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
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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(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() 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 methods_do(void f(Method*));
187 void modules_do(void f(ModuleEntry*));
188 void packages_do(void f(PackageEntry*));
189
190 // Deallocate free list during class unloading.
191 void free_deallocate_list(); // for the classes that are not unloaded
192 void free_deallocate_list_C_heap_structures(); // for the classes that are unloaded
193
194 Dictionary* create_dictionary();
195
196 void initialize_name(Handle class_loader);
197
198 public:
199 // GC interface.
200
201 // The "claim" is typically used to check if oops_do needs to be applied on
202 // the CLD or not. Most GCs only perform strong marking during the marking phase.
203 enum Claim {
204 _claim_none = 0,
205 _claim_finalizable = 2,
206 _claim_strong = 3,
207 _claim_other = 4
208 };
209 void clear_claim() { _claim = 0; }
210 void clear_claim(int claim);
211 bool claimed() const { return _claim != 0; }
212 bool claimed(int claim) const { return (_claim & claim) == claim; }
213 bool try_claim(int claim);
214
215 // Computes if the CLD is alive or not. This is safe to call in concurrent
216 // contexts.
217 bool is_alive() const;
218
219 // Accessors
220 ClassLoaderMetaspace* metaspace_or_null() const { return _metaspace; }
221
222 static ClassLoaderData* the_null_class_loader_data() {
223 return _the_null_class_loader_data;
224 }
225
226 Mutex* metaspace_lock() const { return _metaspace_lock; }
227
228 bool has_class_mirror_holder() const { return _has_class_mirror_holder; }
229
230 static void init_null_class_loader_data();
231
232 bool is_the_null_class_loader_data() const {
233 return this == _the_null_class_loader_data;
234 }
235
236 // Returns true if this class loader data is for the system class loader.
237 // (Note that the class loader data may be for a non-strong hidden class)
238 bool is_system_class_loader_data() const;
239
240 // Returns true if this class loader data is for the platform class loader.
241 // (Note that the class loader data may be for a non-strong hidden class)
242 bool is_platform_class_loader_data() const;
243
244 // Returns true if this class loader data is for the boot class loader.
245 // (Note that the class loader data may be for a non-strong hidden class)
246 inline bool is_boot_class_loader_data() const;
247
248 bool is_builtin_class_loader_data() const;
249 bool is_permanent_class_loader_data() const;
250
251 // The Metaspace is created lazily so may be NULL. This
252 // method will allocate a Metaspace if needed.
253 ClassLoaderMetaspace* metaspace_non_null();
254
255 inline oop class_loader() const;
256
257 // Returns true if this class loader data is for a loader going away.
258 // Note that this is only safe after the GC has computed if the CLD is
259 // unloading or not. In concurrent contexts where there are no such
260 // guarantees, is_alive() should be used instead.
261 bool is_unloading() const {
262 assert(!(is_the_null_class_loader_data() && _unloading), "The null class loader can never be unloaded");
263 return _unloading;
264 }
265
266 // Used to refcount a non-strong hidden class's s CLD in order to indicate their aliveness.
267 void inc_keep_alive();
268 void dec_keep_alive();
269
270 void initialize_holder(Handle holder);
271
272 void oops_do(OopClosure* f, int claim_value, bool clear_modified_oops = false);
273
274 void classes_do(KlassClosure* klass_closure);
275 Klass* klasses() { return _klasses; }
276
277 JNIMethodBlock* jmethod_ids() const { return _jmethod_ids; }
278 void set_jmethod_ids(JNIMethodBlock* new_block) { _jmethod_ids = new_block; }
279
280 void print() const;
281 void print_on(outputStream* out) const PRODUCT_RETURN;
282 void print_value() const;
283 void print_value_on(outputStream* out) const;
284 void verify();
285
286 OopHandle add_handle(Handle h);
287 void remove_handle(OopHandle h);
288 void init_handle_locked(OopHandle& pd, Handle h); // used for concurrent access to ModuleEntry::_pd field
289 void add_class(Klass* k, bool publicize = true);
290 void remove_class(Klass* k);
291 bool contains_klass(Klass* k);
292 void record_dependency(const Klass* to);
293 PackageEntryTable* packages() { return _packages; }
294 ModuleEntry* unnamed_module() { return _unnamed_module; }
295 ModuleEntryTable* modules();
296 bool modules_defined() { return (_modules != NULL); }
297
298 // Offsets
299 static ByteSize holder_offset() { return in_ByteSize(offset_of(ClassLoaderData, _holder)); }
300 static ByteSize keep_alive_offset() { return in_ByteSize(offset_of(ClassLoaderData, _keep_alive)); }
301
302 // Loaded class dictionary
303 Dictionary* dictionary() const { return _dictionary; }
304
305 void add_to_deallocate_list(Metadata* m);
306
307 static ClassLoaderData* class_loader_data(oop loader);
308 static ClassLoaderData* class_loader_data_or_null(oop loader);
309
310 // Returns Klass* of associated class loader, or NULL if associated loader is 'bootstrap'.
311 // Also works if unloading.
312 Klass* class_loader_klass() const { return _class_loader_klass; }
313
314 // Returns the class loader's explict name as specified during
315 // construction or the class loader's qualified class name.
316 // Works during unloading.
317 const char* loader_name() const;
318 // Returns the explicitly specified class loader name or NULL.
319 Symbol* name() const { return _name; }
320
321 // Obtain the class loader's _name_and_id, works during unloading.
322 const char* loader_name_and_id() const;
323 Symbol* name_and_id() const { return _name_and_id; }
324
325 unsigned identity_hash() const {
326 return (unsigned)((uintptr_t)this >> LogBytesPerWord);
327 }
328
329 JFR_ONLY(DEFINE_TRACE_ID_METHODS;)
330 };
331
332 #endif // SHARE_CLASSFILE_CLASSLOADERDATA_HPP