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

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 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 "oops/access.inline.hpp"
 32 #include "oops/arrayKlass.hpp"
 33 #include "oops/arrayOop.hpp"
 34 #include "oops/compressedOops.inline.hpp"
 35 #include "oops/markWord.inline.hpp"
 36 #include "oops/oopsHierarchy.hpp"
 37 #include "runtime/atomic.hpp"
 38 #include "runtime/globals.hpp"


 39 #include "utilities/align.hpp"
 40 #include "utilities/debug.hpp"
 41 #include "utilities/macros.hpp"
 42 #include "utilities/globalDefinitions.hpp"
 43 
 44 // Implementation of all inlined member functions defined in oop.hpp
 45 // We need a separate file to avoid circular references
 46 
 47 markWord oopDesc::mark() const {
 48   uintptr_t v = HeapAccess<MO_RELAXED>::load_at(as_oop(), mark_offset_in_bytes());
 49   return markWord(v);
 50 }
 51 



 52 markWord* oopDesc::mark_addr() const {
 53   return (markWord*) &_mark;
 54 }
 55 
 56 void oopDesc::set_mark(markWord m) {
 57   HeapAccess<MO_RELAXED>::store_at(as_oop(), mark_offset_in_bytes(), m.value());
 58 }
 59 
 60 void oopDesc::set_mark(HeapWord* mem, markWord m) {
 61   *(markWord*)(((char*)mem) + mark_offset_in_bytes()) = m;
 62 }
 63 
 64 void oopDesc::release_set_mark(markWord m) {
 65   HeapAccess<MO_RELEASE>::store_at(as_oop(), mark_offset_in_bytes(), m.value());
 66 }
 67 




 68 markWord oopDesc::cas_set_mark(markWord new_mark, markWord old_mark) {
 69   uintptr_t v = HeapAccess<>::atomic_cmpxchg_at(as_oop(), mark_offset_in_bytes(), old_mark.value(), new_mark.value());
 70   return markWord(v);
 71 }
 72 
 73 markWord oopDesc::cas_set_mark(markWord new_mark, markWord old_mark, atomic_memory_order order) {
 74   return Atomic::cmpxchg(&_mark, old_mark, new_mark, order);
 75 }
 76 

















 77 void oopDesc::init_mark() {
 78   set_mark(markWord::prototype_for_klass(klass()));
 79 }
 80 
 81 Klass* oopDesc::klass() const {
 82   if (UseCompressedClassPointers) {





 83     return CompressedKlassPointers::decode_not_null(_metadata._compressed_klass);
 84   } else {
 85     return _metadata._klass;
 86   }
 87 }
 88 
 89 Klass* oopDesc::klass_or_null() const {
 90   if (UseCompressedClassPointers) {





 91     return CompressedKlassPointers::decode(_metadata._compressed_klass);
 92   } else {
 93     return _metadata._klass;
 94   }
 95 }
 96 
 97 Klass* oopDesc::klass_or_null_acquire() const {
 98   if (UseCompressedClassPointers) {
 99     narrowKlass nklass = Atomic::load_acquire(&_metadata._compressed_klass);
100     return CompressedKlassPointers::decode(nklass);
101   } else {
102     return Atomic::load_acquire(&_metadata._klass);
103   }








104 }
105 
106 void oopDesc::set_klass(Klass* k) {
107   assert(Universe::is_bootstrapping() || (k != NULL && k->is_klass()), "incorrect Klass");

108   if (UseCompressedClassPointers) {
109     _metadata._compressed_klass = CompressedKlassPointers::encode_not_null(k);
110   } else {
111     _metadata._klass = k;
112   }
113 }
114 
115 void oopDesc::release_set_klass(HeapWord* mem, Klass* k) {
116   assert(Universe::is_bootstrapping() || (k != NULL && k->is_klass()), "incorrect Klass");

117   char* raw_mem = ((char*)mem + klass_offset_in_bytes());
118   if (UseCompressedClassPointers) {
119     Atomic::release_store((narrowKlass*)raw_mem,
120                           CompressedKlassPointers::encode_not_null(k));
121   } else {
122     Atomic::release_store((Klass**)raw_mem, k);
123   }
124 }
125 
126 int oopDesc::klass_gap() const {

127   return *(int*)(((intptr_t)this) + klass_gap_offset_in_bytes());
128 }
129 
130 void oopDesc::set_klass_gap(HeapWord* mem, int v) {

131   if (UseCompressedClassPointers) {
132     *(int*)(((char*)mem) + klass_gap_offset_in_bytes()) = v;
133   }
134 }
135 
136 void oopDesc::set_klass_gap(int v) {

137   set_klass_gap((HeapWord*)this, v);
138 }
139 
140 bool oopDesc::is_a(Klass* k) const {
141   return klass()->is_subtype_of(k);
142 }
143 
144 int oopDesc::size()  {
145   return size_given_klass(klass());
146 }
147 
148 int oopDesc::size_given_klass(Klass* klass)  {
149   int lh = klass->layout_helper();
150   int s;
151 
152   // lh is now a value computed at class initialization that may hint
153   // at the size.  For instances, this is positive and equal to the
154   // size.  For arrays, this is negative and provides log2 of the
155   // array element size.  For other oops, it is zero and thus requires
156   // a virtual call.

184 
185       // UseParallelGC and UseG1GC can change the length field
186       // of an "old copy" of an object array in the young gen so it indicates
187       // the grey portion of an already copied array. This will cause the first
188       // disjunct below to fail if the two comparands are computed across such
189       // a concurrent change.
190       assert((s == klass->oop_size(this)) ||
191              (Universe::is_gc_active() && is_objArray() && is_forwarded() && (get_UseParallelGC() || get_UseG1GC())),
192              "wrong array object size");
193     } else {
194       // Must be zero, so bite the bullet and take the virtual call.
195       s = klass->oop_size(this);
196     }
197   }
198 
199   assert(s > 0, "Oop size must be greater than zero, not %d", s);
200   assert(is_object_aligned(s), "Oop size is not properly aligned: %d", s);
201   return s;
202 }
203 















































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

255 }
256 
257 bool oopDesc::has_bias_pattern() const {
258   return mark().has_bias_pattern();
259 }
260 
261 // Used only for markSweep, scavenging
262 bool oopDesc::is_gc_marked() const {
263   return mark().is_marked();
264 }
265 
266 // Used by scavengers
267 bool oopDesc::is_forwarded() const {
268   // The extra heap check is needed since the obj might be locked, in which case the
269   // mark would point to a stack location and have the sentinel bit cleared
270   return mark().is_marked();
271 }
272 
273 // Used by scavengers
274 void oopDesc::forward_to(oop p) {

275   verify_forwardee(p);
276   markWord m = markWord::encode_pointer_as_mark(p);
277   assert(m.decode_pointer() == p, "encoding must be reversable");
278   set_mark(m);
279 }
280 
281 // Used by parallel scavengers
282 bool oopDesc::cas_forward_to(oop p, markWord compare, atomic_memory_order order) {
283   verify_forwardee(p);
284   markWord m = markWord::encode_pointer_as_mark(p);
285   assert(m.decode_pointer() == p, "encoding must be reversable");
286   return cas_set_mark(m, compare, order) == compare;












287 }
288 
289 oop oopDesc::forward_to_atomic(oop p, markWord compare, atomic_memory_order order) {

290   verify_forwardee(p);
291   markWord m = markWord::encode_pointer_as_mark(p);
292   assert(m.decode_pointer() == p, "encoding must be reversable");
293   markWord old_mark = cas_set_mark(m, compare, order);
294   if (old_mark == compare) {
295     return NULL;
296   } else {
297     return cast_to_oop(old_mark.decode_pointer());






































298   }
299 }
300 
301 // Note that the forwardee is not the same thing as the displaced_mark.
302 // The forwardee is used when copying during scavenge and mark-sweep.
303 // It does need to clear the low two locking- and GC-related bits.
304 oop oopDesc::forwardee() const {
305   return cast_to_oop(mark().decode_pointer());
306 }
307 
308 // The following method needs to be MT safe.
309 uint oopDesc::age() const {
310   assert(!is_forwarded(), "Attempt to read age from forwarded mark");
311   if (has_displaced_mark()) {
312     return displaced_mark().age();
313   } else {
314     return mark().age();
315   }
316 }
317 
318 void oopDesc::incr_age() {
319   assert(!is_forwarded(), "Attempt to increment age of forwarded mark");
320   if (has_displaced_mark()) {
321     set_displaced_mark(displaced_mark().incr_age());
322   } else {
323     set_mark(mark().incr_age());
324   }
325 }

340   int size = size_given_klass(k);
341   OopIteratorClosureDispatch::oop_oop_iterate(cl, this, k);
342   return size;
343 }
344 
345 template <typename OopClosureType>
346 int oopDesc::oop_iterate_size(OopClosureType* cl, MemRegion mr) {
347   Klass* k = klass();
348   int size = size_given_klass(k);
349   OopIteratorClosureDispatch::oop_oop_iterate(cl, this, k, mr);
350   return size;
351 }
352 
353 template <typename OopClosureType>
354 void oopDesc::oop_iterate_backwards(OopClosureType* cl) {
355   oop_iterate_backwards(cl, klass());
356 }
357 
358 template <typename OopClosureType>
359 void oopDesc::oop_iterate_backwards(OopClosureType* cl, Klass* k) {
360   assert(k == klass(), "wrong klass");
361   OopIteratorClosureDispatch::oop_oop_iterate_backwards(cl, this, k);
362 }
363 
364 bool oopDesc::is_instanceof_or_null(oop obj, Klass* klass) {
365   return obj == NULL || obj->klass()->is_subtype_of(klass);
366 }
367 
368 intptr_t oopDesc::identity_hash() {
369   // Fast case; if the object is unlocked and the hash value is set, no locking is needed
370   // Note: The mark must be read into local variable to avoid concurrent updates.
371   markWord mrk = mark();
372   if (mrk.is_unlocked() && !mrk.has_no_hash()) {
373     return mrk.hash();
374   } else if (mrk.is_marked()) {
375     return mrk.hash();
376   } else {
377     return slow_identity_hash();
378   }
379 }
380 

 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 "oops/access.inline.hpp"
 32 #include "oops/arrayKlass.hpp"
 33 #include "oops/arrayOop.hpp"
 34 #include "oops/compressedOops.inline.hpp"
 35 #include "oops/markWord.inline.hpp"
 36 #include "oops/oopsHierarchy.hpp"
 37 #include "runtime/atomic.hpp"
 38 #include "runtime/globals.hpp"
 39 #include "runtime/safepoint.hpp"
 40 #include "runtime/objectMonitor.inline.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   uintptr_t v = HeapAccess<MO_RELAXED>::load_at(as_oop(), mark_offset_in_bytes());
 51   return markWord(v);
 52 }
 53 
 54 markWord oopDesc::mark_acquire() const {
 55   return Atomic::load_acquire(&_mark);
 56 }
 57 markWord* oopDesc::mark_addr() const {
 58   return (markWord*) &_mark;
 59 }
 60 
 61 void oopDesc::set_mark(markWord m) {
 62   HeapAccess<MO_RELAXED>::store_at(as_oop(), mark_offset_in_bytes(), m.value());
 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   HeapAccess<MO_RELEASE>::store_at(as_oop(), mark_offset_in_bytes(), m.value());
 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   uintptr_t v = HeapAccess<>::atomic_cmpxchg_at(as_oop(), mark_offset_in_bytes(), old_mark.value(), new_mark.value());
 79   return markWord(v);
 80 }
 81 
 82 markWord oopDesc::cas_set_mark(markWord new_mark, markWord old_mark, atomic_memory_order order) {
 83   return Atomic::cmpxchg(&_mark, old_mark, new_mark, order);
 84 }
 85 
 86 markWord oopDesc::resolve_mark() const {
 87   assert(LockingMode != LM_LEGACY, "Not safe with legacy stack-locking");
 88   markWord hdr = mark();
 89   if (hdr.has_displaced_mark_helper()) {
 90     hdr = hdr.displaced_mark_helper();
 91   }
 92   return hdr;
 93 }
 94 
 95 markWord oopDesc::prototype_mark() const {
 96   if (UseCompactObjectHeaders) {
 97     return klass()->prototype_header();
 98   } else {
 99     return markWord::prototype();
100   }
101 }
102 
103 void oopDesc::init_mark() {
104   set_mark(markWord::prototype_for_klass(klass()));
105 }
106 
107 Klass* oopDesc::klass() const {
108 #ifdef _LP64
109   if (UseCompactObjectHeaders) {
110     assert(UseCompressedClassPointers, "only with compressed class pointers");
111     markWord header = resolve_mark();
112     return header.klass();
113   } else if (UseCompressedClassPointers) {
114     return CompressedKlassPointers::decode_not_null(_metadata._compressed_klass);
115   } else
116 #endif
117   return _metadata._klass;
118 }
119 
120 Klass* oopDesc::klass_or_null() const {
121 #ifdef _LP64
122   if (UseCompactObjectHeaders) {
123     assert(UseCompressedClassPointers, "only with compressed class pointers");
124     markWord header = resolve_mark();
125     return header.klass_or_null();
126   } else if (UseCompressedClassPointers) {
127     return CompressedKlassPointers::decode(_metadata._compressed_klass);
128   } else
129 #endif
130   return _metadata._klass;
131 }
132 
133 Klass* oopDesc::klass_or_null_acquire() const {
134 #ifdef _LP64
135   if (UseCompactObjectHeaders) {
136     assert(UseCompressedClassPointers, "only with compressed class pointers");
137     markWord header = mark_acquire();
138     if (header.has_monitor()) {
139       header = header.monitor()->header();
140     }
141     return header.klass_or_null();
142   } else if (UseCompressedClassPointers) {
143      narrowKlass nklass = Atomic::load_acquire(&_metadata._compressed_klass);
144      return CompressedKlassPointers::decode(nklass);
145   } else
146 #endif
147   return Atomic::load_acquire(&_metadata._klass);
148 }
149 
150 void oopDesc::set_klass(Klass* k) {
151   assert(Universe::is_bootstrapping() || (k != NULL && k->is_klass()), "incorrect Klass");
152   assert(!UseCompactObjectHeaders, "don't set Klass* with compact headers");
153   if (UseCompressedClassPointers) {
154     _metadata._compressed_klass = CompressedKlassPointers::encode_not_null(k);
155   } else {
156     _metadata._klass = k;
157   }
158 }
159 
160 void oopDesc::release_set_klass(HeapWord* mem, Klass* k) {
161   assert(Universe::is_bootstrapping() || (k != NULL && k->is_klass()), "incorrect Klass");
162   assert(!UseCompactObjectHeaders, "don't set Klass* with compact headers");
163   char* raw_mem = ((char*)mem + klass_offset_in_bytes());
164   if (UseCompressedClassPointers) {
165     Atomic::release_store((narrowKlass*)raw_mem,
166                           CompressedKlassPointers::encode_not_null(k));
167   } else {
168     Atomic::release_store((Klass**)raw_mem, k);
169   }
170 }
171 
172 int oopDesc::klass_gap() const {
173   assert(!UseCompactObjectHeaders, "don't get Klass* gap with compact headers");
174   return *(int*)(((intptr_t)this) + klass_gap_offset_in_bytes());
175 }
176 
177 void oopDesc::set_klass_gap(HeapWord* mem, int v) {
178   assert(!UseCompactObjectHeaders, "don't set Klass* gap with compact headers");
179   if (UseCompressedClassPointers) {
180     *(int*)(((char*)mem) + klass_gap_offset_in_bytes()) = v;
181   }
182 }
183 
184 void oopDesc::set_klass_gap(int v) {
185   assert(!UseCompactObjectHeaders, "don't set Klass* gap with compact headers");
186   set_klass_gap((HeapWord*)this, v);
187 }
188 
189 bool oopDesc::is_a(Klass* k) const {
190   return klass()->is_subtype_of(k);
191 }
192 
193 int oopDesc::size()  {
194   return size_given_klass(klass());
195 }
196 
197 int oopDesc::size_given_klass(Klass* klass)  {
198   int lh = klass->layout_helper();
199   int s;
200 
201   // lh is now a value computed at class initialization that may hint
202   // at the size.  For instances, this is positive and equal to the
203   // size.  For arrays, this is negative and provides log2 of the
204   // array element size.  For other oops, it is zero and thus requires
205   // a virtual call.

233 
234       // UseParallelGC and UseG1GC can change the length field
235       // of an "old copy" of an object array in the young gen so it indicates
236       // the grey portion of an already copied array. This will cause the first
237       // disjunct below to fail if the two comparands are computed across such
238       // a concurrent change.
239       assert((s == klass->oop_size(this)) ||
240              (Universe::is_gc_active() && is_objArray() && is_forwarded() && (get_UseParallelGC() || get_UseG1GC())),
241              "wrong array object size");
242     } else {
243       // Must be zero, so bite the bullet and take the virtual call.
244       s = klass->oop_size(this);
245     }
246   }
247 
248   assert(s > 0, "Oop size must be greater than zero, not %d", s);
249   assert(is_object_aligned(s), "Oop size is not properly aligned: %d", s);
250   return s;
251 }
252 
253 #ifdef _LP64
254 Klass* oopDesc::forward_safe_klass_impl(markWord m) const {
255   assert(UseCompactObjectHeaders, "Only get here with compact headers");
256   if (m.is_marked()) {
257     oop fwd = forwardee(m);
258     markWord m2 = fwd->mark();
259     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());
260     m = m2;
261   }
262   return m.actual_mark().klass();
263 }
264 #endif
265 
266 Klass* oopDesc::forward_safe_klass(markWord m) const {
267 #ifdef _LP64
268   if (UseCompactObjectHeaders) {
269     return forward_safe_klass_impl(m);
270   } else
271 #endif
272   {
273     return klass();
274   }
275 }
276 
277 Klass* oopDesc::forward_safe_klass() const {
278 #ifdef _LP64
279   if (UseCompactObjectHeaders) {
280     return forward_safe_klass_impl(mark());
281   } else
282 #endif
283   {
284     return klass();
285   }
286 }
287 
288 size_t oopDesc::forward_safe_size() {
289   return size_given_klass(forward_safe_klass());
290 }
291 
292 void oopDesc::forward_safe_init_mark() {
293   if (UseCompactObjectHeaders) {
294     set_mark(forward_safe_klass()->prototype_header());
295   } else {
296     init_mark();
297   }
298 }
299 
300 bool oopDesc::is_instance()  const { return klass()->is_instance_klass();  }
301 bool oopDesc::is_array()     const { return klass()->is_array_klass();     }
302 bool oopDesc::is_objArray()  const { return klass()->is_objArray_klass();  }
303 bool oopDesc::is_typeArray() const { return klass()->is_typeArray_klass(); }
304 
305 void*    oopDesc::field_addr(int offset)     const { return reinterpret_cast<void*>(cast_from_oop<intptr_t>(as_oop()) + offset); }
306 
307 template <class T>
308 T*       oopDesc::obj_field_addr(int offset) const { return (T*) field_addr(offset); }
309 
310 template <typename T>
311 size_t   oopDesc::field_offset(T* p) const { return pointer_delta((void*)p, (void*)this, 1); }
312 
313 template <DecoratorSet decorators>
314 inline oop  oopDesc::obj_field_access(int offset) const             { return HeapAccess<decorators>::oop_load_at(as_oop(), offset); }
315 inline oop  oopDesc::obj_field(int offset) const                    { return HeapAccess<>::oop_load_at(as_oop(), offset);  }
316 
317 inline void oopDesc::obj_field_put(int offset, oop value)           { HeapAccess<>::oop_store_at(as_oop(), offset, value); }
318 
319 inline jbyte oopDesc::byte_field(int offset) const                  { return HeapAccess<>::load_at(as_oop(), offset);  }

351 }
352 
353 bool oopDesc::has_bias_pattern() const {
354   return mark().has_bias_pattern();
355 }
356 
357 // Used only for markSweep, scavenging
358 bool oopDesc::is_gc_marked() const {
359   return mark().is_marked();
360 }
361 
362 // Used by scavengers
363 bool oopDesc::is_forwarded() const {
364   // The extra heap check is needed since the obj might be locked, in which case the
365   // mark would point to a stack location and have the sentinel bit cleared
366   return mark().is_marked();
367 }
368 
369 // Used by scavengers
370 void oopDesc::forward_to(oop p) {
371   assert(p != cast_to_oop(this) || !UseAltGCForwarding, "Must not be called with self-forwarding");
372   verify_forwardee(p);
373   markWord m = markWord::encode_pointer_as_mark(p);
374   assert(forwardee(m) == p, "encoding must be reversable");
375   set_mark(m);
376 }
377 
378 void oopDesc::forward_to_self() {
379 #ifdef _LP64
380   if (UseAltGCForwarding) {
381     markWord m = mark();
382     // If mark is displaced, we need to preserve the real header during GC.
383     // It will be restored to the displaced header after GC.
384     assert(SafepointSynchronize::is_at_safepoint(), "we can only safely fetch the displaced header at safepoint");
385     if (m.has_displaced_mark_helper()) {
386       m = m.displaced_mark_helper();
387     }
388     m = m.set_self_forwarded();
389     assert(forwardee(m) == cast_to_oop(this), "encoding must be reversible");
390     set_mark(m);
391   } else
392 #endif
393   {
394     forward_to(oop(this));
395   }
396 }
397 
398 oop oopDesc::forward_to_atomic(oop p, markWord compare, atomic_memory_order order) {
399   assert(p != cast_to_oop(this) || !UseAltGCForwarding, "Must not be called with self-forwarding");
400   verify_forwardee(p);
401   markWord m = markWord::encode_pointer_as_mark(p);
402   assert(forwardee(m) == p, "encoding must be reversable");
403   markWord old_mark = cas_set_mark(m, compare, order);
404   if (old_mark == compare) {
405     return NULL;
406   } else {
407     return forwardee(old_mark);
408   }
409 }
410 
411 oop oopDesc::forward_to_self_atomic(markWord compare, atomic_memory_order order) {
412 #ifdef _LP64
413   if (UseAltGCForwarding) {
414    markWord m = compare;
415     // If mark is displaced, we need to preserve the real header during GC.
416     // It will be restored to the displaced header after GC.
417     assert(SafepointSynchronize::is_at_safepoint(), "we can only safely fetch the displaced header at safepoint");
418     if (m.has_displaced_mark_helper()) {
419       m = m.displaced_mark_helper();
420     }
421     m = m.set_self_forwarded();
422     assert(forwardee(m) == cast_to_oop(this), "encoding must be reversible");
423     markWord old_mark = cas_set_mark(m, compare, order);
424     if (old_mark == compare) {
425       return nullptr;
426     } else {
427       assert(old_mark.is_marked(), "must be marked here");
428       return forwardee(old_mark);
429     }
430   } else
431 #endif
432   {
433     return forward_to_atomic(cast_to_oop(this), compare, order);
434   }
435 }
436 
437 oop oopDesc::forwardee(markWord header) const {
438   assert(header.is_marked(), "only decode when actually forwarded");
439 #ifdef _LP64
440   if (header.self_forwarded()) {
441     return cast_to_oop(this);
442   } else
443 #endif
444   {
445     return cast_to_oop(header.decode_pointer());
446   }
447 }
448 
449 // Note that the forwardee is not the same thing as the displaced_mark.
450 // The forwardee is used when copying during scavenge and mark-sweep.
451 // It does need to clear the low two locking- and GC-related bits.
452 oop oopDesc::forwardee() const {
453   return forwardee(mark());
454 }
455 
456 // The following method needs to be MT safe.
457 uint oopDesc::age() const {
458   assert(!is_forwarded(), "Attempt to read age from forwarded mark");
459   if (has_displaced_mark()) {
460     return displaced_mark().age();
461   } else {
462     return mark().age();
463   }
464 }
465 
466 void oopDesc::incr_age() {
467   assert(!is_forwarded(), "Attempt to increment age of forwarded mark");
468   if (has_displaced_mark()) {
469     set_displaced_mark(displaced_mark().incr_age());
470   } else {
471     set_mark(mark().incr_age());
472   }
473 }

488   int size = size_given_klass(k);
489   OopIteratorClosureDispatch::oop_oop_iterate(cl, this, k);
490   return size;
491 }
492 
493 template <typename OopClosureType>
494 int oopDesc::oop_iterate_size(OopClosureType* cl, MemRegion mr) {
495   Klass* k = klass();
496   int size = size_given_klass(k);
497   OopIteratorClosureDispatch::oop_oop_iterate(cl, this, k, mr);
498   return size;
499 }
500 
501 template <typename OopClosureType>
502 void oopDesc::oop_iterate_backwards(OopClosureType* cl) {
503   oop_iterate_backwards(cl, klass());
504 }
505 
506 template <typename OopClosureType>
507 void oopDesc::oop_iterate_backwards(OopClosureType* cl, Klass* k) {
508   assert(UseCompactObjectHeaders || k == klass(), "wrong klass");
509   OopIteratorClosureDispatch::oop_oop_iterate_backwards(cl, this, k);
510 }
511 
512 bool oopDesc::is_instanceof_or_null(oop obj, Klass* klass) {
513   return obj == NULL || obj->klass()->is_subtype_of(klass);
514 }
515 
516 intptr_t oopDesc::identity_hash() {
517   // Fast case; if the object is unlocked and the hash value is set, no locking is needed
518   // Note: The mark must be read into local variable to avoid concurrent updates.
519   markWord mrk = mark();
520   if (mrk.is_unlocked() && !mrk.has_no_hash()) {
521     return mrk.hash();
522   } else if (mrk.is_marked()) {
523     return mrk.hash();
524   } else {
525     return slow_identity_hash();
526   }
527 }
528 
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