1 /*
   2  * Copyright (c) 2012, 2020, 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_CLASSFILE_CLASSLOADERDATA_HPP
  26 #define SHARE_CLASSFILE_CLASSLOADERDATA_HPP
  27 
  28 #include "memory/allocation.hpp"
  29 #include "memory/memRegion.hpp"
  30 #include "memory/metaspace.hpp"
  31 #include "oops/oopHandle.hpp"
  32 #include "oops/weakHandle.hpp"
  33 #include "runtime/atomic.hpp"
  34 #include "runtime/mutex.hpp"
  35 #include "utilities/growableArray.hpp"
  36 #include "utilities/macros.hpp"
  37 #if INCLUDE_JFR
  38 #include "jfr/support/jfrTraceIdExtension.hpp"
  39 #endif
  40 
  41 // external name (synthetic) for the primordial "bootstrap" class loader instance
  42 #define BOOTSTRAP_LOADER_NAME "bootstrap"
  43 #define BOOTSTRAP_LOADER_NAME_LEN 9
  44 
  45 //
  46 // A class loader represents a linkset. Conceptually, a linkset identifies
  47 // the complete transitive closure of resolved links that a dynamic linker can
  48 // produce.
  49 //
  50 // A ClassLoaderData also encapsulates the allocation space, called a metaspace,
  51 // used by the dynamic linker to allocate the runtime representation of all
  52 // the types it defines.
  53 //
  54 // ClassLoaderData are stored in the runtime representation of classes,
  55 // and provides iterators for root tracing and other GC operations.
  56 
  57 class ClassLoaderDataGraph;
  58 class JNIMethodBlock;
  59 class ModuleEntry;
  60 class PackageEntry;
  61 class ModuleEntryTable;
  62 class PackageEntryTable;
  63 class DictionaryEntry;
  64 class Dictionary;
  65 
  66 // ClassLoaderData class
  67 
  68 class ClassLoaderData : public CHeapObj<mtClass> {
  69   friend class VMStructs;
  70 
  71  private:
  72   class ChunkedHandleList {
  73     struct Chunk : public CHeapObj<mtClass> {
  74       static const size_t CAPACITY = 32;
  75 
  76       oop _data[CAPACITY];
  77       volatile juint _size;
  78       Chunk* _next;
  79 
  80       Chunk(Chunk* c) : _size(0), _next(c) { }
  81     };
  82 
  83     Chunk* volatile _head;
  84 
  85     void oops_do_chunk(OopClosure* f, Chunk* c, const juint size);
  86 
  87    public:
  88     ChunkedHandleList() : _head(NULL) {}
  89     ~ChunkedHandleList();
  90 
  91     // Only one thread at a time can add, guarded by ClassLoaderData::metaspace_lock().
  92     // However, multiple threads can execute oops_do concurrently with add.
  93     oop* add(oop o);
  94     bool contains(oop p);
  95     NOT_PRODUCT(bool owner_of(oop* p);)
  96     void oops_do(OopClosure* f);
  97 
  98     int count() const;
  99   };
 100 
 101   friend class ClassLoaderDataGraph;
 102   friend class ClassLoaderDataGraphIterator;
 103   friend class ClassLoaderDataGraphKlassIteratorAtomic;
 104   friend class ClassLoaderDataGraphKlassIteratorStatic;
 105   friend class ClassLoaderDataGraphMetaspaceIterator;
 106   friend class Klass;
 107   friend class MetaDataFactory;
 108   friend class Method;
 109 
 110   static ClassLoaderData * _the_null_class_loader_data;
 111 
 112   WeakHandle<vm_class_loader_data> _holder; // The oop that determines lifetime of this class loader
 113   OopHandle _class_loader;    // The instance of java/lang/ClassLoader associated with
 114                               // this ClassLoaderData
 115 
 116   ClassLoaderMetaspace * volatile _metaspace;  // Meta-space where meta-data defined by the
 117                                     // classes in the class loader are allocated.
 118   Mutex* _metaspace_lock;  // Locks the metaspace for allocations and setup.
 119   bool _unloading;         // true if this class loader goes away
 120   bool _has_class_mirror_holder; // If true, CLD is dedicated to one class and that class determines
 121                                  // the CLDs lifecycle.  For example, a non-strong hidden class or an
 122                                  // unsafe anonymous class.  Arrays of these classes are also assigned
 123                                  // to these class loader datas.
 124 
 125   // Remembered sets support for the oops in the class loader data.
 126   bool _modified_oops;             // Card Table Equivalent (YC/CMS support)
 127   bool _accumulated_modified_oops; // Mod Union Equivalent (CMS support)
 128 
 129   int _keep_alive;         // if this CLD is kept alive.
 130                            // Used for non-strong hidden classes, unsafe anonymous classes and the
 131                            // boot class loader. _keep_alive does not need to be volatile or
 132                            // atomic since there is one unique CLD per non-strong hidden class
 133                            // or unsafe anonymous class.
 134 
 135   volatile int _claim; // non-zero if claimed, for example during GC traces.
 136                        // To avoid applying oop closure more than once.
 137   ChunkedHandleList _handles; // Handles to constant pool arrays, Modules, etc, which
 138                               // have the same life cycle of the corresponding ClassLoader.
 139 
 140   NOT_PRODUCT(volatile int _dependency_count;)  // number of class loader dependencies
 141 
 142   Klass* volatile _klasses;              // The classes defined by the class loader.
 143   PackageEntryTable* volatile _packages; // The packages defined by the class loader.
 144   ModuleEntryTable*  volatile _modules;  // The modules defined by the class loader.
 145   ModuleEntry* _unnamed_module;          // This class loader's unnamed module.
 146   Dictionary*  _dictionary;              // The loaded InstanceKlasses, including initiated by this class loader
 147 
 148   // These method IDs are created for the class loader and set to NULL when the
 149   // class loader is unloaded.  They are rarely freed, only for redefine classes
 150   // and if they lose a data race in InstanceKlass.
 151   JNIMethodBlock*                  _jmethod_ids;
 152 
 153   // Metadata to be deallocated when it's safe at class unloading, when
 154   // this class loader isn't unloaded itself.
 155   GrowableArray<Metadata*>*      _deallocate_list;
 156 
 157   // Support for walking class loader data objects
 158   ClassLoaderData* _next; /// Next loader_datas created
 159 
 160   Klass*  _class_loader_klass;
 161   Symbol* _name;
 162   Symbol* _name_and_id;
 163   JFR_ONLY(DEFINE_TRACE_ID_FIELD;)
 164 
 165   void set_next(ClassLoaderData* next) { _next = next; }
 166   ClassLoaderData* next() const        { return Atomic::load(&_next); }
 167 
 168   ClassLoaderData(Handle h_class_loader, bool has_class_mirror_holder);
 169   ~ClassLoaderData();
 170 
 171   // The CLD are not placed in the Heap, so the Card Table or
 172   // the Mod Union Table can't be used to mark when CLD have modified oops.
 173   // The CT and MUT bits saves this information for the whole class loader data.
 174   void clear_modified_oops()             { _modified_oops = false; }
 175  public:
 176   void record_modified_oops()            { _modified_oops = true; }
 177   bool has_modified_oops()               { return _modified_oops; }
 178 
 179   void accumulate_modified_oops()        { if (has_modified_oops()) _accumulated_modified_oops = true; }
 180   void clear_accumulated_modified_oops() { _accumulated_modified_oops = false; }
 181   bool has_accumulated_modified_oops()   { return _accumulated_modified_oops; }
 182   oop holder_no_keepalive() const;
 183   oop holder_phantom() const;
 184 
 185  private:
 186   void unload();
 187   bool keep_alive() const       { return _keep_alive > 0; }
 188 
 189   void classes_do(void f(Klass* const));
 190   void loaded_classes_do(KlassClosure* klass_closure);
 191   void classes_do(void f(InstanceKlass*));
 192   void methods_do(void f(Method*));
 193   void modules_do(void f(ModuleEntry*));
 194   void packages_do(void f(PackageEntry*));
 195 
 196   // Deallocate free list during class unloading.
 197   void free_deallocate_list();                      // for the classes that are not unloaded
 198   void free_deallocate_list_C_heap_structures();    // for the classes that are unloaded
 199 
 200   // Allocate out of this class loader data
 201   MetaWord* allocate(size_t size);
 202 
 203   Dictionary* create_dictionary();
 204 
 205   void initialize_name(Handle class_loader);
 206 
 207  public:
 208   // GC interface.
 209 
 210   // The "claim" is typically used to check if oops_do needs to be applied on
 211   // the CLD or not. Most GCs only perform strong marking during the marking phase.
 212   enum Claim {
 213     _claim_none         = 0,
 214     _claim_finalizable  = 2,
 215     _claim_strong       = 3,
 216     _claim_other        = 4
 217   };
 218   void clear_claim() { _claim = 0; }
 219   void clear_claim(int claim);
 220   bool claimed() const { return _claim != 0; }
 221   bool claimed(int claim) const { return (_claim & claim) == claim; }
 222   bool try_claim(int claim);
 223 
 224   // Computes if the CLD is alive or not. This is safe to call in concurrent
 225   // contexts.
 226   bool is_alive() const;
 227 
 228   // Accessors
 229   ClassLoaderMetaspace* metaspace_or_null() const { return _metaspace; }
 230 
 231   static ClassLoaderData* the_null_class_loader_data() {
 232     return _the_null_class_loader_data;
 233   }
 234 
 235   Mutex* metaspace_lock() const { return _metaspace_lock; }
 236 
 237   bool has_class_mirror_holder() const { return _has_class_mirror_holder; }
 238 
 239   static void init_null_class_loader_data();
 240 
 241   bool is_the_null_class_loader_data() const {
 242     return this == _the_null_class_loader_data;
 243   }
 244 
 245   // Returns true if this class loader data is for the system class loader.
 246   // (Note that the class loader data may be for a non-strong hidden class or unsafe anonymous class)
 247   bool is_system_class_loader_data() const;
 248 
 249   // Returns true if this class loader data is for the platform class loader.
 250   // (Note that the class loader data may be for a non-strong hidden class or unsafe anonymous class)
 251   bool is_platform_class_loader_data() const;
 252 
 253   // Returns true if this class loader data is for the boot class loader.
 254   // (Note that the class loader data may be for a non-strong hidden class or unsafe anonymous class)
 255   inline bool is_boot_class_loader_data() const;
 256 
 257   bool is_builtin_class_loader_data() const;
 258   bool is_permanent_class_loader_data() const;
 259 
 260   // The Metaspace is created lazily so may be NULL.  This
 261   // method will allocate a Metaspace if needed.
 262   ClassLoaderMetaspace* metaspace_non_null();
 263 
 264   inline oop class_loader() const;
 265 
 266   // Returns true if this class loader data is for a loader going away.
 267   // Note that this is only safe after the GC has computed if the CLD is
 268   // unloading or not. In concurrent contexts where there are no such
 269   // guarantees, is_alive() should be used instead.
 270   bool is_unloading() const     {
 271     assert(!(is_the_null_class_loader_data() && _unloading), "The null class loader can never be unloaded");
 272     return _unloading;
 273   }
 274 
 275   // Used to refcount a non-strong hidden class's or unsafe anonymous class's CLD in order to
 276   // indicate their aliveness.
 277   void inc_keep_alive();
 278   void dec_keep_alive();
 279 
 280   void initialize_holder(Handle holder);
 281 
 282   void oops_do(OopClosure* f, int claim_value, bool clear_modified_oops = false);
 283 
 284   void classes_do(KlassClosure* klass_closure);
 285   Klass* klasses() { return _klasses; }
 286 
 287   JNIMethodBlock* jmethod_ids() const              { return _jmethod_ids; }
 288   void set_jmethod_ids(JNIMethodBlock* new_block)  { _jmethod_ids = new_block; }
 289 
 290   void print() const;
 291   void print_on(outputStream* out) const PRODUCT_RETURN;
 292   void print_value() const;
 293   void print_value_on(outputStream* out) const;
 294   void verify();
 295 
 296   OopHandle add_handle(Handle h);
 297   void remove_handle(OopHandle h);
 298   void init_handle_locked(OopHandle& pd, Handle h);  // used for concurrent access to ModuleEntry::_pd field
 299   void add_class(Klass* k, bool publicize = true);
 300   void remove_class(Klass* k);
 301   bool contains_klass(Klass* k);
 302   void record_dependency(const Klass* to);
 303   PackageEntryTable* packages() { return _packages; }
 304   ModuleEntry* unnamed_module() { return _unnamed_module; }
 305   ModuleEntryTable* modules();
 306   bool modules_defined() { return (_modules != NULL); }
 307 
 308   // Offsets
 309   static ByteSize holder_offset()     { return in_ByteSize(offset_of(ClassLoaderData, _holder)); }
 310   static ByteSize keep_alive_offset() { return in_ByteSize(offset_of(ClassLoaderData, _keep_alive)); }
 311 
 312   // Loaded class dictionary
 313   Dictionary* dictionary() const { return _dictionary; }
 314 
 315   void add_to_deallocate_list(Metadata* m);
 316 
 317   static ClassLoaderData* class_loader_data(oop loader);
 318   static ClassLoaderData* class_loader_data_or_null(oop loader);
 319   static ClassLoaderData* has_class_mirror_holder_cld(Handle loader);
 320 
 321   // Returns Klass* of associated class loader, or NULL if associated loader is 'bootstrap'.
 322   // Also works if unloading.
 323   Klass* class_loader_klass() const { return _class_loader_klass; }
 324 
 325   // Returns the class loader's explict name as specified during
 326   // construction or the class loader's qualified class name.
 327   // Works during unloading.
 328   const char* loader_name() const;
 329   // Returns the explicitly specified class loader name or NULL.
 330   Symbol* name() const { return _name; }
 331 
 332   // Obtain the class loader's _name_and_id, works during unloading.
 333   const char* loader_name_and_id() const;
 334   Symbol* name_and_id() const { return _name_and_id; }
 335 
 336   JFR_ONLY(DEFINE_TRACE_ID_METHODS;)
 337 };
 338 
 339 #endif // SHARE_CLASSFILE_CLASSLOADERDATA_HPP
--- EOF ---