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 "runtime/mutex.hpp"
  33 #include "trace/traceMacros.hpp"
  34 #include "utilities/growableArray.hpp"
  35 #include "utilities/macros.hpp"
  36 #if INCLUDE_TRACE
  37 #include "utilities/ticks.hpp"
  38 #endif
  39 
  40 //
  41 // A class loader represents a linkset. Conceptually, a linkset identifies
  42 // the complete transitive closure of resolved links that a dynamic linker can
  43 // produce.
  44 //
  45 // A ClassLoaderData also encapsulates the allocation space, called a metaspace,
  46 // used by the dynamic linker to allocate the runtime representation of all
  47 // the types it defines.
  48 //
  49 // ClassLoaderData are stored in the runtime representation of classes and the
  50 // system dictionary, are roots of garbage collection, and provides iterators
  51 // 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 
  61 // GC root for walking class loader data created
  62 
  63 class ClassLoaderDataGraph : public AllStatic {
  64   friend class ClassLoaderData;
  65   friend class ClassLoaderDataGraphMetaspaceIterator;
  66   friend class ClassLoaderDataGraphKlassIteratorAtomic;
  67   friend class VMStructs;
  68  private:
  69   // All CLDs (except the null CLD) can be reached by walking _head->_next->...
  70   static ClassLoaderData* _head;
  71   static ClassLoaderData* _unloading;
  72   // CMS support.
  73   static ClassLoaderData* _saved_head;
  74   static ClassLoaderData* _saved_unloading;
  75   static bool _should_purge;
  76   // OOM has been seen in metaspace allocation. Used to prevent some
  77   // allocations until class unloading
  78   static bool _metaspace_oom;
  79 
  80   static ClassLoaderData* add(Handle class_loader, bool anonymous, TRAPS);
  81   static void post_class_unload_events();
  82  public:
  83   static ClassLoaderData* find_or_create(Handle class_loader, TRAPS);
  84   static void purge();
  85   static void clear_claimed_marks();
  86   // oops do
  87   static void oops_do(OopClosure* f, KlassClosure* klass_closure, bool must_claim);
  88   static void keep_alive_oops_do(OopClosure* blk, KlassClosure* klass_closure, bool must_claim);
  89   static void always_strong_oops_do(OopClosure* blk, KlassClosure* klass_closure, bool must_claim);
  90   // cld do
  91   static void cld_do(CLDClosure* cl);
  92   static void cld_unloading_do(CLDClosure* cl);
  93   static void roots_cld_do(CLDClosure* strong, CLDClosure* weak);
  94   static void keep_alive_cld_do(CLDClosure* cl);
  95   static void always_strong_cld_do(CLDClosure* cl);
  96   // klass do
  97   // Walking classes through the ClassLoaderDataGraph include array classes.  It also includes
  98   // classes that are allocated but not loaded, classes that have errors, and scratch classes
  99   // for redefinition.  These classes are removed during the next class unloading.
 100   // Walking the ClassLoaderDataGraph also includes anonymous classes.
 101   static void classes_do(KlassClosure* klass_closure);
 102   static void classes_do(void f(Klass* const));
 103   static void methods_do(void f(Method*));
 104   static void modules_do(void f(ModuleEntry*));
 105   static void modules_unloading_do(void f(ModuleEntry*));
 106   static void packages_do(void f(PackageEntry*));
 107   static void packages_unloading_do(void f(PackageEntry*));
 108   static void loaded_classes_do(KlassClosure* klass_closure);
 109   static void classes_unloading_do(void f(Klass* const));
 110   static bool do_unloading(BoolObjectClosure* is_alive, bool clean_previous_versions);
 111 
 112   // CMS support.
 113   static void remember_new_clds(bool remember) { _saved_head = (remember ? _head : NULL); }
 114   static GrowableArray<ClassLoaderData*>* new_clds();
 115 
 116   static void set_should_purge(bool b) { _should_purge = b; }
 117   static void purge_if_needed() {
 118     // Only purge the CLDG for CMS if concurrent sweep is complete.
 119     if (_should_purge) {
 120       purge();
 121       // reset for next time.
 122       set_should_purge(false);
 123     }
 124   }
 125 
 126   static bool has_metaspace_oom()           { return _metaspace_oom; }
 127   static void set_metaspace_oom(bool value) { _metaspace_oom = value; }
 128 
 129   static void dump_on(outputStream * const out) PRODUCT_RETURN;
 130   static void dump() { dump_on(tty); }
 131   static void verify();
 132   static void print_creation(outputStream* out, Handle loader, ClassLoaderData* cld, TRAPS);
 133 
 134   static bool unload_list_contains(const void* x);
 135 #ifndef PRODUCT
 136   static bool contains_loader_data(ClassLoaderData* loader_data);
 137 #endif
 138 
 139 #if INCLUDE_TRACE
 140  private:
 141   static Ticks _class_unload_time;
 142   static void class_unload_event(Klass* const k);
 143 #endif
 144 };
 145 
 146 // ClassLoaderData class
 147 
 148 class ClassLoaderData : public CHeapObj<mtClass> {
 149   friend class VMStructs;
 150  private:
 151   class Dependencies VALUE_OBJ_CLASS_SPEC {
 152     objArrayOop _list_head;
 153     void locked_add(objArrayHandle last,
 154                     objArrayHandle new_dependency,
 155                     Thread* THREAD);
 156    public:
 157     Dependencies() : _list_head(NULL) {}
 158     Dependencies(TRAPS) : _list_head(NULL) {
 159       init(CHECK);
 160     }
 161     void add(Handle dependency, TRAPS);
 162     void init(TRAPS);
 163     void oops_do(OopClosure* f);
 164   };
 165 
 166   class ChunkedHandleList VALUE_OBJ_CLASS_SPEC {
 167     struct Chunk : public CHeapObj<mtClass> {
 168       static const size_t CAPACITY = 32;
 169 
 170       oop _data[CAPACITY];
 171       volatile juint _size;
 172       Chunk* _next;
 173 
 174       Chunk(Chunk* c) : _next(c), _size(0) { }
 175     };
 176 
 177     Chunk* _head;
 178 
 179     void oops_do_chunk(OopClosure* f, Chunk* c, const juint size);
 180 
 181    public:
 182     ChunkedHandleList() : _head(NULL) {}
 183     ~ChunkedHandleList();
 184 
 185     // Only one thread at a time can add, guarded by ClassLoaderData::metaspace_lock().
 186     // However, multiple threads can execute oops_do concurrently with add.
 187     oop* add(oop o);
 188 #ifdef ASSERT
 189     bool contains(oop* p);
 190 #endif
 191     void oops_do(OopClosure* f);
 192   };
 193 
 194   friend class ClassLoaderDataGraph;
 195   friend class ClassLoaderDataGraphKlassIteratorAtomic;
 196   friend class ClassLoaderDataGraphMetaspaceIterator;
 197   friend class MetaDataFactory;
 198   friend class Method;
 199 
 200   static ClassLoaderData * _the_null_class_loader_data;
 201 
 202   oop _class_loader;          // oop used to uniquely identify a class loader
 203                               // class loader or a canonical class path
 204   Dependencies _dependencies; // holds dependencies from this class loader
 205                               // data to others.
 206 
 207   Metaspace * volatile _metaspace;  // Meta-space where meta-data defined by the
 208                                     // classes in the class loader are allocated.
 209   Mutex* _metaspace_lock;  // Locks the metaspace for allocations and setup.
 210   bool _unloading;         // true if this class loader goes away
 211   bool _is_anonymous;      // if this CLD is for an anonymous class
 212   s2 _keep_alive;          // if this CLD is kept alive without a keep_alive_object().
 213                            // Used for anonymous classes and the boot class
 214                            // loader. _keep_alive does not need to be volatile or
 215                            // atomic since there is one unique CLD per anonymous class.
 216   volatile int _claimed;   // true if claimed, for example during GC traces.
 217                            // To avoid applying oop closure more than once.
 218                            // Has to be an int because we cas it.
 219   ChunkedHandleList _handles; // Handles to constant pool arrays, Modules, etc, which
 220                               // have the same life cycle of the corresponding ClassLoader.
 221 
 222   Klass* volatile _klasses;              // The classes defined by the class loader.
 223   PackageEntryTable* volatile _packages; // The packages defined by the class loader.
 224   ModuleEntry* _unnamed_module;          // This class loader's unnamed module.
 225   ModuleEntryTable* volatile _modules;   // The modules defined by the class loader.
 226 
 227   // These method IDs are created for the class loader and set to NULL when the
 228   // class loader is unloaded.  They are rarely freed, only for redefine classes
 229   // and if they lose a data race in InstanceKlass.
 230   JNIMethodBlock*                  _jmethod_ids;
 231 
 232   // Metadata to be deallocated when it's safe at class unloading, when
 233   // this class loader isn't unloaded itself.
 234   GrowableArray<Metadata*>*      _deallocate_list;
 235 
 236   // Support for walking class loader data objects
 237   ClassLoaderData* _next; /// Next loader_datas created
 238 
 239   // ReadOnly and ReadWrite metaspaces (static because only on the null
 240   // class loader for now).
 241   static Metaspace* _ro_metaspace;
 242   static Metaspace* _rw_metaspace;
 243 
 244   TRACE_DEFINE_TRACE_ID_FIELD;
 245 
 246   void set_next(ClassLoaderData* next) { _next = next; }
 247   ClassLoaderData* next() const        { return _next; }
 248 
 249   ClassLoaderData(Handle h_class_loader, bool is_anonymous, Dependencies dependencies);
 250   ~ClassLoaderData();
 251 
 252   // GC interface.
 253   void clear_claimed()          { _claimed = 0; }
 254   bool claimed() const          { return _claimed == 1; }
 255   bool claim();
 256 
 257   void unload();
 258   bool keep_alive() const       { return _keep_alive > 0; }
 259   void classes_do(void f(Klass*));
 260   void loaded_classes_do(KlassClosure* klass_closure);
 261   void classes_do(void f(InstanceKlass*));
 262   void methods_do(void f(Method*));
 263   void modules_do(void f(ModuleEntry*));
 264   void packages_do(void f(PackageEntry*));
 265 
 266   // Deallocate free list during class unloading.
 267   void free_deallocate_list();
 268 
 269   // Allocate out of this class loader data
 270   MetaWord* allocate(size_t size);
 271 
 272  public:
 273 
 274   bool is_alive(BoolObjectClosure* is_alive_closure) const;
 275 
 276   // Accessors
 277   Metaspace* metaspace_or_null() const     { return _metaspace; }
 278 
 279   static ClassLoaderData* the_null_class_loader_data() {
 280     return _the_null_class_loader_data;
 281   }
 282 
 283   Mutex* metaspace_lock() const { return _metaspace_lock; }
 284 
 285   bool is_anonymous() const { return _is_anonymous; }
 286 
 287   static void init_null_class_loader_data() {
 288     assert(_the_null_class_loader_data == NULL, "cannot initialize twice");
 289     assert(ClassLoaderDataGraph::_head == NULL, "cannot initialize twice");
 290 
 291     // We explicitly initialize the Dependencies object at a later phase in the initialization
 292     _the_null_class_loader_data = new ClassLoaderData(Handle(), false, Dependencies());
 293     ClassLoaderDataGraph::_head = _the_null_class_loader_data;
 294     assert(_the_null_class_loader_data->is_the_null_class_loader_data(), "Must be");
 295     if (DumpSharedSpaces) {
 296       _the_null_class_loader_data->initialize_shared_metaspaces();
 297     }
 298   }
 299 
 300   bool is_the_null_class_loader_data() const {
 301     return this == _the_null_class_loader_data;
 302   }
 303   bool is_system_class_loader_data() const;
 304   bool is_platform_class_loader_data() const;
 305   bool is_builtin_class_loader_data() const;
 306 
 307   // The Metaspace is created lazily so may be NULL.  This
 308   // method will allocate a Metaspace if needed.
 309   Metaspace* metaspace_non_null();
 310 
 311   oop class_loader() const      { return _class_loader; }
 312 
 313   // The object the GC is using to keep this ClassLoaderData alive.
 314   oop keep_alive_object() const;
 315 
 316   // Returns true if this class loader data is for a loader going away.
 317   bool is_unloading() const     {
 318     assert(!(is_the_null_class_loader_data() && _unloading), "The null class loader can never be unloaded");
 319     return _unloading;
 320   }
 321 
 322   // Used to refcount an anonymous class's CLD in order to
 323   // indicate their aliveness without a keep_alive_object().
 324   void inc_keep_alive();
 325   void dec_keep_alive();
 326 
 327   inline unsigned int identity_hash() const;
 328 
 329   // Used when tracing from klasses.
 330   void oops_do(OopClosure* f, KlassClosure* klass_closure, bool must_claim);
 331 
 332   void classes_do(KlassClosure* klass_closure);
 333 
 334   JNIMethodBlock* jmethod_ids() const              { return _jmethod_ids; }
 335   void set_jmethod_ids(JNIMethodBlock* new_block)  { _jmethod_ids = new_block; }
 336 
 337   void print_value() { print_value_on(tty); }
 338   void print_value_on(outputStream* out) const;
 339   void dump(outputStream * const out) PRODUCT_RETURN;
 340   void verify();
 341   const char* loader_name();
 342 
 343   jobject add_handle(Handle h);
 344   void remove_handle_unsafe(jobject h);
 345   void add_class(Klass* k, bool publicize = true);
 346   void remove_class(Klass* k);
 347   bool contains_klass(Klass* k);
 348   void record_dependency(const Klass* to, TRAPS);
 349   void init_dependencies(TRAPS);
 350   PackageEntryTable* packages() { return _packages; }
 351   ModuleEntry* unnamed_module() { return _unnamed_module; }
 352   ModuleEntryTable* modules();
 353   bool modules_defined() { return (_modules != NULL); }
 354 
 355   void add_to_deallocate_list(Metadata* m);
 356 
 357   static ClassLoaderData* class_loader_data(oop loader);
 358   static ClassLoaderData* class_loader_data_or_null(oop loader);
 359   static ClassLoaderData* anonymous_class_loader_data(oop loader, TRAPS);
 360   static void print_loader(ClassLoaderData *loader_data, outputStream *out);
 361 
 362   // CDS support
 363   Metaspace* ro_metaspace();
 364   Metaspace* rw_metaspace();
 365   void initialize_shared_metaspaces();
 366 
 367   TRACE_DEFINE_TRACE_ID_METHODS;
 368 };
 369 
 370 // An iterator that distributes Klasses to parallel worker threads.
 371 class ClassLoaderDataGraphKlassIteratorAtomic : public StackObj {
 372  Klass* volatile _next_klass;
 373  public:
 374   ClassLoaderDataGraphKlassIteratorAtomic();
 375   Klass* next_klass();
 376  private:
 377   static Klass* next_klass_in_cldg(Klass* klass);
 378 };
 379 
 380 class ClassLoaderDataGraphMetaspaceIterator : public StackObj {
 381   ClassLoaderData* _data;
 382  public:
 383   ClassLoaderDataGraphMetaspaceIterator();
 384   ~ClassLoaderDataGraphMetaspaceIterator();
 385   bool repeat() { return _data != NULL; }
 386   Metaspace* get_next() {
 387     assert(_data != NULL, "Should not be NULL in call to the iterator");
 388     Metaspace* result = _data->metaspace_or_null();
 389     _data = _data->next();
 390     // This result might be NULL for class loaders without metaspace
 391     // yet.  It would be nice to return only non-null results but
 392     // there is no guarantee that there will be a non-null result
 393     // down the list so the caller is going to have to check.
 394     return result;
 395   }
 396 };
 397 #endif // SHARE_VM_CLASSFILE_CLASSLOADERDATA_HPP