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/classLoadInfo.hpp"
  34 #include "classfile/dictionary.hpp"
  35 #include "classfile/javaClasses.inline.hpp"
  36 #include "classfile/klassFactory.hpp"
  37 #include "classfile/loaderConstraints.hpp"
  38 #include "classfile/modules.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/constantPool.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/oopHandle.inline.hpp"
  66 #include "oops/symbol.hpp"
  67 #include "oops/typeArrayKlass.hpp"
  68 #include "prims/jvmtiExport.hpp"
  69 #include "prims/methodHandles.hpp"
  70 #include "runtime/arguments.hpp"
  71 #include "runtime/atomicAccess.hpp"
  72 #include "runtime/handles.inline.hpp"
  73 #include "runtime/java.hpp"
  74 #include "runtime/javaCalls.hpp"
  75 #include "runtime/mutexLocker.hpp"
  76 #include "runtime/sharedRuntime.hpp"
  77 #include "runtime/signature.hpp"
  78 #include "runtime/synchronizer.hpp"
  79 #include "services/classLoadingService.hpp"
  80 #include "services/diagnosticCommand.hpp"
  81 #include "services/finalizerService.hpp"
  82 #include "services/threadService.hpp"
  83 #include "utilities/growableArray.hpp"
  84 #include "utilities/macros.hpp"
  85 #include "utilities/utf8.hpp"
  86 #if INCLUDE_CDS
  87 #include "classfile/systemDictionaryShared.hpp"
  88 #endif
  89 #if INCLUDE_JFR
  90 #include "jfr/jfr.hpp"
  91 #endif
  92 
  93 class InvokeMethodKey : public StackObj {
  94   private:
  95     Symbol* _symbol;
  96     intptr_t _iid;
  97 
  98   public:
  99     InvokeMethodKey(Symbol* symbol, intptr_t iid) :
 100         _symbol(symbol),
 101         _iid(iid) {}
 102 
 103     static bool key_comparison(InvokeMethodKey const &k1, InvokeMethodKey const &k2){
 104         return k1._symbol == k2._symbol && k1._iid == k2._iid;
 105     }
 106 
 107     static unsigned int compute_hash(const InvokeMethodKey &k) {
 108         Symbol* sym = k._symbol;
 109         intptr_t iid = k._iid;
 110         unsigned int hash = (unsigned int) sym -> identity_hash();
 111         return (unsigned int) (hash ^ iid);
 112     }
 113 
 114 };
 115 
 116 using InvokeMethodIntrinsicTable = HashTable<InvokeMethodKey, Method*, 139, AnyObj::C_HEAP, mtClass,
 117                   InvokeMethodKey::compute_hash, InvokeMethodKey::key_comparison>;
 118 static InvokeMethodIntrinsicTable* _invoke_method_intrinsic_table;
 119 using InvokeMethodTypeTable = HashTable<SymbolHandle, OopHandle, 139, AnyObj::C_HEAP, mtClass, SymbolHandle::compute_hash>;
 120 static InvokeMethodTypeTable* _invoke_method_type_table;
 121 
 122 OopHandle   SystemDictionary::_java_system_loader;
 123 OopHandle   SystemDictionary::_java_platform_loader;
 124 
 125 // ----------------------------------------------------------------------------
 126 // Java-level SystemLoader and PlatformLoader
 127 oop SystemDictionary::java_system_loader() {
 128   return _java_system_loader.resolve();
 129 }
 130 
 131 oop SystemDictionary::java_platform_loader() {
 132   return _java_platform_loader.resolve();
 133 }
 134 
 135 void SystemDictionary::compute_java_loaders(TRAPS) {
 136   if (_java_platform_loader.is_empty()) {
 137     oop platform_loader = get_platform_class_loader_impl(CHECK);
 138     _java_platform_loader = OopHandle(Universe::vm_global(), platform_loader);
 139   } else {
 140     // It must have been restored from the archived module graph
 141     assert(CDSConfig::is_using_archive(), "must be");
 142     assert(CDSConfig::is_using_full_module_graph(), "must be");
 143     DEBUG_ONLY(
 144       oop platform_loader = get_platform_class_loader_impl(CHECK);
 145       assert(_java_platform_loader.resolve() == platform_loader, "must be");
 146     )
 147  }
 148 
 149   if (_java_system_loader.is_empty()) {
 150     oop system_loader = get_system_class_loader_impl(CHECK);
 151     _java_system_loader = OopHandle(Universe::vm_global(), system_loader);
 152   } else {
 153     // It must have been restored from the archived module graph
 154     assert(CDSConfig::is_using_archive(), "must be");
 155     assert(CDSConfig::is_using_full_module_graph(), "must be");
 156     DEBUG_ONLY(
 157       oop system_loader = get_system_class_loader_impl(CHECK);
 158       assert(_java_system_loader.resolve() == system_loader, "must be");
 159     )
 160   }
 161 }
 162 
 163 oop SystemDictionary::get_system_class_loader_impl(TRAPS) {
 164   JavaValue result(T_OBJECT);
 165   InstanceKlass* class_loader_klass = vmClasses::ClassLoader_klass();
 166   JavaCalls::call_static(&result,
 167                          class_loader_klass,
 168                          vmSymbols::getSystemClassLoader_name(),
 169                          vmSymbols::void_classloader_signature(),
 170                          CHECK_NULL);
 171   return result.get_oop();
 172 }
 173 
 174 oop SystemDictionary::get_platform_class_loader_impl(TRAPS) {
 175   JavaValue result(T_OBJECT);
 176   InstanceKlass* class_loader_klass = vmClasses::ClassLoader_klass();
 177   JavaCalls::call_static(&result,
 178                          class_loader_klass,
 179                          vmSymbols::getPlatformClassLoader_name(),
 180                          vmSymbols::void_classloader_signature(),
 181                          CHECK_NULL);
 182   return result.get_oop();
 183 }
 184 
 185 // Helper function
 186 inline ClassLoaderData* class_loader_data(Handle class_loader) {
 187   return ClassLoaderData::class_loader_data(class_loader());
 188 }
 189 
 190 ClassLoaderData* SystemDictionary::register_loader(Handle class_loader, bool create_mirror_cld) {
 191   if (create_mirror_cld) {
 192     // Add a new class loader data to the graph.
 193     return ClassLoaderDataGraph::add(class_loader, true);
 194   } else {
 195     return (class_loader() == nullptr) ? ClassLoaderData::the_null_class_loader_data() :
 196                                       ClassLoaderDataGraph::find_or_create(class_loader);
 197   }
 198 }
 199 
 200 void SystemDictionary::set_system_loader(ClassLoaderData *cld) {
 201   if (_java_system_loader.is_empty()) {
 202     _java_system_loader = cld->class_loader_handle();
 203   } else {
 204     assert(_java_system_loader.resolve() == cld->class_loader(), "sanity");
 205   }
 206 }
 207 
 208 void SystemDictionary::set_platform_loader(ClassLoaderData *cld) {
 209   if (_java_platform_loader.is_empty()) {
 210     _java_platform_loader = cld->class_loader_handle();
 211   } else {
 212     assert(_java_platform_loader.resolve() == cld->class_loader(), "sanity");
 213   }
 214 }
 215 
 216 // ----------------------------------------------------------------------------
 217 // Parallel class loading check
 218 
 219 static bool is_parallelCapable(Handle class_loader) {
 220   if (class_loader.is_null()) return true;
 221   return java_lang_ClassLoader::parallelCapable(class_loader());
 222 }
 223 // ----------------------------------------------------------------------------
 224 // ParallelDefineClass flag does not apply to bootclass loader
 225 static bool is_parallelDefine(Handle class_loader) {
 226    if (class_loader.is_null()) return false;
 227    if (AllowParallelDefineClass && java_lang_ClassLoader::parallelCapable(class_loader())) {
 228      return true;
 229    }
 230    return false;
 231 }
 232 
 233 // Returns true if the passed class loader is the builtin application class loader
 234 // or a custom system class loader. A customer system class loader can be
 235 // specified via -Djava.system.class.loader.
 236 bool SystemDictionary::is_system_class_loader(oop class_loader) {
 237   if (class_loader == nullptr) {
 238     return false;
 239   }
 240   return (class_loader->klass() == vmClasses::jdk_internal_loader_ClassLoaders_AppClassLoader_klass() ||
 241          class_loader == _java_system_loader.peek());
 242 }
 243 
 244 // Returns true if the passed class loader is the platform class loader.
 245 bool SystemDictionary::is_platform_class_loader(oop class_loader) {
 246   if (class_loader == nullptr) {
 247     return false;
 248   }
 249   return (class_loader->klass() == vmClasses::jdk_internal_loader_ClassLoaders_PlatformClassLoader_klass());
 250 }
 251 
 252 Handle SystemDictionary::get_loader_lock_or_null(Handle class_loader) {
 253   // If class_loader is null or parallelCapable, the JVM doesn't acquire a lock while loading.
 254   if (is_parallelCapable(class_loader)) {
 255     return Handle();
 256   } else {
 257     return class_loader;
 258   }
 259 }
 260 
 261 // ----------------------------------------------------------------------------
 262 // Resolving of classes
 263 
 264 Symbol* SystemDictionary::class_name_symbol(const char* name, Symbol* exception, TRAPS) {
 265   if (name == nullptr) {
 266     THROW_MSG_NULL(exception, "No class name given");
 267   }
 268   size_t name_len = strlen(name);
 269   if (name_len > static_cast<size_t>(Symbol::max_length())) {
 270     // It's impossible to create this class;  the name cannot fit
 271     // into the constant pool. If necessary report an abridged name
 272     // in the exception message.
 273     if (name_len > static_cast<size_t>(MaxStringPrintSize)) {
 274       Exceptions::fthrow(THREAD_AND_LOCATION, exception,
 275                          "Class name exceeds maximum length of %d: %.*s ... (%zu characters omitted) ... %.*s",
 276                          Symbol::max_length(),
 277                          MaxStringPrintSize / 2,
 278                          name,
 279                          name_len - 2 * (MaxStringPrintSize / 2), // allows for odd value
 280                          MaxStringPrintSize / 2,
 281                          name + name_len - MaxStringPrintSize / 2);
 282     }
 283     else {
 284       Exceptions::fthrow(THREAD_AND_LOCATION, exception,
 285                          "Class name exceeds maximum length of %d: %s",
 286                          Symbol::max_length(),
 287                          name);
 288     }
 289     return nullptr;
 290   }
 291   // Callers should ensure that the name is never an illegal UTF8 string.
 292   assert(UTF8::is_legal_utf8((const unsigned char*)name, name_len, false),
 293          "Class name is not a valid utf8 string.");
 294 
 295   // Make a new symbol for the class name.
 296   return SymbolTable::new_symbol(name);
 297 }
 298 
 299 #ifdef ASSERT
 300 // Used to verify that class loading succeeded in adding k to the dictionary.
 301 static void verify_dictionary_entry(Symbol* class_name, InstanceKlass* k) {
 302   MutexLocker mu(SystemDictionary_lock);
 303   ClassLoaderData* loader_data = k->class_loader_data();
 304   Dictionary* dictionary = loader_data->dictionary();
 305   assert(class_name == k->name(), "Must be the same");
 306   InstanceKlass* kk = dictionary->find_class(JavaThread::current(), class_name);
 307   assert(kk == k, "should be present in dictionary");
 308 }
 309 #endif
 310 
 311 static void handle_resolution_exception(Symbol* class_name, bool throw_error, TRAPS) {
 312   if (HAS_PENDING_EXCEPTION) {
 313     // If we have a pending exception we forward it to the caller, unless throw_error is true,
 314     // in which case we have to check whether the pending exception is a ClassNotFoundException,
 315     // and convert it to a NoClassDefFoundError and chain the original ClassNotFoundException.
 316     if (throw_error && PENDING_EXCEPTION->is_a(vmClasses::ClassNotFoundException_klass())) {
 317       ResourceMark rm(THREAD);
 318       Handle e(THREAD, PENDING_EXCEPTION);
 319       CLEAR_PENDING_EXCEPTION;
 320       THROW_MSG_CAUSE(vmSymbols::java_lang_NoClassDefFoundError(), class_name->as_C_string(), e);
 321     } else {
 322       return; // the caller will throw the incoming exception
 323     }
 324   }
 325   // If the class is not found, ie, caller has checked that klass is null, throw the appropriate
 326   // error or exception depending on the value of throw_error.
 327   ResourceMark rm(THREAD);
 328   if (throw_error) {
 329     THROW_MSG(vmSymbols::java_lang_NoClassDefFoundError(), class_name->as_C_string());
 330   } else {
 331     THROW_MSG(vmSymbols::java_lang_ClassNotFoundException(), class_name->as_C_string());
 332   }
 333 }
 334 
 335 // Forwards to resolve_or_null
 336 
 337 Klass* SystemDictionary::resolve_or_fail(Symbol* class_name, Handle class_loader,
 338                                          bool throw_error, TRAPS) {
 339   Klass* klass = resolve_or_null(class_name, class_loader, THREAD);
 340   // Check for pending exception or null klass, and throw exception
 341   if (HAS_PENDING_EXCEPTION || klass == nullptr) {
 342     handle_resolution_exception(class_name, throw_error, CHECK_NULL);
 343   }
 344   return klass;
 345 }
 346 
 347 // Forwards to resolve_array_class_or_null or resolve_instance_class_or_null
 348 
 349 Klass* SystemDictionary::resolve_or_null(Symbol* class_name, Handle class_loader, TRAPS) {
 350   if (Signature::is_array(class_name)) {
 351     return resolve_array_class_or_null(class_name, class_loader, THREAD);
 352   } else {
 353     assert(class_name != nullptr && !Signature::is_array(class_name), "must be");
 354     if (Signature::has_envelope(class_name)) {
 355       ResourceMark rm(THREAD);
 356       // Ignore wrapping L and ;.
 357       TempNewSymbol name = SymbolTable::new_symbol(class_name->as_C_string() + 1,
 358                                                    class_name->utf8_length() - 2);
 359       return resolve_instance_class_or_null(name, class_loader, THREAD);
 360     } else {
 361       return resolve_instance_class_or_null(class_name, class_loader, THREAD);
 362     }
 363   }
 364 }
 365 
 366 // Forwards to resolve_instance_class_or_null
 367 
 368 Klass* SystemDictionary::resolve_array_class_or_null(Symbol* class_name,
 369                                                      Handle class_loader,
 370                                                      TRAPS) {
 371   assert(Signature::is_array(class_name), "must be array");
 372   ResourceMark rm(THREAD);
 373   SignatureStream ss(class_name, false);
 374   int ndims = ss.skip_array_prefix();  // skip all '['s
 375   Klass* k = nullptr;
 376   BasicType t = ss.type();
 377   if (ss.has_envelope()) {
 378     Symbol* obj_class = ss.as_symbol();
 379     k = SystemDictionary::resolve_instance_class_or_null(obj_class,
 380                                                          class_loader,
 381                                                          CHECK_NULL);
 382     if (k != nullptr) {
 383       k = k->array_klass(ndims, CHECK_NULL);
 384     }
 385   } else {
 386     k = Universe::typeArrayKlass(t);
 387     k = k->array_klass(ndims, CHECK_NULL);
 388   }
 389   return k;
 390 }
 391 
 392 static inline void log_circularity_error(Symbol* name, PlaceholderEntry* probe) {
 393   LogTarget(Debug, class, load, placeholders) lt;
 394   if (lt.is_enabled()) {
 395     ResourceMark rm;
 396     LogStream ls(lt);
 397     ls.print("ClassCircularityError detected for placeholder entry %s", name->as_C_string());
 398     probe->print_on(&ls);
 399     ls.cr();
 400   }
 401 }
 402 
 403 // Must be called for any superclass or superinterface resolution
 404 // during class definition to allow class circularity checking
 405 // superinterface callers:
 406 //    parse_interfaces - from defineClass
 407 // superclass callers:
 408 //   ClassFileParser - from defineClass
 409 //   load_shared_class - while loading a class from shared archive
 410 //   resolve_instance_class_or_null:
 411 //     via: handle_parallel_super_load
 412 //      when resolving a class that has an existing placeholder with
 413 //      a saved superclass [i.e. a defineClass is currently in progress]
 414 //      If another thread is trying to resolve the class, it must do
 415 //      superclass checks on its own thread to catch class circularity and
 416 //      to avoid deadlock.
 417 //
 418 // resolve_with_circularity_detection adds a DETECT_CIRCULARITY placeholder to the placeholder table before calling
 419 // resolve_instance_class_or_null. ClassCircularityError is detected when a DETECT_CIRCULARITY or LOAD_INSTANCE
 420 // placeholder for the same thread, class, classloader is found.
 421 // This can be seen with logging option: -Xlog:class+load+placeholders=debug.
 422 //
 423 InstanceKlass* SystemDictionary::resolve_with_circularity_detection(Symbol* class_name,
 424                                                                     Symbol* next_name,
 425                                                                     Handle class_loader,
 426                                                                     bool is_superclass,
 427                                                                     TRAPS) {
 428 
 429   assert(next_name != nullptr, "null superclass for resolving");
 430   assert(!Signature::is_array(next_name), "invalid superclass name");
 431 
 432   ClassLoaderData* loader_data = class_loader_data(class_loader);
 433 
 434   if (is_superclass) {
 435     InstanceKlass* klassk = loader_data->dictionary()->find_class(THREAD, class_name);
 436     if (klassk != nullptr) {
 437       // We can come here for two reasons:
 438       // (a) RedefineClasses -- the class is already loaded
 439       // (b) Rarely, the class might have been loaded by a parallel thread
 440       // We can do a quick check against the already assigned superclass's name and loader.
 441       InstanceKlass* superk = klassk->super();
 442       if (superk != nullptr &&
 443           superk->name() == next_name &&
 444           superk->class_loader() == class_loader()) {
 445         return superk;
 446       }
 447     }
 448   }
 449 
 450   // can't throw error holding a lock
 451   bool throw_circularity_error = false;
 452   {
 453     MutexLocker mu(THREAD, SystemDictionary_lock);
 454 
 455     // Must check ClassCircularity before resolving next_name (superclass or interface).
 456     PlaceholderEntry* probe = PlaceholderTable::get_entry(class_name, loader_data);
 457     if (probe != nullptr && probe->check_seen_thread(THREAD, PlaceholderTable::DETECT_CIRCULARITY)) {
 458         log_circularity_error(class_name, probe);
 459         throw_circularity_error = true;
 460     }
 461 
 462     // Make sure there's a placeholder for the class_name before resolving.
 463     // This is used as a claim that this thread is currently loading superclass/classloader
 464     // and for ClassCircularity checks.
 465     if (!throw_circularity_error) {
 466       // Be careful not to exit resolve_with_circularity_detection without removing this placeholder.
 467       PlaceholderEntry* newprobe = PlaceholderTable::find_and_add(class_name,
 468                                                                   loader_data,
 469                                                                   PlaceholderTable::DETECT_CIRCULARITY,
 470                                                                   next_name, THREAD);
 471     }
 472   }
 473 
 474   if (throw_circularity_error) {
 475       ResourceMark rm(THREAD);
 476       THROW_MSG_NULL(vmSymbols::java_lang_ClassCircularityError(), class_name->as_C_string());
 477   }
 478 
 479   // Resolve the superclass or superinterface, check results on return
 480   InstanceKlass* superk =
 481     SystemDictionary::resolve_instance_class_or_null(next_name,
 482                                                      class_loader,
 483                                                      THREAD);
 484 
 485   // Clean up placeholder entry.
 486   {
 487     MutexLocker mu(THREAD, SystemDictionary_lock);
 488     PlaceholderTable::find_and_remove(class_name, loader_data, PlaceholderTable::DETECT_CIRCULARITY, THREAD);
 489     SystemDictionary_lock->notify_all();
 490   }
 491 
 492   // Check for pending exception or null superk, and throw exception
 493   if (HAS_PENDING_EXCEPTION || superk == nullptr) {
 494     handle_resolution_exception(next_name, true, CHECK_NULL);
 495   }
 496 
 497   return superk;
 498 }
 499 
 500 // If the class in is in the placeholder table, class loading is in progress.
 501 // For cases where the application changes threads to load classes, it
 502 // is critical to ClassCircularity detection that we try loading
 503 // the superclass on the new thread internally, so we do parallel
 504 // superclass loading here.  This avoids deadlock for ClassCircularity
 505 // detection for parallelCapable class loaders that lock on a per-class lock.
 506 static void handle_parallel_super_load(Symbol* name,
 507                                        Symbol* superclassname,
 508                                        Handle class_loader,
 509                                        TRAPS) {
 510 
 511   // The result superk is not used; resolve_with_circularity_detection is called for circularity check only.
 512   // This passes false to is_superclass to skip doing the unlikely optimization.
 513   Klass* superk = SystemDictionary::resolve_with_circularity_detection(name,
 514                                                                        superclassname,
 515                                                                        class_loader,
 516                                                                        false,
 517                                                                        CHECK);
 518 }
 519 
 520 // Bootstrap and non-parallel capable class loaders use the LOAD_INSTANCE placeholder to
 521 // wait for parallel class loading and/or to check for circularity error for Xcomp when loading.
 522 static bool needs_load_placeholder(Handle class_loader) {
 523   return class_loader.is_null() || !is_parallelCapable(class_loader);
 524 }
 525 
 526 // Check for other threads loading this class either to throw CCE or wait in the case of the boot loader.
 527 static InstanceKlass* handle_parallel_loading(JavaThread* current,
 528                                               Symbol* name,
 529                                               ClassLoaderData* loader_data,
 530                                               bool must_wait_for_class_loading,
 531                                               bool* throw_circularity_error) {
 532   PlaceholderEntry* oldprobe = PlaceholderTable::get_entry(name, loader_data);
 533   if (oldprobe != nullptr) {
 534     // -Xcomp calls load_signature_classes which might result in loading
 535     // a class that's already in the process of loading, so we detect CCE here also.
 536     // Only need check_seen_thread once, not on each loop
 537     if (oldprobe->check_seen_thread(current, PlaceholderTable::LOAD_INSTANCE)) {
 538       log_circularity_error(name, oldprobe);
 539       *throw_circularity_error = true;
 540       return nullptr;
 541     } else if (must_wait_for_class_loading) {
 542       // Wait until the first thread has finished loading this class. Also wait until all the
 543       // threads trying to load its superclass have removed their placeholders.
 544       while (oldprobe != nullptr &&
 545              (oldprobe->instance_load_in_progress() || oldprobe->circularity_detection_in_progress())) {
 546 
 547         // LOAD_INSTANCE placeholders are used to implement parallel capable class loading
 548         // for the bootclass loader.
 549         SystemDictionary_lock->wait();
 550 
 551         // Check if classloading completed while we were waiting
 552         InstanceKlass* check = loader_data->dictionary()->find_class(current, name);
 553         if (check != nullptr) {
 554           // Klass is already loaded, so just return it
 555           return check;
 556         }
 557         // check if other thread failed to load and cleaned up
 558         oldprobe = PlaceholderTable::get_entry(name, loader_data);
 559       }
 560     }
 561   }
 562   return nullptr;
 563 }
 564 
 565 // SystemDictionary::resolve_instance_class_or_null is the main function for class name resolution.
 566 // After checking if the InstanceKlass already exists, it checks for ClassCircularityError and
 567 // whether the thread must wait for loading in parallel.  It eventually calls load_instance_class,
 568 // which will load the class via the bootstrap loader or call ClassLoader.loadClass().
 569 // This can return null, an exception or an InstanceKlass.
 570 InstanceKlass* SystemDictionary::resolve_instance_class_or_null(Symbol* name,
 571                                                                 Handle class_loader,
 572                                                                 TRAPS) {
 573   // name must be in the form of "java/lang/Object" -- cannot be "Ljava/lang/Object;"
 574   DEBUG_ONLY(ResourceMark rm(THREAD));
 575   assert(name != nullptr && !Signature::is_array(name) &&
 576          !Signature::has_envelope(name), "invalid class name: %s", name == nullptr ? "nullptr" : name->as_C_string());
 577 
 578   EventClassLoad class_load_event;
 579 
 580   HandleMark hm(THREAD);
 581 
 582   ClassLoaderData* loader_data = register_loader(class_loader);
 583   Dictionary* dictionary = loader_data->dictionary();
 584 
 585   // Do lookup to see if class already exists.
 586   InstanceKlass* probe = dictionary->find_class(THREAD, name);
 587   if (probe != nullptr) return probe;
 588 
 589   // Non-bootstrap class loaders will call out to class loader and
 590   // define via jvm/jni_DefineClass which will acquire the
 591   // class loader object lock to protect against multiple threads
 592   // defining the class in parallel by accident.
 593   // This lock must be acquired here so the waiter will find
 594   // any successful result in the SystemDictionary and not attempt
 595   // the define.
 596   // ParallelCapable class loaders and the bootstrap classloader
 597   // do not acquire lock here.
 598   Handle lockObject = get_loader_lock_or_null(class_loader);
 599   ObjectLocker ol(lockObject, THREAD);
 600 
 601   bool circularity_detection_in_progress  = false;
 602   InstanceKlass* loaded_class = nullptr;
 603   SymbolHandle superclassname; // Keep alive while loading in parallel thread.
 604 
 605   guarantee(THREAD->can_call_java(),
 606          "can not load classes with compiler thread: class=%s, classloader=%s",
 607          name->as_C_string(),
 608          class_loader.is_null() ? "null" : class_loader->klass()->name()->as_C_string());
 609 
 610   // Check again (after locking) if the class already exists in SystemDictionary
 611   {
 612     MutexLocker mu(THREAD, SystemDictionary_lock);
 613     InstanceKlass* check = dictionary->find_class(THREAD, name);
 614     if (check != nullptr) {
 615       // InstanceKlass is already loaded, but we still need to check protection domain below.
 616       loaded_class = check;
 617     } else {
 618       PlaceholderEntry* placeholder = PlaceholderTable::get_entry(name, loader_data);
 619       if (placeholder != nullptr && placeholder->circularity_detection_in_progress()) {
 620          circularity_detection_in_progress = true;
 621          superclassname = placeholder->next_klass_name();
 622          assert(superclassname != nullptr, "superclass has to have a name");
 623       }
 624     }
 625   }
 626 
 627   // If the class is in the placeholder table with super_class set,
 628   // handle superclass loading in progress.
 629   if (circularity_detection_in_progress) {
 630     handle_parallel_super_load(name, superclassname,
 631                                class_loader,
 632                                CHECK_NULL);
 633   }
 634 
 635   bool throw_circularity_error = false;
 636   if (loaded_class == nullptr) {
 637     bool load_placeholder_added = false;
 638 
 639     // Add placeholder entry to record loading instance class
 640     // case 1. Bootstrap classloader
 641     //    This classloader supports parallelism at the classloader level
 642     //    but only allows a single thread to load a class/classloader pair.
 643     //    The LOAD_INSTANCE placeholder is the mechanism for mutual exclusion.
 644     // case 2. parallelCapable user level classloaders
 645     //    These class loaders lock a per-class object lock when ClassLoader.loadClass()
 646     //    is called. A LOAD_INSTANCE placeholder isn't used for mutual exclusion.
 647     // case 3. traditional classloaders that rely on the classloader object lock
 648     //    There should be no need for need for LOAD_INSTANCE for mutual exclusion,
 649     //    except the LOAD_INSTANCE placeholder is used to detect CCE for -Xcomp.
 650     //    TODO: should also be used to detect CCE for parallel capable class loaders but it's not.
 651     {
 652       MutexLocker mu(THREAD, SystemDictionary_lock);
 653       if (needs_load_placeholder(class_loader)) {
 654         loaded_class = handle_parallel_loading(THREAD,
 655                                                name,
 656                                                loader_data,
 657                                                class_loader.is_null(),
 658                                                &throw_circularity_error);
 659       }
 660 
 661       // Recheck if the class has been loaded for all class loader cases and
 662       // add a LOAD_INSTANCE placeholder while holding the SystemDictionary_lock.
 663       if (!throw_circularity_error && loaded_class == nullptr) {
 664         InstanceKlass* check = dictionary->find_class(THREAD, name);
 665         if (check != nullptr) {
 666           loaded_class = check;
 667         } else if (needs_load_placeholder(class_loader)) {
 668           // Add the LOAD_INSTANCE token. Threads will wait on loading to complete for this thread.
 669           PlaceholderEntry* newprobe = PlaceholderTable::find_and_add(name, loader_data,
 670                                                                       PlaceholderTable::LOAD_INSTANCE,
 671                                                                       nullptr,
 672                                                                       THREAD);
 673           load_placeholder_added = true;
 674         }
 675       }
 676     }
 677 
 678     // Must throw error outside of owning lock
 679     if (throw_circularity_error) {
 680       assert(!HAS_PENDING_EXCEPTION && !load_placeholder_added, "circularity error cleanup");
 681       ResourceMark rm(THREAD);
 682       THROW_MSG_NULL(vmSymbols::java_lang_ClassCircularityError(), name->as_C_string());
 683     }
 684 
 685     // Be careful when modifying this code: once you have run
 686     // PlaceholderTable::find_and_add(PlaceholderTable::LOAD_INSTANCE),
 687     // you need to find_and_remove it before returning.
 688     // So be careful to not exit with a CHECK_ macro between these calls.
 689 
 690     if (loaded_class == nullptr) {
 691       // Do actual loading
 692       loaded_class = load_instance_class(name, class_loader, THREAD);
 693     }
 694 
 695     if (load_placeholder_added) {
 696       // clean up placeholder entries for LOAD_INSTANCE success or error
 697       // This brackets the SystemDictionary updates for both defining
 698       // and initiating loaders
 699       MutexLocker mu(THREAD, SystemDictionary_lock);
 700       PlaceholderTable::find_and_remove(name, loader_data, PlaceholderTable::LOAD_INSTANCE, THREAD);
 701       SystemDictionary_lock->notify_all();
 702     }
 703   }
 704 
 705   if (HAS_PENDING_EXCEPTION || loaded_class == nullptr) {
 706     return nullptr;
 707   }
 708 
 709   if (class_load_event.should_commit()) {
 710     JFR_ONLY(post_class_load_event(&class_load_event, loaded_class, loader_data);)
 711   }
 712 
 713   // Make sure we have the right class in the dictionary
 714   DEBUG_ONLY(verify_dictionary_entry(name, loaded_class));
 715 
 716   return loaded_class;
 717 }
 718 
 719 
 720 // This routine does not lock the system dictionary.
 721 //
 722 // Since readers don't hold a lock, we must make sure that system
 723 // dictionary entries are added to in a safe way (all links must
 724 // be updated in an MT-safe manner). All entries are removed during class
 725 // unloading, when this class loader is no longer referenced.
 726 //
 727 // Callers should be aware that an entry could be added just after
 728 // Dictionary is read here, so the caller will not see
 729 // the new entry.
 730 
 731 InstanceKlass* SystemDictionary::find_instance_klass(Thread* current,
 732                                                      Symbol* class_name,
 733                                                      Handle class_loader) {
 734 
 735   ClassLoaderData* loader_data = ClassLoaderData::class_loader_data_or_null(class_loader());
 736   if (loader_data == nullptr) {
 737     // If the ClassLoaderData has not been setup,
 738     // then the class loader has no entries in the dictionary.
 739     return nullptr;
 740   }
 741 
 742   Dictionary* dictionary = loader_data->dictionary();
 743   return dictionary->find_class(current, class_name);
 744 }
 745 
 746 // Look for a loaded instance or array klass by name.  Do not do any loading.
 747 // return null in case of error.
 748 Klass* SystemDictionary::find_instance_or_array_klass(Thread* current,
 749                                                       Symbol* class_name,
 750                                                       Handle class_loader) {
 751   Klass* k = nullptr;
 752   assert(class_name != nullptr, "class name must be non nullptr");
 753 
 754   if (Signature::is_array(class_name)) {
 755     // The name refers to an array.  Parse the name.
 756     // dimension and object_key in FieldArrayInfo are assigned as a
 757     // side-effect of this call
 758     SignatureStream ss(class_name, false);
 759     int ndims = ss.skip_array_prefix();  // skip all '['s
 760     BasicType t = ss.type();
 761     if (t != T_OBJECT) {
 762       k = Universe::typeArrayKlass(t);
 763     } else {
 764       k = SystemDictionary::find_instance_klass(current, ss.as_symbol(), class_loader);
 765     }
 766     if (k != nullptr) {
 767       k = k->array_klass_or_null(ndims);
 768     }
 769   } else {
 770     k = find_instance_klass(current, class_name, class_loader);
 771   }
 772   return k;
 773 }
 774 
 775 // Note: this method is much like resolve_class_from_stream, but
 776 // does not publish the classes in the SystemDictionary.
 777 // Handles Lookup.defineClass hidden.
 778 InstanceKlass* SystemDictionary::resolve_hidden_class_from_stream(
 779                                                      ClassFileStream* st,
 780                                                      Symbol* class_name,
 781                                                      Handle class_loader,
 782                                                      const ClassLoadInfo& cl_info,
 783                                                      TRAPS) {
 784 
 785   EventClassLoad class_load_event;
 786   ClassLoaderData* loader_data;
 787 
 788   // - for hidden classes that are not strong: create a new CLD that has a class holder and
 789   //                                           whose loader is the Lookup class's loader.
 790   // - for hidden class: add the class to the Lookup class's loader's CLD.
 791   assert (cl_info.is_hidden(), "only used for hidden classes");
 792   bool create_mirror_cld = !cl_info.is_strong_hidden();
 793   loader_data = register_loader(class_loader, create_mirror_cld);
 794 
 795   assert(st != nullptr, "invariant");
 796 
 797   // Parse stream and create a klass.
 798   InstanceKlass* k = KlassFactory::create_from_stream(st,
 799                                                       class_name,
 800                                                       loader_data,
 801                                                       cl_info,
 802                                                       CHECK_NULL);
 803   assert(k != nullptr, "no klass created");
 804 
 805   // Hidden classes that are not strong must update ClassLoaderData holder
 806   // so that they can be unloaded when the mirror is no longer referenced.
 807   if (!cl_info.is_strong_hidden()) {
 808     k->class_loader_data()->initialize_holder(Handle(THREAD, k->java_mirror()));
 809   }
 810 
 811   // Add to class hierarchy, and do possible deoptimizations.
 812   k->add_to_hierarchy(THREAD);
 813   // But, do not add to dictionary.
 814 
 815   if (class_load_event.should_commit()) {
 816     JFR_ONLY(post_class_load_event(&class_load_event, k, loader_data);)
 817   }
 818 
 819   k->link_class(CHECK_NULL);
 820 
 821   // notify jvmti
 822   if (JvmtiExport::should_post_class_load()) {
 823     JvmtiExport::post_class_load(THREAD, k);
 824   }
 825 
 826   return k;
 827 }
 828 
 829 // Add a klass to the system from a stream (called by jni_DefineClass and
 830 // JVM_DefineClass).
 831 // Note: class_name can be null. In that case we do not know the name of
 832 // the class until we have parsed the stream.
 833 // This function either returns an InstanceKlass or throws an exception.  It does
 834 // not return null without a pending exception.
 835 InstanceKlass* SystemDictionary::resolve_class_from_stream(
 836                                                      ClassFileStream* st,
 837                                                      Symbol* class_name,
 838                                                      Handle class_loader,
 839                                                      const ClassLoadInfo& cl_info,
 840                                                      TRAPS) {
 841 
 842   HandleMark hm(THREAD);
 843 
 844   ClassLoaderData* loader_data = register_loader(class_loader);
 845 
 846   // Classloaders that support parallelism, e.g. bootstrap classloader,
 847   // do not acquire lock here
 848   Handle lockObject = get_loader_lock_or_null(class_loader);
 849   ObjectLocker ol(lockObject, THREAD);
 850 
 851   // Parse the stream and create a klass.
 852   // Note that we do this even though this klass might
 853   // already be present in the SystemDictionary, otherwise we would not
 854   // throw potential ClassFormatErrors.
 855  InstanceKlass* k = nullptr;
 856 
 857 #if INCLUDE_CDS
 858   if (!CDSConfig::is_dumping_static_archive()) {
 859     k = SystemDictionaryShared::lookup_from_stream(class_name,
 860                                                    class_loader,
 861                                                    cl_info.protection_domain(),
 862                                                    st,
 863                                                    CHECK_NULL);
 864   }
 865 #endif
 866 
 867   if (k == nullptr) {
 868     k = KlassFactory::create_from_stream(st, class_name, loader_data, cl_info, CHECK_NULL);
 869   }
 870 
 871   assert(k != nullptr, "no klass created");
 872   Symbol* h_name = k->name();
 873   assert(class_name == nullptr || class_name == h_name, "name mismatch");
 874 
 875   // Add class just loaded
 876   // If a class loader supports parallel classloading, handle parallel define requests.
 877   // find_or_define_instance_class may return a different InstanceKlass,
 878   // in which case the old k would be deallocated
 879   if (is_parallelCapable(class_loader)) {
 880     k = find_or_define_instance_class(h_name, class_loader, k, CHECK_NULL);
 881   } else {
 882     define_instance_class(k, class_loader, THREAD);
 883 
 884     // If defining the class throws an exception register 'k' for cleanup.
 885     if (HAS_PENDING_EXCEPTION) {
 886       assert(k != nullptr, "Must have an instance klass here!");
 887       loader_data->add_to_deallocate_list(k);
 888       return nullptr;
 889     }
 890   }
 891 
 892   // Make sure we have an entry in the SystemDictionary on success
 893   DEBUG_ONLY(verify_dictionary_entry(h_name, k));
 894 
 895   return k;
 896 }
 897 
 898 InstanceKlass* SystemDictionary::resolve_from_stream(ClassFileStream* st,
 899                                                      Symbol* class_name,
 900                                                      Handle class_loader,
 901                                                      const ClassLoadInfo& cl_info,
 902                                                      TRAPS) {
 903   if (cl_info.is_hidden()) {
 904     return resolve_hidden_class_from_stream(st, class_name, class_loader, cl_info, CHECK_NULL);
 905   } else {
 906     return resolve_class_from_stream(st, class_name, class_loader, cl_info, CHECK_NULL);
 907   }
 908 }
 909 
 910 
 911 #if INCLUDE_CDS
 912 // Check if a shared class can be loaded by the specific classloader.
 913 bool SystemDictionary::is_shared_class_visible(Symbol* class_name,
 914                                                InstanceKlass* ik,
 915                                                PackageEntry* pkg_entry,
 916                                                Handle class_loader) {
 917   assert(!ModuleEntryTable::javabase_moduleEntry()->is_patched(),
 918          "Cannot use sharing if java.base is patched");
 919 
 920   // (1) Check if we are loading into the same loader as in dump time.
 921 
 922   if (ik->defined_by_boot_loader()) {
 923     if (class_loader() != nullptr) {
 924       return false;
 925     }
 926   } else if (ik->defined_by_platform_loader()) {
 927     if (class_loader() != java_platform_loader()) {
 928       return false;
 929     }
 930   } else if (ik->defined_by_app_loader()) {
 931     if (class_loader() != java_system_loader()) {
 932       return false;
 933     }
 934   } else {
 935     // ik was loaded by a custom loader during dump time
 936     if (class_loader_data(class_loader)->is_builtin_class_loader_data()) {
 937       return false;
 938     } else {
 939       return true;
 940     }
 941   }
 942 
 943   // (2) Check if we are loading into the same module from the same location as in dump time.
 944 
 945   if (CDSConfig::is_using_optimized_module_handling()) {
 946     // Class visibility has not changed between dump time and run time, so a class
 947     // that was visible (and thus archived) during dump time is always visible during runtime.
 948     assert(SystemDictionary::is_shared_class_visible_impl(class_name, ik, pkg_entry, class_loader),
 949            "visibility cannot change between dump time and runtime");
 950     return true;
 951   }
 952   return is_shared_class_visible_impl(class_name, ik, pkg_entry, class_loader);
 953 }
 954 
 955 bool SystemDictionary::is_shared_class_visible_impl(Symbol* class_name,
 956                                                     InstanceKlass* ik,
 957                                                     PackageEntry* pkg_entry,
 958                                                     Handle class_loader) {
 959   int scp_index = ik->shared_classpath_index();
 960   assert(!ik->defined_by_other_loaders(), "this function should be called for built-in classes only");
 961   assert(scp_index >= 0, "must be");
 962   const AOTClassLocation* cl = AOTClassLocationConfig::runtime()->class_location_at(scp_index);
 963   if (!Universe::is_module_initialized()) {
 964     assert(cl != nullptr, "must be");
 965     // At this point, no modules have been defined yet. KlassSubGraphInfo::check_allowed_klass()
 966     // has restricted the classes can be loaded at this step to be only:
 967     // [1] cs->is_modules_image(): classes in java.base, or,
 968     // [2] HeapShared::is_a_test_class_in_unnamed_module(ik): classes in bootstrap/unnamed module
 969     assert(cl->is_modules_image() || HeapShared::is_a_test_class_in_unnamed_module(ik),
 970            "only these classes can be loaded before the module system is initialized");
 971     assert(class_loader.is_null(), "sanity");
 972     return true;
 973   }
 974 
 975   if (pkg_entry == nullptr) {
 976     // We might have looked up pkg_entry before the module system was initialized.
 977     // Need to reload it now.
 978     TempNewSymbol pkg_name = ClassLoader::package_from_class_name(class_name);
 979     if (pkg_name != nullptr) {
 980       pkg_entry = class_loader_data(class_loader)->packages()->lookup_only(pkg_name);
 981     }
 982   }
 983 
 984   ModuleEntry* mod_entry = (pkg_entry == nullptr) ? nullptr : pkg_entry->module();
 985   bool should_be_in_named_module = (mod_entry != nullptr && mod_entry->is_named());
 986   bool was_archived_from_named_module = !cl->has_unnamed_module();
 987   bool visible;
 988 
 989   if (mod_entry != nullptr && mod_entry->location() == nullptr && mod_entry->is_named()) {
 990     // Archived module for dynamic proxies. It's always visible.
 991     assert(Modules::is_dynamic_proxy_module(mod_entry), "must be");
 992     visible = true;
 993   } else if (was_archived_from_named_module) {
 994     if (should_be_in_named_module) {
 995       // Is the module loaded from the same location as during dump time?
 996       visible = mod_entry->shared_path_index() == scp_index;
 997       if (visible) {
 998         assert(!mod_entry->is_patched(), "cannot load archived classes for patched module");
 999       }
1000     } else {
1001       // During dump time, this class was in a named module, but at run time, this class should be
1002       // in an unnamed module.
1003       visible = false;
1004     }
1005   } else {
1006     if (should_be_in_named_module) {
1007       // During dump time, this class was in an unnamed, but at run time, this class should be
1008       // in a named module.
1009       visible = false;
1010     } else {
1011       visible = true;
1012     }
1013   }
1014 
1015   return visible;
1016 }
1017 
1018 bool SystemDictionary::check_shared_class_super_type(InstanceKlass* klass, InstanceKlass* super_type,
1019                                                      Handle class_loader, bool is_superclass, TRAPS) {
1020   assert(super_type->in_aot_cache(), "must be");
1021 
1022   // Quick check if the super type has been already loaded.
1023   // + Don't do it for unregistered classes -- they can be unloaded so
1024   //   super_type->class_loader_data() could be stale.
1025   // + Don't check if loader data is null, ie. the super_type isn't fully loaded.
1026   if (!super_type->defined_by_other_loaders() && super_type->class_loader_data() != nullptr) {
1027     // Check if the superclass is loaded by the current class_loader
1028     Symbol* name = super_type->name();
1029     InstanceKlass* check = find_instance_klass(THREAD, name, class_loader);
1030     if (check == super_type) {
1031       return true;
1032     }
1033   }
1034 
1035   Klass *found = resolve_with_circularity_detection(klass->name(), super_type->name(),
1036                                                     class_loader, is_superclass, CHECK_false);
1037   if (found == super_type) {
1038     return true;
1039   } else {
1040     // The dynamically resolved super type is not the same as the one we used during dump time,
1041     // so we cannot use the class.
1042     return false;
1043   }
1044 }
1045 
1046 bool SystemDictionary::check_shared_class_super_types(InstanceKlass* ik, Handle class_loader, TRAPS) {
1047   // Check the superclass and interfaces. They must be the same
1048   // as in dump time, because the layout of <ik> depends on
1049   // the specific layout of ik->super() and ik->local_interfaces().
1050   //
1051   // If unexpected superclass or interfaces are found, we cannot
1052   // load <ik> from the shared archive.
1053 
1054   if (ik->super() != nullptr) {
1055     bool check_super = check_shared_class_super_type(ik, ik->super(),
1056                                                      class_loader, true,
1057                                                      CHECK_false);
1058     if (!check_super) {
1059       return false;
1060     }
1061   }
1062 
1063   Array<InstanceKlass*>* interfaces = ik->local_interfaces();
1064   int num_interfaces = interfaces->length();
1065   for (int index = 0; index < num_interfaces; index++) {
1066     bool check_interface = check_shared_class_super_type(ik, interfaces->at(index), class_loader, false,
1067                                                          CHECK_false);
1068     if (!check_interface) {
1069       return false;
1070     }
1071   }
1072 
1073   return true;
1074 }
1075 
1076 InstanceKlass* SystemDictionary::load_shared_class(InstanceKlass* ik,
1077                                                    Handle class_loader,
1078                                                    Handle protection_domain,
1079                                                    const ClassFileStream *cfs,
1080                                                    PackageEntry* pkg_entry,
1081                                                    TRAPS) {
1082   assert(ik != nullptr, "sanity");
1083   assert(ik->in_aot_cache(), "sanity");
1084   assert(!ik->is_unshareable_info_restored(), "shared class can be restored only once");
1085   assert(AtomicAccess::add(&ik->_shared_class_load_count, 1) == 1, "shared class loaded more than once");
1086   Symbol* class_name = ik->name();
1087 
1088   if (!is_shared_class_visible(class_name, ik, pkg_entry, class_loader)) {
1089     ik->set_shared_loading_failed();
1090     return nullptr;
1091   }
1092 
1093   bool check = check_shared_class_super_types(ik, class_loader, CHECK_NULL);
1094   if (!check) {
1095     ik->set_shared_loading_failed();
1096     return nullptr;
1097   }
1098 
1099   InstanceKlass* new_ik = nullptr;
1100   // CFLH check is skipped for VM hidden classes (see KlassFactory::create_from_stream).
1101   // It will be skipped for shared VM hidden lambda proxy classes.
1102   if (!ik->is_hidden()) {
1103     new_ik = KlassFactory::check_shared_class_file_load_hook(
1104       ik, class_name, class_loader, protection_domain, cfs, CHECK_NULL);
1105   }
1106   if (new_ik != nullptr) {
1107     // The class is changed by CFLH. Return the new class. The shared class is
1108     // not used.
1109     return new_ik;
1110   }
1111 
1112   // Adjust methods to recover missing data.  They need addresses for
1113   // interpreter entry points and their default native method address
1114   // must be reset.
1115 
1116   // Shared classes are all currently loaded by either the bootstrap or
1117   // internal parallel class loaders, so this will never cause a deadlock
1118   // on a custom class loader lock.
1119   // Since this class is already locked with parallel capable class
1120   // loaders, including the bootstrap loader via the placeholder table,
1121   // this lock is currently a nop.
1122 
1123   ClassLoaderData* loader_data = class_loader_data(class_loader);
1124   {
1125     HandleMark hm(THREAD);
1126     Handle lockObject = get_loader_lock_or_null(class_loader);
1127     ObjectLocker ol(lockObject, THREAD);
1128     // prohibited package check assumes all classes loaded from archive call
1129     // restore_unshareable_info which calls ik->set_package()
1130     ik->restore_unshareable_info(loader_data, protection_domain, pkg_entry, CHECK_NULL);
1131   }
1132 
1133   load_shared_class_misc(ik, loader_data);
1134   return ik;
1135 }
1136 
1137 void SystemDictionary::load_shared_class_misc(InstanceKlass* ik, ClassLoaderData* loader_data) {
1138   ik->print_class_load_logging(loader_data, nullptr, nullptr);
1139 
1140   // For boot loader, ensure that GetSystemPackage knows that a class in this
1141   // package was loaded.
1142   if (loader_data->is_the_null_class_loader_data()) {
1143     s2 path_index = ik->shared_classpath_index();
1144     if (path_index >= 0) { // FIXME ... for lambda form classes
1145       ik->set_classpath_index(path_index);
1146 
1147       if (CDSConfig::is_dumping_final_static_archive()) {
1148         AOTClassLocationConfig::dumptime_update_max_used_index(path_index);
1149       }
1150     }
1151   }
1152 
1153   // notify a class loaded from shared object
1154   ClassLoadingService::notify_class_loaded(ik, true /* shared class */);
1155 
1156   if (CDSConfig::is_dumping_final_static_archive()) {
1157     SystemDictionaryShared::init_dumptime_info_from_preimage(ik);
1158   }
1159 }
1160 
1161 // This is much more lightweight than SystemDictionary::resolve_or_null
1162 // - There's only a single Java thread at this point. No need for placeholder.
1163 // - All supertypes of ik have been loaded
1164 // - There's no circularity (checked in AOT assembly phase)
1165 // - There's no need to call java.lang.ClassLoader::load_class() because the boot/platform/app
1166 //   loaders are well-behaved
1167 void SystemDictionary::preload_class(Handle class_loader, InstanceKlass* ik, TRAPS) {
1168   precond(Universe::is_bootstrapping());
1169   precond(java_platform_loader() != nullptr && java_system_loader() != nullptr);
1170   precond(class_loader() == nullptr || class_loader() == java_platform_loader() ||class_loader() == java_system_loader());
1171   precond(CDSConfig::is_using_aot_linked_classes());
1172   precond(AOTMetaspace::in_aot_cache_static_region((void*)ik));
1173   precond(!ik->is_loaded());
1174 
1175 #ifdef ASSERT
1176   // preload_class() must be called in the correct order -- all super types must have
1177   // already been loaded.
1178   if (ik->java_super() != nullptr) {
1179     assert(ik->java_super()->is_loaded(), "must be");
1180   }
1181 
1182   Array<InstanceKlass*>* interfaces = ik->local_interfaces();
1183   int num_interfaces = interfaces->length();
1184   for (int index = 0; index < num_interfaces; index++) {
1185     assert(interfaces->at(index)->is_loaded(), "must be");
1186   }
1187 #endif
1188 
1189   EventClassLoad class_load_event;
1190 
1191   ClassLoaderData* loader_data = ClassLoaderData::class_loader_data(class_loader());
1192   oop java_mirror = ik->archived_java_mirror();
1193   precond(java_mirror != nullptr);
1194   assert(java_lang_Class::module(java_mirror) != nullptr, "must have been archived");
1195 
1196   Handle pd(THREAD, java_lang_Class::protection_domain(java_mirror));
1197   PackageEntry* pkg_entry = ik->package();
1198   assert(pkg_entry != nullptr || ClassLoader::package_from_class_name(ik->name()) == nullptr,
1199          "non-empty packages must have been archived");
1200 
1201   // TODO: the following assert requires JDK-8365580
1202   // assert(is_shared_class_visible(ik->name(), ik, pkg_entry, class_loader), "must be");
1203 
1204   ik->restore_unshareable_info(loader_data, pd, pkg_entry, CHECK);
1205   load_shared_class_misc(ik, loader_data);
1206   ik->add_to_hierarchy(THREAD);
1207 
1208   if (!ik->is_hidden()) {
1209     update_dictionary(THREAD, ik, loader_data);
1210   }
1211 
1212   if (class_load_event.should_commit()) {
1213     JFR_ONLY(post_class_load_event(&class_load_event, ik, loader_data);)
1214   }
1215 
1216   assert(ik->is_loaded(), "Must be in at least loaded state");
1217 }
1218 
1219 #endif // INCLUDE_CDS
1220 
1221 #if INCLUDE_JFR
1222 void SystemDictionary::post_class_load_event(EventClassLoad* event, const InstanceKlass* k, const ClassLoaderData* init_cld) {
1223   assert(event != nullptr, "invariant");
1224   assert(k != nullptr, "invariant");
1225   event->set_loadedClass(k);
1226   event->set_definingClassLoader(k->class_loader_data());
1227   event->set_initiatingClassLoader(init_cld);
1228   event->commit();
1229 }
1230 #endif // INCLUDE_JFR
1231 
1232 InstanceKlass* SystemDictionary::load_instance_class_impl(Symbol* class_name, Handle class_loader, TRAPS) {
1233 
1234   if (class_loader.is_null()) {
1235     ResourceMark rm(THREAD);
1236     PackageEntry* pkg_entry = nullptr;
1237     bool search_only_bootloader_append = false;
1238 
1239     // Find the package in the boot loader's package entry table.
1240     TempNewSymbol pkg_name = ClassLoader::package_from_class_name(class_name);
1241     if (pkg_name != nullptr) {
1242       pkg_entry = class_loader_data(class_loader)->packages()->lookup_only(pkg_name);
1243     }
1244 
1245     // Prior to attempting to load the class, enforce the boot loader's
1246     // visibility boundaries.
1247     if (!Universe::is_module_initialized()) {
1248       // During bootstrapping, prior to module initialization, any
1249       // class attempting to be loaded must be checked against the
1250       // java.base packages in the boot loader's PackageEntryTable.
1251       // No class outside of java.base is allowed to be loaded during
1252       // this bootstrapping window.
1253       if (pkg_entry == nullptr || pkg_entry->in_unnamed_module()) {
1254         // Class is either in the unnamed package or in
1255         // a named package within the unnamed module.  Either
1256         // case is outside of java.base, do not attempt to
1257         // load the class post java.base definition.  If
1258         // java.base has not been defined, let the class load
1259         // and its package will be checked later by
1260         // ModuleEntryTable::verify_javabase_packages.
1261         if (ModuleEntryTable::javabase_defined()) {
1262           return nullptr;
1263         }
1264       } else {
1265         // Check that the class' package is defined within java.base.
1266         ModuleEntry* mod_entry = pkg_entry->module();
1267         Symbol* mod_entry_name = mod_entry->name();
1268         if (mod_entry_name->fast_compare(vmSymbols::java_base()) != 0) {
1269           return nullptr;
1270         }
1271       }
1272     } else {
1273       // After the module system has been initialized, check if the class'
1274       // package is in a module defined to the boot loader.
1275       if (pkg_name == nullptr || pkg_entry == nullptr || pkg_entry->in_unnamed_module()) {
1276         // Class is either in the unnamed package, in a named package
1277         // within a module not defined to the boot loader or in a
1278         // a named package within the unnamed module.  In all cases,
1279         // limit visibility to search for the class only in the boot
1280         // loader's append path.
1281         if (!ClassLoader::has_bootclasspath_append()) {
1282            // If there is no bootclasspath append entry, no need to continue
1283            // searching.
1284            return nullptr;
1285         }
1286         search_only_bootloader_append = true;
1287       }
1288     }
1289 
1290     // Prior to bootstrapping's module initialization, never load a class outside
1291     // of the boot loader's module path
1292     assert(Universe::is_module_initialized() ||
1293            !search_only_bootloader_append,
1294            "Attempt to load a class outside of boot loader's module path");
1295 
1296     // Search for classes in the CDS archive.
1297     InstanceKlass* k = nullptr;
1298 
1299 #if INCLUDE_CDS
1300     if (CDSConfig::is_using_archive())
1301     {
1302       PerfTraceElapsedTime vmtimer(ClassLoader::perf_shared_classload_time());
1303       InstanceKlass* ik = SystemDictionaryShared::find_builtin_class(class_name);
1304       if (ik != nullptr && ik->defined_by_boot_loader() && !ik->shared_loading_failed()) {
1305         SharedClassLoadingMark slm(THREAD, ik);
1306         k = load_shared_class(ik, class_loader, Handle(), nullptr,  pkg_entry, CHECK_NULL);
1307       }
1308     }
1309 #endif
1310 
1311     if (k == nullptr) {
1312       // Use VM class loader
1313       PerfTraceElapsedTime vmtimer(ClassLoader::perf_sys_classload_time());
1314       k = ClassLoader::load_class(class_name, pkg_entry, search_only_bootloader_append, CHECK_NULL);
1315     }
1316 
1317     // find_or_define_instance_class may return a different InstanceKlass
1318     if (k != nullptr) {
1319       CDS_ONLY(SharedClassLoadingMark slm(THREAD, k);)
1320       k = find_or_define_instance_class(class_name, class_loader, k, CHECK_NULL);
1321     }
1322     return k;
1323   } else {
1324     // Use user specified class loader to load class. Call loadClass operation on class_loader.
1325     ResourceMark rm(THREAD);
1326 
1327     JavaThread* jt = THREAD;
1328 
1329     PerfClassTraceTime vmtimer(ClassLoader::perf_app_classload_time(),
1330                                ClassLoader::perf_app_classload_selftime(),
1331                                ClassLoader::perf_app_classload_count(),
1332                                jt->get_thread_stat()->perf_recursion_counts_addr(),
1333                                jt->get_thread_stat()->perf_timers_addr(),
1334                                PerfClassTraceTime::CLASS_LOAD);
1335 
1336     // Translate to external class name format, i.e., convert '/' chars to '.'
1337     Handle string = java_lang_String::externalize_classname(class_name, CHECK_NULL);
1338 
1339     JavaValue result(T_OBJECT);
1340 
1341     InstanceKlass* spec_klass = vmClasses::ClassLoader_klass();
1342 
1343     // Call public unsynchronized loadClass(String) directly for all class loaders.
1344     // For parallelCapable class loaders, JDK >=7, loadClass(String, boolean) will
1345     // acquire a class-name based lock rather than the class loader object lock.
1346     // JDK < 7 already acquire the class loader lock in loadClass(String, boolean).
1347     JavaCalls::call_virtual(&result,
1348                             class_loader,
1349                             spec_klass,
1350                             vmSymbols::loadClass_name(),
1351                             vmSymbols::string_class_signature(),
1352                             string,
1353                             CHECK_NULL);
1354 
1355     assert(result.get_type() == T_OBJECT, "just checking");
1356     oop obj = result.get_oop();
1357 
1358     // Primitive classes return null since forName() cannot be
1359     // used to obtain any of the Class objects representing primitives or void
1360     if ((obj != nullptr) && !(java_lang_Class::is_primitive(obj))) {
1361       InstanceKlass* k = java_lang_Class::as_InstanceKlass(obj);
1362       // For user defined Java class loaders, check that the name returned is
1363       // the same as that requested.  This check is done for the bootstrap
1364       // loader when parsing the class file.
1365       if (class_name == k->name()) {
1366         return k;
1367       }
1368     }
1369     // Class is not found or has the wrong name, return null
1370     return nullptr;
1371   }
1372 }
1373 
1374 InstanceKlass* SystemDictionary::load_instance_class(Symbol* name,
1375                                                      Handle class_loader,
1376                                                      TRAPS) {
1377 
1378   InstanceKlass* loaded_class = load_instance_class_impl(name, class_loader, CHECK_NULL);
1379 
1380   // If everything was OK (no exceptions, no null return value), and
1381   // class_loader is NOT the defining loader, do a little more bookkeeping.
1382   if (loaded_class != nullptr &&
1383       loaded_class->class_loader() != class_loader()) {
1384 
1385     ClassLoaderData* loader_data = class_loader_data(class_loader);
1386     check_constraints(loaded_class, loader_data, false, CHECK_NULL);
1387 
1388     // Record dependency for non-parent delegation.
1389     // This recording keeps the defining class loader of the klass (loaded_class) found
1390     // from being unloaded while the initiating class loader is loaded
1391     // even if the reference to the defining class loader is dropped
1392     // before references to the initiating class loader.
1393     loader_data->record_dependency(loaded_class);
1394 
1395     update_dictionary(THREAD, loaded_class, loader_data);
1396 
1397     if (JvmtiExport::should_post_class_load()) {
1398       JvmtiExport::post_class_load(THREAD, loaded_class);
1399     }
1400   }
1401   return loaded_class;
1402 }
1403 
1404 void SystemDictionary::define_instance_class(InstanceKlass* k, Handle class_loader, TRAPS) {
1405 
1406   ClassLoaderData* loader_data = k->class_loader_data();
1407   assert(loader_data->class_loader() == class_loader(), "they must be the same");
1408 
1409   // Bootstrap and other parallel classloaders don't acquire a lock,
1410   // they use placeholder token.
1411   // If a parallelCapable class loader calls define_instance_class instead of
1412   // find_or_define_instance_class to get here, we have a timing
1413   // hole with systemDictionary updates and check_constraints
1414   if (!is_parallelCapable(class_loader)) {
1415     assert(ObjectSynchronizer::current_thread_holds_lock(THREAD,
1416            get_loader_lock_or_null(class_loader)),
1417            "define called without lock");
1418   }
1419 
1420   // Check class-loading constraints. Throw exception if violation is detected.
1421   // Grabs and releases SystemDictionary_lock
1422   // The check_constraints/find_class call and update_dictionary sequence
1423   // must be "atomic" for a specific class/classloader pair so we never
1424   // define two different instanceKlasses for that class/classloader pair.
1425   // Existing classloaders will call define_instance_class with the
1426   // classloader lock held
1427   // Parallel classloaders will call find_or_define_instance_class
1428   // which will require a token to perform the define class
1429   check_constraints(k, loader_data, true, CHECK);
1430 
1431   // Register class just loaded with class loader (placed in ArrayList)
1432   // Note we do this before updating the dictionary, as this can
1433   // fail with an OutOfMemoryError (if it does, we will *not* put this
1434   // class in the dictionary and will not update the class hierarchy).
1435   // JVMTI FollowReferences needs to find the classes this way.
1436   if (k->class_loader() != nullptr) {
1437     methodHandle m(THREAD, Universe::loader_addClass_method());
1438     JavaValue result(T_VOID);
1439     JavaCallArguments args(class_loader);
1440     args.push_oop(Handle(THREAD, k->java_mirror()));
1441     JavaCalls::call(&result, m, &args, CHECK);
1442   }
1443 
1444   // Add to class hierarchy, and do possible deoptimizations.
1445   k->add_to_hierarchy(THREAD);
1446 
1447   // Add to systemDictionary - so other classes can see it.
1448   // Grabs and releases SystemDictionary_lock
1449   update_dictionary(THREAD, k, loader_data);
1450 
1451   // notify jvmti
1452   if (JvmtiExport::should_post_class_load()) {
1453     JvmtiExport::post_class_load(THREAD, k);
1454   }
1455 }
1456 
1457 // Support parallel classloading
1458 // All parallel class loaders, including bootstrap classloader
1459 // lock a placeholder entry for this class/class_loader pair
1460 // to allow parallel defines of different classes for this class loader
1461 // With AllowParallelDefine flag==true, in case they do not synchronize around
1462 // FindLoadedClass/DefineClass, calls, we check for parallel
1463 // loading for them, wait if a defineClass is in progress
1464 // and return the initial requestor's results
1465 // This flag does not apply to the bootstrap classloader.
1466 // With AllowParallelDefine flag==false, call through to define_instance_class
1467 // which will throw LinkageError: duplicate class definition.
1468 // False is the requested default.
1469 // For better performance, the class loaders should synchronize
1470 // findClass(), i.e. FindLoadedClass/DefineClassIfAbsent or they
1471 // potentially waste time reading and parsing the bytestream.
1472 // Note: VM callers should ensure consistency of k/class_name,class_loader
1473 // Be careful when modifying this code: once you have run
1474 // PlaceholderTable::find_and_add(PlaceholderTable::DEFINE_CLASS),
1475 // you need to find_and_remove it before returning.
1476 // So be careful to not exit with a CHECK_ macro between these calls.
1477 InstanceKlass* SystemDictionary::find_or_define_helper(Symbol* class_name, Handle class_loader,
1478                                                        InstanceKlass* k, TRAPS) {
1479 
1480   Symbol* name_h = k->name();
1481   ClassLoaderData* loader_data = class_loader_data(class_loader);
1482   Dictionary* dictionary = loader_data->dictionary();
1483 
1484   // Hold SD lock around find_class and placeholder creation for DEFINE_CLASS
1485   {
1486     MutexLocker mu(THREAD, SystemDictionary_lock);
1487     // First check if class already defined
1488     if (is_parallelDefine(class_loader)) {
1489       InstanceKlass* check = dictionary->find_class(THREAD, name_h);
1490       if (check != nullptr) {
1491         return check;
1492       }
1493     }
1494 
1495     // Acquire define token for this class/classloader
1496     PlaceholderEntry* probe = PlaceholderTable::find_and_add(name_h, loader_data,
1497                                                              PlaceholderTable::DEFINE_CLASS, nullptr, THREAD);
1498     // Wait if another thread defining in parallel
1499     // All threads wait - even those that will throw duplicate class: otherwise
1500     // caller is surprised by LinkageError: duplicate, but findLoadedClass fails
1501     // if other thread has not finished updating dictionary
1502     while (probe->definer() != nullptr) {
1503       SystemDictionary_lock->wait();
1504     }
1505     // Only special cases allow parallel defines and can use other thread's results
1506     // Other cases fall through, and may run into duplicate defines
1507     // caught by finding an entry in the SystemDictionary
1508     if (is_parallelDefine(class_loader) && (probe->instance_klass() != nullptr)) {
1509       InstanceKlass* ik = probe->instance_klass();
1510       PlaceholderTable::find_and_remove(name_h, loader_data, PlaceholderTable::DEFINE_CLASS, THREAD);
1511       SystemDictionary_lock->notify_all();
1512 #ifdef ASSERT
1513       InstanceKlass* check = dictionary->find_class(THREAD, name_h);
1514       assert(check != nullptr, "definer missed recording success");
1515 #endif
1516       return ik;
1517     } else {
1518       // This thread will define the class (even if earlier thread tried and had an error)
1519       probe->set_definer(THREAD);
1520     }
1521   }
1522 
1523   define_instance_class(k, class_loader, THREAD);
1524 
1525   // definer must notify any waiting threads
1526   {
1527     MutexLocker mu(THREAD, SystemDictionary_lock);
1528     PlaceholderEntry* probe = PlaceholderTable::get_entry(name_h, loader_data);
1529     assert(probe != nullptr, "DEFINE_CLASS placeholder lost?");
1530     if (!HAS_PENDING_EXCEPTION) {
1531       probe->set_instance_klass(k);
1532     }
1533     probe->set_definer(nullptr);
1534     PlaceholderTable::find_and_remove(name_h, loader_data, PlaceholderTable::DEFINE_CLASS, THREAD);
1535     SystemDictionary_lock->notify_all();
1536   }
1537 
1538   return HAS_PENDING_EXCEPTION ? nullptr : k;
1539 }
1540 
1541 // If a class loader supports parallel classloading handle parallel define requests.
1542 // find_or_define_instance_class may return a different InstanceKlass
1543 InstanceKlass* SystemDictionary::find_or_define_instance_class(Symbol* class_name, Handle class_loader,
1544                                                                InstanceKlass* k, TRAPS) {
1545   InstanceKlass* defined_k = find_or_define_helper(class_name, class_loader, k, THREAD);
1546   // Clean up original InstanceKlass if duplicate or error
1547   if (!HAS_PENDING_EXCEPTION && defined_k != k) {
1548     // If a parallel capable class loader already defined this class, register 'k' for cleanup.
1549     assert(defined_k != nullptr, "Should have a klass if there's no exception");
1550     k->class_loader_data()->add_to_deallocate_list(k);
1551   } else if (HAS_PENDING_EXCEPTION) {
1552     // Remove this InstanceKlass from the LoaderConstraintTable if added.
1553     LoaderConstraintTable::remove_failed_loaded_klass(k, class_loader_data(class_loader));
1554     assert(defined_k == nullptr, "Should not have a klass if there's an exception");
1555     k->class_loader_data()->add_to_deallocate_list(k);
1556   }
1557   return defined_k;
1558 }
1559 
1560 
1561 // ----------------------------------------------------------------------------
1562 // GC support
1563 
1564 // Assumes classes in the SystemDictionary are only unloaded at a safepoint
1565 bool SystemDictionary::do_unloading(GCTimer* gc_timer) {
1566 
1567   bool unloading_occurred;
1568   bool is_concurrent = !SafepointSynchronize::is_at_safepoint();
1569   {
1570     GCTraceTime(Debug, gc, phases) t("ClassLoaderData", gc_timer);
1571     assert_locked_or_safepoint(ClassLoaderDataGraph_lock);  // caller locks.
1572     // First, mark for unload all ClassLoaderData referencing a dead class loader.
1573     unloading_occurred = ClassLoaderDataGraph::do_unloading();
1574     if (unloading_occurred) {
1575       ConditionalMutexLocker ml2(Module_lock, is_concurrent);
1576       JFR_ONLY(Jfr::on_unloading_classes();)
1577       MANAGEMENT_ONLY(FinalizerService::purge_unloaded();)
1578       ConditionalMutexLocker ml1(SystemDictionary_lock, is_concurrent);
1579       ClassLoaderDataGraph::clean_module_and_package_info();
1580       LoaderConstraintTable::purge_loader_constraints();
1581       ResolutionErrorTable::purge_resolution_errors();
1582     }
1583   }
1584 
1585   GCTraceTime(Debug, gc, phases) t("Trigger cleanups", gc_timer);
1586 
1587   if (unloading_occurred) {
1588     SymbolTable::trigger_cleanup();
1589 
1590     ConditionalMutexLocker ml(ClassInitError_lock, is_concurrent);
1591     InstanceKlass::clean_initialization_error_table();
1592   }
1593 
1594   return unloading_occurred;
1595 }
1596 
1597 void SystemDictionary::methods_do(void f(Method*)) {
1598   // Walk methods in loaded classes
1599 
1600   {
1601     MutexLocker ml(ClassLoaderDataGraph_lock);
1602     ClassLoaderDataGraph::methods_do(f);
1603   }
1604 
1605   auto doit = [&] (InvokeMethodKey key, Method* method) {
1606     if (method != nullptr) {
1607       f(method);
1608     }
1609   };
1610 
1611   {
1612     MutexLocker ml(InvokeMethodIntrinsicTable_lock);
1613     _invoke_method_intrinsic_table->iterate_all(doit);
1614   }
1615 
1616 }
1617 
1618 // ----------------------------------------------------------------------------
1619 // Initialization
1620 
1621 void SystemDictionary::initialize(TRAPS) {
1622   _invoke_method_intrinsic_table = new (mtClass) InvokeMethodIntrinsicTable();
1623   _invoke_method_type_table = new (mtClass) InvokeMethodTypeTable();
1624   ResolutionErrorTable::initialize();
1625   LoaderConstraintTable::initialize();
1626   PlaceholderTable::initialize();
1627 #if INCLUDE_CDS
1628   SystemDictionaryShared::initialize();
1629   if (CDSConfig::is_dumping_archive()) {
1630     AOTClassLocationConfig::dumptime_init(THREAD);
1631   }
1632 #endif
1633   // Resolve basic classes
1634   vmClasses::resolve_all(CHECK);
1635   // Resolve classes used by archived heap objects
1636   if (CDSConfig::is_using_archive()) {
1637     HeapShared::resolve_classes(THREAD);
1638   }
1639 }
1640 
1641 // Constraints on class loaders. The details of the algorithm can be
1642 // found in the OOPSLA'98 paper "Dynamic Class Loading in the Java
1643 // Virtual Machine" by Sheng Liang and Gilad Bracha.  The basic idea is
1644 // that the dictionary needs to maintain a set of constraints that
1645 // must be satisfied by all classes in the dictionary.
1646 // if defining is true, then LinkageError if already in dictionary
1647 // if initiating loader, then ok if InstanceKlass matches existing entry
1648 
1649 void SystemDictionary::check_constraints(InstanceKlass* k,
1650                                          ClassLoaderData* loader_data,
1651                                          bool defining,
1652                                          TRAPS) {
1653   ResourceMark rm(THREAD);
1654   stringStream ss;
1655   bool throwException = false;
1656 
1657   {
1658     Symbol* name = k->name();
1659 
1660     MutexLocker mu(THREAD, SystemDictionary_lock);
1661 
1662     InstanceKlass* check = loader_data->dictionary()->find_class(THREAD, name);
1663     if (check != nullptr) {
1664       // If different InstanceKlass - duplicate class definition,
1665       // else - ok, class loaded by a different thread in parallel.
1666       // We should only have found it if it was done loading and ok to use.
1667 
1668       if ((defining == true) || (k != check)) {
1669         throwException = true;
1670         ss.print("loader %s", loader_data->loader_name_and_id());
1671         ss.print(" attempted duplicate %s definition for %s. (%s)",
1672                  k->external_kind(), k->external_name(), k->class_in_module_of_loader(false, true));
1673       } else {
1674         return;
1675       }
1676     }
1677 
1678     if (throwException == false) {
1679       if (LoaderConstraintTable::check_or_update(k, loader_data, name) == false) {
1680         throwException = true;
1681         ss.print("loader constraint violation: loader %s", loader_data->loader_name_and_id());
1682         ss.print(" wants to load %s %s.",
1683                  k->external_kind(), k->external_name());
1684         Klass *existing_klass = LoaderConstraintTable::find_constrained_klass(name, loader_data);
1685         if (existing_klass != nullptr && existing_klass->class_loader_data() != loader_data) {
1686           ss.print(" A different %s with the same name was previously loaded by %s. (%s)",
1687                    existing_klass->external_kind(),
1688                    existing_klass->class_loader_data()->loader_name_and_id(),
1689                    existing_klass->class_in_module_of_loader(false, true));
1690         } else {
1691           ss.print(" (%s)", k->class_in_module_of_loader(false, true));
1692         }
1693       }
1694     }
1695   }
1696 
1697   // Throw error now if needed (cannot throw while holding
1698   // SystemDictionary_lock because of rank ordering)
1699   if (throwException == true) {
1700     THROW_MSG(vmSymbols::java_lang_LinkageError(), ss.as_string());
1701   }
1702 }
1703 
1704 // Update class loader data dictionary - done after check_constraint and add_to_hierarchy
1705 // have been called.
1706 void SystemDictionary::update_dictionary(JavaThread* current,
1707                                          InstanceKlass* k,
1708                                          ClassLoaderData* loader_data) {
1709   MonitorLocker mu1(SystemDictionary_lock);
1710 
1711   // Make a new dictionary entry.
1712   Symbol* name  = k->name();
1713   Dictionary* dictionary = loader_data->dictionary();
1714   InstanceKlass* sd_check = dictionary->find_class(current, name);
1715   if (sd_check == nullptr) {
1716     dictionary->add_klass(current, name, k);
1717   }
1718   mu1.notify_all();
1719 }
1720 
1721 #if INCLUDE_CDS
1722 // Indicate that loader_data has initiated the loading of class k, which
1723 // has already been defined by a parent loader.
1724 // This API should be used only by AOTLinkedClassBulkLoader
1725 void SystemDictionary::add_to_initiating_loader(JavaThread* current,
1726                                                 InstanceKlass* k,
1727                                                 ClassLoaderData* loader_data) {
1728   assert(CDSConfig::is_using_aot_linked_classes(), "must be");
1729   assert_locked_or_safepoint(SystemDictionary_lock);
1730   Symbol* name  = k->name();
1731   Dictionary* dictionary = loader_data->dictionary();
1732   assert(k->is_loaded(), "must be");
1733   assert(k->class_loader_data() != loader_data, "only for classes defined by a parent loader");
1734   assert(dictionary->find_class(current, name) == nullptr, "sanity");
1735   dictionary->add_klass(current, name, k);
1736 }
1737 #endif
1738 
1739 // Try to find a class name using the loader constraints.  The
1740 // loader constraints might know about a class that isn't fully loaded
1741 // yet and these will be ignored.
1742 Klass* SystemDictionary::find_constrained_instance_or_array_klass(
1743                     Thread* current, Symbol* class_name, Handle class_loader) {
1744 
1745   // First see if it has been loaded directly.
1746   Klass* klass = find_instance_or_array_klass(current, class_name, class_loader);
1747   if (klass != nullptr)
1748     return klass;
1749 
1750   // Now look to see if it has been loaded elsewhere, and is subject to
1751   // a loader constraint that would require this loader to return the
1752   // klass that is already loaded.
1753   if (Signature::is_array(class_name)) {
1754     // For array classes, their Klass*s are not kept in the
1755     // constraint table. The element Klass*s are.
1756     SignatureStream ss(class_name, false);
1757     int ndims = ss.skip_array_prefix();  // skip all '['s
1758     BasicType t = ss.type();
1759     if (t != T_OBJECT) {
1760       klass = Universe::typeArrayKlass(t);
1761     } else {
1762       MutexLocker mu(current, SystemDictionary_lock);
1763       klass = LoaderConstraintTable::find_constrained_klass(ss.as_symbol(), class_loader_data(class_loader));
1764     }
1765     // If element class already loaded, allocate array klass
1766     if (klass != nullptr) {
1767       klass = klass->array_klass_or_null(ndims);
1768     }
1769   } else {
1770     MutexLocker mu(current, SystemDictionary_lock);
1771     // Non-array classes are easy: simply check the constraint table.
1772     klass = LoaderConstraintTable::find_constrained_klass(class_name, class_loader_data(class_loader));
1773   }
1774 
1775   return klass;
1776 }
1777 
1778 bool SystemDictionary::add_loader_constraint(Symbol* class_name,
1779                                              Klass* klass_being_linked,
1780                                              Handle class_loader1,
1781                                              Handle class_loader2) {
1782   ClassLoaderData* loader_data1 = class_loader_data(class_loader1);
1783   ClassLoaderData* loader_data2 = class_loader_data(class_loader2);
1784 
1785   Symbol* constraint_name = nullptr;
1786 
1787   if (!Signature::is_array(class_name)) {
1788     constraint_name = class_name;
1789   } else {
1790     // For array classes, their Klass*s are not kept in the
1791     // constraint table. The element classes are.
1792     SignatureStream ss(class_name, false);
1793     ss.skip_array_prefix();  // skip all '['s
1794     if (!ss.has_envelope()) {
1795       return true;     // primitive types always pass
1796     }
1797     constraint_name = ss.as_symbol();
1798     // Increment refcount to keep constraint_name alive after
1799     // SignatureStream is destructed. It will be decremented below
1800     // before returning.
1801     constraint_name->increment_refcount();
1802   }
1803 
1804   Dictionary* dictionary1 = loader_data1->dictionary();
1805   Dictionary* dictionary2 = loader_data2->dictionary();
1806 
1807   JavaThread* current = JavaThread::current();
1808   {
1809     MutexLocker mu_s(SystemDictionary_lock);
1810     InstanceKlass* klass1 = dictionary1->find_class(current, constraint_name);
1811     InstanceKlass* klass2 = dictionary2->find_class(current, constraint_name);
1812     bool result = LoaderConstraintTable::add_entry(constraint_name, klass1, loader_data1,
1813                                                    klass2, loader_data2);
1814 #if INCLUDE_CDS
1815     if (CDSConfig::is_dumping_archive() && klass_being_linked != nullptr &&
1816         !klass_being_linked->in_aot_cache()) {
1817          SystemDictionaryShared::record_linking_constraint(constraint_name,
1818                                      InstanceKlass::cast(klass_being_linked),
1819                                      class_loader1, class_loader2);
1820     }
1821 #endif // INCLUDE_CDS
1822     if (Signature::is_array(class_name)) {
1823       constraint_name->decrement_refcount();
1824     }
1825     return result;
1826   }
1827 }
1828 
1829 // Add entry to resolution error table to record the error when the first
1830 // attempt to resolve a reference to a class has failed.
1831 void SystemDictionary::add_resolution_error(const constantPoolHandle& pool, int which,
1832                                             Symbol* error, const char* message,
1833                                             Symbol* cause, const char* cause_msg) {
1834   {
1835     MutexLocker ml(Thread::current(), SystemDictionary_lock);
1836     ResolutionErrorEntry* entry = ResolutionErrorTable::find_entry(pool, which);
1837     if (entry == nullptr) {
1838       ResolutionErrorTable::add_entry(pool, which, error, message, cause, cause_msg);
1839     }
1840   }
1841 }
1842 
1843 // Delete a resolution error for RedefineClasses for a constant pool is going away
1844 void SystemDictionary::delete_resolution_error(ConstantPool* pool) {
1845   ResolutionErrorTable::delete_entry(pool);
1846 }
1847 
1848 // Lookup resolution error table. Returns error if found, otherwise null.
1849 Symbol* SystemDictionary::find_resolution_error(const constantPoolHandle& pool, int which,
1850                                                 const char** message,
1851                                                 Symbol** cause, const char** cause_msg) {
1852 
1853   {
1854     MutexLocker ml(Thread::current(), SystemDictionary_lock);
1855     ResolutionErrorEntry* entry = ResolutionErrorTable::find_entry(pool, which);
1856     if (entry != nullptr) {
1857       *message = entry->message();
1858       *cause = entry->cause();
1859       *cause_msg = entry->cause_msg();
1860       return entry->error();
1861     } else {
1862       return nullptr;
1863     }
1864   }
1865 }
1866 
1867 // Add an entry to resolution error table to record an error in resolving or
1868 // validating a nest host. This is used to construct informative error
1869 // messages when IllegalAccessError's occur. If an entry already exists it will
1870 // be updated with the nest host error message.
1871 
1872 void SystemDictionary::add_nest_host_error(const constantPoolHandle& pool,
1873                                            int which,
1874                                            const stringStream& message) {
1875   {
1876     MutexLocker ml(Thread::current(), SystemDictionary_lock);
1877     ResolutionErrorEntry* entry = ResolutionErrorTable::find_entry(pool, which);
1878     if (entry == nullptr) {
1879       // Only add a new entry to the resolution error table if one hasn't been found for this
1880       // constant pool index. In this case resolution succeeded but there's an error in this nest host
1881       // that we use the table to record.
1882       assert(pool->resolved_klass_at(which) != nullptr, "klass should be resolved if there is no entry");
1883       ResolutionErrorTable::add_entry(pool, which, message.as_string(true /* on C-heap */));
1884     } else {
1885       // An existing entry means we had a true resolution failure (LinkageError) with our nest host, but we
1886       // still want to add the error message for the higher-level access checks to report. We should
1887       // only reach here under the same error condition, so we can ignore the potential race with setting
1888       // the message.
1889       const char* nhe = entry->nest_host_error();
1890       if (nhe == nullptr) {
1891         entry->set_nest_host_error(message.as_string(true /* on C-heap */));
1892       } else {
1893         DEBUG_ONLY(const char* msg = message.base();)
1894         assert(strcmp(nhe, msg) == 0, "New message %s, differs from original %s", msg, nhe);
1895       }
1896     }
1897   }
1898 }
1899 
1900 // Lookup any nest host error
1901 const char* SystemDictionary::find_nest_host_error(const constantPoolHandle& pool, int which) {
1902   {
1903     MutexLocker ml(Thread::current(), SystemDictionary_lock);
1904     ResolutionErrorEntry* entry = ResolutionErrorTable::find_entry(pool, which);
1905     if (entry != nullptr) {
1906       return entry->nest_host_error();
1907     } else {
1908       return nullptr;
1909     }
1910   }
1911 }
1912 
1913 // Signature constraints ensure that callers and callees agree about
1914 // the meaning of type names in their signatures.  This routine is the
1915 // intake for constraints.  It collects them from several places:
1916 //
1917 //  * LinkResolver::resolve_method (if check_access is true) requires
1918 //    that the resolving class (the caller) and the defining class of
1919 //    the resolved method (the callee) agree on each type in the
1920 //    method's signature.
1921 //
1922 //  * LinkResolver::resolve_interface_method performs exactly the same
1923 //    checks.
1924 //
1925 //  * LinkResolver::resolve_field requires that the constant pool
1926 //    attempting to link to a field agree with the field's defining
1927 //    class about the type of the field signature.
1928 //
1929 //  * klassVtable::initialize_vtable requires that, when a class
1930 //    overrides a vtable entry allocated by a superclass, that the
1931 //    overriding method (i.e., the callee) agree with the superclass
1932 //    on each type in the method's signature.
1933 //
1934 //  * klassItable::initialize_itable requires that, when a class fills
1935 //    in its itables, for each non-abstract method installed in an
1936 //    itable, the method (i.e., the callee) agree with the interface
1937 //    on each type in the method's signature.
1938 //
1939 // All those methods have a boolean (check_access, checkconstraints)
1940 // which turns off the checks.  This is used from specialized contexts
1941 // such as bootstrapping, dumping, and debugging.
1942 //
1943 // No direct constraint is placed between the class and its
1944 // supertypes.  Constraints are only placed along linked relations
1945 // between callers and callees.  When a method overrides or implements
1946 // an abstract method in a supertype (superclass or interface), the
1947 // constraints are placed as if the supertype were the caller to the
1948 // overriding method.  (This works well, since callers to the
1949 // supertype have already established agreement between themselves and
1950 // the supertype.)  As a result of all this, a class can disagree with
1951 // its supertype about the meaning of a type name, as long as that
1952 // class neither calls a relevant method of the supertype, nor is
1953 // called (perhaps via an override) from the supertype.
1954 //
1955 //
1956 // SystemDictionary::check_signature_loaders(sig, klass_being_linked, l1, l2)
1957 //
1958 // Make sure all class components (including arrays) in the given
1959 // signature will be resolved to the same class in both loaders.
1960 // Returns the name of the type that failed a loader constraint check, or
1961 // null if no constraint failed.  No exception except OOME is thrown.
1962 // Arrays are not added to the loader constraint table, their elements are.
1963 Symbol* SystemDictionary::check_signature_loaders(Symbol* signature,
1964                                                   Klass* klass_being_linked,
1965                                                   Handle loader1, Handle loader2,
1966                                                   bool is_method)  {
1967   // Nothing to do if loaders are the same.
1968   if (loader1() == loader2()) {
1969     return nullptr;
1970   }
1971 
1972   for (SignatureStream ss(signature, is_method); !ss.is_done(); ss.next()) {
1973     if (ss.is_reference()) {
1974       Symbol* sig = ss.as_symbol();
1975       // Note: In the future, if template-like types can take
1976       // arguments, we will want to recognize them and dig out class
1977       // names hiding inside the argument lists.
1978       if (!add_loader_constraint(sig, klass_being_linked, loader1, loader2)) {
1979         return sig;
1980       }
1981     }
1982   }
1983   return nullptr;
1984 }
1985 
1986 Method* SystemDictionary::find_method_handle_intrinsic(vmIntrinsicID iid,
1987                                                        Symbol* signature,
1988                                                        TRAPS) {
1989 
1990   const int iid_as_int = vmIntrinsics::as_int(iid);
1991   assert(MethodHandles::is_signature_polymorphic(iid) &&
1992          MethodHandles::is_signature_polymorphic_intrinsic(iid) &&
1993          iid != vmIntrinsics::_invokeGeneric,
1994          "must be a known MH intrinsic iid=%d: %s", iid_as_int, vmIntrinsics::name_at(iid));
1995 
1996   InvokeMethodKey key(signature, iid_as_int);
1997   Method** met = nullptr;
1998 
1999   // We only want one entry in the table for this (signature/id, method) pair but the code
2000   // to create the intrinsic method needs to be outside the lock.
2001   // The first thread claims the entry by adding the key and the other threads wait, until the
2002   // Method has been added as the value.
2003   {
2004     MonitorLocker ml(THREAD, InvokeMethodIntrinsicTable_lock);
2005     while (true) {
2006       bool created;
2007       met = _invoke_method_intrinsic_table->put_if_absent(key, &created);
2008       assert(met != nullptr, "either created or found");
2009       if (*met != nullptr) {
2010         return *met;
2011       } else if (created) {
2012         // The current thread won the race and will try to create the full entry.
2013         break;
2014       } else {
2015         // Another thread beat us to it, so wait for them to complete
2016         // and return *met; or if they hit an error we get another try.
2017         ml.wait();
2018         // Note it is not safe to read *met here as that entry could have
2019         // been deleted, so we must loop and try put_if_absent again.
2020       }
2021     }
2022   }
2023 
2024   methodHandle m = Method::make_method_handle_intrinsic(iid, signature, THREAD);
2025   bool throw_error = HAS_PENDING_EXCEPTION;
2026   if (!throw_error && (!Arguments::is_interpreter_only() || iid == vmIntrinsics::_linkToNative)) {
2027     // Generate a compiled form of the MH intrinsic
2028     // linkToNative doesn't have interpreter-specific implementation, so always has to go through compiled version.
2029     AdapterHandlerLibrary::create_native_wrapper(m);
2030     // Check if have the compiled code.
2031     throw_error = (!m->has_compiled_code());
2032   }
2033 
2034   {
2035     MonitorLocker ml(THREAD, InvokeMethodIntrinsicTable_lock);
2036     if (throw_error) {
2037       // Remove the entry and let another thread try, or get the same exception.
2038       bool removed = _invoke_method_intrinsic_table->remove(key);
2039       assert(removed, "must be the owner");
2040       ml.notify_all();
2041     } else {
2042       signature->make_permanent(); // The signature is never unloaded.
2043       assert(Arguments::is_interpreter_only() || (m->has_compiled_code() &&
2044              m->code()->entry_point() == m->from_compiled_entry()),
2045              "MH intrinsic invariant");
2046       *met = m(); // insert the element
2047       ml.notify_all();
2048       return m();
2049     }
2050   }
2051 
2052   // Throw OOM or the pending exception in the JavaThread
2053   if (throw_error && !HAS_PENDING_EXCEPTION) {
2054     THROW_MSG_NULL(vmSymbols::java_lang_OutOfMemoryError(),
2055                    "Out of space in CodeCache for method handle intrinsic");
2056   }
2057   return nullptr;
2058 }
2059 
2060 #if INCLUDE_CDS
2061 void SystemDictionary::get_all_method_handle_intrinsics(GrowableArray<Method*>* methods) {
2062   assert(SafepointSynchronize::is_at_safepoint(), "must be");
2063   auto do_method = [&] (InvokeMethodKey& key, Method*& m) {
2064     methods->append(m);
2065   };
2066   _invoke_method_intrinsic_table->iterate_all(do_method);
2067 }
2068 
2069 void SystemDictionary::restore_archived_method_handle_intrinsics() {
2070   if (UseSharedSpaces) {
2071     EXCEPTION_MARK;
2072     restore_archived_method_handle_intrinsics_impl(THREAD);
2073     if (HAS_PENDING_EXCEPTION) {
2074       // This is probably caused by OOM -- other parts of the CDS archive have direct pointers to
2075       // the archived method handle intrinsics, so we can't really recover from this failure.
2076       vm_exit_during_initialization(err_msg("Failed to restore archived method handle intrinsics. Try to increase heap size."));
2077     }
2078   }
2079 }
2080 
2081 void SystemDictionary::restore_archived_method_handle_intrinsics_impl(TRAPS) {
2082   Array<Method*>* list = AOTMetaspace::archived_method_handle_intrinsics();
2083   for (int i = 0; i < list->length(); i++) {
2084     methodHandle m(THREAD, list->at(i));
2085     Method::restore_archived_method_handle_intrinsic(m, CHECK);
2086     m->constants()->restore_unshareable_info(CHECK);
2087     if (!Arguments::is_interpreter_only() || m->intrinsic_id() == vmIntrinsics::_linkToNative) {
2088       AdapterHandlerLibrary::create_native_wrapper(m);
2089       if (!m->has_compiled_code()) {
2090         ResourceMark rm(THREAD);
2091         vm_exit_during_initialization(err_msg("Failed to initialize method %s", m->external_name()));
2092       }
2093     }
2094 
2095     // There's no need to grab the InvokeMethodIntrinsicTable_lock, as we are still very early in
2096     // VM start-up -- in init_globals2() -- so we are still running a single Java thread. It's not
2097     // possible to have a contention.
2098     const int iid_as_int = vmIntrinsics::as_int(m->intrinsic_id());
2099     InvokeMethodKey key(m->signature(), iid_as_int);
2100     bool created = _invoke_method_intrinsic_table->put(key, m());
2101     assert(created, "unexpected contention");
2102   }
2103 }
2104 #endif // INCLUDE_CDS
2105 
2106 // Helper for unpacking the return value from linkMethod and linkCallSite.
2107 static Method* unpack_method_and_appendix(Handle mname,
2108                                           Klass* accessing_klass,
2109                                           objArrayHandle appendix_box,
2110                                           Handle* appendix_result,
2111                                           TRAPS) {
2112   if (mname.not_null()) {
2113     Method* m = java_lang_invoke_MemberName::vmtarget(mname());
2114     if (m != nullptr) {
2115       oop appendix = appendix_box->obj_at(0);
2116       LogTarget(Info, methodhandles) lt;
2117       if (lt.develop_is_enabled()) {
2118         ResourceMark rm(THREAD);
2119         LogStream ls(lt);
2120         ls.print("Linked method=" INTPTR_FORMAT ": ", p2i(m));
2121         m->print_on(&ls);
2122         if (appendix != nullptr) { ls.print("appendix = "); appendix->print_on(&ls); }
2123         ls.cr();
2124       }
2125 
2126       (*appendix_result) = Handle(THREAD, appendix);
2127       // the target is stored in the cpCache and if a reference to this
2128       // MemberName is dropped we need a way to make sure the
2129       // class_loader containing this method is kept alive.
2130       methodHandle mh(THREAD, m); // record_dependency can safepoint.
2131       ClassLoaderData* this_key = accessing_klass->class_loader_data();
2132       this_key->record_dependency(m->method_holder());
2133       return mh();
2134     }
2135   }
2136   THROW_MSG_NULL(vmSymbols::java_lang_LinkageError(), "bad value from MethodHandleNatives");
2137 }
2138 
2139 Method* SystemDictionary::find_method_handle_invoker(Klass* klass,
2140                                                      Symbol* name,
2141                                                      Symbol* signature,
2142                                                      Klass* accessing_klass,
2143                                                      Handle* appendix_result,
2144                                                      TRAPS) {
2145   guarantee(THREAD->can_call_java(), "");
2146   Handle method_type =
2147     SystemDictionary::find_method_handle_type(signature, accessing_klass, CHECK_NULL);
2148 
2149   int ref_kind = JVM_REF_invokeVirtual;
2150   oop name_oop = StringTable::intern(name, CHECK_NULL);
2151   Handle name_str (THREAD, name_oop);
2152   objArrayHandle appendix_box = oopFactory::new_objArray_handle(vmClasses::Object_klass(), 1, CHECK_NULL);
2153   assert(appendix_box->obj_at(0) == nullptr, "");
2154 
2155   // This should not happen.  JDK code should take care of that.
2156   if (accessing_klass == nullptr || method_type.is_null()) {
2157     THROW_MSG_NULL(vmSymbols::java_lang_InternalError(), "bad invokehandle");
2158   }
2159 
2160   // call java.lang.invoke.MethodHandleNatives::linkMethod(... String, MethodType) -> MemberName
2161   JavaCallArguments args;
2162   args.push_oop(Handle(THREAD, accessing_klass->java_mirror()));
2163   args.push_int(ref_kind);
2164   args.push_oop(Handle(THREAD, klass->java_mirror()));
2165   args.push_oop(name_str);
2166   args.push_oop(method_type);
2167   args.push_oop(appendix_box);
2168   JavaValue result(T_OBJECT);
2169   JavaCalls::call_static(&result,
2170                          vmClasses::MethodHandleNatives_klass(),
2171                          vmSymbols::linkMethod_name(),
2172                          vmSymbols::linkMethod_signature(),
2173                          &args, CHECK_NULL);
2174   Handle mname(THREAD, result.get_oop());
2175   return unpack_method_and_appendix(mname, accessing_klass, appendix_box, appendix_result, THREAD);
2176 }
2177 
2178 // Decide if we can globally cache a lookup of this class, to be returned to any client that asks.
2179 // We must ensure that all class loaders everywhere will reach this class, for any client.
2180 // This is a safe bet for public classes in java.lang, such as Object and String.
2181 // We also include public classes in java.lang.invoke, because they appear frequently in system-level method types.
2182 // Out of an abundance of caution, we do not include any other classes, not even for packages like java.util.
2183 static bool is_always_visible_class(oop mirror) {
2184   Klass* klass = java_lang_Class::as_Klass(mirror);
2185   if (klass->is_objArray_klass()) {
2186     klass = ObjArrayKlass::cast(klass)->bottom_klass(); // check element type
2187   }
2188   if (klass->is_typeArray_klass()) {
2189     return true; // primitive array
2190   }
2191   assert(klass->is_instance_klass(), "%s", klass->external_name());
2192   InstanceKlass* ik = InstanceKlass::cast(klass);
2193   return ik->is_public() &&
2194          (ik->is_same_class_package(vmClasses::Object_klass()) ||       // java.lang
2195           ik->is_same_class_package(vmClasses::MethodHandle_klass()));  // java.lang.invoke
2196 }
2197 
2198 // Find or construct the Java mirror (java.lang.Class instance) for
2199 // the given field type signature, as interpreted relative to the
2200 // given class loader.  Handles primitives, void, references, arrays,
2201 // and all other reflectable types, except method types.
2202 // N.B.  Code in reflection should use this entry point.
2203 Handle SystemDictionary::find_java_mirror_for_type(Symbol* signature,
2204                                                    Klass* accessing_klass,
2205                                                    SignatureStream::FailureMode failure_mode,
2206                                                    TRAPS) {
2207 
2208   Handle class_loader;
2209 
2210   // What we have here must be a valid field descriptor,
2211   // and all valid field descriptors are supported.
2212   // Produce the same java.lang.Class that reflection reports.
2213   if (accessing_klass != nullptr) {
2214     class_loader      = Handle(THREAD, accessing_klass->class_loader());
2215   }
2216   ResolvingSignatureStream ss(signature, class_loader, false);
2217   oop mirror_oop = ss.as_java_mirror(failure_mode, CHECK_NH);
2218   if (mirror_oop == nullptr) {
2219     return Handle();  // report failure this way
2220   }
2221   Handle mirror(THREAD, mirror_oop);
2222 
2223   if (accessing_klass != nullptr) {
2224     // Check accessibility, emulating ConstantPool::verify_constant_pool_resolve.
2225     Klass* sel_klass = java_lang_Class::as_Klass(mirror());
2226     if (sel_klass != nullptr) {
2227       LinkResolver::check_klass_accessibility(accessing_klass, sel_klass, CHECK_NH);
2228     }
2229   }
2230   return mirror;
2231 }
2232 
2233 
2234 // Ask Java code to find or construct a java.lang.invoke.MethodType for the given
2235 // signature, as interpreted relative to the given class loader.
2236 // Because of class loader constraints, all method handle usage must be
2237 // consistent with this loader.
2238 Handle SystemDictionary::find_method_handle_type(Symbol* signature,
2239                                                  Klass* accessing_klass,
2240                                                  TRAPS) {
2241   Handle empty;
2242   OopHandle* o;
2243   {
2244     MutexLocker ml(THREAD, InvokeMethodTypeTable_lock);
2245     o = _invoke_method_type_table->get(signature);
2246   }
2247 
2248   if (o != nullptr) {
2249     oop mt = o->resolve();
2250     assert(java_lang_invoke_MethodType::is_instance(mt), "");
2251     return Handle(THREAD, mt);
2252   } else if (!THREAD->can_call_java()) {
2253     warning("SystemDictionary::find_method_handle_type called from compiler thread");  // FIXME
2254     return Handle();  // do not attempt from within compiler, unless it was cached
2255   }
2256 
2257   Handle class_loader;
2258   if (accessing_klass != nullptr) {
2259     class_loader      = Handle(THREAD, accessing_klass->class_loader());
2260   }
2261   bool can_be_cached = true;
2262   int npts = ArgumentCount(signature).size();
2263   objArrayHandle pts = oopFactory::new_objArray_handle(vmClasses::Class_klass(), npts, CHECK_(empty));
2264   int arg = 0;
2265   Handle rt; // the return type from the signature
2266   ResourceMark rm(THREAD);
2267   for (SignatureStream ss(signature); !ss.is_done(); ss.next()) {
2268     oop mirror = nullptr;
2269     if (can_be_cached) {
2270       // Use neutral class loader to lookup candidate classes to be placed in the cache.
2271       mirror = ss.as_java_mirror(Handle(), SignatureStream::ReturnNull, CHECK_(empty));
2272       if (mirror == nullptr || (ss.is_reference() && !is_always_visible_class(mirror))) {
2273         // Fall back to accessing_klass context.
2274         can_be_cached = false;
2275       }
2276     }
2277     if (!can_be_cached) {
2278       // Resolve, throwing a real error if it doesn't work.
2279       mirror = ss.as_java_mirror(class_loader, SignatureStream::NCDFError, CHECK_(empty));
2280     }
2281     assert(mirror != nullptr, "%s", ss.as_symbol()->as_C_string());
2282     if (ss.at_return_type())
2283       rt = Handle(THREAD, mirror);
2284     else
2285       pts->obj_at_put(arg++, mirror);
2286 
2287     // Check accessibility.
2288     if (!java_lang_Class::is_primitive(mirror) && accessing_klass != nullptr) {
2289       Klass* sel_klass = java_lang_Class::as_Klass(mirror);
2290       mirror = nullptr;  // safety
2291       // Emulate ConstantPool::verify_constant_pool_resolve.
2292       LinkResolver::check_klass_accessibility(accessing_klass, sel_klass, CHECK_(empty));
2293     }
2294   }
2295   assert(arg == npts, "");
2296 
2297   // call java.lang.invoke.MethodHandleNatives::findMethodHandleType(Class rt, Class[] pts) -> MethodType
2298   JavaCallArguments args(Handle(THREAD, rt()));
2299   args.push_oop(pts);
2300   JavaValue result(T_OBJECT);
2301   JavaCalls::call_static(&result,
2302                          vmClasses::MethodHandleNatives_klass(),
2303                          vmSymbols::findMethodHandleType_name(),
2304                          vmSymbols::findMethodHandleType_signature(),
2305                          &args, CHECK_(empty));
2306   Handle method_type(THREAD, result.get_oop());
2307 
2308   if (can_be_cached) {
2309     // We can cache this MethodType inside the JVM.
2310     MutexLocker ml(THREAD, InvokeMethodTypeTable_lock);
2311     bool created = false;
2312     assert(method_type != nullptr, "unexpected null");
2313     OopHandle* h = _invoke_method_type_table->get(signature);
2314     if (h == nullptr) {
2315       signature->make_permanent(); // The signature is never unloaded.
2316       OopHandle elem = OopHandle(Universe::vm_global(), method_type());
2317       bool created = _invoke_method_type_table->put(signature, elem);
2318       assert(created, "better be created");
2319     }
2320   }
2321   // report back to the caller with the MethodType
2322   return method_type;
2323 }
2324 
2325 Handle SystemDictionary::find_field_handle_type(Symbol* signature,
2326                                                 Klass* accessing_klass,
2327                                                 TRAPS) {
2328   Handle empty;
2329   ResourceMark rm(THREAD);
2330   SignatureStream ss(signature, /*is_method=*/ false);
2331   if (!ss.is_done()) {
2332     Handle class_loader;
2333     if (accessing_klass != nullptr) {
2334       class_loader      = Handle(THREAD, accessing_klass->class_loader());
2335     }
2336     oop mirror = ss.as_java_mirror(class_loader, SignatureStream::NCDFError, CHECK_(empty));
2337     ss.next();
2338     if (ss.is_done()) {
2339       return Handle(THREAD, mirror);
2340     }
2341   }
2342   return empty;
2343 }
2344 
2345 // Ask Java code to find or construct a method handle constant.
2346 Handle SystemDictionary::link_method_handle_constant(Klass* caller,
2347                                                      int ref_kind, //e.g., JVM_REF_invokeVirtual
2348                                                      Klass* callee,
2349                                                      Symbol* name,
2350                                                      Symbol* signature,
2351                                                      TRAPS) {
2352   Handle empty;
2353   if (caller == nullptr) {
2354     THROW_MSG_(vmSymbols::java_lang_InternalError(), "bad MH constant", empty);
2355   }
2356   Handle name_str      = java_lang_String::create_from_symbol(name,      CHECK_(empty));
2357   Handle signature_str = java_lang_String::create_from_symbol(signature, CHECK_(empty));
2358 
2359   // Put symbolic info from the MH constant into freshly created MemberName and resolve it.
2360   Handle mname = vmClasses::MemberName_klass()->allocate_instance_handle(CHECK_(empty));
2361   java_lang_invoke_MemberName::set_clazz(mname(), callee->java_mirror());
2362   java_lang_invoke_MemberName::set_name (mname(), name_str());
2363   java_lang_invoke_MemberName::set_type (mname(), signature_str());
2364   java_lang_invoke_MemberName::set_flags(mname(), MethodHandles::ref_kind_to_flags(ref_kind));
2365 
2366   if (ref_kind == JVM_REF_invokeVirtual &&
2367       MethodHandles::is_signature_polymorphic_public_name(callee, name)) {
2368     // Skip resolution for public signature polymorphic methods such as
2369     // j.l.i.MethodHandle.invoke()/invokeExact() and those on VarHandle
2370     // They require appendix argument which MemberName resolution doesn't handle.
2371     // There's special logic on JDK side to handle them
2372     // (see MethodHandles.linkMethodHandleConstant() and MethodHandles.findVirtualForMH()).
2373   } else {
2374     MethodHandles::resolve_MemberName(mname, caller, 0, false /*speculative_resolve*/, CHECK_(empty));
2375   }
2376 
2377   // After method/field resolution succeeded, it's safe to resolve MH signature as well.
2378   Handle type = MethodHandles::resolve_MemberName_type(mname, caller, CHECK_(empty));
2379 
2380   // call java.lang.invoke.MethodHandleNatives::linkMethodHandleConstant(Class caller, int refKind, Class callee, String name, Object type) -> MethodHandle
2381   JavaCallArguments args;
2382   args.push_oop(Handle(THREAD, caller->java_mirror()));  // the referring class
2383   args.push_int(ref_kind);
2384   args.push_oop(Handle(THREAD, callee->java_mirror()));  // the target class
2385   args.push_oop(name_str);
2386   args.push_oop(type);
2387   JavaValue result(T_OBJECT);
2388   JavaCalls::call_static(&result,
2389                          vmClasses::MethodHandleNatives_klass(),
2390                          vmSymbols::linkMethodHandleConstant_name(),
2391                          vmSymbols::linkMethodHandleConstant_signature(),
2392                          &args, CHECK_(empty));
2393   return Handle(THREAD, result.get_oop());
2394 }
2395 
2396 // Ask Java to run a bootstrap method, in order to create a dynamic call site
2397 // while linking an invokedynamic op, or compute a constant for Dynamic_info CP entry
2398 // with linkage results being stored back into the bootstrap specifier.
2399 void SystemDictionary::invoke_bootstrap_method(BootstrapInfo& bootstrap_specifier, TRAPS) {
2400   // Resolve the bootstrap specifier, its name, type, and static arguments
2401   bootstrap_specifier.resolve_bsm(CHECK);
2402 
2403   // This should not happen.  JDK code should take care of that.
2404   if (bootstrap_specifier.caller() == nullptr || bootstrap_specifier.type_arg().is_null()) {
2405     THROW_MSG(vmSymbols::java_lang_InternalError(), "Invalid bootstrap method invocation with no caller or type argument");
2406   }
2407 
2408   bool is_indy = bootstrap_specifier.is_method_call();
2409   objArrayHandle appendix_box;
2410   if (is_indy) {
2411     // Some method calls may require an appendix argument.  Arrange to receive it.
2412     appendix_box = oopFactory::new_objArray_handle(vmClasses::Object_klass(), 1, CHECK);
2413     assert(appendix_box->obj_at(0) == nullptr, "");
2414   }
2415 
2416   // call condy: java.lang.invoke.MethodHandleNatives::linkDynamicConstant(caller, bsm, type, info)
2417   //       indy: java.lang.invoke.MethodHandleNatives::linkCallSite(caller, bsm, name, mtype, info, &appendix)
2418   JavaCallArguments args;
2419   args.push_oop(Handle(THREAD, bootstrap_specifier.caller_mirror()));
2420   args.push_oop(bootstrap_specifier.bsm());
2421   args.push_oop(bootstrap_specifier.name_arg());
2422   args.push_oop(bootstrap_specifier.type_arg());
2423   args.push_oop(bootstrap_specifier.arg_values());
2424   if (is_indy) {
2425     args.push_oop(appendix_box);
2426   }
2427   JavaValue result(T_OBJECT);
2428   JavaCalls::call_static(&result,
2429                          vmClasses::MethodHandleNatives_klass(),
2430                          is_indy ? vmSymbols::linkCallSite_name() : vmSymbols::linkDynamicConstant_name(),
2431                          is_indy ? vmSymbols::linkCallSite_signature() : vmSymbols::linkDynamicConstant_signature(),
2432                          &args, CHECK);
2433 
2434   Handle value(THREAD, result.get_oop());
2435   if (is_indy) {
2436     Handle appendix;
2437     Method* method = unpack_method_and_appendix(value,
2438                                                 bootstrap_specifier.caller(),
2439                                                 appendix_box,
2440                                                 &appendix, CHECK);
2441     methodHandle mh(THREAD, method);
2442     bootstrap_specifier.set_resolved_method(mh, appendix);
2443   } else {
2444     bootstrap_specifier.set_resolved_value(value);
2445   }
2446 
2447   // sanity check
2448   assert(bootstrap_specifier.is_resolved() ||
2449          (bootstrap_specifier.is_method_call() &&
2450           bootstrap_specifier.resolved_method().not_null()), "bootstrap method call failed");
2451 }
2452 
2453 
2454 bool SystemDictionary::is_nonpublic_Object_method(Method* m) {
2455   assert(m != nullptr, "Unexpected nullptr Method*");
2456   return !m->is_public() && m->method_holder() == vmClasses::Object_klass();
2457 }
2458 
2459 // ----------------------------------------------------------------------------
2460 
2461 void SystemDictionary::print_on(outputStream *st) {
2462   CDS_ONLY(SystemDictionaryShared::print_on(st));
2463   GCMutexLocker mu(SystemDictionary_lock);
2464 
2465   ClassLoaderDataGraph::print_dictionary(st);
2466 
2467   // Placeholders
2468   PlaceholderTable::print_on(st);
2469   st->cr();
2470 
2471   // loader constraints - print under SD_lock
2472   LoaderConstraintTable::print_on(st);
2473   st->cr();
2474 }
2475 
2476 void SystemDictionary::print() { print_on(tty); }
2477 
2478 void SystemDictionary::verify() {
2479 
2480   GCMutexLocker mu(SystemDictionary_lock);
2481 
2482   // Verify dictionary
2483   ClassLoaderDataGraph::verify_dictionary();
2484 
2485   // Verify constraint table
2486   LoaderConstraintTable::verify();
2487 }
2488 
2489 void SystemDictionary::dump(outputStream *st, bool verbose) {
2490   assert_locked_or_safepoint(SystemDictionary_lock);
2491   if (verbose) {
2492     print_on(st);
2493   } else {
2494     CDS_ONLY(SystemDictionaryShared::print_table_statistics(st));
2495     ClassLoaderDataGraph::print_table_statistics(st);
2496     LoaderConstraintTable::print_table_statistics(st);
2497   }
2498 }
2499 
2500 // Utility for dumping dictionaries.
2501 SystemDictionaryDCmd::SystemDictionaryDCmd(outputStream* output, bool heap) :
2502                                  DCmdWithParser(output, heap),
2503   _verbose("-verbose", "Dump the content of each dictionary entry for all class loaders",
2504            "BOOLEAN", false, "false") {
2505   _dcmdparser.add_dcmd_option(&_verbose);
2506 }
2507 
2508 void SystemDictionaryDCmd::execute(DCmdSource source, TRAPS) {
2509   VM_DumpHashtable dumper(output(), VM_DumpHashtable::DumpSysDict,
2510                          _verbose.value());
2511   VMThread::execute(&dumper);
2512 }
--- EOF ---