1 /*
   2  * Copyright (c) 2012, 2018, 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
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  24 
  25 #ifndef SHARE_VM_CLASSFILE_CLASSLOADERDATA_HPP
  26 #define SHARE_VM_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/mutex.hpp"
  34 #include "utilities/growableArray.hpp"
  35 #include "utilities/macros.hpp"
  36 #if INCLUDE_JFR
  37 #include "jfr/support/jfrTraceIdExtension.hpp"
  38 #endif
  39 
  40 // external name (synthetic) for the primordial "'bootstrap'" class loader instance
  41 #define BOOTSTRAP_LOADER_NAME "'bootstrap'"
  42 #define BOOTSTRAP_LOADER_NAME_LEN 11
  43 
  44 //
  45 // A class loader represents a linkset. Conceptually, a linkset identifies
  46 // the complete transitive closure of resolved links that a dynamic linker can
  47 // produce.
  48 //
  49 // A ClassLoaderData also encapsulates the allocation space, called a metaspace,
  50 // used by the dynamic linker to allocate the runtime representation of all
  51 // the types it defines.
  52 //
  53 // ClassLoaderData are stored in the runtime representation of classes,
  54 // and provides iterators for root tracing and other GC operations.
  55 
  56 class ClassLoaderData;
  57 class JNIMethodBlock;
  58 class Metadebug;
  59 class ModuleEntry;
  60 class PackageEntry;
  61 class ModuleEntryTable;
  62 class PackageEntryTable;
  63 class DictionaryEntry;
  64 class Dictionary;
  65 
  66 // GC root for walking class loader data created
  67 
  68 class ClassLoaderDataGraph : public AllStatic {
  69   friend class ClassLoaderData;
  70   friend class ClassLoaderDataGraphMetaspaceIterator;
  71   friend class ClassLoaderDataGraphKlassIteratorAtomic;
  72   friend class ClassLoaderDataGraphKlassIteratorStatic;
  73   friend class VMStructs;
  74  private:
  75   // All CLDs (except the null CLD) can be reached by walking _head->_next->...
  76   static ClassLoaderData* _head;
  77   static ClassLoaderData* _unloading;
  78   // CMS support.
  79   static ClassLoaderData* _saved_head;
  80   static ClassLoaderData* _saved_unloading;
  81   static bool _should_purge;
  82   // OOM has been seen in metaspace allocation. Used to prevent some
  83   // allocations until class unloading
  84   static bool _metaspace_oom;
  85 
  86   static volatile size_t  _num_instance_classes;
  87   static volatile size_t  _num_array_classes;
  88 
  89   static ClassLoaderData* add_to_graph(Handle class_loader, bool anonymous);
  90   static ClassLoaderData* add(Handle class_loader, bool anonymous);
  91  public:
  92   static ClassLoaderData* find_or_create(Handle class_loader);
  93   static void purge();
  94   static void clear_claimed_marks();
  95   // oops do
  96   static void oops_do(OopClosure* f, bool must_claim);
  97   static void keep_alive_oops_do(OopClosure* blk, bool must_claim);
  98   static void always_strong_oops_do(OopClosure* blk, bool must_claim);
  99   // cld do
 100   static void cld_do(CLDClosure* cl);
 101   static void cld_unloading_do(CLDClosure* cl);
 102   static void roots_cld_do(CLDClosure* strong, CLDClosure* weak);
 103   static void keep_alive_cld_do(CLDClosure* cl);
 104   static void always_strong_cld_do(CLDClosure* cl);
 105   // klass do
 106   // Walking classes through the ClassLoaderDataGraph include array classes.  It also includes
 107   // classes that are allocated but not loaded, classes that have errors, and scratch classes
 108   // for redefinition.  These classes are removed during the next class unloading.
 109   // Walking the ClassLoaderDataGraph also includes anonymous classes.
 110   static void classes_do(KlassClosure* klass_closure);
 111   static void classes_do(void f(Klass* const));
 112   static void methods_do(void f(Method*));
 113   static void modules_do(void f(ModuleEntry*));
 114   static void modules_unloading_do(void f(ModuleEntry*));
 115   static void packages_do(void f(PackageEntry*));
 116   static void packages_unloading_do(void f(PackageEntry*));
 117   static void loaded_classes_do(KlassClosure* klass_closure);
 118   static void classes_unloading_do(void f(Klass* const));
 119   static bool do_unloading(bool clean_previous_versions);
 120 
 121   // dictionary do
 122   // Iterate over all klasses in dictionary, but
 123   // just the classes from defining class loaders.
 124   static void dictionary_classes_do(void f(InstanceKlass*));
 125   // Added for initialize_itable_for_klass to handle exceptions.
 126   static void dictionary_classes_do(void f(InstanceKlass*, TRAPS), TRAPS);
 127 
 128   // Iterate all classes and their class loaders, including initiating class loaders.
 129   static void dictionary_all_entries_do(void f(InstanceKlass*, ClassLoaderData*));
 130 
 131   // VM_CounterDecay iteration support
 132   static InstanceKlass* try_get_next_class();
 133 
 134   static void verify_dictionary();
 135   static void print_dictionary(outputStream* st);
 136   static void print_dictionary_statistics(outputStream* st);
 137 
 138   // CMS support.
 139   static void remember_new_clds(bool remember) { _saved_head = (remember ? _head : NULL); }
 140   static GrowableArray<ClassLoaderData*>* new_clds();
 141 
 142   static void set_should_purge(bool b) { _should_purge = b; }
 143   static void purge_if_needed() {
 144     // Only purge the CLDG for CMS if concurrent sweep is complete.
 145     if (_should_purge) {
 146       purge();
 147       // reset for next time.
 148       set_should_purge(false);
 149     }
 150   }
 151 
 152   static int resize_if_needed();
 153 
 154   static bool has_metaspace_oom()           { return _metaspace_oom; }
 155   static void set_metaspace_oom(bool value) { _metaspace_oom = value; }
 156 
 157   static void print_on(outputStream * const out) PRODUCT_RETURN;
 158   static void print() { print_on(tty); }
 159   static void verify();
 160 
 161   // instance and array class counters
 162   static inline size_t num_instance_classes();
 163   static inline size_t num_array_classes();
 164   static inline void inc_instance_classes(size_t count);
 165   static inline void dec_instance_classes(size_t count);
 166   static inline void inc_array_classes(size_t count);
 167   static inline void dec_array_classes(size_t count);
 168 
 169 #ifndef PRODUCT
 170   static bool contains_loader_data(ClassLoaderData* loader_data);
 171 #endif
 172 };
 173 
 174 // ClassLoaderData class
 175 
 176 class ClassLoaderData : public CHeapObj<mtClass> {
 177   friend class VMStructs;
 178 
 179  private:
 180   class ChunkedHandleList {
 181     struct Chunk : public CHeapObj<mtClass> {
 182       static const size_t CAPACITY = 32;
 183 
 184       oop _data[CAPACITY];
 185       volatile juint _size;
 186       Chunk* _next;
 187 
 188       Chunk(Chunk* c) : _next(c), _size(0) { }
 189     };
 190 
 191     Chunk* volatile _head;
 192 
 193     void oops_do_chunk(OopClosure* f, Chunk* c, const juint size);
 194 
 195    public:
 196     ChunkedHandleList() : _head(NULL) {}
 197     ~ChunkedHandleList();
 198 
 199     // Only one thread at a time can add, guarded by ClassLoaderData::metaspace_lock().
 200     // However, multiple threads can execute oops_do concurrently with add.
 201     oop* add(oop o);
 202     bool contains(oop p);
 203     NOT_PRODUCT(bool owner_of(oop* p);)
 204     void oops_do(OopClosure* f);
 205 
 206     int count() const;
 207   };
 208 
 209   friend class ClassLoaderDataGraph;
 210   friend class ClassLoaderDataGraphKlassIteratorAtomic;
 211   friend class ClassLoaderDataGraphKlassIteratorStatic;
 212   friend class ClassLoaderDataGraphMetaspaceIterator;
 213   friend class InstanceKlass;
 214   friend class MetaDataFactory;
 215   friend class Method;
 216 
 217   static ClassLoaderData * _the_null_class_loader_data;
 218 
 219   WeakHandle<vm_class_loader_data> _holder; // The oop that determines lifetime of this class loader
 220   OopHandle _class_loader;    // The instance of java/lang/ClassLoader associated with
 221                               // this ClassLoaderData
 222 
 223   ClassLoaderMetaspace * volatile _metaspace;  // Meta-space where meta-data defined by the
 224                                     // classes in the class loader are allocated.
 225   Mutex* _metaspace_lock;  // Locks the metaspace for allocations and setup.
 226   bool _unloading;         // true if this class loader goes away
 227   bool _is_anonymous;      // if this CLD is for an anonymous class
 228 
 229   // Remembered sets support for the oops in the class loader data.
 230   bool _modified_oops;             // Card Table Equivalent (YC/CMS support)
 231   bool _accumulated_modified_oops; // Mod Union Equivalent (CMS support)
 232 
 233   s2 _keep_alive;          // if this CLD is kept alive.
 234                            // Used for anonymous classes and the boot class
 235                            // loader. _keep_alive does not need to be volatile or
 236                            // atomic since there is one unique CLD per anonymous class.
 237 
 238   volatile int _claimed;   // true if claimed, for example during GC traces.
 239                            // To avoid applying oop closure more than once.
 240                            // Has to be an int because we cas it.
 241   ChunkedHandleList _handles; // Handles to constant pool arrays, Modules, etc, which
 242                               // have the same life cycle of the corresponding ClassLoader.
 243 
 244   NOT_PRODUCT(volatile int _dependency_count;)  // number of class loader dependencies
 245 
 246   Klass* volatile _klasses;              // The classes defined by the class loader.
 247   PackageEntryTable* volatile _packages; // The packages defined by the class loader.
 248   ModuleEntryTable*  volatile _modules;  // The modules defined by the class loader.
 249   ModuleEntry* _unnamed_module;          // This class loader's unnamed module.
 250   Dictionary*  _dictionary;              // The loaded InstanceKlasses, including initiated by this class loader
 251 
 252   // These method IDs are created for the class loader and set to NULL when the
 253   // class loader is unloaded.  They are rarely freed, only for redefine classes
 254   // and if they lose a data race in InstanceKlass.
 255   JNIMethodBlock*                  _jmethod_ids;
 256 
 257   // Metadata to be deallocated when it's safe at class unloading, when
 258   // this class loader isn't unloaded itself.
 259   GrowableArray<Metadata*>*      _deallocate_list;
 260 
 261   // Support for walking class loader data objects
 262   ClassLoaderData* _next; /// Next loader_datas created
 263 
 264   Klass*  _class_loader_klass;
 265   Symbol* _name;
 266   Symbol* _name_and_id;
 267   JFR_ONLY(DEFINE_TRACE_ID_FIELD;)
 268 
 269   void set_next(ClassLoaderData* next) { _next = next; }
 270   ClassLoaderData* next() const        { return _next; }
 271 
 272   ClassLoaderData(Handle h_class_loader, bool is_anonymous);
 273   ~ClassLoaderData();
 274 
 275   // The CLD are not placed in the Heap, so the Card Table or
 276   // the Mod Union Table can't be used to mark when CLD have modified oops.
 277   // The CT and MUT bits saves this information for the whole class loader data.
 278   void clear_modified_oops()             { _modified_oops = false; }
 279  public:
 280   void record_modified_oops()            { _modified_oops = true; }
 281   bool has_modified_oops()               { return _modified_oops; }
 282 
 283   void accumulate_modified_oops()        { if (has_modified_oops()) _accumulated_modified_oops = true; }
 284   void clear_accumulated_modified_oops() { _accumulated_modified_oops = false; }
 285   bool has_accumulated_modified_oops()   { return _accumulated_modified_oops; }
 286  private:
 287 
 288   void unload();
 289   bool keep_alive() const       { return _keep_alive > 0; }
 290 
 291   oop holder_phantom() const;
 292   void classes_do(void f(Klass*));
 293   void loaded_classes_do(KlassClosure* klass_closure);
 294   void classes_do(void f(InstanceKlass*));
 295   void methods_do(void f(Method*));
 296   void modules_do(void f(ModuleEntry*));
 297   void packages_do(void f(PackageEntry*));
 298 
 299   // Deallocate free list during class unloading.
 300   void free_deallocate_list();      // for the classes that are not unloaded
 301   void unload_deallocate_list();    // for the classes that are unloaded
 302 
 303   // Allocate out of this class loader data
 304   MetaWord* allocate(size_t size);
 305 
 306   Dictionary* create_dictionary();
 307 
 308   void initialize_name_and_klass(Handle class_loader);
 309  public:
 310   // GC interface.
 311   void clear_claimed() { _claimed = 0; }
 312   bool claimed() const { return _claimed == 1; }
 313   bool claim();
 314 
 315   bool is_alive() const;
 316 
 317   // Accessors
 318   ClassLoaderMetaspace* metaspace_or_null() const { return _metaspace; }
 319 
 320   static ClassLoaderData* the_null_class_loader_data() {
 321     return _the_null_class_loader_data;
 322   }
 323 
 324   Mutex* metaspace_lock() const { return _metaspace_lock; }
 325 
 326   bool is_anonymous() const { return _is_anonymous; }
 327 
 328   static void init_null_class_loader_data();
 329 
 330   bool is_the_null_class_loader_data() const {
 331     return this == _the_null_class_loader_data;
 332   }
 333 
 334   // Returns true if this class loader data is for the system class loader.
 335   // (Note that the class loader data may be anonymous.)
 336   bool is_system_class_loader_data() const;
 337 
 338   // Returns true if this class loader data is for the platform class loader.
 339   // (Note that the class loader data may be anonymous.)
 340   bool is_platform_class_loader_data() const;
 341 
 342   // Returns true if this class loader data is for the boot class loader.
 343   // (Note that the class loader data may be anonymous.)
 344   inline bool is_boot_class_loader_data() const;
 345 
 346   bool is_builtin_class_loader_data() const;
 347   bool is_permanent_class_loader_data() const;
 348 
 349   // The Metaspace is created lazily so may be NULL.  This
 350   // method will allocate a Metaspace if needed.
 351   ClassLoaderMetaspace* metaspace_non_null();
 352 
 353   inline oop class_loader() const;
 354 
 355   // Returns true if this class loader data is for a loader going away.
 356   bool is_unloading() const     {
 357     assert(!(is_the_null_class_loader_data() && _unloading), "The null class loader can never be unloaded");
 358     return _unloading;
 359   }
 360 
 361   // Used to refcount an anonymous class's CLD in order to
 362   // indicate their aliveness.
 363   void inc_keep_alive();
 364   void dec_keep_alive();
 365 
 366   void initialize_holder(Handle holder);
 367 
 368   void oops_do(OopClosure* f, bool must_claim, bool clear_modified_oops = false);
 369 
 370   void classes_do(KlassClosure* klass_closure);
 371   Klass* klasses() { return _klasses; }
 372 
 373   JNIMethodBlock* jmethod_ids() const              { return _jmethod_ids; }
 374   void set_jmethod_ids(JNIMethodBlock* new_block)  { _jmethod_ids = new_block; }
 375 
 376   void print()                                     { print_on(tty); }
 377   void print_on(outputStream* out) const PRODUCT_RETURN;
 378   void print_value()                               { print_value_on(tty); }
 379   void print_value_on(outputStream* out) const;
 380   void verify();
 381 
 382   OopHandle add_handle(Handle h);
 383   void remove_handle(OopHandle h);
 384   void init_handle_locked(OopHandle& pd, Handle h);  // used for concurrent access to ModuleEntry::_pd field
 385   void add_class(Klass* k, bool publicize = true);
 386   void remove_class(Klass* k);
 387   bool contains_klass(Klass* k);
 388   void record_dependency(const Klass* to);
 389   PackageEntryTable* packages() { return _packages; }
 390   ModuleEntry* unnamed_module() { return _unnamed_module; }
 391   ModuleEntryTable* modules();
 392   bool modules_defined() { return (_modules != NULL); }
 393 
 394   // Loaded class dictionary
 395   Dictionary* dictionary() const { return _dictionary; }
 396 
 397   void add_to_deallocate_list(Metadata* m);
 398 
 399   static ClassLoaderData* class_loader_data(oop loader);
 400   static ClassLoaderData* class_loader_data_or_null(oop loader);
 401   static ClassLoaderData* anonymous_class_loader_data(Handle loader);
 402 
 403   // Returns Klass* of associated class loader, or NULL if associated loader is 'bootstrap'.
 404   // Also works if unloading.
 405   Klass* class_loader_klass() const { return _class_loader_klass; }
 406 
 407   // Obtain the class loader's _name, works during unloading.
 408   const char* loader_name() const;
 409   Symbol* name() const { return _name; }
 410 
 411   // Obtain the class loader's _name_and_id, works during unloading.
 412   const char* loader_name_and_id() const;
 413   Symbol* name_and_id() const { return _name_and_id; }
 414 
 415   JFR_ONLY(DEFINE_TRACE_ID_METHODS;)
 416 };
 417 
 418 // An iterator that distributes Klasses to parallel worker threads.
 419 class ClassLoaderDataGraphKlassIteratorAtomic : public StackObj {
 420  Klass* volatile _next_klass;
 421  public:
 422   ClassLoaderDataGraphKlassIteratorAtomic();
 423   Klass* next_klass();
 424  private:
 425   static Klass* next_klass_in_cldg(Klass* klass);
 426 };
 427 
 428 class ClassLoaderDataGraphMetaspaceIterator : public StackObj {
 429   ClassLoaderData* _data;
 430  public:
 431   ClassLoaderDataGraphMetaspaceIterator();
 432   ~ClassLoaderDataGraphMetaspaceIterator();
 433   bool repeat() { return _data != NULL; }
 434   ClassLoaderMetaspace* get_next() {
 435     assert(_data != NULL, "Should not be NULL in call to the iterator");
 436     ClassLoaderMetaspace* result = _data->metaspace_or_null();
 437     _data = _data->next();
 438     // This result might be NULL for class loaders without metaspace
 439     // yet.  It would be nice to return only non-null results but
 440     // there is no guarantee that there will be a non-null result
 441     // down the list so the caller is going to have to check.
 442     return result;
 443   }
 444 };
 445 #endif // SHARE_VM_CLASSFILE_CLASSLOADERDATA_HPP