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
  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_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 "utilities/growableArray.hpp"
  34 #include "utilities/macros.hpp"
  35 #if INCLUDE_JFR
  36 #include "jfr/support/jfrTraceIdExtension.hpp"
  37 #endif
  38 
  39 //
  40 // A class loader represents a linkset. Conceptually, a linkset identifies
  41 // the complete transitive closure of resolved links that a dynamic linker can
  42 // produce.
  43 //
  44 // A ClassLoaderData also encapsulates the allocation space, called a metaspace,
  45 // used by the dynamic linker to allocate the runtime representation of all
  46 // the types it defines.
  47 //
  48 // ClassLoaderData are stored in the runtime representation of classes and the
  49 // system dictionary, are roots of garbage collection, and provides iterators
  50 // for root tracing and other GC operations.
  51 
  52 class ClassLoaderData;
  53 class JNIMethodBlock;
  54 class Metadebug;
  55 
  56 // GC root for walking class loader data created
  57 
  58 class ClassLoaderDataGraph : public AllStatic {
  59   friend class ClassLoaderData;
  60   friend class ClassLoaderDataGraphMetaspaceIterator;
  61   friend class ClassLoaderDataGraphKlassIteratorAtomic;
  62   friend class VMStructs;
  63  private:
  64   // All CLDs (except the null CLD) can be reached by walking _head->_next->...
  65   static ClassLoaderData* _head;
  66   static ClassLoaderData* _unloading;
  67   // CMS support.
  68   static ClassLoaderData* _saved_head;
  69   static ClassLoaderData* _saved_unloading;
  70   static bool _should_purge;
  71 
  72   static ClassLoaderData* add(Handle class_loader, bool anonymous, TRAPS);
  73   static void clean_metaspaces();
  74  public:
  75   static ClassLoaderData* find_or_create(Handle class_loader, TRAPS);
  76   static void purge();
  77   static void clear_claimed_marks();
  78   // oops do
  79   static void oops_do(OopClosure* f, KlassClosure* klass_closure, bool must_claim);
  80   static void keep_alive_oops_do(OopClosure* blk, KlassClosure* klass_closure, bool must_claim);
  81   static void always_strong_oops_do(OopClosure* blk, KlassClosure* klass_closure, bool must_claim);
  82   // cld do
  83   static void cld_do(CLDClosure* cl);
  84   static void cld_unloading_do(CLDClosure* cl);
  85   static void roots_cld_do(CLDClosure* strong, CLDClosure* weak);
  86   static void keep_alive_cld_do(CLDClosure* cl);
  87   static void always_strong_cld_do(CLDClosure* cl);
  88   // klass do
  89   static void classes_do(KlassClosure* klass_closure);
  90   static void classes_do(void f(Klass* const));
  91   static void loaded_classes_do(KlassClosure* klass_closure);
  92   static void classes_unloading_do(void f(Klass* const));
  93   static bool do_unloading(BoolObjectClosure* is_alive, bool clean_alive);
  94 
  95   // CMS support.
  96   static void remember_new_clds(bool remember) { _saved_head = (remember ? _head : NULL); }
  97   static GrowableArray<ClassLoaderData*>* new_clds();
  98 
  99   static void set_should_purge(bool b) { _should_purge = b; }
 100   static void purge_if_needed() {
 101     // Only purge the CLDG for CMS if concurrent sweep is complete.
 102     if (_should_purge) {
 103       purge();
 104       // reset for next time.
 105       set_should_purge(false);
 106     }
 107   }
 108 
 109   static void free_deallocate_lists();
 110 
 111   static void dump_on(outputStream * const out) PRODUCT_RETURN;
 112   static void dump() { dump_on(tty); }
 113   static void verify();
 114 
 115   static bool unload_list_contains(const void* x);
 116 #ifndef PRODUCT
 117   static bool contains_loader_data(ClassLoaderData* loader_data);
 118 #endif
 119 };
 120 
 121 // ClassLoaderData class
 122 
 123 class ClassLoaderData : public CHeapObj<mtClass> {
 124   friend class VMStructs;
 125  private:
 126   class Dependencies VALUE_OBJ_CLASS_SPEC {
 127     objArrayOop _list_head;
 128     void locked_add(objArrayHandle last,
 129                     objArrayHandle new_dependency,
 130                     Thread* THREAD);
 131    public:
 132     Dependencies() : _list_head(NULL) {}
 133     Dependencies(TRAPS) : _list_head(NULL) {
 134       init(CHECK);
 135     }
 136     void add(Handle dependency, TRAPS);
 137     void init(TRAPS);
 138     void oops_do(OopClosure* f);
 139   };
 140 
 141   class ChunkedHandleList VALUE_OBJ_CLASS_SPEC {
 142     struct Chunk : public CHeapObj<mtClass> {
 143       static const size_t CAPACITY = 32;
 144 
 145       oop _data[CAPACITY];
 146       volatile juint _size;
 147       Chunk* _next;
 148 
 149       Chunk(Chunk* c) : _next(c), _size(0) { }
 150     };
 151 
 152     Chunk* _head;
 153 
 154     void oops_do_chunk(OopClosure* f, Chunk* c, const juint size);
 155 
 156    public:
 157     ChunkedHandleList() : _head(NULL) {}
 158     ~ChunkedHandleList();
 159 
 160     // Only one thread at a time can add, guarded by ClassLoaderData::metaspace_lock().
 161     // However, multiple threads can execute oops_do concurrently with add.
 162     oop* add(oop o);
 163     void oops_do(OopClosure* f);
 164   };
 165 
 166   friend class ClassLoaderDataGraph;
 167   friend class ClassLoaderDataGraphKlassIteratorAtomic;
 168   friend class ClassLoaderDataGraphMetaspaceIterator;
 169   friend class MetaDataFactory;
 170   friend class Method;
 171 
 172   static ClassLoaderData * _the_null_class_loader_data;
 173 
 174   oop _class_loader;          // oop used to uniquely identify a class loader
 175                               // class loader or a canonical class path
 176   Dependencies _dependencies; // holds dependencies from this class loader
 177                               // data to others.
 178 
 179   Metaspace * _metaspace;  // Meta-space where meta-data defined by the
 180                            // classes in the class loader are allocated.
 181   Mutex* _metaspace_lock;  // Locks the metaspace for allocations and setup.
 182   bool _unloading;         // true if this class loader goes away
 183   bool _keep_alive;        // if this CLD is kept alive without a keep_alive_object().
 184   bool _is_anonymous;      // if this CLD is for an anonymous class
 185   volatile int _claimed;   // true if claimed, for example during GC traces.
 186                            // To avoid applying oop closure more than once.
 187                            // Has to be an int because we cas it.
 188   Klass* _klasses;         // The classes defined by the class loader.
 189 
 190   ChunkedHandleList _handles; // Handles to constant pool arrays, etc, which
 191                               // have the same life cycle of the corresponding ClassLoader.
 192 
 193   // These method IDs are created for the class loader and set to NULL when the
 194   // class loader is unloaded.  They are rarely freed, only for redefine classes
 195   // and if they lose a data race in InstanceKlass.
 196   JNIMethodBlock*                  _jmethod_ids;
 197 
 198   // Metadata to be deallocated when it's safe at class unloading, when
 199   // this class loader isn't unloaded itself.
 200   GrowableArray<Metadata*>*      _deallocate_list;
 201 
 202   // Support for walking class loader data objects
 203   ClassLoaderData* _next; /// Next loader_datas created
 204 
 205   // ReadOnly and ReadWrite metaspaces (static because only on the null
 206   // class loader for now).
 207   static Metaspace* _ro_metaspace;
 208   static Metaspace* _rw_metaspace;
 209 
 210   JFR_ONLY(DEFINE_TRACE_ID_FIELD;)
 211 
 212   void set_next(ClassLoaderData* next) { _next = next; }
 213   ClassLoaderData* next() const        { return _next; }
 214 
 215   ClassLoaderData(Handle h_class_loader, bool is_anonymous, Dependencies dependencies);
 216   ~ClassLoaderData();
 217 
 218   void set_metaspace(Metaspace* m) { _metaspace = m; }
 219 
 220   Mutex* metaspace_lock() const { return _metaspace_lock; }
 221 
 222   void unload();
 223   bool keep_alive() const       { return _keep_alive; }
 224   void classes_do(void f(Klass*));
 225   void loaded_classes_do(KlassClosure* klass_closure);
 226   void classes_do(void f(InstanceKlass*));
 227 
 228   // Deallocate free list during class unloading.
 229   void free_deallocate_list();
 230 
 231   // Allocate out of this class loader data
 232   MetaWord* allocate(size_t size);
 233 
 234  public:
 235 
 236   // GC interface.
 237   void clear_claimed()          { _claimed = 0; }
 238   bool claimed() const          { return _claimed == 1; }
 239   bool claim();
 240 
 241   bool is_alive(BoolObjectClosure* is_alive_closure) const;
 242 
 243   // Accessors
 244   Metaspace* metaspace_or_null() const     { return _metaspace; }
 245 
 246   static ClassLoaderData* the_null_class_loader_data() {
 247     return _the_null_class_loader_data;
 248   }
 249 
 250   bool is_anonymous() const { return _is_anonymous; }
 251 
 252   static void init_null_class_loader_data() {
 253     assert(_the_null_class_loader_data == NULL, "cannot initialize twice");
 254     assert(ClassLoaderDataGraph::_head == NULL, "cannot initialize twice");
 255 
 256     // We explicitly initialize the Dependencies object at a later phase in the initialization
 257     _the_null_class_loader_data = new ClassLoaderData((oop)NULL, false, Dependencies());
 258     ClassLoaderDataGraph::_head = _the_null_class_loader_data;
 259     assert(_the_null_class_loader_data->is_the_null_class_loader_data(), "Must be");
 260     if (DumpSharedSpaces) {
 261       _the_null_class_loader_data->initialize_shared_metaspaces();
 262     }
 263   }
 264 
 265   bool is_the_null_class_loader_data() const {
 266     return this == _the_null_class_loader_data;
 267   }
 268   bool is_ext_class_loader_data() const;
 269 
 270   // The Metaspace is created lazily so may be NULL.  This
 271   // method will allocate a Metaspace if needed.
 272   Metaspace* metaspace_non_null();
 273 
 274   oop class_loader() const      { return _class_loader; }
 275 
 276   // The object the GC is using to keep this ClassLoaderData alive.
 277   oop keep_alive_object() const;
 278 
 279   // Returns true if this class loader data is for a loader going away.
 280   bool is_unloading() const     {
 281     assert(!(is_the_null_class_loader_data() && _unloading), "The null class loader can never be unloaded");
 282     return _unloading;
 283   }
 284 
 285   // Used to make sure that this CLD is not unloaded.
 286   void set_keep_alive(bool value) { _keep_alive = value; }
 287 
 288   unsigned int identity_hash() {
 289     return _class_loader == NULL ? 0 : _class_loader->identity_hash();
 290   }
 291 
 292   // Used when tracing from klasses.
 293   void oops_do(OopClosure* f, KlassClosure* klass_closure, bool must_claim);
 294 
 295   void classes_do(KlassClosure* klass_closure);
 296 
 297   JNIMethodBlock* jmethod_ids() const              { return _jmethod_ids; }
 298   void set_jmethod_ids(JNIMethodBlock* new_block)  { _jmethod_ids = new_block; }
 299 
 300   void print_value() { print_value_on(tty); }
 301   void print_value_on(outputStream* out) const;
 302   void dump(outputStream * const out) PRODUCT_RETURN;
 303   void verify();
 304   const char* loader_name();
 305 
 306   jobject add_handle(Handle h);
 307   void add_class(Klass* k);
 308   void remove_class(Klass* k);
 309   bool contains_klass(Klass* k);
 310   void record_dependency(Klass* to, TRAPS);
 311   void init_dependencies(TRAPS);
 312 
 313   void add_to_deallocate_list(Metadata* m);
 314 
 315   static ClassLoaderData* class_loader_data(oop loader);
 316   static ClassLoaderData* class_loader_data_or_null(oop loader);
 317   static ClassLoaderData* anonymous_class_loader_data(oop loader, TRAPS);
 318   static void print_loader(ClassLoaderData *loader_data, outputStream *out);
 319 
 320   // CDS support
 321   Metaspace* ro_metaspace();
 322   Metaspace* rw_metaspace();
 323   void initialize_shared_metaspaces();
 324 
 325   JFR_ONLY(DEFINE_TRACE_ID_METHODS;)
 326 };
 327 
 328 // An iterator that distributes Klasses to parallel worker threads.
 329 class ClassLoaderDataGraphKlassIteratorAtomic : public StackObj {
 330  Klass* volatile _next_klass;
 331  public:
 332   ClassLoaderDataGraphKlassIteratorAtomic();
 333   Klass* next_klass();
 334  private:
 335   static Klass* next_klass_in_cldg(Klass* klass);
 336 };
 337 
 338 class ClassLoaderDataGraphMetaspaceIterator : public StackObj {
 339   ClassLoaderData* _data;
 340  public:
 341   ClassLoaderDataGraphMetaspaceIterator();
 342   ~ClassLoaderDataGraphMetaspaceIterator();
 343   bool repeat() { return _data != NULL; }
 344   Metaspace* get_next() {
 345     assert(_data != NULL, "Should not be NULL in call to the iterator");
 346     Metaspace* result = _data->metaspace_or_null();
 347     _data = _data->next();
 348     // This result might be NULL for class loaders without metaspace
 349     // yet.  It would be nice to return only non-null results but
 350     // there is no guarantee that there will be a non-null result
 351     // down the list so the caller is going to have to check.
 352     return result;
 353   }
 354 };
 355 #endif // SHARE_VM_CLASSFILE_CLASSLOADERDATA_HPP
--- EOF ---