1 /*
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  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  *
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 18  *
 19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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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 "oops/oopHandle.hpp"
 32 #include "oops/weakHandle.hpp"
 33 #include "runtime/mutex.hpp"
 34 #include "utilities/growableArray.hpp"
 35 #include "utilities/macros.hpp"
 36 #if INCLUDE_JFR
 37 #include "jfr/support/jfrTraceIdExtension.hpp"
 38 #endif
 39 
 40 // external name (synthetic) for the primordial "bootstrap" class loader instance
 41 #define BOOTSTRAP_LOADER_NAME "bootstrap"
 42 #define BOOTSTRAP_LOADER_NAME_LEN 9
 43 
 44 //
 45 // A class loader represents a linkset. Conceptually, a linkset identifies
 46 // the complete transitive closure of resolved links that a dynamic linker can
 47 // produce.
 48 //
 49 // A ClassLoaderData also encapsulates the allocation space, called a metaspace,
 50 // used by the dynamic linker to allocate the runtime representation of all
 51 // the types it defines.
 52 //
 53 // ClassLoaderData are stored in the runtime representation of classes,
 54 // and provides iterators for root tracing and other GC operations.
 55 
 56 class ClassLoaderData;
 57 class JNIMethodBlock;
 58 class Metadebug;
 59 class ModuleEntry;
 60 class PackageEntry;
 61 class ModuleEntryTable;
 62 class PackageEntryTable;
 63 class DictionaryEntry;
 64 class Dictionary;
 65 
 66 // GC root for walking class loader data created
 67 
 68 class ClassLoaderDataGraph : public AllStatic {
 69   friend class ClassLoaderData;
 70   friend class ClassLoaderDataGraphMetaspaceIterator;
 71   friend class ClassLoaderDataGraphKlassIteratorAtomic;
 72   friend class ClassLoaderDataGraphKlassIteratorStatic;
 73   friend class ClassLoaderDataGraphIterator;
 74   friend class VMStructs;
 75  private:
 76   // All CLDs (except the null CLD) can be reached by walking _head->_next->...
 77   static ClassLoaderData* _head;
 78   static ClassLoaderData* _unloading;
 79   // CMS support.
 80   static ClassLoaderData* _saved_head;
 81   static ClassLoaderData* _saved_unloading;
 82   static bool _should_purge;
 83 
 84   // Set if there's anything to purge in the deallocate lists or previous versions
 85   // during a safepoint after class unloading in a full GC.
 86   static bool _should_clean_deallocate_lists;
 87   static bool _safepoint_cleanup_needed;
 88 
 89   // OOM has been seen in metaspace allocation. Used to prevent some
 90   // allocations until class unloading
 91   static bool _metaspace_oom;
 92 
 93   static volatile size_t  _num_instance_classes;
 94   static volatile size_t  _num_array_classes;
 95 
 96   static ClassLoaderData* add_to_graph(Handle class_loader, bool is_unsafe_anonymous);
 97   static ClassLoaderData* add(Handle class_loader, bool is_unsafe_anonymous);
 98 
 99  public:
100   static ClassLoaderData* find_or_create(Handle class_loader);
101   static void clean_module_and_package_info();
102   static void purge();
103   static void clear_claimed_marks();
104   // Iteration through CLDG inside a safepoint; GC support
105   static void cld_do(CLDClosure* cl);
106   static void cld_unloading_do(CLDClosure* cl);
107   static void roots_cld_do(CLDClosure* strong, CLDClosure* weak);
108   static void always_strong_cld_do(CLDClosure* cl);
109   // klass do
110   // Walking classes through the ClassLoaderDataGraph include array classes.  It also includes
111   // classes that are allocated but not loaded, classes that have errors, and scratch classes
112   // for redefinition.  These classes are removed during the next class unloading.
113   // Walking the ClassLoaderDataGraph also includes unsafe anonymous classes.
114   static void classes_do(KlassClosure* klass_closure);
115   static void classes_do(void f(Klass* const));
116   static void methods_do(void f(Method*));
117   static void modules_do(void f(ModuleEntry*));
118   static void modules_unloading_do(void f(ModuleEntry*));
119   static void packages_do(void f(PackageEntry*));
120   static void packages_unloading_do(void f(PackageEntry*));
121   static void loaded_classes_do(KlassClosure* klass_closure);
122   static void unlocked_loaded_classes_do(KlassClosure* klass_closure);
123   static void classes_unloading_do(void f(Klass* const));
124   static bool do_unloading(bool do_cleaning);
125 
126   // Expose state to avoid logging overhead in safepoint cleanup tasks.
127   static inline bool should_clean_metaspaces_and_reset();
128   static void set_should_clean_deallocate_lists() { _should_clean_deallocate_lists = true; }
129   static void clean_deallocate_lists(bool purge_previous_versions);
130   static void walk_metadata_and_clean_metaspaces();
131 
132   // dictionary do
133   // Iterate over all klasses in dictionary, but
134   // just the classes from defining class loaders.
135   static void dictionary_classes_do(void f(InstanceKlass*));
136   // Added for initialize_itable_for_klass to handle exceptions.
137   static void dictionary_classes_do(void f(InstanceKlass*, TRAPS), TRAPS);
138 
139   // VM_CounterDecay iteration support
140   static InstanceKlass* try_get_next_class();
141 
142   static void verify_dictionary();
143   static void print_dictionary(outputStream* st);
144   static void print_dictionary_statistics(outputStream* st);
145 
146   // CMS support.
147   static void remember_new_clds(bool remember) { _saved_head = (remember ? _head : NULL); }
148   static GrowableArray<ClassLoaderData*>* new_clds();
149 
150   static void set_should_purge(bool b) { _should_purge = b; }
151   static void purge_if_needed() {
152     // Only purge the CLDG for CMS if concurrent sweep is complete.
153     if (_should_purge) {
154       purge();
155       // reset for next time.
156       set_should_purge(false);
157     }
158   }
159 
160   static int resize_if_needed();
161 
162   static bool has_metaspace_oom()           { return _metaspace_oom; }
163   static void set_metaspace_oom(bool value) { _metaspace_oom = value; }
164 
165   static void print_on(outputStream * const out) PRODUCT_RETURN;
166   static void print() { print_on(tty); }
167   static void verify();
168 
169   // instance and array class counters
170   static inline size_t num_instance_classes();
171   static inline size_t num_array_classes();
172   static inline void inc_instance_classes(size_t count);
173   static inline void dec_instance_classes(size_t count);
174   static inline void inc_array_classes(size_t count);
175   static inline void dec_array_classes(size_t count);
176 
177 #ifndef PRODUCT
178   static bool contains_loader_data(ClassLoaderData* loader_data);
179 #endif
180 };
181 
182 class LockedClassesDo : public KlassClosure {
183   typedef void (*classes_do_func_t)(Klass*);
184   classes_do_func_t _function;
185 public:
186   LockedClassesDo();  // For callers who provide their own do_klass
187   LockedClassesDo(classes_do_func_t function);
188   ~LockedClassesDo();
189 
190   void do_klass(Klass* k) {
191     (*_function)(k);
192   }
193 };
194 
195 
196 // ClassLoaderData class
197 
198 class ClassLoaderData : public CHeapObj<mtClass> {
199   friend class VMStructs;
200 
201  private:
202   class ChunkedHandleList {
203     struct Chunk : public CHeapObj<mtClass> {
204       static const size_t CAPACITY = 32;
205 
206       oop _data[CAPACITY];
207       volatile juint _size;
208       Chunk* _next;
209 
210       Chunk(Chunk* c) : _size(0), _next(c) { }
211     };
212 
213     Chunk* volatile _head;
214 
215     void oops_do_chunk(OopClosure* f, Chunk* c, const juint size);
216 
217    public:
218     ChunkedHandleList() : _head(NULL) {}
219     ~ChunkedHandleList();
220 
221     // Only one thread at a time can add, guarded by ClassLoaderData::metaspace_lock().
222     // However, multiple threads can execute oops_do concurrently with add.
223     oop* add(oop o);
224     bool contains(oop p);
225     NOT_PRODUCT(bool owner_of(oop* p);)
226     void oops_do(OopClosure* f);
227 
228     int count() const;
229   };
230 
231   friend class ClassLoaderDataGraph;
232   friend class ClassLoaderDataGraphIterator;
233   friend class ClassLoaderDataGraphKlassIteratorAtomic;
234   friend class ClassLoaderDataGraphKlassIteratorStatic;
235   friend class ClassLoaderDataGraphMetaspaceIterator;
236   friend class Klass;
237   friend class MetaDataFactory;
238   friend class Method;
239 
240   static ClassLoaderData * _the_null_class_loader_data;
241 
242   WeakHandle<vm_class_loader_data> _holder; // The oop that determines lifetime of this class loader
243   OopHandle _class_loader;    // The instance of java/lang/ClassLoader associated with
244                               // this ClassLoaderData
245 
246   ClassLoaderMetaspace * volatile _metaspace;  // Meta-space where meta-data defined by the
247                                     // classes in the class loader are allocated.
248   Mutex* _metaspace_lock;  // Locks the metaspace for allocations and setup.
249   bool _unloading;         // true if this class loader goes away
250   bool _is_unsafe_anonymous; // CLD is dedicated to one class and that class determines the CLDs lifecycle.
251                              // For example, an unsafe anonymous class.
252 
253   // Remembered sets support for the oops in the class loader data.
254   bool _modified_oops;             // Card Table Equivalent (YC/CMS support)
255   bool _accumulated_modified_oops; // Mod Union Equivalent (CMS support)
256 
257   s2 _keep_alive;          // if this CLD is kept alive.
258                            // Used for unsafe anonymous classes and the boot class
259                            // loader. _keep_alive does not need to be volatile or
260                            // atomic since there is one unique CLD per unsafe anonymous class.
261 
262   volatile int _claimed;   // true if claimed, for example during GC traces.
263                            // To avoid applying oop closure more than once.
264                            // Has to be an int because we cas it.
265   ChunkedHandleList _handles; // Handles to constant pool arrays, Modules, etc, which
266                               // have the same life cycle of the corresponding ClassLoader.
267 
268   NOT_PRODUCT(volatile int _dependency_count;)  // number of class loader dependencies
269 
270   Klass* volatile _klasses;              // The classes defined by the class loader.
271   PackageEntryTable* volatile _packages; // The packages defined by the class loader.
272   ModuleEntryTable*  volatile _modules;  // The modules defined by the class loader.
273   ModuleEntry* _unnamed_module;          // This class loader's unnamed module.
274   Dictionary*  _dictionary;              // The loaded InstanceKlasses, including initiated by this class loader
275 
276   // These method IDs are created for the class loader and set to NULL when the
277   // class loader is unloaded.  They are rarely freed, only for redefine classes
278   // and if they lose a data race in InstanceKlass.
279   JNIMethodBlock*                  _jmethod_ids;
280 
281   // Metadata to be deallocated when it's safe at class unloading, when
282   // this class loader isn't unloaded itself.
283   GrowableArray<Metadata*>*      _deallocate_list;
284 
285   // Support for walking class loader data objects
286   ClassLoaderData* _next; /// Next loader_datas created
287 
288   Klass*  _class_loader_klass;
289   Symbol* _name;
290   Symbol* _name_and_id;
291   JFR_ONLY(DEFINE_TRACE_ID_FIELD;)
292 
293   void set_next(ClassLoaderData* next) { _next = next; }
294   ClassLoaderData* next() const        { return _next; }
295 
296   ClassLoaderData(Handle h_class_loader, bool is_unsafe_anonymous);
297   ~ClassLoaderData();
298 
299   // The CLD are not placed in the Heap, so the Card Table or
300   // the Mod Union Table can't be used to mark when CLD have modified oops.
301   // The CT and MUT bits saves this information for the whole class loader data.
302   void clear_modified_oops()             { _modified_oops = false; }
303  public:
304   void record_modified_oops()            { _modified_oops = true; }
305   bool has_modified_oops()               { return _modified_oops; }
306 
307   void accumulate_modified_oops()        { if (has_modified_oops()) _accumulated_modified_oops = true; }
308   void clear_accumulated_modified_oops() { _accumulated_modified_oops = false; }
309   bool has_accumulated_modified_oops()   { return _accumulated_modified_oops; }
310  private:
311 
312   void unload();
313   bool keep_alive() const       { return _keep_alive > 0; }
314 
315   oop holder_phantom() const;
316   void classes_do(void f(Klass*));
317   void loaded_classes_do(KlassClosure* klass_closure);
318   void classes_do(void f(InstanceKlass*));
319   void methods_do(void f(Method*));
320   void modules_do(void f(ModuleEntry*));
321   void packages_do(void f(PackageEntry*));
322 
323   // Deallocate free list during class unloading.
324   void free_deallocate_list();                      // for the classes that are not unloaded
325   void free_deallocate_list_C_heap_structures();    // for the classes that are unloaded
326 
327   // Allocate out of this class loader data
328   MetaWord* allocate(size_t size);
329 
330   Dictionary* create_dictionary();
331 
332   void initialize_name(Handle class_loader);
333  public:
334   // GC interface.
335   void clear_claimed() { _claimed = 0; }
336   bool claimed() const { return _claimed == 1; }
337   bool claim();
338 
339   // Computes if the CLD is alive or not. This is safe to call in concurrent
340   // contexts.
341   bool is_alive() const;
342 
343   // Accessors
344   ClassLoaderMetaspace* metaspace_or_null() const { return _metaspace; }
345 
346   static ClassLoaderData* the_null_class_loader_data() {
347     return _the_null_class_loader_data;
348   }
349 
350   Mutex* metaspace_lock() const { return _metaspace_lock; }
351 
352   bool is_unsafe_anonymous() const { return _is_unsafe_anonymous; }
353 
354   static void init_null_class_loader_data();
355 
356   bool is_the_null_class_loader_data() const {
357     return this == _the_null_class_loader_data;
358   }
359 
360   // Returns true if this class loader data is for the system class loader.
361   // (Note that the class loader data may be unsafe anonymous.)
362   bool is_system_class_loader_data() const;
363 
364   // Returns true if this class loader data is for the platform class loader.
365   // (Note that the class loader data may be unsafe anonymous.)
366   bool is_platform_class_loader_data() const;
367 
368   // Returns true if this class loader data is for the boot class loader.
369   // (Note that the class loader data may be unsafe anonymous.)
370   inline bool is_boot_class_loader_data() const;
371 
372   bool is_builtin_class_loader_data() const;
373   bool is_permanent_class_loader_data() const;
374 
375   // The Metaspace is created lazily so may be NULL.  This
376   // method will allocate a Metaspace if needed.
377   ClassLoaderMetaspace* metaspace_non_null();
378 
379   inline oop class_loader() const;
380 
381   // Returns true if this class loader data is for a loader going away.
382   // Note that this is only safe after the GC has computed if the CLD is
383   // unloaded or not. In concurrent contexts where there are no such
384   // guarantees, is_alive() should be used instead.
385   bool is_unloading() const     {
386     assert(!(is_the_null_class_loader_data() && _unloading), "The null class loader can never be unloaded");
387     return _unloading;
388   }
389 
390   // Used to refcount an unsafe anonymous class's CLD in order to
391   // indicate their aliveness.
392   void inc_keep_alive();
393   void dec_keep_alive();
394 
395   void initialize_holder(Handle holder);
396 
397   void oops_do(OopClosure* f, bool must_claim, bool clear_modified_oops = false);
398 
399   void classes_do(KlassClosure* klass_closure);
400   Klass* klasses() { return _klasses; }
401 
402   JNIMethodBlock* jmethod_ids() const              { return _jmethod_ids; }
403   void set_jmethod_ids(JNIMethodBlock* new_block)  { _jmethod_ids = new_block; }
404 
405   void print()                                     { print_on(tty); }
406   void print_on(outputStream* out) const PRODUCT_RETURN;
407   void print_value()                               { print_value_on(tty); }
408   void print_value_on(outputStream* out) const;
409   void verify();
410 
411   OopHandle add_handle(Handle h);
412   void remove_handle(OopHandle h);
413   void init_handle_locked(OopHandle& pd, Handle h);  // used for concurrent access to ModuleEntry::_pd field
414   void add_class(Klass* k, bool publicize = true);
415   void remove_class(Klass* k);
416   bool contains_klass(Klass* k);
417   void record_dependency(const Klass* to);
418   PackageEntryTable* packages() { return _packages; }
419   ModuleEntry* unnamed_module() { return _unnamed_module; }
420   ModuleEntryTable* modules();
421   bool modules_defined() { return (_modules != NULL); }
422 
423   // Loaded class dictionary
424   Dictionary* dictionary() const { return _dictionary; }
425 
426   void add_to_deallocate_list(Metadata* m);
427 
428   static ClassLoaderData* class_loader_data(oop loader);
429   static ClassLoaderData* class_loader_data_or_null(oop loader);
430   static ClassLoaderData* unsafe_anonymous_class_loader_data(Handle loader);
431 
432   // Returns Klass* of associated class loader, or NULL if associated loader is 'bootstrap'.
433   // Also works if unloading.
434   Klass* class_loader_klass() const { return _class_loader_klass; }
435 
436   // Returns the class loader's explict name as specified during
437   // construction or the class loader's qualified class name.
438   // Works during unloading.
439   const char* loader_name() const;
440   // Returns the explicitly specified class loader name or NULL.
441   Symbol* name() const { return _name; }
442 
443   // Obtain the class loader's _name_and_id, works during unloading.
444   const char* loader_name_and_id() const;
445   Symbol* name_and_id() const { return _name_and_id; }
446 
447   JFR_ONLY(DEFINE_TRACE_ID_METHODS;)
448 };
449 
450 // An iterator that distributes Klasses to parallel worker threads.
451 class ClassLoaderDataGraphKlassIteratorAtomic : public StackObj {
452  Klass* volatile _next_klass;
453  public:
454   ClassLoaderDataGraphKlassIteratorAtomic();
455   Klass* next_klass();
456  private:
457   static Klass* next_klass_in_cldg(Klass* klass);
458 };
459 
460 class ClassLoaderDataGraphMetaspaceIterator : public StackObj {
461   ClassLoaderData* _data;
462  public:
463   ClassLoaderDataGraphMetaspaceIterator();
464   ~ClassLoaderDataGraphMetaspaceIterator();
465   bool repeat() { return _data != NULL; }
466   ClassLoaderMetaspace* get_next() {
467     assert(_data != NULL, "Should not be NULL in call to the iterator");
468     ClassLoaderMetaspace* result = _data->metaspace_or_null();
469     _data = _data->next();
470     // This result might be NULL for class loaders without metaspace
471     // yet.  It would be nice to return only non-null results but
472     // there is no guarantee that there will be a non-null result
473     // down the list so the caller is going to have to check.
474     return result;
475   }
476 };
477 #endif // SHARE_VM_CLASSFILE_CLASSLOADERDATA_HPP