1 /*
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 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
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 24 
 25 #ifndef SHARE_GC_SHARED_SPACE_INLINE_HPP
 26 #define SHARE_GC_SHARED_SPACE_INLINE_HPP
 27 
 28 #include "gc/shared/space.hpp"
 29 
 30 #include "gc/shared/blockOffsetTable.inline.hpp"
 31 #include "gc/shared/collectedHeap.hpp"
 32 #include "gc/shared/generation.hpp"
 33 #include "gc/shared/spaceDecorator.hpp"
 34 #include "oops/oopsHierarchy.hpp"
 35 #include "oops/oop.inline.hpp"
 36 #include "runtime/prefetch.inline.hpp"
 37 #include "runtime/safepoint.hpp"
 38 #if INCLUDE_SERIALGC
 39 #include "gc/serial/markSweep.inline.hpp"
 40 #endif
 41 
 42 inline HeapWord* Space::block_start(const void* p) {
 43   return block_start_const(p);
 44 }
 45 
 46 inline HeapWord* OffsetTableContigSpace::allocate(size_t size) {
 47   HeapWord* res = ContiguousSpace::allocate(size);
 48   if (res != NULL) {
 49     _offsets.alloc_block(res, size);
 50   }
 51   return res;
 52 }
 53 
 54 // Because of the requirement of keeping "_offsets" up to date with the
 55 // allocations, we sequentialize these with a lock.  Therefore, best if
 56 // this is used for larger LAB allocations only.
 57 inline HeapWord* OffsetTableContigSpace::par_allocate(size_t size) {
 58   MutexLocker x(&_par_alloc_lock);
 59   // This ought to be just "allocate", because of the lock above, but that
 60   // ContiguousSpace::allocate asserts that either the allocating thread
 61   // holds the heap lock or it is the VM thread and we're at a safepoint.
 62   // The best I (dld) could figure was to put a field in ContiguousSpace
 63   // meaning "locking at safepoint taken care of", and set/reset that
 64   // here.  But this will do for now, especially in light of the comment
 65   // above.  Perhaps in the future some lock-free manner of keeping the
 66   // coordination.
 67   HeapWord* res = ContiguousSpace::par_allocate(size);
 68   if (res != NULL) {
 69     _offsets.alloc_block(res, size);
 70   }
 71   return res;
 72 }
 73 
 74 inline HeapWord*
 75 OffsetTableContigSpace::block_start_const(const void* p) const {
 76   return _offsets.block_start(p);
 77 }
 78 
 79 size_t CompactibleSpace::obj_size(const HeapWord* addr) const {
 80   return cast_to_oop(addr)->size();
 81 }
 82 
 83 #if INCLUDE_SERIALGC
 84 
 85 class DeadSpacer : StackObj {
 86   size_t _allowed_deadspace_words;
 87   bool _active;
 88   CompactibleSpace* _space;
 89 
 90 public:
 91   DeadSpacer(CompactibleSpace* space) : _allowed_deadspace_words(0), _space(space) {
 92     size_t ratio = _space->allowed_dead_ratio();
 93     _active = ratio > 0;
 94 
 95     if (_active) {
 96       assert(!UseG1GC, "G1 should not be using dead space");
 97 
 98       // We allow some amount of garbage towards the bottom of the space, so
 99       // we don't start compacting before there is a significant gain to be made.
100       // Occasionally, we want to ensure a full compaction, which is determined
101       // by the MarkSweepAlwaysCompactCount parameter.
102       if ((MarkSweep::total_invocations() % MarkSweepAlwaysCompactCount) != 0) {
103         _allowed_deadspace_words = (space->capacity() * ratio / 100) / HeapWordSize;
104       } else {
105         _active = false;
106       }
107     }
108   }
109 
110 
111   bool insert_deadspace(HeapWord* dead_start, HeapWord* dead_end) {
112     if (!_active) {
113       return false;
114     }
115 
116     size_t dead_length = pointer_delta(dead_end, dead_start);
117     if (_allowed_deadspace_words >= dead_length) {
118       _allowed_deadspace_words -= dead_length;
119       CollectedHeap::fill_with_object(dead_start, dead_length);
120       oop obj = cast_to_oop(dead_start);
121       obj->set_mark(obj->mark().set_marked());
122 
123       assert(dead_length == (size_t)obj->size(), "bad filler object size");
124       log_develop_trace(gc, compaction)("Inserting object to dead space: " PTR_FORMAT ", " PTR_FORMAT ", " SIZE_FORMAT "b",
125           p2i(dead_start), p2i(dead_end), dead_length * HeapWordSize);
126 
127       return true;
128     } else {
129       _active = false;
130       return false;
131     }
132   }
133 
134 };
135 
136 template <bool ALT_FWD, class SpaceType>
137 inline void CompactibleSpace::scan_and_forward(SpaceType* space, CompactPoint* cp) {
138   // Compute the new addresses for the live objects and store it in the mark
139   // Used by universe::mark_sweep_phase2()
140 
141   // We're sure to be here before any objects are compacted into this
142   // space, so this is a good time to initialize this:
143   space->set_compaction_top(space->bottom());
144 
145   if (cp->space == NULL) {
146     assert(cp->gen != NULL, "need a generation");
147     assert(cp->threshold == NULL, "just checking");
148     assert(cp->gen->first_compaction_space() == space, "just checking");
149     cp->space = cp->gen->first_compaction_space();
150     cp->threshold = cp->space->initialize_threshold();
151     cp->space->set_compaction_top(cp->space->bottom());
152   }
153 
154   HeapWord* compact_top = cp->space->compaction_top(); // This is where we are currently compacting to.
155 
156   DeadSpacer dead_spacer(space);
157 
158   HeapWord*  end_of_live = space->bottom();  // One byte beyond the last byte of the last live object.
159   HeapWord*  first_dead = NULL; // The first dead object.
160 
161   const intx interval = PrefetchScanIntervalInBytes;
162 
163   HeapWord* cur_obj = space->bottom();
164   HeapWord* scan_limit = space->scan_limit();
165 
166   while (cur_obj < scan_limit) {
167     if (space->scanned_block_is_obj(cur_obj) && cast_to_oop(cur_obj)->is_gc_marked()) {
168       // prefetch beyond cur_obj
169       Prefetch::write(cur_obj, interval);
170       size_t size = space->scanned_block_size(cur_obj);
171       compact_top = cp->space->forward<ALT_FWD>(cast_to_oop(cur_obj), size, cp, compact_top);
172       cur_obj += size;
173       end_of_live = cur_obj;
174     } else {
175       // run over all the contiguous dead objects
176       HeapWord* end = cur_obj;
177       do {
178         // prefetch beyond end
179         Prefetch::write(end, interval);
180         end += space->scanned_block_size(end);
181       } while (end < scan_limit && (!space->scanned_block_is_obj(end) || !cast_to_oop(end)->is_gc_marked()));
182 
183       // see if we might want to pretend this object is alive so that
184       // we don't have to compact quite as often.
185       if (cur_obj == compact_top && dead_spacer.insert_deadspace(cur_obj, end)) {
186         oop obj = cast_to_oop(cur_obj);
187         compact_top = cp->space->forward<ALT_FWD>(obj, obj->size(), cp, compact_top);
188         end_of_live = end;
189       } else {
190         // otherwise, it really is a free region.
191 
192         // cur_obj is a pointer to a dead object. Use this dead memory to store a pointer to the next live object.
193         *(HeapWord**)cur_obj = end;
194 
195         // see if this is the first dead region.
196         if (first_dead == NULL) {
197           first_dead = cur_obj;
198         }
199       }
200 
201       // move on to the next object
202       cur_obj = end;
203     }
204   }
205 
206   assert(cur_obj == scan_limit, "just checking");
207   space->_end_of_live = end_of_live;
208   if (first_dead != NULL) {
209     space->_first_dead = first_dead;
210   } else {
211     space->_first_dead = end_of_live;
212   }
213 
214   // save the compaction_top of the compaction space.
215   cp->space->set_compaction_top(compact_top);
216 }
217 
218 template <bool ALT_FWD, class SpaceType>
219 inline void CompactibleSpace::scan_and_adjust_pointers(SpaceType* space) {
220   // adjust all the interior pointers to point at the new locations of objects
221   // Used by MarkSweep::mark_sweep_phase3()
222 
223   HeapWord* cur_obj = space->bottom();
224   HeapWord* const end_of_live = space->_end_of_live;  // Established by "scan_and_forward".
225   HeapWord* const first_dead = space->_first_dead;    // Established by "scan_and_forward".
226 
227   assert(first_dead <= end_of_live, "Stands to reason, no?");
228 
229   const intx interval = PrefetchScanIntervalInBytes;
230 
231   debug_only(HeapWord* prev_obj = NULL);
232   while (cur_obj < end_of_live) {
233     Prefetch::write(cur_obj, interval);
234     if (cur_obj < first_dead || cast_to_oop(cur_obj)->is_gc_marked()) {
235       // cur_obj is alive
236       // point all the oops to the new location
237       size_t size = MarkSweep::adjust_pointers<ALT_FWD>(cast_to_oop(cur_obj));
238       size = space->adjust_obj_size(size);
239       debug_only(prev_obj = cur_obj);
240       cur_obj += size;
241     } else {
242       debug_only(prev_obj = cur_obj);
243       // cur_obj is not a live object, instead it points at the next live object
244       cur_obj = *(HeapWord**)cur_obj;
245       assert(cur_obj > prev_obj, "we should be moving forward through memory, cur_obj: " PTR_FORMAT ", prev_obj: " PTR_FORMAT, p2i(cur_obj), p2i(prev_obj));
246     }
247   }
248 
249   assert(cur_obj == end_of_live, "just checking");
250 }
251 
252 #ifdef ASSERT
253 template <class SpaceType>
254 inline void CompactibleSpace::verify_up_to_first_dead(SpaceType* space) {
255   HeapWord* cur_obj = space->bottom();
256 
257   if (cur_obj < space->_end_of_live && space->_first_dead > cur_obj && !cast_to_oop(cur_obj)->is_gc_marked()) {
258      // we have a chunk of the space which hasn't moved and we've reinitialized
259      // the mark word during the previous pass, so we can't use is_gc_marked for
260      // the traversal.
261      HeapWord* prev_obj = NULL;
262 
263      while (cur_obj < space->_first_dead) {
264        size_t size = space->obj_size(cur_obj);
265        assert(!cast_to_oop(cur_obj)->is_gc_marked(), "should be unmarked (special dense prefix handling)");
266        prev_obj = cur_obj;
267        cur_obj += size;
268      }
269   }
270 }
271 #endif
272 
273 template <class SpaceType>
274 inline void CompactibleSpace::clear_empty_region(SpaceType* space) {
275   // Let's remember if we were empty before we did the compaction.
276   bool was_empty = space->used_region().is_empty();
277   // Reset space after compaction is complete
278   space->reset_after_compaction();
279   // We do this clear, below, since it has overloaded meanings for some
280   // space subtypes.  For example, OffsetTableContigSpace's that were
281   // compacted into will have had their offset table thresholds updated
282   // continuously, but those that weren't need to have their thresholds
283   // re-initialized.  Also mangles unused area for debugging.
284   if (space->used_region().is_empty()) {
285     if (!was_empty) space->clear(SpaceDecorator::Mangle);
286   } else {
287     if (ZapUnusedHeapArea) space->mangle_unused_area();
288   }
289 }
290 
291 template <bool ALT_FWD, class SpaceType>
292 inline void CompactibleSpace::scan_and_compact(SpaceType* space) {
293   // Copy all live objects to their new location
294   // Used by MarkSweep::mark_sweep_phase4()
295 
296   verify_up_to_first_dead(space);
297 
298   HeapWord* const bottom = space->bottom();
299   HeapWord* const end_of_live = space->_end_of_live;
300 
301   assert(space->_first_dead <= end_of_live, "Invariant. _first_dead: " PTR_FORMAT " <= end_of_live: " PTR_FORMAT, p2i(space->_first_dead), p2i(end_of_live));
302   if (space->_first_dead == end_of_live && (bottom == end_of_live || !cast_to_oop(bottom)->is_gc_marked())) {
303     // Nothing to compact. The space is either empty or all live object should be left in place.
304     clear_empty_region(space);
305     return;
306   }
307 
308   const intx scan_interval = PrefetchScanIntervalInBytes;
309   const intx copy_interval = PrefetchCopyIntervalInBytes;
310 
311   assert(bottom < end_of_live, "bottom: " PTR_FORMAT " should be < end_of_live: " PTR_FORMAT, p2i(bottom), p2i(end_of_live));
312   HeapWord* cur_obj = bottom;
313   if (space->_first_dead > cur_obj && !cast_to_oop(cur_obj)->is_gc_marked()) {
314     // All object before _first_dead can be skipped. They should not be moved.
315     // A pointer to the first live object is stored at the memory location for _first_dead.
316     cur_obj = *(HeapWord**)(space->_first_dead);
317   }
318 
319   debug_only(HeapWord* prev_obj = NULL);
320   while (cur_obj < end_of_live) {
321     if (!cast_to_oop(cur_obj)->is_gc_marked()) {
322       debug_only(prev_obj = cur_obj);
323       // The first word of the dead object contains a pointer to the next live object or end of space.
324       cur_obj = *(HeapWord**)cur_obj;
325       assert(cur_obj > prev_obj, "we should be moving forward through memory");
326     } else {
327       // prefetch beyond q
328       Prefetch::read(cur_obj, scan_interval);
329 
330       // size and destination
331       size_t size = space->obj_size(cur_obj);
332       HeapWord* compaction_top = cast_from_oop<HeapWord*>(SlidingForwarding::forwardee<ALT_FWD>(cast_to_oop(cur_obj)));
333 
334       // prefetch beyond compaction_top
335       Prefetch::write(compaction_top, copy_interval);
336 
337       // copy object and reinit its mark
338       assert(cur_obj != compaction_top, "everything in this pass should be moving");
339       Copy::aligned_conjoint_words(cur_obj, compaction_top, size);
340       cast_to_oop(compaction_top)->init_mark();
341       assert(cast_to_oop(compaction_top)->klass() != NULL, "should have a class");
342 
343       debug_only(prev_obj = cur_obj);
344       cur_obj += size;
345     }
346   }
347 
348   clear_empty_region(space);
349 }
350 
351 #endif // INCLUDE_SERIALGC
352 
353 size_t ContiguousSpace::scanned_block_size(const HeapWord* addr) const {
354   return cast_to_oop(addr)->size();
355 }
356 
357 template <typename OopClosureType>
358 void ContiguousSpace::oop_since_save_marks_iterate(OopClosureType* blk) {
359   HeapWord* t;
360   HeapWord* p = saved_mark_word();
361   assert(p != NULL, "expected saved mark");
362 
363   const intx interval = PrefetchScanIntervalInBytes;
364   do {
365     t = top();
366     while (p < t) {
367       Prefetch::write(p, interval);
368       debug_only(HeapWord* prev = p);
369       oop m = cast_to_oop(p);
370       p += m->oop_iterate_size(blk);
371     }
372   } while (t < top());
373 
374   set_saved_mark_word(p);
375 }
376 
377 #endif // SHARE_GC_SHARED_SPACE_INLINE_HPP