Mercurial > hg > truffle
annotate src/share/vm/oops/markOop.hpp @ 113:ba764ed4b6f2
6420645: Create a vm that uses compressed oops for up to 32gb heapsizes
Summary: Compressed oops in instances, arrays, and headers. Code contributors are coleenp, phh, never, swamyv
Reviewed-by: jmasa, kamg, acorn, tbell, kvn, rasbold
| author | coleenp |
|---|---|
| date | Sun, 13 Apr 2008 17:43:42 -0400 |
| parents | d8b3ef7ee3e5 |
| children | 790e66e5fbac 37f87013dfd8 |
| rev | line source |
|---|---|
| 0 | 1 /* |
| 2 * Copyright 1997-2006 Sun Microsystems, Inc. All Rights Reserved. | |
| 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 // | |
| 32 // | |
| 33 // unused:0/25 hash:25/31 age:4 biased_lock:1 lock:2 = 32/64 bits | |
| 34 // | |
| 35 // - hash contains the identity hash value: largest value is | |
| 36 // 31 bits, see os::random(). Also, 64-bit vm's require | |
| 37 // a hash value no bigger than 32 bits because they will not | |
| 38 // properly generate a mask larger than that: see library_call.cpp | |
| 39 // and c1_CodePatterns_sparc.cpp. | |
| 40 // | |
| 41 // - the biased lock pattern is used to bias a lock toward a given | |
| 42 // thread. When this pattern is set in the low three bits, the lock | |
| 43 // is either biased toward a given thread or "anonymously" biased, | |
| 44 // indicating that it is possible for it to be biased. When the | |
| 45 // lock is biased toward a given thread, locking and unlocking can | |
| 46 // be performed by that thread without using atomic operations. | |
| 47 // When a lock's bias is revoked, it reverts back to the normal | |
| 48 // locking scheme described below. | |
| 49 // | |
| 50 // Note that we are overloading the meaning of the "unlocked" state | |
| 51 // of the header. Because we steal a bit from the age we can | |
| 52 // guarantee that the bias pattern will never be seen for a truly | |
| 53 // unlocked object. | |
| 54 // | |
| 55 // Note also that the biased state contains the age bits normally | |
| 56 // contained in the object header. Large increases in scavenge | |
| 57 // times were seen when these bits were absent and an arbitrary age | |
| 58 // assigned to all biased objects, because they tended to consume a | |
| 59 // significant fraction of the eden semispaces and were not | |
| 60 // promoted promptly, causing an increase in the amount of copying | |
| 61 // performed. The runtime system aligns all JavaThread* pointers to | |
| 62 // a very large value (currently 128 bytes) to make room for the | |
| 63 // age bits when biased locking is enabled. | |
| 64 // | |
| 65 // [JavaThread* | epoch | age | 1 | 01] lock is biased toward given thread | |
| 66 // [0 | epoch | age | 1 | 01] lock is anonymously biased | |
| 67 // | |
| 68 // - the two lock bits are used to describe three states: locked/unlocked and monitor. | |
| 69 // | |
| 70 // [ptr | 00] locked ptr points to real header on stack | |
| 71 // [header | 0 | 01] unlocked regular object header | |
| 72 // [ptr | 10] monitor inflated lock (header is wapped out) | |
| 73 // [ptr | 11] marked used by markSweep to mark an object | |
| 74 // not valid at any other time | |
| 75 // | |
| 76 // We assume that stack/thread pointers have the lowest two bits cleared. | |
| 77 | |
| 78 class BasicLock; | |
| 79 class ObjectMonitor; | |
| 80 class JavaThread; | |
| 81 | |
| 82 class markOopDesc: public oopDesc { | |
| 83 private: | |
| 84 // Conversion | |
| 85 uintptr_t value() const { return (uintptr_t) this; } | |
| 86 | |
| 87 public: | |
| 88 // Constants | |
| 89 enum { age_bits = 4, | |
| 90 lock_bits = 2, | |
| 91 biased_lock_bits = 1, | |
|
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92 max_hash_bits = BitsPerWord - age_bits - lock_bits - biased_lock_bits, |
| 0 | 93 hash_bits = max_hash_bits > 31 ? 31 : max_hash_bits, |
| 94 epoch_bits = 2 | |
| 95 }; | |
| 96 | |
| 97 // The biased locking code currently requires that the age bits be | |
| 98 // contiguous to the lock bits. Class data sharing would prefer the | |
| 99 // hash bits to be lower down to provide more random hash codes for | |
| 100 // shared read-only symbolOop objects, because these objects' mark | |
| 101 // words are set to their own address with marked_value in the lock | |
| 102 // bit, and using lower bits would make their identity hash values | |
| 103 // more random. However, the performance decision was made in favor | |
| 104 // of the biased locking code. | |
| 105 | |
| 106 enum { lock_shift = 0, | |
| 107 biased_lock_shift = lock_bits, | |
| 108 age_shift = lock_bits + biased_lock_bits, | |
| 109 hash_shift = lock_bits + biased_lock_bits + age_bits, | |
| 110 epoch_shift = hash_shift | |
| 111 }; | |
| 112 | |
| 113 enum { lock_mask = right_n_bits(lock_bits), | |
| 114 lock_mask_in_place = lock_mask << lock_shift, | |
| 115 biased_lock_mask = right_n_bits(lock_bits + biased_lock_bits), | |
| 116 biased_lock_mask_in_place= biased_lock_mask << lock_shift, | |
| 117 biased_lock_bit_in_place = 1 << biased_lock_shift, | |
| 118 age_mask = right_n_bits(age_bits), | |
| 119 age_mask_in_place = age_mask << age_shift, | |
| 120 epoch_mask = right_n_bits(epoch_bits), | |
| 121 epoch_mask_in_place = epoch_mask << epoch_shift | |
| 122 #ifndef _WIN64 | |
| 123 ,hash_mask = right_n_bits(hash_bits), | |
| 124 hash_mask_in_place = (address_word)hash_mask << hash_shift | |
| 125 #endif | |
| 126 }; | |
| 127 | |
| 128 // Alignment of JavaThread pointers encoded in object header required by biased locking | |
| 129 enum { biased_lock_alignment = 2 << (epoch_shift + epoch_bits) | |
| 130 }; | |
| 131 | |
| 132 #ifdef _WIN64 | |
| 133 // These values are too big for Win64 | |
| 134 const static uintptr_t hash_mask = right_n_bits(hash_bits); | |
| 135 const static uintptr_t hash_mask_in_place = | |
| 136 (address_word)hash_mask << hash_shift; | |
| 137 #endif | |
| 138 | |
| 139 enum { locked_value = 0, | |
| 140 unlocked_value = 1, | |
| 141 monitor_value = 2, | |
| 142 marked_value = 3, | |
| 143 biased_lock_pattern = 5 | |
| 144 }; | |
| 145 | |
| 146 enum { no_hash = 0 }; // no hash value assigned | |
| 147 | |
| 148 enum { no_hash_in_place = (address_word)no_hash << hash_shift, | |
| 149 no_lock_in_place = unlocked_value | |
| 150 }; | |
| 151 | |
| 152 enum { max_age = age_mask }; | |
| 153 | |
| 154 enum { max_bias_epoch = epoch_mask }; | |
| 155 | |
| 156 // Biased Locking accessors. | |
| 157 // These must be checked by all code which calls into the | |
| 158 // ObjectSynchronizer and other code. The biasing is not understood | |
| 159 // by the lower-level CAS-based locking code, although the runtime | |
| 160 // fixes up biased locks to be compatible with it when a bias is | |
| 161 // revoked. | |
| 162 bool has_bias_pattern() const { | |
| 163 return (mask_bits(value(), biased_lock_mask_in_place) == biased_lock_pattern); | |
| 164 } | |
| 165 JavaThread* biased_locker() const { | |
| 166 assert(has_bias_pattern(), "should not call this otherwise"); | |
| 167 return (JavaThread*) ((intptr_t) (mask_bits(value(), ~(biased_lock_mask_in_place | age_mask_in_place | epoch_mask_in_place)))); | |
| 168 } | |
| 169 // Indicates that the mark has the bias bit set but that it has not | |
| 170 // yet been biased toward a particular thread | |
| 171 bool is_biased_anonymously() const { | |
| 172 return (has_bias_pattern() && (biased_locker() == NULL)); | |
| 173 } | |
| 174 // Indicates epoch in which this bias was acquired. If the epoch | |
| 175 // changes due to too many bias revocations occurring, the biases | |
| 176 // from the previous epochs are all considered invalid. | |
| 177 int bias_epoch() const { | |
| 178 assert(has_bias_pattern(), "should not call this otherwise"); | |
| 179 return (mask_bits(value(), epoch_mask_in_place) >> epoch_shift); | |
| 180 } | |
| 181 markOop set_bias_epoch(int epoch) { | |
| 182 assert(has_bias_pattern(), "should not call this otherwise"); | |
| 183 assert((epoch & (~epoch_mask)) == 0, "epoch overflow"); | |
| 184 return markOop(mask_bits(value(), ~epoch_mask_in_place) | (epoch << epoch_shift)); | |
| 185 } | |
| 186 markOop incr_bias_epoch() { | |
| 187 return set_bias_epoch((1 + bias_epoch()) & epoch_mask); | |
| 188 } | |
| 189 // Prototype mark for initialization | |
| 190 static markOop biased_locking_prototype() { | |
| 191 return markOop( biased_lock_pattern ); | |
| 192 } | |
| 193 | |
| 194 // lock accessors (note that these assume lock_shift == 0) | |
| 195 bool is_locked() const { | |
| 196 return (mask_bits(value(), lock_mask_in_place) != unlocked_value); | |
| 197 } | |
| 198 bool is_unlocked() const { | |
| 199 return (mask_bits(value(), biased_lock_mask_in_place) == unlocked_value); | |
| 200 } | |
| 201 bool is_marked() const { | |
| 202 return (mask_bits(value(), lock_mask_in_place) == marked_value); | |
| 203 } | |
| 204 bool is_neutral() const { return (mask_bits(value(), biased_lock_mask_in_place) == unlocked_value); } | |
| 205 | |
| 206 // Special temporary state of the markOop while being inflated. | |
| 207 // Code that looks at mark outside a lock need to take this into account. | |
| 208 bool is_being_inflated() const { return (value() == 0); } | |
| 209 | |
| 210 // Distinguished markword value - used when inflating over | |
| 211 // an existing stacklock. 0 indicates the markword is "BUSY". | |
| 212 // Lockword mutators that use a LD...CAS idiom should always | |
| 213 // check for and avoid overwriting a 0 value installed by some | |
| 214 // other thread. (They should spin or block instead. The 0 value | |
| 215 // is transient and *should* be short-lived). | |
| 216 static markOop INFLATING() { return (markOop) 0; } // inflate-in-progress | |
| 217 | |
| 218 // Should this header be preserved during GC? | |
| 219 bool must_be_preserved(oop obj_containing_mark) const { | |
| 220 if (!UseBiasedLocking) | |
| 221 return (!is_unlocked() || !has_no_hash()); | |
| 222 return must_be_preserved_with_bias(obj_containing_mark); | |
| 223 } | |
| 224 inline bool must_be_preserved_with_bias(oop obj_containing_mark) const; | |
| 225 | |
| 226 // Should this header (including its age bits) be preserved in the | |
| 227 // case of a promotion failure during scavenge? | |
| 228 // Note that we special case this situation. We want to avoid | |
| 229 // calling BiasedLocking::preserve_marks()/restore_marks() (which | |
| 230 // decrease the number of mark words that need to be preserved | |
| 231 // during GC) during each scavenge. During scavenges in which there | |
| 232 // is no promotion failure, we actually don't need to call the above | |
| 233 // routines at all, since we don't mutate and re-initialize the | |
| 234 // marks of promoted objects using init_mark(). However, during | |
| 235 // scavenges which result in promotion failure, we do re-initialize | |
| 236 // the mark words of objects, meaning that we should have called | |
| 237 // these mark word preservation routines. Currently there's no good | |
| 238 // place in which to call them in any of the scavengers (although | |
| 239 // guarded by appropriate locks we could make one), but the | |
| 240 // observation is that promotion failures are quite rare and | |
| 241 // reducing the number of mark words preserved during them isn't a | |
| 242 // high priority. | |
| 243 bool must_be_preserved_for_promotion_failure(oop obj_containing_mark) const { | |
| 244 if (!UseBiasedLocking) | |
| 245 return (this != prototype()); | |
| 246 return must_be_preserved_with_bias_for_promotion_failure(obj_containing_mark); | |
| 247 } | |
| 248 inline bool must_be_preserved_with_bias_for_promotion_failure(oop obj_containing_mark) const; | |
| 249 | |
| 250 // Should this header be preserved during a scavenge where CMS is | |
| 251 // the old generation? | |
| 252 // (This is basically the same body as must_be_preserved_for_promotion_failure(), | |
| 253 // but takes the klassOop as argument instead) | |
| 254 bool must_be_preserved_for_cms_scavenge(klassOop klass_of_obj_containing_mark) const { | |
| 255 if (!UseBiasedLocking) | |
| 256 return (this != prototype()); | |
| 257 return must_be_preserved_with_bias_for_cms_scavenge(klass_of_obj_containing_mark); | |
| 258 } | |
| 259 inline bool must_be_preserved_with_bias_for_cms_scavenge(klassOop klass_of_obj_containing_mark) const; | |
| 260 | |
| 261 // WARNING: The following routines are used EXCLUSIVELY by | |
| 262 // synchronization functions. They are not really gc safe. | |
| 263 // They must get updated if markOop layout get changed. | |
| 264 markOop set_unlocked() const { | |
| 265 return markOop(value() | unlocked_value); | |
| 266 } | |
| 267 bool has_locker() const { | |
| 268 return ((value() & lock_mask_in_place) == locked_value); | |
| 269 } | |
| 270 BasicLock* locker() const { | |
| 271 assert(has_locker(), "check"); | |
| 272 return (BasicLock*) value(); | |
| 273 } | |
| 274 bool has_monitor() const { | |
| 275 return ((value() & monitor_value) != 0); | |
| 276 } | |
| 277 ObjectMonitor* monitor() const { | |
| 278 assert(has_monitor(), "check"); | |
| 279 // Use xor instead of &~ to provide one extra tag-bit check. | |
| 280 return (ObjectMonitor*) (value() ^ monitor_value); | |
| 281 } | |
| 282 bool has_displaced_mark_helper() const { | |
| 283 return ((value() & unlocked_value) == 0); | |
| 284 } | |
| 285 markOop displaced_mark_helper() const { | |
| 286 assert(has_displaced_mark_helper(), "check"); | |
| 287 intptr_t ptr = (value() & ~monitor_value); | |
| 288 return *(markOop*)ptr; | |
| 289 } | |
| 290 void set_displaced_mark_helper(markOop m) const { | |
| 291 assert(has_displaced_mark_helper(), "check"); | |
| 292 intptr_t ptr = (value() & ~monitor_value); | |
| 293 *(markOop*)ptr = m; | |
| 294 } | |
| 295 markOop copy_set_hash(intptr_t hash) const { | |
| 296 intptr_t tmp = value() & (~hash_mask_in_place); | |
| 297 tmp |= ((hash & hash_mask) << hash_shift); | |
| 298 return (markOop)tmp; | |
| 299 } | |
| 300 // it is only used to be stored into BasicLock as the | |
| 301 // indicator that the lock is using heavyweight monitor | |
| 302 static markOop unused_mark() { | |
| 303 return (markOop) marked_value; | |
| 304 } | |
| 305 // the following two functions create the markOop to be | |
| 306 // stored into object header, it encodes monitor info | |
| 307 static markOop encode(BasicLock* lock) { | |
| 308 return (markOop) lock; | |
| 309 } | |
| 310 static markOop encode(ObjectMonitor* monitor) { | |
| 311 intptr_t tmp = (intptr_t) monitor; | |
| 312 return (markOop) (tmp | monitor_value); | |
| 313 } | |
| 314 static markOop encode(JavaThread* thread, int age, int bias_epoch) { | |
| 315 intptr_t tmp = (intptr_t) thread; | |
| 316 assert(UseBiasedLocking && ((tmp & (epoch_mask_in_place | age_mask_in_place | biased_lock_mask_in_place)) == 0), "misaligned JavaThread pointer"); | |
| 317 assert(age <= max_age, "age too large"); | |
| 318 assert(bias_epoch <= max_bias_epoch, "bias epoch too large"); | |
| 319 return (markOop) (tmp | (bias_epoch << epoch_shift) | (age << age_shift) | biased_lock_pattern); | |
| 320 } | |
| 321 | |
| 322 // used to encode pointers during GC | |
| 323 markOop clear_lock_bits() { return markOop(value() & ~lock_mask_in_place); } | |
| 324 | |
| 325 // age operations | |
| 326 markOop set_marked() { return markOop((value() & ~lock_mask_in_place) | marked_value); } | |
| 327 | |
| 328 int age() const { return mask_bits(value() >> age_shift, age_mask); } | |
| 329 markOop set_age(int v) const { | |
| 330 assert((v & ~age_mask) == 0, "shouldn't overflow age field"); | |
| 331 return markOop((value() & ~age_mask_in_place) | (((intptr_t)v & age_mask) << age_shift)); | |
| 332 } | |
| 333 markOop incr_age() const { return age() == max_age ? markOop(this) : set_age(age() + 1); } | |
| 334 | |
| 335 // hash operations | |
| 336 intptr_t hash() const { | |
| 337 return mask_bits(value() >> hash_shift, hash_mask); | |
| 338 } | |
| 339 | |
| 340 bool has_no_hash() const { | |
| 341 return hash() == no_hash; | |
| 342 } | |
| 343 | |
| 344 // Prototype mark for initialization | |
| 345 static markOop prototype() { | |
| 346 return markOop( no_hash_in_place | no_lock_in_place ); | |
| 347 } | |
| 348 | |
| 349 // Helper function for restoration of unmarked mark oops during GC | |
| 350 static inline markOop prototype_for_object(oop obj); | |
| 351 | |
| 352 // Debugging | |
| 353 void print_on(outputStream* st) const; | |
| 354 | |
| 355 // Prepare address of oop for placement into mark | |
| 356 inline static markOop encode_pointer_as_mark(void* p) { return markOop(p)->set_marked(); } | |
| 357 | |
| 358 // Recover address of oop from encoded form used in mark | |
| 359 inline void* decode_pointer() { if (UseBiasedLocking && has_bias_pattern()) return NULL; return clear_lock_bits(); } | |
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360 |
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361 // see the definition in markOop.cpp for the gory details |
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362 bool should_not_be_cached() const; |
| 0 | 363 }; |