1 /*
  2  * Copyright (c) 1997, 2021, 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/vmClasses.hpp"
 27 #include "classfile/vmSymbols.hpp"
 28 #include "gc/shared/blockOffsetTable.inline.hpp"
 29 #include "gc/shared/collectedHeap.inline.hpp"
 30 #include "gc/shared/genCollectedHeap.hpp"
 31 #include "gc/shared/genOopClosures.inline.hpp"
 32 #include "gc/shared/slidingForwarding.inline.hpp"
 33 #include "gc/shared/space.hpp"
 34 #include "gc/shared/space.inline.hpp"
 35 #include "gc/shared/spaceDecorator.inline.hpp"
 36 #include "memory/iterator.inline.hpp"
 37 #include "memory/universe.hpp"
 38 #include "oops/oop.inline.hpp"
 39 #include "runtime/atomic.hpp"
 40 #include "runtime/java.hpp"
 41 #include "runtime/prefetch.inline.hpp"
 42 #include "runtime/safepoint.hpp"
 43 #include "utilities/align.hpp"
 44 #include "utilities/copy.hpp"
 45 #include "utilities/globalDefinitions.hpp"
 46 #include "utilities/macros.hpp"
 47 #if INCLUDE_SERIALGC
 48 #include "gc/serial/defNewGeneration.hpp"
 49 #endif
 50 
 51 HeapWord* DirtyCardToOopClosure::get_actual_top(HeapWord* top,
 52                                                 HeapWord* top_obj) {
 53   if (top_obj != NULL) {
 54     if (_sp->block_is_obj(top_obj)) {
 55       if (_precision == CardTable::ObjHeadPreciseArray) {
 56         if (cast_to_oop(top_obj)->is_objArray() || cast_to_oop(top_obj)->is_typeArray()) {
 57           // An arrayOop is starting on the dirty card - since we do exact
 58           // store checks for objArrays we are done.
 59         } else {
 60           // Otherwise, it is possible that the object starting on the dirty
 61           // card spans the entire card, and that the store happened on a
 62           // later card.  Figure out where the object ends.
 63           // Use the block_size() method of the space over which
 64           // the iteration is being done.  That space (e.g. CMS) may have
 65           // specific requirements on object sizes which will
 66           // be reflected in the block_size() method.
 67           top = top_obj + cast_to_oop(top_obj)->size();
 68         }
 69       }
 70     } else {
 71       top = top_obj;
 72     }
 73   } else {
 74     assert(top == _sp->end(), "only case where top_obj == NULL");
 75   }
 76   return top;
 77 }
 78 
 79 void DirtyCardToOopClosure::walk_mem_region(MemRegion mr,
 80                                             HeapWord* bottom,
 81                                             HeapWord* top) {
 82   // 1. Blocks may or may not be objects.
 83   // 2. Even when a block_is_obj(), it may not entirely
 84   //    occupy the block if the block quantum is larger than
 85   //    the object size.
 86   // We can and should try to optimize by calling the non-MemRegion
 87   // version of oop_iterate() for all but the extremal objects
 88   // (for which we need to call the MemRegion version of
 89   // oop_iterate()) To be done post-beta XXX
 90   for (; bottom < top; bottom += _sp->block_size(bottom)) {
 91     // As in the case of contiguous space above, we'd like to
 92     // just use the value returned by oop_iterate to increment the
 93     // current pointer; unfortunately, that won't work in CMS because
 94     // we'd need an interface change (it seems) to have the space
 95     // "adjust the object size" (for instance pad it up to its
 96     // block alignment or minimum block size restrictions. XXX
 97     if (_sp->block_is_obj(bottom) &&
 98         !_sp->obj_allocated_since_save_marks(cast_to_oop(bottom))) {
 99       cast_to_oop(bottom)->oop_iterate(_cl, mr);
100     }
101   }
102 }
103 
104 // We get called with "mr" representing the dirty region
105 // that we want to process. Because of imprecise marking,
106 // we may need to extend the incoming "mr" to the right,
107 // and scan more. However, because we may already have
108 // scanned some of that extended region, we may need to
109 // trim its right-end back some so we do not scan what
110 // we (or another worker thread) may already have scanned
111 // or planning to scan.
112 void DirtyCardToOopClosure::do_MemRegion(MemRegion mr) {
113   HeapWord* bottom = mr.start();
114   HeapWord* last = mr.last();
115   HeapWord* top = mr.end();
116   HeapWord* bottom_obj;
117   HeapWord* top_obj;
118 
119   assert(_precision == CardTable::ObjHeadPreciseArray ||
120          _precision == CardTable::Precise,
121          "Only ones we deal with for now.");
122 
123   assert(_precision != CardTable::ObjHeadPreciseArray ||
124          _last_bottom == NULL || top <= _last_bottom,
125          "Not decreasing");
126   NOT_PRODUCT(_last_bottom = mr.start());
127 
128   bottom_obj = _sp->block_start(bottom);
129   top_obj    = _sp->block_start(last);
130 
131   assert(bottom_obj <= bottom, "just checking");
132   assert(top_obj    <= top,    "just checking");
133 
134   // Given what we think is the top of the memory region and
135   // the start of the object at the top, get the actual
136   // value of the top.
137   top = get_actual_top(top, top_obj);
138 
139   // If the previous call did some part of this region, don't redo.
140   if (_precision == CardTable::ObjHeadPreciseArray &&
141       _min_done != NULL &&
142       _min_done < top) {
143     top = _min_done;
144   }
145 
146   // Top may have been reset, and in fact may be below bottom,
147   // e.g. the dirty card region is entirely in a now free object
148   // -- something that could happen with a concurrent sweeper.
149   bottom = MIN2(bottom, top);
150   MemRegion extended_mr = MemRegion(bottom, top);
151   assert(bottom <= top &&
152          (_precision != CardTable::ObjHeadPreciseArray ||
153           _min_done == NULL ||
154           top <= _min_done),
155          "overlap!");
156 
157   // Walk the region if it is not empty; otherwise there is nothing to do.
158   if (!extended_mr.is_empty()) {
159     walk_mem_region(extended_mr, bottom_obj, top);
160   }
161 
162   _min_done = bottom;
163 }
164 
165 DirtyCardToOopClosure* Space::new_dcto_cl(OopIterateClosure* cl,
166                                           CardTable::PrecisionStyle precision,
167                                           HeapWord* boundary) {
168   return new DirtyCardToOopClosure(this, cl, precision, boundary);
169 }
170 
171 HeapWord* ContiguousSpaceDCTOC::get_actual_top(HeapWord* top,
172                                                HeapWord* top_obj) {
173   if (top_obj != NULL && top_obj < (_sp->toContiguousSpace())->top()) {
174     if (_precision == CardTable::ObjHeadPreciseArray) {
175       if (cast_to_oop(top_obj)->is_objArray() || cast_to_oop(top_obj)->is_typeArray()) {
176         // An arrayOop is starting on the dirty card - since we do exact
177         // store checks for objArrays we are done.
178       } else {
179         // Otherwise, it is possible that the object starting on the dirty
180         // card spans the entire card, and that the store happened on a
181         // later card.  Figure out where the object ends.
182         assert(_sp->block_size(top_obj) == (size_t) cast_to_oop(top_obj)->size(),
183           "Block size and object size mismatch");
184         top = top_obj + cast_to_oop(top_obj)->size();
185       }
186     }
187   } else {
188     top = (_sp->toContiguousSpace())->top();
189   }
190   return top;
191 }
192 
193 void FilteringDCTOC::walk_mem_region(MemRegion mr,
194                                      HeapWord* bottom,
195                                      HeapWord* top) {
196   // Note that this assumption won't hold if we have a concurrent
197   // collector in this space, which may have freed up objects after
198   // they were dirtied and before the stop-the-world GC that is
199   // examining cards here.
200   assert(bottom < top, "ought to be at least one obj on a dirty card.");
201 
202   if (_boundary != NULL) {
203     // We have a boundary outside of which we don't want to look
204     // at objects, so create a filtering closure around the
205     // oop closure before walking the region.
206     FilteringClosure filter(_boundary, _cl);
207     walk_mem_region_with_cl(mr, bottom, top, &filter);
208   } else {
209     // No boundary, simply walk the heap with the oop closure.
210     walk_mem_region_with_cl(mr, bottom, top, _cl);
211   }
212 
213 }
214 
215 // We must replicate this so that the static type of "FilteringClosure"
216 // (see above) is apparent at the oop_iterate calls.
217 #define ContiguousSpaceDCTOC__walk_mem_region_with_cl_DEFN(ClosureType) \
218 void ContiguousSpaceDCTOC::walk_mem_region_with_cl(MemRegion mr,        \
219                                                    HeapWord* bottom,    \
220                                                    HeapWord* top,       \
221                                                    ClosureType* cl) {   \
222   bottom += cast_to_oop(bottom)->oop_iterate_size(cl, mr);              \
223   if (bottom < top) {                                                   \
224     HeapWord* next_obj = bottom + cast_to_oop(bottom)->size();          \
225     while (next_obj < top) {                                            \
226       /* Bottom lies entirely below top, so we can call the */          \
227       /* non-memRegion version of oop_iterate below. */                 \
228       cast_to_oop(bottom)->oop_iterate(cl);                             \
229       bottom = next_obj;                                                \
230       next_obj = bottom + cast_to_oop(bottom)->size();                  \
231     }                                                                   \
232     /* Last object. */                                                  \
233     cast_to_oop(bottom)->oop_iterate(cl, mr);                           \
234   }                                                                     \
235 }
236 
237 // (There are only two of these, rather than N, because the split is due
238 // only to the introduction of the FilteringClosure, a local part of the
239 // impl of this abstraction.)
240 ContiguousSpaceDCTOC__walk_mem_region_with_cl_DEFN(OopIterateClosure)
241 ContiguousSpaceDCTOC__walk_mem_region_with_cl_DEFN(FilteringClosure)
242 
243 DirtyCardToOopClosure*
244 ContiguousSpace::new_dcto_cl(OopIterateClosure* cl,
245                              CardTable::PrecisionStyle precision,
246                              HeapWord* boundary) {
247   return new ContiguousSpaceDCTOC(this, cl, precision, boundary);
248 }
249 
250 void Space::initialize(MemRegion mr,
251                        bool clear_space,
252                        bool mangle_space) {
253   HeapWord* bottom = mr.start();
254   HeapWord* end    = mr.end();
255   assert(Universe::on_page_boundary(bottom) && Universe::on_page_boundary(end),
256          "invalid space boundaries");
257   set_bottom(bottom);
258   set_end(end);
259   if (clear_space) clear(mangle_space);
260 }
261 
262 void Space::clear(bool mangle_space) {
263   if (ZapUnusedHeapArea && mangle_space) {
264     mangle_unused_area();
265   }
266 }
267 
268 ContiguousSpace::ContiguousSpace(): CompactibleSpace(), _top(NULL) {
269   _mangler = new GenSpaceMangler(this);
270 }
271 
272 ContiguousSpace::~ContiguousSpace() {
273   delete _mangler;
274 }
275 
276 void ContiguousSpace::initialize(MemRegion mr,
277                                  bool clear_space,
278                                  bool mangle_space)
279 {
280   CompactibleSpace::initialize(mr, clear_space, mangle_space);
281 }
282 
283 void ContiguousSpace::clear(bool mangle_space) {
284   set_top(bottom());
285   set_saved_mark();
286   CompactibleSpace::clear(mangle_space);
287 }
288 
289 bool ContiguousSpace::is_free_block(const HeapWord* p) const {
290   return p >= _top;
291 }
292 
293 void OffsetTableContigSpace::clear(bool mangle_space) {
294   ContiguousSpace::clear(mangle_space);
295   _offsets.initialize_threshold();
296 }
297 
298 void OffsetTableContigSpace::set_bottom(HeapWord* new_bottom) {
299   Space::set_bottom(new_bottom);
300   _offsets.set_bottom(new_bottom);
301 }
302 
303 void OffsetTableContigSpace::set_end(HeapWord* new_end) {
304   // Space should not advertise an increase in size
305   // until after the underlying offset table has been enlarged.
306   _offsets.resize(pointer_delta(new_end, bottom()));
307   Space::set_end(new_end);
308 }
309 
310 #ifndef PRODUCT
311 
312 void ContiguousSpace::set_top_for_allocations(HeapWord* v) {
313   mangler()->set_top_for_allocations(v);
314 }
315 void ContiguousSpace::set_top_for_allocations() {
316   mangler()->set_top_for_allocations(top());
317 }
318 void ContiguousSpace::check_mangled_unused_area(HeapWord* limit) {
319   mangler()->check_mangled_unused_area(limit);
320 }
321 
322 void ContiguousSpace::check_mangled_unused_area_complete() {
323   mangler()->check_mangled_unused_area_complete();
324 }
325 
326 // Mangled only the unused space that has not previously
327 // been mangled and that has not been allocated since being
328 // mangled.
329 void ContiguousSpace::mangle_unused_area() {
330   mangler()->mangle_unused_area();
331 }
332 void ContiguousSpace::mangle_unused_area_complete() {
333   mangler()->mangle_unused_area_complete();
334 }
335 #endif  // NOT_PRODUCT
336 
337 void CompactibleSpace::initialize(MemRegion mr,
338                                   bool clear_space,
339                                   bool mangle_space) {
340   Space::initialize(mr, clear_space, mangle_space);
341   set_compaction_top(bottom());
342   _next_compaction_space = NULL;
343 }
344 
345 void CompactibleSpace::clear(bool mangle_space) {
346   Space::clear(mangle_space);
347   _compaction_top = bottom();
348 }
349 
350 HeapWord* CompactibleSpace::forward(oop q, size_t size,
351                                     CompactPoint* cp, HeapWord* compact_top, SlidingForwarding* const forwarding) {
352   // q is alive
353   // First check if we should switch compaction space
354   assert(this == cp->space, "'this' should be current compaction space.");
355   size_t compaction_max_size = pointer_delta(end(), compact_top);
356   while (size > compaction_max_size) {
357     // switch to next compaction space
358     cp->space->set_compaction_top(compact_top);
359     cp->space = cp->space->next_compaction_space();
360     if (cp->space == NULL) {
361       cp->gen = GenCollectedHeap::heap()->young_gen();
362       assert(cp->gen != NULL, "compaction must succeed");
363       cp->space = cp->gen->first_compaction_space();
364       assert(cp->space != NULL, "generation must have a first compaction space");
365     }
366     compact_top = cp->space->bottom();
367     cp->space->set_compaction_top(compact_top);
368     cp->threshold = cp->space->initialize_threshold();
369     compaction_max_size = pointer_delta(cp->space->end(), compact_top);
370   }
371 
372   // store the forwarding pointer into the mark word
373   if (cast_from_oop<HeapWord*>(q) != compact_top) {
374     forwarding->forward_to(q, cast_to_oop(compact_top));
375     assert(q->is_gc_marked(), "encoding the pointer should preserve the mark");
376   } else {
377     // if the object isn't moving we can just set the mark to the default
378     // mark and handle it specially later on.
379     q->init_mark();
380     assert(!q->is_forwarded(), "should not be forwarded");
381   }
382 
383   compact_top += size;
384 
385   // we need to update the offset table so that the beginnings of objects can be
386   // found during scavenge.  Note that we are updating the offset table based on
387   // where the object will be once the compaction phase finishes.
388   if (compact_top > cp->threshold)
389     cp->threshold =
390       cp->space->cross_threshold(compact_top - size, compact_top);
391   return compact_top;
392 }
393 
394 #if INCLUDE_SERIALGC
395 
396 void ContiguousSpace::prepare_for_compaction(CompactPoint* cp) {
397   scan_and_forward(this, cp);
398 }
399 
400 void CompactibleSpace::adjust_pointers() {
401   // Check first is there is any work to do.
402   if (used() == 0) {
403     return;   // Nothing to do.
404   }
405 
406   scan_and_adjust_pointers(this);
407 }
408 
409 void CompactibleSpace::compact() {
410   scan_and_compact(this);
411 }
412 
413 #endif // INCLUDE_SERIALGC
414 
415 void Space::print_short() const { print_short_on(tty); }
416 
417 void Space::print_short_on(outputStream* st) const {
418   st->print(" space " SIZE_FORMAT "K, %3d%% used", capacity() / K,
419               (int) ((double) used() * 100 / capacity()));
420 }
421 
422 void Space::print() const { print_on(tty); }
423 
424 void Space::print_on(outputStream* st) const {
425   print_short_on(st);
426   st->print_cr(" [" INTPTR_FORMAT ", " INTPTR_FORMAT ")",
427                 p2i(bottom()), p2i(end()));
428 }
429 
430 void ContiguousSpace::print_on(outputStream* st) const {
431   print_short_on(st);
432   st->print_cr(" [" INTPTR_FORMAT ", " INTPTR_FORMAT ", " INTPTR_FORMAT ")",
433                 p2i(bottom()), p2i(top()), p2i(end()));
434 }
435 
436 void OffsetTableContigSpace::print_on(outputStream* st) const {
437   print_short_on(st);
438   st->print_cr(" [" INTPTR_FORMAT ", " INTPTR_FORMAT ", "
439                 INTPTR_FORMAT ", " INTPTR_FORMAT ")",
440               p2i(bottom()), p2i(top()), p2i(_offsets.threshold()), p2i(end()));
441 }
442 
443 void ContiguousSpace::verify() const {
444   HeapWord* p = bottom();
445   HeapWord* t = top();
446   HeapWord* prev_p = NULL;
447   while (p < t) {
448     oopDesc::verify(cast_to_oop(p));
449     prev_p = p;
450     p += cast_to_oop(p)->size();
451   }
452   guarantee(p == top(), "end of last object must match end of space");
453   if (top() != end()) {
454     guarantee(top() == block_start_const(end()-1) &&
455               top() == block_start_const(top()),
456               "top should be start of unallocated block, if it exists");
457   }
458 }
459 
460 void Space::oop_iterate(OopIterateClosure* blk) {
461   ObjectToOopClosure blk2(blk);
462   object_iterate(&blk2);
463 }
464 
465 bool Space::obj_is_alive(const HeapWord* p) const {
466   assert (block_is_obj(p), "The address should point to an object");
467   return true;
468 }
469 
470 void ContiguousSpace::oop_iterate(OopIterateClosure* blk) {
471   if (is_empty()) return;
472   HeapWord* obj_addr = bottom();
473   HeapWord* t = top();
474   // Could call objects iterate, but this is easier.
475   while (obj_addr < t) {
476     obj_addr += cast_to_oop(obj_addr)->oop_iterate_size(blk);
477   }
478 }
479 
480 void ContiguousSpace::object_iterate(ObjectClosure* blk) {
481   if (is_empty()) return;
482   object_iterate_from(bottom(), blk);
483 }
484 
485 void ContiguousSpace::object_iterate_from(HeapWord* mark, ObjectClosure* blk) {
486   while (mark < top()) {
487     blk->do_object(cast_to_oop(mark));
488     mark += cast_to_oop(mark)->size();
489   }
490 }
491 
492 // Very general, slow implementation.
493 HeapWord* ContiguousSpace::block_start_const(const void* p) const {
494   assert(MemRegion(bottom(), end()).contains(p),
495          "p (" PTR_FORMAT ") not in space [" PTR_FORMAT ", " PTR_FORMAT ")",
496          p2i(p), p2i(bottom()), p2i(end()));
497   if (p >= top()) {
498     return top();
499   } else {
500     HeapWord* last = bottom();
501     HeapWord* cur = last;
502     while (cur <= p) {
503       last = cur;
504       cur += cast_to_oop(cur)->size();
505     }
506     assert(oopDesc::is_oop(cast_to_oop(last)), PTR_FORMAT " should be an object start", p2i(last));
507     return last;
508   }
509 }
510 
511 size_t ContiguousSpace::block_size(const HeapWord* p) const {
512   assert(MemRegion(bottom(), end()).contains(p),
513          "p (" PTR_FORMAT ") not in space [" PTR_FORMAT ", " PTR_FORMAT ")",
514          p2i(p), p2i(bottom()), p2i(end()));
515   HeapWord* current_top = top();
516   assert(p <= current_top,
517          "p > current top - p: " PTR_FORMAT ", current top: " PTR_FORMAT,
518          p2i(p), p2i(current_top));
519   assert(p == current_top || oopDesc::is_oop(cast_to_oop(p)),
520          "p (" PTR_FORMAT ") is not a block start - "
521          "current_top: " PTR_FORMAT ", is_oop: %s",
522          p2i(p), p2i(current_top), BOOL_TO_STR(oopDesc::is_oop(cast_to_oop(p))));
523   if (p < current_top) {
524     return cast_to_oop(p)->size();
525   } else {
526     assert(p == current_top, "just checking");
527     return pointer_delta(end(), (HeapWord*) p);
528   }
529 }
530 
531 // This version requires locking.
532 inline HeapWord* ContiguousSpace::allocate_impl(size_t size) {
533   assert(Heap_lock->owned_by_self() ||
534          (SafepointSynchronize::is_at_safepoint() && Thread::current()->is_VM_thread()),
535          "not locked");
536   HeapWord* obj = top();
537   if (pointer_delta(end(), obj) >= size) {
538     HeapWord* new_top = obj + size;
539     set_top(new_top);
540     assert(is_aligned(obj) && is_aligned(new_top), "checking alignment");
541     return obj;
542   } else {
543     return NULL;
544   }
545 }
546 
547 // This version is lock-free.
548 inline HeapWord* ContiguousSpace::par_allocate_impl(size_t size) {
549   do {
550     HeapWord* obj = top();
551     if (pointer_delta(end(), obj) >= size) {
552       HeapWord* new_top = obj + size;
553       HeapWord* result = Atomic::cmpxchg(top_addr(), obj, new_top);
554       // result can be one of two:
555       //  the old top value: the exchange succeeded
556       //  otherwise: the new value of the top is returned.
557       if (result == obj) {
558         assert(is_aligned(obj) && is_aligned(new_top), "checking alignment");
559         return obj;
560       }
561     } else {
562       return NULL;
563     }
564   } while (true);
565 }
566 
567 // Requires locking.
568 HeapWord* ContiguousSpace::allocate(size_t size) {
569   return allocate_impl(size);
570 }
571 
572 // Lock-free.
573 HeapWord* ContiguousSpace::par_allocate(size_t size) {
574   return par_allocate_impl(size);
575 }
576 
577 void ContiguousSpace::allocate_temporary_filler(int factor) {
578   // allocate temporary type array decreasing free size with factor 'factor'
579   assert(factor >= 0, "just checking");
580   size_t size = pointer_delta(end(), top());
581 
582   // if space is full, return
583   if (size == 0) return;
584 
585   if (factor > 0) {
586     size -= size/factor;
587   }
588   size = align_object_size(size);
589 
590   const size_t array_header_size = (arrayOopDesc::base_offset_in_bytes(T_INT) + BytesPerWord) / BytesPerWord;
591   if (size >= align_object_size(array_header_size)) {
592     size_t length = (size - array_header_size) * (HeapWordSize / sizeof(jint));
593     // allocate uninitialized int array
594     typeArrayOop t = (typeArrayOop) cast_to_oop(allocate(size));
595     assert(t != NULL, "allocation should succeed");
596 #ifdef _LP64
597     t->set_mark(Universe::intArrayKlassObj()->prototype_header());
598 #else
599     t->set_mark(markWord::prototype());
600     t->set_klass(Universe::intArrayKlassObj());
601 #endif
602     t->set_length((int)length);
603   } else {
604     assert(size == CollectedHeap::min_fill_size(),
605            "size for smallest fake object doesn't match");
606     instanceOop obj = (instanceOop) cast_to_oop(allocate(size));
607 #ifdef _LP64
608     obj->set_mark(vmClasses::Object_klass()->prototype_header());
609 #else
610     obj->set_mark(markWord::prototype());
611     obj->set_klass(vmClasses::Object_klass());
612 #endif
613   }
614 }
615 
616 HeapWord* OffsetTableContigSpace::initialize_threshold() {
617   return _offsets.initialize_threshold();
618 }
619 
620 HeapWord* OffsetTableContigSpace::cross_threshold(HeapWord* start, HeapWord* end) {
621   _offsets.alloc_block(start, end);
622   return _offsets.threshold();
623 }
624 
625 OffsetTableContigSpace::OffsetTableContigSpace(BlockOffsetSharedArray* sharedOffsetArray,
626                                                MemRegion mr) :
627   _offsets(sharedOffsetArray, mr),
628   _par_alloc_lock(Mutex::leaf, "OffsetTableContigSpace par alloc lock", true)
629 {
630   _offsets.set_contig_space(this);
631   initialize(mr, SpaceDecorator::Clear, SpaceDecorator::Mangle);
632 }
633 
634 #define OBJ_SAMPLE_INTERVAL 0
635 #define BLOCK_SAMPLE_INTERVAL 100
636 
637 void OffsetTableContigSpace::verify() const {
638   HeapWord* p = bottom();
639   HeapWord* prev_p = NULL;
640   int objs = 0;
641   int blocks = 0;
642 
643   if (VerifyObjectStartArray) {
644     _offsets.verify();
645   }
646 
647   while (p < top()) {
648     size_t size = cast_to_oop(p)->size();
649     // For a sampling of objects in the space, find it using the
650     // block offset table.
651     if (blocks == BLOCK_SAMPLE_INTERVAL) {
652       guarantee(p == block_start_const(p + (size/2)),
653                 "check offset computation");
654       blocks = 0;
655     } else {
656       blocks++;
657     }
658 
659     if (objs == OBJ_SAMPLE_INTERVAL) {
660       oopDesc::verify(cast_to_oop(p));
661       objs = 0;
662     } else {
663       objs++;
664     }
665     prev_p = p;
666     p += size;
667   }
668   guarantee(p == top(), "end of last object must match end of space");
669 }
670 
671 
672 size_t TenuredSpace::allowed_dead_ratio() const {
673   return MarkSweepDeadRatio;
674 }