1 /*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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24
25 #ifndef SHARE_OOPS_MARKOOP_HPP
26 #define SHARE_OOPS_MARKOOP_HPP
27
28 #include "metaprogramming/integralConstant.hpp"
29 #include "metaprogramming/primitiveConversions.hpp"
30 #include "oops/oopsHierarchy.hpp"
31
32 // The markWord describes the header of an object.
33 //
34 // Bit-format of an object header (most significant first, big endian layout below):
35 //
36 // 32 bits:
37 // --------
38 // hash:25 ------------>| age:4 biased_lock:1 lock:2 (normal object)
39 // JavaThread*:23 epoch:2 age:4 biased_lock:1 lock:2 (biased object)
40 // size:32 ------------------------------------------>| (CMS free block)
41 // PromotedObject*:29 ---------->| promo_bits:3 ----->| (CMS promoted object)
42 //
43 // 64 bits:
44 // --------
45 // unused:25 hash:31 -->| unused:1 age:4 biased_lock:1 lock:2 (normal object)
46 // JavaThread*:54 epoch:2 unused:1 age:4 biased_lock:1 lock:2 (biased object)
47 // PromotedObject*:61 --------------------->| promo_bits:3 ----->| (CMS promoted object)
48 // size:64 ----------------------------------------------------->| (CMS free block)
49 //
50 // unused:25 hash:31 -->| cms_free:1 age:4 biased_lock:1 lock:2 (COOPs && normal object)
51 // JavaThread*:54 epoch:2 cms_free:1 age:4 biased_lock:1 lock:2 (COOPs && biased object)
52 // narrowOop:32 unused:24 cms_free:1 unused:4 promo_bits:3 ----->| (COOPs && CMS promoted object)
53 // unused:21 size:35 -->| cms_free:1 unused:7 ------------------>| (COOPs && CMS free block)
54 //
55 // - hash contains the identity hash value: largest value is
56 // 31 bits, see os::random(). Also, 64-bit vm's require
57 // a hash value no bigger than 32 bits because they will not
58 // properly generate a mask larger than that: see library_call.cpp
59 // and c1_CodePatterns_sparc.cpp.
60 //
61 // - the biased lock pattern is used to bias a lock toward a given
62 // thread. When this pattern is set in the low three bits, the lock
63 // is either biased toward a given thread or "anonymously" biased,
64 // indicating that it is possible for it to be biased. When the
65 // lock is biased toward a given thread, locking and unlocking can
66 // be performed by that thread without using atomic operations.
67 // When a lock's bias is revoked, it reverts back to the normal
68 // locking scheme described below.
69 //
70 // Note that we are overloading the meaning of the "unlocked" state
71 // of the header. Because we steal a bit from the age we can
72 // guarantee that the bias pattern will never be seen for a truly
73 // unlocked object.
74 //
75 // Note also that the biased state contains the age bits normally
76 // contained in the object header. Large increases in scavenge
77 // times were seen when these bits were absent and an arbitrary age
78 // assigned to all biased objects, because they tended to consume a
79 // significant fraction of the eden semispaces and were not
80 // promoted promptly, causing an increase in the amount of copying
81 // performed. The runtime system aligns all JavaThread* pointers to
82 // a very large value (currently 128 bytes (32bVM) or 256 bytes (64bVM))
83 // to make room for the age bits & the epoch bits (used in support of
84 // biased locking), and for the CMS "freeness" bit in the 64bVM (+COOPs).
85 //
86 // [JavaThread* | epoch | age | 1 | 01] lock is biased toward given thread
87 // [0 | epoch | age | 1 | 01] lock is anonymously biased
88 //
89 // - the two lock bits are used to describe three states: locked/unlocked and monitor.
90 //
91 // [ptr | 00] locked ptr points to real header on stack
92 // [header | 0 | 01] unlocked regular object header
93 // [ptr | 10] monitor inflated lock (header is wapped out)
94 // [ptr | 11] marked used by markSweep to mark an object
95 // not valid at any other time
96 //
97 // We assume that stack/thread pointers have the lowest two bits cleared.
98
99 class BasicLock;
100 class ObjectMonitor;
101 class JavaThread;
102
103 class markWord {
104 private:
105 uintptr_t _value;
106
107 // Poison - prevent casts and pointer conversions.
108 // Use to_pointer and from_pointer instead.
109 template<typename T> operator T();
110 markWord(const volatile void*);
111
112 public:
113 explicit markWord(uintptr_t value) : _value(value) {}
114
115 markWord() { /* uninitialized */}
116
117 // It is critical for performance that this class be trivially
118 // destructable, copyable, and assignable.
119
120 static markWord from_pointer(void* ptr) {
121 return markWord((uintptr_t)ptr);
122 }
123 void* to_pointer() const {
124 return (void*)_value;
125 }
126
127 bool operator==(const markWord& other) const {
128 return _value == other._value;
129 }
130 bool operator!=(const markWord& other) const {
131 return !operator==(other);
132 }
133
134 // Conversion
135 uintptr_t value() const { return _value; }
136
137 // Constants
138 static const uintptr_t zero = 0;
139
140 enum { age_bits = 4,
141 lock_bits = 2,
142 biased_lock_bits = 1,
143 max_hash_bits = BitsPerWord - age_bits - lock_bits - biased_lock_bits,
144 hash_bits = max_hash_bits > 31 ? 31 : max_hash_bits,
145 cms_bits = LP64_ONLY(1) NOT_LP64(0),
146 epoch_bits = 2
147 };
148
149 // The biased locking code currently requires that the age bits be
150 // contiguous to the lock bits.
151 enum { lock_shift = 0,
152 biased_lock_shift = lock_bits,
153 age_shift = lock_bits + biased_lock_bits,
154 cms_shift = age_shift + age_bits,
155 hash_shift = cms_shift + cms_bits,
156 epoch_shift = hash_shift
157 };
158
159 enum { lock_mask = right_n_bits(lock_bits),
160 lock_mask_in_place = lock_mask << lock_shift,
161 biased_lock_mask = right_n_bits(lock_bits + biased_lock_bits),
162 biased_lock_mask_in_place= biased_lock_mask << lock_shift,
163 biased_lock_bit_in_place = 1 << biased_lock_shift,
164 age_mask = right_n_bits(age_bits),
165 age_mask_in_place = age_mask << age_shift,
166 epoch_mask = right_n_bits(epoch_bits),
167 epoch_mask_in_place = epoch_mask << epoch_shift,
168 cms_mask = right_n_bits(cms_bits),
169 cms_mask_in_place = cms_mask << cms_shift
170 };
171
172 const static uintptr_t hash_mask = right_n_bits(hash_bits);
173 const static uintptr_t hash_mask_in_place = hash_mask << hash_shift;
174
175 // Alignment of JavaThread pointers encoded in object header required by biased locking
176 enum { biased_lock_alignment = 2 << (epoch_shift + epoch_bits)
177 };
178
179 enum { locked_value = 0,
180 unlocked_value = 1,
181 monitor_value = 2,
182 marked_value = 3,
183 biased_lock_pattern = 5
184 };
185
186 enum { no_hash = 0 }; // no hash value assigned
187
188 enum { no_hash_in_place = (address_word)no_hash << hash_shift,
189 no_lock_in_place = unlocked_value
190 };
191
192 enum { max_age = age_mask };
193
194 enum { max_bias_epoch = epoch_mask };
195
196 // Biased Locking accessors.
197 // These must be checked by all code which calls into the
198 // ObjectSynchronizer and other code. The biasing is not understood
199 // by the lower-level CAS-based locking code, although the runtime
200 // fixes up biased locks to be compatible with it when a bias is
201 // revoked.
202 bool has_bias_pattern() const {
203 return (mask_bits(value(), biased_lock_mask_in_place) == biased_lock_pattern);
204 }
205 JavaThread* biased_locker() const {
206 assert(has_bias_pattern(), "should not call this otherwise");
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 markWord set_bias_epoch(int epoch) {
222 assert(has_bias_pattern(), "should not call this otherwise");
223 assert((epoch & (~epoch_mask)) == 0, "epoch overflow");
224 return markWord(mask_bits(value(), ~epoch_mask_in_place) | (epoch << epoch_shift));
225 }
226 markWord incr_bias_epoch() {
227 return set_bias_epoch((1 + bias_epoch()) & epoch_mask);
228 }
229 // Prototype mark for initialization
230 static markWord biased_locking_prototype() {
231 return markWord( biased_lock_pattern );
232 }
233
234 // lock accessors (note that these assume lock_shift == 0)
235 bool is_locked() const {
236 return (mask_bits(value(), lock_mask_in_place) != unlocked_value);
237 }
238 bool is_unlocked() const {
239 return (mask_bits(value(), biased_lock_mask_in_place) == unlocked_value);
240 }
241 bool is_marked() const {
242 return (mask_bits(value(), lock_mask_in_place) == marked_value);
243 }
244 bool is_neutral() const { return (mask_bits(value(), biased_lock_mask_in_place) == unlocked_value); }
245
246 // Special temporary state of the markWord while being inflated.
247 // Code that looks at mark outside a lock need to take this into account.
248 bool is_being_inflated() const { return (value() == 0); }
249
250 // Distinguished markword value - used when inflating over
251 // an existing stacklock. 0 indicates the markword is "BUSY".
252 // Lockword mutators that use a LD...CAS idiom should always
253 // check for and avoid overwriting a 0 value installed by some
254 // other thread. (They should spin or block instead. The 0 value
255 // is transient and *should* be short-lived).
256 static markWord INFLATING() { return markWord(zero); } // inflate-in-progress
257
258 // Should this header be preserved during GC?
259 inline bool must_be_preserved(oop obj_containing_mark) const;
260 inline bool must_be_preserved_with_bias(oop obj_containing_mark) const;
261
262 // Should this header (including its age bits) be preserved in the
263 // case of a promotion failure during scavenge?
264 // Note that we special case this situation. We want to avoid
265 // calling BiasedLocking::preserve_marks()/restore_marks() (which
266 // decrease the number of mark words that need to be preserved
267 // during GC) during each scavenge. During scavenges in which there
268 // is no promotion failure, we actually don't need to call the above
269 // routines at all, since we don't mutate and re-initialize the
270 // marks of promoted objects using init_mark(). However, during
271 // scavenges which result in promotion failure, we do re-initialize
272 // the mark words of objects, meaning that we should have called
273 // these mark word preservation routines. Currently there's no good
274 // place in which to call them in any of the scavengers (although
275 // guarded by appropriate locks we could make one), but the
276 // observation is that promotion failures are quite rare and
277 // reducing the number of mark words preserved during them isn't a
278 // high priority.
279 inline bool must_be_preserved_for_promotion_failure(oop obj_containing_mark) const;
280 inline bool must_be_preserved_with_bias_for_promotion_failure(oop obj_containing_mark) const;
281
282 // Should this header be preserved during a scavenge where CMS is
283 // the old generation?
284 // (This is basically the same body as must_be_preserved_for_promotion_failure(),
285 // but takes the Klass* as argument instead)
286 inline bool must_be_preserved_for_cms_scavenge(Klass* klass_of_obj_containing_mark) const;
287 inline bool must_be_preserved_with_bias_for_cms_scavenge(Klass* klass_of_obj_containing_mark) const;
288
289 // WARNING: The following routines are used EXCLUSIVELY by
290 // synchronization functions. They are not really gc safe.
291 // They must get updated if markWord layout get changed.
292 markWord set_unlocked() const {
293 return markWord(value() | unlocked_value);
294 }
295 bool has_locker() const {
296 return ((value() & lock_mask_in_place) == locked_value);
297 }
298 BasicLock* locker() const {
299 assert(has_locker(), "check");
300 return (BasicLock*) value();
301 }
302 bool has_monitor() const {
303 return ((value() & monitor_value) != 0);
304 }
305 ObjectMonitor* monitor() const {
306 assert(has_monitor(), "check");
307 // Use xor instead of &~ to provide one extra tag-bit check.
308 return (ObjectMonitor*) (value() ^ monitor_value);
309 }
310 bool has_displaced_mark_helper() const {
311 return ((value() & unlocked_value) == 0);
312 }
313 markWord displaced_mark_helper() const {
314 assert(has_displaced_mark_helper(), "check");
315 intptr_t ptr = (value() & ~monitor_value);
316 return *(markWord*)ptr;
317 }
318 void set_displaced_mark_helper(markWord m) const {
319 assert(has_displaced_mark_helper(), "check");
320 intptr_t ptr = (value() & ~monitor_value);
321 ((markWord*)ptr)->_value = m._value;
322 }
323 markWord copy_set_hash(intptr_t hash) const {
324 intptr_t tmp = value() & (~hash_mask_in_place);
325 tmp |= ((hash & hash_mask) << hash_shift);
326 return markWord(tmp);
327 }
328 // it is only used to be stored into BasicLock as the
329 // indicator that the lock is using heavyweight monitor
330 static markWord unused_mark() {
331 return markWord(marked_value);
332 }
333 // the following two functions create the markWord to be
334 // stored into object header, it encodes monitor info
335 static markWord encode(BasicLock* lock) {
336 return from_pointer(lock);
337 }
338 static markWord encode(ObjectMonitor* monitor) {
339 intptr_t tmp = (intptr_t) monitor;
340 return markWord(tmp | monitor_value);
341 }
342 static markWord encode(JavaThread* thread, uint age, int bias_epoch) {
343 intptr_t tmp = (intptr_t) thread;
344 assert(UseBiasedLocking && ((tmp & (epoch_mask_in_place | age_mask_in_place | biased_lock_mask_in_place)) == 0), "misaligned JavaThread pointer");
345 assert(age <= max_age, "age too large");
346 assert(bias_epoch <= max_bias_epoch, "bias epoch too large");
347 return markWord(tmp | (bias_epoch << epoch_shift) | (age << age_shift) | biased_lock_pattern);
348 }
349
350 // used to encode pointers during GC
351 markWord clear_lock_bits() { return markWord(value() & ~lock_mask_in_place); }
352
353 // age operations
354 markWord set_marked() { return markWord((value() & ~lock_mask_in_place) | marked_value); }
355 markWord set_unmarked() { return markWord((value() & ~lock_mask_in_place) | unlocked_value); }
356
357 uint age() const { return mask_bits(value() >> age_shift, age_mask); }
358 markWord set_age(uint v) const {
359 assert((v & ~age_mask) == 0, "shouldn't overflow age field");
360 return markWord((value() & ~age_mask_in_place) | (((uintptr_t)v & age_mask) << age_shift));
361 }
362 markWord incr_age() const { return age() == max_age ? markWord(_value) : set_age(age() + 1); }
363
364 // hash operations
365 intptr_t hash() const {
366 return mask_bits(value() >> hash_shift, hash_mask);
367 }
368
369 bool has_no_hash() const {
370 return hash() == no_hash;
371 }
372
373 // Prototype mark for initialization
374 static markWord prototype() {
375 return markWord( no_hash_in_place | no_lock_in_place );
376 }
377
378 // Helper function for restoration of unmarked mark oops during GC
379 static inline markWord prototype_for_object(oop obj);
380
381 // Debugging
382 void print_on(outputStream* st) const;
383
384 // Prepare address of oop for placement into mark
385 inline static markWord encode_pointer_as_mark(void* p) { return from_pointer(p).set_marked(); }
386
387 // Recover address of oop from encoded form used in mark
388 inline void* decode_pointer() { if (UseBiasedLocking && has_bias_pattern()) return NULL; return (void*)clear_lock_bits().value(); }
389
390 // These markWords indicate cms free chunk blocks and not objects.
391 // In 64 bit, the markWord is set to distinguish them from oops.
392 // These are defined in 32 bit mode for vmStructs.
393 const static uintptr_t cms_free_chunk_pattern = 0x1;
394
395 // Constants for the size field.
396 enum { size_shift = cms_shift + cms_bits,
397 size_bits = 35 // need for compressed oops 32G
398 };
399 // These values are too big for Win64
400 const static uintptr_t size_mask = LP64_ONLY(right_n_bits(size_bits))
401 NOT_LP64(0);
402 const static uintptr_t size_mask_in_place =
403 (address_word)size_mask << size_shift;
404
405 #ifdef _LP64
406 static markWord cms_free_prototype() {
407 return markWord(((intptr_t)prototype().value() & ~cms_mask_in_place) |
408 ((cms_free_chunk_pattern & cms_mask) << cms_shift));
409 }
410 uintptr_t cms_encoding() const {
411 return mask_bits(value() >> cms_shift, cms_mask);
412 }
413 bool is_cms_free_chunk() const {
414 return is_neutral() &&
415 (cms_encoding() & cms_free_chunk_pattern) == cms_free_chunk_pattern;
416 }
417
418 size_t get_size() const { return (size_t)(value() >> size_shift); }
419 static markWord set_size_and_free(size_t size) {
420 assert((size & ~size_mask) == 0, "shouldn't overflow size field");
421 return markWord(((intptr_t)cms_free_prototype().value() & ~size_mask_in_place) |
422 (((intptr_t)size & size_mask) << size_shift));
423 }
424 #endif // _LP64
425 };
426
427 // Support atomic operations.
428 template<>
429 struct PrimitiveConversions::Translate<markWord> : public TrueType {
430 typedef markWord Value;
431 typedef uintptr_t Decayed;
432
433 static Decayed decay(const Value& x) { return x.value(); }
434 static Value recover(Decayed x) { return Value(x); }
435 };
436
437 #endif // SHARE_OOPS_MARKOOP_HPP