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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/oopsHierarchy.hpp"
 30 #include "runtime/globals.hpp"
 31 
 32 #include <type_traits>
 33 
 34 // The markWord describes the header of an object.
 35 //
 36 // Bit-format of an object header (most significant first, big endian layout below):
 37 //
 38 //  32 bits:
 39 //  --------
 40 //             hash:25 ------------>| age:4  unused_gap:1  lock:2 (normal object)
 41 //
 42 //  64 bits:
 43 //  --------
 44 //  unused:25 hash:31 -->| unused_gap:1  age:4  unused_gap:1  lock:2 (normal object)
 45 //




 46 //  - hash contains the identity hash value: largest value is
 47 //    31 bits, see os::random().  Also, 64-bit vm's require
 48 //    a hash value no bigger than 32 bits because they will not
 49 //    properly generate a mask larger than that: see library_call.cpp
 50 //
 51 //  - the two lock bits are used to describe three states: locked/unlocked and monitor.
 52 //
 53 //    [ptr             | 00]  locked             ptr points to real header on stack (stack-locking in use)
 54 //    [header          | 00]  locked             locked regular object header (fast-locking in use)
 55 //    [header          | 01]  unlocked           regular object header
 56 //    [ptr             | 10]  monitor            inflated lock (header is swapped out)
 57 //    [ptr             | 11]  marked             used to mark an object
 58 //    [0 ............ 0| 00]  inflating          inflation in progress (stack-locking in use)
 59 //
 60 //    We assume that stack/thread pointers have the lowest two bits cleared.
 61 //
 62 //  - INFLATING() is a distinguished markword value of all zeros that is
 63 //    used when inflating an existing stack-lock into an ObjectMonitor.
 64 //    See below for is_being_inflated() and INFLATING().
 65 

 86   static markWord from_pointer(void* ptr) {
 87     return markWord((uintptr_t)ptr);
 88   }
 89   void* to_pointer() const {
 90     return (void*)_value;
 91   }
 92 
 93   bool operator==(const markWord& other) const {
 94     return _value == other._value;
 95   }
 96   bool operator!=(const markWord& other) const {
 97     return !operator==(other);
 98   }
 99 
100   // Conversion
101   uintptr_t value() const { return _value; }
102 
103   // Constants
104   static const int age_bits                       = 4;
105   static const int lock_bits                      = 2;
106   static const int first_unused_gap_bits          = 1;
107   static const int max_hash_bits                  = BitsPerWord - age_bits - lock_bits - first_unused_gap_bits;
108   static const int hash_bits                      = max_hash_bits > 31 ? 31 : max_hash_bits;
109   static const int second_unused_gap_bits         = LP64_ONLY(1) NOT_LP64(0);






110 
111   static const int lock_shift                     = 0;
112   static const int age_shift                      = lock_bits + first_unused_gap_bits;
113   static const int hash_shift                     = age_shift + age_bits + second_unused_gap_bits;






114 
115   static const uintptr_t lock_mask                = right_n_bits(lock_bits);
116   static const uintptr_t lock_mask_in_place       = lock_mask << lock_shift;


117   static const uintptr_t age_mask                 = right_n_bits(age_bits);
118   static const uintptr_t age_mask_in_place        = age_mask << age_shift;
119   static const uintptr_t hash_mask                = right_n_bits(hash_bits);
120   static const uintptr_t hash_mask_in_place       = hash_mask << hash_shift;






121 
122   static const uintptr_t locked_value             = 0;
123   static const uintptr_t unlocked_value           = 1;
124   static const uintptr_t monitor_value            = 2;
125   static const uintptr_t marked_value             = 3;
126 
127   static const uintptr_t no_hash                  = 0 ;  // no hash value assigned
128   static const uintptr_t no_hash_in_place         = (uintptr_t)no_hash << hash_shift;
129   static const uintptr_t no_lock_in_place         = unlocked_value;
130 
131   static const uint max_age                       = age_mask;
132 
133   // Creates a markWord with all bits set to zero.
134   static markWord zero() { return markWord(uintptr_t(0)); }
135 
136   // lock accessors (note that these assume lock_shift == 0)
137   bool is_locked()   const {
138     return (mask_bits(value(), lock_mask_in_place) != unlocked_value);
139   }
140   bool is_unlocked() const {

188     // Clear the lock_mask_in_place bits to set locked_value:
189     return markWord(value() & ~lock_mask_in_place);
190   }
191 
192   bool has_monitor() const {
193     return ((value() & lock_mask_in_place) == monitor_value);
194   }
195   ObjectMonitor* monitor() const {
196     assert(has_monitor(), "check");
197     // Use xor instead of &~ to provide one extra tag-bit check.
198     return (ObjectMonitor*) (value() ^ monitor_value);
199   }
200   bool has_displaced_mark_helper() const {
201     intptr_t lockbits = value() & lock_mask_in_place;
202     return LockingMode == LM_LIGHTWEIGHT  ? lockbits == monitor_value   // monitor?
203                                           : (lockbits & unlocked_value) == 0; // monitor | stack-locked?
204   }
205   markWord displaced_mark_helper() const;
206   void set_displaced_mark_helper(markWord m) const;
207   markWord copy_set_hash(intptr_t hash) const {
208     uintptr_t tmp = value() & (~hash_mask_in_place);
209     tmp |= ((hash & hash_mask) << hash_shift);
210     return markWord(tmp);






211   }
212   // it is only used to be stored into BasicLock as the
213   // indicator that the lock is using heavyweight monitor
214   static markWord unused_mark() {
215     return markWord(marked_value);
216   }
217   // the following two functions create the markWord to be
218   // stored into object header, it encodes monitor info
219   static markWord encode(BasicLock* lock) {
220     return from_pointer(lock);
221   }
222   static markWord encode(ObjectMonitor* monitor) {
223     uintptr_t tmp = (uintptr_t) monitor;
224     return markWord(tmp | monitor_value);
225   }
226 
227   // used to encode pointers during GC
228   markWord clear_lock_bits() { return markWord(value() & ~lock_mask_in_place); }
229 
230   // age operations
231   markWord set_marked()   { return markWord((value() & ~lock_mask_in_place) | marked_value); }
232   markWord set_unmarked() { return markWord((value() & ~lock_mask_in_place) | unlocked_value); }
233 
234   uint     age()           const { return (uint) mask_bits(value() >> age_shift, age_mask); }
235   markWord set_age(uint v) const {
236     assert((v & ~age_mask) == 0, "shouldn't overflow age field");
237     return markWord((value() & ~age_mask_in_place) | ((v & age_mask) << age_shift));
238   }
239   markWord incr_age()      const { return age() == max_age ? markWord(_value) : set_age(age() + 1); }
240 
241   // hash operations
242   intptr_t hash() const {
243     return mask_bits(value() >> hash_shift, hash_mask);




244   }
245 
246   bool has_no_hash() const {
247     return hash() == no_hash;
248   }
249 









250   // Prototype mark for initialization
251   static markWord prototype() {
252     return markWord( no_hash_in_place | no_lock_in_place );
253   }
254 
255   // Debugging
256   void print_on(outputStream* st, bool print_monitor_info = true) const;
257 
258   // Prepare address of oop for placement into mark
259   inline static markWord encode_pointer_as_mark(void* p) { return from_pointer(p).set_marked(); }
260 
261   // Recover address of oop from encoded form used in mark
262   inline void* decode_pointer() { return (void*)clear_lock_bits().value(); }













263 };
264 
265 // Support atomic operations.
266 template<>
267 struct PrimitiveConversions::Translate<markWord> : public std::true_type {
268   typedef markWord Value;
269   typedef uintptr_t Decayed;
270 
271   static Decayed decay(const Value& x) { return x.value(); }
272   static Value recover(Decayed x) { return Value(x); }
273 };
274 
275 #endif // SHARE_OOPS_MARKWORD_HPP

  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 "gc/shared/gc_globals.hpp"
 29 #include "metaprogramming/primitiveConversions.hpp"
 30 #include "oops/compressedKlass.hpp"
 31 #include "oops/oopsHierarchy.hpp"
 32 #include "runtime/globals.hpp"
 33 
 34 #include <type_traits>
 35 
 36 // The markWord describes the header of an object.
 37 //
 38 // Bit-format of an object header (most significant first, big endian layout below):
 39 //
 40 //  32 bits:
 41 //  --------
 42 //             hash:25 ------------>| age:4  unused_gap:1  lock:2 (normal object)
 43 //
 44 //  64 bits:
 45 //  --------
 46 //  unused:25 hash:31 -->| unused_gap:1  age:4  unused_gap:1  lock:2 (normal object)
 47 //
 48 //  64 bits (with compact headers):
 49 //  -------------------------------
 50 //  nklass:32 hash:25 -->| unused_gap:1  age:4  self-fwded:1  lock:2 (normal object)
 51 //
 52 //  - hash contains the identity hash value: largest value is
 53 //    31 bits, see os::random().  Also, 64-bit vm's require
 54 //    a hash value no bigger than 32 bits because they will not
 55 //    properly generate a mask larger than that: see library_call.cpp
 56 //
 57 //  - the two lock bits are used to describe three states: locked/unlocked and monitor.
 58 //
 59 //    [ptr             | 00]  locked             ptr points to real header on stack (stack-locking in use)
 60 //    [header          | 00]  locked             locked regular object header (fast-locking in use)
 61 //    [header          | 01]  unlocked           regular object header
 62 //    [ptr             | 10]  monitor            inflated lock (header is swapped out)
 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 

 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_forwarded_bits            = 1;
113   static const int max_hash_bits                  = BitsPerWord - age_bits - lock_bits - self_forwarded_bits;
114   static const int hash_bits                      = max_hash_bits > 31 ? 31 : max_hash_bits;
115   static const int hash_bits_compact              = max_hash_bits > 25 ? 25 : max_hash_bits;
116   // Used only without compact headers.
117   static const int unused_gap_bits                = LP64_ONLY(1) NOT_LP64(0);
118 #ifdef _LP64
119   // Used only with compact headers.
120   static const int klass_bits                     = 32;
121 #endif
122 
123   static const int lock_shift                     = 0;
124   static const int self_forwarded_shift           = lock_shift + lock_bits;
125   static const int age_shift                      = self_forwarded_shift + self_forwarded_bits;
126   static const int hash_shift                     = age_shift + age_bits + unused_gap_bits;
127   static const int hash_shift_compact             = age_shift + age_bits;
128 #ifdef _LP64
129   // Used only with compact headers.
130   static const int klass_shift                    = hash_shift_compact + hash_bits_compact;
131 #endif
132 
133   static const uintptr_t lock_mask                = right_n_bits(lock_bits);
134   static const uintptr_t lock_mask_in_place       = lock_mask << lock_shift;
135   static const uintptr_t self_forwarded_mask      = right_n_bits(self_forwarded_bits);
136   static const uintptr_t self_forwarded_mask_in_place = self_forwarded_mask << self_forwarded_shift;
137   static const uintptr_t age_mask                 = right_n_bits(age_bits);
138   static const uintptr_t age_mask_in_place        = age_mask << age_shift;
139   static const uintptr_t hash_mask                = right_n_bits(hash_bits);
140   static const uintptr_t hash_mask_in_place       = hash_mask << hash_shift;
141   static const uintptr_t hash_mask_compact        = right_n_bits(hash_bits_compact);
142   static const uintptr_t hash_mask_compact_in_place = hash_mask_compact << hash_shift_compact;
143 #ifdef _LP64
144   static const uintptr_t klass_mask               = right_n_bits(klass_bits);
145   static const uintptr_t klass_mask_in_place      = klass_mask << klass_shift;
146 #endif
147 
148   static const uintptr_t locked_value             = 0;
149   static const uintptr_t unlocked_value           = 1;
150   static const uintptr_t monitor_value            = 2;
151   static const uintptr_t marked_value             = 3;
152 
153   static const uintptr_t no_hash                  = 0 ;  // no hash value assigned
154   static const uintptr_t no_hash_in_place         = (uintptr_t)no_hash << hash_shift;
155   static const uintptr_t no_lock_in_place         = unlocked_value;
156 
157   static const uint max_age                       = age_mask;
158 
159   // Creates a markWord with all bits set to zero.
160   static markWord zero() { return markWord(uintptr_t(0)); }
161 
162   // lock accessors (note that these assume lock_shift == 0)
163   bool is_locked()   const {
164     return (mask_bits(value(), lock_mask_in_place) != unlocked_value);
165   }
166   bool is_unlocked() const {

214     // Clear the lock_mask_in_place bits to set locked_value:
215     return markWord(value() & ~lock_mask_in_place);
216   }
217 
218   bool has_monitor() const {
219     return ((value() & lock_mask_in_place) == monitor_value);
220   }
221   ObjectMonitor* monitor() const {
222     assert(has_monitor(), "check");
223     // Use xor instead of &~ to provide one extra tag-bit check.
224     return (ObjectMonitor*) (value() ^ monitor_value);
225   }
226   bool has_displaced_mark_helper() const {
227     intptr_t lockbits = value() & lock_mask_in_place;
228     return LockingMode == LM_LIGHTWEIGHT  ? lockbits == monitor_value   // monitor?
229                                           : (lockbits & unlocked_value) == 0; // monitor | stack-locked?
230   }
231   markWord displaced_mark_helper() const;
232   void set_displaced_mark_helper(markWord m) const;
233   markWord copy_set_hash(intptr_t hash) const {
234     if (UseCompactObjectHeaders) {
235       uintptr_t tmp = value() & (~hash_mask_compact_in_place);
236       tmp |= ((hash & hash_mask_compact) << hash_shift_compact);
237       return markWord(tmp);
238     } else {
239       uintptr_t tmp = value() & (~hash_mask_in_place);
240       tmp |= ((hash & hash_mask) << hash_shift);
241       return markWord(tmp);
242     }
243   }
244   // it is only used to be stored into BasicLock as the
245   // indicator that the lock is using heavyweight monitor
246   static markWord unused_mark() {
247     return markWord(marked_value);
248   }
249   // the following two functions create the markWord to be
250   // stored into object header, it encodes monitor info
251   static markWord encode(BasicLock* lock) {
252     return from_pointer(lock);
253   }
254   static markWord encode(ObjectMonitor* monitor) {
255     uintptr_t tmp = (uintptr_t) monitor;
256     return markWord(tmp | monitor_value);
257   }
258 
259   // used to encode pointers during GC
260   markWord clear_lock_bits() { return markWord(value() & ~lock_mask_in_place); }
261 
262   // age operations
263   markWord set_marked()   { return markWord((value() & ~lock_mask_in_place) | marked_value); }
264   markWord set_unmarked() { return markWord((value() & ~lock_mask_in_place) | unlocked_value); }
265 
266   uint     age()           const { return (uint) mask_bits(value() >> age_shift, age_mask); }
267   markWord set_age(uint v) const {
268     assert((v & ~age_mask) == 0, "shouldn't overflow age field");
269     return markWord((value() & ~age_mask_in_place) | ((v & age_mask) << age_shift));
270   }
271   markWord incr_age()      const { return age() == max_age ? markWord(_value) : set_age(age() + 1); }
272 
273   // hash operations
274   intptr_t hash() const {
275     if (UseCompactObjectHeaders) {
276       return mask_bits(value() >> hash_shift_compact, hash_mask_compact);
277     } else {
278       return mask_bits(value() >> hash_shift, hash_mask);
279     }
280   }
281 
282   bool has_no_hash() const {
283     return hash() == no_hash;
284   }
285 
286 #ifdef _LP64
287   inline markWord actual_mark() const;
288   inline Klass* klass() const;
289   inline Klass* klass_or_null() const;
290   inline narrowKlass narrow_klass() const;
291   inline markWord set_narrow_klass(narrowKlass nklass) const;
292   inline markWord set_klass(Klass* klass) const;
293 #endif
294 
295   // Prototype mark for initialization
296   static markWord prototype() {
297     return markWord( no_hash_in_place | no_lock_in_place );
298   }
299 
300   // Debugging
301   void print_on(outputStream* st, bool print_monitor_info = true) const;
302 
303   // Prepare address of oop for placement into mark
304   inline static markWord encode_pointer_as_mark(void* p) { return from_pointer(p).set_marked(); }
305 
306   // Recover address of oop from encoded form used in mark
307   inline void* decode_pointer() { return (void*)clear_lock_bits().value(); }
308 
309 #ifdef _LP64
310   inline bool self_forwarded() const {
311     bool self_fwd = mask_bits(value(), self_forwarded_mask_in_place) != 0;
312     assert(!self_fwd || UseAltGCForwarding, "Only set self-fwd bit when using alt GC forwarding");
313     return self_fwd;
314   }
315 
316   inline markWord set_self_forwarded() const {
317     assert(UseAltGCForwarding, "Only call this with alt GC forwarding");
318     return markWord(value() | self_forwarded_mask_in_place | marked_value);
319   }
320 #endif
321 };
322 
323 // Support atomic operations.
324 template<>
325 struct PrimitiveConversions::Translate<markWord> : public std::true_type {
326   typedef markWord Value;
327   typedef uintptr_t Decayed;
328 
329   static Decayed decay(const Value& x) { return x.value(); }
330   static Value recover(Decayed x) { return Value(x); }
331 };
332 
333 #endif // SHARE_OOPS_MARKWORD_HPP
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