1 /*
   2  * Copyright (c) 2012, 2017, 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
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  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 "memory/metaspaceCounters.hpp"
  32 #include "oops/oopHandle.hpp"
  33 #include "runtime/mutex.hpp"
  34 #include "trace/traceMacros.hpp"
  35 #include "utilities/growableArray.hpp"
  36 #include "utilities/macros.hpp"
  37 #if INCLUDE_TRACE
  38 #include "utilities/ticks.hpp"
  39 #endif
  40 
  41 //
  42 // A class loader represents a linkset. Conceptually, a linkset identifies
  43 // the complete transitive closure of resolved links that a dynamic linker can
  44 // produce.
  45 //
  46 // A ClassLoaderData also encapsulates the allocation space, called a metaspace,
  47 // used by the dynamic linker to allocate the runtime representation of all
  48 // the types it defines.
  49 //
  50 // ClassLoaderData are stored in the runtime representation of classes,
  51 // and provides iterators for root tracing and other GC operations.
  52 
  53 class ClassLoaderData;
  54 class JNIMethodBlock;
  55 class Metadebug;
  56 class ModuleEntry;
  57 class PackageEntry;
  58 class ModuleEntryTable;
  59 class PackageEntryTable;
  60 class DictionaryEntry;
  61 class Dictionary;
  62 
  63 // GC root for walking class loader data created
  64 
  65 class ClassLoaderDataGraph : public AllStatic {
  66   friend class ClassLoaderData;
  67   friend class ClassLoaderDataGraphMetaspaceIterator;
  68   friend class ClassLoaderDataGraphKlassIteratorAtomic;
  69   friend class ClassLoaderDataGraphKlassIteratorStatic;
  70   friend class VMStructs;
  71  private:
  72   // All CLDs (except the null CLD) can be reached by walking _head->_next->...
  73   static ClassLoaderData* _head;
  74   static ClassLoaderData* _unloading;
  75   // CMS support.
  76   static ClassLoaderData* _saved_head;
  77   static ClassLoaderData* _saved_unloading;
  78   static bool _should_purge;
  79   // OOM has been seen in metaspace allocation. Used to prevent some
  80   // allocations until class unloading
  81   static bool _metaspace_oom;
  82 
  83   static ClassLoaderData* add(Handle class_loader, bool anonymous, TRAPS);
  84   static void post_class_unload_events();
  85  public:
  86   static ClassLoaderData* find_or_create(Handle class_loader, TRAPS);
  87   static void purge();
  88   static void clear_claimed_marks();
  89   // oops do
  90   static void oops_do(OopClosure* f, bool must_claim);
  91   static void keep_alive_oops_do(OopClosure* blk, bool must_claim);
  92   static void always_strong_oops_do(OopClosure* blk, bool must_claim);
  93   // cld do
  94   static void cld_do(CLDClosure* cl);
  95   static void cld_unloading_do(CLDClosure* cl);
  96   static void roots_cld_do(CLDClosure* strong, CLDClosure* weak);
  97   static void keep_alive_cld_do(CLDClosure* cl);
  98   static void always_strong_cld_do(CLDClosure* cl);
  99   // klass do
 100   // Walking classes through the ClassLoaderDataGraph include array classes.  It also includes
 101   // classes that are allocated but not loaded, classes that have errors, and scratch classes
 102   // for redefinition.  These classes are removed during the next class unloading.
 103   // Walking the ClassLoaderDataGraph also includes anonymous classes.
 104   static void classes_do(KlassClosure* klass_closure);
 105   static void classes_do(void f(Klass* const));
 106   static void methods_do(void f(Method*));
 107   static void modules_do(void f(ModuleEntry*));
 108   static void modules_unloading_do(void f(ModuleEntry*));
 109   static void packages_do(void f(PackageEntry*));
 110   static void packages_unloading_do(void f(PackageEntry*));
 111   static void loaded_classes_do(KlassClosure* klass_closure);
 112   static void classes_unloading_do(void f(Klass* const));
 113   static bool do_unloading(BoolObjectClosure* is_alive, bool clean_previous_versions);
 114 
 115   // dictionary do
 116   // Iterate over all klasses in dictionary, but
 117   // just the classes from defining class loaders.
 118   static void dictionary_classes_do(void f(InstanceKlass*));
 119   // Added for initialize_itable_for_klass to handle exceptions.
 120   static void dictionary_classes_do(void f(InstanceKlass*, TRAPS), TRAPS);
 121 
 122   // Iterate all classes and their class loaders, including initiating class loaders.
 123   static void dictionary_all_entries_do(void f(InstanceKlass*, ClassLoaderData*));
 124 
 125   // VM_CounterDecay iteration support
 126   static InstanceKlass* try_get_next_class();
 127 
 128   static void verify_dictionary();
 129   static void print_dictionary(outputStream* st);
 130   static void print_dictionary_statistics(outputStream* st);
 131 
 132   // CMS support.
 133   static void remember_new_clds(bool remember) { _saved_head = (remember ? _head : NULL); }
 134   static GrowableArray<ClassLoaderData*>* new_clds();
 135 
 136   static void set_should_purge(bool b) { _should_purge = b; }
 137   static void purge_if_needed() {
 138     // Only purge the CLDG for CMS if concurrent sweep is complete.
 139     if (_should_purge) {
 140       purge();
 141       // reset for next time.
 142       set_should_purge(false);
 143     }
 144   }
 145 
 146   static bool has_metaspace_oom()           { return _metaspace_oom; }
 147   static void set_metaspace_oom(bool value) { _metaspace_oom = value; }
 148 
 149   static void dump_on(outputStream * const out) PRODUCT_RETURN;
 150   static void dump() { dump_on(tty); }
 151   static void verify();
 152   static void print_creation(outputStream* out, Handle loader, ClassLoaderData* cld, TRAPS);
 153 
 154   static bool unload_list_contains(const void* x);
 155 #ifndef PRODUCT
 156   static bool contains_loader_data(ClassLoaderData* loader_data);
 157 #endif
 158 
 159 #if INCLUDE_TRACE
 160  private:
 161   static Ticks _class_unload_time;
 162   static void class_unload_event(Klass* const k);
 163 #endif
 164 };
 165 
 166 // ClassLoaderData class
 167 
 168 class ClassLoaderData : public CHeapObj<mtClass> {
 169   friend class VMStructs;
 170  private:
 171   class Dependencies VALUE_OBJ_CLASS_SPEC {
 172     objArrayOop _list_head;
 173     void locked_add(objArrayHandle last,
 174                     objArrayHandle new_dependency,
 175                     Thread* THREAD);
 176    public:
 177     Dependencies() : _list_head(NULL) {}
 178     Dependencies(TRAPS) : _list_head(NULL) {
 179       init(CHECK);
 180     }
 181     void add(Handle dependency, TRAPS);
 182     void init(TRAPS);
 183     void oops_do(OopClosure* f);
 184   };
 185 
 186   class ChunkedHandleList VALUE_OBJ_CLASS_SPEC {
 187     struct Chunk : public CHeapObj<mtClass> {
 188       static const size_t CAPACITY = 32;
 189 
 190       oop _data[CAPACITY];
 191       volatile juint _size;
 192       Chunk* _next;
 193 
 194       Chunk(Chunk* c) : _next(c), _size(0) { }
 195     };
 196 
 197     Chunk* _head;
 198 
 199     void oops_do_chunk(OopClosure* f, Chunk* c, const juint size);
 200 
 201    public:
 202     ChunkedHandleList() : _head(NULL) {}
 203     ~ChunkedHandleList();
 204 
 205     // Only one thread at a time can add, guarded by ClassLoaderData::metaspace_lock().
 206     // However, multiple threads can execute oops_do concurrently with add.
 207     oop* add(oop o);
 208 #ifdef ASSERT
 209     bool contains(oop* p);
 210 #endif
 211     void oops_do(OopClosure* f);
 212   };
 213 
 214   friend class ClassLoaderDataGraph;
 215   friend class ClassLoaderDataGraphKlassIteratorAtomic;
 216   friend class ClassLoaderDataGraphKlassIteratorStatic;
 217   friend class ClassLoaderDataGraphMetaspaceIterator;
 218   friend class MetaDataFactory;
 219   friend class Method;
 220 
 221   static ClassLoaderData * _the_null_class_loader_data;
 222 
 223   oop _class_loader;          // oop used to uniquely identify a class loader
 224                               // class loader or a canonical class path
 225   Dependencies _dependencies; // holds dependencies from this class loader
 226                               // data to others.
 227 
 228   Metaspace * volatile _metaspace;  // Meta-space where meta-data defined by the
 229                                     // classes in the class loader are allocated.
 230   Mutex* _metaspace_lock;  // Locks the metaspace for allocations and setup.
 231   bool _unloading;         // true if this class loader goes away
 232   bool _is_anonymous;      // if this CLD is for an anonymous class
 233   s2 _keep_alive;          // if this CLD is kept alive without a keep_alive_object().
 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   // Remembered sets support for the oops in the class loader data.
 239   jbyte _modified_oops;             // Card Table Equivalent (YC/CMS support)
 240   jbyte _accumulated_modified_oops; // Mod Union Equivalent (CMS support)
 241 
 242   volatile int _claimed;   // true if claimed, for example during GC traces.
 243                            // To avoid applying oop closure more than once.
 244                            // Has to be an int because we cas it.
 245   ChunkedHandleList _handles; // Handles to constant pool arrays, Modules, etc, which
 246                               // have the same life cycle of the corresponding ClassLoader.
 247 
 248   Klass* volatile _klasses;              // The classes defined by the class loader.
 249   PackageEntryTable* volatile _packages; // The packages defined by the class loader.
 250   ModuleEntryTable*  volatile _modules;  // The modules defined by the class loader.
 251   ModuleEntry* _unnamed_module;          // This class loader's unnamed module.
 252   Dictionary*  _dictionary;              // The loaded InstanceKlasses, including initiated by this class loader
 253 
 254   // These method IDs are created for the class loader and set to NULL when the
 255   // class loader is unloaded.  They are rarely freed, only for redefine classes
 256   // and if they lose a data race in InstanceKlass.
 257   JNIMethodBlock*                  _jmethod_ids;
 258 
 259   // Metadata to be deallocated when it's safe at class unloading, when
 260   // this class loader isn't unloaded itself.
 261   GrowableArray<Metadata*>*      _deallocate_list;
 262 
 263   // Support for walking class loader data objects
 264   ClassLoaderData* _next; /// Next loader_datas created
 265 
 266   // ReadOnly and ReadWrite metaspaces (static because only on the null
 267   // class loader for now).
 268   static Metaspace* _ro_metaspace;
 269   static Metaspace* _rw_metaspace;
 270 
 271   TRACE_DEFINE_TRACE_ID_FIELD;
 272 
 273   void set_next(ClassLoaderData* next) { _next = next; }
 274   ClassLoaderData* next() const        { return _next; }
 275 
 276   ClassLoaderData(Handle h_class_loader, bool is_anonymous, Dependencies dependencies);
 277   ~ClassLoaderData();
 278 
 279   // GC interface.
 280   void clear_claimed()          { _claimed = 0; }
 281   bool claimed() const          { return _claimed == 1; }
 282   bool claim();
 283 
 284   // The CLD are not placed in the Heap, so the Card Table or
 285   // the Mod Union Table can't be used to mark when CLD have modified oops.
 286   // The CT and MUT bits saves this information for the whole class loader data.
 287   void clear_modified_oops()             { _modified_oops = 0; }
 288  public:
 289   void record_modified_oops()            { _modified_oops = 1; }
 290   bool has_modified_oops()               { return _modified_oops == 1; }
 291 
 292   void accumulate_modified_oops()        { if (has_modified_oops()) _accumulated_modified_oops = 1; }
 293   void clear_accumulated_modified_oops() { _accumulated_modified_oops = 0; }
 294   bool has_accumulated_modified_oops()   { return _accumulated_modified_oops == 1; }
 295  private:
 296 
 297   void unload();
 298   bool keep_alive() const       { return _keep_alive > 0; }
 299   void classes_do(void f(Klass*));
 300   void loaded_classes_do(KlassClosure* klass_closure);
 301   void classes_do(void f(InstanceKlass*));
 302   void methods_do(void f(Method*));
 303   void modules_do(void f(ModuleEntry*));
 304   void packages_do(void f(PackageEntry*));
 305 
 306   // Deallocate free list during class unloading.
 307   void free_deallocate_list();
 308 
 309   // Allocate out of this class loader data
 310   MetaWord* allocate(size_t size);
 311 
 312   Dictionary* create_dictionary();
 313  public:
 314 
 315   bool is_alive(BoolObjectClosure* is_alive_closure) const;
 316 
 317   // Accessors
 318   Metaspace* 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     assert(_the_null_class_loader_data == NULL, "cannot initialize twice");
 330     assert(ClassLoaderDataGraph::_head == NULL, "cannot initialize twice");
 331 
 332     // We explicitly initialize the Dependencies object at a later phase in the initialization
 333     _the_null_class_loader_data = new ClassLoaderData(Handle(), false, Dependencies());
 334     ClassLoaderDataGraph::_head = _the_null_class_loader_data;
 335     assert(_the_null_class_loader_data->is_the_null_class_loader_data(), "Must be");
 336   }
 337 
 338   bool is_the_null_class_loader_data() const {
 339     return this == _the_null_class_loader_data;
 340   }
 341   bool is_system_class_loader_data() const;
 342   bool is_platform_class_loader_data() const;
 343   bool is_builtin_class_loader_data() const;
 344 
 345   // The Metaspace is created lazily so may be NULL.  This
 346   // method will allocate a Metaspace if needed.
 347   Metaspace* metaspace_non_null();
 348 
 349   oop class_loader() const      { return _class_loader; }
 350 
 351   // The object the GC is using to keep this ClassLoaderData alive.
 352   oop keep_alive_object() const;
 353 
 354   // Returns true if this class loader data is for a loader going away.
 355   bool is_unloading() const     {
 356     assert(!(is_the_null_class_loader_data() && _unloading), "The null class loader can never be unloaded");
 357     return _unloading;
 358   }
 359 
 360   // Used to refcount an anonymous class's CLD in order to
 361   // indicate their aliveness without a keep_alive_object().
 362   void inc_keep_alive();
 363   void dec_keep_alive();
 364 
 365   inline unsigned int identity_hash() const { return (unsigned int)(((intptr_t)this) >> 3); }
 366 
 367   void oops_do(OopClosure* f, bool must_claim, bool clear_modified_oops = false);
 368 
 369   void classes_do(KlassClosure* klass_closure);
 370   Klass* klasses() { return _klasses; }
 371 
 372   JNIMethodBlock* jmethod_ids() const              { return _jmethod_ids; }
 373   void set_jmethod_ids(JNIMethodBlock* new_block)  { _jmethod_ids = new_block; }
 374 
 375   void print()                                     { print_on(tty); }
 376   void print_on(outputStream* out) const;
 377   void print_value()                               { print_value_on(tty); }
 378   void print_value_on(outputStream* out) const;
 379   void dump(outputStream * const out) PRODUCT_RETURN;
 380   void verify();
 381   const char* loader_name();
 382 
 383   OopHandle add_handle(Handle h);
 384   void remove_handle(OopHandle h);
 385   void init_handle_locked(OopHandle& pd, Handle h);  // used for concurrent access to ModuleEntry::_pd field
 386   void add_class(Klass* k, bool publicize = true);
 387   void remove_class(Klass* k);
 388   bool contains_klass(Klass* k);
 389   void record_dependency(const Klass* to, TRAPS);
 390   void init_dependencies(TRAPS);
 391   PackageEntryTable* packages() { return _packages; }
 392   ModuleEntry* unnamed_module() { return _unnamed_module; }
 393   ModuleEntryTable* modules();
 394   bool modules_defined() { return (_modules != NULL); }
 395 
 396   // Loaded class dictionary
 397   Dictionary* dictionary() const { return _dictionary; }
 398 
 399   void add_to_deallocate_list(Metadata* m);
 400 
 401   static ClassLoaderData* class_loader_data(oop loader);
 402   static ClassLoaderData* class_loader_data_or_null(oop loader);
 403   static ClassLoaderData* anonymous_class_loader_data(oop loader, TRAPS);
 404   static void print_loader(ClassLoaderData *loader_data, outputStream *out);
 405 
 406   TRACE_DEFINE_TRACE_ID_METHODS;
 407 };
 408 
 409 // An iterator that distributes Klasses to parallel worker threads.
 410 class ClassLoaderDataGraphKlassIteratorAtomic : public StackObj {
 411  Klass* volatile _next_klass;
 412  public:
 413   ClassLoaderDataGraphKlassIteratorAtomic();
 414   Klass* next_klass();
 415  private:
 416   static Klass* next_klass_in_cldg(Klass* klass);
 417 };
 418 
 419 class ClassLoaderDataGraphMetaspaceIterator : public StackObj {
 420   ClassLoaderData* _data;
 421  public:
 422   ClassLoaderDataGraphMetaspaceIterator();
 423   ~ClassLoaderDataGraphMetaspaceIterator();
 424   bool repeat() { return _data != NULL; }
 425   Metaspace* get_next() {
 426     assert(_data != NULL, "Should not be NULL in call to the iterator");
 427     Metaspace* result = _data->metaspace_or_null();
 428     _data = _data->next();
 429     // This result might be NULL for class loaders without metaspace
 430     // yet.  It would be nice to return only non-null results but
 431     // there is no guarantee that there will be a non-null result
 432     // down the list so the caller is going to have to check.
 433     return result;
 434   }
 435 };
 436 #endif // SHARE_VM_CLASSFILE_CLASSLOADERDATA_HPP