1 /*
   2  * Copyright (c) 1997, 2025, 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 "cds/aotClassLocation.hpp"
  26 #include "cds/cdsConfig.hpp"
  27 #include "cds/heapShared.hpp"
  28 #include "classfile/classFileParser.hpp"
  29 #include "classfile/classFileStream.hpp"
  30 #include "classfile/classLoader.hpp"
  31 #include "classfile/classLoaderData.inline.hpp"
  32 #include "classfile/classLoaderDataGraph.inline.hpp"
  33 #include "classfile/classLoaderExt.hpp"
  34 #include "classfile/classLoadInfo.hpp"
  35 #include "classfile/dictionary.hpp"
  36 #include "classfile/javaClasses.inline.hpp"
  37 #include "classfile/klassFactory.hpp"
  38 #include "classfile/loaderConstraints.hpp"
  39 #include "classfile/packageEntry.hpp"
  40 #include "classfile/placeholders.hpp"
  41 #include "classfile/resolutionErrors.hpp"
  42 #include "classfile/stringTable.hpp"
  43 #include "classfile/symbolTable.hpp"
  44 #include "classfile/systemDictionary.hpp"
  45 #include "classfile/vmClasses.hpp"
  46 #include "classfile/vmSymbols.hpp"
  47 #include "gc/shared/gcTraceTime.inline.hpp"
  48 #include "interpreter/bootstrapInfo.hpp"
  49 #include "jfr/jfrEvents.hpp"
  50 #include "jvm.h"
  51 #include "logging/log.hpp"
  52 #include "logging/logStream.hpp"
  53 #include "memory/metaspaceClosure.hpp"
  54 #include "memory/oopFactory.hpp"
  55 #include "memory/resourceArea.hpp"
  56 #include "memory/universe.hpp"
  57 #include "oops/access.inline.hpp"
  58 #include "oops/fieldStreams.inline.hpp"
  59 #include "oops/instanceKlass.hpp"
  60 #include "oops/klass.inline.hpp"
  61 #include "oops/method.inline.hpp"
  62 #include "oops/objArrayKlass.hpp"
  63 #include "oops/objArrayOop.inline.hpp"
  64 #include "oops/oop.inline.hpp"
  65 #include "oops/oop.hpp"
  66 #include "oops/oopHandle.hpp"
  67 #include "oops/oopHandle.inline.hpp"
  68 #include "oops/symbol.hpp"
  69 #include "oops/typeArrayKlass.hpp"
  70 #include "oops/inlineKlass.inline.hpp"
  71 #include "prims/jvmtiExport.hpp"
  72 #include "prims/methodHandles.hpp"
  73 #include "runtime/arguments.hpp"
  74 #include "runtime/atomic.hpp"
  75 #include "runtime/handles.inline.hpp"
  76 #include "runtime/java.hpp"
  77 #include "runtime/javaCalls.hpp"
  78 #include "runtime/mutexLocker.hpp"
  79 #include "runtime/os.hpp"
  80 #include "runtime/sharedRuntime.hpp"
  81 #include "runtime/signature.hpp"
  82 #include "runtime/synchronizer.hpp"
  83 #include "services/classLoadingService.hpp"
  84 #include "services/diagnosticCommand.hpp"
  85 #include "services/finalizerService.hpp"
  86 #include "services/threadService.hpp"
  87 #include "utilities/growableArray.hpp"
  88 #include "utilities/macros.hpp"
  89 #include "utilities/utf8.hpp"
  90 #if INCLUDE_CDS
  91 #include "classfile/systemDictionaryShared.hpp"
  92 #endif
  93 #if INCLUDE_JFR
  94 #include "jfr/jfr.hpp"
  95 #endif
  96 
  97 class InvokeMethodKey : public StackObj {
  98   private:
  99     Symbol* _symbol;
 100     intptr_t _iid;
 101 
 102   public:
 103     InvokeMethodKey(Symbol* symbol, intptr_t iid) :
 104         _symbol(symbol),
 105         _iid(iid) {}
 106 
 107     static bool key_comparison(InvokeMethodKey const &k1, InvokeMethodKey const &k2){
 108         return k1._symbol == k2._symbol && k1._iid == k2._iid;
 109     }
 110 
 111     static unsigned int compute_hash(const InvokeMethodKey &k) {
 112         Symbol* sym = k._symbol;
 113         intptr_t iid = k._iid;
 114         unsigned int hash = (unsigned int) sym -> identity_hash();
 115         return (unsigned int) (hash ^ iid);
 116     }
 117 
 118 };
 119 
 120 using InvokeMethodIntrinsicTable = ResourceHashtable<InvokeMethodKey, Method*, 139, AnyObj::C_HEAP, mtClass,
 121                   InvokeMethodKey::compute_hash, InvokeMethodKey::key_comparison>;
 122 static InvokeMethodIntrinsicTable* _invoke_method_intrinsic_table;
 123 using InvokeMethodTypeTable = ResourceHashtable<SymbolHandle, OopHandle, 139, AnyObj::C_HEAP, mtClass, SymbolHandle::compute_hash>;
 124 static InvokeMethodTypeTable* _invoke_method_type_table;
 125 
 126 OopHandle   SystemDictionary::_java_system_loader;
 127 OopHandle   SystemDictionary::_java_platform_loader;
 128 
 129 // ----------------------------------------------------------------------------
 130 // Java-level SystemLoader and PlatformLoader
 131 oop SystemDictionary::java_system_loader() {
 132   return _java_system_loader.resolve();
 133 }
 134 
 135 oop SystemDictionary::java_platform_loader() {
 136   return _java_platform_loader.resolve();
 137 }
 138 
 139 void SystemDictionary::compute_java_loaders(TRAPS) {
 140   if (_java_platform_loader.is_empty()) {
 141     oop platform_loader = get_platform_class_loader_impl(CHECK);
 142     _java_platform_loader = OopHandle(Universe::vm_global(), platform_loader);
 143   } else {
 144     // It must have been restored from the archived module graph
 145     assert(CDSConfig::is_using_archive(), "must be");
 146     assert(CDSConfig::is_using_full_module_graph(), "must be");
 147     DEBUG_ONLY(
 148       oop platform_loader = get_platform_class_loader_impl(CHECK);
 149       assert(_java_platform_loader.resolve() == platform_loader, "must be");
 150     )
 151  }
 152 
 153   if (_java_system_loader.is_empty()) {
 154     oop system_loader = get_system_class_loader_impl(CHECK);
 155     _java_system_loader = OopHandle(Universe::vm_global(), system_loader);
 156   } else {
 157     // It must have been restored from the archived module graph
 158     assert(CDSConfig::is_using_archive(), "must be");
 159     assert(CDSConfig::is_using_full_module_graph(), "must be");
 160     DEBUG_ONLY(
 161       oop system_loader = get_system_class_loader_impl(CHECK);
 162       assert(_java_system_loader.resolve() == system_loader, "must be");
 163     )
 164   }
 165 }
 166 
 167 oop SystemDictionary::get_system_class_loader_impl(TRAPS) {
 168   JavaValue result(T_OBJECT);
 169   InstanceKlass* class_loader_klass = vmClasses::ClassLoader_klass();
 170   JavaCalls::call_static(&result,
 171                          class_loader_klass,
 172                          vmSymbols::getSystemClassLoader_name(),
 173                          vmSymbols::void_classloader_signature(),
 174                          CHECK_NULL);
 175   return result.get_oop();
 176 }
 177 
 178 oop SystemDictionary::get_platform_class_loader_impl(TRAPS) {
 179   JavaValue result(T_OBJECT);
 180   InstanceKlass* class_loader_klass = vmClasses::ClassLoader_klass();
 181   JavaCalls::call_static(&result,
 182                          class_loader_klass,
 183                          vmSymbols::getPlatformClassLoader_name(),
 184                          vmSymbols::void_classloader_signature(),
 185                          CHECK_NULL);
 186   return result.get_oop();
 187 }
 188 
 189 // Helper function
 190 inline ClassLoaderData* class_loader_data(Handle class_loader) {
 191   return ClassLoaderData::class_loader_data(class_loader());
 192 }
 193 
 194 static void add_wrapper_class(JavaThread* current, ClassLoaderData* cld, Symbol* classname) {
 195   InstanceKlass* ik = SystemDictionary::find_instance_klass(current, classname, Handle(current, nullptr));
 196   assert(ik != nullptr, "Must exist");
 197   SystemDictionary::add_to_initiating_loader(current, ik, cld);
 198 }
 199 
 200 static void add_wrapper_classes(ClassLoaderData* cld) {
 201   MonitorLocker mu1(SystemDictionary_lock);
 202   JavaThread* current = JavaThread::current();
 203   add_wrapper_class(current, cld, vmSymbols::java_lang_Boolean());
 204   add_wrapper_class(current, cld, vmSymbols::java_lang_Byte());
 205   add_wrapper_class(current, cld, vmSymbols::java_lang_Character());
 206   add_wrapper_class(current, cld, vmSymbols::java_lang_Short());
 207   add_wrapper_class(current, cld, vmSymbols::java_lang_Integer());
 208   add_wrapper_class(current, cld, vmSymbols::java_lang_Long());
 209   add_wrapper_class(current, cld, vmSymbols::java_lang_Float());
 210   add_wrapper_class(current, cld, vmSymbols::java_lang_Double());
 211 }
 212 
 213 ClassLoaderData* SystemDictionary::register_loader(Handle class_loader, bool create_mirror_cld) {
 214   if (create_mirror_cld) {
 215     // Add a new class loader data to the graph.
 216     return ClassLoaderDataGraph::add(class_loader, true);
 217   } else {
 218     if (class_loader() == nullptr) {
 219       return ClassLoaderData::the_null_class_loader_data();
 220     } else {
 221       ClassLoaderData* cld = ClassLoaderDataGraph::find_or_create(class_loader);
 222       add_wrapper_classes(cld);
 223       return cld;
 224     }
 225   }
 226 }
 227 
 228 void SystemDictionary::set_system_loader(ClassLoaderData *cld) {
 229   assert(_java_system_loader.is_empty(), "already set!");
 230   _java_system_loader = cld->class_loader_handle();
 231 
 232 }
 233 
 234 void SystemDictionary::set_platform_loader(ClassLoaderData *cld) {
 235   assert(_java_platform_loader.is_empty(), "already set!");
 236   _java_platform_loader = cld->class_loader_handle();
 237 }
 238 
 239 // ----------------------------------------------------------------------------
 240 // Parallel class loading check
 241 
 242 static bool is_parallelCapable(Handle class_loader) {
 243   if (class_loader.is_null()) return true;
 244   return java_lang_ClassLoader::parallelCapable(class_loader());
 245 }
 246 // ----------------------------------------------------------------------------
 247 // ParallelDefineClass flag does not apply to bootclass loader
 248 static bool is_parallelDefine(Handle class_loader) {
 249    if (class_loader.is_null()) return false;
 250    if (AllowParallelDefineClass && java_lang_ClassLoader::parallelCapable(class_loader())) {
 251      return true;
 252    }
 253    return false;
 254 }
 255 
 256 // Returns true if the passed class loader is the builtin application class loader
 257 // or a custom system class loader. A customer system class loader can be
 258 // specified via -Djava.system.class.loader.
 259 bool SystemDictionary::is_system_class_loader(oop class_loader) {
 260   if (class_loader == nullptr) {
 261     return false;
 262   }
 263   return (class_loader->klass() == vmClasses::jdk_internal_loader_ClassLoaders_AppClassLoader_klass() ||
 264          class_loader == _java_system_loader.peek());
 265 }
 266 
 267 // Returns true if the passed class loader is the platform class loader.
 268 bool SystemDictionary::is_platform_class_loader(oop class_loader) {
 269   if (class_loader == nullptr) {
 270     return false;
 271   }
 272   return (class_loader->klass() == vmClasses::jdk_internal_loader_ClassLoaders_PlatformClassLoader_klass());
 273 }
 274 
 275 Handle SystemDictionary::get_loader_lock_or_null(Handle class_loader) {
 276   // If class_loader is null or parallelCapable, the JVM doesn't acquire a lock while loading.
 277   if (is_parallelCapable(class_loader)) {
 278     return Handle();
 279   } else {
 280     return class_loader;
 281   }
 282 }
 283 
 284 // ----------------------------------------------------------------------------
 285 // Resolving of classes
 286 
 287 Symbol* SystemDictionary::class_name_symbol(const char* name, Symbol* exception, TRAPS) {
 288   if (name == nullptr) {
 289     THROW_MSG_NULL(exception, "No class name given");
 290   }
 291   size_t name_len = strlen(name);
 292   if (name_len > static_cast<size_t>(Symbol::max_length())) {
 293     // It's impossible to create this class;  the name cannot fit
 294     // into the constant pool. If necessary report an abridged name
 295     // in the exception message.
 296     if (name_len > static_cast<size_t>(MaxStringPrintSize)) {
 297       Exceptions::fthrow(THREAD_AND_LOCATION, exception,
 298                          "Class name exceeds maximum length of %d: %.*s ... (%zu characters omitted) ... %.*s",
 299                          Symbol::max_length(),
 300                          MaxStringPrintSize / 2,
 301                          name,
 302                          name_len - 2 * (MaxStringPrintSize / 2), // allows for odd value
 303                          MaxStringPrintSize / 2,
 304                          name + name_len - MaxStringPrintSize / 2);
 305     }
 306     else {
 307       Exceptions::fthrow(THREAD_AND_LOCATION, exception,
 308                          "Class name exceeds maximum length of %d: %s",
 309                          Symbol::max_length(),
 310                          name);
 311     }
 312     return nullptr;
 313   }
 314   // Callers should ensure that the name is never an illegal UTF8 string.
 315   assert(UTF8::is_legal_utf8((const unsigned char*)name, name_len, false),
 316          "Class name is not a valid utf8 string.");
 317 
 318   // Make a new symbol for the class name.
 319   return SymbolTable::new_symbol(name);
 320 }
 321 
 322 #ifdef ASSERT
 323 // Used to verify that class loading succeeded in adding k to the dictionary.
 324 static void verify_dictionary_entry(Symbol* class_name, InstanceKlass* k) {
 325   MutexLocker mu(SystemDictionary_lock);
 326   ClassLoaderData* loader_data = k->class_loader_data();
 327   Dictionary* dictionary = loader_data->dictionary();
 328   assert(class_name == k->name(), "Must be the same");
 329   InstanceKlass* kk = dictionary->find_class(JavaThread::current(), class_name);
 330   assert(kk == k, "should be present in dictionary");
 331 }
 332 #endif
 333 
 334 static void handle_resolution_exception(Symbol* class_name, bool throw_error, TRAPS) {
 335   if (HAS_PENDING_EXCEPTION) {
 336     // If we have a pending exception we forward it to the caller, unless throw_error is true,
 337     // in which case we have to check whether the pending exception is a ClassNotFoundException,
 338     // and convert it to a NoClassDefFoundError and chain the original ClassNotFoundException.
 339     if (throw_error && PENDING_EXCEPTION->is_a(vmClasses::ClassNotFoundException_klass())) {
 340       ResourceMark rm(THREAD);
 341       Handle e(THREAD, PENDING_EXCEPTION);
 342       CLEAR_PENDING_EXCEPTION;
 343       THROW_MSG_CAUSE(vmSymbols::java_lang_NoClassDefFoundError(), class_name->as_C_string(), e);
 344     } else {
 345       return; // the caller will throw the incoming exception
 346     }
 347   }
 348   // If the class is not found, ie, caller has checked that klass is null, throw the appropriate
 349   // error or exception depending on the value of throw_error.
 350   ResourceMark rm(THREAD);
 351   if (throw_error) {
 352     THROW_MSG(vmSymbols::java_lang_NoClassDefFoundError(), class_name->as_C_string());
 353   } else {
 354     THROW_MSG(vmSymbols::java_lang_ClassNotFoundException(), class_name->as_C_string());
 355   }
 356 }
 357 
 358 // Forwards to resolve_or_null
 359 
 360 Klass* SystemDictionary::resolve_or_fail(Symbol* class_name, Handle class_loader,
 361                                          bool throw_error, TRAPS) {
 362   Klass* klass = resolve_or_null(class_name, class_loader, THREAD);
 363   // Check for pending exception or null klass, and throw exception
 364   if (HAS_PENDING_EXCEPTION || klass == nullptr) {
 365     handle_resolution_exception(class_name, throw_error, CHECK_NULL);
 366   }
 367   return klass;
 368 }
 369 
 370 // Forwards to resolve_array_class_or_null or resolve_instance_class_or_null
 371 
 372 Klass* SystemDictionary::resolve_or_null(Symbol* class_name, Handle class_loader, TRAPS) {
 373   if (Signature::is_array(class_name)) {
 374     return resolve_array_class_or_null(class_name, class_loader, THREAD);
 375   } else {
 376     assert(class_name != nullptr && !Signature::is_array(class_name), "must be");
 377     if (Signature::has_envelope(class_name)) {
 378       ResourceMark rm(THREAD);
 379       // Ignore wrapping L and ; (and Q and ; for value types).
 380       TempNewSymbol name = SymbolTable::new_symbol(class_name->as_C_string() + 1,
 381                                                    class_name->utf8_length() - 2);
 382       return resolve_instance_class_or_null(name, class_loader, THREAD);
 383     } else {
 384       return resolve_instance_class_or_null(class_name, class_loader, THREAD);
 385     }
 386   }
 387 }
 388 
 389 // Forwards to resolve_instance_class_or_null
 390 
 391 Klass* SystemDictionary::resolve_array_class_or_null(Symbol* class_name,
 392                                                      Handle class_loader,
 393                                                      TRAPS) {
 394   assert(Signature::is_array(class_name), "must be array");
 395   ResourceMark rm(THREAD);
 396   SignatureStream ss(class_name, false);
 397   int ndims = ss.skip_array_prefix();  // skip all '['s
 398   Klass* k = nullptr;
 399   BasicType t = ss.type();
 400   if (ss.has_envelope()) {
 401     Symbol* obj_class = ss.as_symbol();
 402     k = SystemDictionary::resolve_instance_class_or_null(obj_class,
 403                                                          class_loader,
 404                                                          CHECK_NULL);
 405     if (k != nullptr) {
 406       k = k->array_klass(ndims, CHECK_NULL);
 407     }
 408   } else {
 409     k = Universe::typeArrayKlass(t);
 410     k = k->array_klass(ndims, CHECK_NULL);
 411   }
 412   return k;
 413 }
 414 
 415 static inline void log_circularity_error(Symbol* name, PlaceholderEntry* probe) {
 416   LogTarget(Debug, class, load, placeholders) lt;
 417   if (lt.is_enabled()) {
 418     ResourceMark rm;
 419     LogStream ls(lt);
 420     ls.print("ClassCircularityError detected for placeholder entry %s", name->as_C_string());
 421     probe->print_on(&ls);
 422     ls.cr();
 423   }
 424 }
 425 
 426 // Must be called for any superclass or superinterface resolution
 427 // during class definition to allow class circularity checking
 428 // superinterface callers:
 429 //    parse_interfaces - from defineClass
 430 // superclass callers:
 431 //   ClassFileParser - from defineClass
 432 //   load_shared_class - while loading a class from shared archive
 433 //   resolve_instance_class_or_null:
 434 //     via: handle_parallel_super_load
 435 //      when resolving a class that has an existing placeholder with
 436 //      a saved superclass [i.e. a defineClass is currently in progress]
 437 //      If another thread is trying to resolve the class, it must do
 438 //      superclass checks on its own thread to catch class circularity and
 439 //      to avoid deadlock.
 440 //
 441 // resolve_with_circularity_detection adds a DETECT_CIRCULARITY placeholder to the placeholder table before calling
 442 // resolve_instance_class_or_null. ClassCircularityError is detected when a DETECT_CIRCULARITY or LOAD_INSTANCE
 443 // placeholder for the same thread, class, classloader is found.
 444 // This can be seen with logging option: -Xlog:class+load+placeholders=debug.
 445 //
 446 InstanceKlass* SystemDictionary::resolve_with_circularity_detection(Symbol* class_name,
 447                                                                     Symbol* next_name,
 448                                                                     Handle class_loader,
 449                                                                     bool is_superclass,
 450                                                                     TRAPS) {
 451 
 452   assert(next_name != nullptr, "null superclass for resolving");
 453   assert(!Signature::is_array(next_name), "invalid superclass name");
 454 
 455   ClassLoaderData* loader_data = class_loader_data(class_loader);
 456 
 457   if (is_superclass) {
 458     InstanceKlass* klassk = loader_data->dictionary()->find_class(THREAD, class_name);
 459     if (klassk != nullptr) {
 460       // We can come here for two reasons:
 461       // (a) RedefineClasses -- the class is already loaded
 462       // (b) Rarely, the class might have been loaded by a parallel thread
 463       // We can do a quick check against the already assigned superclass's name and loader.
 464       InstanceKlass* superk = klassk->java_super();
 465       if (superk != nullptr &&
 466           superk->name() == next_name &&
 467           superk->class_loader() == class_loader()) {
 468         return superk;
 469       }
 470     }
 471   }
 472 
 473   // can't throw error holding a lock
 474   bool throw_circularity_error = false;
 475   {
 476     MutexLocker mu(THREAD, SystemDictionary_lock);
 477 
 478     // Must check ClassCircularity before resolving next_name (superclass or interface).
 479     PlaceholderEntry* probe = PlaceholderTable::get_entry(class_name, loader_data);
 480     if (probe != nullptr && probe->check_seen_thread(THREAD, PlaceholderTable::DETECT_CIRCULARITY)) {
 481         log_circularity_error(class_name, probe);
 482         throw_circularity_error = true;
 483     }
 484 
 485     // Make sure there's a placeholder for the class_name before resolving.
 486     // This is used as a claim that this thread is currently loading superclass/classloader
 487     // and for ClassCircularity checks.
 488     if (!throw_circularity_error) {
 489       // Be careful not to exit resolve_with_circularity_detection without removing this placeholder.
 490       PlaceholderEntry* newprobe = PlaceholderTable::find_and_add(class_name,
 491                                                                   loader_data,
 492                                                                   PlaceholderTable::DETECT_CIRCULARITY,
 493                                                                   next_name, THREAD);
 494     }
 495   }
 496 
 497   if (throw_circularity_error) {
 498       ResourceMark rm(THREAD);
 499       THROW_MSG_NULL(vmSymbols::java_lang_ClassCircularityError(), class_name->as_C_string());
 500   }
 501 
 502   // Resolve the superclass or superinterface, check results on return
 503   InstanceKlass* superk =
 504     SystemDictionary::resolve_instance_class_or_null(next_name,
 505                                                      class_loader,
 506                                                      THREAD);
 507 
 508   // Clean up placeholder entry.
 509   {
 510     MutexLocker mu(THREAD, SystemDictionary_lock);
 511     PlaceholderTable::find_and_remove(class_name, loader_data, PlaceholderTable::DETECT_CIRCULARITY, THREAD);
 512     SystemDictionary_lock->notify_all();
 513   }
 514 
 515   // Check for pending exception or null superk, and throw exception
 516   if (HAS_PENDING_EXCEPTION || superk == nullptr) {
 517     handle_resolution_exception(next_name, true, CHECK_NULL);
 518   }
 519 
 520   return superk;
 521 }
 522 
 523 // If the class in is in the placeholder table, class loading is in progress.
 524 // For cases where the application changes threads to load classes, it
 525 // is critical to ClassCircularity detection that we try loading
 526 // the superclass on the new thread internally, so we do parallel
 527 // superclass loading here.  This avoids deadlock for ClassCircularity
 528 // detection for parallelCapable class loaders that lock on a per-class lock.
 529 static void handle_parallel_super_load(Symbol* name,
 530                                        Symbol* superclassname,
 531                                        Handle class_loader,
 532                                        TRAPS) {
 533 
 534   // The result superk is not used; resolve_with_circularity_detection is called for circularity check only.
 535   // This passes false to is_superclass to skip doing the unlikely optimization.
 536   Klass* superk = SystemDictionary::resolve_with_circularity_detection(name,
 537                                                                        superclassname,
 538                                                                        class_loader,
 539                                                                        false,
 540                                                                        CHECK);
 541 }
 542 
 543 // Bootstrap and non-parallel capable class loaders use the LOAD_INSTANCE placeholder to
 544 // wait for parallel class loading and/or to check for circularity error for Xcomp when loading.
 545 static bool needs_load_placeholder(Handle class_loader) {
 546   return class_loader.is_null() || !is_parallelCapable(class_loader);
 547 }
 548 
 549 // Check for other threads loading this class either to throw CCE or wait in the case of the boot loader.
 550 static InstanceKlass* handle_parallel_loading(JavaThread* current,
 551                                               Symbol* name,
 552                                               ClassLoaderData* loader_data,
 553                                               bool must_wait_for_class_loading,
 554                                               bool* throw_circularity_error) {
 555   PlaceholderEntry* oldprobe = PlaceholderTable::get_entry(name, loader_data);
 556   if (oldprobe != nullptr) {
 557     // -Xcomp calls load_signature_classes which might result in loading
 558     // a class that's already in the process of loading, so we detect CCE here also.
 559     // Only need check_seen_thread once, not on each loop
 560     if (oldprobe->check_seen_thread(current, PlaceholderTable::LOAD_INSTANCE)) {
 561       log_circularity_error(name, oldprobe);
 562       *throw_circularity_error = true;
 563       return nullptr;
 564     } else if (must_wait_for_class_loading) {
 565       // Wait until the first thread has finished loading this class. Also wait until all the
 566       // threads trying to load its superclass have removed their placeholders.
 567       while (oldprobe != nullptr &&
 568              (oldprobe->instance_load_in_progress() || oldprobe->circularity_detection_in_progress())) {
 569 
 570         // LOAD_INSTANCE placeholders are used to implement parallel capable class loading
 571         // for the bootclass loader.
 572         SystemDictionary_lock->wait();
 573 
 574         // Check if classloading completed while we were waiting
 575         InstanceKlass* check = loader_data->dictionary()->find_class(current, name);
 576         if (check != nullptr) {
 577           // Klass is already loaded, so just return it
 578           return check;
 579         }
 580         // check if other thread failed to load and cleaned up
 581         oldprobe = PlaceholderTable::get_entry(name, loader_data);
 582       }
 583     }
 584   }
 585   return nullptr;
 586 }
 587 
 588 void SystemDictionary::post_class_load_event(EventClassLoad* event, const InstanceKlass* k, const ClassLoaderData* init_cld) {
 589   assert(event != nullptr, "invariant");
 590   assert(k != nullptr, "invariant");
 591   event->set_loadedClass(k);
 592   event->set_definingClassLoader(k->class_loader_data());
 593   event->set_initiatingClassLoader(init_cld);
 594   event->commit();
 595 }
 596 
 597 // SystemDictionary::resolve_instance_class_or_null is the main function for class name resolution.
 598 // After checking if the InstanceKlass already exists, it checks for ClassCircularityError and
 599 // whether the thread must wait for loading in parallel.  It eventually calls load_instance_class,
 600 // which will load the class via the bootstrap loader or call ClassLoader.loadClass().
 601 // This can return null, an exception or an InstanceKlass.
 602 InstanceKlass* SystemDictionary::resolve_instance_class_or_null(Symbol* name,
 603                                                                 Handle class_loader,
 604                                                                 TRAPS) {
 605   // name must be in the form of "java/lang/Object" -- cannot be "Ljava/lang/Object;"
 606   DEBUG_ONLY(ResourceMark rm(THREAD));
 607   assert(name != nullptr && !Signature::is_array(name) &&
 608          !Signature::has_envelope(name), "invalid class name: %s", name == nullptr ? "nullptr" : name->as_C_string());
 609 
 610   EventClassLoad class_load_start_event;
 611 
 612   HandleMark hm(THREAD);
 613 
 614   ClassLoaderData* loader_data = register_loader(class_loader);
 615   Dictionary* dictionary = loader_data->dictionary();
 616 
 617   // Do lookup to see if class already exists.
 618   InstanceKlass* probe = dictionary->find_class(THREAD, name);
 619   if (probe != nullptr) return probe;
 620 
 621   // Non-bootstrap class loaders will call out to class loader and
 622   // define via jvm/jni_DefineClass which will acquire the
 623   // class loader object lock to protect against multiple threads
 624   // defining the class in parallel by accident.
 625   // This lock must be acquired here so the waiter will find
 626   // any successful result in the SystemDictionary and not attempt
 627   // the define.
 628   // ParallelCapable class loaders and the bootstrap classloader
 629   // do not acquire lock here.
 630   Handle lockObject = get_loader_lock_or_null(class_loader);
 631   ObjectLocker ol(lockObject, THREAD);
 632 
 633   bool circularity_detection_in_progress  = false;
 634   InstanceKlass* loaded_class = nullptr;
 635   SymbolHandle superclassname; // Keep alive while loading in parallel thread.
 636 
 637   guarantee(THREAD->can_call_java(),
 638          "can not load classes with compiler thread: class=%s, classloader=%s",
 639          name->as_C_string(),
 640          class_loader.is_null() ? "null" : class_loader->klass()->name()->as_C_string());
 641 
 642   // Check again (after locking) if the class already exists in SystemDictionary
 643   {
 644     MutexLocker mu(THREAD, SystemDictionary_lock);
 645     InstanceKlass* check = dictionary->find_class(THREAD, name);
 646     if (check != nullptr) {
 647       // InstanceKlass is already loaded, but we still need to check protection domain below.
 648       loaded_class = check;
 649     } else {
 650       PlaceholderEntry* placeholder = PlaceholderTable::get_entry(name, loader_data);
 651       if (placeholder != nullptr && placeholder->circularity_detection_in_progress()) {
 652          circularity_detection_in_progress = true;
 653          superclassname = placeholder->next_klass_name();
 654          assert(superclassname != nullptr, "superclass has to have a name");
 655       }
 656     }
 657   }
 658 
 659   // If the class is in the placeholder table with super_class set,
 660   // handle superclass loading in progress.
 661   if (circularity_detection_in_progress) {
 662     handle_parallel_super_load(name, superclassname,
 663                                class_loader,
 664                                CHECK_NULL);
 665   }
 666 
 667   bool throw_circularity_error = false;
 668   if (loaded_class == nullptr) {
 669     bool load_placeholder_added = false;
 670 
 671     // Add placeholder entry to record loading instance class
 672     // case 1. Bootstrap classloader
 673     //    This classloader supports parallelism at the classloader level
 674     //    but only allows a single thread to load a class/classloader pair.
 675     //    The LOAD_INSTANCE placeholder is the mechanism for mutual exclusion.
 676     // case 2. parallelCapable user level classloaders
 677     //    These class loaders lock a per-class object lock when ClassLoader.loadClass()
 678     //    is called. A LOAD_INSTANCE placeholder isn't used for mutual exclusion.
 679     // case 3. traditional classloaders that rely on the classloader object lock
 680     //    There should be no need for need for LOAD_INSTANCE for mutual exclusion,
 681     //    except the LOAD_INSTANCE placeholder is used to detect CCE for -Xcomp.
 682     //    TODO: should also be used to detect CCE for parallel capable class loaders but it's not.
 683     {
 684       MutexLocker mu(THREAD, SystemDictionary_lock);
 685       if (needs_load_placeholder(class_loader)) {
 686         loaded_class = handle_parallel_loading(THREAD,
 687                                                name,
 688                                                loader_data,
 689                                                class_loader.is_null(),
 690                                                &throw_circularity_error);
 691       }
 692 
 693       // Recheck if the class has been loaded for all class loader cases and
 694       // add a LOAD_INSTANCE placeholder while holding the SystemDictionary_lock.
 695       if (!throw_circularity_error && loaded_class == nullptr) {
 696         InstanceKlass* check = dictionary->find_class(THREAD, name);
 697         if (check != nullptr) {
 698           loaded_class = check;
 699         } else if (needs_load_placeholder(class_loader)) {
 700           // Add the LOAD_INSTANCE token. Threads will wait on loading to complete for this thread.
 701           PlaceholderEntry* newprobe = PlaceholderTable::find_and_add(name, loader_data,
 702                                                                       PlaceholderTable::LOAD_INSTANCE,
 703                                                                       nullptr,
 704                                                                       THREAD);
 705           load_placeholder_added = true;
 706         }
 707       }
 708     }
 709 
 710     // Must throw error outside of owning lock
 711     if (throw_circularity_error) {
 712       assert(!HAS_PENDING_EXCEPTION && !load_placeholder_added, "circularity error cleanup");
 713       ResourceMark rm(THREAD);
 714       THROW_MSG_NULL(vmSymbols::java_lang_ClassCircularityError(), name->as_C_string());
 715     }
 716 
 717     // Be careful when modifying this code: once you have run
 718     // PlaceholderTable::find_and_add(PlaceholderTable::LOAD_INSTANCE),
 719     // you need to find_and_remove it before returning.
 720     // So be careful to not exit with a CHECK_ macro between these calls.
 721 
 722     if (loaded_class == nullptr) {
 723       // Do actual loading
 724       loaded_class = load_instance_class(name, class_loader, THREAD);
 725     }
 726 
 727     if (load_placeholder_added) {
 728       // clean up placeholder entries for LOAD_INSTANCE success or error
 729       // This brackets the SystemDictionary updates for both defining
 730       // and initiating loaders
 731       MutexLocker mu(THREAD, SystemDictionary_lock);
 732       PlaceholderTable::find_and_remove(name, loader_data, PlaceholderTable::LOAD_INSTANCE, THREAD);
 733       SystemDictionary_lock->notify_all();
 734     }
 735   }
 736 
 737   if (HAS_PENDING_EXCEPTION || loaded_class == nullptr) {
 738     return nullptr;
 739   }
 740 
 741   if (class_load_start_event.should_commit()) {
 742     post_class_load_event(&class_load_start_event, loaded_class, loader_data);
 743   }
 744 
 745   // Make sure we have the right class in the dictionary
 746   DEBUG_ONLY(verify_dictionary_entry(name, loaded_class));
 747 
 748   return loaded_class;
 749 }
 750 
 751 
 752 // This routine does not lock the system dictionary.
 753 //
 754 // Since readers don't hold a lock, we must make sure that system
 755 // dictionary entries are added to in a safe way (all links must
 756 // be updated in an MT-safe manner). All entries are removed during class
 757 // unloading, when this class loader is no longer referenced.
 758 //
 759 // Callers should be aware that an entry could be added just after
 760 // Dictionary is read here, so the caller will not see
 761 // the new entry.
 762 
 763 InstanceKlass* SystemDictionary::find_instance_klass(Thread* current,
 764                                                      Symbol* class_name,
 765                                                      Handle class_loader) {
 766 
 767   ClassLoaderData* loader_data = ClassLoaderData::class_loader_data_or_null(class_loader());
 768   if (loader_data == nullptr) {
 769     // If the ClassLoaderData has not been setup,
 770     // then the class loader has no entries in the dictionary.
 771     return nullptr;
 772   }
 773 
 774   Dictionary* dictionary = loader_data->dictionary();
 775   return dictionary->find_class(current, class_name);
 776 }
 777 
 778 // Look for a loaded instance or array klass by name.  Do not do any loading.
 779 // return null in case of error.
 780 Klass* SystemDictionary::find_instance_or_array_klass(Thread* current,
 781                                                       Symbol* class_name,
 782                                                       Handle class_loader) {
 783   Klass* k = nullptr;
 784   assert(class_name != nullptr, "class name must be non nullptr");
 785 
 786   if (Signature::is_array(class_name)) {
 787     // The name refers to an array.  Parse the name.
 788     // dimension and object_key in FieldArrayInfo are assigned as a
 789     // side-effect of this call
 790     SignatureStream ss(class_name, false);
 791     int ndims = ss.skip_array_prefix();  // skip all '['s
 792     BasicType t = ss.type();
 793     if (t != T_OBJECT) {
 794       k = Universe::typeArrayKlass(t);
 795     } else {
 796       k = SystemDictionary::find_instance_klass(current, ss.as_symbol(), class_loader);
 797     }
 798     if (k != nullptr) {
 799       k = k->array_klass_or_null(ndims);
 800     }
 801   } else {
 802     k = find_instance_klass(current, class_name, class_loader);
 803   }
 804   return k;
 805 }
 806 
 807 // Note: this method is much like resolve_class_from_stream, but
 808 // does not publish the classes in the SystemDictionary.
 809 // Handles Lookup.defineClass hidden.
 810 InstanceKlass* SystemDictionary::resolve_hidden_class_from_stream(
 811                                                      ClassFileStream* st,
 812                                                      Symbol* class_name,
 813                                                      Handle class_loader,
 814                                                      const ClassLoadInfo& cl_info,
 815                                                      TRAPS) {
 816 
 817   EventClassLoad class_load_start_event;
 818   ClassLoaderData* loader_data;
 819 
 820   // - for hidden classes that are not strong: create a new CLD that has a class holder and
 821   //                                           whose loader is the Lookup class's loader.
 822   // - for hidden class: add the class to the Lookup class's loader's CLD.
 823   assert (cl_info.is_hidden(), "only used for hidden classes");
 824   bool create_mirror_cld = !cl_info.is_strong_hidden();
 825   loader_data = register_loader(class_loader, create_mirror_cld);
 826 
 827   assert(st != nullptr, "invariant");
 828 
 829   // Parse stream and create a klass.
 830   InstanceKlass* k = KlassFactory::create_from_stream(st,
 831                                                       class_name,
 832                                                       loader_data,
 833                                                       cl_info,
 834                                                       CHECK_NULL);
 835   assert(k != nullptr, "no klass created");
 836 
 837   // Hidden classes that are not strong must update ClassLoaderData holder
 838   // so that they can be unloaded when the mirror is no longer referenced.
 839   if (!cl_info.is_strong_hidden()) {
 840     k->class_loader_data()->initialize_holder(Handle(THREAD, k->java_mirror()));
 841   }
 842 
 843   // Add to class hierarchy, and do possible deoptimizations.
 844   k->add_to_hierarchy(THREAD);
 845   // But, do not add to dictionary.
 846 
 847   k->link_class(CHECK_NULL);
 848 
 849   // notify jvmti
 850   if (JvmtiExport::should_post_class_load()) {
 851     JvmtiExport::post_class_load(THREAD, k);
 852   }
 853   if (class_load_start_event.should_commit()) {
 854     post_class_load_event(&class_load_start_event, k, loader_data);
 855   }
 856 
 857   return k;
 858 }
 859 
 860 // Add a klass to the system from a stream (called by jni_DefineClass and
 861 // JVM_DefineClass).
 862 // Note: class_name can be null. In that case we do not know the name of
 863 // the class until we have parsed the stream.
 864 // This function either returns an InstanceKlass or throws an exception.  It does
 865 // not return null without a pending exception.
 866 InstanceKlass* SystemDictionary::resolve_class_from_stream(
 867                                                      ClassFileStream* st,
 868                                                      Symbol* class_name,
 869                                                      Handle class_loader,
 870                                                      const ClassLoadInfo& cl_info,
 871                                                      TRAPS) {
 872 
 873   HandleMark hm(THREAD);
 874 
 875   ClassLoaderData* loader_data = register_loader(class_loader);
 876 
 877   // Classloaders that support parallelism, e.g. bootstrap classloader,
 878   // do not acquire lock here
 879   Handle lockObject = get_loader_lock_or_null(class_loader);
 880   ObjectLocker ol(lockObject, THREAD);
 881 
 882   // Parse the stream and create a klass.
 883   // Note that we do this even though this klass might
 884   // already be present in the SystemDictionary, otherwise we would not
 885   // throw potential ClassFormatErrors.
 886  InstanceKlass* k = nullptr;
 887 
 888 #if INCLUDE_CDS
 889   if (!CDSConfig::is_dumping_static_archive()) {
 890     k = SystemDictionaryShared::lookup_from_stream(class_name,
 891                                                    class_loader,
 892                                                    cl_info.protection_domain(),
 893                                                    st,
 894                                                    CHECK_NULL);
 895   }
 896 #endif
 897 
 898   if (k == nullptr) {
 899     k = KlassFactory::create_from_stream(st, class_name, loader_data, cl_info, CHECK_NULL);
 900   }
 901 
 902   assert(k != nullptr, "no klass created");
 903   Symbol* h_name = k->name();
 904   assert(class_name == nullptr || class_name == h_name, "name mismatch");
 905 
 906   // Add class just loaded
 907   // If a class loader supports parallel classloading, handle parallel define requests.
 908   // find_or_define_instance_class may return a different InstanceKlass,
 909   // in which case the old k would be deallocated
 910   if (is_parallelCapable(class_loader)) {
 911     k = find_or_define_instance_class(h_name, class_loader, k, CHECK_NULL);
 912   } else {
 913     define_instance_class(k, class_loader, THREAD);
 914 
 915     // If defining the class throws an exception register 'k' for cleanup.
 916     if (HAS_PENDING_EXCEPTION) {
 917       assert(k != nullptr, "Must have an instance klass here!");
 918       loader_data->add_to_deallocate_list(k);
 919       return nullptr;
 920     }
 921   }
 922 
 923   // Make sure we have an entry in the SystemDictionary on success
 924   DEBUG_ONLY(verify_dictionary_entry(h_name, k));
 925 
 926   return k;
 927 }
 928 
 929 InstanceKlass* SystemDictionary::resolve_from_stream(ClassFileStream* st,
 930                                                      Symbol* class_name,
 931                                                      Handle class_loader,
 932                                                      const ClassLoadInfo& cl_info,
 933                                                      TRAPS) {
 934   if (cl_info.is_hidden()) {
 935     return resolve_hidden_class_from_stream(st, class_name, class_loader, cl_info, CHECK_NULL);
 936   } else {
 937     return resolve_class_from_stream(st, class_name, class_loader, cl_info, CHECK_NULL);
 938   }
 939 }
 940 
 941 
 942 #if INCLUDE_CDS
 943 // Check if a shared class can be loaded by the specific classloader.
 944 bool SystemDictionary::is_shared_class_visible(Symbol* class_name,
 945                                                InstanceKlass* ik,
 946                                                PackageEntry* pkg_entry,
 947                                                Handle class_loader) {
 948   assert(!CDSConfig::module_patching_disables_cds(), "Cannot use CDS");
 949 
 950   // (1) Check if we are loading into the same loader as in dump time.
 951 
 952   if (ik->is_shared_boot_class()) {
 953     if (class_loader() != nullptr) {
 954       return false;
 955     }
 956   } else if (ik->is_shared_platform_class()) {
 957     if (class_loader() != java_platform_loader()) {
 958       return false;
 959     }
 960   } else if (ik->is_shared_app_class()) {
 961     if (class_loader() != java_system_loader()) {
 962       return false;
 963     }
 964   } else {
 965     // ik was loaded by a custom loader during dump time
 966     if (class_loader_data(class_loader)->is_builtin_class_loader_data()) {
 967       return false;
 968     } else {
 969       return true;
 970     }
 971   }
 972 
 973   // (2) Check if we are loading into the same module from the same location as in dump time.
 974 
 975   if (CDSConfig::is_using_optimized_module_handling()) {
 976     // Class visibility has not changed between dump time and run time, so a class
 977     // that was visible (and thus archived) during dump time is always visible during runtime.
 978     assert(SystemDictionary::is_shared_class_visible_impl(class_name, ik, pkg_entry, class_loader),
 979            "visibility cannot change between dump time and runtime");
 980     return true;
 981   }
 982   return is_shared_class_visible_impl(class_name, ik, pkg_entry, class_loader);
 983 }
 984 
 985 bool SystemDictionary::is_shared_class_visible_impl(Symbol* class_name,
 986                                                     InstanceKlass* ik,
 987                                                     PackageEntry* pkg_entry,
 988                                                     Handle class_loader) {
 989   int scp_index = ik->shared_classpath_index();
 990   assert(!ik->is_shared_unregistered_class(), "this function should be called for built-in classes only");
 991   assert(scp_index >= 0, "must be");
 992   const AOTClassLocation* cl = AOTClassLocationConfig::runtime()->class_location_at(scp_index);
 993   if (!Universe::is_module_initialized()) {
 994     assert(cl != nullptr, "must be");
 995     // At this point, no modules have been defined yet. KlassSubGraphInfo::check_allowed_klass()
 996     // has restricted the classes can be loaded at this step to be only:
 997     // [1] cs->is_modules_image(): classes in java.base, or,
 998     // [2] HeapShared::is_a_test_class_in_unnamed_module(ik): classes in bootstrap/unnamed module
 999     assert(cl->is_modules_image() || HeapShared::is_a_test_class_in_unnamed_module(ik),
1000            "only these classes can be loaded before the module system is initialized");
1001     assert(class_loader.is_null(), "sanity");
1002     return true;
1003   }
1004 
1005   if (pkg_entry == nullptr) {
1006     // We might have looked up pkg_entry before the module system was initialized.
1007     // Need to reload it now.
1008     TempNewSymbol pkg_name = ClassLoader::package_from_class_name(class_name);
1009     if (pkg_name != nullptr) {
1010       pkg_entry = class_loader_data(class_loader)->packages()->lookup_only(pkg_name);
1011     }
1012   }
1013 
1014   ModuleEntry* mod_entry = (pkg_entry == nullptr) ? nullptr : pkg_entry->module();
1015   bool should_be_in_named_module = (mod_entry != nullptr && mod_entry->is_named());
1016   bool was_archived_from_named_module = !cl->has_unnamed_module();
1017   bool visible;
1018 
1019   if (was_archived_from_named_module) {
1020     if (should_be_in_named_module) {
1021       // Is the module loaded from the same location as during dump time?
1022       visible = mod_entry->shared_path_index() == scp_index;
1023       if (visible) {
1024         assert(!CDSConfig::module_patching_disables_cds(), "Cannot use CDS");
1025       }
1026     } else {
1027       // During dump time, this class was in a named module, but at run time, this class should be
1028       // in an unnamed module.
1029       visible = false;
1030     }
1031   } else {
1032     if (should_be_in_named_module) {
1033       // During dump time, this class was in an unnamed, but at run time, this class should be
1034       // in a named module.
1035       visible = false;
1036     } else {
1037       visible = true;
1038     }
1039   }
1040 
1041   return visible;
1042 }
1043 
1044 bool SystemDictionary::check_shared_class_super_type(InstanceKlass* klass, InstanceKlass* super_type,
1045                                                      Handle class_loader, bool is_superclass, TRAPS) {
1046   assert(super_type->is_shared(), "must be");
1047 
1048   // Quick check if the super type has been already loaded.
1049   // + Don't do it for unregistered classes -- they can be unloaded so
1050   //   super_type->class_loader_data() could be stale.
1051   // + Don't check if loader data is null, ie. the super_type isn't fully loaded.
1052   if (!super_type->is_shared_unregistered_class() && super_type->class_loader_data() != nullptr) {
1053     // Check if the superclass is loaded by the current class_loader
1054     Symbol* name = super_type->name();
1055     InstanceKlass* check = find_instance_klass(THREAD, name, class_loader);
1056     if (check == super_type) {
1057       return true;
1058     }
1059   }
1060 
1061   Klass *found = resolve_with_circularity_detection(klass->name(), super_type->name(),
1062                                                     class_loader, is_superclass, CHECK_false);
1063   if (found == super_type) {
1064     return true;
1065   } else {
1066     // The dynamically resolved super type is not the same as the one we used during dump time,
1067     // so we cannot use the class.
1068     return false;
1069   }
1070 }
1071 
1072 bool SystemDictionary::check_shared_class_super_types(InstanceKlass* ik, Handle class_loader, TRAPS) {
1073   // Check the superclass and interfaces. They must be the same
1074   // as in dump time, because the layout of <ik> depends on
1075   // the specific layout of ik->super() and ik->local_interfaces().
1076   //
1077   // If unexpected superclass or interfaces are found, we cannot
1078   // load <ik> from the shared archive.
1079 
1080   if (ik->super() != nullptr) {
1081     bool check_super = check_shared_class_super_type(ik, InstanceKlass::cast(ik->super()),
1082                                                      class_loader, true,
1083                                                      CHECK_false);
1084     if (!check_super) {
1085       return false;
1086     }
1087   }
1088 
1089   Array<InstanceKlass*>* interfaces = ik->local_interfaces();
1090   int num_interfaces = interfaces->length();
1091   for (int index = 0; index < num_interfaces; index++) {
1092     bool check_interface = check_shared_class_super_type(ik, interfaces->at(index), class_loader, false,
1093                                                          CHECK_false);
1094     if (!check_interface) {
1095       return false;
1096     }
1097   }
1098 
1099   return true;
1100 }
1101 
1102 // Pre-load class referred to in non-static null-free instance field. These fields trigger MANDATORY loading.
1103 // Some pre-loading does not fail fatally
1104 bool SystemDictionary::preload_from_null_free_field(InstanceKlass* ik, Handle class_loader, Symbol* sig, int field_index, TRAPS) {
1105   TempNewSymbol name = Signature::strip_envelope(sig);
1106   log_info(class, preload)("Preloading class %s during loading of shared class %s. "
1107                            "Cause: a null-free non-static field is declared with this type",
1108                            name->as_C_string(), ik->name()->as_C_string());
1109   InstanceKlass* real_k = SystemDictionary::resolve_with_circularity_detection_or_fail(ik->name(), name,
1110                                                                                class_loader, false, CHECK_false);
1111   if (HAS_PENDING_EXCEPTION) {
1112     log_warning(class, preload)("Preloading of class %s during loading of class %s "
1113                                 "(cause: null-free non-static field) failed: %s",
1114                                 name->as_C_string(), ik->name()->as_C_string(),
1115                                 PENDING_EXCEPTION->klass()->name()->as_C_string());
1116     return false; // Exception is still pending
1117   }
1118 
1119   InstanceKlass* k = ik->get_inline_type_field_klass_or_null(field_index);
1120   if (real_k != k) {
1121     // oops, the app has substituted a different version of k! Does not fail fatally
1122     log_warning(class, preload)("Preloading of class %s during loading of shared class %s "
1123                                 "(cause: null-free non-static field) failed : "
1124                                 "app substituted a different version of %s",
1125                                 name->as_C_string(), ik->name()->as_C_string(),
1126                                 name->as_C_string());
1127     return false;
1128   }
1129   log_info(class, preload)("Preloading of class %s during loading of shared class %s "
1130                            "(cause: null-free non-static field) succeeded",
1131                            name->as_C_string(), ik->name()->as_C_string());
1132 
1133   assert(real_k != nullptr, "Sanity check");
1134   InstanceKlass::check_can_be_annotated_with_NullRestricted(real_k, ik->name(), CHECK_false);
1135 
1136   return true;
1137 }
1138 
1139 // Tries to pre-load classes referred to in non-static nullable instance fields if they are found in the
1140 // loadable descriptors attribute. If loading fails, we can fail silently.
1141 void SystemDictionary::try_preload_from_loadable_descriptors(InstanceKlass* ik, Handle class_loader, Symbol* sig, int field_index, TRAPS) {
1142   TempNewSymbol name = Signature::strip_envelope(sig);
1143   if (name != ik->name() && ik->is_class_in_loadable_descriptors_attribute(sig)) {
1144     log_info(class, preload)("Preloading class %s during loading of shared class %s. "
1145                              "Cause: field type in LoadableDescriptors attribute",
1146                              name->as_C_string(), ik->name()->as_C_string());
1147     InstanceKlass* real_k = SystemDictionary::resolve_with_circularity_detection_or_fail(ik->name(), name,
1148                                                                                  class_loader, false, THREAD);
1149     if (HAS_PENDING_EXCEPTION) {
1150       CLEAR_PENDING_EXCEPTION;
1151     }
1152 
1153     InstanceKlass* k = ik->get_inline_type_field_klass_or_null(field_index);
1154     if (real_k != k) {
1155       // oops, the app has substituted a different version of k!
1156       log_warning(class, preload)("Preloading of class %s during loading of shared class %s "
1157                                   "(cause: field type in LoadableDescriptors attribute) failed : "
1158                                   "app substituted a different version of %s",
1159                                   name->as_C_string(), ik->name()->as_C_string(),
1160                                   k->name()->as_C_string());
1161       return;
1162     } else if (real_k != nullptr) {
1163       log_info(class, preload)("Preloading of class %s during loading of shared class %s "
1164                                "(cause: field type in LoadableDescriptors attribute) succeeded",
1165                                 name->as_C_string(), ik->name()->as_C_string());
1166     }
1167   }
1168 }
1169 
1170 
1171 InstanceKlass* SystemDictionary::load_shared_class(InstanceKlass* ik,
1172                                                    Handle class_loader,
1173                                                    Handle protection_domain,
1174                                                    const ClassFileStream *cfs,
1175                                                    PackageEntry* pkg_entry,
1176                                                    TRAPS) {
1177   assert(ik != nullptr, "sanity");
1178   assert(ik->is_shared(), "sanity");
1179   assert(!ik->is_unshareable_info_restored(), "shared class can be restored only once");
1180   assert(Atomic::add(&ik->_shared_class_load_count, 1) == 1, "shared class loaded more than once");
1181   Symbol* class_name = ik->name();
1182 
1183   if (!is_shared_class_visible(class_name, ik, pkg_entry, class_loader)) {
1184     ik->set_shared_loading_failed();
1185     return nullptr;
1186   }
1187 
1188   bool check = check_shared_class_super_types(ik, class_loader, CHECK_NULL);
1189   if (!check) {
1190     ik->set_shared_loading_failed();
1191     return nullptr;
1192   }
1193 
1194   if (ik->has_inline_type_fields()) {
1195     for (AllFieldStream fs(ik); !fs.done(); fs.next()) {
1196       if (fs.access_flags().is_static()) continue;
1197 
1198       Symbol* sig = fs.signature();
1199       int field_index = fs.index();
1200 
1201       if (fs.is_null_free_inline_type()) {
1202         // A false return means that the class didn't load for other reasons than an exception.
1203         bool check = preload_from_null_free_field(ik, class_loader, sig, field_index, CHECK_NULL);
1204         if (!check) {
1205           ik->set_shared_loading_failed();
1206           return nullptr;
1207         }
1208       } else if (Signature::has_envelope(sig)) {
1209           // Pending exceptions are cleared so we can fail silently
1210           try_preload_from_loadable_descriptors(ik, class_loader, sig, field_index, CHECK_NULL);
1211       }
1212     }
1213   }
1214 
1215   InstanceKlass* new_ik = nullptr;
1216   // CFLH check is skipped for VM hidden classes (see KlassFactory::create_from_stream).
1217   // It will be skipped for shared VM hidden lambda proxy classes.
1218   if (!ik->is_hidden()) {
1219     new_ik = KlassFactory::check_shared_class_file_load_hook(
1220       ik, class_name, class_loader, protection_domain, cfs, CHECK_NULL);
1221   }
1222   if (new_ik != nullptr) {
1223     // The class is changed by CFLH. Return the new class. The shared class is
1224     // not used.
1225     return new_ik;
1226   }
1227 
1228   // Adjust methods to recover missing data.  They need addresses for
1229   // interpreter entry points and their default native method address
1230   // must be reset.
1231 
1232   // Shared classes are all currently loaded by either the bootstrap or
1233   // internal parallel class loaders, so this will never cause a deadlock
1234   // on a custom class loader lock.
1235   // Since this class is already locked with parallel capable class
1236   // loaders, including the bootstrap loader via the placeholder table,
1237   // this lock is currently a nop.
1238 
1239   ClassLoaderData* loader_data = class_loader_data(class_loader);
1240   {
1241     HandleMark hm(THREAD);
1242     Handle lockObject = get_loader_lock_or_null(class_loader);
1243     ObjectLocker ol(lockObject, THREAD);
1244     // prohibited package check assumes all classes loaded from archive call
1245     // restore_unshareable_info which calls ik->set_package()
1246     ik->restore_unshareable_info(loader_data, protection_domain, pkg_entry, CHECK_NULL);
1247   }
1248 
1249   load_shared_class_misc(ik, loader_data);
1250 
1251   return ik;
1252 }
1253 
1254 void SystemDictionary::load_shared_class_misc(InstanceKlass* ik, ClassLoaderData* loader_data) {
1255   ik->print_class_load_logging(loader_data, nullptr, nullptr);
1256 
1257   // For boot loader, ensure that GetSystemPackage knows that a class in this
1258   // package was loaded.
1259   if (loader_data->is_the_null_class_loader_data()) {
1260     s2 path_index = ik->shared_classpath_index();
1261     ik->set_classpath_index(path_index);
1262   }
1263 
1264   // notify a class loaded from shared object
1265   ClassLoadingService::notify_class_loaded(ik, true /* shared class */);
1266 
1267   if (CDSConfig::is_dumping_final_static_archive()) {
1268     SystemDictionaryShared::init_dumptime_info_from_preimage(ik);
1269   }
1270 }
1271 
1272 #endif // INCLUDE_CDS
1273 
1274 InstanceKlass* SystemDictionary::load_instance_class_impl(Symbol* class_name, Handle class_loader, TRAPS) {
1275 
1276   if (class_loader.is_null()) {
1277     ResourceMark rm(THREAD);
1278     PackageEntry* pkg_entry = nullptr;
1279     bool search_only_bootloader_append = false;
1280 
1281     // Find the package in the boot loader's package entry table.
1282     TempNewSymbol pkg_name = ClassLoader::package_from_class_name(class_name);
1283     if (pkg_name != nullptr) {
1284       pkg_entry = class_loader_data(class_loader)->packages()->lookup_only(pkg_name);
1285     }
1286 
1287     // Prior to attempting to load the class, enforce the boot loader's
1288     // visibility boundaries.
1289     if (!Universe::is_module_initialized()) {
1290       // During bootstrapping, prior to module initialization, any
1291       // class attempting to be loaded must be checked against the
1292       // java.base packages in the boot loader's PackageEntryTable.
1293       // No class outside of java.base is allowed to be loaded during
1294       // this bootstrapping window.
1295       if (pkg_entry == nullptr || pkg_entry->in_unnamed_module()) {
1296         // Class is either in the unnamed package or in
1297         // a named package within the unnamed module.  Either
1298         // case is outside of java.base, do not attempt to
1299         // load the class post java.base definition.  If
1300         // java.base has not been defined, let the class load
1301         // and its package will be checked later by
1302         // ModuleEntryTable::verify_javabase_packages.
1303         if (ModuleEntryTable::javabase_defined()) {
1304           return nullptr;
1305         }
1306       } else {
1307         // Check that the class' package is defined within java.base.
1308         ModuleEntry* mod_entry = pkg_entry->module();
1309         Symbol* mod_entry_name = mod_entry->name();
1310         if (mod_entry_name->fast_compare(vmSymbols::java_base()) != 0) {
1311           return nullptr;
1312         }
1313       }
1314     } else {
1315       // After the module system has been initialized, check if the class'
1316       // package is in a module defined to the boot loader.
1317       if (pkg_name == nullptr || pkg_entry == nullptr || pkg_entry->in_unnamed_module()) {
1318         // Class is either in the unnamed package, in a named package
1319         // within a module not defined to the boot loader or in a
1320         // a named package within the unnamed module.  In all cases,
1321         // limit visibility to search for the class only in the boot
1322         // loader's append path.
1323         if (!ClassLoader::has_bootclasspath_append()) {
1324            // If there is no bootclasspath append entry, no need to continue
1325            // searching.
1326            return nullptr;
1327         }
1328         search_only_bootloader_append = true;
1329       }
1330     }
1331 
1332     // Prior to bootstrapping's module initialization, never load a class outside
1333     // of the boot loader's module path
1334     assert(Universe::is_module_initialized() ||
1335            !search_only_bootloader_append,
1336            "Attempt to load a class outside of boot loader's module path");
1337 
1338     // Search for classes in the CDS archive.
1339     InstanceKlass* k = nullptr;
1340 
1341 #if INCLUDE_CDS
1342     if (CDSConfig::is_using_archive())
1343     {
1344       PerfTraceTime vmtimer(ClassLoader::perf_shared_classload_time());
1345       InstanceKlass* ik = SystemDictionaryShared::find_builtin_class(class_name);
1346       if (ik != nullptr && ik->is_shared_boot_class() && !ik->shared_loading_failed()) {
1347         SharedClassLoadingMark slm(THREAD, ik);
1348         k = load_shared_class(ik, class_loader, Handle(), nullptr,  pkg_entry, CHECK_NULL);
1349       }
1350     }
1351 #endif
1352 
1353     if (k == nullptr) {
1354       // Use VM class loader
1355       PerfTraceTime vmtimer(ClassLoader::perf_sys_classload_time());
1356       k = ClassLoader::load_class(class_name, pkg_entry, search_only_bootloader_append, CHECK_NULL);
1357     }
1358 
1359     // find_or_define_instance_class may return a different InstanceKlass
1360     if (k != nullptr) {
1361       CDS_ONLY(SharedClassLoadingMark slm(THREAD, k);)
1362       k = find_or_define_instance_class(class_name, class_loader, k, CHECK_NULL);
1363     }
1364     return k;
1365   } else {
1366     // Use user specified class loader to load class. Call loadClass operation on class_loader.
1367     ResourceMark rm(THREAD);
1368 
1369     JavaThread* jt = THREAD;
1370 
1371     PerfClassTraceTime vmtimer(ClassLoader::perf_app_classload_time(),
1372                                ClassLoader::perf_app_classload_selftime(),
1373                                ClassLoader::perf_app_classload_count(),
1374                                jt->get_thread_stat()->perf_recursion_counts_addr(),
1375                                jt->get_thread_stat()->perf_timers_addr(),
1376                                PerfClassTraceTime::CLASS_LOAD);
1377 
1378     // Translate to external class name format, i.e., convert '/' chars to '.'
1379     Handle string = java_lang_String::externalize_classname(class_name, CHECK_NULL);
1380 
1381     JavaValue result(T_OBJECT);
1382 
1383     InstanceKlass* spec_klass = vmClasses::ClassLoader_klass();
1384 
1385     // Call public unsynchronized loadClass(String) directly for all class loaders.
1386     // For parallelCapable class loaders, JDK >=7, loadClass(String, boolean) will
1387     // acquire a class-name based lock rather than the class loader object lock.
1388     // JDK < 7 already acquire the class loader lock in loadClass(String, boolean).
1389     JavaCalls::call_virtual(&result,
1390                             class_loader,
1391                             spec_klass,
1392                             vmSymbols::loadClass_name(),
1393                             vmSymbols::string_class_signature(),
1394                             string,
1395                             CHECK_NULL);
1396 
1397     assert(result.get_type() == T_OBJECT, "just checking");
1398     oop obj = result.get_oop();
1399 
1400     // Primitive classes return null since forName() can not be
1401     // used to obtain any of the Class objects representing primitives or void
1402     if ((obj != nullptr) && !(java_lang_Class::is_primitive(obj))) {
1403       InstanceKlass* k = InstanceKlass::cast(java_lang_Class::as_Klass(obj));
1404       // For user defined Java class loaders, check that the name returned is
1405       // the same as that requested.  This check is done for the bootstrap
1406       // loader when parsing the class file.
1407       if (class_name == k->name()) {
1408         return k;
1409       }
1410     }
1411     // Class is not found or has the wrong name, return null
1412     return nullptr;
1413   }
1414 }
1415 
1416 InstanceKlass* SystemDictionary::load_instance_class(Symbol* name,
1417                                                      Handle class_loader,
1418                                                      TRAPS) {
1419 
1420   InstanceKlass* loaded_class = load_instance_class_impl(name, class_loader, CHECK_NULL);
1421 
1422   // If everything was OK (no exceptions, no null return value), and
1423   // class_loader is NOT the defining loader, do a little more bookkeeping.
1424   if (loaded_class != nullptr &&
1425       loaded_class->class_loader() != class_loader()) {
1426 
1427     ClassLoaderData* loader_data = class_loader_data(class_loader);
1428     check_constraints(loaded_class, loader_data, false, CHECK_NULL);
1429 
1430     // Record dependency for non-parent delegation.
1431     // This recording keeps the defining class loader of the klass (loaded_class) found
1432     // from being unloaded while the initiating class loader is loaded
1433     // even if the reference to the defining class loader is dropped
1434     // before references to the initiating class loader.
1435     loader_data->record_dependency(loaded_class);
1436 
1437     update_dictionary(THREAD, loaded_class, loader_data);
1438 
1439     if (JvmtiExport::should_post_class_load()) {
1440       JvmtiExport::post_class_load(THREAD, loaded_class);
1441     }
1442   }
1443   return loaded_class;
1444 }
1445 
1446 static void post_class_define_event(InstanceKlass* k, const ClassLoaderData* def_cld) {
1447   EventClassDefine event;
1448   if (event.should_commit()) {
1449     event.set_definedClass(k);
1450     event.set_definingClassLoader(def_cld);
1451     event.commit();
1452   }
1453 }
1454 
1455 void SystemDictionary::define_instance_class(InstanceKlass* k, Handle class_loader, TRAPS) {
1456 
1457   ClassLoaderData* loader_data = k->class_loader_data();
1458   assert(loader_data->class_loader() == class_loader(), "they must be the same");
1459 
1460   // Bootstrap and other parallel classloaders don't acquire a lock,
1461   // they use placeholder token.
1462   // If a parallelCapable class loader calls define_instance_class instead of
1463   // find_or_define_instance_class to get here, we have a timing
1464   // hole with systemDictionary updates and check_constraints
1465   if (!is_parallelCapable(class_loader)) {
1466     assert(ObjectSynchronizer::current_thread_holds_lock(THREAD,
1467            get_loader_lock_or_null(class_loader)),
1468            "define called without lock");
1469   }
1470 
1471   // Check class-loading constraints. Throw exception if violation is detected.
1472   // Grabs and releases SystemDictionary_lock
1473   // The check_constraints/find_class call and update_dictionary sequence
1474   // must be "atomic" for a specific class/classloader pair so we never
1475   // define two different instanceKlasses for that class/classloader pair.
1476   // Existing classloaders will call define_instance_class with the
1477   // classloader lock held
1478   // Parallel classloaders will call find_or_define_instance_class
1479   // which will require a token to perform the define class
1480   check_constraints(k, loader_data, true, CHECK);
1481 
1482   // Register class just loaded with class loader (placed in ArrayList)
1483   // Note we do this before updating the dictionary, as this can
1484   // fail with an OutOfMemoryError (if it does, we will *not* put this
1485   // class in the dictionary and will not update the class hierarchy).
1486   // JVMTI FollowReferences needs to find the classes this way.
1487   if (k->class_loader() != nullptr) {
1488     methodHandle m(THREAD, Universe::loader_addClass_method());
1489     JavaValue result(T_VOID);
1490     JavaCallArguments args(class_loader);
1491     args.push_oop(Handle(THREAD, k->java_mirror()));
1492     JavaCalls::call(&result, m, &args, CHECK);
1493   }
1494 
1495   // Add to class hierarchy, and do possible deoptimizations.
1496   k->add_to_hierarchy(THREAD);
1497 
1498   // Add to systemDictionary - so other classes can see it.
1499   // Grabs and releases SystemDictionary_lock
1500   update_dictionary(THREAD, k, loader_data);
1501 
1502   // notify jvmti
1503   if (JvmtiExport::should_post_class_load()) {
1504     JvmtiExport::post_class_load(THREAD, k);
1505   }
1506   post_class_define_event(k, loader_data);
1507 }
1508 
1509 // Support parallel classloading
1510 // All parallel class loaders, including bootstrap classloader
1511 // lock a placeholder entry for this class/class_loader pair
1512 // to allow parallel defines of different classes for this class loader
1513 // With AllowParallelDefine flag==true, in case they do not synchronize around
1514 // FindLoadedClass/DefineClass, calls, we check for parallel
1515 // loading for them, wait if a defineClass is in progress
1516 // and return the initial requestor's results
1517 // This flag does not apply to the bootstrap classloader.
1518 // With AllowParallelDefine flag==false, call through to define_instance_class
1519 // which will throw LinkageError: duplicate class definition.
1520 // False is the requested default.
1521 // For better performance, the class loaders should synchronize
1522 // findClass(), i.e. FindLoadedClass/DefineClassIfAbsent or they
1523 // potentially waste time reading and parsing the bytestream.
1524 // Note: VM callers should ensure consistency of k/class_name,class_loader
1525 // Be careful when modifying this code: once you have run
1526 // PlaceholderTable::find_and_add(PlaceholderTable::DEFINE_CLASS),
1527 // you need to find_and_remove it before returning.
1528 // So be careful to not exit with a CHECK_ macro between these calls.
1529 InstanceKlass* SystemDictionary::find_or_define_helper(Symbol* class_name, Handle class_loader,
1530                                                        InstanceKlass* k, TRAPS) {
1531 
1532   Symbol* name_h = k->name();
1533   ClassLoaderData* loader_data = class_loader_data(class_loader);
1534   Dictionary* dictionary = loader_data->dictionary();
1535 
1536   // Hold SD lock around find_class and placeholder creation for DEFINE_CLASS
1537   {
1538     MutexLocker mu(THREAD, SystemDictionary_lock);
1539     // First check if class already defined
1540     if (is_parallelDefine(class_loader)) {
1541       InstanceKlass* check = dictionary->find_class(THREAD, name_h);
1542       if (check != nullptr) {
1543         return check;
1544       }
1545     }
1546 
1547     // Acquire define token for this class/classloader
1548     PlaceholderEntry* probe = PlaceholderTable::find_and_add(name_h, loader_data,
1549                                                              PlaceholderTable::DEFINE_CLASS, nullptr, THREAD);
1550     // Wait if another thread defining in parallel
1551     // All threads wait - even those that will throw duplicate class: otherwise
1552     // caller is surprised by LinkageError: duplicate, but findLoadedClass fails
1553     // if other thread has not finished updating dictionary
1554     while (probe->definer() != nullptr) {
1555       SystemDictionary_lock->wait();
1556     }
1557     // Only special cases allow parallel defines and can use other thread's results
1558     // Other cases fall through, and may run into duplicate defines
1559     // caught by finding an entry in the SystemDictionary
1560     if (is_parallelDefine(class_loader) && (probe->instance_klass() != nullptr)) {
1561       InstanceKlass* ik = probe->instance_klass();
1562       PlaceholderTable::find_and_remove(name_h, loader_data, PlaceholderTable::DEFINE_CLASS, THREAD);
1563       SystemDictionary_lock->notify_all();
1564 #ifdef ASSERT
1565       InstanceKlass* check = dictionary->find_class(THREAD, name_h);
1566       assert(check != nullptr, "definer missed recording success");
1567 #endif
1568       return ik;
1569     } else {
1570       // This thread will define the class (even if earlier thread tried and had an error)
1571       probe->set_definer(THREAD);
1572     }
1573   }
1574 
1575   define_instance_class(k, class_loader, THREAD);
1576 
1577   // definer must notify any waiting threads
1578   {
1579     MutexLocker mu(THREAD, SystemDictionary_lock);
1580     PlaceholderEntry* probe = PlaceholderTable::get_entry(name_h, loader_data);
1581     assert(probe != nullptr, "DEFINE_CLASS placeholder lost?");
1582     if (!HAS_PENDING_EXCEPTION) {
1583       probe->set_instance_klass(k);
1584     }
1585     probe->set_definer(nullptr);
1586     PlaceholderTable::find_and_remove(name_h, loader_data, PlaceholderTable::DEFINE_CLASS, THREAD);
1587     SystemDictionary_lock->notify_all();
1588   }
1589 
1590   return HAS_PENDING_EXCEPTION ? nullptr : k;
1591 }
1592 
1593 // If a class loader supports parallel classloading handle parallel define requests.
1594 // find_or_define_instance_class may return a different InstanceKlass
1595 InstanceKlass* SystemDictionary::find_or_define_instance_class(Symbol* class_name, Handle class_loader,
1596                                                                InstanceKlass* k, TRAPS) {
1597   InstanceKlass* defined_k = find_or_define_helper(class_name, class_loader, k, THREAD);
1598   // Clean up original InstanceKlass if duplicate or error
1599   if (!HAS_PENDING_EXCEPTION && defined_k != k) {
1600     // If a parallel capable class loader already defined this class, register 'k' for cleanup.
1601     assert(defined_k != nullptr, "Should have a klass if there's no exception");
1602     k->class_loader_data()->add_to_deallocate_list(k);
1603   } else if (HAS_PENDING_EXCEPTION) {
1604     // Remove this InstanceKlass from the LoaderConstraintTable if added.
1605     LoaderConstraintTable::remove_failed_loaded_klass(k, class_loader_data(class_loader));
1606     assert(defined_k == nullptr, "Should not have a klass if there's an exception");
1607     k->class_loader_data()->add_to_deallocate_list(k);
1608   }
1609   return defined_k;
1610 }
1611 
1612 
1613 // ----------------------------------------------------------------------------
1614 // GC support
1615 
1616 // Assumes classes in the SystemDictionary are only unloaded at a safepoint
1617 bool SystemDictionary::do_unloading(GCTimer* gc_timer) {
1618 
1619   bool unloading_occurred;
1620   bool is_concurrent = !SafepointSynchronize::is_at_safepoint();
1621   {
1622     GCTraceTime(Debug, gc, phases) t("ClassLoaderData", gc_timer);
1623     assert_locked_or_safepoint(ClassLoaderDataGraph_lock);  // caller locks.
1624     // First, mark for unload all ClassLoaderData referencing a dead class loader.
1625     unloading_occurred = ClassLoaderDataGraph::do_unloading();
1626     if (unloading_occurred) {
1627       ConditionalMutexLocker ml2(Module_lock, is_concurrent);
1628       JFR_ONLY(Jfr::on_unloading_classes();)
1629       MANAGEMENT_ONLY(FinalizerService::purge_unloaded();)
1630       ConditionalMutexLocker ml1(SystemDictionary_lock, is_concurrent);
1631       ClassLoaderDataGraph::clean_module_and_package_info();
1632       LoaderConstraintTable::purge_loader_constraints();
1633       ResolutionErrorTable::purge_resolution_errors();
1634     }
1635   }
1636 
1637   GCTraceTime(Debug, gc, phases) t("Trigger cleanups", gc_timer);
1638 
1639   if (unloading_occurred) {
1640     SymbolTable::trigger_cleanup();
1641 
1642     ConditionalMutexLocker ml(ClassInitError_lock, is_concurrent);
1643     InstanceKlass::clean_initialization_error_table();
1644   }
1645 
1646   return unloading_occurred;
1647 }
1648 
1649 void SystemDictionary::methods_do(void f(Method*)) {
1650   // Walk methods in loaded classes
1651 
1652   {
1653     MutexLocker ml(ClassLoaderDataGraph_lock);
1654     ClassLoaderDataGraph::methods_do(f);
1655   }
1656 
1657   auto doit = [&] (InvokeMethodKey key, Method* method) {
1658     if (method != nullptr) {
1659       f(method);
1660     }
1661   };
1662 
1663   {
1664     MutexLocker ml(InvokeMethodIntrinsicTable_lock);
1665     _invoke_method_intrinsic_table->iterate_all(doit);
1666   }
1667 
1668 }
1669 
1670 // ----------------------------------------------------------------------------
1671 // Initialization
1672 
1673 void SystemDictionary::initialize(TRAPS) {
1674   _invoke_method_intrinsic_table = new (mtClass) InvokeMethodIntrinsicTable();
1675   _invoke_method_type_table = new (mtClass) InvokeMethodTypeTable();
1676   ResolutionErrorTable::initialize();
1677   LoaderConstraintTable::initialize();
1678   PlaceholderTable::initialize();
1679 #if INCLUDE_CDS
1680   SystemDictionaryShared::initialize();
1681   if (CDSConfig::is_dumping_archive()) {
1682     AOTClassLocationConfig::dumptime_init(THREAD);
1683   }
1684 #endif
1685   // Resolve basic classes
1686   vmClasses::resolve_all(CHECK);
1687   // Resolve classes used by archived heap objects
1688   if (CDSConfig::is_using_archive()) {
1689     HeapShared::resolve_classes(THREAD);
1690   }
1691 }
1692 
1693 // Constraints on class loaders. The details of the algorithm can be
1694 // found in the OOPSLA'98 paper "Dynamic Class Loading in the Java
1695 // Virtual Machine" by Sheng Liang and Gilad Bracha.  The basic idea is
1696 // that the dictionary needs to maintain a set of constraints that
1697 // must be satisfied by all classes in the dictionary.
1698 // if defining is true, then LinkageError if already in dictionary
1699 // if initiating loader, then ok if InstanceKlass matches existing entry
1700 
1701 void SystemDictionary::check_constraints(InstanceKlass* k,
1702                                          ClassLoaderData* loader_data,
1703                                          bool defining,
1704                                          TRAPS) {
1705   ResourceMark rm(THREAD);
1706   stringStream ss;
1707   bool throwException = false;
1708 
1709   {
1710     Symbol* name = k->name();
1711 
1712     MutexLocker mu(THREAD, SystemDictionary_lock);
1713 
1714     InstanceKlass* check = loader_data->dictionary()->find_class(THREAD, name);
1715     if (check != nullptr) {
1716       // If different InstanceKlass - duplicate class definition,
1717       // else - ok, class loaded by a different thread in parallel.
1718       // We should only have found it if it was done loading and ok to use.
1719 
1720       if ((defining == true) || (k != check)) {
1721         throwException = true;
1722         ss.print("loader %s", loader_data->loader_name_and_id());
1723         ss.print(" attempted duplicate %s definition for %s. (%s)",
1724                  k->external_kind(), k->external_name(), k->class_in_module_of_loader(false, true));
1725       } else {
1726         return;
1727       }
1728     }
1729 
1730     if (throwException == false) {
1731       if (LoaderConstraintTable::check_or_update(k, loader_data, name) == false) {
1732         throwException = true;
1733         ss.print("loader constraint violation: loader %s", loader_data->loader_name_and_id());
1734         ss.print(" wants to load %s %s.",
1735                  k->external_kind(), k->external_name());
1736         Klass *existing_klass = LoaderConstraintTable::find_constrained_klass(name, loader_data);
1737         if (existing_klass != nullptr && existing_klass->class_loader_data() != loader_data) {
1738           ss.print(" A different %s with the same name was previously loaded by %s. (%s)",
1739                    existing_klass->external_kind(),
1740                    existing_klass->class_loader_data()->loader_name_and_id(),
1741                    existing_klass->class_in_module_of_loader(false, true));
1742         } else {
1743           ss.print(" (%s)", k->class_in_module_of_loader(false, true));
1744         }
1745       }
1746     }
1747   }
1748 
1749   // Throw error now if needed (cannot throw while holding
1750   // SystemDictionary_lock because of rank ordering)
1751   if (throwException == true) {
1752     THROW_MSG(vmSymbols::java_lang_LinkageError(), ss.as_string());
1753   }
1754 }
1755 
1756 // Update class loader data dictionary - done after check_constraint and add_to_hierarchy
1757 // have been called.
1758 void SystemDictionary::update_dictionary(JavaThread* current,
1759                                          InstanceKlass* k,
1760                                          ClassLoaderData* loader_data) {
1761   MonitorLocker mu1(SystemDictionary_lock);
1762 
1763   // Make a new dictionary entry.
1764   Symbol* name  = k->name();
1765   Dictionary* dictionary = loader_data->dictionary();
1766   InstanceKlass* sd_check = dictionary->find_class(current, name);
1767   if (sd_check == nullptr) {
1768     dictionary->add_klass(current, name, k);
1769   }
1770   mu1.notify_all();
1771 }
1772 
1773 // Indicate that loader_data has initiated the loading of class k, which
1774 // has already been defined by a parent loader.
1775 // This API is used by AOTLinkedClassBulkLoader and to register boxing
1776 // classes from java.lang in all class loaders to enable more value
1777 // classes optimizations
1778 void SystemDictionary::add_to_initiating_loader(JavaThread* current,
1779                                                 InstanceKlass* k,
1780                                                 ClassLoaderData* loader_data) {
1781   assert_locked_or_safepoint(SystemDictionary_lock);
1782   Symbol* name  = k->name();
1783   Dictionary* dictionary = loader_data->dictionary();
1784   assert(k->is_loaded(), "must be");
1785   assert(k->class_loader_data() != loader_data, "only for classes defined by a parent loader");
1786   if (dictionary->find_class(current, name) == nullptr) {
1787     dictionary->add_klass(current, name, k);
1788   }
1789 }
1790 
1791 // Try to find a class name using the loader constraints.  The
1792 // loader constraints might know about a class that isn't fully loaded
1793 // yet and these will be ignored.
1794 Klass* SystemDictionary::find_constrained_instance_or_array_klass(
1795                     Thread* current, Symbol* class_name, Handle class_loader) {
1796 
1797   // First see if it has been loaded directly.
1798   Klass* klass = find_instance_or_array_klass(current, class_name, class_loader);
1799   if (klass != nullptr)
1800     return klass;
1801 
1802   // Now look to see if it has been loaded elsewhere, and is subject to
1803   // a loader constraint that would require this loader to return the
1804   // klass that is already loaded.
1805   if (Signature::is_array(class_name)) {
1806     // For array classes, their Klass*s are not kept in the
1807     // constraint table. The element Klass*s are.
1808     SignatureStream ss(class_name, false);
1809     int ndims = ss.skip_array_prefix();  // skip all '['s
1810     BasicType t = ss.type();
1811     if (t != T_OBJECT) {
1812       klass = Universe::typeArrayKlass(t);
1813     } else {
1814       MutexLocker mu(current, SystemDictionary_lock);
1815       klass = LoaderConstraintTable::find_constrained_klass(ss.as_symbol(), class_loader_data(class_loader));
1816     }
1817     // If element class already loaded, allocate array klass
1818     if (klass != nullptr) {
1819       klass = klass->array_klass_or_null(ndims);
1820     }
1821   } else {
1822     MutexLocker mu(current, SystemDictionary_lock);
1823     // Non-array classes are easy: simply check the constraint table.
1824     klass = LoaderConstraintTable::find_constrained_klass(class_name, class_loader_data(class_loader));
1825   }
1826 
1827   return klass;
1828 }
1829 
1830 bool SystemDictionary::add_loader_constraint(Symbol* class_name,
1831                                              Klass* klass_being_linked,
1832                                              Handle class_loader1,
1833                                              Handle class_loader2) {
1834   ClassLoaderData* loader_data1 = class_loader_data(class_loader1);
1835   ClassLoaderData* loader_data2 = class_loader_data(class_loader2);
1836 
1837   Symbol* constraint_name = nullptr;
1838 
1839   if (!Signature::is_array(class_name)) {
1840     constraint_name = class_name;
1841   } else {
1842     // For array classes, their Klass*s are not kept in the
1843     // constraint table. The element classes are.
1844     SignatureStream ss(class_name, false);
1845     ss.skip_array_prefix();  // skip all '['s
1846     if (!ss.has_envelope()) {
1847       return true;     // primitive types always pass
1848     }
1849     constraint_name = ss.as_symbol();
1850     // Increment refcount to keep constraint_name alive after
1851     // SignatureStream is destructed. It will be decremented below
1852     // before returning.
1853     constraint_name->increment_refcount();
1854   }
1855 
1856   Dictionary* dictionary1 = loader_data1->dictionary();
1857   Dictionary* dictionary2 = loader_data2->dictionary();
1858 
1859   JavaThread* current = JavaThread::current();
1860   {
1861     MutexLocker mu_s(SystemDictionary_lock);
1862     InstanceKlass* klass1 = dictionary1->find_class(current, constraint_name);
1863     InstanceKlass* klass2 = dictionary2->find_class(current, constraint_name);
1864     bool result = LoaderConstraintTable::add_entry(constraint_name, klass1, loader_data1,
1865                                                    klass2, loader_data2);
1866 #if INCLUDE_CDS
1867     if (CDSConfig::is_dumping_archive() && klass_being_linked != nullptr &&
1868         !klass_being_linked->is_shared()) {
1869          SystemDictionaryShared::record_linking_constraint(constraint_name,
1870                                      InstanceKlass::cast(klass_being_linked),
1871                                      class_loader1, class_loader2);
1872     }
1873 #endif // INCLUDE_CDS
1874     if (Signature::is_array(class_name)) {
1875       constraint_name->decrement_refcount();
1876     }
1877     return result;
1878   }
1879 }
1880 
1881 // Add entry to resolution error table to record the error when the first
1882 // attempt to resolve a reference to a class has failed.
1883 void SystemDictionary::add_resolution_error(const constantPoolHandle& pool, int which,
1884                                             Symbol* error, const char* message,
1885                                             Symbol* cause, const char* cause_msg) {
1886   {
1887     MutexLocker ml(Thread::current(), SystemDictionary_lock);
1888     ResolutionErrorEntry* entry = ResolutionErrorTable::find_entry(pool, which);
1889     if (entry == nullptr) {
1890       ResolutionErrorTable::add_entry(pool, which, error, message, cause, cause_msg);
1891     }
1892   }
1893 }
1894 
1895 // Delete a resolution error for RedefineClasses for a constant pool is going away
1896 void SystemDictionary::delete_resolution_error(ConstantPool* pool) {
1897   ResolutionErrorTable::delete_entry(pool);
1898 }
1899 
1900 // Lookup resolution error table. Returns error if found, otherwise null.
1901 Symbol* SystemDictionary::find_resolution_error(const constantPoolHandle& pool, int which,
1902                                                 const char** message,
1903                                                 Symbol** cause, const char** cause_msg) {
1904 
1905   {
1906     MutexLocker ml(Thread::current(), SystemDictionary_lock);
1907     ResolutionErrorEntry* entry = ResolutionErrorTable::find_entry(pool, which);
1908     if (entry != nullptr) {
1909       *message = entry->message();
1910       *cause = entry->cause();
1911       *cause_msg = entry->cause_msg();
1912       return entry->error();
1913     } else {
1914       return nullptr;
1915     }
1916   }
1917 }
1918 
1919 // Add an entry to resolution error table to record an error in resolving or
1920 // validating a nest host. This is used to construct informative error
1921 // messages when IllegalAccessError's occur. If an entry already exists it will
1922 // be updated with the nest host error message.
1923 
1924 void SystemDictionary::add_nest_host_error(const constantPoolHandle& pool,
1925                                            int which,
1926                                            const char* message) {
1927   {
1928     MutexLocker ml(Thread::current(), SystemDictionary_lock);
1929     ResolutionErrorEntry* entry = ResolutionErrorTable::find_entry(pool, which);
1930     if (entry != nullptr && entry->nest_host_error() == nullptr) {
1931       // An existing entry means we had a true resolution failure (LinkageError) with our nest host, but we
1932       // still want to add the error message for the higher-level access checks to report. We should
1933       // only reach here under the same error condition, so we can ignore the potential race with setting
1934       // the message. If we see it is already set then we can ignore it.
1935       entry->set_nest_host_error(message);
1936     } else {
1937       ResolutionErrorTable::add_entry(pool, which, message);
1938     }
1939   }
1940 }
1941 
1942 // Lookup any nest host error
1943 const char* SystemDictionary::find_nest_host_error(const constantPoolHandle& pool, int which) {
1944   {
1945     MutexLocker ml(Thread::current(), SystemDictionary_lock);
1946     ResolutionErrorEntry* entry = ResolutionErrorTable::find_entry(pool, which);
1947     if (entry != nullptr) {
1948       return entry->nest_host_error();
1949     } else {
1950       return nullptr;
1951     }
1952   }
1953 }
1954 
1955 // Signature constraints ensure that callers and callees agree about
1956 // the meaning of type names in their signatures.  This routine is the
1957 // intake for constraints.  It collects them from several places:
1958 //
1959 //  * LinkResolver::resolve_method (if check_access is true) requires
1960 //    that the resolving class (the caller) and the defining class of
1961 //    the resolved method (the callee) agree on each type in the
1962 //    method's signature.
1963 //
1964 //  * LinkResolver::resolve_interface_method performs exactly the same
1965 //    checks.
1966 //
1967 //  * LinkResolver::resolve_field requires that the constant pool
1968 //    attempting to link to a field agree with the field's defining
1969 //    class about the type of the field signature.
1970 //
1971 //  * klassVtable::initialize_vtable requires that, when a class
1972 //    overrides a vtable entry allocated by a superclass, that the
1973 //    overriding method (i.e., the callee) agree with the superclass
1974 //    on each type in the method's signature.
1975 //
1976 //  * klassItable::initialize_itable requires that, when a class fills
1977 //    in its itables, for each non-abstract method installed in an
1978 //    itable, the method (i.e., the callee) agree with the interface
1979 //    on each type in the method's signature.
1980 //
1981 // All those methods have a boolean (check_access, checkconstraints)
1982 // which turns off the checks.  This is used from specialized contexts
1983 // such as bootstrapping, dumping, and debugging.
1984 //
1985 // No direct constraint is placed between the class and its
1986 // supertypes.  Constraints are only placed along linked relations
1987 // between callers and callees.  When a method overrides or implements
1988 // an abstract method in a supertype (superclass or interface), the
1989 // constraints are placed as if the supertype were the caller to the
1990 // overriding method.  (This works well, since callers to the
1991 // supertype have already established agreement between themselves and
1992 // the supertype.)  As a result of all this, a class can disagree with
1993 // its supertype about the meaning of a type name, as long as that
1994 // class neither calls a relevant method of the supertype, nor is
1995 // called (perhaps via an override) from the supertype.
1996 //
1997 //
1998 // SystemDictionary::check_signature_loaders(sig, klass_being_linked, l1, l2)
1999 //
2000 // Make sure all class components (including arrays) in the given
2001 // signature will be resolved to the same class in both loaders.
2002 // Returns the name of the type that failed a loader constraint check, or
2003 // null if no constraint failed.  No exception except OOME is thrown.
2004 // Arrays are not added to the loader constraint table, their elements are.
2005 Symbol* SystemDictionary::check_signature_loaders(Symbol* signature,
2006                                                   Klass* klass_being_linked,
2007                                                   Handle loader1, Handle loader2,
2008                                                   bool is_method)  {
2009   // Nothing to do if loaders are the same.
2010   if (loader1() == loader2()) {
2011     return nullptr;
2012   }
2013 
2014   for (SignatureStream ss(signature, is_method); !ss.is_done(); ss.next()) {
2015     if (ss.is_reference()) {
2016       Symbol* sig = ss.as_symbol();
2017       // Note: In the future, if template-like types can take
2018       // arguments, we will want to recognize them and dig out class
2019       // names hiding inside the argument lists.
2020       if (!add_loader_constraint(sig, klass_being_linked, loader1, loader2)) {
2021         return sig;
2022       }
2023     }
2024   }
2025   return nullptr;
2026 }
2027 
2028 Method* SystemDictionary::find_method_handle_intrinsic(vmIntrinsicID iid,
2029                                                        Symbol* signature,
2030                                                        TRAPS) {
2031 
2032   const int iid_as_int = vmIntrinsics::as_int(iid);
2033   assert(MethodHandles::is_signature_polymorphic(iid) &&
2034          MethodHandles::is_signature_polymorphic_intrinsic(iid) &&
2035          iid != vmIntrinsics::_invokeGeneric,
2036          "must be a known MH intrinsic iid=%d: %s", iid_as_int, vmIntrinsics::name_at(iid));
2037 
2038   InvokeMethodKey key(signature, iid_as_int);
2039   Method** met = nullptr;
2040 
2041   // We only want one entry in the table for this (signature/id, method) pair but the code
2042   // to create the intrinsic method needs to be outside the lock.
2043   // The first thread claims the entry by adding the key and the other threads wait, until the
2044   // Method has been added as the value.
2045   {
2046     MonitorLocker ml(THREAD, InvokeMethodIntrinsicTable_lock);
2047     while (true) {
2048       bool created;
2049       met = _invoke_method_intrinsic_table->put_if_absent(key, &created);
2050       assert(met != nullptr, "either created or found");
2051       if (*met != nullptr) {
2052         return *met;
2053       } else if (created) {
2054         // The current thread won the race and will try to create the full entry.
2055         break;
2056       } else {
2057         // Another thread beat us to it, so wait for them to complete
2058         // and return *met; or if they hit an error we get another try.
2059         ml.wait();
2060         // Note it is not safe to read *met here as that entry could have
2061         // been deleted, so we must loop and try put_if_absent again.
2062       }
2063     }
2064   }
2065 
2066   methodHandle m = Method::make_method_handle_intrinsic(iid, signature, THREAD);
2067   bool throw_error = HAS_PENDING_EXCEPTION;
2068   if (!throw_error && (!Arguments::is_interpreter_only() || iid == vmIntrinsics::_linkToNative)) {
2069     // Generate a compiled form of the MH intrinsic
2070     // linkToNative doesn't have interpreter-specific implementation, so always has to go through compiled version.
2071     AdapterHandlerLibrary::create_native_wrapper(m);
2072     // Check if have the compiled code.
2073     throw_error = (!m->has_compiled_code());
2074   }
2075 
2076   {
2077     MonitorLocker ml(THREAD, InvokeMethodIntrinsicTable_lock);
2078     if (throw_error) {
2079       // Remove the entry and let another thread try, or get the same exception.
2080       bool removed = _invoke_method_intrinsic_table->remove(key);
2081       assert(removed, "must be the owner");
2082       ml.notify_all();
2083     } else {
2084       signature->make_permanent(); // The signature is never unloaded.
2085       assert(Arguments::is_interpreter_only() || (m->has_compiled_code() &&
2086              m->code()->entry_point() == m->from_compiled_entry()),
2087              "MH intrinsic invariant");
2088       *met = m(); // insert the element
2089       ml.notify_all();
2090       return m();
2091     }
2092   }
2093 
2094   // Throw OOM or the pending exception in the JavaThread
2095   if (throw_error && !HAS_PENDING_EXCEPTION) {
2096     THROW_MSG_NULL(vmSymbols::java_lang_OutOfMemoryError(),
2097                    "Out of space in CodeCache for method handle intrinsic");
2098   }
2099   return nullptr;
2100 }
2101 
2102 #if INCLUDE_CDS
2103 void SystemDictionary::get_all_method_handle_intrinsics(GrowableArray<Method*>* methods) {
2104   assert(SafepointSynchronize::is_at_safepoint(), "must be");
2105   auto do_method = [&] (InvokeMethodKey& key, Method*& m) {
2106     methods->append(m);
2107   };
2108   _invoke_method_intrinsic_table->iterate_all(do_method);
2109 }
2110 
2111 void SystemDictionary::restore_archived_method_handle_intrinsics() {
2112   if (UseSharedSpaces) {
2113     EXCEPTION_MARK;
2114     restore_archived_method_handle_intrinsics_impl(THREAD);
2115     if (HAS_PENDING_EXCEPTION) {
2116       // This is probably caused by OOM -- other parts of the CDS archive have direct pointers to
2117       // the archived method handle intrinsics, so we can't really recover from this failure.
2118       vm_exit_during_initialization(err_msg("Failed to restore archived method handle intrinsics. Try to increase heap size."));
2119     }
2120   }
2121 }
2122 
2123 void SystemDictionary::restore_archived_method_handle_intrinsics_impl(TRAPS) {
2124   Array<Method*>* list = MetaspaceShared::archived_method_handle_intrinsics();
2125   for (int i = 0; i < list->length(); i++) {
2126     methodHandle m(THREAD, list->at(i));
2127     Method::restore_archived_method_handle_intrinsic(m, CHECK);
2128     m->constants()->restore_unshareable_info(CHECK);
2129     if (!Arguments::is_interpreter_only() || m->intrinsic_id() == vmIntrinsics::_linkToNative) {
2130       AdapterHandlerLibrary::create_native_wrapper(m);
2131       if (!m->has_compiled_code()) {
2132         ResourceMark rm(THREAD);
2133         vm_exit_during_initialization(err_msg("Failed to initialize method %s", m->external_name()));
2134       }
2135     }
2136 
2137     // There's no need to grab the InvokeMethodIntrinsicTable_lock, as we are still very early in
2138     // VM start-up -- in init_globals2() -- so we are still running a single Java thread. It's not
2139     // possible to have a contention.
2140     const int iid_as_int = vmIntrinsics::as_int(m->intrinsic_id());
2141     InvokeMethodKey key(m->signature(), iid_as_int);
2142     bool created = _invoke_method_intrinsic_table->put(key, m());
2143     assert(created, "unexpected contention");
2144   }
2145 }
2146 #endif // INCLUDE_CDS
2147 
2148 // Helper for unpacking the return value from linkMethod and linkCallSite.
2149 static Method* unpack_method_and_appendix(Handle mname,
2150                                           Klass* accessing_klass,
2151                                           objArrayHandle appendix_box,
2152                                           Handle* appendix_result,
2153                                           TRAPS) {
2154   if (mname.not_null()) {
2155     Method* m = java_lang_invoke_MemberName::vmtarget(mname());
2156     if (m != nullptr) {
2157       oop appendix = appendix_box->obj_at(0);
2158       LogTarget(Info, methodhandles) lt;
2159       if (lt.develop_is_enabled()) {
2160         ResourceMark rm(THREAD);
2161         LogStream ls(lt);
2162         ls.print("Linked method=" INTPTR_FORMAT ": ", p2i(m));
2163         m->print_on(&ls);
2164         if (appendix != nullptr) { ls.print("appendix = "); appendix->print_on(&ls); }
2165         ls.cr();
2166       }
2167 
2168       (*appendix_result) = Handle(THREAD, appendix);
2169       // the target is stored in the cpCache and if a reference to this
2170       // MemberName is dropped we need a way to make sure the
2171       // class_loader containing this method is kept alive.
2172       methodHandle mh(THREAD, m); // record_dependency can safepoint.
2173       ClassLoaderData* this_key = accessing_klass->class_loader_data();
2174       this_key->record_dependency(m->method_holder());
2175       return mh();
2176     }
2177   }
2178   THROW_MSG_NULL(vmSymbols::java_lang_LinkageError(), "bad value from MethodHandleNatives");
2179 }
2180 
2181 Method* SystemDictionary::find_method_handle_invoker(Klass* klass,
2182                                                      Symbol* name,
2183                                                      Symbol* signature,
2184                                                      Klass* accessing_klass,
2185                                                      Handle* appendix_result,
2186                                                      TRAPS) {
2187   guarantee(THREAD->can_call_java(), "");
2188   Handle method_type =
2189     SystemDictionary::find_method_handle_type(signature, accessing_klass, CHECK_NULL);
2190 
2191   int ref_kind = JVM_REF_invokeVirtual;
2192   oop name_oop = StringTable::intern(name, CHECK_NULL);
2193   Handle name_str (THREAD, name_oop);
2194   objArrayHandle appendix_box = oopFactory::new_objArray_handle(vmClasses::Object_klass(), 1, CHECK_NULL);
2195   assert(appendix_box->obj_at(0) == nullptr, "");
2196 
2197   // This should not happen.  JDK code should take care of that.
2198   if (accessing_klass == nullptr || method_type.is_null()) {
2199     THROW_MSG_NULL(vmSymbols::java_lang_InternalError(), "bad invokehandle");
2200   }
2201 
2202   // call java.lang.invoke.MethodHandleNatives::linkMethod(... String, MethodType) -> MemberName
2203   JavaCallArguments args;
2204   args.push_oop(Handle(THREAD, accessing_klass->java_mirror()));
2205   args.push_int(ref_kind);
2206   args.push_oop(Handle(THREAD, klass->java_mirror()));
2207   args.push_oop(name_str);
2208   args.push_oop(method_type);
2209   args.push_oop(appendix_box);
2210   JavaValue result(T_OBJECT);
2211   JavaCalls::call_static(&result,
2212                          vmClasses::MethodHandleNatives_klass(),
2213                          vmSymbols::linkMethod_name(),
2214                          vmSymbols::linkMethod_signature(),
2215                          &args, CHECK_NULL);
2216   Handle mname(THREAD, result.get_oop());
2217   return unpack_method_and_appendix(mname, accessing_klass, appendix_box, appendix_result, THREAD);
2218 }
2219 
2220 // Decide if we can globally cache a lookup of this class, to be returned to any client that asks.
2221 // We must ensure that all class loaders everywhere will reach this class, for any client.
2222 // This is a safe bet for public classes in java.lang, such as Object and String.
2223 // We also include public classes in java.lang.invoke, because they appear frequently in system-level method types.
2224 // Out of an abundance of caution, we do not include any other classes, not even for packages like java.util.
2225 static bool is_always_visible_class(oop mirror) {
2226   Klass* klass = java_lang_Class::as_Klass(mirror);
2227   if (klass->is_objArray_klass()) {
2228     klass = ObjArrayKlass::cast(klass)->bottom_klass(); // check element type
2229   }
2230   if (klass->is_typeArray_klass()) {
2231     return true; // primitive array
2232   }
2233   assert(klass->is_instance_klass(), "%s", klass->external_name());
2234   return klass->is_public() &&
2235          (InstanceKlass::cast(klass)->is_same_class_package(vmClasses::Object_klass()) ||       // java.lang
2236           InstanceKlass::cast(klass)->is_same_class_package(vmClasses::MethodHandle_klass()));  // java.lang.invoke
2237 }
2238 
2239 // Find or construct the Java mirror (java.lang.Class instance) for
2240 // the given field type signature, as interpreted relative to the
2241 // given class loader.  Handles primitives, void, references, arrays,
2242 // and all other reflectable types, except method types.
2243 // N.B.  Code in reflection should use this entry point.
2244 Handle SystemDictionary::find_java_mirror_for_type(Symbol* signature,
2245                                                    Klass* accessing_klass,
2246                                                    SignatureStream::FailureMode failure_mode,
2247                                                    TRAPS) {
2248 
2249   Handle class_loader;
2250 
2251   // What we have here must be a valid field descriptor,
2252   // and all valid field descriptors are supported.
2253   // Produce the same java.lang.Class that reflection reports.
2254   if (accessing_klass != nullptr) {
2255     class_loader      = Handle(THREAD, accessing_klass->class_loader());
2256   }
2257   ResolvingSignatureStream ss(signature, class_loader, false);
2258   oop mirror_oop = ss.as_java_mirror(failure_mode, CHECK_NH);
2259   if (mirror_oop == nullptr) {
2260     return Handle();  // report failure this way
2261   }
2262   Handle mirror(THREAD, mirror_oop);
2263 
2264   if (accessing_klass != nullptr) {
2265     // Check accessibility, emulating ConstantPool::verify_constant_pool_resolve.
2266     Klass* sel_klass = java_lang_Class::as_Klass(mirror());
2267     if (sel_klass != nullptr) {
2268       LinkResolver::check_klass_accessibility(accessing_klass, sel_klass, CHECK_NH);
2269     }
2270   }
2271   return mirror;
2272 }
2273 
2274 
2275 // Ask Java code to find or construct a java.lang.invoke.MethodType for the given
2276 // signature, as interpreted relative to the given class loader.
2277 // Because of class loader constraints, all method handle usage must be
2278 // consistent with this loader.
2279 Handle SystemDictionary::find_method_handle_type(Symbol* signature,
2280                                                  Klass* accessing_klass,
2281                                                  TRAPS) {
2282   Handle empty;
2283   OopHandle* o;
2284   {
2285     MutexLocker ml(THREAD, InvokeMethodTypeTable_lock);
2286     o = _invoke_method_type_table->get(signature);
2287   }
2288 
2289   if (o != nullptr) {
2290     oop mt = o->resolve();
2291     assert(java_lang_invoke_MethodType::is_instance(mt), "");
2292     return Handle(THREAD, mt);
2293   } else if (!THREAD->can_call_java()) {
2294     warning("SystemDictionary::find_method_handle_type called from compiler thread");  // FIXME
2295     return Handle();  // do not attempt from within compiler, unless it was cached
2296   }
2297 
2298   Handle class_loader;
2299   if (accessing_klass != nullptr) {
2300     class_loader      = Handle(THREAD, accessing_klass->class_loader());
2301   }
2302   bool can_be_cached = true;
2303   int npts = ArgumentCount(signature).size();
2304   objArrayHandle pts = oopFactory::new_objArray_handle(vmClasses::Class_klass(), npts, CHECK_(empty));
2305   int arg = 0;
2306   Handle rt; // the return type from the signature
2307   ResourceMark rm(THREAD);
2308   for (SignatureStream ss(signature); !ss.is_done(); ss.next()) {
2309     oop mirror = nullptr;
2310     if (can_be_cached) {
2311       // Use neutral class loader to lookup candidate classes to be placed in the cache.
2312       mirror = ss.as_java_mirror(Handle(), SignatureStream::ReturnNull, CHECK_(empty));
2313       if (mirror == nullptr || (ss.is_reference() && !is_always_visible_class(mirror))) {
2314         // Fall back to accessing_klass context.
2315         can_be_cached = false;
2316       }
2317     }
2318     if (!can_be_cached) {
2319       // Resolve, throwing a real error if it doesn't work.
2320       mirror = ss.as_java_mirror(class_loader, SignatureStream::NCDFError, CHECK_(empty));
2321     }
2322     assert(mirror != nullptr, "%s", ss.as_symbol()->as_C_string());
2323     if (ss.at_return_type())
2324       rt = Handle(THREAD, mirror);
2325     else
2326       pts->obj_at_put(arg++, mirror);
2327 
2328     // Check accessibility.
2329     if (!java_lang_Class::is_primitive(mirror) && accessing_klass != nullptr) {
2330       Klass* sel_klass = java_lang_Class::as_Klass(mirror);
2331       mirror = nullptr;  // safety
2332       // Emulate ConstantPool::verify_constant_pool_resolve.
2333       LinkResolver::check_klass_accessibility(accessing_klass, sel_klass, CHECK_(empty));
2334     }
2335   }
2336   assert(arg == npts, "");
2337 
2338   // call java.lang.invoke.MethodHandleNatives::findMethodHandleType(Class rt, Class[] pts) -> MethodType
2339   JavaCallArguments args(Handle(THREAD, rt()));
2340   args.push_oop(pts);
2341   JavaValue result(T_OBJECT);
2342   JavaCalls::call_static(&result,
2343                          vmClasses::MethodHandleNatives_klass(),
2344                          vmSymbols::findMethodHandleType_name(),
2345                          vmSymbols::findMethodHandleType_signature(),
2346                          &args, CHECK_(empty));
2347   Handle method_type(THREAD, result.get_oop());
2348 
2349   if (can_be_cached) {
2350     // We can cache this MethodType inside the JVM.
2351     MutexLocker ml(THREAD, InvokeMethodTypeTable_lock);
2352     bool created = false;
2353     assert(method_type != nullptr, "unexpected null");
2354     OopHandle* h = _invoke_method_type_table->get(signature);
2355     if (h == nullptr) {
2356       signature->make_permanent(); // The signature is never unloaded.
2357       OopHandle elem = OopHandle(Universe::vm_global(), method_type());
2358       bool created = _invoke_method_type_table->put(signature, elem);
2359       assert(created, "better be created");
2360     }
2361   }
2362   // report back to the caller with the MethodType
2363   return method_type;
2364 }
2365 
2366 Handle SystemDictionary::find_field_handle_type(Symbol* signature,
2367                                                 Klass* accessing_klass,
2368                                                 TRAPS) {
2369   Handle empty;
2370   ResourceMark rm(THREAD);
2371   SignatureStream ss(signature, /*is_method=*/ false);
2372   if (!ss.is_done()) {
2373     Handle class_loader;
2374     if (accessing_klass != nullptr) {
2375       class_loader      = Handle(THREAD, accessing_klass->class_loader());
2376     }
2377     oop mirror = ss.as_java_mirror(class_loader, SignatureStream::NCDFError, CHECK_(empty));
2378     ss.next();
2379     if (ss.is_done()) {
2380       return Handle(THREAD, mirror);
2381     }
2382   }
2383   return empty;
2384 }
2385 
2386 // Ask Java code to find or construct a method handle constant.
2387 Handle SystemDictionary::link_method_handle_constant(Klass* caller,
2388                                                      int ref_kind, //e.g., JVM_REF_invokeVirtual
2389                                                      Klass* callee,
2390                                                      Symbol* name,
2391                                                      Symbol* signature,
2392                                                      TRAPS) {
2393   Handle empty;
2394   if (caller == nullptr) {
2395     THROW_MSG_(vmSymbols::java_lang_InternalError(), "bad MH constant", empty);
2396   }
2397   Handle name_str      = java_lang_String::create_from_symbol(name,      CHECK_(empty));
2398   Handle signature_str = java_lang_String::create_from_symbol(signature, CHECK_(empty));
2399 
2400   // Put symbolic info from the MH constant into freshly created MemberName and resolve it.
2401   Handle mname = vmClasses::MemberName_klass()->allocate_instance_handle(CHECK_(empty));
2402   java_lang_invoke_MemberName::set_clazz(mname(), callee->java_mirror());
2403   java_lang_invoke_MemberName::set_name (mname(), name_str());
2404   java_lang_invoke_MemberName::set_type (mname(), signature_str());
2405   java_lang_invoke_MemberName::set_flags(mname(), MethodHandles::ref_kind_to_flags(ref_kind));
2406 
2407   if (ref_kind == JVM_REF_invokeVirtual &&
2408       MethodHandles::is_signature_polymorphic_public_name(callee, name)) {
2409     // Skip resolution for public signature polymorphic methods such as
2410     // j.l.i.MethodHandle.invoke()/invokeExact() and those on VarHandle
2411     // They require appendix argument which MemberName resolution doesn't handle.
2412     // There's special logic on JDK side to handle them
2413     // (see MethodHandles.linkMethodHandleConstant() and MethodHandles.findVirtualForMH()).
2414   } else {
2415     MethodHandles::resolve_MemberName(mname, caller, 0, false /*speculative_resolve*/, CHECK_(empty));
2416   }
2417 
2418   // After method/field resolution succeeded, it's safe to resolve MH signature as well.
2419   Handle type = MethodHandles::resolve_MemberName_type(mname, caller, CHECK_(empty));
2420 
2421   // call java.lang.invoke.MethodHandleNatives::linkMethodHandleConstant(Class caller, int refKind, Class callee, String name, Object type) -> MethodHandle
2422   JavaCallArguments args;
2423   args.push_oop(Handle(THREAD, caller->java_mirror()));  // the referring class
2424   args.push_int(ref_kind);
2425   args.push_oop(Handle(THREAD, callee->java_mirror()));  // the target class
2426   args.push_oop(name_str);
2427   args.push_oop(type);
2428   JavaValue result(T_OBJECT);
2429   JavaCalls::call_static(&result,
2430                          vmClasses::MethodHandleNatives_klass(),
2431                          vmSymbols::linkMethodHandleConstant_name(),
2432                          vmSymbols::linkMethodHandleConstant_signature(),
2433                          &args, CHECK_(empty));
2434   return Handle(THREAD, result.get_oop());
2435 }
2436 
2437 // Ask Java to run a bootstrap method, in order to create a dynamic call site
2438 // while linking an invokedynamic op, or compute a constant for Dynamic_info CP entry
2439 // with linkage results being stored back into the bootstrap specifier.
2440 void SystemDictionary::invoke_bootstrap_method(BootstrapInfo& bootstrap_specifier, TRAPS) {
2441   // Resolve the bootstrap specifier, its name, type, and static arguments
2442   bootstrap_specifier.resolve_bsm(CHECK);
2443 
2444   // This should not happen.  JDK code should take care of that.
2445   if (bootstrap_specifier.caller() == nullptr || bootstrap_specifier.type_arg().is_null()) {
2446     THROW_MSG(vmSymbols::java_lang_InternalError(), "Invalid bootstrap method invocation with no caller or type argument");
2447   }
2448 
2449   bool is_indy = bootstrap_specifier.is_method_call();
2450   objArrayHandle appendix_box;
2451   if (is_indy) {
2452     // Some method calls may require an appendix argument.  Arrange to receive it.
2453     appendix_box = oopFactory::new_objArray_handle(vmClasses::Object_klass(), 1, CHECK);
2454     assert(appendix_box->obj_at(0) == nullptr, "");
2455   }
2456 
2457   // call condy: java.lang.invoke.MethodHandleNatives::linkDynamicConstant(caller, bsm, type, info)
2458   //       indy: java.lang.invoke.MethodHandleNatives::linkCallSite(caller, bsm, name, mtype, info, &appendix)
2459   JavaCallArguments args;
2460   args.push_oop(Handle(THREAD, bootstrap_specifier.caller_mirror()));
2461   args.push_oop(bootstrap_specifier.bsm());
2462   args.push_oop(bootstrap_specifier.name_arg());
2463   args.push_oop(bootstrap_specifier.type_arg());
2464   args.push_oop(bootstrap_specifier.arg_values());
2465   if (is_indy) {
2466     args.push_oop(appendix_box);
2467   }
2468   JavaValue result(T_OBJECT);
2469   JavaCalls::call_static(&result,
2470                          vmClasses::MethodHandleNatives_klass(),
2471                          is_indy ? vmSymbols::linkCallSite_name() : vmSymbols::linkDynamicConstant_name(),
2472                          is_indy ? vmSymbols::linkCallSite_signature() : vmSymbols::linkDynamicConstant_signature(),
2473                          &args, CHECK);
2474 
2475   Handle value(THREAD, result.get_oop());
2476   if (is_indy) {
2477     Handle appendix;
2478     Method* method = unpack_method_and_appendix(value,
2479                                                 bootstrap_specifier.caller(),
2480                                                 appendix_box,
2481                                                 &appendix, CHECK);
2482     methodHandle mh(THREAD, method);
2483     bootstrap_specifier.set_resolved_method(mh, appendix);
2484   } else {
2485     bootstrap_specifier.set_resolved_value(value);
2486   }
2487 
2488   // sanity check
2489   assert(bootstrap_specifier.is_resolved() ||
2490          (bootstrap_specifier.is_method_call() &&
2491           bootstrap_specifier.resolved_method().not_null()), "bootstrap method call failed");
2492 }
2493 
2494 
2495 bool SystemDictionary::is_nonpublic_Object_method(Method* m) {
2496   assert(m != nullptr, "Unexpected nullptr Method*");
2497   return !m->is_public() && m->method_holder() == vmClasses::Object_klass();
2498 }
2499 
2500 // ----------------------------------------------------------------------------
2501 
2502 void SystemDictionary::print_on(outputStream *st) {
2503   CDS_ONLY(SystemDictionaryShared::print_on(st));
2504   GCMutexLocker mu(SystemDictionary_lock);
2505 
2506   ClassLoaderDataGraph::print_dictionary(st);
2507 
2508   // Placeholders
2509   PlaceholderTable::print_on(st);
2510   st->cr();
2511 
2512   // loader constraints - print under SD_lock
2513   LoaderConstraintTable::print_on(st);
2514   st->cr();
2515 }
2516 
2517 void SystemDictionary::print() { print_on(tty); }
2518 
2519 void SystemDictionary::verify() {
2520 
2521   GCMutexLocker mu(SystemDictionary_lock);
2522 
2523   // Verify dictionary
2524   ClassLoaderDataGraph::verify_dictionary();
2525 
2526   // Verify constraint table
2527   LoaderConstraintTable::verify();
2528 }
2529 
2530 void SystemDictionary::dump(outputStream *st, bool verbose) {
2531   assert_locked_or_safepoint(SystemDictionary_lock);
2532   if (verbose) {
2533     print_on(st);
2534   } else {
2535     CDS_ONLY(SystemDictionaryShared::print_table_statistics(st));
2536     ClassLoaderDataGraph::print_table_statistics(st);
2537     LoaderConstraintTable::print_table_statistics(st);
2538   }
2539 }
2540 
2541 // Utility for dumping dictionaries.
2542 SystemDictionaryDCmd::SystemDictionaryDCmd(outputStream* output, bool heap) :
2543                                  DCmdWithParser(output, heap),
2544   _verbose("-verbose", "Dump the content of each dictionary entry for all class loaders",
2545            "BOOLEAN", false, "false") {
2546   _dcmdparser.add_dcmd_option(&_verbose);
2547 }
2548 
2549 void SystemDictionaryDCmd::execute(DCmdSource source, TRAPS) {
2550   VM_DumpHashtable dumper(output(), VM_DumpHashtable::DumpSysDict,
2551                          _verbose.value());
2552   VMThread::execute(&dumper);
2553 }