1 /* 2 * Copyright (c) 1997, 2010, Oracle and/or its affiliates. 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 * 23 */ 24 25 #ifndef SHARE_VM_OOPS_MARKOOP_HPP 26 #define SHARE_VM_OOPS_MARKOOP_HPP 27 28 #include "oops/oop.hpp" 29 30 // The markOop describes the header of an object. 31 // 32 // Note that the mark is not a real oop but just a word. 33 // It is placed in the oop hierarchy for historical reasons. 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 markOopDesc: public oopDesc { 105 private: 106 // Conversion 107 uintptr_t value() const { return (uintptr_t) this; } 108 109 public: 110 // Constants 111 enum { age_bits = 4, 112 lock_bits = 2, 113 biased_lock_bits = 1, 114 max_hash_bits = BitsPerWord - age_bits - lock_bits - biased_lock_bits, 115 hash_bits = max_hash_bits > 31 ? 31 : max_hash_bits, 116 cms_bits = LP64_ONLY(1) NOT_LP64(0), 117 epoch_bits = 2 118 }; 119 120 // The biased locking code currently requires that the age bits be 121 // contiguous to the lock bits. Class data sharing would prefer the 122 // hash bits to be lower down to provide more random hash codes for 123 // shared read-only symbolOop objects, because these objects' mark 124 // words are set to their own address with marked_value in the lock 125 // bit, and using lower bits would make their identity hash values 126 // more random. However, the performance decision was made in favor 127 // of the biased locking code. 128 129 enum { lock_shift = 0, 130 biased_lock_shift = lock_bits, 131 age_shift = lock_bits + biased_lock_bits, 132 cms_shift = age_shift + age_bits, 133 hash_shift = cms_shift + cms_bits, 134 epoch_shift = hash_shift 135 }; 136 137 enum { lock_mask = right_n_bits(lock_bits), 138 lock_mask_in_place = lock_mask << lock_shift, 139 biased_lock_mask = right_n_bits(lock_bits + biased_lock_bits), 140 biased_lock_mask_in_place= biased_lock_mask << lock_shift, 141 biased_lock_bit_in_place = 1 << biased_lock_shift, 142 age_mask = right_n_bits(age_bits), 143 age_mask_in_place = age_mask << age_shift, 144 epoch_mask = right_n_bits(epoch_bits), 145 epoch_mask_in_place = epoch_mask << epoch_shift, 146 cms_mask = right_n_bits(cms_bits), 147 cms_mask_in_place = cms_mask << cms_shift 148 #ifndef _WIN64 149 ,hash_mask = right_n_bits(hash_bits), 150 hash_mask_in_place = (address_word)hash_mask << hash_shift 151 #endif 152 }; 153 154 // Alignment of JavaThread pointers encoded in object header required by biased locking 155 enum { biased_lock_alignment = 2 << (epoch_shift + epoch_bits) 156 }; 157 158 #ifdef _WIN64 159 // These values are too big for Win64 160 const static uintptr_t hash_mask = right_n_bits(hash_bits); 161 const static uintptr_t hash_mask_in_place = 162 (address_word)hash_mask << hash_shift; 163 #endif 164 165 enum { locked_value = 0, 166 unlocked_value = 1, 167 monitor_value = 2, 168 marked_value = 3, 169 biased_lock_pattern = 5 170 }; 171 172 enum { no_hash = 0 }; // no hash value assigned 173 174 enum { no_hash_in_place = (address_word)no_hash << hash_shift, 175 no_lock_in_place = unlocked_value 176 }; 177 178 enum { max_age = age_mask }; 179 180 enum { max_bias_epoch = epoch_mask }; 181 182 // Biased Locking accessors. 183 // These must be checked by all code which calls into the 184 // ObjectSynchronizer and other code. The biasing is not understood 185 // by the lower-level CAS-based locking code, although the runtime 186 // fixes up biased locks to be compatible with it when a bias is 187 // revoked. 188 bool has_bias_pattern() const { 189 return (mask_bits(value(), biased_lock_mask_in_place) == biased_lock_pattern); 190 } 191 JavaThread* biased_locker() const { 192 assert(has_bias_pattern(), "should not call this otherwise"); 193 return (JavaThread*) ((intptr_t) (mask_bits(value(), ~(biased_lock_mask_in_place | age_mask_in_place | epoch_mask_in_place)))); 194 } 195 // Indicates that the mark has the bias bit set but that it has not 196 // yet been biased toward a particular thread 197 bool is_biased_anonymously() const { 198 return (has_bias_pattern() && (biased_locker() == NULL)); 199 } 200 // Indicates epoch in which this bias was acquired. If the epoch 201 // changes due to too many bias revocations occurring, the biases 202 // from the previous epochs are all considered invalid. 203 int bias_epoch() const { 204 assert(has_bias_pattern(), "should not call this otherwise"); 205 return (mask_bits(value(), epoch_mask_in_place) >> epoch_shift); 206 } 207 markOop set_bias_epoch(int epoch) { 208 assert(has_bias_pattern(), "should not call this otherwise"); 209 assert((epoch & (~epoch_mask)) == 0, "epoch overflow"); 210 return markOop(mask_bits(value(), ~epoch_mask_in_place) | (epoch << epoch_shift)); 211 } 212 markOop incr_bias_epoch() { 213 return set_bias_epoch((1 + bias_epoch()) & epoch_mask); 214 } 215 // Prototype mark for initialization 216 static markOop biased_locking_prototype() { 217 return markOop( biased_lock_pattern ); 218 } 219 220 // lock accessors (note that these assume lock_shift == 0) 221 bool is_locked() const { 222 return (mask_bits(value(), lock_mask_in_place) != unlocked_value); 223 } 224 bool is_unlocked() const { 225 return (mask_bits(value(), biased_lock_mask_in_place) == unlocked_value); 226 } 227 bool is_marked() const { 228 return (mask_bits(value(), lock_mask_in_place) == marked_value); 229 } 230 bool is_neutral() const { return (mask_bits(value(), biased_lock_mask_in_place) == unlocked_value); } 231 232 // Special temporary state of the markOop while being inflated. 233 // Code that looks at mark outside a lock need to take this into account. 234 bool is_being_inflated() const { return (value() == 0); } 235 236 // Distinguished markword value - used when inflating over 237 // an existing stacklock. 0 indicates the markword is "BUSY". 238 // Lockword mutators that use a LD...CAS idiom should always 239 // check for and avoid overwriting a 0 value installed by some 240 // other thread. (They should spin or block instead. The 0 value 241 // is transient and *should* be short-lived). 242 static markOop INFLATING() { return (markOop) 0; } // inflate-in-progress 243 244 // Should this header be preserved during GC? 245 inline bool must_be_preserved(oop obj_containing_mark) const; 246 inline bool must_be_preserved_with_bias(oop obj_containing_mark) const; 247 248 // Should this header (including its age bits) be preserved in the 249 // case of a promotion failure during scavenge? 250 // Note that we special case this situation. We want to avoid 251 // calling BiasedLocking::preserve_marks()/restore_marks() (which 252 // decrease the number of mark words that need to be preserved 253 // during GC) during each scavenge. During scavenges in which there 254 // is no promotion failure, we actually don't need to call the above 255 // routines at all, since we don't mutate and re-initialize the 256 // marks of promoted objects using init_mark(). However, during 257 // scavenges which result in promotion failure, we do re-initialize 258 // the mark words of objects, meaning that we should have called 259 // these mark word preservation routines. Currently there's no good 260 // place in which to call them in any of the scavengers (although 261 // guarded by appropriate locks we could make one), but the 262 // observation is that promotion failures are quite rare and 263 // reducing the number of mark words preserved during them isn't a 264 // high priority. 265 inline bool must_be_preserved_for_promotion_failure(oop obj_containing_mark) const; 266 inline bool must_be_preserved_with_bias_for_promotion_failure(oop obj_containing_mark) const; 267 268 // Should this header be preserved during a scavenge where CMS is 269 // the old generation? 270 // (This is basically the same body as must_be_preserved_for_promotion_failure(), 271 // but takes the klassOop as argument instead) 272 inline bool must_be_preserved_for_cms_scavenge(klassOop klass_of_obj_containing_mark) const; 273 inline bool must_be_preserved_with_bias_for_cms_scavenge(klassOop klass_of_obj_containing_mark) const; 274 275 // WARNING: The following routines are used EXCLUSIVELY by 276 // synchronization functions. They are not really gc safe. 277 // They must get updated if markOop layout get changed. 278 markOop set_unlocked() const { 279 return markOop(value() | unlocked_value); 280 } 281 bool has_locker() const { 282 return ((value() & lock_mask_in_place) == locked_value); 283 } 284 BasicLock* locker() const { 285 assert(has_locker(), "check"); 286 return (BasicLock*) value(); 287 } 288 bool has_monitor() const { 289 return ((value() & monitor_value) != 0); 290 } 291 ObjectMonitor* monitor() const { 292 assert(has_monitor(), "check"); 293 // Use xor instead of &~ to provide one extra tag-bit check. 294 return (ObjectMonitor*) (value() ^ monitor_value); 295 } 296 bool has_displaced_mark_helper() const { 297 return ((value() & unlocked_value) == 0); 298 } 299 markOop displaced_mark_helper() const { 300 assert(has_displaced_mark_helper(), "check"); 301 intptr_t ptr = (value() & ~monitor_value); 302 return *(markOop*)ptr; 303 } 304 void set_displaced_mark_helper(markOop m) const { 305 assert(has_displaced_mark_helper(), "check"); 306 intptr_t ptr = (value() & ~monitor_value); 307 *(markOop*)ptr = m; 308 } 309 markOop copy_set_hash(intptr_t hash) const { 310 intptr_t tmp = value() & (~hash_mask_in_place); 311 tmp |= ((hash & hash_mask) << hash_shift); 312 return (markOop)tmp; 313 } 314 // it is only used to be stored into BasicLock as the 315 // indicator that the lock is using heavyweight monitor 316 static markOop unused_mark() { 317 return (markOop) marked_value; 318 } 319 // the following two functions create the markOop to be 320 // stored into object header, it encodes monitor info 321 static markOop encode(BasicLock* lock) { 322 return (markOop) lock; 323 } 324 static markOop encode(ObjectMonitor* monitor) { 325 intptr_t tmp = (intptr_t) monitor; 326 return (markOop) (tmp | monitor_value); 327 } 328 static markOop encode(JavaThread* thread, int age, int bias_epoch) { 329 intptr_t tmp = (intptr_t) thread; 330 assert(UseBiasedLocking && ((tmp & (epoch_mask_in_place | age_mask_in_place | biased_lock_mask_in_place)) == 0), "misaligned JavaThread pointer"); 331 assert(age <= max_age, "age too large"); 332 assert(bias_epoch <= max_bias_epoch, "bias epoch too large"); 333 return (markOop) (tmp | (bias_epoch << epoch_shift) | (age << age_shift) | biased_lock_pattern); 334 } 335 336 // used to encode pointers during GC 337 markOop clear_lock_bits() { return markOop(value() & ~lock_mask_in_place); } 338 339 // age operations 340 markOop set_marked() { return markOop((value() & ~lock_mask_in_place) | marked_value); } 341 342 int age() const { return mask_bits(value() >> age_shift, age_mask); } 343 markOop set_age(int v) const { 344 assert((v & ~age_mask) == 0, "shouldn't overflow age field"); 345 return markOop((value() & ~age_mask_in_place) | (((intptr_t)v & age_mask) << age_shift)); 346 } 347 markOop incr_age() const { return age() == max_age ? markOop(this) : set_age(age() + 1); } 348 349 // hash operations 350 intptr_t hash() const { 351 return mask_bits(value() >> hash_shift, hash_mask); 352 } 353 354 bool has_no_hash() const { 355 return hash() == no_hash; 356 } 357 358 // Prototype mark for initialization 359 static markOop prototype() { 360 return markOop( no_hash_in_place | no_lock_in_place ); 361 } 362 363 // Helper function for restoration of unmarked mark oops during GC 364 static inline markOop prototype_for_object(oop obj); 365 366 // Debugging 367 void print_on(outputStream* st) const; 368 369 // Prepare address of oop for placement into mark 370 inline static markOop encode_pointer_as_mark(void* p) { return markOop(p)->set_marked(); } 371 372 // Recover address of oop from encoded form used in mark 373 inline void* decode_pointer() { if (UseBiasedLocking && has_bias_pattern()) return NULL; return clear_lock_bits(); } 374 375 // see the definition in markOop.cpp for the gory details 376 bool should_not_be_cached() const; 377 378 // These markOops indicate cms free chunk blocks and not objects. 379 // In 64 bit, the markOop is set to distinguish them from oops. 380 // These are defined in 32 bit mode for vmStructs. 381 const static uintptr_t cms_free_chunk_pattern = 0x1; 382 383 // Constants for the size field. 384 enum { size_shift = cms_shift + cms_bits, 385 size_bits = 35 // need for compressed oops 32G 386 }; 387 // These values are too big for Win64 388 const static uintptr_t size_mask = LP64_ONLY(right_n_bits(size_bits)) 389 NOT_LP64(0); 390 const static uintptr_t size_mask_in_place = 391 (address_word)size_mask << size_shift; 392 393 #ifdef _LP64 394 static markOop cms_free_prototype() { 395 return markOop(((intptr_t)prototype() & ~cms_mask_in_place) | 396 ((cms_free_chunk_pattern & cms_mask) << cms_shift)); 397 } 398 uintptr_t cms_encoding() const { 399 return mask_bits(value() >> cms_shift, cms_mask); 400 } 401 bool is_cms_free_chunk() const { 402 return is_neutral() && 403 (cms_encoding() & cms_free_chunk_pattern) == cms_free_chunk_pattern; 404 } 405 406 size_t get_size() const { return (size_t)(value() >> size_shift); } 407 static markOop set_size_and_free(size_t size) { 408 assert((size & ~size_mask) == 0, "shouldn't overflow size field"); 409 return markOop(((intptr_t)cms_free_prototype() & ~size_mask_in_place) | 410 (((intptr_t)size & size_mask) << size_shift)); 411 } 412 #endif // _LP64 413 }; 414 415 #endif // SHARE_VM_OOPS_MARKOOP_HPP