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24
25 #ifndef SHARE_OOPS_MARKOOP_HPP
26 #define SHARE_OOPS_MARKOOP_HPP
27
28 #include "oops/oop.hpp"
29
30 // The markOop describes the header of an object.
31 //
32 // Note that the mark is not a real oop but just a word.
33 // It is placed in the oop hierarchy for historical reasons.
34 //
35 // Bit-format of an object header (most significant first, big endian layout below):
36 //
37 // 32 bits:
38 // --------
39 // hash:25 ------------>| age:4 biased_lock:1 lock:2 (normal object)
40 // JavaThread*:23 epoch:2 age:4 biased_lock:1 lock:2 (biased object)
41 // size:32 ------------------------------------------>| (CMS free block)
42 // PromotedObject*:29 ---------->| promo_bits:3 ----->| (CMS promoted object)
43 //
44 // 64 bits:
45 // --------
46 // unused:25 hash:31 -->| unused:1 age:4 biased_lock:1 lock:2 (normal object)
47 // JavaThread*:54 epoch:2 unused:1 age:4 biased_lock:1 lock:2 (biased object)
48 // PromotedObject*:61 --------------------->| promo_bits:3 ----->| (CMS promoted object)
49 // size:64 ----------------------------------------------------->| (CMS free block)
50 //
51 // unused:25 hash:31 -->| cms_free:1 age:4 biased_lock:1 lock:2 (COOPs && normal object)
52 // JavaThread*:54 epoch:2 cms_free:1 age:4 biased_lock:1 lock:2 (COOPs && biased object)
53 // narrowOop:32 unused:24 cms_free:1 unused:4 promo_bits:3 ----->| (COOPs && CMS promoted object)
54 // unused:21 size:35 -->| cms_free:1 unused:7 ------------------>| (COOPs && CMS free block)
55 //
56 // - hash contains the identity hash value: largest value is
57 // 31 bits, see os::random(). Also, 64-bit vm's require
58 // a hash value no bigger than 32 bits because they will not
59 // properly generate a mask larger than that: see library_call.cpp
60 // and c1_CodePatterns_sparc.cpp.
61 //
62 // - the biased lock pattern is used to bias a lock toward a given
63 // thread. When this pattern is set in the low three bits, the lock
64 // is either biased toward a given thread or "anonymously" biased,
65 // indicating that it is possible for it to be biased. When the
66 // lock is biased toward a given thread, locking and unlocking can
67 // be performed by that thread without using atomic operations.
68 // When a lock's bias is revoked, it reverts back to the normal
69 // locking scheme described below.
70 //
71 // Note that we are overloading the meaning of the "unlocked" state
72 // of the header. Because we steal a bit from the age we can
73 // guarantee that the bias pattern will never be seen for a truly
74 // unlocked object.
75 //
76 // Note also that the biased state contains the age bits normally
77 // contained in the object header. Large increases in scavenge
78 // times were seen when these bits were absent and an arbitrary age
79 // assigned to all biased objects, because they tended to consume a
80 // significant fraction of the eden semispaces and were not
81 // promoted promptly, causing an increase in the amount of copying
82 // performed. The runtime system aligns all JavaThread* pointers to
83 // a very large value (currently 128 bytes (32bVM) or 256 bytes (64bVM))
84 // to make room for the age bits & the epoch bits (used in support of
85 // biased locking), and for the CMS "freeness" bit in the 64bVM (+COOPs).
86 //
87 // [JavaThread* | epoch | age | 1 | 01] lock is biased toward given thread
88 // [0 | epoch | age | 1 | 01] lock is anonymously biased
89 //
90 // - the two lock bits are used to describe three states: locked/unlocked and monitor.
91 //
92 // [ptr | 00] locked ptr points to real header on stack
93 // [header | 0 | 01] unlocked regular object header
94 // [ptr | 10] monitor inflated lock (header is wapped out)
95 // [ptr | 11] marked used by markSweep to mark an object
96 // not valid at any other time
97 //
98 // We assume that stack/thread pointers have the lowest two bits cleared.
99
100 class BasicLock;
101 class ObjectMonitor;
102 class JavaThread;
103
104 class markOopDesc: public oopDesc {
105 private:
106 // Conversion
107 uintptr_t value() const { return (uintptr_t) this; }
108
109 public:
110 // Constants
111 enum { age_bits = 4,
112 lock_bits = 2,
113 biased_lock_bits = 1,
114 max_hash_bits = BitsPerWord - age_bits - lock_bits - biased_lock_bits,
115 hash_bits = max_hash_bits > 31 ? 31 : max_hash_bits,
116 cms_bits = LP64_ONLY(1) NOT_LP64(0),
117 epoch_bits = 2
118 };
119
120 // The biased locking code currently requires that the age bits be
121 // contiguous to the lock bits.
122 enum { lock_shift = 0,
123 biased_lock_shift = lock_bits,
124 age_shift = lock_bits + biased_lock_bits,
125 cms_shift = age_shift + age_bits,
126 hash_shift = cms_shift + cms_bits,
127 epoch_shift = hash_shift
128 };
129
130 enum { lock_mask = right_n_bits(lock_bits),
131 lock_mask_in_place = lock_mask << lock_shift,
132 biased_lock_mask = right_n_bits(lock_bits + biased_lock_bits),
133 biased_lock_mask_in_place= biased_lock_mask << lock_shift,
134 biased_lock_bit_in_place = 1 << biased_lock_shift,
135 age_mask = right_n_bits(age_bits),
136 age_mask_in_place = age_mask << age_shift,
137 epoch_mask = right_n_bits(epoch_bits),
138 epoch_mask_in_place = epoch_mask << epoch_shift,
139 cms_mask = right_n_bits(cms_bits),
140 cms_mask_in_place = cms_mask << cms_shift
141 };
142
143 const static uintptr_t hash_mask = right_n_bits(hash_bits);
144 const static uintptr_t hash_mask_in_place = hash_mask << hash_shift;
145
146 // Alignment of JavaThread pointers encoded in object header required by biased locking
147 enum { biased_lock_alignment = 2 << (epoch_shift + epoch_bits)
148 };
149
150 enum { locked_value = 0,
151 unlocked_value = 1,
152 monitor_value = 2,
153 marked_value = 3,
154 biased_lock_pattern = 5
155 };
156
157 enum { no_hash = 0 }; // no hash value assigned
158
159 enum { no_hash_in_place = (address_word)no_hash << hash_shift,
160 no_lock_in_place = unlocked_value
161 };
162
163 enum { max_age = age_mask };
164
165 enum { max_bias_epoch = epoch_mask };
166
167 // Biased Locking accessors.
168 // These must be checked by all code which calls into the
169 // ObjectSynchronizer and other code. The biasing is not understood
170 // by the lower-level CAS-based locking code, although the runtime
171 // fixes up biased locks to be compatible with it when a bias is
172 // revoked.
173 bool has_bias_pattern() const {
174 return (mask_bits(value(), biased_lock_mask_in_place) == biased_lock_pattern);
175 }
176 JavaThread* biased_locker() const {
177 assert(has_bias_pattern(), "should not call this otherwise");
178 return (JavaThread*) ((intptr_t) (mask_bits(value(), ~(biased_lock_mask_in_place | age_mask_in_place | epoch_mask_in_place))));
179 }
180 bool biased_locker_is(JavaThread* thread) const {
181 if (!has_bias_pattern()) {
182 return false;
183 }
184 // If current thread is not the owner it can be unbiased at anytime.
185 JavaThread* jt = (JavaThread*) ((intptr_t) (mask_bits(value(), ~(biased_lock_mask_in_place | age_mask_in_place | epoch_mask_in_place))));
186 return jt == thread;
187 }
188
189 // Indicates that the mark has the bias bit set but that it has not
190 // yet been biased toward a particular thread
191 bool is_biased_anonymously() const {
192 return (has_bias_pattern() && (biased_locker() == NULL));
193 }
194 // Indicates epoch in which this bias was acquired. If the epoch
195 // changes due to too many bias revocations occurring, the biases
196 // from the previous epochs are all considered invalid.
197 int bias_epoch() const {
198 assert(has_bias_pattern(), "should not call this otherwise");
199 return (mask_bits(value(), epoch_mask_in_place) >> epoch_shift);
200 }
201 markOop set_bias_epoch(int epoch) {
202 assert(has_bias_pattern(), "should not call this otherwise");
203 assert((epoch & (~epoch_mask)) == 0, "epoch overflow");
204 return markOop(mask_bits(value(), ~epoch_mask_in_place) | (epoch << epoch_shift));
205 }
206 markOop incr_bias_epoch() {
207 return set_bias_epoch((1 + bias_epoch()) & epoch_mask);
208 }
209 // Prototype mark for initialization
210 static markOop biased_locking_prototype() {
211 return markOop( biased_lock_pattern );
212 }
213
214 // lock accessors (note that these assume lock_shift == 0)
215 bool is_locked() const {
216 return (mask_bits(value(), lock_mask_in_place) != unlocked_value);
217 }
218 bool is_unlocked() const {
219 return (mask_bits(value(), biased_lock_mask_in_place) == unlocked_value);
220 }
221 bool is_marked() const {
222 return (mask_bits(value(), lock_mask_in_place) == marked_value);
223 }
224 bool is_neutral() const { return (mask_bits(value(), biased_lock_mask_in_place) == unlocked_value); }
225
226 // Special temporary state of the markOop while being inflated.
227 // Code that looks at mark outside a lock need to take this into account.
228 bool is_being_inflated() const { return (value() == 0); }
229
230 // Distinguished markword value - used when inflating over
231 // an existing stacklock. 0 indicates the markword is "BUSY".
232 // Lockword mutators that use a LD...CAS idiom should always
233 // check for and avoid overwriting a 0 value installed by some
234 // other thread. (They should spin or block instead. The 0 value
235 // is transient and *should* be short-lived).
236 static markOop INFLATING() { return (markOop) 0; } // inflate-in-progress
237
238 // Should this header be preserved during GC?
239 inline bool must_be_preserved(oop obj_containing_mark) const;
240 inline bool must_be_preserved_with_bias(oop obj_containing_mark) const;
241
242 // Should this header (including its age bits) be preserved in the
243 // case of a promotion failure during scavenge?
244 // Note that we special case this situation. We want to avoid
245 // calling BiasedLocking::preserve_marks()/restore_marks() (which
246 // decrease the number of mark words that need to be preserved
247 // during GC) during each scavenge. During scavenges in which there
248 // is no promotion failure, we actually don't need to call the above
249 // routines at all, since we don't mutate and re-initialize the
250 // marks of promoted objects using init_mark(). However, during
251 // scavenges which result in promotion failure, we do re-initialize
252 // the mark words of objects, meaning that we should have called
253 // these mark word preservation routines. Currently there's no good
254 // place in which to call them in any of the scavengers (although
255 // guarded by appropriate locks we could make one), but the
256 // observation is that promotion failures are quite rare and
257 // reducing the number of mark words preserved during them isn't a
258 // high priority.
259 inline bool must_be_preserved_for_promotion_failure(oop obj_containing_mark) const;
260 inline bool must_be_preserved_with_bias_for_promotion_failure(oop obj_containing_mark) const;
261
262 // Should this header be preserved during a scavenge where CMS is
263 // the old generation?
264 // (This is basically the same body as must_be_preserved_for_promotion_failure(),
265 // but takes the Klass* as argument instead)
266 inline bool must_be_preserved_for_cms_scavenge(Klass* klass_of_obj_containing_mark) const;
267 inline bool must_be_preserved_with_bias_for_cms_scavenge(Klass* klass_of_obj_containing_mark) const;
268
269 // WARNING: The following routines are used EXCLUSIVELY by
270 // synchronization functions. They are not really gc safe.
271 // They must get updated if markOop layout get changed.
272 markOop set_unlocked() const {
273 return markOop(value() | unlocked_value);
274 }
275 bool has_locker() const {
276 return ((value() & lock_mask_in_place) == locked_value);
277 }
278 BasicLock* locker() const {
279 assert(has_locker(), "check");
280 return (BasicLock*) value();
281 }
282 bool has_monitor() const {
283 return ((value() & monitor_value) != 0);
284 }
285 ObjectMonitor* monitor() const {
286 assert(has_monitor(), "check");
287 // Use xor instead of &~ to provide one extra tag-bit check.
288 return (ObjectMonitor*) (value() ^ monitor_value);
289 }
290 bool has_displaced_mark_helper() const {
291 return ((value() & unlocked_value) == 0);
292 }
293 markOop displaced_mark_helper() const {
294 assert(has_displaced_mark_helper(), "check");
295 intptr_t ptr = (value() & ~monitor_value);
296 return *(markOop*)ptr;
297 }
298 void set_displaced_mark_helper(markOop m) const {
299 assert(has_displaced_mark_helper(), "check");
300 intptr_t ptr = (value() & ~monitor_value);
301 *(markOop*)ptr = m;
302 }
303 markOop copy_set_hash(intptr_t hash) const {
304 intptr_t tmp = value() & (~hash_mask_in_place);
305 tmp |= ((hash & hash_mask) << hash_shift);
306 return (markOop)tmp;
307 }
308 // it is only used to be stored into BasicLock as the
309 // indicator that the lock is using heavyweight monitor
310 static markOop unused_mark() {
311 return (markOop) marked_value;
312 }
313 // the following two functions create the markOop to be
314 // stored into object header, it encodes monitor info
315 static markOop encode(BasicLock* lock) {
316 return (markOop) lock;
317 }
318 static markOop encode(ObjectMonitor* monitor) {
319 intptr_t tmp = (intptr_t) monitor;
320 return (markOop) (tmp | monitor_value);
321 }
322 static markOop encode(JavaThread* thread, uint age, int bias_epoch) {
323 intptr_t tmp = (intptr_t) thread;
324 assert(UseBiasedLocking && ((tmp & (epoch_mask_in_place | age_mask_in_place | biased_lock_mask_in_place)) == 0), "misaligned JavaThread pointer");
325 assert(age <= max_age, "age too large");
326 assert(bias_epoch <= max_bias_epoch, "bias epoch too large");
327 return (markOop) (tmp | (bias_epoch << epoch_shift) | (age << age_shift) | biased_lock_pattern);
328 }
329
330 // used to encode pointers during GC
331 markOop clear_lock_bits() { return markOop(value() & ~lock_mask_in_place); }
332
333 // age operations
334 markOop set_marked() { return markOop((value() & ~lock_mask_in_place) | marked_value); }
335 markOop set_unmarked() { return markOop((value() & ~lock_mask_in_place) | unlocked_value); }
336
337 uint age() const { return mask_bits(value() >> age_shift, age_mask); }
338 markOop set_age(uint v) const {
339 assert((v & ~age_mask) == 0, "shouldn't overflow age field");
340 return markOop((value() & ~age_mask_in_place) | (((uintptr_t)v & age_mask) << age_shift));
341 }
342 markOop incr_age() const { return age() == max_age ? markOop(this) : set_age(age() + 1); }
343
344 // hash operations
345 intptr_t hash() const {
346 return mask_bits(value() >> hash_shift, hash_mask);
347 }
348
349 bool has_no_hash() const {
350 return hash() == no_hash;
351 }
352
353 // Prototype mark for initialization
354 static markOop prototype() {
355 return markOop( no_hash_in_place | no_lock_in_place );
356 }
357
358 // Helper function for restoration of unmarked mark oops during GC
359 static inline markOop prototype_for_object(oop obj);
360
361 // Debugging
362 void print_on(outputStream* st) const;
363
364 // Prepare address of oop for placement into mark
365 inline static markOop encode_pointer_as_mark(void* p) { return markOop(p)->set_marked(); }
366
367 // Recover address of oop from encoded form used in mark
368 inline void* decode_pointer() { if (UseBiasedLocking && has_bias_pattern()) return NULL; return clear_lock_bits(); }
369
370 // These markOops indicate cms free chunk blocks and not objects.
371 // In 64 bit, the markOop is set to distinguish them from oops.
372 // These are defined in 32 bit mode for vmStructs.
373 const static uintptr_t cms_free_chunk_pattern = 0x1;
374
375 // Constants for the size field.
376 enum { size_shift = cms_shift + cms_bits,
377 size_bits = 35 // need for compressed oops 32G
378 };
379 // These values are too big for Win64
380 const static uintptr_t size_mask = LP64_ONLY(right_n_bits(size_bits))
381 NOT_LP64(0);
382 const static uintptr_t size_mask_in_place =
383 (address_word)size_mask << size_shift;
384
385 #ifdef _LP64
386 static markOop cms_free_prototype() {
387 return markOop(((intptr_t)prototype() & ~cms_mask_in_place) |
388 ((cms_free_chunk_pattern & cms_mask) << cms_shift));
389 }
390 uintptr_t cms_encoding() const {
391 return mask_bits(value() >> cms_shift, cms_mask);
392 }
393 bool is_cms_free_chunk() const {
394 return is_neutral() &&
395 (cms_encoding() & cms_free_chunk_pattern) == cms_free_chunk_pattern;
396 }
397
398 size_t get_size() const { return (size_t)(value() >> size_shift); }
399 static markOop set_size_and_free(size_t size) {
400 assert((size & ~size_mask) == 0, "shouldn't overflow size field");
401 return markOop(((intptr_t)cms_free_prototype() & ~size_mask_in_place) |
402 (((intptr_t)size & size_mask) << size_shift));
403 }
404 #endif // _LP64
405 };
406
407 #endif // SHARE_OOPS_MARKOOP_HPP