1 /* 2 * Copyright (c) 1997, 2019, 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_OOPS_MARKOOP_HPP 26 #define SHARE_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. 122 enum { lock_shift = 0, 123 biased_lock_shift = lock_bits, 124 age_shift = lock_bits + biased_lock_bits, 125 cms_shift = age_shift + age_bits, 126 hash_shift = cms_shift + cms_bits, 127 epoch_shift = hash_shift 128 }; 129 130 enum { lock_mask = right_n_bits(lock_bits), 131 lock_mask_in_place = lock_mask << lock_shift, 132 biased_lock_mask = right_n_bits(lock_bits + biased_lock_bits), 133 biased_lock_mask_in_place= biased_lock_mask << lock_shift, 134 biased_lock_bit_in_place = 1 << biased_lock_shift, 135 age_mask = right_n_bits(age_bits), 136 age_mask_in_place = age_mask << age_shift, 137 epoch_mask = right_n_bits(epoch_bits), 138 epoch_mask_in_place = epoch_mask << epoch_shift, 139 cms_mask = right_n_bits(cms_bits), 140 cms_mask_in_place = cms_mask << cms_shift 141 }; 142 143 const static uintptr_t hash_mask = right_n_bits(hash_bits); 144 const static uintptr_t hash_mask_in_place = hash_mask << hash_shift; 145 146 // Alignment of JavaThread pointers encoded in object header required by biased locking 147 enum { biased_lock_alignment = 2 << (epoch_shift + epoch_bits) 148 }; 149 150 enum { locked_value = 0, 151 unlocked_value = 1, 152 monitor_value = 2, 153 marked_value = 3, 154 biased_lock_pattern = 5 155 }; 156 157 enum { no_hash = 0 }; // no hash value assigned 158 159 enum { no_hash_in_place = (address_word)no_hash << hash_shift, 160 no_lock_in_place = unlocked_value 161 }; 162 163 enum { max_age = age_mask }; 164 165 enum { max_bias_epoch = epoch_mask }; 166 167 // Biased Locking accessors. 168 // These must be checked by all code which calls into the 169 // ObjectSynchronizer and other code. The biasing is not understood 170 // by the lower-level CAS-based locking code, although the runtime 171 // fixes up biased locks to be compatible with it when a bias is 172 // revoked. 173 bool has_bias_pattern() const { 174 return (mask_bits(value(), biased_lock_mask_in_place) == biased_lock_pattern); 175 } 176 JavaThread* biased_locker() const { 177 assert(has_bias_pattern(), "should not call this otherwise"); 178 return (JavaThread*) ((intptr_t) (mask_bits(value(), ~(biased_lock_mask_in_place | age_mask_in_place | epoch_mask_in_place)))); 179 } 180 // Indicates that the mark has the bias bit set but that it has not 181 // yet been biased toward a particular thread 182 bool is_biased_anonymously() const { 183 return (has_bias_pattern() && (biased_locker() == NULL)); 184 } 185 // Indicates epoch in which this bias was acquired. If the epoch 186 // changes due to too many bias revocations occurring, the biases 187 // from the previous epochs are all considered invalid. 188 int bias_epoch() const { 189 assert(has_bias_pattern(), "should not call this otherwise"); 190 return (mask_bits(value(), epoch_mask_in_place) >> epoch_shift); 191 } 192 markOop set_bias_epoch(int epoch) { 193 assert(has_bias_pattern(), "should not call this otherwise"); 194 assert((epoch & (~epoch_mask)) == 0, "epoch overflow"); 195 return markOop(mask_bits(value(), ~epoch_mask_in_place) | (epoch << epoch_shift)); 196 } 197 markOop incr_bias_epoch() { 198 return set_bias_epoch((1 + bias_epoch()) & epoch_mask); 199 } 200 // Prototype mark for initialization 201 static markOop biased_locking_prototype() { 202 return markOop( biased_lock_pattern ); 203 } 204 205 // lock accessors (note that these assume lock_shift == 0) 206 bool is_locked() const { 207 return (mask_bits(value(), lock_mask_in_place) != unlocked_value); 208 } 209 bool is_unlocked() const { 210 return (mask_bits(value(), biased_lock_mask_in_place) == unlocked_value); 211 } 212 // ObjectMonitor::install_displaced_markword_in_object() uses 213 // is_marked() on ObjectMonitor::_header as part of the restoration 214 // protocol for an object's header. In this usage, the mark bits are 215 // only ever set (and cleared) on the ObjectMonitor::_header field. 216 bool is_marked() const { 217 return (mask_bits(value(), lock_mask_in_place) == marked_value); 218 } 219 bool is_neutral() const { return (mask_bits(value(), biased_lock_mask_in_place) == unlocked_value); } 220 221 // Special temporary state of the markOop while being inflated. 222 // Code that looks at mark outside a lock need to take this into account. 223 bool is_being_inflated() const { return (value() == 0); } 224 225 // Distinguished markword value - used when inflating over 226 // an existing stacklock. 0 indicates the markword is "BUSY". 227 // Lockword mutators that use a LD...CAS idiom should always 228 // check for and avoid overwriting a 0 value installed by some 229 // other thread. (They should spin or block instead. The 0 value 230 // is transient and *should* be short-lived). 231 static markOop INFLATING() { return (markOop) 0; } // inflate-in-progress 232 233 // Should this header be preserved during GC? 234 inline bool must_be_preserved(oop obj_containing_mark) const; 235 inline bool must_be_preserved_with_bias(oop obj_containing_mark) const; 236 237 // Should this header (including its age bits) be preserved in the 238 // case of a promotion failure during scavenge? 239 // Note that we special case this situation. We want to avoid 240 // calling BiasedLocking::preserve_marks()/restore_marks() (which 241 // decrease the number of mark words that need to be preserved 242 // during GC) during each scavenge. During scavenges in which there 243 // is no promotion failure, we actually don't need to call the above 244 // routines at all, since we don't mutate and re-initialize the 245 // marks of promoted objects using init_mark(). However, during 246 // scavenges which result in promotion failure, we do re-initialize 247 // the mark words of objects, meaning that we should have called 248 // these mark word preservation routines. Currently there's no good 249 // place in which to call them in any of the scavengers (although 250 // guarded by appropriate locks we could make one), but the 251 // observation is that promotion failures are quite rare and 252 // reducing the number of mark words preserved during them isn't a 253 // high priority. 254 inline bool must_be_preserved_for_promotion_failure(oop obj_containing_mark) const; 255 inline bool must_be_preserved_with_bias_for_promotion_failure(oop obj_containing_mark) const; 256 257 // Should this header be preserved during a scavenge where CMS is 258 // the old generation? 259 // (This is basically the same body as must_be_preserved_for_promotion_failure(), 260 // but takes the Klass* as argument instead) 261 inline bool must_be_preserved_for_cms_scavenge(Klass* klass_of_obj_containing_mark) const; 262 inline bool must_be_preserved_with_bias_for_cms_scavenge(Klass* klass_of_obj_containing_mark) const; 263 264 // WARNING: The following routines are used EXCLUSIVELY by 265 // synchronization functions. They are not really gc safe. 266 // They must get updated if markOop layout get changed. 267 markOop set_unlocked() const { 268 return markOop(value() | unlocked_value); 269 } 270 bool has_locker() const { 271 return ((value() & lock_mask_in_place) == locked_value); 272 } 273 BasicLock* locker() const { 274 assert(has_locker(), "check"); 275 return (BasicLock*) value(); 276 } 277 bool has_monitor() const { 278 return ((value() & monitor_value) != 0); 279 } 280 ObjectMonitor* monitor() const { 281 assert(has_monitor(), "check"); 282 // Use xor instead of &~ to provide one extra tag-bit check. 283 return (ObjectMonitor*) (value() ^ monitor_value); 284 } 285 bool has_displaced_mark_helper() const { 286 return ((value() & unlocked_value) == 0); 287 } 288 markOop displaced_mark_helper() const { 289 assert(has_displaced_mark_helper(), "check"); 290 intptr_t ptr = (value() & ~monitor_value); 291 return *(markOop*)ptr; 292 } 293 void set_displaced_mark_helper(markOop m) const { 294 assert(has_displaced_mark_helper(), "check"); 295 intptr_t ptr = (value() & ~monitor_value); 296 *(markOop*)ptr = m; 297 } 298 markOop copy_set_hash(intptr_t hash) const { 299 intptr_t tmp = value() & (~hash_mask_in_place); 300 tmp |= ((hash & hash_mask) << hash_shift); 301 return (markOop)tmp; 302 } 303 // it is only used to be stored into BasicLock as the 304 // indicator that the lock is using heavyweight monitor 305 static markOop unused_mark() { 306 return (markOop) marked_value; 307 } 308 // the following two functions create the markOop to be 309 // stored into object header, it encodes monitor info 310 static markOop encode(BasicLock* lock) { 311 return (markOop) lock; 312 } 313 static markOop encode(ObjectMonitor* monitor) { 314 intptr_t tmp = (intptr_t) monitor; 315 return (markOop) (tmp | monitor_value); 316 } 317 static markOop encode(JavaThread* thread, uint age, int bias_epoch) { 318 intptr_t tmp = (intptr_t) thread; 319 assert(UseBiasedLocking && ((tmp & (epoch_mask_in_place | age_mask_in_place | biased_lock_mask_in_place)) == 0), "misaligned JavaThread pointer"); 320 assert(age <= max_age, "age too large"); 321 assert(bias_epoch <= max_bias_epoch, "bias epoch too large"); 322 return (markOop) (tmp | (bias_epoch << epoch_shift) | (age << age_shift) | biased_lock_pattern); 323 } 324 325 // used to encode pointers during GC 326 markOop clear_lock_bits() { return markOop(value() & ~lock_mask_in_place); } 327 328 // age operations 329 markOop set_marked() { return markOop((value() & ~lock_mask_in_place) | marked_value); } 330 markOop set_unmarked() { return markOop((value() & ~lock_mask_in_place) | unlocked_value); } 331 332 uint age() const { return mask_bits(value() >> age_shift, age_mask); } 333 markOop set_age(uint v) const { 334 assert((v & ~age_mask) == 0, "shouldn't overflow age field"); 335 return markOop((value() & ~age_mask_in_place) | (((uintptr_t)v & age_mask) << age_shift)); 336 } 337 markOop incr_age() const { return age() == max_age ? markOop(this) : set_age(age() + 1); } 338 339 // hash operations 340 intptr_t hash() const { 341 return mask_bits(value() >> hash_shift, hash_mask); 342 } 343 344 bool has_no_hash() const { 345 return hash() == no_hash; 346 } 347 348 // Prototype mark for initialization 349 static markOop prototype() { 350 return markOop( no_hash_in_place | no_lock_in_place ); 351 } 352 353 // Helper function for restoration of unmarked mark oops during GC 354 static inline markOop prototype_for_object(oop obj); 355 356 // Debugging 357 void print_on(outputStream* st) const; 358 359 // Prepare address of oop for placement into mark 360 inline static markOop encode_pointer_as_mark(void* p) { return markOop(p)->set_marked(); } 361 362 // Recover address of oop from encoded form used in mark 363 inline void* decode_pointer() { if (UseBiasedLocking && has_bias_pattern()) return NULL; return clear_lock_bits(); } 364 365 // These markOops indicate cms free chunk blocks and not objects. 366 // In 64 bit, the markOop is set to distinguish them from oops. 367 // These are defined in 32 bit mode for vmStructs. 368 const static uintptr_t cms_free_chunk_pattern = 0x1; 369 370 // Constants for the size field. 371 enum { size_shift = cms_shift + cms_bits, 372 size_bits = 35 // need for compressed oops 32G 373 }; 374 // These values are too big for Win64 375 const static uintptr_t size_mask = LP64_ONLY(right_n_bits(size_bits)) 376 NOT_LP64(0); 377 const static uintptr_t size_mask_in_place = 378 (address_word)size_mask << size_shift; 379 380 #ifdef _LP64 381 static markOop cms_free_prototype() { 382 return markOop(((intptr_t)prototype() & ~cms_mask_in_place) | 383 ((cms_free_chunk_pattern & cms_mask) << cms_shift)); 384 } 385 uintptr_t cms_encoding() const { 386 return mask_bits(value() >> cms_shift, cms_mask); 387 } 388 bool is_cms_free_chunk() const { 389 return is_neutral() && 390 (cms_encoding() & cms_free_chunk_pattern) == cms_free_chunk_pattern; 391 } 392 393 size_t get_size() const { return (size_t)(value() >> size_shift); } 394 static markOop set_size_and_free(size_t size) { 395 assert((size & ~size_mask) == 0, "shouldn't overflow size field"); 396 return markOop(((intptr_t)cms_free_prototype() & ~size_mask_in_place) | 397 (((intptr_t)size & size_mask) << size_shift)); 398 } 399 #endif // _LP64 400 }; 401 402 #endif // SHARE_OOPS_MARKOOP_HPP