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src/hotspot/share/oops/oop.inline.hpp

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 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 #ifndef SHARE_OOPS_OOP_INLINE_HPP
 26 #define SHARE_OOPS_OOP_INLINE_HPP
 27 
 28 #include "oops/oop.hpp"
 29 
 30 #include "memory/universe.hpp"
 31 #include "memory/iterator.inline.hpp"
 32 #include "oops/access.inline.hpp"
 33 #include "oops/arrayKlass.hpp"
 34 #include "oops/arrayOop.hpp"
 35 #include "oops/compressedKlass.inline.hpp"
 36 #include "oops/instanceKlass.hpp"
 37 #include "oops/markWord.hpp"
 38 #include "oops/oopsHierarchy.hpp"
 39 #include "runtime/atomic.hpp"
 40 #include "runtime/globals.hpp"
 41 #include "utilities/align.hpp"
 42 #include "utilities/debug.hpp"
 43 #include "utilities/macros.hpp"
 44 #include "utilities/globalDefinitions.hpp"
 45 
 46 // Implementation of all inlined member functions defined in oop.hpp
 47 // We need a separate file to avoid circular references
 48 
 49 markWord oopDesc::mark() const {
 50   return Atomic::load(&_mark);
 51 }
 52 
 53 markWord oopDesc::mark_acquire() const {
 54   return Atomic::load_acquire(&_mark);
 55 }
 56 
 57 markWord* oopDesc::mark_addr() const {
 58   return (markWord*) &_mark;
 59 }
 60 
 61 void oopDesc::set_mark(markWord m) {
 62   Atomic::store(&_mark, m);
 63 }
 64 
 65 void oopDesc::set_mark(HeapWord* mem, markWord m) {
 66   *(markWord*)(((char*)mem) + mark_offset_in_bytes()) = m;
 67 }
 68 
 69 void oopDesc::release_set_mark(HeapWord* mem, markWord m) {
 70   Atomic::release_store((markWord*)(((char*)mem) + mark_offset_in_bytes()), m);
 71 }
 72 
 73 void oopDesc::release_set_mark(markWord m) {
 74   Atomic::release_store(&_mark, m);
 75 }
 76 




 77 markWord oopDesc::cas_set_mark(markWord new_mark, markWord old_mark) {
 78   return Atomic::cmpxchg(&_mark, old_mark, new_mark);
 79 }
 80 
 81 markWord oopDesc::cas_set_mark(markWord new_mark, markWord old_mark, atomic_memory_order order) {
 82   return Atomic::cmpxchg(&_mark, old_mark, new_mark, order);
 83 }
 84 








 85 void oopDesc::init_mark() {
 86   set_mark(markWord::prototype());




 87 }
 88 
 89 Klass* oopDesc::klass() const {
 90   if (UseCompressedClassPointers) {
 91     return CompressedKlassPointers::decode_not_null(_metadata._compressed_klass);


 92   } else {
 93     return _metadata._klass;
 94   }
 95 }
 96 
 97 Klass* oopDesc::klass_or_null() const {
 98   if (UseCompressedClassPointers) {


 99     return CompressedKlassPointers::decode(_metadata._compressed_klass);
100   } else {
101     return _metadata._klass;
102   }
103 }
104 
105 Klass* oopDesc::klass_or_null_acquire() const {
106   if (UseCompressedClassPointers) {


107     narrowKlass nklass = Atomic::load_acquire(&_metadata._compressed_klass);
108     return CompressedKlassPointers::decode(nklass);
109   } else {
110     return Atomic::load_acquire(&_metadata._klass);
111   }
112 }
113 
114 Klass* oopDesc::klass_without_asserts() const {
115   if (UseCompressedClassPointers) {


116     return CompressedKlassPointers::decode_without_asserts(_metadata._compressed_klass);
117   } else {
118     return _metadata._klass;
119   }
120 }
121 
122 void oopDesc::set_klass(Klass* k) {
123   assert(Universe::is_bootstrapping() || (k != nullptr && k->is_klass()), "incorrect Klass");

124   if (UseCompressedClassPointers) {
125     _metadata._compressed_klass = CompressedKlassPointers::encode_not_null(k);
126   } else {
127     _metadata._klass = k;
128   }
129 }
130 
131 void oopDesc::release_set_klass(HeapWord* mem, Klass* k) {
132   assert(Universe::is_bootstrapping() || (k != nullptr && k->is_klass()), "incorrect Klass");

133   char* raw_mem = ((char*)mem + klass_offset_in_bytes());
134   if (UseCompressedClassPointers) {
135     Atomic::release_store((narrowKlass*)raw_mem,
136                           CompressedKlassPointers::encode_not_null(k));
137   } else {
138     Atomic::release_store((Klass**)raw_mem, k);
139   }
140 }
141 
142 void oopDesc::set_klass_gap(HeapWord* mem, int v) {

143   if (UseCompressedClassPointers) {
144     *(int*)(((char*)mem) + klass_gap_offset_in_bytes()) = v;
145   }
146 }
147 
148 bool oopDesc::is_a(Klass* k) const {
149   return klass()->is_subtype_of(k);
150 }
151 
152 size_t oopDesc::size()  {
153   return size_given_klass(klass());
154 }
155 
156 size_t oopDesc::size_given_klass(Klass* klass)  {
157   int lh = klass->layout_helper();
158   size_t s;
159 
160   // lh is now a value computed at class initialization that may hint
161   // at the size.  For instances, this is positive and equal to the
162   // size.  For arrays, this is negative and provides log2 of the

173       s = lh >> LogHeapWordSize;  // deliver size scaled by wordSize
174     } else {
175       s = klass->oop_size(this);
176     }
177   } else if (lh <= Klass::_lh_neutral_value) {
178     // The most common case is instances; fall through if so.
179     if (lh < Klass::_lh_neutral_value) {
180       // Second most common case is arrays.  We have to fetch the
181       // length of the array, shift (multiply) it appropriately,
182       // up to wordSize, add the header, and align to object size.
183       size_t size_in_bytes;
184       size_t array_length = (size_t) ((arrayOop)this)->length();
185       size_in_bytes = array_length << Klass::layout_helper_log2_element_size(lh);
186       size_in_bytes += Klass::layout_helper_header_size(lh);
187 
188       // This code could be simplified, but by keeping array_header_in_bytes
189       // in units of bytes and doing it this way we can round up just once,
190       // skipping the intermediate round to HeapWordSize.
191       s = align_up(size_in_bytes, MinObjAlignmentInBytes) / HeapWordSize;
192 
193       assert(s == klass->oop_size(this) || size_might_change(), "wrong array object size");
194     } else {
195       // Must be zero, so bite the bullet and take the virtual call.
196       s = klass->oop_size(this);
197     }
198   }
199 
200   assert(s > 0, "Oop size must be greater than zero, not " SIZE_FORMAT, s);
201   assert(is_object_aligned(s), "Oop size is not properly aligned: " SIZE_FORMAT, s);
202   return s;
203 }
204 















































205 bool oopDesc::is_instance()    const { return klass()->is_instance_klass();             }
206 bool oopDesc::is_instanceRef() const { return klass()->is_reference_instance_klass();   }
207 bool oopDesc::is_stackChunk()  const { return klass()->is_stack_chunk_instance_klass(); }
208 bool oopDesc::is_array()       const { return klass()->is_array_klass();                }
209 bool oopDesc::is_objArray()    const { return klass()->is_objArray_klass();             }
210 bool oopDesc::is_typeArray()   const { return klass()->is_typeArray_klass();            }
211 
212 template<typename T>
213 T*       oopDesc::field_addr(int offset)     const { return reinterpret_cast<T*>(cast_from_oop<intptr_t>(as_oop()) + offset); }
214 
215 template <typename T>
216 size_t   oopDesc::field_offset(T* p) const { return pointer_delta((void*)p, (void*)this, 1); }
217 
218 template <DecoratorSet decorators>
219 inline oop  oopDesc::obj_field_access(int offset) const             { return HeapAccess<decorators>::oop_load_at(as_oop(), offset); }
220 inline oop  oopDesc::obj_field(int offset) const                    { return HeapAccess<>::oop_load_at(as_oop(), offset);  }
221 
222 inline void oopDesc::obj_field_put(int offset, oop value)           { HeapAccess<>::oop_store_at(as_oop(), offset, value); }
223 template <DecoratorSet decorators>
224 inline void oopDesc::obj_field_put_access(int offset, oop value)    { HeapAccess<decorators>::oop_store_at(as_oop(), offset, value); }

250 inline jdouble oopDesc::double_field(int offset) const              { return *field_addr<jdouble>(offset);  }
251 inline void    oopDesc::double_field_put(int offset, jdouble value) { *field_addr<jdouble>(offset) = value; }
252 
253 bool oopDesc::is_locked() const {
254   return mark().is_locked();
255 }
256 
257 bool oopDesc::is_unlocked() const {
258   return mark().is_unlocked();
259 }
260 
261 bool oopDesc::is_gc_marked() const {
262   return mark().is_marked();
263 }
264 
265 // Used by scavengers
266 bool oopDesc::is_forwarded() const {
267   return mark().is_forwarded();
268 }
269 




270 // Used by scavengers
271 void oopDesc::forward_to(oop p) {
272   markWord m = markWord::encode_pointer_as_mark(p);
273   assert(m.decode_pointer() == p, "encoding must be reversible");
274   set_mark(m);
275 }
276 
277 oop oopDesc::forward_to_atomic(oop p, markWord compare, atomic_memory_order order) {
278   markWord m = markWord::encode_pointer_as_mark(p);
279   assert(m.decode_pointer() == p, "encoding must be reversible");
280   markWord old_mark = cas_set_mark(m, compare, order);


281   if (old_mark == compare) {
282     return nullptr;
283   } else {
284     return cast_to_oop(old_mark.decode_pointer());






















285   }
286 }
287 
288 // Note that the forwardee is not the same thing as the displaced_mark.
289 // The forwardee is used when copying during scavenge and mark-sweep.
290 // It does need to clear the low two locking- and GC-related bits.
291 oop oopDesc::forwardee() const {
292   return mark().forwardee();




293 }
294 
295 // The following method needs to be MT safe.
296 uint oopDesc::age() const {
297   markWord m = mark();
298   assert(!m.is_marked(), "Attempt to read age from forwarded mark");
299   if (m.has_displaced_mark_helper()) {
300     return m.displaced_mark_helper().age();
301   } else {
302     return m.age();
303   }
304 }
305 
306 void oopDesc::incr_age() {
307   markWord m = mark();
308   assert(!m.is_marked(), "Attempt to increment age of forwarded mark");
309   if (m.has_displaced_mark_helper()) {
310     m.set_displaced_mark_helper(m.displaced_mark_helper().incr_age());
311   } else {
312     set_mark(m.incr_age());

329   size_t size = size_given_klass(k);
330   OopIteratorClosureDispatch::oop_oop_iterate(cl, this, k);
331   return size;
332 }
333 
334 template <typename OopClosureType>
335 size_t oopDesc::oop_iterate_size(OopClosureType* cl, MemRegion mr) {
336   Klass* k = klass();
337   size_t size = size_given_klass(k);
338   OopIteratorClosureDispatch::oop_oop_iterate(cl, this, k, mr);
339   return size;
340 }
341 
342 template <typename OopClosureType>
343 void oopDesc::oop_iterate_backwards(OopClosureType* cl) {
344   oop_iterate_backwards(cl, klass());
345 }
346 
347 template <typename OopClosureType>
348 void oopDesc::oop_iterate_backwards(OopClosureType* cl, Klass* k) {
349   assert(k == klass(), "wrong klass");

350   OopIteratorClosureDispatch::oop_oop_iterate_backwards(cl, this, k);
351 }
352 
353 bool oopDesc::is_instanceof_or_null(oop obj, Klass* klass) {
354   return obj == nullptr || obj->klass()->is_subtype_of(klass);
355 }
356 
357 intptr_t oopDesc::identity_hash() {
358   // Fast case; if the object is unlocked and the hash value is set, no locking is needed
359   // Note: The mark must be read into local variable to avoid concurrent updates.
360   markWord mrk = mark();
361   if (mrk.is_unlocked() && !mrk.has_no_hash()) {
362     return mrk.hash();
363   } else if (mrk.is_marked()) {
364     return mrk.hash();
365   } else {
366     return slow_identity_hash();
367   }
368 }
369 

 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 #ifndef SHARE_OOPS_OOP_INLINE_HPP
 26 #define SHARE_OOPS_OOP_INLINE_HPP
 27 
 28 #include "oops/oop.hpp"
 29 
 30 #include "memory/universe.hpp"
 31 #include "memory/iterator.inline.hpp"
 32 #include "oops/access.inline.hpp"
 33 #include "oops/arrayKlass.hpp"
 34 #include "oops/arrayOop.hpp"
 35 #include "oops/compressedKlass.inline.hpp"
 36 #include "oops/instanceKlass.hpp"
 37 #include "oops/markWord.inline.hpp"
 38 #include "oops/oopsHierarchy.hpp"
 39 #include "runtime/atomic.hpp"
 40 #include "runtime/globals.hpp"
 41 #include "utilities/align.hpp"
 42 #include "utilities/debug.hpp"
 43 #include "utilities/macros.hpp"
 44 #include "utilities/globalDefinitions.hpp"
 45 
 46 // Implementation of all inlined member functions defined in oop.hpp
 47 // We need a separate file to avoid circular references
 48 
 49 markWord oopDesc::mark() const {
 50   return Atomic::load(&_mark);
 51 }
 52 
 53 markWord oopDesc::mark_acquire() const {
 54   return Atomic::load_acquire(&_mark);
 55 }
 56 
 57 markWord* oopDesc::mark_addr() const {
 58   return (markWord*) &_mark;
 59 }
 60 
 61 void oopDesc::set_mark(markWord m) {
 62   Atomic::store(&_mark, m);
 63 }
 64 
 65 void oopDesc::set_mark(HeapWord* mem, markWord m) {
 66   *(markWord*)(((char*)mem) + mark_offset_in_bytes()) = m;
 67 }
 68 




 69 void oopDesc::release_set_mark(markWord m) {
 70   Atomic::release_store(&_mark, m);
 71 }
 72 
 73 void oopDesc::release_set_mark(HeapWord* mem, markWord m) {
 74   Atomic::release_store((markWord*)(((char*)mem) + mark_offset_in_bytes()), m);
 75 }
 76 
 77 markWord oopDesc::cas_set_mark(markWord new_mark, markWord old_mark) {
 78   return Atomic::cmpxchg(&_mark, old_mark, new_mark);
 79 }
 80 
 81 markWord oopDesc::cas_set_mark(markWord new_mark, markWord old_mark, atomic_memory_order order) {
 82   return Atomic::cmpxchg(&_mark, old_mark, new_mark, order);
 83 }
 84 
 85 markWord oopDesc::prototype_mark() const {
 86   if (UseCompactObjectHeaders) {
 87     return klass()->prototype_header();
 88   } else {
 89     return markWord::prototype();
 90   }
 91 }
 92 
 93 void oopDesc::init_mark() {
 94   if (UseCompactObjectHeaders) {
 95     set_mark(prototype_mark());
 96   } else {
 97     set_mark(markWord::prototype());
 98   }
 99 }
100 
101 Klass* oopDesc::klass() const {
102   if (UseCompactObjectHeaders) {
103     return mark().klass();
104   } else if (UseCompressedClassPointers) {
105      return CompressedKlassPointers::decode_not_null(_metadata._compressed_klass);
106   } else {
107     return _metadata._klass;
108   }
109 }
110 
111 Klass* oopDesc::klass_or_null() const {
112   if (UseCompactObjectHeaders) {
113     return mark().klass_or_null();
114   } else if (UseCompressedClassPointers) {
115     return CompressedKlassPointers::decode(_metadata._compressed_klass);
116   } else {
117     return _metadata._klass;
118   }
119 }
120 
121 Klass* oopDesc::klass_or_null_acquire() const {
122   if (UseCompactObjectHeaders) {
123     return mark_acquire().klass();
124   } else if (UseCompressedClassPointers) {
125     narrowKlass nklass = Atomic::load_acquire(&_metadata._compressed_klass);
126     return CompressedKlassPointers::decode(nklass);
127   } else {
128     return Atomic::load_acquire(&_metadata._klass);
129   }
130 }
131 
132 Klass* oopDesc::klass_without_asserts() const {
133   if (UseCompactObjectHeaders) {
134     return mark().klass_without_asserts();
135   } else if (UseCompressedClassPointers) {
136     return CompressedKlassPointers::decode_without_asserts(_metadata._compressed_klass);
137   } else {
138     return _metadata._klass;
139   }
140 }
141 
142 void oopDesc::set_klass(Klass* k) {
143   assert(Universe::is_bootstrapping() || (k != nullptr && k->is_klass()), "incorrect Klass");
144   assert(!UseCompactObjectHeaders, "don't set Klass* with compact headers");
145   if (UseCompressedClassPointers) {
146     _metadata._compressed_klass = CompressedKlassPointers::encode_not_null(k);
147   } else {
148     _metadata._klass = k;
149   }
150 }
151 
152 void oopDesc::release_set_klass(HeapWord* mem, Klass* k) {
153   assert(Universe::is_bootstrapping() || (k != nullptr && k->is_klass()), "incorrect Klass");
154   assert(!UseCompactObjectHeaders, "don't set Klass* with compact headers");
155   char* raw_mem = ((char*)mem + klass_offset_in_bytes());
156   if (UseCompressedClassPointers) {
157     Atomic::release_store((narrowKlass*)raw_mem,
158                           CompressedKlassPointers::encode_not_null(k));
159   } else {
160     Atomic::release_store((Klass**)raw_mem, k);
161   }
162 }
163 
164 void oopDesc::set_klass_gap(HeapWord* mem, int v) {
165   assert(!UseCompactObjectHeaders, "don't set Klass* gap with compact headers");
166   if (UseCompressedClassPointers) {
167     *(int*)(((char*)mem) + klass_gap_offset_in_bytes()) = v;
168   }
169 }
170 
171 bool oopDesc::is_a(Klass* k) const {
172   return klass()->is_subtype_of(k);
173 }
174 
175 size_t oopDesc::size()  {
176   return size_given_klass(klass());
177 }
178 
179 size_t oopDesc::size_given_klass(Klass* klass)  {
180   int lh = klass->layout_helper();
181   size_t s;
182 
183   // lh is now a value computed at class initialization that may hint
184   // at the size.  For instances, this is positive and equal to the
185   // size.  For arrays, this is negative and provides log2 of the

196       s = lh >> LogHeapWordSize;  // deliver size scaled by wordSize
197     } else {
198       s = klass->oop_size(this);
199     }
200   } else if (lh <= Klass::_lh_neutral_value) {
201     // The most common case is instances; fall through if so.
202     if (lh < Klass::_lh_neutral_value) {
203       // Second most common case is arrays.  We have to fetch the
204       // length of the array, shift (multiply) it appropriately,
205       // up to wordSize, add the header, and align to object size.
206       size_t size_in_bytes;
207       size_t array_length = (size_t) ((arrayOop)this)->length();
208       size_in_bytes = array_length << Klass::layout_helper_log2_element_size(lh);
209       size_in_bytes += Klass::layout_helper_header_size(lh);
210 
211       // This code could be simplified, but by keeping array_header_in_bytes
212       // in units of bytes and doing it this way we can round up just once,
213       // skipping the intermediate round to HeapWordSize.
214       s = align_up(size_in_bytes, MinObjAlignmentInBytes) / HeapWordSize;
215 
216       assert(s == klass->oop_size(this) || size_might_change(klass), "wrong array object size");
217     } else {
218       // Must be zero, so bite the bullet and take the virtual call.
219       s = klass->oop_size(this);
220     }
221   }
222 
223   assert(s > 0, "Oop size must be greater than zero, not " SIZE_FORMAT, s);
224   assert(is_object_aligned(s), "Oop size is not properly aligned: " SIZE_FORMAT, s);
225   return s;
226 }
227 
228 #ifdef _LP64
229 Klass* oopDesc::forward_safe_klass_impl(markWord m) const {
230   assert(UseCompactObjectHeaders, "Only get here with compact headers");
231   if (m.is_marked()) {
232     oop fwd = forwardee(m);
233     markWord m2 = fwd->mark();
234     assert(!m2.is_marked() || m2.self_forwarded(), "no double forwarding: this: " PTR_FORMAT " (" INTPTR_FORMAT "), fwd: " PTR_FORMAT " (" INTPTR_FORMAT ")", p2i(this), m.value(), p2i(fwd), m2.value());
235     m = m2;
236   }
237   return m.klass();
238 }
239 #endif
240 
241 Klass* oopDesc::forward_safe_klass(markWord m) const {
242 #ifdef _LP64
243   if (UseCompactObjectHeaders) {
244     return forward_safe_klass_impl(m);
245   } else
246 #endif
247   {
248     return klass();
249   }
250 }
251 
252 Klass* oopDesc::forward_safe_klass() const {
253 #ifdef _LP64
254   if (UseCompactObjectHeaders) {
255     return forward_safe_klass_impl(mark());
256   } else
257 #endif
258   {
259     return klass();
260   }
261 }
262 
263 size_t oopDesc::forward_safe_size() {
264   return size_given_klass(forward_safe_klass());
265 }
266 
267 void oopDesc::forward_safe_init_mark() {
268   if (UseCompactObjectHeaders) {
269     set_mark(forward_safe_klass()->prototype_header());
270   } else {
271     set_mark(markWord::prototype());
272   }
273 }
274 
275 bool oopDesc::is_instance()    const { return klass()->is_instance_klass();             }
276 bool oopDesc::is_instanceRef() const { return klass()->is_reference_instance_klass();   }
277 bool oopDesc::is_stackChunk()  const { return klass()->is_stack_chunk_instance_klass(); }
278 bool oopDesc::is_array()       const { return klass()->is_array_klass();                }
279 bool oopDesc::is_objArray()    const { return klass()->is_objArray_klass();             }
280 bool oopDesc::is_typeArray()   const { return klass()->is_typeArray_klass();            }
281 
282 template<typename T>
283 T*       oopDesc::field_addr(int offset)     const { return reinterpret_cast<T*>(cast_from_oop<intptr_t>(as_oop()) + offset); }
284 
285 template <typename T>
286 size_t   oopDesc::field_offset(T* p) const { return pointer_delta((void*)p, (void*)this, 1); }
287 
288 template <DecoratorSet decorators>
289 inline oop  oopDesc::obj_field_access(int offset) const             { return HeapAccess<decorators>::oop_load_at(as_oop(), offset); }
290 inline oop  oopDesc::obj_field(int offset) const                    { return HeapAccess<>::oop_load_at(as_oop(), offset);  }
291 
292 inline void oopDesc::obj_field_put(int offset, oop value)           { HeapAccess<>::oop_store_at(as_oop(), offset, value); }
293 template <DecoratorSet decorators>
294 inline void oopDesc::obj_field_put_access(int offset, oop value)    { HeapAccess<decorators>::oop_store_at(as_oop(), offset, value); }

320 inline jdouble oopDesc::double_field(int offset) const              { return *field_addr<jdouble>(offset);  }
321 inline void    oopDesc::double_field_put(int offset, jdouble value) { *field_addr<jdouble>(offset) = value; }
322 
323 bool oopDesc::is_locked() const {
324   return mark().is_locked();
325 }
326 
327 bool oopDesc::is_unlocked() const {
328   return mark().is_unlocked();
329 }
330 
331 bool oopDesc::is_gc_marked() const {
332   return mark().is_marked();
333 }
334 
335 // Used by scavengers
336 bool oopDesc::is_forwarded() const {
337   return mark().is_forwarded();
338 }
339 
340 bool oopDesc::is_self_forwarded() const {
341   return mark().self_forwarded();
342 }
343 
344 // Used by scavengers
345 void oopDesc::forward_to(oop p) {
346   markWord m = markWord::encode_pointer_as_mark(p);
347   assert(m.decode_pointer() == p, "encoding must be reversible");
348   set_mark(m);
349 }
350 
351 void oopDesc::forward_to_self() {
352   set_mark(mark().set_self_forwarded());
353 }
354 
355 oop oopDesc::cas_set_forwardee(markWord new_mark, markWord compare, atomic_memory_order order) {
356   markWord old_mark = cas_set_mark(new_mark, compare, order);
357   if (old_mark == compare) {
358     return nullptr;
359   } else {
360     assert(old_mark.is_forwarded(), "must be forwarded here");
361     return forwardee(old_mark);
362   }
363 }
364 
365 oop oopDesc::forward_to_atomic(oop p, markWord compare, atomic_memory_order order) {
366   markWord m = markWord::encode_pointer_as_mark(p);
367   assert(forwardee(m) == p, "encoding must be reversible");
368   return cas_set_forwardee(m, compare, order);
369 }
370 
371 oop oopDesc::forward_to_self_atomic(markWord old_mark, atomic_memory_order order) {
372   markWord new_mark = old_mark.set_self_forwarded();
373   assert(forwardee(new_mark) == cast_to_oop(this), "encoding must be reversible");
374   return cas_set_forwardee(new_mark, old_mark, order);
375 }
376 
377 oop oopDesc::forwardee(markWord mark) const {
378   assert(mark.is_forwarded(), "only decode when actually forwarded");
379   if (mark.self_forwarded()) {
380     return cast_to_oop(this);
381   } else {
382     return mark.forwardee();
383   }
384 }
385 
386 // Note that the forwardee is not the same thing as the displaced_mark.
387 // The forwardee is used when copying during scavenge and mark-sweep.
388 // It does need to clear the low two locking- and GC-related bits.
389 oop oopDesc::forwardee() const {
390   return forwardee(mark());
391 }
392 
393 void oopDesc::unset_self_forwarded() {
394   set_mark(mark().unset_self_forwarded());
395 }
396 
397 // The following method needs to be MT safe.
398 uint oopDesc::age() const {
399   markWord m = mark();
400   assert(!m.is_marked(), "Attempt to read age from forwarded mark");
401   if (m.has_displaced_mark_helper()) {
402     return m.displaced_mark_helper().age();
403   } else {
404     return m.age();
405   }
406 }
407 
408 void oopDesc::incr_age() {
409   markWord m = mark();
410   assert(!m.is_marked(), "Attempt to increment age of forwarded mark");
411   if (m.has_displaced_mark_helper()) {
412     m.set_displaced_mark_helper(m.displaced_mark_helper().incr_age());
413   } else {
414     set_mark(m.incr_age());

431   size_t size = size_given_klass(k);
432   OopIteratorClosureDispatch::oop_oop_iterate(cl, this, k);
433   return size;
434 }
435 
436 template <typename OopClosureType>
437 size_t oopDesc::oop_iterate_size(OopClosureType* cl, MemRegion mr) {
438   Klass* k = klass();
439   size_t size = size_given_klass(k);
440   OopIteratorClosureDispatch::oop_oop_iterate(cl, this, k, mr);
441   return size;
442 }
443 
444 template <typename OopClosureType>
445 void oopDesc::oop_iterate_backwards(OopClosureType* cl) {
446   oop_iterate_backwards(cl, klass());
447 }
448 
449 template <typename OopClosureType>
450 void oopDesc::oop_iterate_backwards(OopClosureType* cl, Klass* k) {
451   // In this assert, we cannot safely access the Klass* with compact headers.
452   assert(UseCompactObjectHeaders || k == klass(), "wrong klass");
453   OopIteratorClosureDispatch::oop_oop_iterate_backwards(cl, this, k);
454 }
455 
456 bool oopDesc::is_instanceof_or_null(oop obj, Klass* klass) {
457   return obj == nullptr || obj->klass()->is_subtype_of(klass);
458 }
459 
460 intptr_t oopDesc::identity_hash() {
461   // Fast case; if the object is unlocked and the hash value is set, no locking is needed
462   // Note: The mark must be read into local variable to avoid concurrent updates.
463   markWord mrk = mark();
464   if (mrk.is_unlocked() && !mrk.has_no_hash()) {
465     return mrk.hash();
466   } else if (mrk.is_marked()) {
467     return mrk.hash();
468   } else {
469     return slow_identity_hash();
470   }
471 }
472 
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