1 /*
   2  * Copyright (c) 2012, 2013, 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 
  35 #if INCLUDE_TRACE
  36 # include "trace/traceTime.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 JNIHandleBlock;
  55 class Metadebug;
  56 
  57 // GC root for walking class loader data created
  58 
  59 class ClassLoaderDataGraph : public AllStatic {
  60   friend class ClassLoaderData;
  61   friend class ClassLoaderDataGraphMetaspaceIterator;
  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 
  70   static ClassLoaderData* add(Handle class_loader, bool anonymous, TRAPS);
  71   static void post_class_unload_events(void);
  72  public:
  73   static ClassLoaderData* find_or_create(Handle class_loader, TRAPS);
  74   static void purge();
  75   static void clear_claimed_marks();
  76   static void oops_do(OopClosure* f, KlassClosure* klass_closure, bool must_claim);
  77   static void always_strong_oops_do(OopClosure* blk, KlassClosure* klass_closure, bool must_claim);
  78   static void keep_alive_oops_do(OopClosure* blk, KlassClosure* klass_closure, bool must_claim);
  79   static void classes_do(KlassClosure* klass_closure);
  80   static void classes_do(void f(Klass* const));
  81   static void loaded_classes_do(KlassClosure* klass_closure);
  82   static void classes_unloading_do(void f(Klass* const));
  83   static bool do_unloading(BoolObjectClosure* is_alive);
  84 
  85   // CMS support.
  86   static void remember_new_clds(bool remember) { _saved_head = (remember ? _head : NULL); }
  87   static GrowableArray<ClassLoaderData*>* new_clds();
  88 
  89   static void dump_on(outputStream * const out) PRODUCT_RETURN;
  90   static void dump() { dump_on(tty); }
  91   static void verify();
  92 
  93 #ifndef PRODUCT
  94   // expensive test for pointer in metaspace for debugging
  95   static bool contains(address x);
  96   static bool contains_loader_data(ClassLoaderData* loader_data);
  97 #endif
  98 
  99 #if INCLUDE_TRACE
 100  private:
 101   static TracingTime _class_unload_time;
 102   static void class_unload_event(Klass* const k);
 103 #endif
 104 };
 105 
 106 // ClassLoaderData class
 107 
 108 class ClassLoaderData : public CHeapObj<mtClass> {
 109   friend class VMStructs;
 110  private:
 111   class Dependencies VALUE_OBJ_CLASS_SPEC {
 112     objArrayOop _list_head;
 113     void locked_add(objArrayHandle last,
 114                     objArrayHandle new_dependency,
 115                     Thread* THREAD);
 116    public:
 117     Dependencies() : _list_head(NULL) {}
 118     Dependencies(TRAPS) : _list_head(NULL) {
 119       init(CHECK);
 120     }
 121     void add(Handle dependency, TRAPS);
 122     void init(TRAPS);
 123     void oops_do(OopClosure* f);
 124   };
 125 
 126   friend class ClassLoaderDataGraph;
 127   friend class ClassLoaderDataGraphMetaspaceIterator;
 128   friend class MetaDataFactory;
 129   friend class Method;
 130 
 131   static ClassLoaderData * _the_null_class_loader_data;
 132 
 133   oop _class_loader;          // oop used to uniquely identify a class loader
 134                               // class loader or a canonical class path
 135   Dependencies _dependencies; // holds dependencies from this class loader
 136                               // data to others.
 137 
 138   Metaspace * _metaspace;  // Meta-space where meta-data defined by the
 139                            // classes in the class loader are allocated.
 140   Mutex* _metaspace_lock;  // Locks the metaspace for allocations and setup.
 141   bool _unloading;         // true if this class loader goes away
 142   bool _keep_alive;        // if this CLD can be unloaded for anonymous loaders
 143   bool _is_anonymous;      // if this CLD is for an anonymous class
 144   volatile int _claimed;   // true if claimed, for example during GC traces.
 145                            // To avoid applying oop closure more than once.
 146                            // Has to be an int because we cas it.
 147   Klass* _klasses;         // The classes defined by the class loader.
 148 
 149   JNIHandleBlock* _handles; // Handles to constant pool arrays
 150 
 151   // These method IDs are created for the class loader and set to NULL when the
 152   // class loader is unloaded.  They are rarely freed, only for redefine classes
 153   // and if they lose a data race in InstanceKlass.
 154   JNIMethodBlock*                  _jmethod_ids;
 155 
 156   // Metadata to be deallocated when it's safe at class unloading, when
 157   // this class loader isn't unloaded itself.
 158   GrowableArray<Metadata*>*      _deallocate_list;
 159 
 160   // Support for walking class loader data objects
 161   ClassLoaderData* _next; /// Next loader_datas created
 162 
 163   // ReadOnly and ReadWrite metaspaces (static because only on the null
 164   // class loader for now).
 165   static Metaspace* _ro_metaspace;
 166   static Metaspace* _rw_metaspace;
 167 
 168   void set_next(ClassLoaderData* next) { _next = next; }
 169   ClassLoaderData* next() const        { return _next; }
 170 
 171   ClassLoaderData(Handle h_class_loader, bool is_anonymous, Dependencies dependencies);
 172   ~ClassLoaderData();
 173 
 174   void set_metaspace(Metaspace* m) { _metaspace = m; }
 175 
 176   JNIHandleBlock* handles() const;
 177   void set_handles(JNIHandleBlock* handles);
 178 
 179   Mutex* metaspace_lock() const { return _metaspace_lock; }
 180 
 181   // GC interface.
 182   void clear_claimed()          { _claimed = 0; }
 183   bool claimed() const          { return _claimed == 1; }
 184   bool claim();
 185 
 186   void unload();
 187   bool keep_alive() const       { return _keep_alive; }
 188   bool is_alive(BoolObjectClosure* is_alive_closure) const;
 189   void classes_do(void f(Klass*));
 190   void loaded_classes_do(KlassClosure* klass_closure);
 191   void classes_do(void f(InstanceKlass*));
 192 
 193   // Deallocate free list during class unloading.
 194   void free_deallocate_list();
 195 
 196   // Allocate out of this class loader data
 197   MetaWord* allocate(size_t size);
 198 
 199  public:
 200   // Accessors
 201   Metaspace* metaspace_or_null() const     { return _metaspace; }
 202 
 203   static ClassLoaderData* the_null_class_loader_data() {
 204     return _the_null_class_loader_data;
 205   }
 206 
 207   bool is_anonymous() const { return _is_anonymous; }
 208 
 209   static void init_null_class_loader_data() {
 210     assert(_the_null_class_loader_data == NULL, "cannot initialize twice");
 211     assert(ClassLoaderDataGraph::_head == NULL, "cannot initialize twice");
 212 
 213     // We explicitly initialize the Dependencies object at a later phase in the initialization
 214     _the_null_class_loader_data = new ClassLoaderData((oop)NULL, false, Dependencies());
 215     ClassLoaderDataGraph::_head = _the_null_class_loader_data;
 216     assert(_the_null_class_loader_data->is_the_null_class_loader_data(), "Must be");
 217     if (DumpSharedSpaces) {
 218       _the_null_class_loader_data->initialize_shared_metaspaces();
 219     }
 220   }
 221 
 222   bool is_the_null_class_loader_data() const {
 223     return this == _the_null_class_loader_data;
 224   }
 225   bool is_ext_class_loader_data() const;
 226 
 227   // The Metaspace is created lazily so may be NULL.  This
 228   // method will allocate a Metaspace if needed.
 229   Metaspace* metaspace_non_null();
 230 
 231   oop class_loader() const      { return _class_loader; }
 232 
 233   // Returns true if this class loader data is for a loader going away.
 234   bool is_unloading() const     {
 235     assert(!(is_the_null_class_loader_data() && _unloading), "The null class loader can never be unloaded");
 236     return _unloading;
 237   }
 238   // Anonymous class loader data doesn't have anything to keep them from
 239   // being unloaded during parsing the anonymous class.
 240   void set_keep_alive(bool value) { _keep_alive = value; }
 241 
 242   unsigned int identity_hash() {
 243     return _class_loader == NULL ? 0 : _class_loader->identity_hash();
 244   }
 245 
 246   // Used when tracing from klasses.
 247   void oops_do(OopClosure* f, KlassClosure* klass_closure, bool must_claim);
 248 
 249   void classes_do(KlassClosure* klass_closure);
 250 
 251   JNIMethodBlock* jmethod_ids() const              { return _jmethod_ids; }
 252   void set_jmethod_ids(JNIMethodBlock* new_block)  { _jmethod_ids = new_block; }
 253 
 254   void print_value() { print_value_on(tty); }
 255   void print_value_on(outputStream* out) const;
 256   void dump(outputStream * const out) PRODUCT_RETURN;
 257   void verify();
 258   const char* loader_name();
 259 
 260   jobject add_handle(Handle h);
 261   void add_class(Klass* k);
 262   void remove_class(Klass* k);
 263   void record_dependency(Klass* to, TRAPS);
 264   void init_dependencies(TRAPS);
 265 
 266   void add_to_deallocate_list(Metadata* m);
 267 
 268   static ClassLoaderData* class_loader_data(oop loader);
 269   static ClassLoaderData* class_loader_data_or_null(oop loader);
 270   static ClassLoaderData* anonymous_class_loader_data(oop loader, TRAPS);
 271   static void print_loader(ClassLoaderData *loader_data, outputStream *out);
 272 
 273   // CDS support
 274   Metaspace* ro_metaspace();
 275   Metaspace* rw_metaspace();
 276   void initialize_shared_metaspaces();
 277 };
 278 
 279 class ClassLoaderDataGraphMetaspaceIterator : public StackObj {
 280   ClassLoaderData* _data;
 281  public:
 282   ClassLoaderDataGraphMetaspaceIterator();
 283   ~ClassLoaderDataGraphMetaspaceIterator();
 284   bool repeat() { return _data != NULL; }
 285   Metaspace* get_next() {
 286     assert(_data != NULL, "Should not be NULL in call to the iterator");
 287     Metaspace* result = _data->metaspace_or_null();
 288     _data = _data->next();
 289     // This result might be NULL for class loaders without metaspace
 290     // yet.  It would be nice to return only non-null results but
 291     // there is no guarantee that there will be a non-null result
 292     // down the list so the caller is going to have to check.
 293     return result;
 294   }
 295 };
 296 #endif // SHARE_VM_CLASSFILE_CLASSLOADERDATA_HPP