Mercurial > hg > truffle
annotate src/share/vm/oops/markOop.hpp @ 1339:09ac706c2623
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0 | 1 /* |
196 | 2 * Copyright 1997-2008 Sun Microsystems, Inc. All Rights Reserved. |
0 | 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
4 * | |
5 * This code is free software; you can redistribute it and/or modify it | |
6 * under the terms of the GNU General Public License version 2 only, as | |
7 * published by the Free Software Foundation. | |
8 * | |
9 * This code is distributed in the hope that it will be useful, but WITHOUT | |
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | |
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | |
12 * version 2 for more details (a copy is included in the LICENSE file that | |
13 * accompanied this code). | |
14 * | |
15 * You should have received a copy of the GNU General Public License version | |
16 * 2 along with this work; if not, write to the Free Software Foundation, | |
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. | |
18 * | |
19 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, | |
20 * CA 95054 USA or visit www.sun.com if you need additional information or | |
21 * have any questions. | |
22 * | |
23 */ | |
24 | |
25 // The markOop describes the header of an object. | |
26 // | |
27 // Note that the mark is not a real oop but just a word. | |
28 // It is placed in the oop hierarchy for historical reasons. | |
29 // | |
30 // Bit-format of an object header (most significant first): | |
31 // | |
187 | 32 // 32 bits: unused:0 hash:25 age:4 biased_lock:1 lock:2 |
33 // 64 bits: unused:24 hash:31 cms:2 age:4 biased_lock:1 lock:2 | |
34 // unused:20 size:35 cms:2 age:4 biased_lock:1 lock:2 (if cms | |
35 // free chunk) | |
0 | 36 // |
37 // - hash contains the identity hash value: largest value is | |
38 // 31 bits, see os::random(). Also, 64-bit vm's require | |
39 // a hash value no bigger than 32 bits because they will not | |
40 // properly generate a mask larger than that: see library_call.cpp | |
41 // and c1_CodePatterns_sparc.cpp. | |
42 // | |
43 // - the biased lock pattern is used to bias a lock toward a given | |
44 // thread. When this pattern is set in the low three bits, the lock | |
45 // is either biased toward a given thread or "anonymously" biased, | |
46 // indicating that it is possible for it to be biased. When the | |
47 // lock is biased toward a given thread, locking and unlocking can | |
48 // be performed by that thread without using atomic operations. | |
49 // When a lock's bias is revoked, it reverts back to the normal | |
50 // locking scheme described below. | |
51 // | |
52 // Note that we are overloading the meaning of the "unlocked" state | |
53 // of the header. Because we steal a bit from the age we can | |
54 // guarantee that the bias pattern will never be seen for a truly | |
55 // unlocked object. | |
56 // | |
57 // Note also that the biased state contains the age bits normally | |
58 // contained in the object header. Large increases in scavenge | |
59 // times were seen when these bits were absent and an arbitrary age | |
60 // assigned to all biased objects, because they tended to consume a | |
61 // significant fraction of the eden semispaces and were not | |
62 // promoted promptly, causing an increase in the amount of copying | |
63 // performed. The runtime system aligns all JavaThread* pointers to | |
64 // a very large value (currently 128 bytes) to make room for the | |
65 // age bits when biased locking is enabled. | |
66 // | |
67 // [JavaThread* | epoch | age | 1 | 01] lock is biased toward given thread | |
68 // [0 | epoch | age | 1 | 01] lock is anonymously biased | |
69 // | |
70 // - the two lock bits are used to describe three states: locked/unlocked and monitor. | |
71 // | |
72 // [ptr | 00] locked ptr points to real header on stack | |
73 // [header | 0 | 01] unlocked regular object header | |
74 // [ptr | 10] monitor inflated lock (header is wapped out) | |
75 // [ptr | 11] marked used by markSweep to mark an object | |
76 // not valid at any other time | |
77 // | |
78 // We assume that stack/thread pointers have the lowest two bits cleared. | |
79 | |
80 class BasicLock; | |
81 class ObjectMonitor; | |
82 class JavaThread; | |
83 | |
84 class markOopDesc: public oopDesc { | |
85 private: | |
86 // Conversion | |
87 uintptr_t value() const { return (uintptr_t) this; } | |
88 | |
89 public: | |
90 // Constants | |
91 enum { age_bits = 4, | |
92 lock_bits = 2, | |
93 biased_lock_bits = 1, | |
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94 max_hash_bits = BitsPerWord - age_bits - lock_bits - biased_lock_bits, |
0 | 95 hash_bits = max_hash_bits > 31 ? 31 : max_hash_bits, |
187 | 96 cms_bits = LP64_ONLY(1) NOT_LP64(0), |
0 | 97 epoch_bits = 2 |
98 }; | |
99 | |
100 // The biased locking code currently requires that the age bits be | |
101 // contiguous to the lock bits. Class data sharing would prefer the | |
102 // hash bits to be lower down to provide more random hash codes for | |
103 // shared read-only symbolOop objects, because these objects' mark | |
104 // words are set to their own address with marked_value in the lock | |
105 // bit, and using lower bits would make their identity hash values | |
106 // more random. However, the performance decision was made in favor | |
107 // of the biased locking code. | |
108 | |
109 enum { lock_shift = 0, | |
110 biased_lock_shift = lock_bits, | |
111 age_shift = lock_bits + biased_lock_bits, | |
187 | 112 cms_shift = age_shift + age_bits, |
113 hash_shift = cms_shift + cms_bits, | |
0 | 114 epoch_shift = hash_shift |
115 }; | |
116 | |
117 enum { lock_mask = right_n_bits(lock_bits), | |
118 lock_mask_in_place = lock_mask << lock_shift, | |
119 biased_lock_mask = right_n_bits(lock_bits + biased_lock_bits), | |
120 biased_lock_mask_in_place= biased_lock_mask << lock_shift, | |
121 biased_lock_bit_in_place = 1 << biased_lock_shift, | |
122 age_mask = right_n_bits(age_bits), | |
123 age_mask_in_place = age_mask << age_shift, | |
124 epoch_mask = right_n_bits(epoch_bits), | |
187 | 125 epoch_mask_in_place = epoch_mask << epoch_shift, |
126 cms_mask = right_n_bits(cms_bits), | |
127 cms_mask_in_place = cms_mask << cms_shift | |
0 | 128 #ifndef _WIN64 |
129 ,hash_mask = right_n_bits(hash_bits), | |
130 hash_mask_in_place = (address_word)hash_mask << hash_shift | |
131 #endif | |
132 }; | |
133 | |
134 // Alignment of JavaThread pointers encoded in object header required by biased locking | |
135 enum { biased_lock_alignment = 2 << (epoch_shift + epoch_bits) | |
136 }; | |
137 | |
138 #ifdef _WIN64 | |
139 // These values are too big for Win64 | |
140 const static uintptr_t hash_mask = right_n_bits(hash_bits); | |
141 const static uintptr_t hash_mask_in_place = | |
142 (address_word)hash_mask << hash_shift; | |
143 #endif | |
144 | |
145 enum { locked_value = 0, | |
146 unlocked_value = 1, | |
147 monitor_value = 2, | |
148 marked_value = 3, | |
149 biased_lock_pattern = 5 | |
150 }; | |
151 | |
152 enum { no_hash = 0 }; // no hash value assigned | |
153 | |
154 enum { no_hash_in_place = (address_word)no_hash << hash_shift, | |
155 no_lock_in_place = unlocked_value | |
156 }; | |
157 | |
158 enum { max_age = age_mask }; | |
159 | |
160 enum { max_bias_epoch = epoch_mask }; | |
161 | |
162 // Biased Locking accessors. | |
163 // These must be checked by all code which calls into the | |
164 // ObjectSynchronizer and other code. The biasing is not understood | |
165 // by the lower-level CAS-based locking code, although the runtime | |
166 // fixes up biased locks to be compatible with it when a bias is | |
167 // revoked. | |
168 bool has_bias_pattern() const { | |
169 return (mask_bits(value(), biased_lock_mask_in_place) == biased_lock_pattern); | |
170 } | |
171 JavaThread* biased_locker() const { | |
172 assert(has_bias_pattern(), "should not call this otherwise"); | |
173 return (JavaThread*) ((intptr_t) (mask_bits(value(), ~(biased_lock_mask_in_place | age_mask_in_place | epoch_mask_in_place)))); | |
174 } | |
175 // Indicates that the mark has the bias bit set but that it has not | |
176 // yet been biased toward a particular thread | |
177 bool is_biased_anonymously() const { | |
178 return (has_bias_pattern() && (biased_locker() == NULL)); | |
179 } | |
180 // Indicates epoch in which this bias was acquired. If the epoch | |
181 // changes due to too many bias revocations occurring, the biases | |
182 // from the previous epochs are all considered invalid. | |
183 int bias_epoch() const { | |
184 assert(has_bias_pattern(), "should not call this otherwise"); | |
185 return (mask_bits(value(), epoch_mask_in_place) >> epoch_shift); | |
186 } | |
187 markOop set_bias_epoch(int epoch) { | |
188 assert(has_bias_pattern(), "should not call this otherwise"); | |
189 assert((epoch & (~epoch_mask)) == 0, "epoch overflow"); | |
190 return markOop(mask_bits(value(), ~epoch_mask_in_place) | (epoch << epoch_shift)); | |
191 } | |
192 markOop incr_bias_epoch() { | |
193 return set_bias_epoch((1 + bias_epoch()) & epoch_mask); | |
194 } | |
195 // Prototype mark for initialization | |
196 static markOop biased_locking_prototype() { | |
197 return markOop( biased_lock_pattern ); | |
198 } | |
199 | |
200 // lock accessors (note that these assume lock_shift == 0) | |
201 bool is_locked() const { | |
202 return (mask_bits(value(), lock_mask_in_place) != unlocked_value); | |
203 } | |
204 bool is_unlocked() const { | |
205 return (mask_bits(value(), biased_lock_mask_in_place) == unlocked_value); | |
206 } | |
207 bool is_marked() const { | |
208 return (mask_bits(value(), lock_mask_in_place) == marked_value); | |
209 } | |
210 bool is_neutral() const { return (mask_bits(value(), biased_lock_mask_in_place) == unlocked_value); } | |
211 | |
212 // Special temporary state of the markOop while being inflated. | |
213 // Code that looks at mark outside a lock need to take this into account. | |
214 bool is_being_inflated() const { return (value() == 0); } | |
215 | |
216 // Distinguished markword value - used when inflating over | |
217 // an existing stacklock. 0 indicates the markword is "BUSY". | |
218 // Lockword mutators that use a LD...CAS idiom should always | |
219 // check for and avoid overwriting a 0 value installed by some | |
220 // other thread. (They should spin or block instead. The 0 value | |
221 // is transient and *should* be short-lived). | |
222 static markOop INFLATING() { return (markOop) 0; } // inflate-in-progress | |
223 | |
224 // Should this header be preserved during GC? | |
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225 inline bool must_be_preserved(oop obj_containing_mark) const; |
0 | 226 inline bool must_be_preserved_with_bias(oop obj_containing_mark) const; |
227 | |
228 // Should this header (including its age bits) be preserved in the | |
229 // case of a promotion failure during scavenge? | |
230 // Note that we special case this situation. We want to avoid | |
231 // calling BiasedLocking::preserve_marks()/restore_marks() (which | |
232 // decrease the number of mark words that need to be preserved | |
233 // during GC) during each scavenge. During scavenges in which there | |
234 // is no promotion failure, we actually don't need to call the above | |
235 // routines at all, since we don't mutate and re-initialize the | |
236 // marks of promoted objects using init_mark(). However, during | |
237 // scavenges which result in promotion failure, we do re-initialize | |
238 // the mark words of objects, meaning that we should have called | |
239 // these mark word preservation routines. Currently there's no good | |
240 // place in which to call them in any of the scavengers (although | |
241 // guarded by appropriate locks we could make one), but the | |
242 // observation is that promotion failures are quite rare and | |
243 // reducing the number of mark words preserved during them isn't a | |
244 // high priority. | |
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245 inline bool must_be_preserved_for_promotion_failure(oop obj_containing_mark) const; |
0 | 246 inline bool must_be_preserved_with_bias_for_promotion_failure(oop obj_containing_mark) const; |
247 | |
248 // Should this header be preserved during a scavenge where CMS is | |
249 // the old generation? | |
250 // (This is basically the same body as must_be_preserved_for_promotion_failure(), | |
251 // but takes the klassOop as argument instead) | |
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252 inline bool must_be_preserved_for_cms_scavenge(klassOop klass_of_obj_containing_mark) const; |
0 | 253 inline bool must_be_preserved_with_bias_for_cms_scavenge(klassOop klass_of_obj_containing_mark) const; |
254 | |
255 // WARNING: The following routines are used EXCLUSIVELY by | |
256 // synchronization functions. They are not really gc safe. | |
257 // They must get updated if markOop layout get changed. | |
258 markOop set_unlocked() const { | |
259 return markOop(value() | unlocked_value); | |
260 } | |
261 bool has_locker() const { | |
262 return ((value() & lock_mask_in_place) == locked_value); | |
263 } | |
264 BasicLock* locker() const { | |
265 assert(has_locker(), "check"); | |
266 return (BasicLock*) value(); | |
267 } | |
268 bool has_monitor() const { | |
269 return ((value() & monitor_value) != 0); | |
270 } | |
271 ObjectMonitor* monitor() const { | |
272 assert(has_monitor(), "check"); | |
273 // Use xor instead of &~ to provide one extra tag-bit check. | |
274 return (ObjectMonitor*) (value() ^ monitor_value); | |
275 } | |
276 bool has_displaced_mark_helper() const { | |
277 return ((value() & unlocked_value) == 0); | |
278 } | |
279 markOop displaced_mark_helper() const { | |
280 assert(has_displaced_mark_helper(), "check"); | |
281 intptr_t ptr = (value() & ~monitor_value); | |
282 return *(markOop*)ptr; | |
283 } | |
284 void set_displaced_mark_helper(markOop m) const { | |
285 assert(has_displaced_mark_helper(), "check"); | |
286 intptr_t ptr = (value() & ~monitor_value); | |
287 *(markOop*)ptr = m; | |
288 } | |
289 markOop copy_set_hash(intptr_t hash) const { | |
290 intptr_t tmp = value() & (~hash_mask_in_place); | |
291 tmp |= ((hash & hash_mask) << hash_shift); | |
292 return (markOop)tmp; | |
293 } | |
294 // it is only used to be stored into BasicLock as the | |
295 // indicator that the lock is using heavyweight monitor | |
296 static markOop unused_mark() { | |
297 return (markOop) marked_value; | |
298 } | |
299 // the following two functions create the markOop to be | |
300 // stored into object header, it encodes monitor info | |
301 static markOop encode(BasicLock* lock) { | |
302 return (markOop) lock; | |
303 } | |
304 static markOop encode(ObjectMonitor* monitor) { | |
305 intptr_t tmp = (intptr_t) monitor; | |
306 return (markOop) (tmp | monitor_value); | |
307 } | |
308 static markOop encode(JavaThread* thread, int age, int bias_epoch) { | |
309 intptr_t tmp = (intptr_t) thread; | |
310 assert(UseBiasedLocking && ((tmp & (epoch_mask_in_place | age_mask_in_place | biased_lock_mask_in_place)) == 0), "misaligned JavaThread pointer"); | |
311 assert(age <= max_age, "age too large"); | |
312 assert(bias_epoch <= max_bias_epoch, "bias epoch too large"); | |
313 return (markOop) (tmp | (bias_epoch << epoch_shift) | (age << age_shift) | biased_lock_pattern); | |
314 } | |
315 | |
316 // used to encode pointers during GC | |
317 markOop clear_lock_bits() { return markOop(value() & ~lock_mask_in_place); } | |
318 | |
319 // age operations | |
320 markOop set_marked() { return markOop((value() & ~lock_mask_in_place) | marked_value); } | |
321 | |
322 int age() const { return mask_bits(value() >> age_shift, age_mask); } | |
323 markOop set_age(int v) const { | |
324 assert((v & ~age_mask) == 0, "shouldn't overflow age field"); | |
325 return markOop((value() & ~age_mask_in_place) | (((intptr_t)v & age_mask) << age_shift)); | |
326 } | |
327 markOop incr_age() const { return age() == max_age ? markOop(this) : set_age(age() + 1); } | |
328 | |
329 // hash operations | |
330 intptr_t hash() const { | |
331 return mask_bits(value() >> hash_shift, hash_mask); | |
332 } | |
333 | |
334 bool has_no_hash() const { | |
335 return hash() == no_hash; | |
336 } | |
337 | |
338 // Prototype mark for initialization | |
339 static markOop prototype() { | |
340 return markOop( no_hash_in_place | no_lock_in_place ); | |
341 } | |
342 | |
343 // Helper function for restoration of unmarked mark oops during GC | |
344 static inline markOop prototype_for_object(oop obj); | |
345 | |
346 // Debugging | |
347 void print_on(outputStream* st) const; | |
348 | |
349 // Prepare address of oop for placement into mark | |
350 inline static markOop encode_pointer_as_mark(void* p) { return markOop(p)->set_marked(); } | |
351 | |
352 // Recover address of oop from encoded form used in mark | |
353 inline void* decode_pointer() { if (UseBiasedLocking && has_bias_pattern()) return NULL; return clear_lock_bits(); } | |
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354 |
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355 // see the definition in markOop.cpp for the gory details |
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356 bool should_not_be_cached() const; |
187 | 357 |
358 // These markOops indicate cms free chunk blocks and not objects. | |
359 // In 64 bit, the markOop is set to distinguish them from oops. | |
360 // These are defined in 32 bit mode for vmStructs. | |
361 const static uintptr_t cms_free_chunk_pattern = 0x1; | |
362 | |
363 // Constants for the size field. | |
364 enum { size_shift = cms_shift + cms_bits, | |
365 size_bits = 35 // need for compressed oops 32G | |
366 }; | |
367 // These values are too big for Win64 | |
368 const static uintptr_t size_mask = LP64_ONLY(right_n_bits(size_bits)) | |
369 NOT_LP64(0); | |
370 const static uintptr_t size_mask_in_place = | |
371 (address_word)size_mask << size_shift; | |
372 | |
373 #ifdef _LP64 | |
374 static markOop cms_free_prototype() { | |
375 return markOop(((intptr_t)prototype() & ~cms_mask_in_place) | | |
376 ((cms_free_chunk_pattern & cms_mask) << cms_shift)); | |
377 } | |
378 uintptr_t cms_encoding() const { | |
379 return mask_bits(value() >> cms_shift, cms_mask); | |
380 } | |
381 bool is_cms_free_chunk() const { | |
382 return is_neutral() && | |
383 (cms_encoding() & cms_free_chunk_pattern) == cms_free_chunk_pattern; | |
384 } | |
385 | |
386 size_t get_size() const { return (size_t)(value() >> size_shift); } | |
387 static markOop set_size_and_free(size_t size) { | |
388 assert((size & ~size_mask) == 0, "shouldn't overflow size field"); | |
389 return markOop(((intptr_t)cms_free_prototype() & ~size_mask_in_place) | | |
390 (((intptr_t)size & size_mask) << size_shift)); | |
391 } | |
392 #endif // _LP64 | |
0 | 393 }; |