1 /*
2 * Copyright (c) 2012, 2025, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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5 * This code is free software; you can redistribute it and/or modify it
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11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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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 ModuleEntry;
57 class PackageEntry;
58 class ModuleEntryTable;
59 class PackageEntryTable;
60 class DictionaryEntry;
61 class Dictionary;
62 class ClassLoaderMetaspace;
63
64 // ClassLoaderData class
65
66 class ClassLoaderData : public CHeapObj<mtClass> {
67 friend class VMStructs;
68
69 private:
70 class ChunkedHandleList {
71 struct Chunk : public CHeapObj<mtClass> {
72 static const size_t CAPACITY = 32;
73
74 oop _data[CAPACITY];
75 volatile juint _size;
76 Chunk* _next;
77
78 Chunk(Chunk* c) : _size(0), _next(c) { }
79 };
80
81 Chunk* volatile _head;
82
83 void oops_do_chunk(OopClosure* f, Chunk* c, const juint size);
84
85 public:
86 ChunkedHandleList() : _head(nullptr) {}
87 ~ChunkedHandleList();
88
89 // Only one thread at a time can add, guarded by ClassLoaderData::metaspace_lock().
90 // However, multiple threads can execute oops_do concurrently with add.
91 OopHandle add(oop o);
92 bool contains(oop p);
93 NOT_PRODUCT(bool owner_of(oop* p);)
94 void oops_do(OopClosure* f);
95
96 int count() const;
97 };
98
99 friend class ClassLoaderDataGraph;
100 template <bool keep_alive>
101 friend class ClassLoaderDataGraphIteratorBase;
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 data.
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_ref_count; // if this CLD should not be considered eligible for unloading.
128 // Used for non-strong hidden classes and the
129 // boot class loader. _keep_alive_ref_count 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 removed when the
146 // class loader is unloaded.
147 GrowableArray<jmethodID>* _jmethod_ids;
148
149 // Metadata to be deallocated when it's safe at class unloading, when
150 // this class loader isn't unloaded itself.
151 GrowableArray<Metadata*>* _deallocate_list;
152
153 // Support for walking class loader data objects
154 //
155 // The ClassLoaderDataGraph maintains two lists to keep track of CLDs.
156 //
157 // The first list [_head, _next] is where new CLDs are registered. The CLDs
158 // are only inserted at the _head, and the _next pointers are only rewritten
159 // from unlink_next() which unlinks one unloading CLD by setting _next to
160 // _next->_next. This allows GCs to concurrently walk the list while the CLDs
161 // are being concurrently unlinked.
162 //
163 // The second list [_unloading_head, _unloading_next] is where dead CLDs get
164 // moved to during class unloading. See: ClassLoaderDataGraph::do_unloading().
165 // This list is never modified while other threads are iterating over it.
166 //
167 // After all dead CLDs have been moved to the unloading list, there's a
168 // synchronization point (handshake) to ensure that all threads reading these
169 // CLDs finish their work. This ensures that we don't have a use-after-free
170 // when we later delete the CLDs.
171 //
172 // And finally, when no threads are using the unloading CLDs anymore, we
173 // remove them from the class unloading list and delete them. See:
174 // ClassLoaderDataGraph::purge();
175 ClassLoaderData* _next;
176 ClassLoaderData* _unloading_next;
177
178 Klass* _class_loader_klass;
179 Symbol* _name;
180 Symbol* _name_and_id;
181 JFR_ONLY(DEFINE_TRACE_ID_FIELD;)
182
183 void set_next(ClassLoaderData* next);
184 ClassLoaderData* next() const;
185 void unlink_next();
186
187 ClassLoaderData(Handle h_class_loader, bool has_class_mirror_holder);
188
189 public:
190 ~ClassLoaderData();
191
192 void set_unloading_next(ClassLoaderData* unloading_next);
193 ClassLoaderData* unloading_next() const;
194 void unload();
195
196 private:
197 // The CLD are not placed in the Heap, so the Card Table or
198 // the Mod Union Table can't be used to mark when CLD have modified oops.
199 // The CT and MUT bits saves this information for the whole class loader data.
200 void clear_modified_oops() { _modified_oops = false; }
201 public:
202 void record_modified_oops() { _modified_oops = true; }
203 bool has_modified_oops() { return _modified_oops; }
204
205 oop holder_no_keepalive() const;
206 // Resolving the holder keeps this CLD alive for the current GC cycle.
207 oop holder() const;
208 void keep_alive() const { (void)holder(); }
209
210 void classes_do(void f(Klass* const));
211
212 private:
213 int keep_alive_ref_count() const { return _keep_alive_ref_count; }
214
215 void loaded_classes_do(KlassClosure* klass_closure);
216 void classes_do(void f(InstanceKlass*));
217 void inline_classes_do(void f(InlineKlass*));
218 void methods_do(void f(Method*));
219 void modules_do(void f(ModuleEntry*));
220 void packages_do(void f(PackageEntry*));
221
222 // Deallocate free list during class unloading.
223 void free_deallocate_list(); // for the classes that are not unloaded
224 void free_deallocate_list_C_heap_structures(); // for the classes that are unloaded
225
226 Dictionary* create_dictionary();
227
228 void demote_strong_roots();
229
230 void initialize_name(Handle class_loader);
231
232 public:
233 // GC interface.
234
235 // The "claim" is typically used to check if oops_do needs to be applied on
236 // the CLD or not. Most GCs only perform strong marking during the marking phase.
237 enum Claim {
238 _claim_none = 0,
239 _claim_finalizable = 2,
240 _claim_strong = 3,
241 _claim_stw_fullgc_mark = 4,
242 _claim_stw_fullgc_adjust = 8,
243 _claim_other = 16
244 };
245 void clear_claim() { _claim = 0; }
246 void clear_claim(int claim);
247 void verify_not_claimed(int claim) NOT_DEBUG_RETURN;
248 bool claimed() const { return _claim != 0; }
249 bool claimed(int claim) const { return (_claim & claim) == claim; }
250 bool try_claim(int claim);
251
252 // Computes if the CLD is alive or not. This is safe to call in concurrent
253 // contexts.
254 bool is_alive() const;
255
256 // Accessors
257 ClassLoaderMetaspace* metaspace_or_null() const { return _metaspace; }
258
259 static ClassLoaderData* the_null_class_loader_data() {
260 return _the_null_class_loader_data;
261 }
262
263 Mutex* metaspace_lock() const { return _metaspace_lock; }
264
265 bool has_class_mirror_holder() const { return _has_class_mirror_holder; }
266
267 static void init_null_class_loader_data();
268
269 bool is_the_null_class_loader_data() const {
270 return this == _the_null_class_loader_data;
271 }
272
273 // Returns true if this class loader data is for the system class loader.
274 // (Note that the class loader data may be for a non-strong hidden class)
275 bool is_system_class_loader_data() const;
276
277 // Returns true if this class loader data is for the platform class loader.
278 // (Note that the class loader data may be for a non-strong hidden class)
279 bool is_platform_class_loader_data() const;
280
281 // Returns true if this class loader data is for the boot class loader.
282 // (Note that the class loader data may be for a non-strong hidden class)
283 inline bool is_boot_class_loader_data() const;
284
285 bool is_builtin_class_loader_data() const;
286 bool is_permanent_class_loader_data() const;
287
288 OopHandle class_loader_handle() const { return _class_loader; }
289
290 // The Metaspace is created lazily so may be null. This
291 // method will allocate a Metaspace if needed.
292 ClassLoaderMetaspace* metaspace_non_null();
293
294 inline oop class_loader() const;
295 inline oop class_loader_no_keepalive() const;
296
297 // Returns true if this class loader data is for a loader going away.
298 // Note that this is only safe after the GC has computed if the CLD is
299 // unloading or not. In concurrent contexts where there are no such
300 // guarantees, is_alive() should be used instead.
301 bool is_unloading() const {
302 assert(!(is_the_null_class_loader_data() && _unloading), "The null class loader can never be unloaded");
303 return _unloading;
304 }
305
306 // Used to refcount a non-strong hidden class's CLD in order to force its aliveness during
307 // loading, when gc tracing may not find this CLD alive through the holder.
308 void inc_keep_alive_ref_count();
309 void dec_keep_alive_ref_count();
310
311 void initialize_holder(Handle holder);
312
313 void oops_do(OopClosure* f, int claim_value, bool clear_modified_oops = false);
314
315 void classes_do(KlassClosure* klass_closure);
316 Klass* klasses() { return _klasses; }
317
318 void add_jmethod_id(jmethodID id);
319 void remove_jmethod_ids();
320 GrowableArray<jmethodID>* jmethod_ids() const { return _jmethod_ids; }
321
322 void print() const;
323 void print_on(outputStream* out) const PRODUCT_RETURN;
324 void print_value() const;
325 void print_value_on(outputStream* out) const;
326 void verify();
327
328 OopHandle add_handle(Handle h);
329 void remove_handle(OopHandle h);
330 void init_handle_locked(OopHandle& pd, Handle h); // used for concurrent access to ModuleEntry::_pd field
331 void add_class(Klass* k, bool publicize = true);
332 void remove_class(Klass* k);
333 bool contains_klass(Klass* k);
334 void record_dependency(const Klass* to);
335 PackageEntryTable* packages() { return _packages; }
336 ModuleEntry* unnamed_module() { return _unnamed_module; }
337 ModuleEntryTable* modules();
338 bool modules_defined() { return (_modules != nullptr); }
339
340 // Offsets
341 static ByteSize holder_offset() { return byte_offset_of(ClassLoaderData, _holder); }
342 static ByteSize keep_alive_ref_count_offset() { return byte_offset_of(ClassLoaderData, _keep_alive_ref_count); }
343
344 // Loaded class dictionary
345 Dictionary* dictionary() const { return _dictionary; }
346
347 void add_to_deallocate_list(Metadata* m);
348
349 static ClassLoaderData* class_loader_data(oop loader);
350 static ClassLoaderData* class_loader_data_or_null(oop loader);
351
352 // Returns Klass* of associated class loader, or null if associated loader is 'bootstrap'.
353 // Also works if unloading.
354 Klass* class_loader_klass() const { return _class_loader_klass; }
355
356 // Returns the class loader's explicit name as specified during
357 // construction or the class loader's qualified class name.
358 // Works during unloading.
359 const char* loader_name() const;
360 // Returns the explicitly specified class loader name or null.
361 Symbol* name() const { return _name; }
362
363 // Obtain the class loader's _name_and_id, works during unloading.
364 const char* loader_name_and_id() const;
365 Symbol* name_and_id() const { return _name_and_id; }
366
367 unsigned identity_hash() const {
368 return (unsigned)((uintptr_t)this >> LogBytesPerWord);
369 }
370
371 JFR_ONLY(DEFINE_TRACE_ID_METHODS;)
372 };
373
374 #endif // SHARE_CLASSFILE_CLASSLOADERDATA_HPP