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 public:
108 explicit markWord(uintptr_t value) : _value(value) {}
109
110 markWord() { /* uninitialized */}
111
112 // It is critical for performance that this class be trivially
113 // destructable, copyable, and assignable.
114
115 static markWord from_pointer(void* ptr) {
116 return markWord((uintptr_t)ptr);
117 }
118
119 bool operator==(const markWord& other) const {
120 return _value == other._value;
121 }
122 bool operator!=(const markWord& other) const {
123 return !operator==(other);
124 }
125
126 // Conversion
127 uintptr_t value() const { return _value; }
128
129 // Constants
130 enum { age_bits = 4,
131 lock_bits = 2,
132 biased_lock_bits = 1,
133 max_hash_bits = BitsPerWord - age_bits - lock_bits - biased_lock_bits,
134 hash_bits = max_hash_bits > 31 ? 31 : max_hash_bits,
135 cms_bits = LP64_ONLY(1) NOT_LP64(0),
136 epoch_bits = 2
137 };
138
139 // The biased locking code currently requires that the age bits be
140 // contiguous to the lock bits.
141 enum { lock_shift = 0,
142 biased_lock_shift = lock_bits,
143 age_shift = lock_bits + biased_lock_bits,
144 cms_shift = age_shift + age_bits,
145 hash_shift = cms_shift + cms_bits,
146 epoch_shift = hash_shift
147 };
148
149 enum { lock_mask = right_n_bits(lock_bits),
150 lock_mask_in_place = lock_mask << lock_shift,
151 biased_lock_mask = right_n_bits(lock_bits + biased_lock_bits),
152 biased_lock_mask_in_place= biased_lock_mask << lock_shift,
153 biased_lock_bit_in_place = 1 << biased_lock_shift,
154 age_mask = right_n_bits(age_bits),
155 age_mask_in_place = age_mask << age_shift,
156 epoch_mask = right_n_bits(epoch_bits),
157 epoch_mask_in_place = epoch_mask << epoch_shift,
158 cms_mask = right_n_bits(cms_bits),
159 cms_mask_in_place = cms_mask << cms_shift
160 };
161
162 const static uintptr_t hash_mask = right_n_bits(hash_bits);
163 const static uintptr_t hash_mask_in_place = hash_mask << hash_shift;
164
165 // Alignment of JavaThread pointers encoded in object header required by biased locking
166 enum { biased_lock_alignment = 2 << (epoch_shift + epoch_bits)
167 };
168
169 enum { locked_value = 0,
170 unlocked_value = 1,
171 monitor_value = 2,
172 marked_value = 3,
173 biased_lock_pattern = 5
174 };
175
176 enum { no_hash = 0 }; // no hash value assigned
177
178 enum { no_hash_in_place = (address_word)no_hash << hash_shift,
179 no_lock_in_place = unlocked_value
180 };
181
182 enum { max_age = age_mask };
183
184 enum { max_bias_epoch = epoch_mask };
185
186 // Biased Locking accessors.
187 // These must be checked by all code which calls into the
188 // ObjectSynchronizer and other code. The biasing is not understood
189 // by the lower-level CAS-based locking code, although the runtime
190 // fixes up biased locks to be compatible with it when a bias is
191 // revoked.
192 bool has_bias_pattern() const {
193 return (mask_bits(value(), biased_lock_mask_in_place) == biased_lock_pattern);
194 }
195 JavaThread* biased_locker() const {
196 assert(has_bias_pattern(), "should not call this otherwise");
197 return (JavaThread*) ((intptr_t) (mask_bits(value(), ~(biased_lock_mask_in_place | age_mask_in_place | epoch_mask_in_place))));
198 }
199 // Indicates that the mark has the bias bit set but that it has not
200 // yet been biased toward a particular thread
201 bool is_biased_anonymously() const {
202 return (has_bias_pattern() && (biased_locker() == NULL));
203 }
204 // Indicates epoch in which this bias was acquired. If the epoch
205 // changes due to too many bias revocations occurring, the biases
206 // from the previous epochs are all considered invalid.
207 int bias_epoch() const {
208 assert(has_bias_pattern(), "should not call this otherwise");
209 return (mask_bits(value(), epoch_mask_in_place) >> epoch_shift);
210 }
211 markWord set_bias_epoch(int epoch) {
212 assert(has_bias_pattern(), "should not call this otherwise");
213 assert((epoch & (~epoch_mask)) == 0, "epoch overflow");
214 return markWord(mask_bits(value(), ~epoch_mask_in_place) | (epoch << epoch_shift));
215 }
216 markWord incr_bias_epoch() {
217 return set_bias_epoch((1 + bias_epoch()) & epoch_mask);
218 }
219 // Prototype mark for initialization
220 static markWord biased_locking_prototype() {
221 return markWord( biased_lock_pattern );
222 }
223
224 // lock accessors (note that these assume lock_shift == 0)
225 bool is_locked() const {
226 return (mask_bits(value(), lock_mask_in_place) != unlocked_value);
227 }
228 bool is_unlocked() const {
229 return (mask_bits(value(), biased_lock_mask_in_place) == unlocked_value);
230 }
231 bool is_marked() const {
232 return (mask_bits(value(), lock_mask_in_place) == marked_value);
233 }
234 bool is_neutral() const { return (mask_bits(value(), biased_lock_mask_in_place) == unlocked_value); }
235
236 // Special temporary state of the markWord while being inflated.
237 // Code that looks at mark outside a lock need to take this into account.
238 bool is_being_inflated() const { return (value() == 0); }
239
240 // Distinguished markword value - used when inflating over
241 // an existing stacklock. 0 indicates the markword is "BUSY".
242 // Lockword mutators that use a LD...CAS idiom should always
243 // check for and avoid overwriting a 0 value installed by some
244 // other thread. (They should spin or block instead. The 0 value
245 // is transient and *should* be short-lived).
246 static markWord INFLATING() { return markWord(0); } // inflate-in-progress
247
248 // Should this header be preserved during GC?
249 inline bool must_be_preserved(oop obj_containing_mark) const;
250 inline bool must_be_preserved_with_bias(oop obj_containing_mark) const;
251
252 // Should this header (including its age bits) be preserved in the
253 // case of a promotion failure during scavenge?
254 // Note that we special case this situation. We want to avoid
255 // calling BiasedLocking::preserve_marks()/restore_marks() (which
256 // decrease the number of mark words that need to be preserved
257 // during GC) during each scavenge. During scavenges in which there
258 // is no promotion failure, we actually don't need to call the above
259 // routines at all, since we don't mutate and re-initialize the
260 // marks of promoted objects using init_mark(). However, during
261 // scavenges which result in promotion failure, we do re-initialize
262 // the mark words of objects, meaning that we should have called
263 // these mark word preservation routines. Currently there's no good
264 // place in which to call them in any of the scavengers (although
265 // guarded by appropriate locks we could make one), but the
266 // observation is that promotion failures are quite rare and
267 // reducing the number of mark words preserved during them isn't a
268 // high priority.
269 inline bool must_be_preserved_for_promotion_failure(oop obj_containing_mark) const;
270 inline bool must_be_preserved_with_bias_for_promotion_failure(oop obj_containing_mark) const;
271
272 // Should this header be preserved during a scavenge where CMS is
273 // the old generation?
274 // (This is basically the same body as must_be_preserved_for_promotion_failure(),
275 // but takes the Klass* as argument instead)
276 inline bool must_be_preserved_for_cms_scavenge(Klass* klass_of_obj_containing_mark) const;
277 inline bool must_be_preserved_with_bias_for_cms_scavenge(Klass* klass_of_obj_containing_mark) const;
278
279 // WARNING: The following routines are used EXCLUSIVELY by
280 // synchronization functions. They are not really gc safe.
281 // They must get updated if markWord layout get changed.
282 markWord set_unlocked() const {
283 return markWord(value() | unlocked_value);
284 }
285 bool has_locker() const {
286 return ((value() & lock_mask_in_place) == locked_value);
287 }
288 BasicLock* locker() const {
289 assert(has_locker(), "check");
290 return (BasicLock*) value();
291 }
292 bool has_monitor() const {
293 return ((value() & monitor_value) != 0);
294 }
295 ObjectMonitor* monitor() const {
296 assert(has_monitor(), "check");
297 // Use xor instead of &~ to provide one extra tag-bit check.
298 return (ObjectMonitor*) (value() ^ monitor_value);
299 }
300 bool has_displaced_mark_helper() const {
301 return ((value() & unlocked_value) == 0);
302 }
303 markWord displaced_mark_helper() const {
304 assert(has_displaced_mark_helper(), "check");
305 intptr_t ptr = (value() & ~monitor_value);
306 return *(markWord*)ptr;
307 }
308 void set_displaced_mark_helper(markWord m) const {
309 assert(has_displaced_mark_helper(), "check");
310 intptr_t ptr = (value() & ~monitor_value);
311 ((markWord*)ptr)->_value = m._value;
312 }
313 markWord copy_set_hash(intptr_t hash) const {
314 intptr_t tmp = value() & (~hash_mask_in_place);
315 tmp |= ((hash & hash_mask) << hash_shift);
316 return markWord(tmp);
317 }
318 // it is only used to be stored into BasicLock as the
319 // indicator that the lock is using heavyweight monitor
320 static markWord unused_mark() {
321 return markWord(marked_value);
322 }
323 // the following two functions create the markWord to be
324 // stored into object header, it encodes monitor info
325 static markWord encode(BasicLock* lock) {
326 return from_pointer(lock);
327 }
328 static markWord encode(ObjectMonitor* monitor) {
329 intptr_t tmp = (intptr_t) monitor;
330 return markWord(tmp | monitor_value);
331 }
332 static markWord encode(JavaThread* thread, uint age, int bias_epoch) {
333 intptr_t tmp = (intptr_t) thread;
334 assert(UseBiasedLocking && ((tmp & (epoch_mask_in_place | age_mask_in_place | biased_lock_mask_in_place)) == 0), "misaligned JavaThread pointer");
335 assert(age <= max_age, "age too large");
336 assert(bias_epoch <= max_bias_epoch, "bias epoch too large");
337 return markWord(tmp | (bias_epoch << epoch_shift) | (age << age_shift) | biased_lock_pattern);
338 }
339
340 // used to encode pointers during GC
341 markWord clear_lock_bits() { return markWord(value() & ~lock_mask_in_place); }
342
343 // age operations
344 markWord set_marked() { return markWord((value() & ~lock_mask_in_place) | marked_value); }
345 markWord set_unmarked() { return markWord((value() & ~lock_mask_in_place) | unlocked_value); }
346
347 uint age() const { return mask_bits(value() >> age_shift, age_mask); }
348 markWord set_age(uint v) const {
349 assert((v & ~age_mask) == 0, "shouldn't overflow age field");
350 return markWord((value() & ~age_mask_in_place) | (((uintptr_t)v & age_mask) << age_shift));
351 }
352 markWord incr_age() const { return age() == max_age ? markWord(_value) : set_age(age() + 1); }
353
354 // hash operations
355 intptr_t hash() const {
356 return mask_bits(value() >> hash_shift, hash_mask);
357 }
358
359 bool has_no_hash() const {
360 return hash() == no_hash;
361 }
362
363 // Prototype mark for initialization
364 static markWord prototype() {
365 return markWord( no_hash_in_place | no_lock_in_place );
366 }
367
368 // Helper function for restoration of unmarked mark oops during GC
369 static inline markWord prototype_for_object(oop obj);
370
371 // Debugging
372 void print_on(outputStream* st) const;
373
374 // Prepare address of oop for placement into mark
375 inline static markWord encode_pointer_as_mark(void* p) { return from_pointer(p).set_marked(); }
376
377 // Recover address of oop from encoded form used in mark
378 inline void* decode_pointer() { if (UseBiasedLocking && has_bias_pattern()) return NULL; return (void*)clear_lock_bits().value(); }
379
380 // These markWords indicate cms free chunk blocks and not objects.
381 // In 64 bit, the markWord is set to distinguish them from oops.
382 // These are defined in 32 bit mode for vmStructs.
383 const static uintptr_t cms_free_chunk_pattern = 0x1;
384
385 // Constants for the size field.
386 enum { size_shift = cms_shift + cms_bits,
387 size_bits = 35 // need for compressed oops 32G
388 };
389 // These values are too big for Win64
390 const static uintptr_t size_mask = LP64_ONLY(right_n_bits(size_bits))
391 NOT_LP64(0);
392 const static uintptr_t size_mask_in_place =
393 (address_word)size_mask << size_shift;
394
395 #ifdef _LP64
396 static markWord cms_free_prototype() {
397 return markWord(((intptr_t)prototype().value() & ~cms_mask_in_place) |
398 ((cms_free_chunk_pattern & cms_mask) << cms_shift));
399 }
400 uintptr_t cms_encoding() const {
401 return mask_bits(value() >> cms_shift, cms_mask);
402 }
403 bool is_cms_free_chunk() const {
404 return is_neutral() &&
405 (cms_encoding() & cms_free_chunk_pattern) == cms_free_chunk_pattern;
406 }
407
408 size_t get_size() const { return (size_t)(value() >> size_shift); }
409 static markWord set_size_and_free(size_t size) {
410 assert((size & ~size_mask) == 0, "shouldn't overflow size field");
411 return markWord(((intptr_t)cms_free_prototype().value() & ~size_mask_in_place) |
412 (((intptr_t)size & size_mask) << size_shift));
413 }
414 #endif // _LP64
415 };
416
417 // Support atomic operations.
418 template<>
419 struct PrimitiveConversions::Translate<markWord> : public TrueType {
420 typedef markWord Value;
421 typedef uintptr_t Decayed;
422
423 static Decayed decay(const Value& x) { return x.value(); }
424 static Value recover(Decayed x) { return Value(x); }
425 };
426
427 #endif // SHARE_OOPS_MARKOOP_HPP