1 /* 2 * Copyright (c) 2012, 2023, 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(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; // if this CLD is kept alive. 129 // Used for non-strong hidden classes and the 130 // boot class loader. _keep_alive 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 oop holder() const; 209 210 void classes_do(void f(Klass* const)); 211 212 private: 213 bool keep_alive() const { return _keep_alive > 0; } 214 215 void loaded_classes_do(KlassClosure* klass_closure); 216 void classes_do(void f(InstanceKlass*)); 217 void methods_do(void f(Method*)); 218 void modules_do(void f(ModuleEntry*)); 219 void packages_do(void f(PackageEntry*)); 220 221 // Deallocate free list during class unloading. 222 void free_deallocate_list(); // for the classes that are not unloaded 223 void free_deallocate_list_C_heap_structures(); // for the classes that are unloaded 224 225 Dictionary* create_dictionary(); 226 227 void demote_strong_roots(); 228 229 void initialize_name(Handle class_loader); 230 231 public: 232 // GC interface. 233 234 // The "claim" is typically used to check if oops_do needs to be applied on 235 // the CLD or not. Most GCs only perform strong marking during the marking phase. 236 enum Claim { 237 _claim_none = 0, 238 _claim_finalizable = 2, 239 _claim_strong = 3, 240 _claim_stw_fullgc_mark = 4, 241 _claim_stw_fullgc_adjust = 8, 242 _claim_other = 16 243 }; 244 void clear_claim() { _claim = 0; } 245 void clear_claim(int claim); 246 void verify_not_claimed(int claim) NOT_DEBUG_RETURN; 247 bool claimed() const { return _claim != 0; } 248 bool claimed(int claim) const { return (_claim & claim) == claim; } 249 bool try_claim(int claim); 250 251 // Computes if the CLD is alive or not. This is safe to call in concurrent 252 // contexts. 253 bool is_alive() const; 254 255 // Accessors 256 ClassLoaderMetaspace* metaspace_or_null() const { return _metaspace; } 257 258 static ClassLoaderData* the_null_class_loader_data() { 259 return _the_null_class_loader_data; 260 } 261 262 Mutex* metaspace_lock() const { return _metaspace_lock; } 263 264 bool has_class_mirror_holder() const { return _has_class_mirror_holder; } 265 266 static void init_null_class_loader_data(); 267 268 bool is_the_null_class_loader_data() const { 269 return this == _the_null_class_loader_data; 270 } 271 272 // Returns true if this class loader data is for the system class loader. 273 // (Note that the class loader data may be for a non-strong hidden class) 274 bool is_system_class_loader_data() const; 275 276 // Returns true if this class loader data is for the platform class loader. 277 // (Note that the class loader data may be for a non-strong hidden class) 278 bool is_platform_class_loader_data() const; 279 280 // Returns true if this class loader data is for the boot class loader. 281 // (Note that the class loader data may be for a non-strong hidden class) 282 inline bool is_boot_class_loader_data() const; 283 284 bool is_builtin_class_loader_data() const; 285 bool is_permanent_class_loader_data() const; 286 287 OopHandle class_loader_handle() const { return _class_loader; } 288 289 // The Metaspace is created lazily so may be null. This 290 // method will allocate a Metaspace if needed. 291 ClassLoaderMetaspace* metaspace_non_null(); 292 293 inline oop class_loader() const; 294 inline oop class_loader_no_keepalive() const; 295 296 // Returns true if this class loader data is for a loader going away. 297 // Note that this is only safe after the GC has computed if the CLD is 298 // unloading or not. In concurrent contexts where there are no such 299 // guarantees, is_alive() should be used instead. 300 bool is_unloading() const { 301 assert(!(is_the_null_class_loader_data() && _unloading), "The null class loader can never be unloaded"); 302 return _unloading; 303 } 304 305 // Used to refcount a non-strong hidden class's s CLD in order to indicate their aliveness. 306 void inc_keep_alive(); 307 void dec_keep_alive(); 308 309 void initialize_holder(Handle holder); 310 311 void oops_do(OopClosure* f, int claim_value, bool clear_modified_oops = false); 312 313 void classes_do(KlassClosure* klass_closure); 314 Klass* klasses() { return _klasses; } 315 316 JNIMethodBlock* jmethod_ids() const { return _jmethod_ids; } 317 void set_jmethod_ids(JNIMethodBlock* new_block) { _jmethod_ids = new_block; } 318 319 void print() const; 320 void print_on(outputStream* out) const PRODUCT_RETURN; 321 void print_value() const; 322 void print_value_on(outputStream* out) const; 323 void verify(); 324 325 OopHandle add_handle(Handle h); 326 void remove_handle(OopHandle h); 327 void init_handle_locked(OopHandle& pd, Handle h); // used for concurrent access to ModuleEntry::_pd field 328 void add_class(Klass* k, bool publicize = true); 329 void remove_class(Klass* k); 330 bool contains_klass(Klass* k); 331 void record_dependency(const Klass* to); 332 PackageEntryTable* packages() { return _packages; } 333 ModuleEntry* unnamed_module() { return _unnamed_module; } 334 ModuleEntryTable* modules(); 335 bool modules_defined() { return (_modules != nullptr); } 336 337 // Offsets 338 static ByteSize holder_offset() { return byte_offset_of(ClassLoaderData, _holder); } 339 static ByteSize keep_alive_offset() { return byte_offset_of(ClassLoaderData, _keep_alive); } 340 341 // Loaded class dictionary 342 Dictionary* dictionary() const { return _dictionary; } 343 344 void add_to_deallocate_list(Metadata* m); 345 346 static ClassLoaderData* class_loader_data(oop loader); 347 static ClassLoaderData* class_loader_data_or_null(oop loader); 348 349 // Returns Klass* of associated class loader, or null if associated loader is 'bootstrap'. 350 // Also works if unloading. 351 Klass* class_loader_klass() const { return _class_loader_klass; } 352 353 // Returns the class loader's explicit name as specified during 354 // construction or the class loader's qualified class name. 355 // Works during unloading. 356 const char* loader_name() const; 357 // Returns the explicitly specified class loader name or null. 358 Symbol* name() const { return _name; } 359 360 // Obtain the class loader's _name_and_id, works during unloading. 361 const char* loader_name_and_id() const; 362 Symbol* name_and_id() const { return _name_and_id; } 363 364 unsigned identity_hash() const { 365 return (unsigned)((uintptr_t)this >> LogBytesPerWord); 366 } 367 368 JFR_ONLY(DEFINE_TRACE_ID_METHODS;) 369 }; 370 371 #endif // SHARE_CLASSFILE_CLASSLOADERDATA_HPP