1 /* 2 * Copyright (c) 1997, 2025, 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_OOP_HPP 26 #define SHARE_OOPS_OOP_HPP 27 28 #include "memory/iterator.hpp" 29 #include "memory/memRegion.hpp" 30 #include "oops/compressedKlass.hpp" 31 #include "oops/accessDecorators.hpp" 32 #include "oops/markWord.hpp" 33 #include "oops/metadata.hpp" 34 #include "oops/objLayout.hpp" 35 #include "runtime/atomic.hpp" 36 #include "utilities/globalDefinitions.hpp" 37 #include "utilities/macros.hpp" 38 #include <type_traits> 39 40 // oopDesc is the top baseclass for objects classes. The {name}Desc classes describe 41 // the format of Java objects so the fields can be accessed from C++. 42 // oopDesc is abstract. 43 // (see oopHierarchy for complete oop class hierarchy) 44 // 45 // no virtual functions allowed 46 47 class oopDesc { 48 friend class VMStructs; 49 friend class JVMCIVMStructs; 50 private: 51 volatile markWord _mark; 52 union _metadata { 53 Klass* _klass; 54 narrowKlass _compressed_klass; 55 } _metadata; 56 57 // There may be ordering constraints on the initialization of fields that 58 // make use of the C++ copy/assign incorrect. 59 NONCOPYABLE(oopDesc); 60 61 inline oop cas_set_forwardee(markWord new_mark, markWord old_mark, atomic_memory_order order); 62 63 public: 64 // Must be trivial; see verifying static assert after the class. 65 oopDesc() = default; 66 67 inline markWord mark() const; 68 inline markWord mark_acquire() const; 69 inline markWord* mark_addr() const; 70 71 inline void set_mark(markWord m); 72 static inline void set_mark(HeapWord* mem, markWord m); 73 inline void set_mark_full(markWord m); 74 static inline void release_set_mark(HeapWord* mem, markWord m); 75 76 inline void release_set_mark(markWord m); 77 inline markWord cas_set_mark(markWord new_mark, markWord old_mark); 78 inline markWord cas_set_mark(markWord new_mark, markWord old_mark, atomic_memory_order order); 79 80 // Returns the prototype mark that should be used for this object. 81 inline markWord prototype_mark() const; 82 83 // Used only to re-initialize the mark word (e.g., of promoted 84 // objects during a GC) -- requires a valid klass pointer 85 inline void init_mark(); 86 87 inline Klass* klass() const; 88 inline Klass* klass_or_null() const; 89 inline Klass* klass_or_null_acquire() const; 90 // Get the klass without running any asserts. 91 inline Klass* klass_without_asserts() const; 92 93 void set_narrow_klass(narrowKlass nk) NOT_CDS_JAVA_HEAP_RETURN; 94 inline void set_klass(Klass* k); 95 static inline void release_set_klass(HeapWord* mem, Klass* k); 96 97 // For klass field compression 98 static inline void set_klass_gap(HeapWord* mem, int z); 99 100 // Size of object header, aligned to platform wordSize 101 static int header_size() { 102 if (UseCompactObjectHeaders) { 103 return sizeof(markWord) / HeapWordSize; 104 } else { 105 return sizeof(oopDesc) / HeapWordSize; 106 } 107 } 108 109 // Returns whether this is an instance of k or an instance of a subclass of k 110 inline bool is_a(Klass* k) const; 111 112 // Returns the actual oop size of the object in machine words 113 inline size_t size(); 114 115 // Returns the size that a copy of this object requires, in machine words. 116 // It can be 1 word larger than its current size to accomodate 117 // an additional 4-byte-field for the identity hash-code. 118 // 119 // size: the current size of this object, we're passing this here for performance 120 // reasons, because all callers compute this anyway, and we want to avoid 121 // recomputing it. 122 // mark: the mark-word of this object. Some callers (e.g. G1ParScanThreadState::do_copy_to_survivor_space()) 123 // need to use a known markWord because of racing GC threads that can change 124 // the markWord at any time. 125 inline size_t copy_size(size_t size, markWord mark) const; 126 // Special version to deal with scratch classes in CDS. There we allocate 127 // temporary scratch classes (which are skeleton versions of InstanceMirrorKlass, 128 // which represent java.lang.Class objects in the CDS archive). At that point, we 129 // don't know whether or not the final archived version will be hashed or expanded, 130 // and therefore we allocate them in the special state not-hashed-but-expanded. 131 // When creating the final copy of those objects, we either populate the hidden hash 132 // field and make the object 'expanded', or we turn it back to 'not-hashed' 133 // and reduce the object's size. We do this by providing a separate method for CDS 134 // so that we don't affect GC performance. 135 inline size_t copy_size_cds(size_t size, markWord mark) const; 136 137 // Sometimes (for complicated concurrency-related reasons), it is useful 138 // to be able to figure out the size of an object knowing its klass. 139 inline size_t base_size_given_klass(markWord m, const Klass* klass); 140 inline size_t size_given_mark_and_klass(markWord mrk, const Klass* kls); 141 142 // type test operations (inlined in oop.inline.hpp) 143 inline bool is_instance() const; 144 inline bool is_instanceRef() const; 145 inline bool is_stackChunk() const; 146 inline bool is_array() const; 147 inline bool is_objArray() const; 148 inline bool is_typeArray() const; 149 150 // type test operations that don't require inclusion of oop.inline.hpp. 151 bool is_instance_noinline() const; 152 bool is_instanceRef_noinline() const; 153 bool is_stackChunk_noinline() const; 154 bool is_array_noinline() const; 155 bool is_objArray_noinline() const; 156 bool is_typeArray_noinline() const; 157 158 protected: 159 inline oop as_oop() const { return const_cast<oopDesc*>(this); } 160 161 public: 162 template<typename T> 163 inline T* field_addr(int offset) const; 164 165 template <typename T> inline size_t field_offset(T* p) const; 166 167 // Standard compare function returns negative value if o1 < o2 168 // 0 if o1 == o2 169 // positive value if o1 > o2 170 inline static int compare(oop o1, oop o2) { 171 void* o1_addr = (void*)o1; 172 void* o2_addr = (void*)o2; 173 if (o1_addr < o2_addr) { 174 return -1; 175 } else if (o1_addr > o2_addr) { 176 return 1; 177 } else { 178 return 0; 179 } 180 } 181 182 // Access to fields in a instanceOop through these methods. 183 template<DecoratorSet decorators> 184 oop obj_field_access(int offset) const; 185 oop obj_field(int offset) const; 186 187 void obj_field_put(int offset, oop value); 188 void obj_field_put_raw(int offset, oop value); 189 void obj_field_put_volatile(int offset, oop value); 190 template<DecoratorSet decorators> 191 void obj_field_put_access(int offset, oop value); 192 193 Metadata* metadata_field(int offset) const; 194 void metadata_field_put(int offset, Metadata* value); 195 196 Metadata* metadata_field_acquire(int offset) const; 197 void release_metadata_field_put(int offset, Metadata* value); 198 199 jbyte byte_field(int offset) const; 200 void byte_field_put(int offset, jbyte contents); 201 202 jchar char_field(int offset) const; 203 void char_field_put(int offset, jchar contents); 204 205 jboolean bool_field(int offset) const; 206 void bool_field_put(int offset, jboolean contents); 207 jboolean bool_field_volatile(int offset) const; 208 void bool_field_put_volatile(int offset, jboolean contents); 209 210 jint int_field(int offset) const; 211 void int_field_put(int offset, jint contents); 212 213 jshort short_field(int offset) const; 214 void short_field_put(int offset, jshort contents); 215 216 jlong long_field(int offset) const; 217 void long_field_put(int offset, jlong contents); 218 219 jfloat float_field(int offset) const; 220 void float_field_put(int offset, jfloat contents); 221 222 jdouble double_field(int offset) const; 223 void double_field_put(int offset, jdouble contents); 224 225 address address_field(int offset) const; 226 void address_field_put(int offset, address contents); 227 228 oop obj_field_acquire(int offset) const; 229 void release_obj_field_put(int offset, oop value); 230 231 jbyte byte_field_acquire(int offset) const; 232 void release_byte_field_put(int offset, jbyte contents); 233 234 jchar char_field_acquire(int offset) const; 235 void release_char_field_put(int offset, jchar contents); 236 237 jboolean bool_field_acquire(int offset) const; 238 void release_bool_field_put(int offset, jboolean contents); 239 240 jint int_field_relaxed(int offset) const; 241 void int_field_put_relaxed(int offset, jint contents); 242 jint int_field_acquire(int offset) const; 243 void release_int_field_put(int offset, jint contents); 244 245 jshort short_field_acquire(int offset) const; 246 void release_short_field_put(int offset, jshort contents); 247 248 jlong long_field_acquire(int offset) const; 249 void release_long_field_put(int offset, jlong contents); 250 251 jfloat float_field_acquire(int offset) const; 252 void release_float_field_put(int offset, jfloat contents); 253 254 jdouble double_field_acquire(int offset) const; 255 void release_double_field_put(int offset, jdouble contents); 256 257 address address_field_acquire(int offset) const; 258 void release_address_field_put(int offset, address contents); 259 260 // printing functions for VM debugging 261 void print_on(outputStream* st) const; // First level print 262 void print_value_on(outputStream* st) const; // Second level print. 263 void print_address_on(outputStream* st) const; // Address printing 264 void print_name_on(outputStream* st) const; // External name printing. 265 266 // printing on default output stream 267 void print(); 268 void print_value(); 269 void print_address(); 270 271 // return the print strings 272 char* print_string(); 273 char* print_value_string(); 274 275 // verification operations 276 static void verify_on(outputStream* st, oopDesc* oop_desc); 277 static void verify(oopDesc* oopDesc); 278 279 // locking operations 280 inline bool is_locked() const; 281 inline bool is_unlocked() const; 282 283 // asserts and guarantees 284 static bool is_oop(oop obj, bool ignore_mark_word = false); 285 static bool is_oop_or_null(oop obj, bool ignore_mark_word = false); 286 287 // garbage collection 288 inline bool is_gc_marked() const; 289 290 // Forward pointer operations for scavenge 291 inline bool is_forwarded() const; 292 inline bool is_self_forwarded() const; 293 294 inline void forward_to(oop p); 295 inline void forward_to_self(); 296 297 // Like "forward_to", but inserts the forwarding pointer atomically. 298 // Exactly one thread succeeds in inserting the forwarding pointer, and 299 // this call returns null for that thread; any other thread has the 300 // value of the forwarding pointer returned and does not modify "this". 301 inline oop forward_to_atomic(oop p, markWord compare, atomic_memory_order order = memory_order_conservative); 302 inline oop forward_to_self_atomic(markWord compare, atomic_memory_order order = memory_order_conservative); 303 304 inline oop forwardee() const; 305 inline oop forwardee(markWord header) const; 306 307 inline void unset_self_forwarded(); 308 inline void reset_forwarded(); 309 310 // Age of object during scavenge 311 inline uint age() const; 312 inline void incr_age(); 313 314 template <typename OopClosureType> 315 inline void oop_iterate(OopClosureType* cl); 316 317 template <typename OopClosureType> 318 inline void oop_iterate(OopClosureType* cl, MemRegion mr); 319 320 template <typename OopClosureType> 321 inline size_t oop_iterate_size(OopClosureType* cl); 322 323 template <typename OopClosureType> 324 inline size_t oop_iterate_size(OopClosureType* cl, MemRegion mr); 325 326 template <typename OopClosureType> 327 inline void oop_iterate_backwards(OopClosureType* cl); 328 329 template <typename OopClosureType> 330 inline void oop_iterate_backwards(OopClosureType* cl, Klass* klass); 331 332 inline static bool is_instanceof_or_null(oop obj, Klass* klass); 333 334 // identity hash; returns the identity hash key (computes it if necessary) 335 inline intptr_t identity_hash(); 336 intptr_t slow_identity_hash(); 337 inline bool fast_no_hash_check(); 338 339 // Initialize identity hash code in hash word of object copy from original object. 340 // Returns true if the object has been expanded, false otherwise. 341 inline void initialize_hash_if_necessary(oop obj); 342 // For CDS only. 343 void initialize_hash_if_necessary(oop obj, Klass* k, markWord m); 344 345 // marks are forwarded to stack when object is locked 346 inline bool has_displaced_mark() const; 347 inline markWord displaced_mark() const; 348 inline void set_displaced_mark(markWord m); 349 350 // Checks if the mark word needs to be preserved 351 inline bool mark_must_be_preserved() const; 352 inline bool mark_must_be_preserved(markWord m) const; 353 354 inline static bool has_klass_gap() { 355 return ObjLayout::oop_has_klass_gap(); 356 } 357 358 // for code generation 359 static int mark_offset_in_bytes() { return (int)offset_of(oopDesc, _mark); } 360 static int klass_offset_in_bytes() { 361 assert(!UseCompactObjectHeaders, "don't use this with compact headers"); 362 return (int)offset_of(oopDesc, _metadata._klass); 363 } 364 static int klass_gap_offset_in_bytes() { 365 assert(has_klass_gap(), "only applicable to compressed klass pointers"); 366 if (UseCompactObjectHeaders) { 367 return base_offset_in_bytes(); 368 } else { 369 return klass_offset_in_bytes() + sizeof(narrowKlass); 370 } 371 } 372 373 static int base_offset_in_bytes() { 374 return ObjLayout::oop_base_offset_in_bytes(); 375 } 376 377 // for error reporting 378 static void* load_oop_raw(oop obj, int offset); 379 }; 380 381 // An oopDesc is not initialized via a constructor. Space is allocated in 382 // the Java heap, and static functions provided here on HeapWord* are used 383 // to fill in certain parts of that memory. The allocated memory is then 384 // treated as referring to an oopDesc. For that to be valid, the oopDesc 385 // class must have a trivial default constructor (C++14 3.8/1). 386 static_assert(std::is_trivially_default_constructible<oopDesc>::value, "required"); 387 388 #endif // SHARE_OOPS_OOP_HPP