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   static inline void release_set_mark(HeapWord* mem, markWord m);
 74 
 75   inline void release_set_mark(markWord m);
 76   inline markWord cas_set_mark(markWord new_mark, markWord old_mark);
 77   inline markWord cas_set_mark(markWord new_mark, markWord old_mark, atomic_memory_order order);
 78 
 79   // Returns the prototype mark that should be used for this object.
 80   inline markWord prototype_mark() const;
 81 
 82   // Used only to re-initialize the mark word (e.g., of promoted
 83   // objects during a GC) -- requires a valid klass pointer
 84   inline void init_mark();
 85 
 86   inline Klass* klass() const;
 87   inline Klass* klass_or_null() const;
 88   inline Klass* klass_or_null_acquire() const;
 89   // Get the klass without running any asserts.
 90   inline Klass* klass_without_asserts() const;
 91 
 92   void set_narrow_klass(narrowKlass nk) NOT_CDS_JAVA_HEAP_RETURN;
 93   inline void set_klass(Klass* k);
 94   static inline void release_set_klass(HeapWord* mem, Klass* k);
 95 
 96   // For klass field compression
 97   static inline void set_klass_gap(HeapWord* mem, int z);
 98 
 99   // Size of object header, aligned to platform wordSize
100   static int header_size() {
101     if (UseCompactObjectHeaders) {
102       return sizeof(markWord) / HeapWordSize;
103     } else {
104       return sizeof(oopDesc)  / HeapWordSize;
105     }
106   }
107 
108   // Returns whether this is an instance of k or an instance of a subclass of k
109   inline bool is_a(Klass* k) const;
110 
111   // Returns the actual oop size of the object in machine words
112   inline size_t size();
113 
114   // Sometimes (for complicated concurrency-related reasons), it is useful
115   // to be able to figure out the size of an object knowing its klass.
116   inline size_t size_given_klass(Klass* klass);
117 
118   // type test operations (inlined in oop.inline.hpp)
119   inline bool is_instance()    const;
120   inline bool is_instanceRef() const;
121   inline bool is_stackChunk()  const;
122   inline bool is_array()       const;
123   inline bool is_objArray()    const;
124   inline bool is_typeArray()   const;
125 
126   // type test operations that don't require inclusion of oop.inline.hpp.
127   bool is_instance_noinline()    const;
128   bool is_instanceRef_noinline() const;
129   bool is_stackChunk_noinline()  const;
130   bool is_array_noinline()       const;
131   bool is_objArray_noinline()    const;
132   bool is_typeArray_noinline()   const;
133 
134  protected:
135   inline oop        as_oop() const { return const_cast<oopDesc*>(this); }
136 
137  public:
138   template<typename T>
139   inline T* field_addr(int offset) const;
140 
141   template <typename T> inline size_t field_offset(T* p) const;
142 
143   // Standard compare function returns negative value if o1 < o2
144   //                                   0              if o1 == o2
145   //                                   positive value if o1 > o2
146   inline static int  compare(oop o1, oop o2) {
147     void* o1_addr = (void*)o1;
148     void* o2_addr = (void*)o2;
149     if (o1_addr < o2_addr) {
150       return -1;
151     } else if (o1_addr > o2_addr) {
152       return 1;
153     } else {
154       return 0;
155     }
156   }
157 
158   // Access to fields in a instanceOop through these methods.
159   template<DecoratorSet decorators>
160   oop obj_field_access(int offset) const;
161   oop obj_field(int offset) const;
162 
163   void obj_field_put(int offset, oop value);
164   void obj_field_put_raw(int offset, oop value);
165   void obj_field_put_volatile(int offset, oop value);
166   template<DecoratorSet decorators>
167   void obj_field_put_access(int offset, oop value);
168 
169   Metadata* metadata_field(int offset) const;
170   void metadata_field_put(int offset, Metadata* value);
171 
172   Metadata* metadata_field_acquire(int offset) const;
173   void release_metadata_field_put(int offset, Metadata* value);
174 
175   jbyte byte_field(int offset) const;
176   void byte_field_put(int offset, jbyte contents);
177 
178   jchar char_field(int offset) const;
179   void char_field_put(int offset, jchar contents);
180 
181   jboolean bool_field(int offset) const;
182   void bool_field_put(int offset, jboolean contents);
183   jboolean bool_field_volatile(int offset) const;
184   void bool_field_put_volatile(int offset, jboolean contents);
185 
186   jint int_field(int offset) const;
187   void int_field_put(int offset, jint contents);
188 
189   jshort short_field(int offset) const;
190   void short_field_put(int offset, jshort contents);
191 
192   jlong long_field(int offset) const;
193   void long_field_put(int offset, jlong contents);
194 
195   jfloat float_field(int offset) const;
196   void float_field_put(int offset, jfloat contents);
197 
198   jdouble double_field(int offset) const;
199   void double_field_put(int offset, jdouble contents);
200 
201   address address_field(int offset) const;
202   void address_field_put(int offset, address contents);
203 
204   oop obj_field_acquire(int offset) const;
205   void release_obj_field_put(int offset, oop value);
206 
207   jbyte byte_field_acquire(int offset) const;
208   void release_byte_field_put(int offset, jbyte contents);
209 
210   jchar char_field_acquire(int offset) const;
211   void release_char_field_put(int offset, jchar contents);
212 
213   jboolean bool_field_acquire(int offset) const;
214   void release_bool_field_put(int offset, jboolean contents);
215 
216   jint int_field_relaxed(int offset) const;
217   void int_field_put_relaxed(int offset, jint contents);
218   jint int_field_acquire(int offset) const;
219   void release_int_field_put(int offset, jint contents);
220 
221   jshort short_field_acquire(int offset) const;
222   void release_short_field_put(int offset, jshort contents);
223 
224   jlong long_field_acquire(int offset) const;
225   void release_long_field_put(int offset, jlong contents);
226 
227   jfloat float_field_acquire(int offset) const;
228   void release_float_field_put(int offset, jfloat contents);
229 
230   jdouble double_field_acquire(int offset) const;
231   void release_double_field_put(int offset, jdouble contents);
232 
233   address address_field_acquire(int offset) const;
234   void release_address_field_put(int offset, address contents);
235 
236   // printing functions for VM debugging
237   void print_on(outputStream* st) const;         // First level print
238   void print_value_on(outputStream* st) const;   // Second level print.
239   void print_address_on(outputStream* st) const; // Address printing
240   void print_name_on(outputStream* st) const;    // External name printing.
241 
242   // printing on default output stream
243   void print();
244   void print_value();
245   void print_address();
246 
247   // return the print strings
248   char* print_string();
249   char* print_value_string();
250 
251   // verification operations
252   static void verify_on(outputStream* st, oopDesc* oop_desc);
253   static void verify(oopDesc* oopDesc);
254 
255   // locking operations
256   inline bool is_locked()   const;
257   inline bool is_unlocked() const;
258 
259   // asserts and guarantees
260   static bool is_oop(oop obj, bool ignore_mark_word = false);
261   static bool is_oop_or_null(oop obj, bool ignore_mark_word = false);
262 
263   // garbage collection
264   inline bool is_gc_marked() const;
265 
266   // Forward pointer operations for scavenge
267   inline bool is_forwarded() const;
268   inline bool is_self_forwarded() const;
269 
270   inline void forward_to(oop p);
271   inline void forward_to_self();
272 
273   // Like "forward_to", but inserts the forwarding pointer atomically.
274   // Exactly one thread succeeds in inserting the forwarding pointer, and
275   // this call returns null for that thread; any other thread has the
276   // value of the forwarding pointer returned and does not modify "this".
277   inline oop forward_to_atomic(oop p, markWord compare, atomic_memory_order order = memory_order_conservative);
278   inline oop forward_to_self_atomic(markWord compare, atomic_memory_order order = memory_order_conservative);
279 
280   inline oop forwardee() const;
281   inline oop forwardee(markWord header) const;
282 
283   inline void unset_self_forwarded();
284 
285   // Age of object during scavenge
286   inline uint age() const;
287   inline void incr_age();
288 
289   template <typename OopClosureType>
290   inline void oop_iterate(OopClosureType* cl);
291 
292   template <typename OopClosureType>
293   inline void oop_iterate(OopClosureType* cl, MemRegion mr);
294 
295   template <typename OopClosureType>
296   inline size_t oop_iterate_size(OopClosureType* cl);
297 
298   template <typename OopClosureType>
299   inline size_t oop_iterate_size(OopClosureType* cl, MemRegion mr);
300 
301   template <typename OopClosureType>
302   inline void oop_iterate_backwards(OopClosureType* cl);
303 
304   template <typename OopClosureType>
305   inline void oop_iterate_backwards(OopClosureType* cl, Klass* klass);
306 
307   inline static bool is_instanceof_or_null(oop obj, Klass* klass);
308 
309   // identity hash; returns the identity hash key (computes it if necessary)
310   inline intptr_t identity_hash();
311   intptr_t slow_identity_hash();
312   inline bool fast_no_hash_check();
313 
314   // marks are forwarded to stack when object is locked
315   inline bool     has_displaced_mark() const;
316   inline markWord displaced_mark() const;
317   inline void     set_displaced_mark(markWord m);
318 
319   // Checks if the mark word needs to be preserved
320   inline bool mark_must_be_preserved() const;
321   inline bool mark_must_be_preserved(markWord m) const;
322 
323   inline static bool has_klass_gap() {
324     return ObjLayout::oop_has_klass_gap();
325   }
326 
327   // for code generation
328   static int mark_offset_in_bytes()      { return (int)offset_of(oopDesc, _mark); }
329   static int klass_offset_in_bytes()     {
330 #ifdef _LP64
331     if (UseCompactObjectHeaders) {
332       // NOTE: The only places where this is used with compact headers are the C2
333       // compiler and JVMCI.
334       return mark_offset_in_bytes() + markWord::klass_offset_in_bytes;
335     } else
336 #endif
337     {
338       return (int)offset_of(oopDesc, _metadata._klass);
339     }
340   }
341   static int klass_gap_offset_in_bytes() {
342     assert(has_klass_gap(), "only applicable to compressed klass pointers");
343     return klass_offset_in_bytes() + sizeof(narrowKlass);
344   }
345 
346   static int base_offset_in_bytes() {
347     return ObjLayout::oop_base_offset_in_bytes();
348   }
349 
350   // for error reporting
351   static void* load_oop_raw(oop obj, int offset);
352 };
353 
354 // An oopDesc is not initialized via a constructor.  Space is allocated in
355 // the Java heap, and static functions provided here on HeapWord* are used
356 // to fill in certain parts of that memory.  The allocated memory is then
357 // treated as referring to an oopDesc.  For that to be valid, the oopDesc
358 // class must have a trivial default constructor (C++14 3.8/1).
359 static_assert(std::is_trivially_default_constructible<oopDesc>::value, "required");
360 
361 #endif // SHARE_OOPS_OOP_HPP