1 /*
   2  * Copyright (c) 2012, 2014, 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.
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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 "utilities/growableArray.hpp"
  34 #include "utilities/macros.hpp"
  35 #if INCLUDE_TRACE
  36 #include "utilities/ticks.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 ClassLoaderDataGraphKlassIteratorAtomic;
  63   friend class VMStructs;
  64  private:
  65   // All CLDs (except the null CLD) can be reached by walking _head->_next->...
  66   static ClassLoaderData* _head;
  67   static ClassLoaderData* _unloading;
  68   // CMS support.
  69   static ClassLoaderData* _saved_head;
  70   static ClassLoaderData* _saved_unloading;
  71   static bool _should_purge;
  72   // OOM has been seen in metaspace allocation. Used to prevent some
  73   // allocations until class unloading
  74   static bool _metaspace_oom;
  75 
  76   static ClassLoaderData* add(Handle class_loader, bool anonymous, TRAPS);
  77   static void post_class_unload_events(void);
  78   static void clean_metaspaces();
  79  public:
  80   static ClassLoaderData* find_or_create(Handle class_loader, TRAPS);
  81   static void purge();
  82   static void clear_claimed_marks();
  83   // oops do
  84   static void oops_do(OopClosure* f, KlassClosure* klass_closure, bool must_claim);
  85   static void keep_alive_oops_do(OopClosure* blk, KlassClosure* klass_closure, bool must_claim);
  86   static void always_strong_oops_do(OopClosure* blk, KlassClosure* klass_closure, bool must_claim);
  87   // cld do
  88   static void cld_do(CLDClosure* cl);
  89   static void roots_cld_do(CLDClosure* strong, CLDClosure* weak);
  90   static void keep_alive_cld_do(CLDClosure* cl);
  91   static void always_strong_cld_do(CLDClosure* cl);
  92   // klass do
  93   static void classes_do(KlassClosure* klass_closure);
  94   static void classes_do(void f(Klass* const));
  95   static void methods_do(void f(Method*));
  96   static void loaded_classes_do(KlassClosure* klass_closure);
  97   static void classes_unloading_do(void f(Klass* const));
  98   static bool do_unloading(BoolObjectClosure* is_alive, bool clean_alive);
  99 
 100   // CMS support.
 101   static void remember_new_clds(bool remember) { _saved_head = (remember ? _head : NULL); }
 102   static GrowableArray<ClassLoaderData*>* new_clds();
 103 
 104   static void set_should_purge(bool b) { _should_purge = b; }
 105   static void purge_if_needed() {
 106     // Only purge the CLDG for CMS if concurrent sweep is complete.
 107     if (_should_purge) {
 108       purge();
 109       // reset for next time.
 110       set_should_purge(false);
 111     }
 112   }
 113 
 114   static bool has_metaspace_oom()           { return _metaspace_oom; }
 115   static void set_metaspace_oom(bool value) { _metaspace_oom = value; }
 116 
 117   static void free_deallocate_lists();
 118 
 119   static void dump_on(outputStream * const out) PRODUCT_RETURN;
 120   static void dump() { dump_on(tty); }
 121   static void verify();
 122 
 123   static bool unload_list_contains(const void* x);
 124 #ifndef PRODUCT
 125   static bool contains_loader_data(ClassLoaderData* loader_data);
 126 #endif
 127 
 128 #if INCLUDE_TRACE
 129  private:
 130   static Ticks _class_unload_time;
 131   static void class_unload_event(Klass* const k);
 132 #endif
 133 };
 134 
 135 // ClassLoaderData class
 136 
 137 class ClassLoaderData : public CHeapObj<mtClass> {
 138   friend class VMStructs;
 139  private:
 140   class Dependencies VALUE_OBJ_CLASS_SPEC {
 141     objArrayOop _list_head;
 142     void locked_add(objArrayHandle last,
 143                     objArrayHandle new_dependency,
 144                     Thread* THREAD);
 145    public:
 146     Dependencies() : _list_head(NULL) {}
 147     Dependencies(TRAPS) : _list_head(NULL) {
 148       init(CHECK);
 149     }
 150     void add(Handle dependency, TRAPS);
 151     void init(TRAPS);
 152     void oops_do(OopClosure* f);
 153   };
 154 
 155   friend class ClassLoaderDataGraph;
 156   friend class ClassLoaderDataGraphKlassIteratorAtomic;
 157   friend class ClassLoaderDataGraphMetaspaceIterator;
 158   friend class MetaDataFactory;
 159   friend class Method;
 160 
 161   static ClassLoaderData * _the_null_class_loader_data;
 162 
 163   oop _class_loader;          // oop used to uniquely identify a class loader
 164                               // class loader or a canonical class path
 165   Dependencies _dependencies; // holds dependencies from this class loader
 166                               // data to others.
 167 
 168   Metaspace * _metaspace;  // Meta-space where meta-data defined by the
 169                            // classes in the class loader are allocated.
 170   Mutex* _metaspace_lock;  // Locks the metaspace for allocations and setup.
 171   bool _unloading;         // true if this class loader goes away
 172   bool _keep_alive;        // if this CLD is kept alive without a keep_alive_object().
 173   bool _is_anonymous;      // if this CLD is for an anonymous class
 174   volatile int _claimed;   // true if claimed, for example during GC traces.
 175                            // To avoid applying oop closure more than once.
 176                            // Has to be an int because we cas it.
 177   Klass* _klasses;         // The classes defined by the class loader.
 178 
 179   JNIHandleBlock* _handles; // Handles to constant pool arrays
 180 
 181   // These method IDs are created for the class loader and set to NULL when the
 182   // class loader is unloaded.  They are rarely freed, only for redefine classes
 183   // and if they lose a data race in InstanceKlass.
 184   JNIMethodBlock*                  _jmethod_ids;
 185 
 186   // Metadata to be deallocated when it's safe at class unloading, when
 187   // this class loader isn't unloaded itself.
 188   GrowableArray<Metadata*>*      _deallocate_list;
 189 
 190   // Support for walking class loader data objects
 191   ClassLoaderData* _next; /// Next loader_datas created
 192 
 193   // ReadOnly and ReadWrite metaspaces (static because only on the null
 194   // class loader for now).
 195   static Metaspace* _ro_metaspace;
 196   static Metaspace* _rw_metaspace;
 197 
 198   void set_next(ClassLoaderData* next) { _next = next; }
 199   ClassLoaderData* next() const        { return _next; }
 200 
 201   ClassLoaderData(Handle h_class_loader, bool is_anonymous, Dependencies dependencies);
 202   ~ClassLoaderData();
 203 
 204   void set_metaspace(Metaspace* m) { _metaspace = m; }
 205 
 206   JNIHandleBlock* handles() const;
 207   void set_handles(JNIHandleBlock* handles);
 208 
 209   // GC interface.
 210   void clear_claimed()          { _claimed = 0; }
 211   bool claimed() const          { return _claimed == 1; }
 212   bool claim();
 213 
 214   void unload();
 215   bool keep_alive() const       { return _keep_alive; }
 216   void classes_do(void f(Klass*));
 217   void loaded_classes_do(KlassClosure* klass_closure);
 218   void classes_do(void f(InstanceKlass*));
 219   void methods_do(void f(Method*));
 220 
 221   // Deallocate free list during class unloading.
 222   void free_deallocate_list();
 223 
 224   // Allocate out of this class loader data
 225   MetaWord* allocate(size_t size);
 226 
 227  public:
 228 
 229   bool is_alive(BoolObjectClosure* is_alive_closure) const;
 230 
 231   // Accessors
 232   Metaspace* metaspace_or_null() const     { return _metaspace; }
 233 
 234   static ClassLoaderData* the_null_class_loader_data() {
 235     return _the_null_class_loader_data;
 236   }
 237 
 238   Mutex* metaspace_lock() const { return _metaspace_lock; }
 239 
 240   bool is_anonymous() const { return _is_anonymous; }
 241 
 242   static void init_null_class_loader_data() {
 243     assert(_the_null_class_loader_data == NULL, "cannot initialize twice");
 244     assert(ClassLoaderDataGraph::_head == NULL, "cannot initialize twice");
 245 
 246     // We explicitly initialize the Dependencies object at a later phase in the initialization
 247     _the_null_class_loader_data = new ClassLoaderData((oop)NULL, false, Dependencies());
 248     ClassLoaderDataGraph::_head = _the_null_class_loader_data;
 249     assert(_the_null_class_loader_data->is_the_null_class_loader_data(), "Must be");
 250     if (DumpSharedSpaces) {
 251       _the_null_class_loader_data->initialize_shared_metaspaces();
 252     }
 253   }
 254 
 255   bool is_the_null_class_loader_data() const {
 256     return this == _the_null_class_loader_data;
 257   }
 258   bool is_ext_class_loader_data() const;
 259 
 260   // The Metaspace is created lazily so may be NULL.  This
 261   // method will allocate a Metaspace if needed.
 262   Metaspace* metaspace_non_null();
 263 
 264   oop class_loader() const      { return _class_loader; }
 265 
 266   // The object the GC is using to keep this ClassLoaderData alive.
 267   oop keep_alive_object() const;
 268 
 269   // Returns true if this class loader data is for a loader going away.
 270   bool is_unloading() const     {
 271     assert(!(is_the_null_class_loader_data() && _unloading), "The null class loader can never be unloaded");
 272     return _unloading;
 273   }
 274 
 275   // Used to make sure that this CLD is not unloaded.
 276   void set_keep_alive(bool value) { _keep_alive = value; }
 277 
 278   unsigned int identity_hash() {
 279     return _class_loader == NULL ? 0 : _class_loader->identity_hash();
 280   }
 281 
 282   // Used when tracing from klasses.
 283   void oops_do(OopClosure* f, KlassClosure* klass_closure, bool must_claim);
 284 
 285   void classes_do(KlassClosure* klass_closure);
 286 
 287   JNIMethodBlock* jmethod_ids() const              { return _jmethod_ids; }
 288   void set_jmethod_ids(JNIMethodBlock* new_block)  { _jmethod_ids = new_block; }
 289 
 290   void print_value() { print_value_on(tty); }
 291   void print_value_on(outputStream* out) const;
 292   void dump(outputStream * const out) PRODUCT_RETURN;
 293   void verify();
 294   const char* loader_name();
 295 
 296   jobject add_handle(Handle h);
 297   void add_class(Klass* k);
 298   void remove_class(Klass* k);
 299   bool contains_klass(Klass* k);
 300   void record_dependency(Klass* to, TRAPS);
 301   void init_dependencies(TRAPS);
 302 
 303   void add_to_deallocate_list(Metadata* m);
 304 
 305   static ClassLoaderData* class_loader_data(oop loader);
 306   static ClassLoaderData* class_loader_data_or_null(oop loader);
 307   static ClassLoaderData* anonymous_class_loader_data(oop loader, TRAPS);
 308   static void print_loader(ClassLoaderData *loader_data, outputStream *out);
 309 
 310   // CDS support
 311   Metaspace* ro_metaspace();
 312   Metaspace* rw_metaspace();
 313   void initialize_shared_metaspaces();
 314 };
 315 
 316 // An iterator that distributes Klasses to parallel worker threads.
 317 class ClassLoaderDataGraphKlassIteratorAtomic : public StackObj {
 318   volatile Klass* _next_klass;
 319  public:
 320   ClassLoaderDataGraphKlassIteratorAtomic();
 321   Klass* next_klass();
 322  private:
 323   static Klass* next_klass_in_cldg(Klass* klass);
 324 };
 325 
 326 class ClassLoaderDataGraphMetaspaceIterator : public StackObj {
 327   ClassLoaderData* _data;
 328  public:
 329   ClassLoaderDataGraphMetaspaceIterator();
 330   ~ClassLoaderDataGraphMetaspaceIterator();
 331   bool repeat() { return _data != NULL; }
 332   Metaspace* get_next() {
 333     assert(_data != NULL, "Should not be NULL in call to the iterator");
 334     Metaspace* result = _data->metaspace_or_null();
 335     _data = _data->next();
 336     // This result might be NULL for class loaders without metaspace
 337     // yet.  It would be nice to return only non-null results but
 338     // there is no guarantee that there will be a non-null result
 339     // down the list so the caller is going to have to check.
 340     return result;
 341   }
 342 };
 343 #endif // SHARE_VM_CLASSFILE_CLASSLOADERDATA_HPP