1 /*
  2  * Copyright (c) 1997, 2022, 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_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 // Klass Kinds for all subclasses of Klass
 41 enum KlassKind {
 42   InstanceKlassKind,
 43   InstanceRefKlassKind,
 44   InstanceMirrorKlassKind,
 45   InstanceClassLoaderKlassKind,
 46   InstanceStackChunkKlassKind,
 47   TypeArrayKlassKind,
 48   ObjArrayKlassKind
 49 };
 50 
 51 const uint KLASS_KIND_COUNT = ObjArrayKlassKind + 1;
 52 
 53 //
 54 // A Klass provides:
 55 //  1: language level class object (method dictionary etc.)
 56 //  2: provide vm dispatch behavior for the object
 57 // Both functions are combined into one C++ class.
 58 
 59 // One reason for the oop/klass dichotomy in the implementation is
 60 // that we don't want a C++ vtbl pointer in every object.  Thus,
 61 // normal oops don't have any virtual functions.  Instead, they
 62 // forward all "virtual" functions to their klass, which does have
 63 // a vtbl and does the C++ dispatch depending on the object's
 64 // actual type.  (See oop.inline.hpp for some of the forwarding code.)
 65 // ALL FUNCTIONS IMPLEMENTING THIS DISPATCH ARE PREFIXED WITH "oop_"!
 66 
 67 // Forward declarations.
 68 template <class T> class Array;
 69 template <class T> class GrowableArray;
 70 class ClassLoaderData;
 71 class fieldDescriptor;
 72 class klassVtable;
 73 class ModuleEntry;
 74 class PackageEntry;
 75 class ParCompactionManager;
 76 class PSPromotionManager;
 77 class vtableEntry;
 78 
 79 class Klass : public Metadata {
 80   friend class VMStructs;
 81   friend class JVMCIVMStructs;
 82  protected:
 83   // If you add a new field that points to any metaspace object, you
 84   // must add this field to Klass::metaspace_pointers_do().
 85 
 86   // note: put frequently-used fields together at start of klass structure
 87   // for better cache behavior (may not make much of a difference but sure won't hurt)
 88   enum { _primary_super_limit = 8 };
 89 
 90   // The "layout helper" is a combined descriptor of object layout.
 91   // For klasses which are neither instance nor array, the value is zero.
 92   //
 93   // For instances, layout helper is a positive number, the instance size.
 94   // This size is already passed through align_object_size and scaled to bytes.
 95   // The low order bit is set if instances of this class cannot be
 96   // allocated using the fastpath.
 97   //
 98   // For arrays, layout helper is a negative number, containing four
 99   // distinct bytes, as follows:
100   //    MSB:[tag, hsz, ebt, log2(esz)]:LSB
101   // where:
102   //    tag is 0x80 if the elements are oops, 0xC0 if non-oops
103   //    hsz is array header size in bytes (i.e., offset of first element)
104   //    ebt is the BasicType of the elements
105   //    esz is the element size in bytes
106   // This packed word is arranged so as to be quickly unpacked by the
107   // various fast paths that use the various subfields.
108   //
109   // The esz bits can be used directly by a SLL instruction, without masking.
110   //
111   // Note that the array-kind tag looks like 0x00 for instance klasses,
112   // since their length in bytes is always less than 24Mb.
113   //
114   // Final note:  This comes first, immediately after C++ vtable,
115   // because it is frequently queried.
116   jint        _layout_helper;
117 
118   // Klass kind used to resolve the runtime type of the instance.
119   //  - Used to implement devirtualized oop closure dispatching.
120   //  - Various type checking in the JVM
121   const KlassKind _kind;
122 
123   // Processed access flags, for use by Class.getModifiers.
124   jint        _modifier_flags;
125 
126   // The fields _super_check_offset, _secondary_super_cache, _secondary_supers
127   // and _primary_supers all help make fast subtype checks.  See big discussion
128   // in doc/server_compiler/checktype.txt
129   //
130   // Where to look to observe a supertype (it is &_secondary_super_cache for
131   // secondary supers, else is &_primary_supers[depth()].
132   juint       _super_check_offset;
133 
134   // Class name.  Instance classes: java/lang/String, etc.  Array classes: [I,
135   // [Ljava/lang/String;, etc.  Set to zero for all other kinds of classes.
136   Symbol*     _name;
137 
138   // Cache of last observed secondary supertype
139   Klass*      _secondary_super_cache;
140   // Array of all secondary supertypes
141   Array<Klass*>* _secondary_supers;
142   // Ordered list of all primary supertypes
143   Klass*      _primary_supers[_primary_super_limit];
144   // java/lang/Class instance mirroring this class
145   OopHandle   _java_mirror;
146   // Superclass
147   Klass*      _super;
148   // First subclass (NULL if none); _subklass->next_sibling() is next one
149   Klass* volatile _subklass;
150   // Sibling link (or NULL); links all subklasses of a klass
151   Klass* volatile _next_sibling;
152 
153   // All klasses loaded by a class loader are chained through these links
154   Klass*      _next_link;
155 
156   // The VM's representation of the ClassLoader used to load this class.
157   // Provide access the corresponding instance java.lang.ClassLoader.
158   ClassLoaderData* _class_loader_data;
159 
160   int _vtable_len;              // vtable length. This field may be read very often when we
161                                 // have lots of itable dispatches (e.g., lambdas and streams).
162                                 // Keep it away from the beginning of a Klass to avoid cacheline
163                                 // contention that may happen when a nearby object is modified.
164   AccessFlags _access_flags;    // Access flags. The class/interface distinction is stored here.
165 
166   JFR_ONLY(DEFINE_TRACE_ID_FIELD;)
167 
168 private:
169   // This is an index into FileMapHeader::_shared_path_table[], to
170   // associate this class with the JAR file where it's loaded from during
171   // dump time. If a class is not loaded from the shared archive, this field is
172   // -1.
173   jshort _shared_class_path_index;
174 
175 #if INCLUDE_CDS
176   // Various attributes for shared classes. Should be zero for a non-shared class.
177   u2     _shared_class_flags;
178   enum CDSSharedClassFlags {
179     _archived_lambda_proxy_is_available    = 1 << 1,
180     _has_value_based_class_annotation      = 1 << 2,
181     _verified_at_dump_time                 = 1 << 3,
182     _has_archived_enum_objs                = 1 << 4,
183     // This class was not loaded from a classfile in the module image
184     // or classpath.
185     _is_generated_shared_class             = 1 << 5
186   };
187 #endif
188 
189   CDS_JAVA_HEAP_ONLY(int _archived_mirror_index;)
190 
191 protected:
192 
193   // Constructor
194   Klass(KlassKind kind);
195   Klass() : _kind(KlassKind(-1)) { assert(DumpSharedSpaces || UseSharedSpaces, "only for cds"); }
196 
197   void* operator new(size_t size, ClassLoaderData* loader_data, size_t word_size, TRAPS) throw();
198 
199  public:
200   int kind() { return _kind; }
201 
202   enum class DefaultsLookupMode { find, skip };
203   enum class OverpassLookupMode { find, skip };
204   enum class StaticLookupMode   { find, skip };
205   enum class PrivateLookupMode  { find, skip };
206 
207   virtual bool is_klass() const { return true; }
208 
209   // super() cannot be InstanceKlass* -- Java arrays are covariant, and _super is used
210   // to implement that. NB: the _super of "[Ljava/lang/Integer;" is "[Ljava/lang/Number;"
211   // If this is not what your code expects, you're probably looking for Klass::java_super().
212   Klass* super() const               { return _super; }
213   void set_super(Klass* k)           { _super = k; }
214 
215   // initializes _super link, _primary_supers & _secondary_supers arrays
216   void initialize_supers(Klass* k, Array<InstanceKlass*>* transitive_interfaces, TRAPS);
217 
218   // klass-specific helper for initializing _secondary_supers
219   virtual GrowableArray<Klass*>* compute_secondary_supers(int num_extra_slots,
220                                                           Array<InstanceKlass*>* transitive_interfaces);
221 
222   // java_super is the Java-level super type as specified by Class.getSuperClass.
223   virtual InstanceKlass* java_super() const  { return NULL; }
224 
225   juint    super_check_offset() const  { return _super_check_offset; }
226   void set_super_check_offset(juint o) { _super_check_offset = o; }
227 
228   Klass* secondary_super_cache() const     { return _secondary_super_cache; }
229   void set_secondary_super_cache(Klass* k) { _secondary_super_cache = k; }
230 
231   Array<Klass*>* secondary_supers() const { return _secondary_supers; }
232   void set_secondary_supers(Array<Klass*>* k) { _secondary_supers = k; }
233 
234   // Return the element of the _super chain of the given depth.
235   // If there is no such element, return either NULL or this.
236   Klass* primary_super_of_depth(juint i) const {
237     assert(i < primary_super_limit(), "oob");
238     Klass* super = _primary_supers[i];
239     assert(super == NULL || super->super_depth() == i, "correct display");
240     return super;
241   }
242 
243   // Can this klass be a primary super?  False for interfaces and arrays of
244   // interfaces.  False also for arrays or classes with long super chains.
245   bool can_be_primary_super() const {
246     const juint secondary_offset = in_bytes(secondary_super_cache_offset());
247     return super_check_offset() != secondary_offset;
248   }
249   virtual bool can_be_primary_super_slow() const;
250 
251   // Returns number of primary supers; may be a number in the inclusive range [0, primary_super_limit].
252   juint super_depth() const {
253     if (!can_be_primary_super()) {
254       return primary_super_limit();
255     } else {
256       juint d = (super_check_offset() - in_bytes(primary_supers_offset())) / sizeof(Klass*);
257       assert(d < primary_super_limit(), "oob");
258       assert(_primary_supers[d] == this, "proper init");
259       return d;
260     }
261   }
262 
263   // java mirror
264   oop java_mirror() const;
265   oop java_mirror_no_keepalive() const;
266   void set_java_mirror(Handle m);
267 
268   oop archived_java_mirror() NOT_CDS_JAVA_HEAP_RETURN_(NULL);
269   void set_archived_java_mirror(oop m) NOT_CDS_JAVA_HEAP_RETURN;
270 
271   // Temporary mirror switch used by RedefineClasses
272   void replace_java_mirror(oop mirror);
273 
274   // Set java mirror OopHandle to NULL for CDS
275   // This leaves the OopHandle in the CLD, but that's ok, you can't release them.
276   void clear_java_mirror_handle() { _java_mirror = OopHandle(); }
277 
278   // modifier flags
279   jint modifier_flags() const          { return _modifier_flags; }
280   void set_modifier_flags(jint flags)  { _modifier_flags = flags; }
281 
282   // size helper
283   int layout_helper() const            { return _layout_helper; }
284   void set_layout_helper(int lh)       { _layout_helper = lh; }
285 
286   // Note: for instances layout_helper() may include padding.
287   // Use InstanceKlass::contains_field_offset to classify field offsets.
288 
289   // sub/superklass links
290   Klass* subklass(bool log = false) const;
291   Klass* next_sibling(bool log = false) const;
292 
293   InstanceKlass* superklass() const;
294   void append_to_sibling_list();           // add newly created receiver to superklass' subklass list
295 
296   void set_next_link(Klass* k) { _next_link = k; }
297   Klass* next_link() const { return _next_link; }   // The next klass defined by the class loader.
298   Klass** next_link_addr() { return &_next_link; }
299 
300   // class loader data
301   ClassLoaderData* class_loader_data() const               { return _class_loader_data; }
302   void set_class_loader_data(ClassLoaderData* loader_data) {  _class_loader_data = loader_data; }
303 
304   int shared_classpath_index() const   {
305     return _shared_class_path_index;
306   };
307 
308   void set_shared_classpath_index(int index) {
309     _shared_class_path_index = index;
310   };
311 
312   bool has_archived_mirror_index() const {
313     CDS_JAVA_HEAP_ONLY(return _archived_mirror_index >= 0;)
314     NOT_CDS_JAVA_HEAP(return false);
315   }
316 
317   void clear_archived_mirror_index() NOT_CDS_JAVA_HEAP_RETURN;
318 
319   void set_lambda_proxy_is_available() {
320     CDS_ONLY(_shared_class_flags |= _archived_lambda_proxy_is_available;)
321   }
322   void clear_lambda_proxy_is_available() {
323     CDS_ONLY(_shared_class_flags &= ~_archived_lambda_proxy_is_available;)
324   }
325   bool lambda_proxy_is_available() const {
326     CDS_ONLY(return (_shared_class_flags & _archived_lambda_proxy_is_available) != 0;)
327     NOT_CDS(return false;)
328   }
329 
330   void set_has_value_based_class_annotation() {
331     CDS_ONLY(_shared_class_flags |= _has_value_based_class_annotation;)
332   }
333   void clear_has_value_based_class_annotation() {
334     CDS_ONLY(_shared_class_flags &= ~_has_value_based_class_annotation;)
335   }
336   bool has_value_based_class_annotation() const {
337     CDS_ONLY(return (_shared_class_flags & _has_value_based_class_annotation) != 0;)
338     NOT_CDS(return false;)
339   }
340 
341   void set_verified_at_dump_time() {
342     CDS_ONLY(_shared_class_flags |= _verified_at_dump_time;)
343   }
344   bool verified_at_dump_time() const {
345     CDS_ONLY(return (_shared_class_flags & _verified_at_dump_time) != 0;)
346     NOT_CDS(return false;)
347   }
348 
349   void set_has_archived_enum_objs() {
350     CDS_ONLY(_shared_class_flags |= _has_archived_enum_objs;)
351   }
352   bool has_archived_enum_objs() const {
353     CDS_ONLY(return (_shared_class_flags & _has_archived_enum_objs) != 0;)
354     NOT_CDS(return false;)
355   }
356 
357   void set_is_generated_shared_class() {
358     CDS_ONLY(_shared_class_flags |= _is_generated_shared_class;)
359   }
360   bool is_generated_shared_class() const {
361     CDS_ONLY(return (_shared_class_flags & _is_generated_shared_class) != 0;)
362     NOT_CDS(return false;)
363   }
364 
365   // Obtain the module or package for this class
366   virtual ModuleEntry* module() const = 0;
367   virtual PackageEntry* package() const = 0;
368 
369  protected:                                // internal accessors
370   void     set_subklass(Klass* s);
371   void     set_next_sibling(Klass* s);
372 
373  public:
374 
375   // Compiler support
376   static ByteSize super_offset()                 { return in_ByteSize(offset_of(Klass, _super)); }
377   static ByteSize super_check_offset_offset()    { return in_ByteSize(offset_of(Klass, _super_check_offset)); }
378   static ByteSize primary_supers_offset()        { return in_ByteSize(offset_of(Klass, _primary_supers)); }
379   static ByteSize secondary_super_cache_offset() { return in_ByteSize(offset_of(Klass, _secondary_super_cache)); }
380   static ByteSize secondary_supers_offset()      { return in_ByteSize(offset_of(Klass, _secondary_supers)); }
381   static ByteSize java_mirror_offset()           { return in_ByteSize(offset_of(Klass, _java_mirror)); }
382   static ByteSize class_loader_data_offset()     { return in_ByteSize(offset_of(Klass, _class_loader_data)); }
383   static ByteSize modifier_flags_offset()        { return in_ByteSize(offset_of(Klass, _modifier_flags)); }
384   static ByteSize layout_helper_offset()         { return in_ByteSize(offset_of(Klass, _layout_helper)); }
385   static ByteSize access_flags_offset()          { return in_ByteSize(offset_of(Klass, _access_flags)); }
386 
387   // Unpacking layout_helper:
388   static const int _lh_neutral_value           = 0;  // neutral non-array non-instance value
389   static const int _lh_instance_slow_path_bit  = 0x01;
390   static const int _lh_log2_element_size_shift = BitsPerByte*0;
391   static const int _lh_log2_element_size_mask  = BitsPerLong-1;
392   static const int _lh_element_type_shift      = BitsPerByte*1;
393   static const int _lh_element_type_mask       = right_n_bits(BitsPerByte);  // shifted mask
394   static const int _lh_header_size_shift       = BitsPerByte*2;
395   static const int _lh_header_size_mask        = right_n_bits(BitsPerByte);  // shifted mask
396   static const int _lh_array_tag_bits          = 2;
397   static const int _lh_array_tag_shift         = BitsPerInt - _lh_array_tag_bits;
398   static const int _lh_array_tag_obj_value     = ~0x01;   // 0x80000000 >> 30
399 
400   static const unsigned int _lh_array_tag_type_value = 0Xffffffff; // ~0x00,  // 0xC0000000 >> 30
401 
402   static int layout_helper_size_in_bytes(jint lh) {
403     assert(lh > (jint)_lh_neutral_value, "must be instance");
404     return (int) lh & ~_lh_instance_slow_path_bit;
405   }
406   static bool layout_helper_needs_slow_path(jint lh) {
407     assert(lh > (jint)_lh_neutral_value, "must be instance");
408     return (lh & _lh_instance_slow_path_bit) != 0;
409   }
410   static bool layout_helper_is_instance(jint lh) {
411     return (jint)lh > (jint)_lh_neutral_value;
412   }
413   static bool layout_helper_is_array(jint lh) {
414     return (jint)lh < (jint)_lh_neutral_value;
415   }
416   static bool layout_helper_is_typeArray(jint lh) {
417     // _lh_array_tag_type_value == (lh >> _lh_array_tag_shift);
418     return (juint)lh >= (juint)(_lh_array_tag_type_value << _lh_array_tag_shift);
419   }
420   static bool layout_helper_is_objArray(jint lh) {
421     // _lh_array_tag_obj_value == (lh >> _lh_array_tag_shift);
422     return (jint)lh < (jint)(_lh_array_tag_type_value << _lh_array_tag_shift);
423   }
424   static int layout_helper_header_size(jint lh) {
425     assert(lh < (jint)_lh_neutral_value, "must be array");
426     int hsize = (lh >> _lh_header_size_shift) & _lh_header_size_mask;
427     assert(hsize > 0 && hsize < (int)sizeof(oopDesc)*3, "sanity");
428     return hsize;
429   }
430   static BasicType layout_helper_element_type(jint lh) {
431     assert(lh < (jint)_lh_neutral_value, "must be array");
432     int btvalue = (lh >> _lh_element_type_shift) & _lh_element_type_mask;
433     assert(btvalue >= T_BOOLEAN && btvalue <= T_OBJECT, "sanity");
434     return (BasicType) btvalue;
435   }
436 
437   // Want a pattern to quickly diff against layout header in register
438   // find something less clever!
439   static int layout_helper_boolean_diffbit() {
440     jint zlh = array_layout_helper(T_BOOLEAN);
441     jint blh = array_layout_helper(T_BYTE);
442     assert(zlh != blh, "array layout helpers must differ");
443     int diffbit = 1;
444     while ((diffbit & (zlh ^ blh)) == 0 && (diffbit & zlh) == 0) {
445       diffbit <<= 1;
446       assert(diffbit != 0, "make sure T_BOOLEAN has a different bit than T_BYTE");
447     }
448     return diffbit;
449   }
450 
451   static int layout_helper_log2_element_size(jint lh) {
452     assert(lh < (jint)_lh_neutral_value, "must be array");
453     int l2esz = (lh >> _lh_log2_element_size_shift) & _lh_log2_element_size_mask;
454     assert(l2esz <= LogBytesPerLong,
455            "sanity. l2esz: 0x%x for lh: 0x%x", (uint)l2esz, (uint)lh);
456     return l2esz;
457   }
458   static jint array_layout_helper(jint tag, int hsize, BasicType etype, int log2_esize) {
459     return (tag        << _lh_array_tag_shift)
460       |    (hsize      << _lh_header_size_shift)
461       |    ((int)etype << _lh_element_type_shift)
462       |    (log2_esize << _lh_log2_element_size_shift);
463   }
464   static jint instance_layout_helper(jint size, bool slow_path_flag) {
465     return (size << LogBytesPerWord)
466       |    (slow_path_flag ? _lh_instance_slow_path_bit : 0);
467   }
468   static int layout_helper_to_size_helper(jint lh) {
469     assert(lh > (jint)_lh_neutral_value, "must be instance");
470     // Note that the following expression discards _lh_instance_slow_path_bit.
471     return lh >> LogBytesPerWord;
472   }
473   // Out-of-line version computes everything based on the etype:
474   static jint array_layout_helper(BasicType etype);
475 
476   // What is the maximum number of primary superclasses any klass can have?
477   static juint primary_super_limit()         { return _primary_super_limit; }
478 
479   // vtables
480   klassVtable vtable() const;
481   int vtable_length() const { return _vtable_len; }
482 
483   // subclass check
484   bool is_subclass_of(const Klass* k) const;
485   // subtype check: true if is_subclass_of, or if k is interface and receiver implements it
486   bool is_subtype_of(Klass* k) const {
487     juint    off = k->super_check_offset();
488     Klass* sup = *(Klass**)( (address)this + off );
489     const juint secondary_offset = in_bytes(secondary_super_cache_offset());
490     if (sup == k) {
491       return true;
492     } else if (off != secondary_offset) {
493       return false;
494     } else {
495       return search_secondary_supers(k);
496     }
497   }
498 
499   bool search_secondary_supers(Klass* k) const;
500 
501   // Find LCA in class hierarchy
502   Klass *LCA( Klass *k );
503 
504   // Check whether reflection/jni/jvm code is allowed to instantiate this class;
505   // if not, throw either an Error or an Exception.
506   virtual void check_valid_for_instantiation(bool throwError, TRAPS);
507 
508   // array copying
509   virtual void  copy_array(arrayOop s, int src_pos, arrayOop d, int dst_pos, int length, TRAPS);
510 
511   // tells if the class should be initialized
512   virtual bool should_be_initialized() const    { return false; }
513   // initializes the klass
514   virtual void initialize(TRAPS);
515   virtual Klass* find_field(Symbol* name, Symbol* signature, fieldDescriptor* fd) const;
516   virtual Method* uncached_lookup_method(const Symbol* name, const Symbol* signature,
517                                          OverpassLookupMode overpass_mode,
518                                          PrivateLookupMode = PrivateLookupMode::find) const;
519  public:
520   Method* lookup_method(const Symbol* name, const Symbol* signature) const {
521     return uncached_lookup_method(name, signature, OverpassLookupMode::find);
522   }
523 
524   // array class with specific rank
525   virtual Klass* array_klass(int rank, TRAPS) = 0;
526 
527   // array class with this klass as element type
528   virtual Klass* array_klass(TRAPS) = 0;
529 
530   // These will return NULL instead of allocating on the heap:
531   virtual Klass* array_klass_or_null(int rank) = 0;
532   virtual Klass* array_klass_or_null() = 0;
533 
534   virtual oop protection_domain() const = 0;
535 
536   oop class_loader() const;
537 
538   inline oop klass_holder() const;
539 
540  protected:
541 
542   // Error handling when length > max_length or length < 0
543   static void check_array_allocation_length(int length, int max_length, TRAPS);
544 
545   void set_vtable_length(int len) { _vtable_len= len; }
546 
547   vtableEntry* start_of_vtable() const;
548   void restore_unshareable_info(ClassLoaderData* loader_data, Handle protection_domain, TRAPS);
549  public:
550   Method* method_at_vtable(int index);
551 
552   static ByteSize vtable_start_offset();
553   static ByteSize vtable_length_offset() {
554     return byte_offset_of(Klass, _vtable_len);
555   }
556 
557   // CDS support - remove and restore oops from metadata. Oops are not shared.
558   virtual void remove_unshareable_info();
559   virtual void remove_java_mirror();
560 
561   bool is_unshareable_info_restored() const {
562     assert(is_shared(), "use this for shared classes only");
563     if (has_archived_mirror_index()) {
564       // _java_mirror is not a valid OopHandle but rather an encoded reference in the shared heap
565       return false;
566     } else if (_java_mirror.ptr_raw() == NULL) {
567       return false;
568     } else {
569       return true;
570     }
571   }
572 
573  public:
574   // ALL FUNCTIONS BELOW THIS POINT ARE DISPATCHED FROM AN OOP
575   // These functions describe behavior for the oop not the KLASS.
576 
577   // actual oop size of obj in memory in word size.
578   virtual size_t oop_size(oop obj) const = 0;
579 
580   // Size of klass in word size.
581   virtual int size() const = 0;
582 
583   // Returns the Java name for a class (Resource allocated)
584   // For arrays, this returns the name of the element with a leading '['.
585   // For classes, this returns the name with the package separators
586   //     turned into '.'s.
587   const char* external_name() const;
588   // Returns the name for a class (Resource allocated) as the class
589   // would appear in a signature.
590   // For arrays, this returns the name of the element with a leading '['.
591   // For classes, this returns the name with a leading 'L' and a trailing ';'
592   //     and the package separators as '/'.
593   virtual const char* signature_name() const;
594 
595   const char* joint_in_module_of_loader(const Klass* class2, bool include_parent_loader = false) const;
596   const char* class_in_module_of_loader(bool use_are = false, bool include_parent_loader = false) const;
597 
598   // Returns "interface", "abstract class" or "class".
599   const char* external_kind() const;
600 
601   // type testing operations
602 #ifdef ASSERT
603  protected:
604   virtual bool is_instance_klass_slow()     const { return false; }
605   virtual bool is_array_klass_slow()        const { return false; }
606   virtual bool is_objArray_klass_slow()     const { return false; }
607   virtual bool is_typeArray_klass_slow()    const { return false; }
608 #endif // ASSERT
609  public:
610 
611   // Fast non-virtual versions
612   #ifndef ASSERT
613   #define assert_same_query(xval, xcheck) xval
614   #else
615  private:
616   static bool assert_same_query(bool xval, bool xslow) {
617     assert(xval == xslow, "slow and fast queries agree");
618     return xval;
619   }
620  public:
621   #endif
622 
623   bool is_instance_klass()              const { return assert_same_query(_kind <= InstanceStackChunkKlassKind, is_instance_klass_slow()); }
624   // Other is anything that is not one of the more specialized kinds of InstanceKlass.
625   bool is_other_instance_klass()        const { return _kind == InstanceKlassKind; }
626   bool is_reference_instance_klass()    const { return _kind == InstanceRefKlassKind; }
627   bool is_mirror_instance_klass()       const { return _kind == InstanceMirrorKlassKind; }
628   bool is_class_loader_instance_klass() const { return _kind == InstanceClassLoaderKlassKind; }
629   bool is_array_klass()                 const { return assert_same_query( _kind >= TypeArrayKlassKind, is_array_klass_slow()); }
630   bool is_stack_chunk_instance_klass()  const { return _kind == InstanceStackChunkKlassKind; }
631   bool is_objArray_klass()              const { return assert_same_query( _kind == ObjArrayKlassKind,  is_objArray_klass_slow()); }
632   bool is_typeArray_klass()             const { return assert_same_query( _kind == TypeArrayKlassKind, is_typeArray_klass_slow()); }
633   #undef assert_same_query
634 
635   // Access flags
636   AccessFlags access_flags() const         { return _access_flags;  }
637   void set_access_flags(AccessFlags flags) { _access_flags = flags; }
638 
639   bool is_public() const                { return _access_flags.is_public(); }
640   bool is_final() const                 { return _access_flags.is_final(); }
641   bool is_interface() const             { return _access_flags.is_interface(); }
642   bool is_abstract() const              { return _access_flags.is_abstract(); }
643   bool is_super() const                 { return _access_flags.is_super(); }
644   bool is_synthetic() const             { return _access_flags.is_synthetic(); }
645   void set_is_synthetic()               { _access_flags.set_is_synthetic(); }
646   bool has_finalizer() const            { return _access_flags.has_finalizer(); }
647   bool has_final_method() const         { return _access_flags.has_final_method(); }
648   void set_has_finalizer()              { _access_flags.set_has_finalizer(); }
649   void set_has_final_method()           { _access_flags.set_has_final_method(); }
650   bool has_vanilla_constructor() const  { return _access_flags.has_vanilla_constructor(); }
651   void set_has_vanilla_constructor()    { _access_flags.set_has_vanilla_constructor(); }
652   bool has_miranda_methods () const     { return access_flags().has_miranda_methods(); }
653   void set_has_miranda_methods()        { _access_flags.set_has_miranda_methods(); }
654   bool is_shared() const                { return access_flags().is_shared_class(); } // shadows MetaspaceObj::is_shared)()
655   void set_is_shared()                  { _access_flags.set_is_shared_class(); }
656   bool is_hidden() const                { return access_flags().is_hidden_class(); }
657   void set_is_hidden()                  { _access_flags.set_is_hidden_class(); }
658   bool is_value_based()                 { return _access_flags.is_value_based_class(); }
659   void set_is_value_based()             { _access_flags.set_is_value_based_class(); }
660 
661   inline bool is_non_strong_hidden() const;
662 
663   bool is_cloneable() const;
664   void set_is_cloneable();
665 
666   JFR_ONLY(DEFINE_TRACE_ID_METHODS;)
667 
668   virtual void metaspace_pointers_do(MetaspaceClosure* iter);
669   virtual MetaspaceObj::Type type() const { return ClassType; }
670 
671   inline bool is_loader_alive() const;
672 
673   void clean_subklass();
674 
675   static void clean_weak_klass_links(bool unloading_occurred, bool clean_alive_klasses = true);
676   static void clean_subklass_tree() {
677     clean_weak_klass_links(/*unloading_occurred*/ true , /* clean_alive_klasses */ false);
678   }
679 
680   // Return self, except for abstract classes with exactly 1
681   // implementor.  Then return the 1 concrete implementation.
682   Klass *up_cast_abstract();
683 
684   // klass name
685   Symbol* name() const                   { return _name; }
686   void set_name(Symbol* n);
687 
688   virtual void release_C_heap_structures(bool release_constant_pool = true);
689 
690  public:
691   virtual jint compute_modifier_flags() const = 0;
692 
693   // JVMTI support
694   virtual jint jvmti_class_status() const;
695 
696   // Printing
697   virtual void print_on(outputStream* st) const;
698 
699   virtual void oop_print_value_on(oop obj, outputStream* st);
700   virtual void oop_print_on      (oop obj, outputStream* st);
701 
702   virtual const char* internal_name() const = 0;
703 
704   // Verification
705   virtual void verify_on(outputStream* st);
706   void verify() { verify_on(tty); }
707 
708 #ifndef PRODUCT
709   bool verify_vtable_index(int index);
710 #endif
711 
712   virtual void oop_verify_on(oop obj, outputStream* st);
713 
714   // for error reporting
715   static bool is_valid(Klass* k);
716 };
717 
718 #endif // SHARE_OOPS_KLASS_HPP