1 /*
2 * Copyright (c) 2012, 2024, 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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7 * published by the Free Software Foundation.
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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
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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(nullptr) {}
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 template <bool keep_alive>
102 friend class ClassLoaderDataGraphIteratorBase;
103 friend class ClassLoaderDataGraphKlassIteratorAtomic;
104 friend class ClassLoaderDataGraphKlassIteratorStatic;
105 friend class ClassLoaderDataGraphMetaspaceIterator;
106 friend class Klass;
107 friend class MetaDataFactory;
108 friend class Method;
109
110 static ClassLoaderData * _the_null_class_loader_data;
111
112 WeakHandle _holder; // The oop that determines lifetime of this class loader
113 OopHandle _class_loader; // The instance of java/lang/ClassLoader associated with
114 // this ClassLoaderData
115
116 ClassLoaderMetaspace * volatile _metaspace; // Meta-space where meta-data defined by the
117 // classes in the class loader are allocated.
118 Mutex* _metaspace_lock; // Locks the metaspace for allocations and setup.
119 bool _unloading; // true if this class loader goes away
120 bool _has_class_mirror_holder; // If true, CLD is dedicated to one class and that class determines
121 // the CLDs lifecycle. For example, a non-strong hidden class.
122 // Arrays of these classes are also assigned
123 // to these class loader data.
124
125 // Remembered sets support for the oops in the class loader data.
126 bool _modified_oops; // Card Table Equivalent
127
128 int _keep_alive_ref_count; // if this CLD should not be considered eligible for unloading.
129 // Used for non-strong hidden classes and the
130 // boot class loader. _keep_alive_ref_count does not need to be volatile or
131 // atomic since there is one unique CLD per non-strong hidden class.
132
133 volatile int _claim; // non-zero if claimed, for example during GC traces.
134 // To avoid applying oop closure more than once.
135 ChunkedHandleList _handles; // Handles to constant pool arrays, Modules, etc, which
136 // have the same life cycle of the corresponding ClassLoader.
137
138 NOT_PRODUCT(volatile int _dependency_count;) // number of class loader dependencies
139
140 Klass* volatile _klasses; // The classes defined by the class loader.
141 PackageEntryTable* volatile _packages; // The packages defined by the class loader.
142 ModuleEntryTable* volatile _modules; // The modules defined by the class loader.
143 ModuleEntry* _unnamed_module; // This class loader's unnamed module.
144 Dictionary* _dictionary; // The loaded InstanceKlasses, including initiated by this class loader
145
146 // These method IDs are created for the class loader and set to null when the
147 // class loader is unloaded. They are rarely freed, only for redefine classes
148 // and if they lose a data race in InstanceKlass.
149 JNIMethodBlock* _jmethod_ids;
150
151 // Metadata to be deallocated when it's safe at class unloading, when
152 // this class loader isn't unloaded itself.
153 GrowableArray<Metadata*>* _deallocate_list;
154
155 // Support for walking class loader data objects
156 //
157 // The ClassLoaderDataGraph maintains two lists to keep track of CLDs.
158 //
159 // The first list [_head, _next] is where new CLDs are registered. The CLDs
160 // are only inserted at the _head, and the _next pointers are only rewritten
161 // from unlink_next() which unlinks one unloading CLD by setting _next to
162 // _next->_next. This allows GCs to concurrently walk the list while the CLDs
163 // are being concurrently unlinked.
164 //
165 // The second list [_unloading_head, _unloading_next] is where dead CLDs get
166 // moved to during class unloading. See: ClassLoaderDataGraph::do_unloading().
167 // This list is never modified while other threads are iterating over it.
168 //
169 // After all dead CLDs have been moved to the unloading list, there's a
170 // synchronization point (handshake) to ensure that all threads reading these
171 // CLDs finish their work. This ensures that we don't have a use-after-free
172 // when we later delete the CLDs.
173 //
174 // And finally, when no threads are using the unloading CLDs anymore, we
175 // remove them from the class unloading list and delete them. See:
176 // ClassLoaderDataGraph::purge();
177 ClassLoaderData* _next;
178 ClassLoaderData* _unloading_next;
179
180 Klass* _class_loader_klass;
181 Symbol* _name;
182 Symbol* _name_and_id;
183 JFR_ONLY(DEFINE_TRACE_ID_FIELD;)
184
185 void set_next(ClassLoaderData* next);
186 ClassLoaderData* next() const;
187 void unlink_next();
188
189 ClassLoaderData(Handle h_class_loader, bool has_class_mirror_holder);
190
191 public:
192 ~ClassLoaderData();
193
194 void set_unloading_next(ClassLoaderData* unloading_next);
195 ClassLoaderData* unloading_next() const;
196 void unload();
197
198 private:
199 // The CLD are not placed in the Heap, so the Card Table or
200 // the Mod Union Table can't be used to mark when CLD have modified oops.
201 // The CT and MUT bits saves this information for the whole class loader data.
202 void clear_modified_oops() { _modified_oops = false; }
203 public:
204 void record_modified_oops() { _modified_oops = true; }
205 bool has_modified_oops() { return _modified_oops; }
206
207 oop holder_no_keepalive() const;
208 // Resolving the holder keeps this CLD alive for the current GC cycle.
209 oop holder() const;
210 void keep_alive() const { (void)holder(); }
211
212 void classes_do(void f(Klass* const));
213
214 private:
215 int keep_alive_ref_count() const { return _keep_alive_ref_count; }
216
217 void loaded_classes_do(KlassClosure* klass_closure);
218 void classes_do(void f(InstanceKlass*));
219 void methods_do(void f(Method*));
220 void modules_do(void f(ModuleEntry*));
221 void packages_do(void f(PackageEntry*));
222
223 // Deallocate free list during class unloading.
224 void free_deallocate_list(); // for the classes that are not unloaded
225 void free_deallocate_list_C_heap_structures(); // for the classes that are unloaded
226
227 Dictionary* create_dictionary();
228
229 void demote_strong_roots();
230
231 void initialize_name(Handle class_loader);
232
233 public:
234 // GC interface.
235
236 // The "claim" is typically used to check if oops_do needs to be applied on
237 // the CLD or not. Most GCs only perform strong marking during the marking phase.
238 enum Claim {
239 _claim_none = 0,
240 _claim_finalizable = 2,
241 _claim_strong = 3,
242 _claim_stw_fullgc_mark = 4,
243 _claim_stw_fullgc_adjust = 8,
244 _claim_other = 16
245 };
246 void clear_claim() { _claim = 0; }
247 void clear_claim(int claim);
248 void verify_not_claimed(int claim) NOT_DEBUG_RETURN;
249 bool claimed() const { return _claim != 0; }
250 bool claimed(int claim) const { return (_claim & claim) == claim; }
251 bool try_claim(int claim);
252
253 // Computes if the CLD is alive or not. This is safe to call in concurrent
254 // contexts.
255 bool is_alive() const;
256
257 // Accessors
258 ClassLoaderMetaspace* metaspace_or_null() const { return _metaspace; }
259
260 static ClassLoaderData* the_null_class_loader_data() {
261 return _the_null_class_loader_data;
262 }
263
264 Mutex* metaspace_lock() const { return _metaspace_lock; }
265
266 bool has_class_mirror_holder() const { return _has_class_mirror_holder; }
267
268 static void init_null_class_loader_data();
269
270 bool is_the_null_class_loader_data() const {
271 return this == _the_null_class_loader_data;
272 }
273
274 // Returns true if this class loader data is for the system class loader.
275 // (Note that the class loader data may be for a non-strong hidden class)
276 bool is_system_class_loader_data() const;
277
278 // Returns true if this class loader data is for the platform class loader.
279 // (Note that the class loader data may be for a non-strong hidden class)
280 bool is_platform_class_loader_data() const;
281
282 // Returns true if this class loader data is for the boot class loader.
283 // (Note that the class loader data may be for a non-strong hidden class)
284 inline bool is_boot_class_loader_data() const;
285
286 bool is_builtin_class_loader_data() const;
287 bool is_permanent_class_loader_data() const;
288
289 OopHandle class_loader_handle() const { return _class_loader; }
290
291 // The Metaspace is created lazily so may be null. This
292 // method will allocate a Metaspace if needed.
293 ClassLoaderMetaspace* metaspace_non_null();
294
295 inline oop class_loader() const;
296 inline oop class_loader_no_keepalive() const;
297
298 // Returns true if this class loader data is for a loader going away.
299 // Note that this is only safe after the GC has computed if the CLD is
300 // unloading or not. In concurrent contexts where there are no such
301 // guarantees, is_alive() should be used instead.
302 bool is_unloading() const {
303 assert(!(is_the_null_class_loader_data() && _unloading), "The null class loader can never be unloaded");
304 return _unloading;
305 }
306
307 // Used to refcount a non-strong hidden class's CLD in order to force its aliveness during
308 // loading, when gc tracing may not find this CLD alive through the holder.
309 void inc_keep_alive_ref_count();
310 void dec_keep_alive_ref_count();
311
312 void initialize_holder(Handle holder);
313
314 void oops_do(OopClosure* f, int claim_value, bool clear_modified_oops = false);
315
316 void classes_do(KlassClosure* klass_closure);
317 Klass* klasses() { return _klasses; }
318
319 JNIMethodBlock* jmethod_ids() const { return _jmethod_ids; }
320 void set_jmethod_ids(JNIMethodBlock* new_block) { _jmethod_ids = new_block; }
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