1 /*
  2  * Copyright (c) 1997, 2024, 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.
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 24 
 25 #ifndef SHARE_OOPS_KLASS_HPP
 26 #define SHARE_OOPS_KLASS_HPP
 27 
 28 #include "memory/iterator.hpp"
 29 #include "memory/memRegion.hpp"
 30 #include "oops/markWord.hpp"
 31 #include "oops/metadata.hpp"
 32 #include "oops/oop.hpp"
 33 #include "oops/oopHandle.hpp"
 34 #include "utilities/accessFlags.hpp"
 35 #include "utilities/macros.hpp"
 36 #if INCLUDE_JFR
 37 #include "jfr/support/jfrTraceIdExtension.hpp"
 38 #endif
 39 
 40 //
 41 // A Klass provides:
 42 //  1: language level class object (method dictionary etc.)
 43 //  2: provide vm dispatch behavior for the object
 44 // Both functions are combined into one C++ class.
 45 
 46 // One reason for the oop/klass dichotomy in the implementation is
 47 // that we don't want a C++ vtbl pointer in every object.  Thus,
 48 // normal oops don't have any virtual functions.  Instead, they
 49 // forward all "virtual" functions to their klass, which does have
 50 // a vtbl and does the C++ dispatch depending on the object's
 51 // actual type.  (See oop.inline.hpp for some of the forwarding code.)
 52 // ALL FUNCTIONS IMPLEMENTING THIS DISPATCH ARE PREFIXED WITH "oop_"!
 53 
 54 // Forward declarations.
 55 template <class T> class Array;
 56 template <class T> class GrowableArray;
 57 class ClassLoaderData;
 58 class fieldDescriptor;
 59 class klassVtable;
 60 class ModuleEntry;
 61 class PackageEntry;
 62 class ParCompactionManager;
 63 class PSPromotionManager;
 64 class vtableEntry;
 65 
 66 class Klass : public Metadata {
 67   friend class VMStructs;
 68   friend class JVMCIVMStructs;
 69  public:
 70   // Klass Kinds for all subclasses of Klass
 71   enum KlassKind {
 72     InstanceKlassKind,
 73     InstanceRefKlassKind,
 74     InstanceMirrorKlassKind,
 75     InstanceClassLoaderKlassKind,
 76     InstanceStackChunkKlassKind,
 77     TypeArrayKlassKind,
 78     ObjArrayKlassKind,
 79     UnknownKlassKind
 80   };
 81 
 82   static const uint KLASS_KIND_COUNT = ObjArrayKlassKind + 1;
 83  protected:
 84 
 85   // If you add a new field that points to any metaspace object, you
 86   // must add this field to Klass::metaspace_pointers_do().
 87 
 88   // note: put frequently-used fields together at start of klass structure
 89   // for better cache behavior (may not make much of a difference but sure won't hurt)
 90   enum { _primary_super_limit = 8 };
 91 
 92   // The "layout helper" is a combined descriptor of object layout.
 93   // For klasses which are neither instance nor array, the value is zero.
 94   //
 95   // For instances, layout helper is a positive number, the instance size.
 96   // This size is already passed through align_object_size and scaled to bytes.
 97   // The low order bit is set if instances of this class cannot be
 98   // allocated using the fastpath.
 99   //
100   // For arrays, layout helper is a negative number, containing four
101   // distinct bytes, as follows:
102   //    MSB:[tag, hsz, ebt, log2(esz)]:LSB
103   // where:
104   //    tag is 0x80 if the elements are oops, 0xC0 if non-oops
105   //    hsz is array header size in bytes (i.e., offset of first element)
106   //    ebt is the BasicType of the elements
107   //    esz is the element size in bytes
108   // This packed word is arranged so as to be quickly unpacked by the
109   // various fast paths that use the various subfields.
110   //
111   // The esz bits can be used directly by a SLL instruction, without masking.
112   //
113   // Note that the array-kind tag looks like 0x00 for instance klasses,
114   // since their length in bytes is always less than 24Mb.
115   //
116   // Final note:  This comes first, immediately after C++ vtable,
117   // because it is frequently queried.
118   jint        _layout_helper;
119 
120   // Klass kind used to resolve the runtime type of the instance.
121   //  - Used to implement devirtualized oop closure dispatching.
122   //  - Various type checking in the JVM
123   const KlassKind _kind;
124 
125   // Processed access flags, for use by Class.getModifiers.
126   jint        _modifier_flags;
127 
128   // The fields _super_check_offset, _secondary_super_cache, _secondary_supers
129   // and _primary_supers all help make fast subtype checks.  See big discussion
130   // in doc/server_compiler/checktype.txt
131   //
132   // Where to look to observe a supertype (it is &_secondary_super_cache for
133   // secondary supers, else is &_primary_supers[depth()].
134   juint       _super_check_offset;
135 
136   // Class name.  Instance classes: java/lang/String, etc.  Array classes: [I,
137   // [Ljava/lang/String;, etc.  Set to zero for all other kinds of classes.
138   Symbol*     _name;
139 
140   // Cache of last observed secondary supertype
141   Klass*      _secondary_super_cache;
142   // Array of all secondary supertypes
143   Array<Klass*>* _secondary_supers;
144   // Ordered list of all primary supertypes
145   Klass*      _primary_supers[_primary_super_limit];
146   // java/lang/Class instance mirroring this class
147   OopHandle   _java_mirror;
148   // Superclass
149   Klass*      _super;
150   // First subclass (null if none); _subklass->next_sibling() is next one
151   Klass* volatile _subklass;
152   // Sibling link (or null); links all subklasses of a klass
153   Klass* volatile _next_sibling;
154 
155   // All klasses loaded by a class loader are chained through these links
156   Klass*      _next_link;
157 
158   // The VM's representation of the ClassLoader used to load this class.
159   // Provide access the corresponding instance java.lang.ClassLoader.
160   ClassLoaderData* _class_loader_data;
161 
162   int _vtable_len;              // vtable length. This field may be read very often when we
163                                 // have lots of itable dispatches (e.g., lambdas and streams).
164                                 // Keep it away from the beginning of a Klass to avoid cacheline
165                                 // contention that may happen when a nearby object is modified.
166   AccessFlags _access_flags;    // Access flags. The class/interface distinction is stored here.
167 
168   JFR_ONLY(DEFINE_TRACE_ID_FIELD;)
169 
170   markWord _prototype_header;   // Used to initialize objects' header
171 
172 private:
173   // This is an index into FileMapHeader::_shared_path_table[], to
174   // associate this class with the JAR file where it's loaded from during
175   // dump time. If a class is not loaded from the shared archive, this field is
176   // -1.
177   s2 _shared_class_path_index;
178 
179 #if INCLUDE_CDS
180   // Various attributes for shared classes. Should be zero for a non-shared class.
181   u2     _shared_class_flags;
182   enum CDSSharedClassFlags {
183     _is_shared_class                       = 1 << 0,  // shadows MetaspaceObj::is_shared
184     _archived_lambda_proxy_is_available    = 1 << 1,
185     _has_value_based_class_annotation      = 1 << 2,
186     _verified_at_dump_time                 = 1 << 3,
187     _has_archived_enum_objs                = 1 << 4,
188     // This class was not loaded from a classfile in the module image
189     // or classpath.
190     _is_generated_shared_class             = 1 << 5
191   };
192 #endif
193 
194   CDS_JAVA_HEAP_ONLY(int _archived_mirror_index;)
195 
196 protected:
197 
198   Klass(KlassKind kind);
199   Klass();
200 
201   void* operator new(size_t size, ClassLoaderData* loader_data, size_t word_size, TRAPS) throw();
202 
203  public:
204   int kind() { return _kind; }
205 
206   enum class DefaultsLookupMode { find, skip };
207   enum class OverpassLookupMode { find, skip };
208   enum class StaticLookupMode   { find, skip };
209   enum class PrivateLookupMode  { find, skip };
210 
211   virtual bool is_klass() const { return true; }
212 
213   // super() cannot be InstanceKlass* -- Java arrays are covariant, and _super is used
214   // to implement that. NB: the _super of "[Ljava/lang/Integer;" is "[Ljava/lang/Number;"
215   // If this is not what your code expects, you're probably looking for Klass::java_super().
216   Klass* super() const               { return _super; }
217   void set_super(Klass* k)           { _super = k; }
218 
219   // initializes _super link, _primary_supers & _secondary_supers arrays
220   void initialize_supers(Klass* k, Array<InstanceKlass*>* transitive_interfaces, TRAPS);
221 
222   // klass-specific helper for initializing _secondary_supers
223   virtual GrowableArray<Klass*>* compute_secondary_supers(int num_extra_slots,
224                                                           Array<InstanceKlass*>* transitive_interfaces);
225 
226   // java_super is the Java-level super type as specified by Class.getSuperClass.
227   virtual InstanceKlass* java_super() const  { return nullptr; }
228 
229   juint    super_check_offset() const  { return _super_check_offset; }
230   void set_super_check_offset(juint o) { _super_check_offset = o; }
231 
232   Klass* secondary_super_cache() const     { return _secondary_super_cache; }
233   void set_secondary_super_cache(Klass* k) { _secondary_super_cache = k; }
234 
235   Array<Klass*>* secondary_supers() const { return _secondary_supers; }
236   void set_secondary_supers(Array<Klass*>* k) { _secondary_supers = k; }
237 
238   // Return the element of the _super chain of the given depth.
239   // If there is no such element, return either null or this.
240   Klass* primary_super_of_depth(juint i) const {
241     assert(i < primary_super_limit(), "oob");
242     Klass* super = _primary_supers[i];
243     assert(super == nullptr || super->super_depth() == i, "correct display");
244     return super;
245   }
246 
247   // Can this klass be a primary super?  False for interfaces and arrays of
248   // interfaces.  False also for arrays or classes with long super chains.
249   bool can_be_primary_super() const {
250     const juint secondary_offset = in_bytes(secondary_super_cache_offset());
251     return super_check_offset() != secondary_offset;
252   }
253   virtual bool can_be_primary_super_slow() const;
254 
255   // Returns number of primary supers; may be a number in the inclusive range [0, primary_super_limit].
256   juint super_depth() const {
257     if (!can_be_primary_super()) {
258       return primary_super_limit();
259     } else {
260       juint d = (super_check_offset() - in_bytes(primary_supers_offset())) / sizeof(Klass*);
261       assert(d < primary_super_limit(), "oob");
262       assert(_primary_supers[d] == this, "proper init");
263       return d;
264     }
265   }
266 
267   // java mirror
268   oop java_mirror() const;
269   oop java_mirror_no_keepalive() const;
270   void set_java_mirror(Handle m);
271 
272   oop archived_java_mirror() NOT_CDS_JAVA_HEAP_RETURN_(nullptr);
273   void set_archived_java_mirror(int mirror_index) NOT_CDS_JAVA_HEAP_RETURN;
274 
275   // Temporary mirror switch used by RedefineClasses
276   OopHandle java_mirror_handle() const { return _java_mirror; }
277   void swap_java_mirror_handle(OopHandle& mirror) { _java_mirror.swap(mirror); }
278 
279   // Set java mirror OopHandle to null for CDS
280   // This leaves the OopHandle in the CLD, but that's ok, you can't release them.
281   void clear_java_mirror_handle() { _java_mirror = OopHandle(); }
282 
283   // modifier flags
284   jint modifier_flags() const          { return _modifier_flags; }
285   void set_modifier_flags(jint flags)  { _modifier_flags = flags; }
286 
287   // size helper
288   int layout_helper() const            { return _layout_helper; }
289   void set_layout_helper(int lh)       { _layout_helper = lh; }
290 
291   // Note: for instances layout_helper() may include padding.
292   // Use InstanceKlass::contains_field_offset to classify field offsets.
293 
294   // sub/superklass links
295   Klass* subklass(bool log = false) const;
296   Klass* next_sibling(bool log = false) const;
297 
298   InstanceKlass* superklass() const;
299   void append_to_sibling_list();           // add newly created receiver to superklass' subklass list
300 
301   void set_next_link(Klass* k) { _next_link = k; }
302   Klass* next_link() const { return _next_link; }   // The next klass defined by the class loader.
303   Klass** next_link_addr() { return &_next_link; }
304 
305   // class loader data
306   ClassLoaderData* class_loader_data() const               { return _class_loader_data; }
307   void set_class_loader_data(ClassLoaderData* loader_data) {  _class_loader_data = loader_data; }
308 
309   s2 shared_classpath_index() const   {
310     return _shared_class_path_index;
311   };
312 
313   void set_shared_classpath_index(s2 index) {
314     _shared_class_path_index = index;
315   };
316 
317   bool has_archived_mirror_index() const {
318     CDS_JAVA_HEAP_ONLY(return _archived_mirror_index >= 0;)
319     NOT_CDS_JAVA_HEAP(return false);
320   }
321 
322   void clear_archived_mirror_index() NOT_CDS_JAVA_HEAP_RETURN;
323 
324   void set_lambda_proxy_is_available() {
325     CDS_ONLY(_shared_class_flags |= _archived_lambda_proxy_is_available;)
326   }
327   void clear_lambda_proxy_is_available() {
328     CDS_ONLY(_shared_class_flags &= (u2)(~_archived_lambda_proxy_is_available);)
329   }
330   bool lambda_proxy_is_available() const {
331     CDS_ONLY(return (_shared_class_flags & _archived_lambda_proxy_is_available) != 0;)
332     NOT_CDS(return false;)
333   }
334 
335   void set_has_value_based_class_annotation() {
336     CDS_ONLY(_shared_class_flags |= _has_value_based_class_annotation;)
337   }
338   void clear_has_value_based_class_annotation() {
339     CDS_ONLY(_shared_class_flags &= (u2)(~_has_value_based_class_annotation);)
340   }
341   bool has_value_based_class_annotation() const {
342     CDS_ONLY(return (_shared_class_flags & _has_value_based_class_annotation) != 0;)
343     NOT_CDS(return false;)
344   }
345 
346   void set_verified_at_dump_time() {
347     CDS_ONLY(_shared_class_flags |= _verified_at_dump_time;)
348   }
349   bool verified_at_dump_time() const {
350     CDS_ONLY(return (_shared_class_flags & _verified_at_dump_time) != 0;)
351     NOT_CDS(return false;)
352   }
353 
354   void set_has_archived_enum_objs() {
355     CDS_ONLY(_shared_class_flags |= _has_archived_enum_objs;)
356   }
357   bool has_archived_enum_objs() const {
358     CDS_ONLY(return (_shared_class_flags & _has_archived_enum_objs) != 0;)
359     NOT_CDS(return false;)
360   }
361 
362   void set_is_generated_shared_class() {
363     CDS_ONLY(_shared_class_flags |= _is_generated_shared_class;)
364   }
365   bool is_generated_shared_class() const {
366     CDS_ONLY(return (_shared_class_flags & _is_generated_shared_class) != 0;)
367     NOT_CDS(return false;)
368   }
369 
370   bool is_shared() const                { // shadows MetaspaceObj::is_shared)()
371     CDS_ONLY(return (_shared_class_flags & _is_shared_class) != 0;)
372     NOT_CDS(return false;)
373   }
374 
375   void set_is_shared() {
376     CDS_ONLY(_shared_class_flags |= _is_shared_class;)
377   }
378 
379   // Obtain the module or package for this class
380   virtual ModuleEntry* module() const = 0;
381   virtual PackageEntry* package() const = 0;
382 
383  protected:                                // internal accessors
384   void     set_subklass(Klass* s);
385   void     set_next_sibling(Klass* s);
386 
387  public:
388 
389   // Compiler support
390   static ByteSize super_offset()                 { return byte_offset_of(Klass, _super); }
391   static ByteSize super_check_offset_offset()    { return byte_offset_of(Klass, _super_check_offset); }
392   static ByteSize primary_supers_offset()        { return byte_offset_of(Klass, _primary_supers); }
393   static ByteSize secondary_super_cache_offset() { return byte_offset_of(Klass, _secondary_super_cache); }
394   static ByteSize secondary_supers_offset()      { return byte_offset_of(Klass, _secondary_supers); }
395   static ByteSize java_mirror_offset()           { return byte_offset_of(Klass, _java_mirror); }
396   static ByteSize class_loader_data_offset()     { return byte_offset_of(Klass, _class_loader_data); }
397   static ByteSize modifier_flags_offset()        { return byte_offset_of(Klass, _modifier_flags); }
398   static ByteSize layout_helper_offset()         { return byte_offset_of(Klass, _layout_helper); }
399   static ByteSize access_flags_offset()          { return byte_offset_of(Klass, _access_flags); }
400 #if INCLUDE_JVMCI
401   static ByteSize subklass_offset()              { return byte_offset_of(Klass, _subklass); }
402   static ByteSize next_sibling_offset()          { return byte_offset_of(Klass, _next_sibling); }
403 #endif
404 
405   // Unpacking layout_helper:
406   static const int _lh_neutral_value           = 0;  // neutral non-array non-instance value
407   static const int _lh_instance_slow_path_bit  = 0x01;
408   static const int _lh_log2_element_size_shift = BitsPerByte*0;
409   static const int _lh_log2_element_size_mask  = BitsPerLong-1;
410   static const int _lh_element_type_shift      = BitsPerByte*1;
411   static const int _lh_element_type_mask       = right_n_bits(BitsPerByte);  // shifted mask
412   static const int _lh_header_size_shift       = BitsPerByte*2;
413   static const int _lh_header_size_mask        = right_n_bits(BitsPerByte);  // shifted mask
414   static const int _lh_array_tag_bits          = 2;
415   static const int _lh_array_tag_shift         = BitsPerInt - _lh_array_tag_bits;
416   static const int _lh_array_tag_obj_value     = ~0x01;   // 0x80000000 >> 30
417 
418   static const unsigned int _lh_array_tag_type_value = 0Xffffffff; // ~0x00,  // 0xC0000000 >> 30
419 
420   static int layout_helper_size_in_bytes(jint lh) {
421     assert(lh > (jint)_lh_neutral_value, "must be instance");
422     return (int) lh & ~_lh_instance_slow_path_bit;
423   }
424   static bool layout_helper_needs_slow_path(jint lh) {
425     assert(lh > (jint)_lh_neutral_value, "must be instance");
426     return (lh & _lh_instance_slow_path_bit) != 0;
427   }
428   static bool layout_helper_is_instance(jint lh) {
429     return (jint)lh > (jint)_lh_neutral_value;
430   }
431   static bool layout_helper_is_array(jint lh) {
432     return (jint)lh < (jint)_lh_neutral_value;
433   }
434   static bool layout_helper_is_typeArray(jint lh) {
435     // _lh_array_tag_type_value == (lh >> _lh_array_tag_shift);
436     return (juint)lh >= (juint)(_lh_array_tag_type_value << _lh_array_tag_shift);
437   }
438   static bool layout_helper_is_objArray(jint lh) {
439     // _lh_array_tag_obj_value == (lh >> _lh_array_tag_shift);
440     return (jint)lh < (jint)(_lh_array_tag_type_value << _lh_array_tag_shift);
441   }
442   static int layout_helper_header_size(jint lh) {
443     assert(lh < (jint)_lh_neutral_value, "must be array");
444     int hsize = (lh >> _lh_header_size_shift) & _lh_header_size_mask;
445     assert(hsize > 0 && hsize < (int)sizeof(oopDesc)*3, "sanity");
446     return hsize;
447   }
448   static BasicType layout_helper_element_type(jint lh) {
449     assert(lh < (jint)_lh_neutral_value, "must be array");
450     int btvalue = (lh >> _lh_element_type_shift) & _lh_element_type_mask;
451     assert(btvalue >= T_BOOLEAN && btvalue <= T_OBJECT, "sanity");
452     return (BasicType) btvalue;
453   }
454 
455   // Want a pattern to quickly diff against layout header in register
456   // find something less clever!
457   static int layout_helper_boolean_diffbit() {
458     jint zlh = array_layout_helper(T_BOOLEAN);
459     jint blh = array_layout_helper(T_BYTE);
460     assert(zlh != blh, "array layout helpers must differ");
461     int diffbit = 1;
462     while ((diffbit & (zlh ^ blh)) == 0 && (diffbit & zlh) == 0) {
463       diffbit <<= 1;
464       assert(diffbit != 0, "make sure T_BOOLEAN has a different bit than T_BYTE");
465     }
466     return diffbit;
467   }
468 
469   static int layout_helper_log2_element_size(jint lh) {
470     assert(lh < (jint)_lh_neutral_value, "must be array");
471     int l2esz = (lh >> _lh_log2_element_size_shift) & _lh_log2_element_size_mask;
472     assert(l2esz <= LogBytesPerLong,
473            "sanity. l2esz: 0x%x for lh: 0x%x", (uint)l2esz, (uint)lh);
474     return l2esz;
475   }
476   static jint array_layout_helper(jint tag, int hsize, BasicType etype, int log2_esize) {
477     return (tag        << _lh_array_tag_shift)
478       |    (hsize      << _lh_header_size_shift)
479       |    ((int)etype << _lh_element_type_shift)
480       |    (log2_esize << _lh_log2_element_size_shift);
481   }
482   static jint instance_layout_helper(jint size, bool slow_path_flag) {
483     return (size << LogBytesPerWord)
484       |    (slow_path_flag ? _lh_instance_slow_path_bit : 0);
485   }
486   static int layout_helper_to_size_helper(jint lh) {
487     assert(lh > (jint)_lh_neutral_value, "must be instance");
488     // Note that the following expression discards _lh_instance_slow_path_bit.
489     return lh >> LogBytesPerWord;
490   }
491   // Out-of-line version computes everything based on the etype:
492   static jint array_layout_helper(BasicType etype);
493 
494   // What is the maximum number of primary superclasses any klass can have?
495   static juint primary_super_limit()         { return _primary_super_limit; }
496 
497   // vtables
498   klassVtable vtable() const;
499   int vtable_length() const { return _vtable_len; }
500 
501   // subclass check
502   bool is_subclass_of(const Klass* k) const;
503   // subtype check: true if is_subclass_of, or if k is interface and receiver implements it
504   bool is_subtype_of(Klass* k) const {
505     juint    off = k->super_check_offset();
506     Klass* sup = *(Klass**)( (address)this + off );
507     const juint secondary_offset = in_bytes(secondary_super_cache_offset());
508     if (sup == k) {
509       return true;
510     } else if (off != secondary_offset) {
511       return false;
512     } else {
513       return search_secondary_supers(k);
514     }
515   }
516 
517   bool search_secondary_supers(Klass* k) const;
518 
519   // Find LCA in class hierarchy
520   Klass *LCA( Klass *k );
521 
522   // Check whether reflection/jni/jvm code is allowed to instantiate this class;
523   // if not, throw either an Error or an Exception.
524   virtual void check_valid_for_instantiation(bool throwError, TRAPS);
525 
526   // array copying
527   virtual void  copy_array(arrayOop s, int src_pos, arrayOop d, int dst_pos, int length, TRAPS);
528 
529   // tells if the class should be initialized
530   virtual bool should_be_initialized() const    { return false; }
531   // initializes the klass
532   virtual void initialize(TRAPS);
533   virtual Klass* find_field(Symbol* name, Symbol* signature, fieldDescriptor* fd) const;
534   virtual Method* uncached_lookup_method(const Symbol* name, const Symbol* signature,
535                                          OverpassLookupMode overpass_mode,
536                                          PrivateLookupMode = PrivateLookupMode::find) const;
537  public:
538   Method* lookup_method(const Symbol* name, const Symbol* signature) const {
539     return uncached_lookup_method(name, signature, OverpassLookupMode::find);
540   }
541 
542   // array class with specific rank
543   virtual ArrayKlass* array_klass(int rank, TRAPS) = 0;
544 
545   // array class with this klass as element type
546   virtual ArrayKlass* array_klass(TRAPS) = 0;
547 
548   // These will return null instead of allocating on the heap:
549   virtual ArrayKlass* array_klass_or_null(int rank) = 0;
550   virtual ArrayKlass* array_klass_or_null() = 0;
551 
552   virtual oop protection_domain() const = 0;
553 
554   oop class_loader() const;
555 
556   inline oop klass_holder() const;
557 
558  protected:
559 
560   // Error handling when length > max_length or length < 0
561   static void check_array_allocation_length(int length, int max_length, TRAPS);
562 
563   void set_vtable_length(int len) { _vtable_len= len; }
564 
565   vtableEntry* start_of_vtable() const;
566 #if INCLUDE_CDS
567   void restore_unshareable_info(ClassLoaderData* loader_data, Handle protection_domain, TRAPS);
568 #endif
569  public:
570   Method* method_at_vtable(int index);
571 
572   static ByteSize vtable_start_offset();
573   static ByteSize vtable_length_offset() {
574     return byte_offset_of(Klass, _vtable_len);
575   }
576 
577 #if INCLUDE_CDS
578   // CDS support - remove and restore oops from metadata. Oops are not shared.
579   virtual void remove_unshareable_info();
580   virtual void remove_java_mirror();
581 
582   bool is_unshareable_info_restored() const {
583     assert(is_shared(), "use this for shared classes only");
584     if (has_archived_mirror_index()) {
585       // _java_mirror is not a valid OopHandle but rather an encoded reference in the shared heap
586       return false;
587     } else if (_java_mirror.is_empty()) {
588       return false;
589     } else {
590       return true;
591     }
592   }
593 #endif // INCLUDE_CDS
594 
595  public:
596   // ALL FUNCTIONS BELOW THIS POINT ARE DISPATCHED FROM AN OOP
597   // These functions describe behavior for the oop not the KLASS.
598 
599   // actual oop size of obj in memory in word size.
600   virtual size_t oop_size(oop obj) const = 0;
601 
602   // Size of klass in word size.
603   virtual int size() const = 0;
604 
605   // Returns the Java name for a class (Resource allocated)
606   // For arrays, this returns the name of the element with a leading '['.
607   // For classes, this returns the name with the package separators
608   //     turned into '.'s.
609   const char* external_name() const;
610   // Returns the name for a class (Resource allocated) as the class
611   // would appear in a signature.
612   // For arrays, this returns the name of the element with a leading '['.
613   // For classes, this returns the name with a leading 'L' and a trailing ';'
614   //     and the package separators as '/'.
615   virtual const char* signature_name() const;
616 
617   const char* joint_in_module_of_loader(const Klass* class2, bool include_parent_loader = false) const;
618   const char* class_in_module_of_loader(bool use_are = false, bool include_parent_loader = false) const;
619 
620   // Returns "interface", "abstract class" or "class".
621   const char* external_kind() const;
622 
623   // type testing operations
624 #ifdef ASSERT
625  protected:
626   virtual bool is_instance_klass_slow()     const { return false; }
627   virtual bool is_array_klass_slow()        const { return false; }
628   virtual bool is_objArray_klass_slow()     const { return false; }
629   virtual bool is_typeArray_klass_slow()    const { return false; }
630 #endif // ASSERT
631  public:
632 
633   // Fast non-virtual versions
634   #ifndef ASSERT
635   #define assert_same_query(xval, xcheck) xval
636   #else
637  private:
638   static bool assert_same_query(bool xval, bool xslow) {
639     assert(xval == xslow, "slow and fast queries agree");
640     return xval;
641   }
642  public:
643   #endif
644 
645   bool is_instance_klass()              const { return assert_same_query(_kind <= InstanceStackChunkKlassKind, is_instance_klass_slow()); }
646   // Other is anything that is not one of the more specialized kinds of InstanceKlass.
647   bool is_other_instance_klass()        const { return _kind == InstanceKlassKind; }
648   bool is_reference_instance_klass()    const { return _kind == InstanceRefKlassKind; }
649   bool is_mirror_instance_klass()       const { return _kind == InstanceMirrorKlassKind; }
650   bool is_class_loader_instance_klass() const { return _kind == InstanceClassLoaderKlassKind; }
651   bool is_array_klass()                 const { return assert_same_query( _kind >= TypeArrayKlassKind, is_array_klass_slow()); }
652   bool is_stack_chunk_instance_klass()  const { return _kind == InstanceStackChunkKlassKind; }
653   bool is_objArray_klass()              const { return assert_same_query( _kind == ObjArrayKlassKind,  is_objArray_klass_slow()); }
654   bool is_typeArray_klass()             const { return assert_same_query( _kind == TypeArrayKlassKind, is_typeArray_klass_slow()); }
655   #undef assert_same_query
656 
657   // Access flags
658   AccessFlags access_flags() const         { return _access_flags;  }
659   void set_access_flags(AccessFlags flags) { _access_flags = flags; }
660 
661   bool is_public() const                { return _access_flags.is_public(); }
662   bool is_final() const                 { return _access_flags.is_final(); }
663   bool is_interface() const             { return _access_flags.is_interface(); }
664   bool is_abstract() const              { return _access_flags.is_abstract(); }
665   bool is_super() const                 { return _access_flags.is_super(); }
666   bool is_synthetic() const             { return _access_flags.is_synthetic(); }
667   void set_is_synthetic()               { _access_flags.set_is_synthetic(); }
668   bool has_finalizer() const            { return _access_flags.has_finalizer(); }
669   void set_has_finalizer()              { _access_flags.set_has_finalizer(); }
670   bool is_hidden() const                { return access_flags().is_hidden_class(); }
671   void set_is_hidden()                  { _access_flags.set_is_hidden_class(); }
672   bool is_value_based()                 { return _access_flags.is_value_based_class(); }
673   void set_is_value_based()             { _access_flags.set_is_value_based_class(); }
674 
675   inline bool is_non_strong_hidden() const;
676 
677   bool is_cloneable() const;
678   void set_is_cloneable();
679 
680   markWord prototype_header() const      {
681     assert(UseCompactObjectHeaders, "only use with compact object headers");
682     return _prototype_header;
683   }
684   inline void set_prototype_header(markWord header);
685   static ByteSize prototype_header_offset() { return in_ByteSize(offset_of(Klass, _prototype_header)); }
686 
687   JFR_ONLY(DEFINE_TRACE_ID_METHODS;)
688 
689   virtual void metaspace_pointers_do(MetaspaceClosure* iter);
690   virtual MetaspaceObj::Type type() const { return ClassType; }
691 
692   inline bool is_loader_alive() const;
693 
694   void clean_subklass();
695 
696   static void clean_weak_klass_links(bool unloading_occurred, bool clean_alive_klasses = true);
697   static void clean_subklass_tree() {
698     clean_weak_klass_links(/*unloading_occurred*/ true , /* clean_alive_klasses */ false);
699   }
700 
701   // Return self, except for abstract classes with exactly 1
702   // implementor.  Then return the 1 concrete implementation.
703   Klass *up_cast_abstract();
704 
705   // klass name
706   Symbol* name() const                   { return _name; }
707   void set_name(Symbol* n);
708 
709   virtual void release_C_heap_structures(bool release_constant_pool = true);
710 
711  public:
712   virtual jint compute_modifier_flags() const = 0;
713 
714   // JVMTI support
715   virtual jint jvmti_class_status() const;
716 
717   // Printing
718   virtual void print_on(outputStream* st) const;
719 
720   virtual void oop_print_value_on(oop obj, outputStream* st);
721   virtual void oop_print_on      (oop obj, outputStream* st);
722 
723   virtual const char* internal_name() const = 0;
724 
725   // Verification
726   virtual void verify_on(outputStream* st);
727   void verify() { verify_on(tty); }
728 
729 #ifndef PRODUCT
730   bool verify_vtable_index(int index);
731 #endif
732 
733   virtual void oop_verify_on(oop obj, outputStream* st);
734 
735   // for error reporting
736   static bool is_valid(Klass* k);
737 };
738 
739 #endif // SHARE_OOPS_KLASS_HPP