1 /* 2 * Copyright (c) 2003, 2024, 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 #include "precompiled.hpp" 26 #include "classfile/classLoaderData.inline.hpp" 27 #include "classfile/placeholders.hpp" 28 #include "logging/log.hpp" 29 #include "logging/logTag.hpp" 30 #include "logging/logStream.hpp" 31 #include "memory/resourceArea.hpp" 32 #include "oops/symbolHandle.hpp" 33 #include "runtime/javaThread.hpp" 34 #include "runtime/mutexLocker.hpp" 35 #include "utilities/resourceHash.hpp" 36 37 class PlaceholderKey { 38 SymbolHandle _name; 39 ClassLoaderData* _loader_data; 40 public: 41 PlaceholderKey(Symbol* name, ClassLoaderData* l) : _name(name), _loader_data(l) {} 42 43 static bool equals(PlaceholderKey const& k1, PlaceholderKey const& k2) { 44 return (k1._name == k2._name && k1._loader_data == k2._loader_data); 45 } 46 static unsigned hash(PlaceholderKey const& k) { 47 return (unsigned) k._name->identity_hash() ^ (int)((intptr_t)k._loader_data >> 3); 48 } 49 void print_on(outputStream* st) const; 50 }; 51 52 const int _placeholder_table_size = 503; // Does this really have to be prime? 53 using InternalPlaceholderTable = ResourceHashtable<PlaceholderKey, PlaceholderEntry, _placeholder_table_size, AnyObj::C_HEAP, mtClass, 54 PlaceholderKey::hash, PlaceholderKey::equals>; 55 static InternalPlaceholderTable* _placeholders; 56 57 // SeenThread objects represent list of threads that are 58 // currently performing a load action on a class. 59 // For class circularity, set before loading a superclass. 60 // For bootclasssearchpath, set before calling load_instance_class. 61 // Defining must be single threaded on a class/classloader basis 62 // For DEFINE_CLASS, the head of the queue owns the 63 // define token and the rest of the threads wait to return the 64 // result the first thread gets. 65 // For INLINE_FIELD, set when loading inline type fields for 66 // class circularity checking. 67 class SeenThread: public CHeapObj<mtInternal> { 68 private: 69 JavaThread* _thread; 70 SeenThread* _stnext; 71 SeenThread* _stprev; 72 public: 73 SeenThread(JavaThread* thread) { 74 _thread = thread; 75 _stnext = nullptr; 76 _stprev = nullptr; 77 } 78 JavaThread* thread() const { return _thread;} 79 void set_thread(JavaThread* thread) { _thread = thread; } 80 81 SeenThread* next() const { return _stnext;} 82 void set_next(SeenThread* seen) { _stnext = seen; } 83 void set_prev(SeenThread* seen) { _stprev = seen; } 84 85 static void print_action_queue(SeenThread* seen, outputStream* st) { 86 while (seen != nullptr) { 87 seen->thread()->print_value_on(st); 88 st->print(", "); 89 seen = seen->next(); 90 } 91 } 92 }; 93 94 SeenThread* PlaceholderEntry::actionToQueue(PlaceholderTable::classloadAction action) { 95 SeenThread* queuehead = nullptr; 96 switch (action) { 97 case PlaceholderTable::LOAD_INSTANCE: 98 queuehead = _loadInstanceThreadQ; 99 break; 100 case PlaceholderTable::DETECT_CIRCULARITY: 101 queuehead = _circularityThreadQ; 102 break; 103 case PlaceholderTable::DEFINE_CLASS: 104 queuehead = _defineThreadQ; 105 break; 106 default: Unimplemented(); 107 } 108 return queuehead; 109 } 110 111 void PlaceholderEntry::set_threadQ(SeenThread* seenthread, PlaceholderTable::classloadAction action) { 112 switch (action) { 113 case PlaceholderTable::LOAD_INSTANCE: 114 _loadInstanceThreadQ = seenthread; 115 break; 116 case PlaceholderTable::DETECT_CIRCULARITY: 117 _circularityThreadQ = seenthread; 118 break; 119 case PlaceholderTable::DEFINE_CLASS: 120 _defineThreadQ = seenthread; 121 break; 122 default: Unimplemented(); 123 } 124 return; 125 } 126 127 // Doubly-linked list of Threads per action for class/classloader pair 128 // Class circularity support: links in thread before loading superclass 129 // bootstrap loader support: links in a thread before load_instance_class 130 // definers: use as queue of define requestors, including owner of 131 // define token. Appends for debugging of requestor order 132 void PlaceholderEntry::add_seen_thread(JavaThread* thread, PlaceholderTable::classloadAction action) { 133 assert_lock_strong(SystemDictionary_lock); 134 SeenThread* threadEntry = new SeenThread(thread); 135 SeenThread* seen = actionToQueue(action); 136 137 if (seen == nullptr) { 138 set_threadQ(threadEntry, action); 139 return; 140 } 141 SeenThread* next; 142 while ((next = seen->next()) != nullptr) { 143 seen = next; 144 } 145 seen->set_next(threadEntry); 146 threadEntry->set_prev(seen); 147 return; 148 } 149 150 bool PlaceholderEntry::check_seen_thread(JavaThread* thread, PlaceholderTable::classloadAction action) { 151 assert_lock_strong(SystemDictionary_lock); 152 SeenThread* threadQ = actionToQueue(action); 153 SeenThread* seen = threadQ; 154 while (seen) { 155 if (thread == seen->thread()) { 156 return true; 157 } 158 seen = seen->next(); 159 } 160 return false; 161 } 162 163 // returns true if seenthreadQ is now empty 164 // Note, caller must ensure probe still exists while holding 165 // SystemDictionary_lock 166 // ignores if cleanup has already been done 167 // if found, deletes SeenThread 168 bool PlaceholderEntry::remove_seen_thread(JavaThread* thread, PlaceholderTable::classloadAction action) { 169 assert_lock_strong(SystemDictionary_lock); 170 SeenThread* threadQ = actionToQueue(action); 171 SeenThread* seen = threadQ; 172 SeenThread* prev = nullptr; 173 while (seen) { 174 if (thread == seen->thread()) { 175 if (prev) { 176 prev->set_next(seen->next()); 177 } else { 178 set_threadQ(seen->next(), action); 179 } 180 if (seen->next()) { 181 seen->next()->set_prev(prev); 182 } 183 delete seen; 184 break; 185 } 186 prev = seen; 187 seen = seen->next(); 188 } 189 return (actionToQueue(action) == nullptr); 190 } 191 192 193 void PlaceholderEntry::set_next_klass_name(Symbol* next_klass_name) { 194 assert_locked_or_safepoint(SystemDictionary_lock); 195 assert(_next_klass_name == nullptr || _next_klass_name->refcount() > 1, "must be referenced also by the loader"); 196 _next_klass_name = next_klass_name; 197 } 198 199 // Placeholder objects represent classes currently being loaded. 200 // All threads examining the placeholder table must hold the 201 // SystemDictionary_lock, so we don't need special precautions 202 // on store ordering here. 203 static PlaceholderEntry* add_entry(Symbol* class_name, ClassLoaderData* loader_data, 204 Symbol* next_klass_name){ 205 assert_locked_or_safepoint(SystemDictionary_lock); 206 assert(class_name != nullptr, "adding nullptr obj"); 207 208 PlaceholderEntry entry; 209 entry.set_next_klass_name(next_klass_name); 210 PlaceholderKey key(class_name, loader_data); 211 bool created; 212 PlaceholderEntry* table_copy = _placeholders->put_if_absent(key, entry, &created); 213 assert(created, "better be absent"); 214 return table_copy; 215 } 216 217 // Remove a placeholder object. 218 static void remove_entry(Symbol* class_name, ClassLoaderData* loader_data) { 219 assert_locked_or_safepoint(SystemDictionary_lock); 220 221 PlaceholderKey key(class_name, loader_data); 222 _placeholders->remove(key); 223 } 224 225 226 PlaceholderEntry* PlaceholderTable::get_entry(Symbol* class_name, ClassLoaderData* loader_data) { 227 assert_locked_or_safepoint(SystemDictionary_lock); 228 PlaceholderKey key(class_name, loader_data); 229 return _placeholders->get(key); 230 } 231 232 static const char* action_to_string(PlaceholderTable::classloadAction action) { 233 switch (action) { 234 case PlaceholderTable::LOAD_INSTANCE: return "LOAD_INSTANCE"; 235 case PlaceholderTable::DETECT_CIRCULARITY: return "DETECT_CIRCULARITY"; 236 case PlaceholderTable::DEFINE_CLASS: return "DEFINE_CLASS"; 237 } 238 return ""; 239 } 240 241 inline void log(Symbol* name, PlaceholderEntry* entry, const char* function, PlaceholderTable::classloadAction action) { 242 if (log_is_enabled(Debug, class, load, placeholders)) { 243 LogTarget(Debug, class, load, placeholders) lt; 244 ResourceMark rm; 245 LogStream ls(lt); 246 ls.print("entry %s : %s %s ", name->as_C_string(), function, action_to_string(action)); 247 entry->print_on(&ls); 248 } 249 } 250 251 // find_and_add returns probe pointer - old or new 252 // If no entry exists, add a placeholder entry 253 // If entry exists, reuse entry 254 // For both, push SeenThread for classloadAction 255 // If DETECT_CIRCULARITY, this is used for circularity detection for instanceklass loading. 256 PlaceholderEntry* PlaceholderTable::find_and_add(Symbol* name, 257 ClassLoaderData* loader_data, 258 classloadAction action, 259 Symbol* next_klass_name, 260 JavaThread* thread) { 261 assert(action != DETECT_CIRCULARITY || next_klass_name != nullptr, "must have a super class name"); 262 PlaceholderEntry* probe = get_entry(name, loader_data); 263 if (probe == nullptr) { 264 // Nothing found, add place holder 265 probe = add_entry(name, loader_data, next_klass_name); 266 } else { 267 if (action == DETECT_CIRCULARITY) { 268 probe->set_next_klass_name(next_klass_name); 269 } 270 } 271 probe->add_seen_thread(thread, action); 272 log(name, probe, "find_and_add", action); 273 return probe; 274 } 275 276 void PlaceholderTable::initialize(){ 277 _placeholders = new (mtClass) InternalPlaceholderTable(); 278 } 279 280 281 // placeholder is used to track class loading internal states 282 // superthreadQ tracks class circularity, while loading superclass/superinterface 283 // loadInstanceThreadQ tracks load_instance_class calls 284 // definer() tracks the single thread that owns define token 285 // defineThreadQ tracks waiters on defining thread's results 286 // 1st claimant creates placeholder 287 // find_and_add adds SeenThread entry for appropriate queue 288 // All claimants remove SeenThread after completing action 289 // On removal: if definer and all queues empty, remove entry 290 // Note: you can be in both placeholders and systemDictionary 291 // Therefore - must always check SD first 292 void PlaceholderTable::find_and_remove(Symbol* name, ClassLoaderData* loader_data, 293 classloadAction action, 294 JavaThread* thread) { 295 assert_locked_or_safepoint(SystemDictionary_lock); 296 PlaceholderEntry* probe = get_entry(name, loader_data); 297 assert(probe != nullptr, "must find an entry"); 298 log(name, probe, "find_and_remove", action); 299 probe->remove_seen_thread(thread, action); 300 if (probe->superThreadQ() == nullptr) { 301 probe->set_next_klass_name(nullptr); 302 } 303 // If no other threads using this entry, and this thread is not using this entry for other states 304 if ((probe->superThreadQ() == nullptr) && (probe->loadInstanceThreadQ() == nullptr) 305 && (probe->defineThreadQ() == nullptr) && (probe->definer() == nullptr)) { 306 remove_entry(name, loader_data); 307 } 308 } 309 310 void PlaceholderKey::print_on(outputStream* st) const { 311 _name->print_value_on(st); 312 st->print(", loader "); 313 _loader_data->print_value_on(st); 314 } 315 316 void PlaceholderEntry::print_on(outputStream* st) const { 317 if (next_klass_name() != nullptr) { 318 st->print(", next_klass_name "); 319 next_klass_name()->print_value_on(st); 320 } 321 if (definer() != nullptr) { 322 st->print(", definer "); 323 definer()->print_value_on(st); 324 } 325 if (instance_klass() != nullptr) { 326 st->print(", InstanceKlass "); 327 instance_klass()->print_value_on(st); 328 } 329 st->cr(); 330 st->print("loadInstanceThreadQ threads:"); 331 SeenThread::print_action_queue(loadInstanceThreadQ(), st); 332 st->cr(); 333 st->print("superThreadQ threads:"); 334 SeenThread::print_action_queue(superThreadQ(), st); 335 st->cr(); 336 st->print("defineThreadQ threads:"); 337 SeenThread::print_action_queue(defineThreadQ(), st); 338 st->cr(); 339 } 340 341 void PlaceholderTable::print_on(outputStream* st) { 342 auto printer = [&] (PlaceholderKey& key, PlaceholderEntry& entry) { 343 st->print("placeholder "); 344 key.print_on(st); 345 entry.print_on(st); 346 return true; 347 }; 348 st->print_cr("Placeholder table (table_size=%d, placeholders=%d)", 349 _placeholders->table_size(), _placeholders->number_of_entries()); 350 _placeholders->iterate(printer); 351 } 352 353 void PlaceholderTable::print() { return print_on(tty); }