1 /* 2 * Copyright (c) 2003, 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 #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 void print_action_queue(outputStream* st) { 86 SeenThread* seen = this; 87 while (seen != nullptr) { 88 seen->thread()->print_value_on(st); 89 st->print(", "); 90 seen = seen->next(); 91 } 92 } 93 }; 94 95 SeenThread* PlaceholderEntry::actionToQueue(PlaceholderTable::classloadAction action) { 96 SeenThread* queuehead = nullptr; 97 switch (action) { 98 case PlaceholderTable::LOAD_INSTANCE: 99 queuehead = _loadInstanceThreadQ; 100 break; 101 case PlaceholderTable::LOAD_SUPER: 102 queuehead = _superThreadQ; 103 break; 104 case PlaceholderTable::DEFINE_CLASS: 105 queuehead = _defineThreadQ; 106 break; 107 case PlaceholderTable::PRIMITIVE_OBJECT_FIELD: 108 queuehead = _inlineTypeFieldQ; 109 break; 110 default: Unimplemented(); 111 } 112 return queuehead; 113 } 114 115 void PlaceholderEntry::set_threadQ(SeenThread* seenthread, PlaceholderTable::classloadAction action) { 116 switch (action) { 117 case PlaceholderTable::LOAD_INSTANCE: 118 _loadInstanceThreadQ = seenthread; 119 break; 120 case PlaceholderTable::LOAD_SUPER: 121 _superThreadQ = seenthread; 122 break; 123 case PlaceholderTable::DEFINE_CLASS: 124 _defineThreadQ = seenthread; 125 break; 126 case PlaceholderTable::PRIMITIVE_OBJECT_FIELD: 127 _inlineTypeFieldQ = seenthread; 128 break; 129 default: Unimplemented(); 130 } 131 return; 132 } 133 134 // Doubly-linked list of Threads per action for class/classloader pair 135 // Class circularity support: links in thread before loading superclass 136 // bootstrap loader support: links in a thread before load_instance_class 137 // definers: use as queue of define requestors, including owner of 138 // define token. Appends for debugging of requestor order 139 void PlaceholderEntry::add_seen_thread(JavaThread* thread, PlaceholderTable::classloadAction action) { 140 assert_lock_strong(SystemDictionary_lock); 141 SeenThread* threadEntry = new SeenThread(thread); 142 SeenThread* seen = actionToQueue(action); 143 144 if (seen == nullptr) { 145 set_threadQ(threadEntry, action); 146 return; 147 } 148 SeenThread* next; 149 while ((next = seen->next()) != nullptr) { 150 seen = next; 151 } 152 seen->set_next(threadEntry); 153 threadEntry->set_prev(seen); 154 return; 155 } 156 157 bool PlaceholderEntry::check_seen_thread(JavaThread* thread, PlaceholderTable::classloadAction action) { 158 assert_lock_strong(SystemDictionary_lock); 159 SeenThread* threadQ = actionToQueue(action); 160 SeenThread* seen = threadQ; 161 while (seen) { 162 if (thread == seen->thread()) { 163 return true; 164 } 165 seen = seen->next(); 166 } 167 return false; 168 } 169 170 // returns true if seenthreadQ is now empty 171 // Note, caller must ensure probe still exists while holding 172 // SystemDictionary_lock 173 // ignores if cleanup has already been done 174 // if found, deletes SeenThread 175 bool PlaceholderEntry::remove_seen_thread(JavaThread* thread, PlaceholderTable::classloadAction action) { 176 assert_lock_strong(SystemDictionary_lock); 177 SeenThread* threadQ = actionToQueue(action); 178 SeenThread* seen = threadQ; 179 SeenThread* prev = nullptr; 180 while (seen) { 181 if (thread == seen->thread()) { 182 if (prev) { 183 prev->set_next(seen->next()); 184 } else { 185 set_threadQ(seen->next(), action); 186 } 187 if (seen->next()) { 188 seen->next()->set_prev(prev); 189 } 190 delete seen; 191 break; 192 } 193 prev = seen; 194 seen = seen->next(); 195 } 196 return (actionToQueue(action) == nullptr); 197 } 198 199 200 void PlaceholderEntry::set_supername(Symbol* supername) { 201 assert_locked_or_safepoint(SystemDictionary_lock); 202 assert(_supername == nullptr || _supername->refcount() > 1, "must be referenced also by the loader"); 203 _supername = supername; 204 } 205 206 // Placeholder objects represent classes currently being loaded. 207 // All threads examining the placeholder table must hold the 208 // SystemDictionary_lock, so we don't need special precautions 209 // on store ordering here. 210 PlaceholderEntry* add_entry(Symbol* class_name, ClassLoaderData* loader_data, 211 Symbol* supername){ 212 assert_locked_or_safepoint(SystemDictionary_lock); 213 assert(class_name != nullptr, "adding nullptr obj"); 214 215 PlaceholderEntry entry; 216 entry.set_supername(supername); 217 PlaceholderKey key(class_name, loader_data); 218 bool created; 219 PlaceholderEntry* table_copy = _placeholders->put_if_absent(key, entry, &created); 220 assert(created, "better be absent"); 221 return table_copy; 222 } 223 224 // Remove a placeholder object. 225 void remove_entry(Symbol* class_name, ClassLoaderData* loader_data) { 226 assert_locked_or_safepoint(SystemDictionary_lock); 227 228 PlaceholderKey key(class_name, loader_data); 229 _placeholders->remove(key); 230 } 231 232 233 PlaceholderEntry* PlaceholderTable::get_entry(Symbol* class_name, ClassLoaderData* loader_data) { 234 assert_locked_or_safepoint(SystemDictionary_lock); 235 PlaceholderKey key(class_name, loader_data); 236 return _placeholders->get(key); 237 } 238 239 static const char* action_to_string(PlaceholderTable::classloadAction action) { 240 switch (action) { 241 case PlaceholderTable::LOAD_INSTANCE: return "LOAD_INSTANCE"; 242 case PlaceholderTable::LOAD_SUPER: return "LOAD_SUPER"; 243 case PlaceholderTable::DEFINE_CLASS: return "DEFINE_CLASS"; 244 case PlaceholderTable::PRIMITIVE_OBJECT_FIELD: return "PRIMITIVE_OBJECT_FIELD"; 245 } 246 return ""; 247 } 248 249 inline void log(Symbol* name, PlaceholderEntry* entry, const char* function, PlaceholderTable::classloadAction action) { 250 if (log_is_enabled(Debug, class, load, placeholders)) { 251 LogTarget(Debug, class, load, placeholders) lt; 252 ResourceMark rm; 253 LogStream ls(lt); 254 ls.print("entry %s : %s %s ", name->as_C_string(), function, action_to_string(action)); 255 entry->print_on(&ls); 256 } 257 } 258 259 // find_and_add returns probe pointer - old or new 260 // If no entry exists, add a placeholder entry 261 // If entry exists, reuse entry 262 // For both, push SeenThread for classloadAction 263 // If LOAD_SUPER, this is used for circularity detection for instanceklass loading. 264 PlaceholderEntry* PlaceholderTable::find_and_add(Symbol* name, 265 ClassLoaderData* loader_data, 266 classloadAction action, 267 Symbol* supername, 268 JavaThread* thread) { 269 assert(action != LOAD_SUPER || supername != nullptr, "must have a super class name"); 270 PlaceholderEntry* probe = get_entry(name, loader_data); 271 if (probe == nullptr) { 272 // Nothing found, add place holder 273 probe = add_entry(name, loader_data, supername); 274 } else { 275 if (action == LOAD_SUPER) { 276 probe->set_supername(supername); 277 } 278 } 279 probe->add_seen_thread(thread, action); 280 log(name, probe, "find_and_add", action); 281 return probe; 282 } 283 284 void PlaceholderTable::initialize(){ 285 _placeholders = new (mtClass) InternalPlaceholderTable(); 286 } 287 288 289 // placeholder is used to track class loading internal states 290 // superthreadQ tracks class circularity, while loading superclass/superinterface 291 // loadInstanceThreadQ tracks load_instance_class calls 292 // definer() tracks the single thread that owns define token 293 // defineThreadQ tracks waiters on defining thread's results 294 // 1st claimant creates placeholder 295 // find_and_add adds SeenThread entry for appropriate queue 296 // All claimants remove SeenThread after completing action 297 // On removal: if definer and all queues empty, remove entry 298 // Note: you can be in both placeholders and systemDictionary 299 // Therefore - must always check SD first 300 void PlaceholderTable::find_and_remove(Symbol* name, ClassLoaderData* loader_data, 301 classloadAction action, 302 JavaThread* thread) { 303 assert_locked_or_safepoint(SystemDictionary_lock); 304 PlaceholderEntry* probe = get_entry(name, loader_data); 305 assert(probe != nullptr, "must find an entry"); 306 log(name, probe, "find_and_remove", action); 307 probe->remove_seen_thread(thread, action); 308 if (probe->superThreadQ() == nullptr) { 309 probe->set_supername(nullptr); 310 } 311 // If no other threads using this entry, and this thread is not using this entry for other states 312 if ((probe->superThreadQ() == nullptr) && (probe->loadInstanceThreadQ() == nullptr) 313 && (probe->defineThreadQ() == nullptr) && (probe->definer() == nullptr) 314 && (probe->inlineTypeFieldQ() == nullptr)) { 315 remove_entry(name, loader_data); 316 } 317 } 318 319 void PlaceholderKey::print_on(outputStream* st) const { 320 _name->print_value_on(st); 321 st->print(", loader "); 322 _loader_data->print_value_on(st); 323 } 324 325 void PlaceholderEntry::print_on(outputStream* st) const { 326 if (supername() != nullptr) { 327 st->print(", supername "); 328 supername()->print_value_on(st); 329 } 330 if (definer() != nullptr) { 331 st->print(", definer "); 332 definer()->print_value_on(st); 333 } 334 if (instance_klass() != nullptr) { 335 st->print(", InstanceKlass "); 336 instance_klass()->print_value_on(st); 337 } 338 st->cr(); 339 st->print("loadInstanceThreadQ threads:"); 340 loadInstanceThreadQ()->print_action_queue(st); 341 st->cr(); 342 st->print("superThreadQ threads:"); 343 superThreadQ()->print_action_queue(st); 344 st->cr(); 345 st->print("defineThreadQ threads:"); 346 defineThreadQ()->print_action_queue(st); 347 st->cr(); 348 st->print("inlineTypeFieldQ threads:"); 349 inlineTypeFieldQ()->print_action_queue(st); 350 st->cr(); 351 } 352 353 void PlaceholderTable::print_on(outputStream* st) { 354 auto printer = [&] (PlaceholderKey& key, PlaceholderEntry& entry) { 355 st->print("placeholder "); 356 key.print_on(st); 357 entry.print_on(st); 358 return true; 359 }; 360 st->print_cr("Placeholder table (table_size=%d, placeholders=%d)", 361 _placeholders->table_size(), _placeholders->number_of_entries()); 362 _placeholders->iterate(printer); 363 } 364 365 void PlaceholderTable::print() { return print_on(tty); }