1 /*
   2  * Copyright (c) 1997, 2015, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "classfile/systemDictionary.hpp"
  27 #include "classfile/vmSymbols.hpp"
  28 #include "gc_implementation/shared/liveRange.hpp"
  29 #include "gc_implementation/shared/markSweep.hpp"
  30 #include "gc_implementation/shared/spaceDecorator.hpp"
  31 #include "gc_interface/collectedHeap.inline.hpp"
  32 #include "memory/blockOffsetTable.inline.hpp"
  33 #include "memory/defNewGeneration.hpp"
  34 #include "memory/genCollectedHeap.hpp"
  35 #include "memory/space.hpp"
  36 #include "memory/space.inline.hpp"
  37 #include "memory/universe.inline.hpp"
  38 #include "oops/oop.inline.hpp"
  39 #include "runtime/java.hpp"
  40 #include "runtime/atomic.inline.hpp"
  41 #include "runtime/prefetch.inline.hpp"
  42 #include "runtime/orderAccess.inline.hpp"
  43 #include "runtime/safepoint.hpp"
  44 #include "utilities/copy.hpp"
  45 #include "utilities/globalDefinitions.hpp"
  46 #include "utilities/macros.hpp"
  47 
  48 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
  49 
  50 HeapWord* DirtyCardToOopClosure::get_actual_top(HeapWord* top,
  51                                                 HeapWord* top_obj) {
  52   if (top_obj != NULL) {
  53     if (_sp->block_is_obj(top_obj)) {
  54       if (_precision == CardTableModRefBS::ObjHeadPreciseArray) {
  55         if (oop(top_obj)->is_objArray() || oop(top_obj)->is_typeArray()) {
  56           // An arrayOop is starting on the dirty card - since we do exact
  57           // store checks for objArrays we are done.
  58         } else {
  59           // Otherwise, it is possible that the object starting on the dirty
  60           // card spans the entire card, and that the store happened on a
  61           // later card.  Figure out where the object ends.
  62           // Use the block_size() method of the space over which
  63           // the iteration is being done.  That space (e.g. CMS) may have
  64           // specific requirements on object sizes which will
  65           // be reflected in the block_size() method.
  66           top = top_obj + oop(top_obj)->size();
  67         }
  68       }
  69     } else {
  70       top = top_obj;
  71     }
  72   } else {
  73     assert(top == _sp->end(), "only case where top_obj == NULL");
  74   }
  75   return top;
  76 }
  77 
  78 void DirtyCardToOopClosure::walk_mem_region(MemRegion mr,
  79                                             HeapWord* bottom,
  80                                             HeapWord* top) {
  81   // 1. Blocks may or may not be objects.
  82   // 2. Even when a block_is_obj(), it may not entirely
  83   //    occupy the block if the block quantum is larger than
  84   //    the object size.
  85   // We can and should try to optimize by calling the non-MemRegion
  86   // version of oop_iterate() for all but the extremal objects
  87   // (for which we need to call the MemRegion version of
  88   // oop_iterate()) To be done post-beta XXX
  89   for (; bottom < top; bottom += _sp->block_size(bottom)) {
  90     // As in the case of contiguous space above, we'd like to
  91     // just use the value returned by oop_iterate to increment the
  92     // current pointer; unfortunately, that won't work in CMS because
  93     // we'd need an interface change (it seems) to have the space
  94     // "adjust the object size" (for instance pad it up to its
  95     // block alignment or minimum block size restrictions. XXX
  96     if (_sp->block_is_obj(bottom) &&
  97         !_sp->obj_allocated_since_save_marks(oop(bottom))) {
  98       oop(bottom)->oop_iterate(_cl, mr);
  99     }
 100   }
 101 }
 102 
 103 // We get called with "mr" representing the dirty region
 104 // that we want to process. Because of imprecise marking,
 105 // we may need to extend the incoming "mr" to the right,
 106 // and scan more. However, because we may already have
 107 // scanned some of that extended region, we may need to
 108 // trim its right-end back some so we do not scan what
 109 // we (or another worker thread) may already have scanned
 110 // or planning to scan.
 111 void DirtyCardToOopClosure::do_MemRegion(MemRegion mr) {
 112 
 113   // Some collectors need to do special things whenever their dirty
 114   // cards are processed. For instance, CMS must remember mutator updates
 115   // (i.e. dirty cards) so as to re-scan mutated objects.
 116   // Such work can be piggy-backed here on dirty card scanning, so as to make
 117   // it slightly more efficient than doing a complete non-destructive pre-scan
 118   // of the card table.
 119   MemRegionClosure* pCl = _sp->preconsumptionDirtyCardClosure();
 120   if (pCl != NULL) {
 121     pCl->do_MemRegion(mr);
 122   }
 123 
 124   HeapWord* bottom = mr.start();
 125   HeapWord* last = mr.last();
 126   HeapWord* top = mr.end();
 127   HeapWord* bottom_obj;
 128   HeapWord* top_obj;
 129 
 130   assert(_precision == CardTableModRefBS::ObjHeadPreciseArray ||
 131          _precision == CardTableModRefBS::Precise,
 132          "Only ones we deal with for now.");
 133 
 134   assert(_precision != CardTableModRefBS::ObjHeadPreciseArray ||
 135          _cl->idempotent() || _last_bottom == NULL ||
 136          top <= _last_bottom,
 137          "Not decreasing");
 138   NOT_PRODUCT(_last_bottom = mr.start());
 139 
 140   bottom_obj = _sp->block_start(bottom);
 141   top_obj    = _sp->block_start(last);
 142 
 143   assert(bottom_obj <= bottom, "just checking");
 144   assert(top_obj    <= top,    "just checking");
 145 
 146   // Given what we think is the top of the memory region and
 147   // the start of the object at the top, get the actual
 148   // value of the top.
 149   top = get_actual_top(top, top_obj);
 150 
 151   // If the previous call did some part of this region, don't redo.
 152   if (_precision == CardTableModRefBS::ObjHeadPreciseArray &&
 153       _min_done != NULL &&
 154       _min_done < top) {
 155     top = _min_done;
 156   }
 157 
 158   // Top may have been reset, and in fact may be below bottom,
 159   // e.g. the dirty card region is entirely in a now free object
 160   // -- something that could happen with a concurrent sweeper.
 161   bottom = MIN2(bottom, top);
 162   MemRegion extended_mr = MemRegion(bottom, top);
 163   assert(bottom <= top &&
 164          (_precision != CardTableModRefBS::ObjHeadPreciseArray ||
 165           _min_done == NULL ||
 166           top <= _min_done),
 167          "overlap!");
 168 
 169   // Walk the region if it is not empty; otherwise there is nothing to do.
 170   if (!extended_mr.is_empty()) {
 171     walk_mem_region(extended_mr, bottom_obj, top);
 172   }
 173 
 174   // An idempotent closure might be applied in any order, so we don't
 175   // record a _min_done for it.
 176   if (!_cl->idempotent()) {
 177     _min_done = bottom;
 178   } else {
 179     assert(_min_done == _last_explicit_min_done,
 180            "Don't update _min_done for idempotent cl");
 181   }
 182 }
 183 
 184 DirtyCardToOopClosure* Space::new_dcto_cl(ExtendedOopClosure* cl,
 185                                           CardTableModRefBS::PrecisionStyle precision,
 186                                           HeapWord* boundary) {
 187   return new DirtyCardToOopClosure(this, cl, precision, boundary);
 188 }
 189 
 190 HeapWord* ContiguousSpaceDCTOC::get_actual_top(HeapWord* top,
 191                                                HeapWord* top_obj) {
 192   if (top_obj != NULL && top_obj < (_sp->toContiguousSpace())->top()) {
 193     if (_precision == CardTableModRefBS::ObjHeadPreciseArray) {
 194       if (oop(top_obj)->is_objArray() || oop(top_obj)->is_typeArray()) {
 195         // An arrayOop is starting on the dirty card - since we do exact
 196         // store checks for objArrays we are done.
 197       } else {
 198         // Otherwise, it is possible that the object starting on the dirty
 199         // card spans the entire card, and that the store happened on a
 200         // later card.  Figure out where the object ends.
 201         assert(_sp->block_size(top_obj) == (size_t) oop(top_obj)->size(),
 202           "Block size and object size mismatch");
 203         top = top_obj + oop(top_obj)->size();
 204       }
 205     }
 206   } else {
 207     top = (_sp->toContiguousSpace())->top();
 208   }
 209   return top;
 210 }
 211 
 212 void Filtering_DCTOC::walk_mem_region(MemRegion mr,
 213                                       HeapWord* bottom,
 214                                       HeapWord* top) {
 215   // Note that this assumption won't hold if we have a concurrent
 216   // collector in this space, which may have freed up objects after
 217   // they were dirtied and before the stop-the-world GC that is
 218   // examining cards here.
 219   assert(bottom < top, "ought to be at least one obj on a dirty card.");
 220 
 221   if (_boundary != NULL) {
 222     // We have a boundary outside of which we don't want to look
 223     // at objects, so create a filtering closure around the
 224     // oop closure before walking the region.
 225     FilteringClosure filter(_boundary, _cl);
 226     walk_mem_region_with_cl(mr, bottom, top, &filter);
 227   } else {
 228     // No boundary, simply walk the heap with the oop closure.
 229     walk_mem_region_with_cl(mr, bottom, top, _cl);
 230   }
 231 
 232 }
 233 
 234 // We must replicate this so that the static type of "FilteringClosure"
 235 // (see above) is apparent at the oop_iterate calls.
 236 #define ContiguousSpaceDCTOC__walk_mem_region_with_cl_DEFN(ClosureType) \
 237 void ContiguousSpaceDCTOC::walk_mem_region_with_cl(MemRegion mr,        \
 238                                                    HeapWord* bottom,    \
 239                                                    HeapWord* top,       \
 240                                                    ClosureType* cl) {   \
 241   bottom += oop(bottom)->oop_iterate(cl, mr);                           \
 242   if (bottom < top) {                                                   \
 243     HeapWord* next_obj = bottom + oop(bottom)->size();                  \
 244     while (next_obj < top) {                                            \
 245       /* Bottom lies entirely below top, so we can call the */          \
 246       /* non-memRegion version of oop_iterate below. */                 \
 247       oop(bottom)->oop_iterate(cl);                                     \
 248       bottom = next_obj;                                                \
 249       next_obj = bottom + oop(bottom)->size();                          \
 250     }                                                                   \
 251     /* Last object. */                                                  \
 252     oop(bottom)->oop_iterate(cl, mr);                                   \
 253   }                                                                     \
 254 }
 255 
 256 // (There are only two of these, rather than N, because the split is due
 257 // only to the introduction of the FilteringClosure, a local part of the
 258 // impl of this abstraction.)
 259 ContiguousSpaceDCTOC__walk_mem_region_with_cl_DEFN(ExtendedOopClosure)
 260 ContiguousSpaceDCTOC__walk_mem_region_with_cl_DEFN(FilteringClosure)
 261 
 262 DirtyCardToOopClosure*
 263 ContiguousSpace::new_dcto_cl(ExtendedOopClosure* cl,
 264                              CardTableModRefBS::PrecisionStyle precision,
 265                              HeapWord* boundary) {
 266   return new ContiguousSpaceDCTOC(this, cl, precision, boundary);
 267 }
 268 
 269 void Space::initialize(MemRegion mr,
 270                        bool clear_space,
 271                        bool mangle_space) {
 272   HeapWord* bottom = mr.start();
 273   HeapWord* end    = mr.end();
 274   assert(Universe::on_page_boundary(bottom) && Universe::on_page_boundary(end),
 275          "invalid space boundaries");
 276   set_bottom(bottom);
 277   set_end(end);
 278   if (clear_space) clear(mangle_space);
 279 }
 280 
 281 void Space::clear(bool mangle_space) {
 282   if (ZapUnusedHeapArea && mangle_space) {
 283     mangle_unused_area();
 284   }
 285 }
 286 
 287 ContiguousSpace::ContiguousSpace(): CompactibleSpace(), _top(NULL),
 288     _concurrent_iteration_safe_limit(NULL) {
 289   _mangler = new GenSpaceMangler(this);
 290 }
 291 
 292 ContiguousSpace::~ContiguousSpace() {
 293   delete _mangler;
 294 }
 295 
 296 void ContiguousSpace::initialize(MemRegion mr,
 297                                  bool clear_space,
 298                                  bool mangle_space)
 299 {
 300   CompactibleSpace::initialize(mr, clear_space, mangle_space);
 301   set_concurrent_iteration_safe_limit(top());
 302 }
 303 
 304 void ContiguousSpace::clear(bool mangle_space) {
 305   set_top(bottom());
 306   set_saved_mark();
 307   CompactibleSpace::clear(mangle_space);
 308 }
 309 
 310 bool ContiguousSpace::is_free_block(const HeapWord* p) const {
 311   return p >= _top;
 312 }
 313 
 314 void OffsetTableContigSpace::clear(bool mangle_space) {
 315   ContiguousSpace::clear(mangle_space);
 316   _offsets.initialize_threshold();
 317 }
 318 
 319 void OffsetTableContigSpace::set_bottom(HeapWord* new_bottom) {
 320   Space::set_bottom(new_bottom);
 321   _offsets.set_bottom(new_bottom);
 322 }
 323 
 324 void OffsetTableContigSpace::set_end(HeapWord* new_end) {
 325   // Space should not advertise an increase in size
 326   // until after the underlying offset table has been enlarged.
 327   _offsets.resize(pointer_delta(new_end, bottom()));
 328   Space::set_end(new_end);
 329 }
 330 
 331 #ifndef PRODUCT
 332 
 333 void ContiguousSpace::set_top_for_allocations(HeapWord* v) {
 334   mangler()->set_top_for_allocations(v);
 335 }
 336 void ContiguousSpace::set_top_for_allocations() {
 337   mangler()->set_top_for_allocations(top());
 338 }
 339 void ContiguousSpace::check_mangled_unused_area(HeapWord* limit) {
 340   mangler()->check_mangled_unused_area(limit);
 341 }
 342 
 343 void ContiguousSpace::check_mangled_unused_area_complete() {
 344   mangler()->check_mangled_unused_area_complete();
 345 }
 346 
 347 // Mangled only the unused space that has not previously
 348 // been mangled and that has not been allocated since being
 349 // mangled.
 350 void ContiguousSpace::mangle_unused_area() {
 351   mangler()->mangle_unused_area();
 352 }
 353 void ContiguousSpace::mangle_unused_area_complete() {
 354   mangler()->mangle_unused_area_complete();
 355 }
 356 void ContiguousSpace::mangle_region(MemRegion mr) {
 357   // Although this method uses SpaceMangler::mangle_region() which
 358   // is not specific to a space, the when the ContiguousSpace version
 359   // is called, it is always with regard to a space and this
 360   // bounds checking is appropriate.
 361   MemRegion space_mr(bottom(), end());
 362   assert(space_mr.contains(mr), "Mangling outside space");
 363   SpaceMangler::mangle_region(mr);
 364 }
 365 #endif  // NOT_PRODUCT
 366 
 367 void CompactibleSpace::initialize(MemRegion mr,
 368                                   bool clear_space,
 369                                   bool mangle_space) {
 370   Space::initialize(mr, clear_space, mangle_space);
 371   set_compaction_top(bottom());
 372   _next_compaction_space = NULL;
 373 }
 374 
 375 void CompactibleSpace::clear(bool mangle_space) {
 376   Space::clear(mangle_space);
 377   _compaction_top = bottom();
 378 }
 379 
 380 HeapWord* CompactibleSpace::forward(oop q, size_t size,
 381                                     CompactPoint* cp, HeapWord* compact_top) {
 382   // q is alive
 383   // First check if we should switch compaction space
 384   assert(this == cp->space, "'this' should be current compaction space.");
 385   size_t compaction_max_size = pointer_delta(end(), compact_top);
 386   while (size > compaction_max_size) {
 387     // switch to next compaction space
 388     cp->space->set_compaction_top(compact_top);
 389     cp->space = cp->space->next_compaction_space();
 390     if (cp->space == NULL) {
 391       cp->gen = GenCollectedHeap::heap()->prev_gen(cp->gen);
 392       assert(cp->gen != NULL, "compaction must succeed");
 393       cp->space = cp->gen->first_compaction_space();
 394       assert(cp->space != NULL, "generation must have a first compaction space");
 395     }
 396     compact_top = cp->space->bottom();
 397     cp->space->set_compaction_top(compact_top);
 398     cp->threshold = cp->space->initialize_threshold();
 399     compaction_max_size = pointer_delta(cp->space->end(), compact_top);
 400   }
 401 
 402   // store the forwarding pointer into the mark word
 403   if ((HeapWord*)q != compact_top) {
 404     q->forward_to(oop(compact_top));
 405     assert(q->is_gc_marked(), "encoding the pointer should preserve the mark");
 406   } else {
 407     // if the object isn't moving we can just set the mark to the default
 408     // mark and handle it specially later on.
 409     q->init_mark();
 410     assert(q->forwardee() == NULL, "should be forwarded to NULL");
 411   }
 412 
 413   compact_top += size;
 414 
 415   // we need to update the offset table so that the beginnings of objects can be
 416   // found during scavenge.  Note that we are updating the offset table based on
 417   // where the object will be once the compaction phase finishes.
 418   if (compact_top > cp->threshold)
 419     cp->threshold =
 420       cp->space->cross_threshold(compact_top - size, compact_top);
 421   return compact_top;
 422 }
 423 
 424 
 425 bool CompactibleSpace::insert_deadspace(size_t& allowed_deadspace_words,
 426                                         HeapWord* q, size_t deadlength) {
 427   if (allowed_deadspace_words >= deadlength) {
 428     allowed_deadspace_words -= deadlength;
 429     CollectedHeap::fill_with_object(q, deadlength);
 430     oop(q)->set_mark(oop(q)->mark()->set_marked());
 431     assert((int) deadlength == oop(q)->size(), "bad filler object size");
 432     // Recall that we required "q == compaction_top".
 433     return true;
 434   } else {
 435     allowed_deadspace_words = 0;
 436     return false;
 437   }
 438 }
 439 
 440 void ContiguousSpace::prepare_for_compaction(CompactPoint* cp) {
 441   scan_and_forward(this, cp);
 442 }
 443 
 444 void CompactibleSpace::adjust_pointers() {
 445   // Check first is there is any work to do.
 446   if (used() == 0) {
 447     return;   // Nothing to do.
 448   }
 449 
 450   scan_and_adjust_pointers(this);
 451 }
 452 
 453 void CompactibleSpace::compact() {
 454   scan_and_compact(this);
 455 }
 456 
 457 void Space::print_short() const { print_short_on(tty); }
 458 
 459 void Space::print_short_on(outputStream* st) const {
 460   st->print(" space " SIZE_FORMAT "K, %3d%% used", capacity() / K,
 461               (int) ((double) used() * 100 / capacity()));
 462 }
 463 
 464 void Space::print() const { print_on(tty); }
 465 
 466 void Space::print_on(outputStream* st) const {
 467   print_short_on(st);
 468   st->print_cr(" [" INTPTR_FORMAT ", " INTPTR_FORMAT ")",
 469                 bottom(), end());
 470 }
 471 
 472 void ContiguousSpace::print_on(outputStream* st) const {
 473   print_short_on(st);
 474   st->print_cr(" [" INTPTR_FORMAT ", " INTPTR_FORMAT ", " INTPTR_FORMAT ")",
 475                 bottom(), top(), end());
 476 }
 477 
 478 void OffsetTableContigSpace::print_on(outputStream* st) const {
 479   print_short_on(st);
 480   st->print_cr(" [" INTPTR_FORMAT ", " INTPTR_FORMAT ", "
 481                 INTPTR_FORMAT ", " INTPTR_FORMAT ")",
 482               bottom(), top(), _offsets.threshold(), end());
 483 }
 484 
 485 void ContiguousSpace::verify() const {
 486   HeapWord* p = bottom();
 487   HeapWord* t = top();
 488   HeapWord* prev_p = NULL;
 489   while (p < t) {
 490     oop(p)->verify();
 491     prev_p = p;
 492     p += oop(p)->size();
 493   }
 494   guarantee(p == top(), "end of last object must match end of space");
 495   if (top() != end()) {
 496     guarantee(top() == block_start_const(end()-1) &&
 497               top() == block_start_const(top()),
 498               "top should be start of unallocated block, if it exists");
 499   }
 500 }
 501 
 502 void Space::oop_iterate(ExtendedOopClosure* blk) {
 503   ObjectToOopClosure blk2(blk);
 504   object_iterate(&blk2);
 505 }
 506 
 507 bool Space::obj_is_alive(const HeapWord* p) const {
 508   assert (block_is_obj(p), "The address should point to an object");
 509   return true;
 510 }
 511 
 512 #if INCLUDE_ALL_GCS
 513 #define ContigSpace_PAR_OOP_ITERATE_DEFN(OopClosureType, nv_suffix)         \
 514                                                                             \
 515   void ContiguousSpace::par_oop_iterate(MemRegion mr, OopClosureType* blk) {\
 516     HeapWord* obj_addr = mr.start();                                        \
 517     HeapWord* t = mr.end();                                                 \
 518     while (obj_addr < t) {                                                  \
 519       assert(oop(obj_addr)->is_oop(), "Should be an oop");                  \
 520       obj_addr += oop(obj_addr)->oop_iterate(blk);                          \
 521     }                                                                       \
 522   }
 523 
 524   ALL_PAR_OOP_ITERATE_CLOSURES(ContigSpace_PAR_OOP_ITERATE_DEFN)
 525 
 526 #undef ContigSpace_PAR_OOP_ITERATE_DEFN
 527 #endif // INCLUDE_ALL_GCS
 528 
 529 void ContiguousSpace::oop_iterate(ExtendedOopClosure* blk) {
 530   if (is_empty()) return;
 531   HeapWord* obj_addr = bottom();
 532   HeapWord* t = top();
 533   // Could call objects iterate, but this is easier.
 534   while (obj_addr < t) {
 535     obj_addr += oop(obj_addr)->oop_iterate(blk);
 536   }
 537 }
 538 
 539 void ContiguousSpace::object_iterate(ObjectClosure* blk) {
 540   if (is_empty()) return;
 541   WaterMark bm = bottom_mark();
 542   object_iterate_from(bm, blk);
 543 }
 544 
 545 // For a ContiguousSpace object_iterate() and safe_object_iterate()
 546 // are the same.
 547 void ContiguousSpace::safe_object_iterate(ObjectClosure* blk) {
 548   object_iterate(blk);
 549 }
 550 
 551 void ContiguousSpace::object_iterate_from(WaterMark mark, ObjectClosure* blk) {
 552   assert(mark.space() == this, "Mark does not match space");
 553   HeapWord* p = mark.point();
 554   while (p < top()) {
 555     blk->do_object(oop(p));
 556     p += oop(p)->size();
 557   }
 558 }
 559 
 560 HeapWord*
 561 ContiguousSpace::object_iterate_careful(ObjectClosureCareful* blk) {
 562   HeapWord * limit = concurrent_iteration_safe_limit();
 563   assert(limit <= top(), "sanity check");
 564   for (HeapWord* p = bottom(); p < limit;) {
 565     size_t size = blk->do_object_careful(oop(p));
 566     if (size == 0) {
 567       return p;  // failed at p
 568     } else {
 569       p += size;
 570     }
 571   }
 572   return NULL; // all done
 573 }
 574 
 575 #define ContigSpace_OOP_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix)  \
 576                                                                           \
 577 void ContiguousSpace::                                                    \
 578 oop_since_save_marks_iterate##nv_suffix(OopClosureType* blk) {            \
 579   HeapWord* t;                                                            \
 580   HeapWord* p = saved_mark_word();                                        \
 581   assert(p != NULL, "expected saved mark");                               \
 582                                                                           \
 583   const intx interval = PrefetchScanIntervalInBytes;                      \
 584   do {                                                                    \
 585     t = top();                                                            \
 586     while (p < t) {                                                       \
 587       Prefetch::write(p, interval);                                       \
 588       debug_only(HeapWord* prev = p);                                     \
 589       oop m = oop(p);                                                     \
 590       p += m->oop_iterate(blk);                                           \
 591     }                                                                     \
 592   } while (t < top());                                                    \
 593                                                                           \
 594   set_saved_mark_word(p);                                                 \
 595 }
 596 
 597 ALL_SINCE_SAVE_MARKS_CLOSURES(ContigSpace_OOP_SINCE_SAVE_MARKS_DEFN)
 598 
 599 #undef ContigSpace_OOP_SINCE_SAVE_MARKS_DEFN
 600 
 601 // Very general, slow implementation.
 602 HeapWord* ContiguousSpace::block_start_const(const void* p) const {
 603   assert(MemRegion(bottom(), end()).contains(p),
 604          err_msg("p (" PTR_FORMAT ") not in space [" PTR_FORMAT ", " PTR_FORMAT ")",
 605                   p, bottom(), end()));
 606   if (p >= top()) {
 607     return top();
 608   } else {
 609     HeapWord* last = bottom();
 610     HeapWord* cur = last;
 611     while (cur <= p) {
 612       last = cur;
 613       cur += oop(cur)->size();
 614     }
 615     assert(oop(last)->is_oop(),
 616            err_msg(PTR_FORMAT " should be an object start", last));
 617     return last;
 618   }
 619 }
 620 
 621 size_t ContiguousSpace::block_size(const HeapWord* p) const {
 622   assert(MemRegion(bottom(), end()).contains(p),
 623          err_msg("p (" PTR_FORMAT ") not in space [" PTR_FORMAT ", " PTR_FORMAT ")",
 624                   p, bottom(), end()));
 625   HeapWord* current_top = top();
 626   assert(p <= current_top,
 627          err_msg("p > current top - p: " PTR_FORMAT ", current top: " PTR_FORMAT,
 628                   p, current_top));
 629   assert(p == current_top || oop(p)->is_oop(),
 630          err_msg("p (" PTR_FORMAT ") is not a block start - "
 631                  "current_top: " PTR_FORMAT ", is_oop: %s",
 632                  p, current_top, BOOL_TO_STR(oop(p)->is_oop())));
 633   if (p < current_top) {
 634     return oop(p)->size();
 635   } else {
 636     assert(p == current_top, "just checking");
 637     return pointer_delta(end(), (HeapWord*) p);
 638   }
 639 }
 640 
 641 // This version requires locking.
 642 inline HeapWord* ContiguousSpace::allocate_impl(size_t size) {
 643   assert(Heap_lock->owned_by_self() ||
 644          (SafepointSynchronize::is_at_safepoint() && Thread::current()->is_VM_thread()),
 645          "not locked");
 646   HeapWord* obj = top();
 647   if (pointer_delta(end(), obj) >= size) {
 648     HeapWord* new_top = obj + size;
 649     set_top(new_top);
 650     assert(is_aligned(obj) && is_aligned(new_top), "checking alignment");
 651     return obj;
 652   } else {
 653     return NULL;
 654   }
 655 }
 656 
 657 // This version is lock-free.
 658 inline HeapWord* ContiguousSpace::par_allocate_impl(size_t size) {
 659   do {
 660     HeapWord* obj = top();
 661     if (pointer_delta(end(), obj) >= size) {
 662       HeapWord* new_top = obj + size;
 663       HeapWord* result = (HeapWord*)Atomic::cmpxchg_ptr(new_top, top_addr(), obj);
 664       // result can be one of two:
 665       //  the old top value: the exchange succeeded
 666       //  otherwise: the new value of the top is returned.
 667       if (result == obj) {
 668         assert(is_aligned(obj) && is_aligned(new_top), "checking alignment");
 669         return obj;
 670       }
 671     } else {
 672       return NULL;
 673     }
 674   } while (true);
 675 }
 676 
 677 HeapWord* ContiguousSpace::allocate_aligned(size_t size) {
 678   assert(Heap_lock->owned_by_self() || (SafepointSynchronize::is_at_safepoint() && Thread::current()->is_VM_thread()), "not locked");
 679   HeapWord* end_value = end();
 680 
 681   HeapWord* obj = CollectedHeap::align_allocation_or_fail(top(), end_value, SurvivorAlignmentInBytes);
 682   if (obj == NULL) {
 683     return NULL;
 684   }
 685 
 686   if (pointer_delta(end_value, obj) >= size) {
 687     HeapWord* new_top = obj + size;
 688     set_top(new_top);
 689     assert(is_ptr_aligned(obj, SurvivorAlignmentInBytes) && is_aligned(new_top),
 690       "checking alignment");
 691     return obj;
 692   } else {
 693     set_top(obj);
 694     return NULL;
 695   }
 696 }
 697 
 698 // Requires locking.
 699 HeapWord* ContiguousSpace::allocate(size_t size) {
 700   return allocate_impl(size);
 701 }
 702 
 703 // Lock-free.
 704 HeapWord* ContiguousSpace::par_allocate(size_t size) {
 705   return par_allocate_impl(size);
 706 }
 707 
 708 void ContiguousSpace::allocate_temporary_filler(int factor) {
 709   // allocate temporary type array decreasing free size with factor 'factor'
 710   assert(factor >= 0, "just checking");
 711   size_t size = pointer_delta(end(), top());
 712 
 713   // if space is full, return
 714   if (size == 0) return;
 715 
 716   if (factor > 0) {
 717     size -= size/factor;
 718   }
 719   size = align_object_size(size);
 720 
 721   const size_t array_header_size = typeArrayOopDesc::header_size(T_INT);
 722   if (size >= (size_t)align_object_size(array_header_size)) {
 723     size_t length = (size - array_header_size) * (HeapWordSize / sizeof(jint));
 724     // allocate uninitialized int array
 725     typeArrayOop t = (typeArrayOop) allocate(size);
 726     assert(t != NULL, "allocation should succeed");
 727     t->set_mark(markOopDesc::prototype());
 728     t->set_klass(Universe::intArrayKlassObj());
 729     t->set_length((int)length);
 730   } else {
 731     assert(size == CollectedHeap::min_fill_size(),
 732            "size for smallest fake object doesn't match");
 733     instanceOop obj = (instanceOop) allocate(size);
 734     obj->set_mark(markOopDesc::prototype());
 735     obj->set_klass_gap(0);
 736     obj->set_klass(SystemDictionary::Object_klass());
 737   }
 738 }
 739 
 740 HeapWord* OffsetTableContigSpace::initialize_threshold() {
 741   return _offsets.initialize_threshold();
 742 }
 743 
 744 HeapWord* OffsetTableContigSpace::cross_threshold(HeapWord* start, HeapWord* end) {
 745   _offsets.alloc_block(start, end);
 746   return _offsets.threshold();
 747 }
 748 
 749 OffsetTableContigSpace::OffsetTableContigSpace(BlockOffsetSharedArray* sharedOffsetArray,
 750                                                MemRegion mr) :
 751   _offsets(sharedOffsetArray, mr),
 752   _par_alloc_lock(Mutex::leaf, "OffsetTableContigSpace par alloc lock", true)
 753 {
 754   _offsets.set_contig_space(this);
 755   initialize(mr, SpaceDecorator::Clear, SpaceDecorator::Mangle);
 756 }
 757 
 758 #define OBJ_SAMPLE_INTERVAL 0
 759 #define BLOCK_SAMPLE_INTERVAL 100
 760 
 761 void OffsetTableContigSpace::verify() const {
 762   HeapWord* p = bottom();
 763   HeapWord* prev_p = NULL;
 764   int objs = 0;
 765   int blocks = 0;
 766 
 767   if (VerifyObjectStartArray) {
 768     _offsets.verify();
 769   }
 770 
 771   while (p < top()) {
 772     size_t size = oop(p)->size();
 773     // For a sampling of objects in the space, find it using the
 774     // block offset table.
 775     if (blocks == BLOCK_SAMPLE_INTERVAL) {
 776       guarantee(p == block_start_const(p + (size/2)),
 777                 "check offset computation");
 778       blocks = 0;
 779     } else {
 780       blocks++;
 781     }
 782 
 783     if (objs == OBJ_SAMPLE_INTERVAL) {
 784       oop(p)->verify();
 785       objs = 0;
 786     } else {
 787       objs++;
 788     }
 789     prev_p = p;
 790     p += size;
 791   }
 792   guarantee(p == top(), "end of last object must match end of space");
 793 }
 794 
 795 
 796 size_t TenuredSpace::allowed_dead_ratio() const {
 797   return MarkSweepDeadRatio;
 798 }