oop-klass

当C,C++和Delphi等程序被编译成二进制程序后,原来所定义的高级数据结构都不复存在了,当windows/linux等操作系统(宿主机)加载这些二进制程序时,是不会加载这些语言中所定义的高级数据结构的,宿主机压根就不知道原来定了那些数据结构,哪些类,所有的数据结构都被转换为对特定内存段的偏移地址.例如C中的Struct结构体,被编译后不复存在,汇编和机器语言中没有与之对应的数据结构的概念,CPU更不知道何为结构体.C++和Delphi中的类概念被编译后也不复存在,所谓的类最终变成内存首地址.而JVM虚拟机在加载字节码程序时,会记录字节码中所定义的所有类型的原始信息(元数据),JVM知道程序中包含了哪些类,以及每个类中所关联的字段,方法,父类等信息.这是JVM虚拟机与操作系统最大的区别所在

oop:ordinary object pointer,用来描述对象实例信息,一般保存在HEAP
klass:用来描述java类,是虚拟机内部java类型结构的对等体,一般保存在PERM
根据最新的oopsHierarchy.hpp里的说明,整个继承树分为以下三个

OBJECT hierarchy

继承关系代码如下

// OBJECT hierarchy
// This hierarchy is a representation hierarchy, i.e. if A is a superclass
// of B, A's representation is a prefix of B's representation.

typedef class oopDesc*                    oop;
typedef class   instanceOopDesc*            instanceOop;
typedef class   arrayOopDesc*               arrayOop;
typedef class     objArrayOopDesc*            objArrayOop;
typedef class     typeArrayOopDesc*           typeArrayOop;

• oopDesc
  这个类定义在oop.hpp中,方法有很对,属性却很少,如下所示

class oopDesc {
  friend class VMStructs;
  friend class JVMCIVMStructs;
 private:
  volatile markWord _mark;
  union _metadata {
    Klass*      _klass;
    narrowKlass _compressed_klass;
  } _metadata;
......
}

_mark属性主要使用标记对象的各种状态,例如锁,分代,线程状态等等.而_metadata可以看出来指向Klass,至于里面的方法很多.上面的narrowKlass是用于指针压缩,相关定义在oopsHierarchy.hpp如下

typedef juint narrowOop; // Offset instead of address for an oop within a java object

// If compressed klass pointers then use narrowKlass.
typedef juint  narrowKlass;

而juint则在globalDefinitions.hpp定义为u4

metadata hierarchy

// The metadata hierarchy is separate from the oop hierarchy
//      class MetaspaceObj
class   ConstMethod;
class   ConstantPoolCache;
class   MethodData;
//      class Metadata
class   Method;
class   ConstantPool;
//      class CHeapObj
class   CompiledICHolder;

klass hierarchy

// The klass hierarchy is separate from the oop hierarchy.
class Klass;
class   InstanceKlass;
class     InstanceMirrorKlass;
class     InstanceClassLoaderKlass;
class     InstanceRefKlass;
class   ArrayKlass;
class     ObjArrayKlass;
class     TypeArrayKlass;

oop

classDiagram

description

这里面各类的作用如下

klass

classDiagram

为了方便起见,下面的方法里省略了各种print*

description

这里面各类的作用如下

InstanceKlass

// See "The Java Virtual Machine Specification" section 2.16.2-5 for a detailed description
  // of the class loading & initialization procedure, and the use of the states.
  enum ClassState {
    allocated,                          // allocated (but not yet linked)
    loaded,                             // loaded and inserted in class hierarchy (but not linked yet)
    linked,                             // successfully linked/verified (but not initialized yet)
    being_initialized,                  // currently running class initializer
    fully_initialized,                  // initialized (successfull final state)
    initialization_error                // error happened during initialization
  };

// Describes where oops are located in instances of this klass.
class OopMapBlock {
 public:
   void increment_count(int diff) { _count += diff; }
  int offset_span() const { return _count * heapOopSize; }
  int end_offset() const {
    return offset() + offset_span();
  }
  bool is_contiguous(int another_offset) const {
    return another_offset == end_offset();
  }
  // sizeof(OopMapBlock) in words.
  static const int size_in_words() {
    return align_up((int)sizeof(OopMapBlock), wordSize) >>
      LogBytesPerWord;
  }
  static int compare_offset(const OopMapBlock* a, const OopMapBlock* b) {
    return a->offset() - b->offset();
  }
 private:
  int  _offset;//PUBLIC
  uint _count;//PUBLIC
};

// An InstanceKlass is the VM level representation of a Java class.
// It contains all information needed for at class at execution runtime.

//  InstanceKlass embedded field layout (after declared fields):
//    [EMBEDDED Java vtable             ] size in words = vtable_len
//    [EMBEDDED nonstatic oop-map blocks] size in words = nonstatic_oop_map_size
//      The embedded nonstatic oop-map blocks are short pairs (offset, length)
//      indicating where oops are located in instances of this klass.
//    [EMBEDDED implementor of the interface] only exist for interface
//    [EMBEDDED unsafe_anonymous_host klass] only exist for an unsafe anonymous class (JSR 292 enabled)
//    [EMBEDDED fingerprint       ] only if should_store_fingerprint()==true

// forward declaration for class -- see below for definition
class InstanceKlass: public Klass {
  friend class VMStructs;
  friend class JVMCIVMStructs;
  friend class ClassFileParser;
  friend class CompileReplay;

 public:
  static const KlassID ID = InstanceKlassID;

 protected:
  InstanceKlass(const ClassFileParser& parser, unsigned kind, KlassID id = ID);

 public:
  InstanceKlass() { assert(DumpSharedSpaces || UseSharedSpaces, "only for CDS"); }
 private:
  static InstanceKlass* allocate_instance_klass(const ClassFileParser& parser, TRAPS);

 protected:
  Annotations*    _annotations;//PUBLIC Annotations for this class
  // Package this class is defined in
  PackageEntry*   _package_entry;
  // Array classes holding elements of this class.
  ObjArrayKlass* volatile _array_klasses;//PUBLIC
  ConstantPool* _constants;//PUBLIC Constant pool for this class.
  Array<jushort>* _inner_classes;//PUBLIC
  Array<jushort>* _nest_members;//PUBLIC class info index for the class that is a nest member

  // Resolved nest-host klass: either true nest-host or self if we are not
  // nested, or an error occurred resolving or validating the nominated
  // nest-host. Can also be set directly by JDK API's that establish nest
  // relationships.
  // By always being set it makes nest-member access checks simpler.
  InstanceKlass* _nest_host;
  Array<jushort>* _permitted_subclasses;//PUBLIC class info index for the class that is a permitted subclass
  Array<RecordComponent*>* _record_components;//PUBLIC The contents of the Record attribute.

  // the source debug extension for this klass, NULL if not specified.
  // Specified as UTF-8 string without terminating zero byte in the classfile,
  // it is stored in the instanceklass as a NULL-terminated UTF-8 string
  const char*     _source_debug_extension;

  // Number of heapOopSize words used by non-static fields in this klass
  // (including inherited fields but after header_size()).
  int             _nonstatic_field_size;//PUBLIC
  int             _static_field_size;    //PUBLIC number words used by static fields (oop and non-oop) in this klass

  int             _nonstatic_oop_map_size;//PUBLIC size in words of nonstatic oop map blocks
  int             _itable_len;           // length of Java itable (in words)

  // The NestHost attribute. The class info index for the class
  // that is the nest-host of this class. This data has not been validated.
  u2              _nest_host_index;//PUBLIC
  u2              _this_class_index;              //PUBLIC constant pool entry

  u2              _static_oop_field_count;//PUBLIC number of static oop fields in this klass
  u2              _java_fields_count;    // The number of declared Java fields

  volatile u2     _idnum_allocated_count;         // JNI/JVMTI: increments with the addition of methods, old ids don't change

  bool            _is_marked_dependent;  //PUBLIC used for marking during flushing and deoptimization

  // Class states are defined as ClassState (see above).
  // Place the _init_state here to utilize the unused 2-byte after
  // _idnum_allocated_count.
  u1              _init_state;                    // state of class

  // This can be used to quickly discriminate among the four kinds of
  // InstanceKlass. This should be an enum (?)
  static const unsigned _kind_other        = 0; // concrete InstanceKlass
  static const unsigned _kind_reference    = 1; // InstanceRefKlass
  static const unsigned _kind_class_loader = 2; // InstanceClassLoaderKlass
  static const unsigned _kind_mirror       = 3; // InstanceMirrorKlass

  u1              _reference_type;                // reference type
  u1              _kind;                          // kind of InstanceKlass
  u2 shared_loader_type_bits() const {
    return _misc_is_shared_boot_class|_misc_is_shared_platform_class|_misc_is_shared_app_class;
  }
  u2              _misc_flags;           // There is more space in access_flags for more flags.

  Thread*         _init_thread;          // Pointer to current thread doing initialization (to handle recursive initialization)
  OopMapCache*    volatile _oop_map_cache;   //PUBLIC OopMapCache for all methods in the klass (allocated lazily)
  JNIid*          _jni_ids;              //PUBLIC First JNI identifier for static fields in this class
  jmethodID*      volatile _methods_jmethod_ids;  // jmethodIDs corresponding to method_idnum, or NULL if none
  nmethodBucket*  volatile _dep_context;          // packed DependencyContext structure
  uint64_t        volatile _dep_context_last_cleaned;
  nmethod*        _osr_nmethods_head;    //PUBLIC Head of list of on-stack replacement nmethods for this class

  Array<Method*>* _methods;//PUBLIC Method array.
  Array<Method*>* _default_methods;//PUBLIC Default Method Array, concrete methods inherited from interfaces
  // Interfaces (InstanceKlass*s) this class declares locally to implement.
  Array<InstanceKlass*>* _local_interfaces;//只被赋值一次
  // Interfaces (InstanceKlass*s) this class implements transitively.
  Array<InstanceKlass*>* _transitive_interfaces;//只被赋值一次
  Array<int>*     _method_ordering;//PUBLIC Int array containing the original order of method in the class file (for JVMTI).
  // Int array containing the vtable_indices for default_methods
  // offset matches _default_methods offset
  Array<int>*     _default_vtable_indices;//PUBLLIC

  // Instance and static variable information, starts with 6-tuples of shorts
  // [access, name index, sig index, initval index, low_offset, high_offset]
  // for all fields, followed by the generic signature data at the end of
  // the array. Only fields with generic signature attributes have the generic
  // signature data set in the array. The fields array looks like following:
  //
  // f1: [access, name index, sig index, initial value index, low_offset, high_offset]
  // f2: [access, name index, sig index, initial value index, low_offset, high_offset]
  //      ...
  // fn: [access, name index, sig index, initial value index, low_offset, high_offset]
  //     [generic signature index]
  //     [generic signature index]
  //     ...
  Array<u2>*      _fields;

  // embedded Java vtable follows here
  // embedded Java itables follows here
  // embedded static fields follows here
  // embedded nonstatic oop-map blocks follows here
  // embedded implementor of this interface follows here
  //   The embedded implementor only exists if the current klass is an
  //   iterface. The possible values of the implementor fall into following
  //   three cases:
  //     NULL: no implementor.
  //     A Klass* that's not itself: one implementor.
  //     Itself: more than one implementors.
  // embedded unsafe_anonymous_host klass follows here
  //   The embedded host klass only exists in an unsafe anonymous class for
  //   dynamic language support (JSR 292 enabled). The host class grants
  //   its access privileges to this class also. The host class is either
  //   named, or a previously loaded unsafe anonymous class. A non-anonymous class
  //   or an anonymous class loaded through normal classloading does not
  //   have this embedded field.
  //

  friend class SystemDictionary;

  static bool _disable_method_binary_search;

 public:
  // The UNREGISTERED class loader type
  bool is_shared_unregistered_class() const {
    return (_misc_flags & shared_loader_type_bits()) == 0;
  }

  void clear_shared_class_loader_type() {
    _misc_flags &= ~shared_loader_type_bits();
  }

  void set_shared_class_loader_type(s2 loader_type);
  void assign_class_loader_type();
  // methods
  Method* method_with_idnum(int idnum);
  Method* method_with_orig_idnum(int idnum);
  Method* method_with_orig_idnum(int idnum, int version);

  // method ordering
  void copy_method_ordering(const intArray* m, TRAPS);

  // default method vtable_indices
  Array<int>* create_new_default_vtable_indices(int len, TRAPS);
  

 private:
  friend class fieldDescriptor;
  FieldInfo* field(int index) const { return FieldInfo::from_field_array(_fields, index); }

 public:
  int     field_offset      (int index) const { return field(index)->offset(); }
  int     field_access_flags(int index) const { return field(index)->access_flags(); }
  Symbol* field_name        (int index) const { return field(index)->name(constants()); }
  Symbol* field_signature   (int index) const { return field(index)->signature(constants()); }

  // Number of Java declared fields
  int java_fields_count() const           { return (int)_java_fields_count; }

  Array<u2>* fields() const            { return _fields; }
  void set_fields(Array<u2>* f, u2 java_fields_count) {
    guarantee(_fields == NULL || f == NULL, "Just checking");
    _fields = f;
    _java_fields_count = java_fields_count;
  }

  // dynamic nest member support
  void set_nest_host(InstanceKlass* host, TRAPS);

  bool is_record() const { return _record_components != NULL; }

private:
  // Called to verify that k is a member of this nest - does not look at k's nest-host
  bool has_nest_member(InstanceKlass* k, TRAPS) const;

public:
  // Used to construct informative IllegalAccessError messages at a higher level,
  // if there was an issue resolving or validating the nest host.
  // Returns NULL if there was no error.
  const char* nest_host_error(TRAPS);
  // Returns nest-host class, resolving and validating it if needed.
  // Returns NULL if resolution is not possible from the calling context.
  InstanceKlass* nest_host(TRAPS);
  // Check if this klass is a nestmate of k - resolves this nest-host and k's
  bool has_nestmate_access_to(InstanceKlass* k, TRAPS);

  // Called to verify that k is a permitted subclass of this class
  bool has_as_permitted_subclass(const InstanceKlass* k) const;

  // method override check
  bool is_override(const methodHandle& super_method, Handle targetclassloader, Symbol* targetclassname, TRAPS);

  // package
  PackageEntry* package() const     { return _package_entry; }
  ModuleEntry* module() const;
  bool in_unnamed_package() const   { return (_package_entry == NULL); }
  void set_package(ClassLoaderData* loader_data, PackageEntry* pkg_entry, TRAPS);
  // If the package for the InstanceKlass is in the boot loader's package entry
  // table then sets the classpath_index field so that
  // get_system_package() will know to return a non-null value for the
  // package's location.  And, so that the package will be added to the list of
  // packages returned by get_system_packages().
  // For packages whose classes are loaded from the boot loader class path, the
  // classpath_index indicates which entry on the boot loader class path.
  void set_classpath_index(s2 path_index, TRAPS);
  bool is_same_class_package(const Klass* class2) const;
  bool is_same_class_package(oop other_class_loader, const Symbol* other_class_name) const;

  // find an enclosing class
  InstanceKlass* compute_enclosing_class(bool* inner_is_member, TRAPS) const;

  // Find InnerClasses attribute and return outer_class_info_index & inner_name_index.
  bool find_inner_classes_attr(int* ooff, int* noff, TRAPS) const;

 private:
  // Check prohibited package ("java/" only loadable by boot or platform loaders)
  static void check_prohibited_package(Symbol* class_name,
                                       ClassLoaderData* loader_data,
                                       TRAPS);
 public:
  // initialization state
  bool is_loaded() const                   { return _init_state >= loaded; }
  bool is_linked() const                   { return _init_state >= linked; }
  bool is_initialized() const              { return _init_state == fully_initialized; }
  bool is_not_initialized() const          { return _init_state <  being_initialized; }
  bool is_being_initialized() const        { return _init_state == being_initialized; }
  bool is_in_error_state() const           { return _init_state == initialization_error; }
  bool is_reentrant_initialization(Thread *thread)  { return thread == _init_thread; }
  ClassState  init_state()                 { return (ClassState)_init_state; }

  // is this a sealed class
  bool is_sealed() const;
  // initialization (virtuals from Klass)
  bool should_be_initialized() const;  // means that initialize should be called
  void initialize(TRAPS);
  void link_class(TRAPS);
  bool link_class_or_fail(TRAPS); // returns false on failure
  void rewrite_class(TRAPS);
  void link_methods(TRAPS);
  Method* class_initializer() const;

  // set the class to initialized if no static initializer is present
  void eager_initialize(Thread *thread);

  // reference type
  ReferenceType reference_type() const     { return (ReferenceType)_reference_type; }
  void set_reference_type(ReferenceType t) {
    assert(t == (u1)t, "overflow");
    _reference_type = (u1)t;
  }


  static ByteSize reference_type_offset() { return in_ByteSize(offset_of(InstanceKlass, _reference_type)); }

  // find local field, returns true if found
  bool find_local_field(Symbol* name, Symbol* sig, fieldDescriptor* fd) const;
  // find field in direct superinterfaces, returns the interface in which the field is defined
  Klass* find_interface_field(Symbol* name, Symbol* sig, fieldDescriptor* fd) const;
  // find field according to JVM spec 5.4.3.2, returns the klass in which the field is defined
  Klass* find_field(Symbol* name, Symbol* sig, fieldDescriptor* fd) const;
  // find instance or static fields according to JVM spec 5.4.3.2, returns the klass in which the field is defined
  Klass* find_field(Symbol* name, Symbol* sig, bool is_static, fieldDescriptor* fd) const;

  // find a non-static or static field given its offset within the class.
  bool contains_field_offset(int offset);

  bool find_local_field_from_offset(int offset, bool is_static, fieldDescriptor* fd) const;
  bool find_field_from_offset(int offset, bool is_static, fieldDescriptor* fd) const;

 private:
  inline static int quick_search(const Array<Method*>* methods, const Symbol* name);

 public:
  static void disable_method_binary_search() {
    _disable_method_binary_search = true;
  }

  // find a local method (returns NULL if not found)
  Method* find_method(const Symbol* name, const Symbol* signature) const;
  static Method* find_method(const Array<Method*>* methods,
                             const Symbol* name,
                             const Symbol* signature);

  // find a local method, but skip static methods
  Method* find_instance_method(const Symbol* name, const Symbol* signature,
                               PrivateLookupMode private_mode) const;
  static Method* find_instance_method(const Array<Method*>* methods,
                                      const Symbol* name,
                                      const Symbol* signature,
                                      PrivateLookupMode private_mode);

  // find a local method (returns NULL if not found)
  Method* find_local_method(const Symbol* name,
                            const Symbol* signature,
                            OverpassLookupMode overpass_mode,
                            StaticLookupMode static_mode,
                            PrivateLookupMode private_mode) const;

  // find a local method from given methods array (returns NULL if not found)
  static Method* find_local_method(const Array<Method*>* methods,
                                   const Symbol* name,
                                   const Symbol* signature,
                                   OverpassLookupMode overpass_mode,
                                   StaticLookupMode static_mode,
                                   PrivateLookupMode private_mode);

  // find a local method index in methods or default_methods (returns -1 if not found)
  static int find_method_index(const Array<Method*>* methods,
                               const Symbol* name,
                               const Symbol* signature,
                               OverpassLookupMode overpass_mode,
                               StaticLookupMode static_mode,
                               PrivateLookupMode private_mode);

  // lookup operation (returns NULL if not found)
  Method* uncached_lookup_method(const Symbol* name,
                                 const Symbol* signature,
                                 OverpassLookupMode overpass_mode,
                                 PrivateLookupMode private_mode = find_private) const;

  // lookup a method in all the interfaces that this class implements
  // (returns NULL if not found)
  Method* lookup_method_in_all_interfaces(Symbol* name, Symbol* signature, DefaultsLookupMode defaults_mode) const;

  // lookup a method in local defaults then in all interfaces
  // (returns NULL if not found)
  Method* lookup_method_in_ordered_interfaces(Symbol* name, Symbol* signature) const;

  // Find method indices by name.  If a method with the specified name is
  // found the index to the first method is returned, and 'end' is filled in
  // with the index of first non-name-matching method.  If no method is found
  // -1 is returned.
  int find_method_by_name(const Symbol* name, int* end) const;
  static int find_method_by_name(const Array<Method*>* methods,
                                 const Symbol* name, int* end);
  // protection domain
  oop protection_domain() const;
  // signers
  objArrayOop signers() const;
  // host class
  InstanceKlass* unsafe_anonymous_host() const {
    InstanceKlass** hk = adr_unsafe_anonymous_host();
    if (hk == NULL) {
      assert(!is_unsafe_anonymous(), "Unsafe anonymous classes have host klasses");
      return NULL;
    } else {
      assert(*hk != NULL, "host klass should always be set if the address is not null");
      assert(is_unsafe_anonymous(), "Only unsafe anonymous classes have host klasses");
      return *hk;
    }
  }
  void set_unsafe_anonymous_host(const InstanceKlass* host) {
    assert(is_unsafe_anonymous(), "not unsafe anonymous");
    const InstanceKlass** addr = (const InstanceKlass **)adr_unsafe_anonymous_host();
    assert(addr != NULL, "no reversed space");
    if (addr != NULL) {
      *addr = host;
    }
  }
  // source debug extension
  const char* source_debug_extension() const { return _source_debug_extension; }
  void set_source_debug_extension(const char* array, int length);
  // nonstatic oop-map blocks
  static int nonstatic_oop_map_size(unsigned int oop_map_count) {
    return oop_map_count * OopMapBlock::size_in_words();
  }
  unsigned int nonstatic_oop_map_count() const {
    return _nonstatic_oop_map_size / OopMapBlock::size_in_words();
  }
// 对于非JVMTI的情况总是NULL
  InstanceKlass* previous_versions() const { return NULL; }
  InstanceKlass* get_klass_version(int version) {   return NULL;  }
  
  bool supers_have_passed_fingerprint_checks();

  static bool should_store_fingerprint(bool is_hidden_or_anonymous);
  bool should_store_fingerprint() const { return should_store_fingerprint(is_hidden() || is_unsafe_anonymous()); }
  bool has_stored_fingerprint() const;
  uint64_t get_stored_fingerprint() const;
  void store_fingerprint(uint64_t fingerprint);
 
private:
  void set_kind(unsigned kind) {    _kind = (u1)kind;  }
  bool is_kind(unsigned desired) const {    return _kind == (u1)desired;  }
public:
  // Other is anything that is not one of the more specialized kinds of InstanceKlass.
  bool is_other_instance_klass() const        { return is_kind(_kind_other); }
  bool is_reference_instance_klass() const    { return is_kind(_kind_reference); }
  bool is_mirror_instance_klass() const       { return is_kind(_kind_mirror); }
  bool is_class_loader_instance_klass() const { return is_kind(_kind_class_loader); }

  static void purge_previous_versions(InstanceKlass* ik) { return; };
  static bool has_previous_versions_and_reset() { return false; }

  void set_cached_class_file(JvmtiCachedClassFileData *data) {
    assert(data == NULL, "unexpected call with JVMTI disabled");
  }
  JvmtiCachedClassFileData * get_cached_class_file() { return (JvmtiCachedClassFileData *)NULL; }
  // for adding methods, ConstMethod::UNSET_IDNUM means no more ids available
  inline u2 next_method_idnum();
  void set_initial_method_idnum(u2 value)             { _idnum_allocated_count = value; }

  u2 enclosing_method_data(int offset) const;
  u2 enclosing_method_class_index() const {
    return enclosing_method_data(enclosing_method_class_index_offset);
  }
  u2 enclosing_method_method_index() {
    return enclosing_method_data(enclosing_method_method_index_offset);
  }
  void set_enclosing_method_indices(u2 class_index,
                                    u2 method_index);

  // jmethodID support
  jmethodID get_jmethod_id(const methodHandle& method_h);
  jmethodID get_jmethod_id_fetch_or_update(size_t idnum,
                     jmethodID new_id, jmethodID* new_jmeths,
                     jmethodID* to_dealloc_id_p,
                     jmethodID** to_dealloc_jmeths_p);
  static void get_jmethod_id_length_value(jmethodID* cache, size_t idnum,
                size_t *length_p, jmethodID* id_p);
  void ensure_space_for_methodids(int start_offset = 0);
  jmethodID jmethod_id_or_null(Method* method);
    
  instanceOop allocate_instance(TRAPS);// allocation
  static instanceOop allocate_instance(oop cls, TRAPS);
  // additional member function to return a handle
  instanceHandle allocate_instance_handle(TRAPS);

  objArrayOop allocate_objArray(int n, int length, TRAPS);
  // Helper function
  static instanceOop register_finalizer(instanceOop i, TRAPS);
  // Check whether reflection/jni/jvm code is allowed to instantiate this class;
  // if not, throw either an Error or an Exception.
  virtual void check_valid_for_instantiation(bool throwError, TRAPS);
  
  void call_class_initializer(TRAPS);// initialization
  void set_initialization_state_and_notify(ClassState state, TRAPS);

  void mask_for(const methodHandle& method, int bci, InterpreterOopMap* entry);

  JNIid* jni_id_for(int offset);

  // maintenance of deoptimization dependencies
  inline DependencyContext dependencies();
  int  mark_dependent_nmethods(KlassDepChange& changes);
  void add_dependent_nmethod(nmethod* nm);
  void remove_dependent_nmethod(nmethod* nm);
  void clean_dependency_context();

  // On-stack replacement support
  void add_osr_nmethod(nmethod* n);
  bool remove_osr_nmethod(nmethod* n);
  int mark_osr_nmethods(const Method* m);
  nmethod* lookup_osr_nmethod(const Method* m, int bci, int level, bool match_level) const;

  // support for stub routines
  static ByteSize init_state_offset()  { return in_ByteSize(offset_of(InstanceKlass, _init_state)); }
  JFR_ONLY(DEFINE_KLASS_TRACE_ID_OFFSET;)
  static ByteSize init_thread_offset() { return in_ByteSize(offset_of(InstanceKlass, _init_thread)); }
  // subclass/subinterface checks
  bool implements_interface(Klass* k) const;
  bool is_same_or_direct_interface(Klass* k) const;
  // Access to the implementor of an interface.
  Klass* implementor() const;
  void set_implementor(Klass* k);
  int  nof_implementors() const;
  void add_implementor(Klass* k);  // k is a new class that implements this interface
  void init_implementor();           // initialize
  // link this class into the implementors list of every interface it implements
  void process_interfaces(Thread *thread);
  // virtual operations from Klass
  GrowableArray<Klass*>* compute_secondary_supers(int num_extra_slots,
                                                  Array<InstanceKlass*>* transitive_interfaces);
  bool can_be_primary_super_slow() const;
  int oop_size(oop obj)  const             { return size_helper(); }
  // slow because it's a virtual call and used for verifying the layout_helper.
  // Using the layout_helper bits, we can call is_instance_klass without a virtual call.
  DEBUG_ONLY(bool is_instance_klass_slow() const      { return true; })
  // Iterators
  void do_local_static_fields(FieldClosure* cl);
  void do_nonstatic_fields(FieldClosure* cl); // including inherited fields
  void do_local_static_fields(void f(fieldDescriptor*, Handle, TRAPS), Handle, TRAPS);

  void methods_do(void f(Method* method));
  void array_klasses_do(void f(Klass* k));
  void array_klasses_do(void f(Klass* k, TRAPS), TRAPS);

  static InstanceKlass* cast(Klass* k) {
    return const_cast<InstanceKlass*>(cast(const_cast<const Klass*>(k)));
  }

  static const InstanceKlass* cast(const Klass* k) {
    assert(k != NULL, "k should not be null");
    assert(k->is_instance_klass(), "cast to InstanceKlass");
    return static_cast<const InstanceKlass*>(k);
  }

  virtual InstanceKlass* java_super() const {
    return (super() == NULL) ? NULL : cast(super());
  }
  // Sizing (in words)
  static int header_size()            { return sizeof(InstanceKlass)/wordSize; }
  static int size(int vtable_length, int itable_length,
                  int nonstatic_oop_map_size,
                  bool is_interface, bool is_unsafe_anonymous, bool has_stored_fingerprint) {
    return align_metadata_size(header_size() +
           vtable_length +
           itable_length +
           nonstatic_oop_map_size +
           (is_interface ? (int)sizeof(Klass*)/wordSize : 0) +
           (is_unsafe_anonymous ? (int)sizeof(Klass*)/wordSize : 0) +
           (has_stored_fingerprint ? (int)sizeof(uint64_t*)/wordSize : 0));
  }
  int size() const{
	   return size(vtable_length(),itable_length(),nonstatic_oop_map_size(),
                is_interface(),is_unsafe_anonymous(), has_stored_fingerprint());
  }

  intptr_t* start_of_itable()   const { return (intptr_t*)start_of_vtable() + vtable_length(); }
  intptr_t* end_of_itable()     const { return start_of_itable() + itable_length(); }

  int  itable_offset_in_words() const { return start_of_itable() - (intptr_t*)this; }

  oop static_field_base_raw() { return java_mirror(); }

  OopMapBlock* start_of_nonstatic_oop_maps() const {
    return (OopMapBlock*)(start_of_itable() + itable_length());
  }

  Klass** end_of_nonstatic_oop_maps() const {
    return (Klass**)(start_of_nonstatic_oop_maps() +
                     nonstatic_oop_map_count());
  }

  Klass* volatile* adr_implementor() const {
    if (is_interface()) {
      return (Klass* volatile*)end_of_nonstatic_oop_maps();
    } else {
      return NULL;
    }
  };

  InstanceKlass** adr_unsafe_anonymous_host() const {
    if (is_unsafe_anonymous()) {
      InstanceKlass** adr_impl = (InstanceKlass**)adr_implementor();
      if (adr_impl != NULL) {
        return adr_impl + 1;
      } else {
        return (InstanceKlass **)end_of_nonstatic_oop_maps();
      }
    } else {
      return NULL;
    }
  }

  address adr_fingerprint() const {
    if (has_stored_fingerprint()) {
      InstanceKlass** adr_host = adr_unsafe_anonymous_host();
      if (adr_host != NULL) {
        return (address)(adr_host + 1);
      }
      Klass* volatile* adr_impl = adr_implementor();
      if (adr_impl != NULL) {
        return (address)(adr_impl + 1);
      }
      return (address)end_of_nonstatic_oop_maps();
    } else {
      return NULL;
    }
  }
  // Use this to return the size of an instance in heap words:
  int size_helper() const {
    return layout_helper_to_size_helper(layout_helper());
  }
  // This bit is initialized in classFileParser.cpp.
  // It is false under any of the following conditions:
  //  - the class is abstract (including any interface)
  //  - the class has a finalizer (if !RegisterFinalizersAtInit)
  //  - the class size is larger than FastAllocateSizeLimit
  //  - the class is java/lang/Class, which cannot be allocated directly
  bool can_be_fastpath_allocated() const {
    return !layout_helper_needs_slow_path(layout_helper());
  }
  // Java itable
  klassItable itable() const;        // return klassItable wrapper
  Method* method_at_itable(Klass* holder, int index, TRAPS);
  void clean_weak_instanceklass_links();
 private:
  void clean_implementors_list();
  void clean_method_data();
 public:
  // Explicit metaspace deallocation of fields
  // For RedefineClasses and class file parsing errors, we need to deallocate
  // instanceKlasses and the metadata they point to.
  void deallocate_contents(ClassLoaderData* loader_data);
  static void deallocate_methods(ClassLoaderData* loader_data,
                                 Array<Method*>* methods);
  void static deallocate_interfaces(ClassLoaderData* loader_data,
                                    const Klass* super_klass,
                                    Array<InstanceKlass*>* local_interfaces,
                                    Array<InstanceKlass*>* transitive_interfaces);
  void static deallocate_record_components(ClassLoaderData* loader_data,
                                           Array<RecordComponent*>* record_component);
  // callbacks for actions during class unloading
  static void unload_class(InstanceKlass* ik);
  virtual void release_C_heap_structures();
  // Naming
  const char* signature_name() const;
  // Oop fields (and metadata) iterators
  //
  // The InstanceKlass iterators also visits the Object's klass.

  // Forward iteration
 public:
  // Iterate over all oop fields in the oop maps.
  template <typename T, class OopClosureType>
  inline void oop_oop_iterate_oop_maps(oop obj, OopClosureType* closure);
  // Iterate over all oop fields and metadata.
  template <typename T, class OopClosureType>
  inline void oop_oop_iterate(oop obj, OopClosureType* closure);
  // Iterate over all oop fields in one oop map.
  template <typename T, class OopClosureType>
  inline void oop_oop_iterate_oop_map(OopMapBlock* map, oop obj, OopClosureType* closure);
  // Reverse iteration
  // Iterate over all oop fields and metadata.
  template <typename T, class OopClosureType>
  inline void oop_oop_iterate_reverse(oop obj, OopClosureType* closure);
 private:
  // Iterate over all oop fields in the oop maps.
  template <typename T, class OopClosureType>
  inline void oop_oop_iterate_oop_maps_reverse(oop obj, OopClosureType* closure);
  // Iterate over all oop fields in one oop map.
  template <typename T, class OopClosureType>
  inline void oop_oop_iterate_oop_map_reverse(OopMapBlock* map, oop obj, OopClosureType* closure);
  // Bounded range iteration
 public:
  // Iterate over all oop fields in the oop maps.
  template <typename T, class OopClosureType>
  inline void oop_oop_iterate_oop_maps_bounded(oop obj, OopClosureType* closure, MemRegion mr);
  // Iterate over all oop fields and metadata.
  template <typename T, class OopClosureType>
  inline void oop_oop_iterate_bounded(oop obj, OopClosureType* closure, MemRegion mr);
 private:
  // Iterate over all oop fields in one oop map.
  template <typename T, class OopClosureType>
  inline void oop_oop_iterate_oop_map_bounded(OopMapBlock* map, oop obj, OopClosureType* closure, MemRegion mr);
 public:
  u2 idnum_allocated_count() const      { return _idnum_allocated_count; }
private:
  // initialization state
  void set_init_state(ClassState state);
  void set_init_thread(Thread *thread)  { _init_thread = thread; }

  // The RedefineClasses() API can cause new method idnums to be needed
  // which will cause the caches to grow. Safety requires different
  // cache management logic if the caches can grow instead of just
  // going from NULL to non-NULL.
  bool idnum_can_increment() const      { return has_been_redefined(); }
  inline jmethodID* methods_jmethod_ids_acquire() const;
  inline void release_set_methods_jmethod_ids(jmethodID* jmeths);

  // Lock during initialization
public:
  // Lock for (1) initialization; (2) access to the ConstantPool of this class.
  // Must be one per class and it has to be a VM internal object so java code
  // cannot lock it (like the mirror).
  // It has to be an object not a Mutex because it's held through java calls.
  oop init_lock() const;
private:
  void fence_and_clear_init_lock();

  bool link_class_impl                           (TRAPS);
  bool verify_code                               (TRAPS);
  void initialize_impl                           (TRAPS);
  void initialize_super_interfaces               (TRAPS);
  void eager_initialize_impl                     ();
  /* jni_id_for_impl for jfieldID only */
  JNIid* jni_id_for_impl                         (int offset);

  // Returns the array class for the n'th dimension
  Klass* array_klass_impl(bool or_null, int n, TRAPS);

  // Returns the array class with this class as element type
  Klass* array_klass_impl(bool or_null, TRAPS);

  // find a local method (returns NULL if not found)
  Method* find_method_impl(const Symbol* name,
                           const Symbol* signature,
                           OverpassLookupMode overpass_mode,
                           StaticLookupMode static_mode,
                           PrivateLookupMode private_mode) const;

  static Method* find_method_impl(const Array<Method*>* methods,
                                  const Symbol* name,
                                  const Symbol* signature,
                                  OverpassLookupMode overpass_mode,
                                  StaticLookupMode static_mode,
                                  PrivateLookupMode private_mode);
  // Free CHeap allocated fields.
  void release_C_heap_structures_internal();
public:
  // CDS support - remove and restore oops from metadata. Oops are not shared.
  virtual void remove_unshareable_info();
  virtual void remove_java_mirror();
  void restore_unshareable_info(ClassLoaderData* loader_data, Handle protection_domain, PackageEntry* pkg_entry, TRAPS);
  // jvm support
  jint compute_modifier_flags(TRAPS) const;
public:
  // JVMTI support
  jint jvmti_class_status() const;

  virtual void metaspace_pointers_do(MetaspaceClosure* iter);
 public:
  // Printing
#ifndef PRODUCT
  void print_on(outputStream* st) const;
#endif
  void print_value_on(outputStream* st) const;

  void oop_print_value_on(oop obj, outputStream* st);

#ifndef PRODUCT
  void oop_print_on      (oop obj, outputStream* st);

  void print_dependent_nmethods(bool verbose = false);
  bool is_dependent_nmethod(nmethod* nm);
  bool verify_itable_index(int index);
#endif
  const char* internal_name() const;
  // Verification
  void verify_on(outputStream* st);

  void oop_verify_on(oop obj, outputStream* st);
  // Logging
  void print_class_load_logging(ClassLoaderData* loader_data,
                                const char* module_name,
                                const ClassFileStream* cfs) const;
};
// for adding methods
// UNSET_IDNUM return means no more ids available
inline u2 InstanceKlass::next_method_idnum() {
  if (_idnum_allocated_count == ConstMethod::MAX_IDNUM) {
    return ConstMethod::UNSET_IDNUM; // no more ids available
  } else {
    return _idnum_allocated_count++;
  }
}

_misc_flags

InstanceKlass里有个位图字段,一个顶十六个,那就是 _misc_flags,它的16位的含义可以参见下面的枚举

enum {
    _misc_rewritten                           = 1 << 0,  // methods rewritten.
    _misc_has_nonstatic_fields                = 1 << 1,  // for sizing with UseCompressedOops
    _misc_should_verify_class                 = 1 << 2,  // allow caching of preverification
    _misc_is_unsafe_anonymous                 = 1 << 3,  // has embedded _unsafe_anonymous_host field
    _misc_is_contended                        = 1 << 4,  // marked with contended annotation
    _misc_has_nonstatic_concrete_methods      = 1 << 5,  // class/superclass/implemented interfaces has non-static, concrete methods
    _misc_declares_nonstatic_concrete_methods = 1 << 6,  // directly declares non-static, concrete methods
    _misc_has_been_redefined                  = 1 << 7,  // class has been redefined
    _misc_has_passed_fingerprint_check        = 1 << 8,  // when this class was loaded, the fingerprint computed from its
                                                         // code source was found to be matching the value recorded by AOT.
    _misc_is_scratch_class                    = 1 << 9,  // class is the redefined scratch class
    _misc_is_shared_boot_class                = 1 << 10, // defining class loader is boot class loader
    _misc_is_shared_platform_class            = 1 << 11, // defining class loader is platform class loader
    _misc_is_shared_app_class                 = 1 << 12, // defining class loader is app class loader
    _misc_has_resolved_methods                = 1 << 13, // resolved methods table entries added for this class
    _misc_is_being_redefined                  = 1 << 14, // used for locking redefinition
    _misc_has_contended_annotations           = 1 << 15  // has @Contended annotation
  };

所以下面众多方法就是通过_misc_flags来读写

_constants

_constants是一个重要属性,很多操作都是委托给_constants的同名方法,包括以下这些

• bool on_stack() const
  The constant pool is on stack if any of the methods are executing or referenced by handles.
• void set_generic_signature_index(u2 sig_index)
• u2 generic_signature_index() const
• Symbol* generic_signature() const
• void set_major_version(u2 major_version)
• u2 major_version() const
• void set_minor_version(u2 minor_version)
• u2 minor_version() const
• Symbol* source_file_name() const
• u2 source_file_name_index() const
• void set_source_file_name_index(u2 sourcefile_index)

_annotations

类似的,有些方法委托给了_annotations同名方法,需要注意的是由于_annotations可能为NULL,所以需要先检查了再调用

• AnnotationArray* class_annotations() const
• Array<AnnotationArray*>* fields_annotations() const
• AnnotationArray* class_type_annotations() const
• Array<AnnotationArray*>* fields_type_annotations() const