_assert (copy);
 734                                                 *link = HIDE_POINTER (copy, track);
 735                                                 add_or_remove_disappearing_link ((GCObject*)copy, link, GENERATION_OLD);
 736                                                 binary_protocol_dislink_update (link, copy, track, 0);
 737
 738                                                 SGEN_LOG (5, "Upgraded dislink at %p to major because object %p moved to %p", link, object, copy);
 739
 740                                                 continue;
 741                                         } else {
 742                                                 *link = HIDE_POINTER (copy, track);
 743                                                 binary_protocol_dislink_update (link, copy, track, 0);
 744                                                 SGEN_LOG (5, "Updated dislink at %p to %p", link, DISLINK_OBJECT (link));
 745                                         }
 746                                 }
 747                         }
 748                 }
 749         } SGEN_HASH_TABLE_FOREACH_END;
 750 }
 751
 752 /* LOCKING: requires that the GC lock is held */
 753 void
 754 sgen_null_links_if (SgenObjectPredicateFunc predicate, void *data, int generation)
 755 {
 756         void **link;
 757         gpointer dummy G_GNUC_UNUSED;
 758         SgenHashTable *hash = get_dislink_hash_table (generation);
 759         SGEN_HASH_TABLE_FOREACH (hash, link, dummy) {
 760                 char *object = DISLINK_OBJECT (link);
 761
 762                 if (!*link)
 763                         continue;
 764
 765                 if (predicate ((GCObject*)object, data)) {
 766                         *link = NULL;
 767                         binary_protocol_dislink_update (link, NULL, 0, 0);
 768                         SGEN_LOG (5, "Dislink nullified by predicate at %p to GCed object %p", link, object);
 769                         SGEN_HASH_TABLE_FOREACH_REMOVE (FALSE /* TRUE */);
 770                         continue;
 771                 }
 772         } SGEN_HASH_TABLE_FOREACH_END;
 773 }
 774
 775 void
 776 sgen_remove_finalizers_if (SgenObjectPredicateFunc predicate, void *user_data, int generation)
 777 {
 778         SgenHashTable *hash_table = get_finalize_entry_hash_table (generation);
 779         GCObject *object;
 780         gpointer dummy G_GNUC_UNUSED;
 781
 782         SGEN_HASH_TABLE_FOREACH (hash_table, object, dummy) {
 783                 object = tagged_object_get_object (object);
 784
 785                 if (predicate (object, user_data)) {
 786                         SGEN_HASH_TABLE_FOREACH_REMOVE (TRUE);
 787                         continue;
 788                 }
 789         } SGEN_HASH_TABLE_FOREACH_END;
 790 }
 791
 792 /* LOCKING: requires that the GC lock is held */
 793 static void
 794 process_dislink_stage_entry (GCObject *obj, void *_link, int index)
 795 {
 796         void **link = _link;
 797
 798         if (index >= 0)
 799                 binary_protocol_dislink_process_staged (link, obj, index);
 800
 801         add_or_remove_disappearing_link (NULL, link, GENERATION_NURSERY);
 802         add_or_remove_disappearing_link (NULL, link, GENERATION_OLD);
 803         if (obj) {
 804                 if (ptr_in_nursery (obj))
 805                         add_or_remove_disappearing_link (obj, link, GENERATION_NURSERY);
 806                 else
 807                         add_or_remove_disappearing_link (obj, link, GENERATION_OLD);
 808         }
 809 }
 810
 811 #define NUM_DISLINK_STAGE_ENTRIES       1024
 812
 813 static volatile gint32 next_dislink_stage_entry = 0;
 814 static StageEntry dislink_stage_entries [NUM_DISLINK_STAGE_ENTRIES];
 815
 816 /* LOCKING: requires that the GC lock is held */
 817 void
 818 sgen_process_dislink_stage_entries (void)
 819 {
 820         lock_stage_for_processing (&next_dislink_stage_entry);
 821         process_stage_entries (NUM_DISLINK_STAGE_ENTRIES, &next_dislink_stage_entry, dislink_stage_entries, process_dislink_stage_entry);
 822 }
 823
 824 void
 825 sgen_register_disappearing_link (GCObject *obj, void **link, gboolean track, gboolean in_gc)
 826 {
 827         if (obj)
 828                 *link = HIDE_POINTER (obj, track);
 829         else
 830                 *link = NULL;
 831
 832 #if 1
 833         if (in_gc) {
 834                 binary_protocol_dislink_update (link, obj, track, 0);
 835                 process_dislink_stage_entry (obj, link, -1);
 836         } else {
 837                 int index;
 838                 binary_protocol_dislink_update (link, obj, track, 1);
 839                 while ((index = add_stage_entry (NUM_DISLINK_STAGE_ENTRIES, &next_dislink_stage_entry, dislink_stage_entries, obj, link)) == -1) {
 840                         if (try_lock_stage_for_processing (NUM_DISLINK_STAGE_ENTRIES, &next_dislink_stage_entry)) {
 841                                 LOCK_GC;
 842                                 process_stage_entries (NUM_DISLINK_STAGE_ENTRIES, &next_dislink_stage_entry, dislink_stage_entries, process_dislink_stage_entry);
 843                                 UNLOCK_GC;
 844                         }
 845                 }
 846                 binary_protocol_dislink_update_staged (link, obj, track, index);
 847         }
 848 #else
 849         if (!in_gc)
 850                 LOCK_GC;
 851         binary_protocol_dislink_update (link, obj, track, 0);
 852         process_dislink_stage_entry (obj, link, -1);
 853         if (!in_gc)
 854                 UNLOCK_GC;
 855 #endif
 856 }
 857
 858 void
 859 sgen_init_fin_weak_hash (void)
 860 {
 861 #ifdef HEAVY_STATISTICS
 862         mono_counters_register ("FinWeak Successes", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &stat_success);
 863         mono_counters_register ("FinWeak Overflow aborts", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &stat_overflow_abort);
 864         mono_counters_register ("FinWeak Wait for processing", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &stat_wait_for_processing);
 865         mono_counters_register ("FinWeak Increment other thread", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &stat_increment_other_thread);
 866         mono_counters_register ("FinWeak Index decremented", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &stat_index_decremented);
 867         mono_counters_register ("FinWeak Entry invalidated", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &stat_entry_invalidated);
 868 #endif
 869 }
 870
 871 #endif /* HAVE_SGEN_GC */