1 /*
  2  * Copyright (c) 2012, 2021, 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_CLASSFILE_CLASSLOADERDATA_HPP
 26 #define SHARE_CLASSFILE_CLASSLOADERDATA_HPP
 27 
 28 #include "memory/allocation.hpp"
 29 #include "oops/oopHandle.hpp"
 30 #include "oops/weakHandle.hpp"
 31 #include "runtime/atomic.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 // external name (synthetic) for the primordial "bootstrap" class loader instance
 40 #define BOOTSTRAP_LOADER_NAME "bootstrap"
 41 #define BOOTSTRAP_LOADER_NAME_LEN 9
 42 
 43 //
 44 // A class loader represents a linkset. Conceptually, a linkset identifies
 45 // the complete transitive closure of resolved links that a dynamic linker can
 46 // produce.
 47 //
 48 // A ClassLoaderData also encapsulates the allocation space, called a metaspace,
 49 // used by the dynamic linker to allocate the runtime representation of all
 50 // the types it defines.
 51 //
 52 // ClassLoaderData are stored in the runtime representation of classes,
 53 // and provides iterators for root tracing and other GC operations.
 54 
 55 class ClassLoaderDataGraph;
 56 class JNIMethodBlock;
 57 class ModuleEntry;
 58 class PackageEntry;
 59 class ModuleEntryTable;
 60 class PackageEntryTable;
 61 class DictionaryEntry;
 62 class Dictionary;
 63 class ClassLoaderMetaspace;
 64 
 65 // ClassLoaderData class
 66 
 67 class ClassLoaderData : public CHeapObj<mtClass> {
 68   friend class VMStructs;
 69 
 70  private:
 71   class ChunkedHandleList {
 72     struct Chunk : public CHeapObj<mtClass> {
 73       static const size_t CAPACITY = 32;
 74 
 75       oop _data[CAPACITY];
 76       volatile juint _size;
 77       Chunk* _next;
 78 
 79       Chunk(Chunk* c) : _size(0), _next(c) { }
 80     };
 81 
 82     Chunk* volatile _head;
 83 
 84     void oops_do_chunk(OopClosure* f, Chunk* c, const juint size);
 85 
 86    public:
 87     ChunkedHandleList() : _head(NULL) {}
 88     ~ChunkedHandleList();
 89 
 90     // Only one thread at a time can add, guarded by ClassLoaderData::metaspace_lock().
 91     // However, multiple threads can execute oops_do concurrently with add.
 92     OopHandle add(oop o);
 93     bool contains(oop p);
 94     NOT_PRODUCT(bool owner_of(oop* p);)
 95     void oops_do(OopClosure* f);
 96 
 97     int count() const;
 98   };
 99 
100   friend class ClassLoaderDataGraph;
101   friend class ClassLoaderDataGraphIterator;
102   friend class ClassLoaderDataGraphKlassIteratorAtomic;
103   friend class ClassLoaderDataGraphKlassIteratorStatic;
104   friend class ClassLoaderDataGraphMetaspaceIterator;
105   friend class Klass;
106   friend class MetaDataFactory;
107   friend class Method;
108 
109   static ClassLoaderData * _the_null_class_loader_data;
110 
111   WeakHandle _holder;       // The oop that determines lifetime of this class loader
112   OopHandle  _class_loader; // The instance of java/lang/ClassLoader associated with
113                             // this ClassLoaderData
114 
115   ClassLoaderMetaspace * volatile _metaspace;  // Meta-space where meta-data defined by the
116                                     // classes in the class loader are allocated.
117   Mutex* _metaspace_lock;  // Locks the metaspace for allocations and setup.
118   bool _unloading;         // true if this class loader goes away
119   bool _has_class_mirror_holder; // If true, CLD is dedicated to one class and that class determines
120                                  // the CLDs lifecycle.  For example, a non-strong hidden class.
121                                  // Arrays of these classes are also assigned
122                                  // to these class loader datas.
123 
124   // Remembered sets support for the oops in the class loader data.
125   bool _modified_oops;     // Card Table Equivalent
126 
127   int _keep_alive;         // if this CLD is kept alive.
128                            // Used for non-strong hidden classes and the
129                            // boot class loader. _keep_alive does not need to be volatile or
130                            // atomic since there is one unique CLD per non-strong hidden class.
131 
132   volatile int _claim; // non-zero if claimed, for example during GC traces.
133                        // To avoid applying oop closure more than once.
134   ChunkedHandleList _handles; // Handles to constant pool arrays, Modules, etc, which
135                               // have the same life cycle of the corresponding ClassLoader.
136 
137   NOT_PRODUCT(volatile int _dependency_count;)  // number of class loader dependencies
138 
139   Klass* volatile _klasses;              // The classes defined by the class loader.
140   PackageEntryTable* volatile _packages; // The packages defined by the class loader.
141   ModuleEntryTable*  volatile _modules;  // The modules defined by the class loader.
142   ModuleEntry* _unnamed_module;          // This class loader's unnamed module.
143   Dictionary*  _dictionary;              // The loaded InstanceKlasses, including initiated by this class loader
144 
145   // These method IDs are created for the class loader and set to NULL when the
146   // class loader is unloaded.  They are rarely freed, only for redefine classes
147   // and if they lose a data race in InstanceKlass.
148   JNIMethodBlock*                  _jmethod_ids;
149 
150   // Metadata to be deallocated when it's safe at class unloading, when
151   // this class loader isn't unloaded itself.
152   GrowableArray<Metadata*>*      _deallocate_list;
153 
154   // Support for walking class loader data objects
155   ClassLoaderData* _next; /// Next loader_datas created
156 
157   Klass*  _class_loader_klass;
158   Symbol* _name;
159   Symbol* _name_and_id;
160   JFR_ONLY(DEFINE_TRACE_ID_FIELD;)
161 
162   void set_next(ClassLoaderData* next) { _next = next; }
163   ClassLoaderData* next() const        { return Atomic::load(&_next); }
164 
165   ClassLoaderData(Handle h_class_loader, bool has_class_mirror_holder);
166   ~ClassLoaderData();
167 
168   // The CLD are not placed in the Heap, so the Card Table or
169   // the Mod Union Table can't be used to mark when CLD have modified oops.
170   // The CT and MUT bits saves this information for the whole class loader data.
171   void clear_modified_oops()             { _modified_oops = false; }
172  public:
173   void record_modified_oops()            { _modified_oops = true; }
174   bool has_modified_oops()               { return _modified_oops; }
175 
176   oop holder_no_keepalive() const;
177   oop holder_phantom() const;
178 
179  private:
180   void unload();
181   bool keep_alive() const       { return _keep_alive > 0; }
182 
183   void classes_do(void f(Klass* const));
184   void loaded_classes_do(KlassClosure* klass_closure);
185   void classes_do(void f(InstanceKlass*));
186   void inline_classes_do(void f(InlineKlass*));
187   void methods_do(void f(Method*));
188   void modules_do(void f(ModuleEntry*));
189   void packages_do(void f(PackageEntry*));
190 
191   // Deallocate free list during class unloading.
192   void free_deallocate_list();                      // for the classes that are not unloaded
193   void free_deallocate_list_C_heap_structures();    // for the classes that are unloaded
194 
195   Dictionary* create_dictionary();
196 
197   void initialize_name(Handle class_loader);
198 
199  public:
200   // GC interface.
201 
202   // The "claim" is typically used to check if oops_do needs to be applied on
203   // the CLD or not. Most GCs only perform strong marking during the marking phase.
204   enum Claim {
205     _claim_none         = 0,
206     _claim_finalizable  = 2,
207     _claim_strong       = 3,
208     _claim_other        = 4
209   };
210   void clear_claim() { _claim = 0; }
211   void clear_claim(int claim);
212   bool claimed() const { return _claim != 0; }
213   bool claimed(int claim) const { return (_claim & claim) == claim; }
214   bool try_claim(int claim);
215 
216   // Computes if the CLD is alive or not. This is safe to call in concurrent
217   // contexts.
218   bool is_alive() const;
219 
220   // Accessors
221   ClassLoaderMetaspace* metaspace_or_null() const { return _metaspace; }
222 
223   static ClassLoaderData* the_null_class_loader_data() {
224     return _the_null_class_loader_data;
225   }
226 
227   Mutex* metaspace_lock() const { return _metaspace_lock; }
228 
229   bool has_class_mirror_holder() const { return _has_class_mirror_holder; }
230 
231   static void init_null_class_loader_data();
232 
233   bool is_the_null_class_loader_data() const {
234     return this == _the_null_class_loader_data;
235   }
236 
237   // Returns true if this class loader data is for the system class loader.
238   // (Note that the class loader data may be for a non-strong hidden class)
239   bool is_system_class_loader_data() const;
240 
241   // Returns true if this class loader data is for the platform class loader.
242   // (Note that the class loader data may be for a non-strong hidden class)
243   bool is_platform_class_loader_data() const;
244 
245   // Returns true if this class loader data is for the boot class loader.
246   // (Note that the class loader data may be for a non-strong hidden class)
247   inline bool is_boot_class_loader_data() const;
248 
249   bool is_builtin_class_loader_data() const;
250   bool is_permanent_class_loader_data() const;
251 
252   // The Metaspace is created lazily so may be NULL.  This
253   // method will allocate a Metaspace if needed.
254   ClassLoaderMetaspace* metaspace_non_null();
255 
256   inline oop class_loader() const;
257 
258   // Returns true if this class loader data is for a loader going away.
259   // Note that this is only safe after the GC has computed if the CLD is
260   // unloading or not. In concurrent contexts where there are no such
261   // guarantees, is_alive() should be used instead.
262   bool is_unloading() const     {
263     assert(!(is_the_null_class_loader_data() && _unloading), "The null class loader can never be unloaded");
264     return _unloading;
265   }
266 
267   // Used to refcount a non-strong hidden class's s CLD in order to indicate their aliveness.
268   void inc_keep_alive();
269   void dec_keep_alive();
270 
271   void initialize_holder(Handle holder);
272 
273   void oops_do(OopClosure* f, int claim_value, bool clear_modified_oops = false);
274 
275   void classes_do(KlassClosure* klass_closure);
276   Klass* klasses() { return _klasses; }
277 
278   JNIMethodBlock* jmethod_ids() const              { return _jmethod_ids; }
279   void set_jmethod_ids(JNIMethodBlock* new_block)  { _jmethod_ids = new_block; }
280 
281   void print() const;
282   void print_on(outputStream* out) const PRODUCT_RETURN;
283   void print_value() const;
284   void print_value_on(outputStream* out) const;
285   void verify();
286 
287   OopHandle add_handle(Handle h);
288   void remove_handle(OopHandle h);
289   void init_handle_locked(OopHandle& pd, Handle h);  // used for concurrent access to ModuleEntry::_pd field
290   void add_class(Klass* k, bool publicize = true);
291   void remove_class(Klass* k);
292   bool contains_klass(Klass* k);
293   void record_dependency(const Klass* to);
294   PackageEntryTable* packages() { return _packages; }
295   ModuleEntry* unnamed_module() { return _unnamed_module; }
296   ModuleEntryTable* modules();
297   bool modules_defined() { return (_modules != NULL); }
298 
299   // Offsets
300   static ByteSize holder_offset()     { return in_ByteSize(offset_of(ClassLoaderData, _holder)); }
301   static ByteSize keep_alive_offset() { return in_ByteSize(offset_of(ClassLoaderData, _keep_alive)); }
302 
303   // Loaded class dictionary
304   Dictionary* dictionary() const { return _dictionary; }
305 
306   void add_to_deallocate_list(Metadata* m);
307 
308   static ClassLoaderData* class_loader_data(oop loader);
309   static ClassLoaderData* class_loader_data_or_null(oop loader);
310 
311   // Returns Klass* of associated class loader, or NULL if associated loader is 'bootstrap'.
312   // Also works if unloading.
313   Klass* class_loader_klass() const { return _class_loader_klass; }
314 
315   // Returns the class loader's explict name as specified during
316   // construction or the class loader's qualified class name.
317   // Works during unloading.
318   const char* loader_name() const;
319   // Returns the explicitly specified class loader name or NULL.
320   Symbol* name() const { return _name; }
321 
322   // Obtain the class loader's _name_and_id, works during unloading.
323   const char* loader_name_and_id() const;
324   Symbol* name_and_id() const { return _name_and_id; }
325 
326   unsigned identity_hash() const {
327     return (unsigned)((uintptr_t)this >> LogBytesPerWord);
328   }
329 
330   JFR_ONLY(DEFINE_TRACE_ID_METHODS;)
331 };
332 
333 #endif // SHARE_CLASSFILE_CLASSLOADERDATA_HPP