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24
25 #ifndef SHARE_VM_OOPS_MARKOOP_HPP
26 #define SHARE_VM_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 // "1" :23 epoch:2 age:4 biased_lock:1 lock:2 (biased always locked object)
42 // size:32 ------------------------------------------>| (CMS free block)
43 // PromotedObject*:29 ---------->| promo_bits:3 ----->| (CMS promoted object)
44 //
45 // 64 bits:
46 // --------
47 // unused:25 hash:31 -->| unused:1 age:4 biased_lock:1 lock:2 (normal object)
48 // JavaThread*:54 epoch:2 unused:1 age:4 biased_lock:1 lock:2 (biased object)
49 // "1" :54 epoch:2 unused:1 age:4 biased_lock:1 lock:2 (biased always locked object)
50 // PromotedObject*:61 --------------------->| promo_bits:3 ----->| (CMS promoted object)
51 // size:64 ----------------------------------------------------->| (CMS free block)
52 //
53 // unused:25 hash:31 -->| cms_free:1 age:4 biased_lock:1 lock:2 (COOPs && normal object)
54 // JavaThread*:54 epoch:2 cms_free:1 age:4 biased_lock:1 lock:2 (COOPs && biased object)
55 // narrowOop:32 unused:24 cms_free:1 unused:4 promo_bits:3 ----->| (COOPs && CMS promoted object)
56 // unused:21 size:35 -->| cms_free:1 unused:7 ------------------>| (COOPs && CMS free block)
57 //
58 // - hash contains the identity hash value: largest value is
59 // 31 bits, see os::random(). Also, 64-bit vm's require
60 // a hash value no bigger than 32 bits because they will not
61 // properly generate a mask larger than that: see library_call.cpp
62 // and c1_CodePatterns_sparc.cpp.
63 //
64 // - the biased lock pattern is used to bias a lock toward a given
65 // thread. When this pattern is set in the low three bits, the lock
66 // is either biased toward a given thread or "anonymously" biased,
67 // indicating that it is possible for it to be biased. When the
68 // lock is biased toward a given thread, locking and unlocking can
69 // be performed by that thread without using atomic operations.
70 // When a lock's bias is revoked, it reverts back to the normal
71 // locking scheme described below.
72 //
73 // Note that we are overloading the meaning of the "unlocked" state
74 // of the header. Because we steal a bit from the age we can
75 // guarantee that the bias pattern will never be seen for a truly
76 // unlocked object.
77 //
78 // Note also that the biased state contains the age bits normally
79 // contained in the object header. Large increases in scavenge
80 // times were seen when these bits were absent and an arbitrary age
81 // assigned to all biased objects, because they tended to consume a
82 // significant fraction of the eden semispaces and were not
83 // promoted promptly, causing an increase in the amount of copying
84 // performed. The runtime system aligns all JavaThread* pointers to
85 // a very large value (currently 128 bytes (32bVM) or 256 bytes (64bVM))
86 // to make room for the age bits & the epoch bits (used in support of
87 // biased locking), and for the CMS "freeness" bit in the 64bVM (+COOPs).
88 //
89 // [JavaThread* | epoch | age | 1 | 01] lock is biased toward given thread
90 // [0 | epoch | age | 1 | 01] lock is anonymously biased
91 //
92 // - the two lock bits are used to describe three states: locked/unlocked and monitor.
93 //
94 // [ptr | 00] locked ptr points to real header on stack
95 // [header | 0 | 01] unlocked regular object header
96 // [ptr | 10] monitor inflated lock (header is wapped out)
97 // [ptr | 11] marked used by markSweep to mark an object
98 // not valid at any other time
99 //
100 // We assume that stack/thread pointers have the lowest two bits cleared.
101 //
102 // Always locked: since displaced and monitor references require memory at a
103 // fixed address, and hash code can be displaced, an efficiently providing a
104 // *permanent lock* leaves us with specializing the biased pattern (even when
105 // biased locking isn't enabled). Since biased_lock_alignment for the thread
106 // reference doesn't use the lowest bit ("2 << thread_shift"), we can use
107 // this illegal thread pointer alignment to denote "always locked" pattern.
108 //
109 // [ <unused> |1| epoch | age | 1 | 01] permanently locked
110 //
111
112 class BasicLock;
113 class ObjectMonitor;
114 class JavaThread;
115
116 class markOopDesc: public oopDesc {
117 private:
118 // Conversion
119 uintptr_t value() const { return (uintptr_t) this; }
120
121 public:
122 // Constants
123 enum { age_bits = 4,
124 lock_bits = 2,
125 biased_lock_bits = 1,
126 max_hash_bits = BitsPerWord - age_bits - lock_bits - biased_lock_bits,
127 hash_bits = max_hash_bits > 31 ? 31 : max_hash_bits,
128 cms_bits = LP64_ONLY(1) NOT_LP64(0),
129 epoch_bits = 2
130 };
131
132 // The biased locking code currently requires that the age bits be
133 // contiguous to the lock bits.
134 enum { lock_shift = 0,
135 biased_lock_shift = lock_bits,
136 age_shift = lock_bits + biased_lock_bits,
137 cms_shift = age_shift + age_bits,
138 hash_shift = cms_shift + cms_bits,
139 epoch_shift = hash_shift,
140 thread_shift = epoch_shift + epoch_bits
141 };
142
143 enum { lock_mask = right_n_bits(lock_bits),
144 lock_mask_in_place = lock_mask << lock_shift,
145 biased_lock_mask = right_n_bits(lock_bits + biased_lock_bits),
146 biased_lock_mask_in_place= biased_lock_mask << lock_shift,
147 biased_lock_bit_in_place = 1 << biased_lock_shift,
148 age_mask = right_n_bits(age_bits),
149 age_mask_in_place = age_mask << age_shift,
150 epoch_mask = right_n_bits(epoch_bits),
151 epoch_mask_in_place = epoch_mask << epoch_shift,
152 cms_mask = right_n_bits(cms_bits),
153 cms_mask_in_place = cms_mask << cms_shift
154 #ifndef _WIN64
155 ,hash_mask = right_n_bits(hash_bits),
156 hash_mask_in_place = (address_word)hash_mask << hash_shift
157 #endif
158 };
159
160 // Alignment of JavaThread pointers encoded in object header required by biased locking
161 enum { biased_lock_alignment = 2 << thread_shift
162 };
163
164 #ifdef _WIN64
165 // These values are too big for Win64
166 const static uintptr_t hash_mask = right_n_bits(hash_bits);
167 const static uintptr_t hash_mask_in_place =
168 (address_word)hash_mask << hash_shift;
169 #endif
170
171 enum { locked_value = 0,
172 unlocked_value = 1,
173 monitor_value = 2,
174 marked_value = 3,
175 biased_lock_pattern = 5,
176 always_locked_pattern = 1 << thread_shift | biased_lock_pattern
177 };
178
179 enum { no_hash = 0 }; // no hash value assigned
180
181 enum { no_hash_in_place = (address_word)no_hash << hash_shift,
182 no_lock_in_place = unlocked_value
183 };
184
185 enum { max_age = age_mask };
186
187 enum { max_bias_epoch = epoch_mask };
188
189 static markOop always_locked_prototype() {
190 return markOop(always_locked_pattern);
191 }
192
193 bool is_always_locked() const { return mask_bits(value(), always_locked_pattern) == always_locked_pattern; }
194
195 // Biased Locking accessors.
196 // These must be checked by all code which calls into the
197 // ObjectSynchronizer and other code. The biasing is not understood
198 // by the lower-level CAS-based locking code, although the runtime
199 // fixes up biased locks to be compatible with it when a bias is
200 // revoked.
201 bool has_bias_pattern() const {
202 return (mask_bits(value(), biased_lock_mask_in_place) == biased_lock_pattern);
203 }
204 JavaThread* biased_locker() const {
205 assert(has_bias_pattern(), "should not call this otherwise");
206 assert(!is_always_locked(), "invariant");
207 return (JavaThread*) ((intptr_t) (mask_bits(value(), ~(biased_lock_mask_in_place | age_mask_in_place | epoch_mask_in_place))));
208 }
209 // Indicates that the mark has the bias bit set but that it has not
210 // yet been biased toward a particular thread
211 bool is_biased_anonymously() const {
212 return (has_bias_pattern() && (biased_locker() == NULL));
213 }
214 // Indicates epoch in which this bias was acquired. If the epoch
215 // changes due to too many bias revocations occurring, the biases
216 // from the previous epochs are all considered invalid.
217 int bias_epoch() const {
218 assert(has_bias_pattern(), "should not call this otherwise");
219 return (mask_bits(value(), epoch_mask_in_place) >> epoch_shift);
220 }
221 markOop set_bias_epoch(int epoch) {
222 assert(has_bias_pattern(), "should not call this otherwise");
223 assert((epoch & (~epoch_mask)) == 0, "epoch overflow");
224 assert(!is_always_locked(), "Rebias needs to fail");
225 return markOop(mask_bits(value(), ~epoch_mask_in_place) | (epoch << epoch_shift));
226 }
227 markOop incr_bias_epoch() {
228 return set_bias_epoch((1 + bias_epoch()) & epoch_mask);
229 }
230 // Prototype mark for initialization
231 static markOop biased_locking_prototype() {
232 return markOop( biased_lock_pattern );
233 }
234
235 // lock accessors (note that these assume lock_shift == 0)
236 bool is_locked() const {
237 return (mask_bits(value(), lock_mask_in_place) != unlocked_value);
238 }
239 bool is_unlocked() const {
240 return (mask_bits(value(), biased_lock_mask_in_place) == unlocked_value);
241 }
242 bool is_marked() const {
243 return (mask_bits(value(), lock_mask_in_place) == marked_value);
244 }
245 bool is_neutral() const { return (mask_bits(value(), biased_lock_mask_in_place) == unlocked_value); }
246
247 // Special temporary state of the markOop while being inflated.
248 // Code that looks at mark outside a lock need to take this into account.
249 bool is_being_inflated() const { return (value() == 0); }
250
251 // Distinguished markword value - used when inflating over
252 // an existing stacklock. 0 indicates the markword is "BUSY".
253 // Lockword mutators that use a LD...CAS idiom should always
254 // check for and avoid overwriting a 0 value installed by some
255 // other thread. (They should spin or block instead. The 0 value
256 // is transient and *should* be short-lived).
257 static markOop INFLATING() { return (markOop) 0; } // inflate-in-progress
258
259 // Should this header be preserved during GC?
260 inline bool must_be_preserved(oop obj_containing_mark) const;
261 inline bool must_be_preserved_with_bias(oop obj_containing_mark) const;
262
263 // Should this header (including its age bits) be preserved in the
264 // case of a promotion failure during scavenge?
265 // Note that we special case this situation. We want to avoid
266 // calling BiasedLocking::preserve_marks()/restore_marks() (which
267 // decrease the number of mark words that need to be preserved
268 // during GC) during each scavenge. During scavenges in which there
269 // is no promotion failure, we actually don't need to call the above
270 // routines at all, since we don't mutate and re-initialize the
271 // marks of promoted objects using init_mark(). However, during
272 // scavenges which result in promotion failure, we do re-initialize
273 // the mark words of objects, meaning that we should have called
274 // these mark word preservation routines. Currently there's no good
275 // place in which to call them in any of the scavengers (although
276 // guarded by appropriate locks we could make one), but the
277 // observation is that promotion failures are quite rare and
278 // reducing the number of mark words preserved during them isn't a
279 // high priority.
280 inline bool must_be_preserved_for_promotion_failure(oop obj_containing_mark) const;
281 inline bool must_be_preserved_with_bias_for_promotion_failure(oop obj_containing_mark) const;
282
283 // Should this header be preserved during a scavenge where CMS is
284 // the old generation?
285 // (This is basically the same body as must_be_preserved_for_promotion_failure(),
286 // but takes the Klass* as argument instead)
287 inline bool must_be_preserved_for_cms_scavenge(Klass* klass_of_obj_containing_mark) const;
288 inline bool must_be_preserved_with_bias_for_cms_scavenge(Klass* klass_of_obj_containing_mark) const;
289
290 // WARNING: The following routines are used EXCLUSIVELY by
291 // synchronization functions. They are not really gc safe.
292 // They must get updated if markOop layout get changed.
293 markOop set_unlocked() const {
294 return markOop(value() | unlocked_value);
295 }
296 bool has_locker() const {
297 return ((value() & lock_mask_in_place) == locked_value);
298 }
299 BasicLock* locker() const {
300 assert(has_locker(), "check");
301 return (BasicLock*) value();
302 }
303 bool has_monitor() const {
304 return ((value() & monitor_value) != 0);
305 }
306 ObjectMonitor* monitor() const {
307 assert(has_monitor(), "check");
308 // Use xor instead of &~ to provide one extra tag-bit check.
309 return (ObjectMonitor*) (value() ^ monitor_value);
310 }
311 bool has_displaced_mark_helper() const {
312 return ((value() & unlocked_value) == 0);
313 }
314 markOop displaced_mark_helper() const {
315 assert(has_displaced_mark_helper(), "check");
316 intptr_t ptr = (value() & ~monitor_value);
317 return *(markOop*)ptr;
318 }
319 void set_displaced_mark_helper(markOop m) const {
320 assert(has_displaced_mark_helper(), "check");
321 intptr_t ptr = (value() & ~monitor_value);
322 *(markOop*)ptr = m;
323 }
324 markOop copy_set_hash(intptr_t hash) const {
325 intptr_t tmp = value() & (~hash_mask_in_place);
326 tmp |= ((hash & hash_mask) << hash_shift);
327 return (markOop)tmp;
328 }
329 // it is only used to be stored into BasicLock as the
330 // indicator that the lock is using heavyweight monitor
331 static markOop unused_mark() {
332 return (markOop) marked_value;
333 }
334 // the following two functions create the markOop to be
335 // stored into object header, it encodes monitor info
336 static markOop encode(BasicLock* lock) {
337 return (markOop) lock;
338 }
339 static markOop encode(ObjectMonitor* monitor) {
340 intptr_t tmp = (intptr_t) monitor;
341 return (markOop) (tmp | monitor_value);
342 }
343 static markOop encode(JavaThread* thread, uint age, int bias_epoch) {
344 intptr_t tmp = (intptr_t) thread;
345 assert(UseBiasedLocking && ((tmp & (epoch_mask_in_place | age_mask_in_place | biased_lock_mask_in_place)) == 0), "misaligned JavaThread pointer");
346 assert(age <= max_age, "age too large");
347 assert(bias_epoch <= max_bias_epoch, "bias epoch too large");
348 return (markOop) (tmp | (bias_epoch << epoch_shift) | (age << age_shift) | biased_lock_pattern);
349 }
350
351 // used to encode pointers during GC
352 markOop clear_lock_bits() { return markOop(value() & ~lock_mask_in_place); }
353
354 // age operations
355 markOop set_marked() { return markOop((value() & ~lock_mask_in_place) | marked_value); }
356 markOop set_unmarked() { return markOop((value() & ~lock_mask_in_place) | unlocked_value); }
357
358 uint age() const { return mask_bits(value() >> age_shift, age_mask); }
359 markOop set_age(uint v) const {
360 assert((v & ~age_mask) == 0, "shouldn't overflow age field");
361 return markOop((value() & ~age_mask_in_place) | (((uintptr_t)v & age_mask) << age_shift));
362 }
363 markOop incr_age() const { return age() == max_age ? markOop(this) : set_age(age() + 1); }
364
365 // hash operations
366 intptr_t hash() const {
367 return mask_bits(value() >> hash_shift, hash_mask);
368 }
369
370 bool has_no_hash() const {
371 return hash() == no_hash;
372 }
373
374 // Prototype mark for initialization
375 static markOop prototype() {
376 return markOop( no_hash_in_place | no_lock_in_place );
377 }
378
379 // Helper function for restoration of unmarked mark oops during GC
380 static inline markOop prototype_for_object(oop obj);
381
382 // Debugging
383 void print_on(outputStream* st) const;
384
385 // Prepare address of oop for placement into mark
386 inline static markOop encode_pointer_as_mark(void* p) { return markOop(p)->set_marked(); }
387
388 // Recover address of oop from encoded form used in mark
389 inline void* decode_pointer() { if (has_bias_pattern()) return NULL; return clear_lock_bits(); }
390
391 // These markOops indicate cms free chunk blocks and not objects.
392 // In 64 bit, the markOop is set to distinguish them from oops.
393 // These are defined in 32 bit mode for vmStructs.
394 const static uintptr_t cms_free_chunk_pattern = 0x1;
395
396 // Constants for the size field.
397 enum { size_shift = cms_shift + cms_bits,
398 size_bits = 35 // need for compressed oops 32G
399 };
400 // These values are too big for Win64
401 const static uintptr_t size_mask = LP64_ONLY(right_n_bits(size_bits))
402 NOT_LP64(0);
403 const static uintptr_t size_mask_in_place =
404 (address_word)size_mask << size_shift;
405
406 #ifdef _LP64
407 static markOop cms_free_prototype() {
408 return markOop(((intptr_t)prototype() & ~cms_mask_in_place) |
409 ((cms_free_chunk_pattern & cms_mask) << cms_shift));
410 }
411 uintptr_t cms_encoding() const {
412 return mask_bits(value() >> cms_shift, cms_mask);
413 }
414 bool is_cms_free_chunk() const {
415 return is_neutral() &&
416 (cms_encoding() & cms_free_chunk_pattern) == cms_free_chunk_pattern;
417 }
418
419 size_t get_size() const { return (size_t)(value() >> size_shift); }
420 static markOop set_size_and_free(size_t size) {
421 assert((size & ~size_mask) == 0, "shouldn't overflow size field");
422 return markOop(((intptr_t)cms_free_prototype() & ~size_mask_in_place) |
423 (((intptr_t)size & size_mask) << size_shift));
424 }
425 #endif // _LP64
426 };
427
428 #endif // SHARE_VM_OOPS_MARKOOP_HPP