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src/hotspot/share/oops/markWord.hpp

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  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 #ifndef SHARE_OOPS_MARKWORD_HPP
 26 #define SHARE_OOPS_MARKWORD_HPP
 27 

 28 #include "metaprogramming/primitiveConversions.hpp"
 29 #include "oops/compressedKlass.hpp"
 30 #include "oops/oopsHierarchy.hpp"
 31 #include "runtime/globals.hpp"

 32 
 33 #include <type_traits>
 34 
 35 // The markWord describes the header of an object.
 36 //
 37 // Bit-format of an object header (most significant first, big endian layout below):
 38 //
 39 //  32 bits:
 40 //  --------
 41 //             hash:25 ------------>| age:4  self-fwd:1  lock:2 (normal object)
 42 //
 43 //  64 bits:
 44 //  --------
 45 //  unused:22 hash:31 -->| unused_gap:4  age:4  self-fwd:1  lock:2 (normal object)
 46 //
 47 //  64 bits (with compact headers):
 48 //  -------------------------------
 49 //  klass:22  hash:31 -->| unused_gap:4  age:4  self-fwd:1  lock:2 (normal object)
 50 //
 51 //  - hash contains the identity hash value: largest value is
 52 //    31 bits, see os::random().  Also, 64-bit vm's require
 53 //    a hash value no bigger than 32 bits because they will not
 54 //    properly generate a mask larger than that: see library_call.cpp
 55 //
 56 //  - the two lock bits are used to describe three states: locked/unlocked and monitor.
 57 //
 58 //    [ptr             | 00]  locked             ptr points to real header on stack (stack-locking in use)
 59 //    [header          | 00]  locked             locked regular object header (fast-locking in use)
 60 //    [header          | 01]  unlocked           regular object header
 61 //    [ptr             | 10]  monitor            inflated lock (header is swapped out, UseObjectMonitorTable == false)
 62 //    [header          | 10]  monitor            inflated lock (UseObjectMonitorTable == true)
 63 //    [ptr             | 11]  marked             used to mark an object
 64 //    [0 ............ 0| 00]  inflating          inflation in progress (stack-locking in use)
 65 //
 66 //    We assume that stack/thread pointers have the lowest two bits cleared.
 67 //

 68 //  - INFLATING() is a distinguished markword value of all zeros that is
 69 //    used when inflating an existing stack-lock into an ObjectMonitor.
 70 //    See below for is_being_inflated() and INFLATING().


















 71 
 72 class BasicLock;
 73 class ObjectMonitor;
 74 class JavaThread;
 75 class outputStream;
 76 
 77 class markWord {
 78  private:
 79   uintptr_t _value;
 80 
 81  public:
 82   explicit markWord(uintptr_t value) : _value(value) {}
 83 
 84   markWord() = default;         // Doesn't initialize _value.
 85 
 86   // It is critical for performance that this class be trivially
 87   // destructable, copyable, and assignable.
 88   ~markWord() = default;
 89   markWord(const markWord&) = default;
 90   markWord& operator=(const markWord&) = default;
 91 
 92   static markWord from_pointer(void* ptr) {
 93     return markWord((uintptr_t)ptr);
 94   }
 95   void* to_pointer() const {
 96     return (void*)_value;
 97   }
 98 
 99   bool operator==(const markWord& other) const {
100     return _value == other._value;
101   }
102   bool operator!=(const markWord& other) const {
103     return !operator==(other);
104   }
105 
106   // Conversion
107   uintptr_t value() const { return _value; }
108 
109   // Constants
110   static const int age_bits                       = 4;
111   static const int lock_bits                      = 2;
112   static const int self_fwd_bits                  = 1;
113   static const int max_hash_bits                  = BitsPerWord - age_bits - lock_bits - self_fwd_bits;







114   static const int hash_bits                      = max_hash_bits > 31 ? 31 : max_hash_bits;
115   static const int unused_gap_bits                = LP64_ONLY(4) NOT_LP64(0); // Reserved for Valhalla.
116 
117   static const int lock_shift                     = 0;
118   static const int self_fwd_shift                 = lock_shift + lock_bits;
119   static const int age_shift                      = self_fwd_shift + self_fwd_bits;
120   static const int hash_shift                     = age_shift + age_bits + unused_gap_bits;




121 
122   static const uintptr_t lock_mask                = right_n_bits(lock_bits);
123   static const uintptr_t lock_mask_in_place       = lock_mask << lock_shift;
124   static const uintptr_t self_fwd_mask            = right_n_bits(self_fwd_bits);
125   static const uintptr_t self_fwd_mask_in_place   = self_fwd_mask << self_fwd_shift;








126   static const uintptr_t age_mask                 = right_n_bits(age_bits);
127   static const uintptr_t age_mask_in_place        = age_mask << age_shift;





128   static const uintptr_t hash_mask                = right_n_bits(hash_bits);
129   static const uintptr_t hash_mask_in_place       = hash_mask << hash_shift;
130 
131 #ifdef _LP64
132   // Used only with compact headers:
133   // We store the (narrow) Klass* in the bits 43 to 64.
134 
135   // These are for bit-precise extraction of the narrow Klass* from the 64-bit Markword
136   static constexpr int klass_offset_in_bytes      = 4;
137   static constexpr int klass_shift                = hash_shift + hash_bits;
138   static constexpr int klass_shift_at_offset      = klass_shift - klass_offset_in_bytes * BitsPerByte;
139   static constexpr int klass_bits                 = 22;
140   static constexpr uintptr_t klass_mask           = right_n_bits(klass_bits);
141   static constexpr uintptr_t klass_mask_in_place  = klass_mask << klass_shift;
142 #endif
143 
144 
145   static const uintptr_t locked_value             = 0;
146   static const uintptr_t unlocked_value           = 1;
147   static const uintptr_t monitor_value            = 2;
148   static const uintptr_t marked_value             = 3;
149 







150   static const uintptr_t no_hash                  = 0 ;  // no hash value assigned
151   static const uintptr_t no_hash_in_place         = (uintptr_t)no_hash << hash_shift;
152   static const uintptr_t no_lock_in_place         = unlocked_value;
153 
154   static const uint max_age                       = age_mask;
155 
156   // Creates a markWord with all bits set to zero.
157   static markWord zero() { return markWord(uintptr_t(0)); }
158 




159   // lock accessors (note that these assume lock_shift == 0)
160   bool is_locked()   const {
161     return (mask_bits(value(), lock_mask_in_place) != unlocked_value);
162   }
163   bool is_unlocked() const {
164     return (mask_bits(value(), lock_mask_in_place) == unlocked_value);
165   }
166   bool is_marked()   const {
167     return (mask_bits(value(), lock_mask_in_place) == marked_value);
168   }







169   bool is_forwarded() const {
170     // Returns true for normal forwarded (0b011) and self-forwarded (0b1xx).
171     return mask_bits(value(), lock_mask_in_place | self_fwd_mask_in_place) >= static_cast<intptr_t>(marked_value);
172   }
173   bool is_neutral()  const {  // Not locked, or marked - a "clean" neutral state
174     return (mask_bits(value(), lock_mask_in_place) == unlocked_value);
175   }
176 
177   // Special temporary state of the markWord while being inflated.
178   // Code that looks at mark outside a lock need to take this into account.
179   bool is_being_inflated() const { return (value() == 0); }
180 
181   // Distinguished markword value - used when inflating over
182   // an existing stack-lock.  0 indicates the markword is "BUSY".
183   // Lockword mutators that use a LD...CAS idiom should always
184   // check for and avoid overwriting a 0 value installed by some
185   // other thread.  (They should spin or block instead.  The 0 value
186   // is transient and *should* be short-lived).
187   // Fast-locking does not use INFLATING.
188   static markWord INFLATING() { return zero(); }    // inflate-in-progress
189 
190   // Should this header be preserved during GC?
191   bool must_be_preserved() const {
192     return (!is_unlocked() || !has_no_hash());

193   }
194 
195   // WARNING: The following routines are used EXCLUSIVELY by
196   // synchronization functions. They are not really gc safe.
197   // They must get updated if markWord layout get changed.
198   markWord set_unlocked() const {
199     return markWord(value() | unlocked_value);
200   }
201 
202   bool is_fast_locked() const {
203     return (value() & lock_mask_in_place) == locked_value;
204   }
205   markWord set_fast_locked() const {
206     // Clear the lock_mask_in_place bits to set locked_value:
207     return markWord(value() & ~lock_mask_in_place);
208   }
209 
210   bool has_monitor() const {
211     return ((value() & lock_mask_in_place) == monitor_value);
212   }

253   // age operations
254   markWord set_marked()   { return markWord((value() & ~lock_mask_in_place) | marked_value); }
255   markWord set_unmarked() { return markWord((value() & ~lock_mask_in_place) | unlocked_value); }
256 
257   uint     age()           const { return (uint) mask_bits(value() >> age_shift, age_mask); }
258   markWord set_age(uint v) const {
259     assert((v & ~age_mask) == 0, "shouldn't overflow age field");
260     return markWord((value() & ~age_mask_in_place) | ((v & age_mask) << age_shift));
261   }
262   markWord incr_age()      const { return age() == max_age ? markWord(_value) : set_age(age() + 1); }
263 
264   // hash operations
265   intptr_t hash() const {
266     return mask_bits(value() >> hash_shift, hash_mask);
267   }
268 
269   bool has_no_hash() const {
270     return hash() == no_hash;
271   }
272 




























273   inline Klass* klass() const;
274   inline Klass* klass_or_null() const;
275   inline Klass* klass_without_asserts() const;
276   inline narrowKlass narrow_klass() const;
277   inline markWord set_narrow_klass(narrowKlass narrow_klass) const;
278 
279   // Prototype mark for initialization
280   static markWord prototype() {
281     return markWord( no_hash_in_place | no_lock_in_place );
282   }
283 












284   // Debugging
285   void print_on(outputStream* st, bool print_monitor_info = true) const;
286 
287   // Prepare address of oop for placement into mark
288   inline static markWord encode_pointer_as_mark(void* p) { return from_pointer(p).set_marked(); }
289 
290   // Recover address of oop from encoded form used in mark
291   inline void* decode_pointer() const { return (void*)clear_lock_bits().value(); }

292 
293   inline bool is_self_forwarded() const {
294     return mask_bits(value(), self_fwd_mask_in_place) != 0;
295   }
296 
297   inline markWord set_self_forwarded() const {
298     return markWord(value() | self_fwd_mask_in_place);
299   }
300 
301   inline markWord unset_self_forwarded() const {
302     return markWord(value() & ~self_fwd_mask_in_place);
303   }
304 
305   inline oop forwardee() const {
306     return cast_to_oop(decode_pointer());
307   }
308 };
309 
310 // Support atomic operations.
311 template<>

  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 #ifndef SHARE_OOPS_MARKWORD_HPP
 26 #define SHARE_OOPS_MARKWORD_HPP
 27 
 28 #include "layoutKind.hpp"
 29 #include "metaprogramming/primitiveConversions.hpp"
 30 #include "oops/compressedKlass.hpp"
 31 #include "oops/oopsHierarchy.hpp"
 32 #include "runtime/globals.hpp"
 33 #include "utilities/vmEnums.hpp"
 34 
 35 #include <type_traits>
 36 
 37 // The markWord describes the header of an object.
 38 //
 39 // Bit-format of an object header (most significant first, big endian layout below):
 40 //
 41 //  32 bits:
 42 //  --------
 43 //             hash:25 ------------>| age:4  self-fwd:1  lock:2 (normal object)
 44 //
 45 //  64 bits:
 46 //  --------
 47 //  unused:22 hash:31 -->| valhalla:4  age:4  self-fwd:1  lock:2 (normal object)
 48 //
 49 //  64 bits (with compact headers):
 50 //  -------------------------------
 51 //  klass:22  hash:31 -->| valhalla:4  age:4  self-fwd:1  lock:2 (normal object)
 52 //
 53 //  - hash contains the identity hash value: largest value is
 54 //    31 bits, see os::random().  Also, 64-bit vm's require
 55 //    a hash value no bigger than 32 bits because they will not
 56 //    properly generate a mask larger than that: see library_call.cpp
 57 //
 58 //  - the two lock bits are used to describe three states: locked/unlocked and monitor.
 59 //
 60 //    [ptr             | 00]  locked             ptr points to real header on stack (stack-locking in use)
 61 //    [header          | 00]  locked             locked regular object header (fast-locking in use)
 62 //    [header          | 01]  unlocked           regular object header
 63 //    [ptr             | 10]  monitor            inflated lock (header is swapped out, UseObjectMonitorTable == false)
 64 //    [header          | 10]  monitor            inflated lock (UseObjectMonitorTable == true)
 65 //    [ptr             | 11]  marked             used to mark an object
 66 //    [0 ............ 0| 00]  inflating          inflation in progress (stack-locking in use)
 67 //
 68 //    We assume that stack/thread pointers have the lowest two bits cleared.
 69 //
 70 //
 71 //  - INFLATING() is a distinguished markword value of all zeros that is
 72 //    used when inflating an existing stack-lock into an ObjectMonitor.
 73 //    See below for is_being_inflated() and INFLATING().
 74 //
 75 //  VALHALLA EXTENSIONS:
 76 //
 77 //  N.B.: 32 bit mode is not supported, this section assumes 64 bit systems.
 78 //
 79 //  Project Valhalla uses markWord bits to denote the following oops (listed least to most significant):
 80 //  * inline types: have alternative bytecode behavior, e.g. can not be locked
 81 //  * flat arrays: load/decode of klass layout helper is expensive for aaload
 82 //  * "null free" arrays: load/decode of klass layout helper again for aaload
 83 //  * inline type: "larval state": mutable state, but only during object init, observable
 84 //      by only by a single thread (generally do not mutate markWord)
 85 //
 86 //  Inline types cannot be locked, monitored or inflating.
 87 //
 88 //  Note the position of 'self-fwd' is not by accident. When forwarding an
 89 //  object to a new heap position, HeapWord alignment guarantees the lower
 90 //  bits, including 'self-fwd' are 0. "is_self_forwarded()" will be correctly
 91 //  set to false. Otherwise encode_pointer_as_mark() may have 'self-fwd' set.
 92 
 93 class BasicLock;
 94 class ObjectMonitor;
 95 class JavaThread;
 96 class outputStream;
 97 
 98 class markWord {
 99  private:
100   uintptr_t _value;
101 
102  public:
103   explicit markWord(uintptr_t value) : _value(value) {}
104 
105   markWord() = default;         // Doesn't initialize _value.
106 
107   // It is critical for performance that this class be trivially
108   // destructable, copyable, and assignable.
109   ~markWord() = default;
110   markWord(const markWord&) = default;
111   markWord& operator=(const markWord&) = default;
112 
113   static markWord from_pointer(void* ptr) {
114     return markWord((uintptr_t)ptr);
115   }
116   void* to_pointer() const {
117     return (void*)_value;
118   }
119 
120   bool operator==(const markWord& other) const {
121     return _value == other._value;
122   }
123   bool operator!=(const markWord& other) const {
124     return !operator==(other);
125   }
126 
127   // Conversion
128   uintptr_t value() const { return _value; }
129 
130   // Constants, in least significant bit order

131   static const int lock_bits                      = 2;
132   static const int self_fwd_bits                  = 1;
133   // instance state
134   static const int age_bits                       = 4;
135   // EnableValhalla: static prototype header bits (fast path instead of klass layout_helper)
136   static const int inline_type_bits               = 1;
137   static const int null_free_array_bits           = LP64_ONLY(1) NOT_LP64(0);
138   static const int flat_array_bits                = LP64_ONLY(1) NOT_LP64(0);
139   static const int larval_bits                    = 1;
140   static const int max_hash_bits                  = BitsPerWord - age_bits - lock_bits - inline_type_bits - larval_bits - flat_array_bits - null_free_array_bits - self_fwd_bits;
141   static const int hash_bits                      = max_hash_bits > 31 ? 31 : max_hash_bits;

142 
143   static const int lock_shift                     = 0;
144   static const int self_fwd_shift                 = lock_shift + lock_bits;
145   static const int age_shift                      = self_fwd_shift + self_fwd_bits;
146   static const int inline_type_shift              = age_shift + age_bits;
147   static const int null_free_array_shift          = inline_type_shift + inline_type_bits;
148   static const int flat_array_shift               = null_free_array_shift + null_free_array_bits;
149   static const int larval_shift                   = flat_array_shift + flat_array_bits;
150   static const int hash_shift                     = larval_shift + larval_bits;
151 
152   static const uintptr_t lock_mask                = right_n_bits(lock_bits);
153   static const uintptr_t lock_mask_in_place       = lock_mask << lock_shift;
154   static const uintptr_t self_fwd_mask            = right_n_bits(self_fwd_bits);
155   static const uintptr_t self_fwd_mask_in_place   = self_fwd_mask << self_fwd_shift;
156   static const uintptr_t inline_type_bit_in_place = right_n_bits(inline_type_bits) << inline_type_shift;
157   static const uintptr_t inline_type_mask_in_place = inline_type_bit_in_place + lock_mask;
158   static const uintptr_t null_free_array_mask     = right_n_bits(null_free_array_bits);
159   static const uintptr_t null_free_array_mask_in_place = (null_free_array_mask << null_free_array_shift) | lock_mask_in_place;
160   static const uintptr_t null_free_array_bit_in_place  = (right_n_bits(null_free_array_bits) << null_free_array_shift);
161   static const uintptr_t flat_array_mask          = right_n_bits(flat_array_bits);
162   static const uintptr_t flat_array_mask_in_place = (flat_array_mask << flat_array_shift) | null_free_array_mask_in_place | lock_mask_in_place;
163   static const uintptr_t flat_array_bit_in_place  = right_n_bits(flat_array_bits) << flat_array_shift;
164   static const uintptr_t age_mask                 = right_n_bits(age_bits);
165   static const uintptr_t age_mask_in_place        = age_mask << age_shift;
166 
167   static const uintptr_t larval_mask              = right_n_bits(larval_bits);
168   static const uintptr_t larval_mask_in_place     = (larval_mask << larval_shift) | inline_type_mask_in_place;
169   static const uintptr_t larval_bit_in_place      = right_n_bits(larval_bits) << larval_shift;
170 
171   static const uintptr_t hash_mask                = right_n_bits(hash_bits);
172   static const uintptr_t hash_mask_in_place       = hash_mask << hash_shift;
173 
174 #ifdef _LP64
175   // Used only with compact headers:
176   // We store the (narrow) Klass* in the bits 43 to 64.
177 
178   // These are for bit-precise extraction of the narrow Klass* from the 64-bit Markword
179   static constexpr int klass_offset_in_bytes      = 4;
180   static constexpr int klass_shift                = hash_shift + hash_bits;
181   static constexpr int klass_shift_at_offset      = klass_shift - klass_offset_in_bytes * BitsPerByte;
182   static constexpr int klass_bits                 = 22;
183   static constexpr uintptr_t klass_mask           = right_n_bits(klass_bits);
184   static constexpr uintptr_t klass_mask_in_place  = klass_mask << klass_shift;
185 #endif
186 
187 
188   static const uintptr_t locked_value             = 0;
189   static const uintptr_t unlocked_value           = 1;
190   static const uintptr_t monitor_value            = 2;
191   static const uintptr_t marked_value             = 3;
192 
193   static const uintptr_t inline_type_pattern      = inline_type_bit_in_place | unlocked_value;
194   static const uintptr_t null_free_array_pattern  = null_free_array_bit_in_place | unlocked_value;
195   static const uintptr_t null_free_flat_array_pattern = flat_array_bit_in_place | null_free_array_pattern;
196   static const uintptr_t nullable_flat_array_pattern = flat_array_bit_in_place | unlocked_value;
197 
198   static const uintptr_t larval_pattern           = larval_bit_in_place | inline_type_pattern;
199 
200   static const uintptr_t no_hash                  = 0 ;  // no hash value assigned
201   static const uintptr_t no_hash_in_place         = (uintptr_t)no_hash << hash_shift;
202   static const uintptr_t no_lock_in_place         = unlocked_value;
203 
204   static const uint max_age                       = age_mask;
205 
206   // Creates a markWord with all bits set to zero.
207   static markWord zero() { return markWord(uintptr_t(0)); }
208 
209   bool is_inline_type() const {
210     return (mask_bits(value(), inline_type_mask_in_place) == inline_type_pattern);
211   }
212 
213   // lock accessors (note that these assume lock_shift == 0)
214   bool is_locked()   const {
215     return (mask_bits(value(), lock_mask_in_place) != unlocked_value);
216   }
217   bool is_unlocked() const {
218     return (mask_bits(value(), lock_mask_in_place) == unlocked_value);
219   }
220   bool is_marked()   const {
221     return (mask_bits(value(), lock_mask_in_place) == marked_value);
222   }
223 
224   // is unlocked and not an inline type (which cannot be involved in locking, displacement or inflation)
225   // i.e. test both lock bits and the inline type bit together
226   bool is_neutral()  const {  // Not locked, or marked - a "clean" neutral state
227     return (mask_bits(value(), inline_type_mask_in_place) == unlocked_value);
228   }
229 
230   bool is_forwarded() const {
231     // Returns true for normal forwarded (0b011) and self-forwarded (0b1xx).
232     return mask_bits(value(), lock_mask_in_place | self_fwd_mask_in_place) >= static_cast<intptr_t>(marked_value);
233   }



234 
235   // Special temporary state of the markWord while being inflated.
236   // Code that looks at mark outside a lock need to take this into account.
237   bool is_being_inflated() const { return (value() == 0); }
238 
239   // Distinguished markword value - used when inflating over
240   // an existing stack-lock.  0 indicates the markword is "BUSY".
241   // Lockword mutators that use a LD...CAS idiom should always
242   // check for and avoid overwriting a 0 value installed by some
243   // other thread.  (They should spin or block instead.  The 0 value
244   // is transient and *should* be short-lived).
245   // Fast-locking does not use INFLATING.
246   static markWord INFLATING() { return zero(); }    // inflate-in-progress
247 
248   // Should this header be preserved during GC?
249   bool must_be_preserved() const {
250     return (!is_unlocked() || !has_no_hash() ||
251       (EnableValhalla && (is_larval_state() || is_inline_type() || is_flat_array() || is_null_free_array())));
252   }
253 
254   // WARNING: The following routines are used EXCLUSIVELY by
255   // synchronization functions. They are not really gc safe.
256   // They must get updated if markWord layout get changed.
257   markWord set_unlocked() const {
258     return markWord(value() | unlocked_value);
259   }
260 
261   bool is_fast_locked() const {
262     return (value() & lock_mask_in_place) == locked_value;
263   }
264   markWord set_fast_locked() const {
265     // Clear the lock_mask_in_place bits to set locked_value:
266     return markWord(value() & ~lock_mask_in_place);
267   }
268 
269   bool has_monitor() const {
270     return ((value() & lock_mask_in_place) == monitor_value);
271   }

312   // age operations
313   markWord set_marked()   { return markWord((value() & ~lock_mask_in_place) | marked_value); }
314   markWord set_unmarked() { return markWord((value() & ~lock_mask_in_place) | unlocked_value); }
315 
316   uint     age()           const { return (uint) mask_bits(value() >> age_shift, age_mask); }
317   markWord set_age(uint v) const {
318     assert((v & ~age_mask) == 0, "shouldn't overflow age field");
319     return markWord((value() & ~age_mask_in_place) | ((v & age_mask) << age_shift));
320   }
321   markWord incr_age()      const { return age() == max_age ? markWord(_value) : set_age(age() + 1); }
322 
323   // hash operations
324   intptr_t hash() const {
325     return mask_bits(value() >> hash_shift, hash_mask);
326   }
327 
328   bool has_no_hash() const {
329     return hash() == no_hash;
330   }
331 
332   // private buffered value operations
333   markWord enter_larval_state() const {
334     return markWord(value() | larval_bit_in_place);
335   }
336   markWord exit_larval_state() const {
337     return markWord(value() & ~larval_bit_in_place);
338   }
339   bool is_larval_state() const {
340     return (mask_bits(value(), larval_mask_in_place) == larval_pattern);
341   }
342 
343   bool is_flat_array() const {
344 #ifdef _LP64 // 64 bit encodings only
345     return (mask_bits(value(), flat_array_mask_in_place) == null_free_flat_array_pattern)
346            || (mask_bits(value(), flat_array_mask_in_place) == nullable_flat_array_pattern);
347 #else
348     return false;
349 #endif
350   }
351 
352   bool is_null_free_array() const {
353 #ifdef _LP64 // 64 bit encodings only
354     return (mask_bits(value(), null_free_array_mask_in_place) == null_free_array_pattern);
355 #else
356     return false;
357 #endif
358   }
359 
360   inline Klass* klass() const;
361   inline Klass* klass_or_null() const;
362   inline Klass* klass_without_asserts() const;
363   inline narrowKlass narrow_klass() const;
364   inline markWord set_narrow_klass(narrowKlass narrow_klass) const;
365 
366   // Prototype mark for initialization
367   static markWord prototype() {
368     return markWord( no_hash_in_place | no_lock_in_place );
369   }
370 
371   static markWord inline_type_prototype() {
372     return markWord(inline_type_pattern);
373   }
374 
375 #ifdef _LP64 // 64 bit encodings only
376   static markWord flat_array_prototype(LayoutKind lk);
377 
378   static markWord null_free_array_prototype() {
379     return markWord(null_free_array_pattern);
380   }
381 #endif
382 
383   // Debugging
384   void print_on(outputStream* st, bool print_monitor_info = true) const;
385 
386   // Prepare address of oop for placement into mark
387   inline static markWord encode_pointer_as_mark(void* p) { return from_pointer(p).set_marked(); }
388 
389   inline void* decode_pointer() const {
390     return (void*) (clear_lock_bits().value());
391   }
392 
393   inline bool is_self_forwarded() const {
394     return mask_bits(value(), self_fwd_mask_in_place) != 0;
395   }
396 
397   inline markWord set_self_forwarded() const {
398     return markWord(value() | self_fwd_mask_in_place);
399   }
400 
401   inline markWord unset_self_forwarded() const {
402     return markWord(value() & ~self_fwd_mask_in_place);
403   }
404 
405   inline oop forwardee() const {
406     return cast_to_oop(decode_pointer());
407   }
408 };
409 
410 // Support atomic operations.
411 template<>
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