1 /*
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24
25 #ifndef SHARE_OOPS_MARKWORD_HPP
26 #define SHARE_OOPS_MARKWORD_HPP
27
28 #include "metaprogramming/integralConstant.hpp"
29 #include "metaprogramming/primitiveConversions.hpp"
30 #include "oops/oopsHierarchy.hpp"
31 #include "runtime/globals.hpp"
32
33 // The markWord describes the header of an object.
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 markWord {
105 private:
106 uintptr_t _value;
107
108 public:
109 explicit markWord(uintptr_t value) : _value(value) {}
110
111 markWord() { /* uninitialized */}
112
113 // It is critical for performance that this class be trivially
114 // destructable, copyable, and assignable.
115
116 static markWord from_pointer(void* ptr) {
117 return markWord((uintptr_t)ptr);
118 }
119 void* to_pointer() const {
120 return (void*)_value;
121 }
122
123 bool operator==(const markWord& other) const {
124 return _value == other._value;
125 }
126 bool operator!=(const markWord& other) const {
127 return !operator==(other);
128 }
129
130 // Conversion
131 uintptr_t value() const { return _value; }
132
133 // Constants
134 static const int age_bits = 4;
135 static const int lock_bits = 2;
136 static const int biased_lock_bits = 1;
137 static const int max_hash_bits = BitsPerWord - age_bits - lock_bits - biased_lock_bits;
138 static const int hash_bits = max_hash_bits > 31 ? 31 : max_hash_bits;
139 static const int cms_bits = LP64_ONLY(1) NOT_LP64(0);
140 static const int epoch_bits = 2;
141
142 // The biased locking code currently requires that the age bits be
143 // contiguous to the lock bits.
144 static const int lock_shift = 0;
145 static const int biased_lock_shift = lock_bits;
146 static const int age_shift = lock_bits + biased_lock_bits;
147 static const int cms_shift = age_shift + age_bits;
148 static const int hash_shift = cms_shift + cms_bits;
149 static const int epoch_shift = hash_shift;
150
151 static const uintptr_t lock_mask = right_n_bits(lock_bits);
152 static const uintptr_t lock_mask_in_place = lock_mask << lock_shift;
153 static const uintptr_t biased_lock_mask = right_n_bits(lock_bits + biased_lock_bits);
154 static const uintptr_t biased_lock_mask_in_place= biased_lock_mask << lock_shift;
155 static const uintptr_t biased_lock_bit_in_place = 1 << biased_lock_shift;
156 static const uintptr_t age_mask = right_n_bits(age_bits);
157 static const uintptr_t age_mask_in_place = age_mask << age_shift;
158 static const uintptr_t epoch_mask = right_n_bits(epoch_bits);
159 static const uintptr_t epoch_mask_in_place = epoch_mask << epoch_shift;
160 static const uintptr_t cms_mask = right_n_bits(cms_bits);
161 static const uintptr_t cms_mask_in_place = cms_mask << cms_shift;
162
163 static const uintptr_t hash_mask = right_n_bits(hash_bits);
164 static const uintptr_t hash_mask_in_place = hash_mask << hash_shift;
165
166 // Alignment of JavaThread pointers encoded in object header required by biased locking
167 static const size_t biased_lock_alignment = 2 << (epoch_shift + epoch_bits);
168
169 static const uintptr_t locked_value = 0;
170 static const uintptr_t unlocked_value = 1;
171 static const uintptr_t monitor_value = 2;
172 static const uintptr_t marked_value = 3;
173 static const uintptr_t biased_lock_pattern = 5;
174
175 static const uintptr_t no_hash = 0 ; // no hash value assigned
176 static const uintptr_t no_hash_in_place = (address_word)no_hash << hash_shift;
177 static const uintptr_t no_lock_in_place = unlocked_value;
178
179 static const uint max_age = age_mask;
180
181 static const int max_bias_epoch = epoch_mask;
182
183 // Creates a markWord with all bits set to zero.
184 static markWord zero() { return markWord(uintptr_t(0)); }
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*) 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 zero(); } // inflate-in-progress
247
248 // Should this header be preserved during GC?
249 template <typename KlassProxy>
250 inline bool must_be_preserved(KlassProxy klass) 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 template <typename KlassProxy>
270 inline bool must_be_preserved_for_promotion_failure(KlassProxy klass) 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
278 // WARNING: The following routines are used EXCLUSIVELY by
279 // synchronization functions. They are not really gc safe.
280 // They must get updated if markWord layout get changed.
281 markWord set_unlocked() const {
282 return markWord(value() | unlocked_value);
283 }
284 bool has_locker() const {
285 return ((value() & lock_mask_in_place) == locked_value);
286 }
287 BasicLock* locker() const {
288 assert(has_locker(), "check");
289 return (BasicLock*) value();
290 }
291 bool has_monitor() const {
292 return ((value() & monitor_value) != 0);
293 }
294 ObjectMonitor* monitor() const {
295 assert(has_monitor(), "check");
296 // Use xor instead of &~ to provide one extra tag-bit check.
297 return (ObjectMonitor*) (value() ^ monitor_value);
298 }
299 bool has_displaced_mark_helper() const {
300 return ((value() & unlocked_value) == 0);
301 }
302 markWord displaced_mark_helper() const {
303 assert(has_displaced_mark_helper(), "check");
304 uintptr_t ptr = (value() & ~monitor_value);
305 return *(markWord*)ptr;
306 }
307 void set_displaced_mark_helper(markWord m) const {
308 assert(has_displaced_mark_helper(), "check");
309 uintptr_t ptr = (value() & ~monitor_value);
310 ((markWord*)ptr)->_value = m._value;
311 }
312 markWord copy_set_hash(intptr_t hash) const {
313 uintptr_t tmp = value() & (~hash_mask_in_place);
314 tmp |= ((hash & hash_mask) << hash_shift);
315 return markWord(tmp);
316 }
317 // it is only used to be stored into BasicLock as the
318 // indicator that the lock is using heavyweight monitor
319 static markWord unused_mark() {
320 return markWord(marked_value);
321 }
322 // the following two functions create the markWord to be
323 // stored into object header, it encodes monitor info
324 static markWord encode(BasicLock* lock) {
325 return from_pointer(lock);
326 }
327 static markWord encode(ObjectMonitor* monitor) {
328 uintptr_t tmp = (uintptr_t) monitor;
329 return markWord(tmp | monitor_value);
330 }
331 static markWord encode(JavaThread* thread, uint age, int bias_epoch) {
332 uintptr_t tmp = (uintptr_t) thread;
333 assert(UseBiasedLocking && ((tmp & (epoch_mask_in_place | age_mask_in_place | biased_lock_mask_in_place)) == 0), "misaligned JavaThread pointer");
334 assert(age <= max_age, "age too large");
335 assert(bias_epoch <= max_bias_epoch, "bias epoch too large");
336 return markWord(tmp | (bias_epoch << epoch_shift) | (age << age_shift) | biased_lock_pattern);
337 }
338
339 // used to encode pointers during GC
340 markWord clear_lock_bits() { return markWord(value() & ~lock_mask_in_place); }
341
342 // age operations
343 markWord set_marked() { return markWord((value() & ~lock_mask_in_place) | marked_value); }
344 markWord set_unmarked() { return markWord((value() & ~lock_mask_in_place) | unlocked_value); }
345
346 uint age() const { return mask_bits(value() >> age_shift, age_mask); }
347 markWord set_age(uint v) const {
348 assert((v & ~age_mask) == 0, "shouldn't overflow age field");
349 return markWord((value() & ~age_mask_in_place) | ((v & age_mask) << age_shift));
350 }
351 markWord incr_age() const { return age() == max_age ? markWord(_value) : set_age(age() + 1); }
352
353 // hash operations
354 intptr_t hash() const {
355 return mask_bits(value() >> hash_shift, hash_mask);
356 }
357
358 bool has_no_hash() const {
359 return hash() == no_hash;
360 }
361
362 // Prototype mark for initialization
363 static markWord prototype() {
364 return markWord( no_hash_in_place | no_lock_in_place );
365 }
366
367 // Helper function for restoration of unmarked mark oops during GC
368 static inline markWord prototype_for_klass(const Klass* klass);
369
370 // Debugging
371 void print_on(outputStream* st) const;
372
373 // Prepare address of oop for placement into mark
374 inline static markWord encode_pointer_as_mark(void* p) { return from_pointer(p).set_marked(); }
375
376 // Recover address of oop from encoded form used in mark
377 inline void* decode_pointer() { if (UseBiasedLocking && has_bias_pattern()) return NULL; return (void*)clear_lock_bits().value(); }
378
379 // These markWords indicate cms free chunk blocks and not objects.
380 // In 64 bit, the markWord is set to distinguish them from oops.
381 // These are defined in 32 bit mode for vmStructs.
382 const static uintptr_t cms_free_chunk_pattern = 0x1;
383
384 // Constants for the size field.
385 enum { size_shift = cms_shift + cms_bits,
386 size_bits = 35 // need for compressed oops 32G
387 };
388 // These values are too big for Win64
389 const static uintptr_t size_mask = LP64_ONLY(right_n_bits(size_bits))
390 NOT_LP64(0);
391 const static uintptr_t size_mask_in_place =
392 (address_word)size_mask << size_shift;
393
394 #ifdef _LP64
395 static markWord cms_free_prototype() {
396 return markWord((prototype().value() & ~cms_mask_in_place) |
397 ((cms_free_chunk_pattern & cms_mask) << cms_shift));
398 }
399 uintptr_t cms_encoding() const {
400 return mask_bits(value() >> cms_shift, cms_mask);
401 }
402 bool is_cms_free_chunk() const {
403 return is_neutral() &&
404 (cms_encoding() & cms_free_chunk_pattern) == cms_free_chunk_pattern;
405 }
406
407 size_t get_size() const { return (size_t)(value() >> size_shift); }
408 static markWord set_size_and_free(size_t size) {
409 assert((size & ~size_mask) == 0, "shouldn't overflow size field");
410 return markWord((cms_free_prototype().value() & ~size_mask_in_place) |
411 ((size & size_mask) << size_shift));
412 }
413 #endif // _LP64
414 };
415
416 // Support atomic operations.
417 template<>
418 struct PrimitiveConversions::Translate<markWord> : public TrueType {
419 typedef markWord Value;
420 typedef uintptr_t Decayed;
421
422 static Decayed decay(const Value& x) { return x.value(); }
423 static Value recover(Decayed x) { return Value(x); }
424 };
425
426 #endif // SHARE_OOPS_MARKWORD_HPP