1 /*
   2  * Copyright (c) 1997, 2025, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "cds/aotClassLocation.hpp"
  26 #include "cds/cdsConfig.hpp"
  27 #include "cds/heapShared.hpp"
  28 #include "classfile/classFileParser.hpp"
  29 #include "classfile/classFileStream.hpp"
  30 #include "classfile/classLoader.hpp"
  31 #include "classfile/classLoaderData.inline.hpp"
  32 #include "classfile/classLoaderDataGraph.inline.hpp"
  33 #include "classfile/classLoaderExt.hpp"
  34 #include "classfile/classLoadInfo.hpp"
  35 #include "classfile/dictionary.hpp"
  36 #include "classfile/javaClasses.inline.hpp"
  37 #include "classfile/klassFactory.hpp"
  38 #include "classfile/loaderConstraints.hpp"
  39 #include "classfile/packageEntry.hpp"
  40 #include "classfile/placeholders.hpp"
  41 #include "classfile/resolutionErrors.hpp"
  42 #include "classfile/stringTable.hpp"
  43 #include "classfile/symbolTable.hpp"
  44 #include "classfile/systemDictionary.hpp"
  45 #include "classfile/vmClasses.hpp"
  46 #include "classfile/vmSymbols.hpp"
  47 #include "gc/shared/gcTraceTime.inline.hpp"
  48 #include "interpreter/bootstrapInfo.hpp"
  49 #include "jfr/jfrEvents.hpp"
  50 #include "jvm.h"
  51 #include "logging/log.hpp"
  52 #include "logging/logStream.hpp"
  53 #include "memory/metaspaceClosure.hpp"
  54 #include "memory/oopFactory.hpp"
  55 #include "memory/resourceArea.hpp"
  56 #include "memory/universe.hpp"
  57 #include "oops/access.inline.hpp"
  58 #include "oops/fieldStreams.inline.hpp"
  59 #include "oops/instanceKlass.hpp"
  60 #include "oops/klass.inline.hpp"
  61 #include "oops/method.inline.hpp"
  62 #include "oops/objArrayKlass.hpp"
  63 #include "oops/objArrayOop.inline.hpp"
  64 #include "oops/oop.inline.hpp"
  65 #include "oops/oop.hpp"
  66 #include "oops/oopHandle.hpp"
  67 #include "oops/oopHandle.inline.hpp"
  68 #include "oops/symbol.hpp"
  69 #include "oops/typeArrayKlass.hpp"
  70 #include "oops/inlineKlass.inline.hpp"
  71 #include "prims/jvmtiExport.hpp"
  72 #include "prims/methodHandles.hpp"
  73 #include "runtime/arguments.hpp"
  74 #include "runtime/atomic.hpp"
  75 #include "runtime/handles.inline.hpp"
  76 #include "runtime/java.hpp"
  77 #include "runtime/javaCalls.hpp"
  78 #include "runtime/mutexLocker.hpp"
  79 #include "runtime/os.hpp"
  80 #include "runtime/sharedRuntime.hpp"
  81 #include "runtime/signature.hpp"
  82 #include "runtime/synchronizer.hpp"
  83 #include "services/classLoadingService.hpp"
  84 #include "services/diagnosticCommand.hpp"
  85 #include "services/finalizerService.hpp"
  86 #include "services/threadService.hpp"
  87 #include "utilities/growableArray.hpp"
  88 #include "utilities/macros.hpp"
  89 #include "utilities/utf8.hpp"
  90 #if INCLUDE_CDS
  91 #include "classfile/systemDictionaryShared.hpp"
  92 #endif
  93 #if INCLUDE_JFR
  94 #include "jfr/jfr.hpp"
  95 #endif
  96 
  97 class InvokeMethodKey : public StackObj {
  98   private:
  99     Symbol* _symbol;
 100     intptr_t _iid;
 101 
 102   public:
 103     InvokeMethodKey(Symbol* symbol, intptr_t iid) :
 104         _symbol(symbol),
 105         _iid(iid) {}
 106 
 107     static bool key_comparison(InvokeMethodKey const &k1, InvokeMethodKey const &k2){
 108         return k1._symbol == k2._symbol && k1._iid == k2._iid;
 109     }
 110 
 111     static unsigned int compute_hash(const InvokeMethodKey &k) {
 112         Symbol* sym = k._symbol;
 113         intptr_t iid = k._iid;
 114         unsigned int hash = (unsigned int) sym -> identity_hash();
 115         return (unsigned int) (hash ^ iid);
 116     }
 117 
 118 };
 119 
 120 using InvokeMethodIntrinsicTable = ResourceHashtable<InvokeMethodKey, Method*, 139, AnyObj::C_HEAP, mtClass,
 121                   InvokeMethodKey::compute_hash, InvokeMethodKey::key_comparison>;
 122 static InvokeMethodIntrinsicTable* _invoke_method_intrinsic_table;
 123 using InvokeMethodTypeTable = ResourceHashtable<SymbolHandle, OopHandle, 139, AnyObj::C_HEAP, mtClass, SymbolHandle::compute_hash>;
 124 static InvokeMethodTypeTable* _invoke_method_type_table;
 125 
 126 OopHandle   SystemDictionary::_java_system_loader;
 127 OopHandle   SystemDictionary::_java_platform_loader;
 128 
 129 // ----------------------------------------------------------------------------
 130 // Java-level SystemLoader and PlatformLoader
 131 oop SystemDictionary::java_system_loader() {
 132   return _java_system_loader.resolve();
 133 }
 134 
 135 oop SystemDictionary::java_platform_loader() {
 136   return _java_platform_loader.resolve();
 137 }
 138 
 139 void SystemDictionary::compute_java_loaders(TRAPS) {
 140   if (_java_platform_loader.is_empty()) {
 141     oop platform_loader = get_platform_class_loader_impl(CHECK);
 142     _java_platform_loader = OopHandle(Universe::vm_global(), platform_loader);
 143   } else {
 144     // It must have been restored from the archived module graph
 145     assert(CDSConfig::is_using_archive(), "must be");
 146     assert(CDSConfig::is_using_full_module_graph(), "must be");
 147     DEBUG_ONLY(
 148       oop platform_loader = get_platform_class_loader_impl(CHECK);
 149       assert(_java_platform_loader.resolve() == platform_loader, "must be");
 150     )
 151  }
 152 
 153   if (_java_system_loader.is_empty()) {
 154     oop system_loader = get_system_class_loader_impl(CHECK);
 155     _java_system_loader = OopHandle(Universe::vm_global(), system_loader);
 156   } else {
 157     // It must have been restored from the archived module graph
 158     assert(CDSConfig::is_using_archive(), "must be");
 159     assert(CDSConfig::is_using_full_module_graph(), "must be");
 160     DEBUG_ONLY(
 161       oop system_loader = get_system_class_loader_impl(CHECK);
 162       assert(_java_system_loader.resolve() == system_loader, "must be");
 163     )
 164   }
 165 }
 166 
 167 oop SystemDictionary::get_system_class_loader_impl(TRAPS) {
 168   JavaValue result(T_OBJECT);
 169   InstanceKlass* class_loader_klass = vmClasses::ClassLoader_klass();
 170   JavaCalls::call_static(&result,
 171                          class_loader_klass,
 172                          vmSymbols::getSystemClassLoader_name(),
 173                          vmSymbols::void_classloader_signature(),
 174                          CHECK_NULL);
 175   return result.get_oop();
 176 }
 177 
 178 oop SystemDictionary::get_platform_class_loader_impl(TRAPS) {
 179   JavaValue result(T_OBJECT);
 180   InstanceKlass* class_loader_klass = vmClasses::ClassLoader_klass();
 181   JavaCalls::call_static(&result,
 182                          class_loader_klass,
 183                          vmSymbols::getPlatformClassLoader_name(),
 184                          vmSymbols::void_classloader_signature(),
 185                          CHECK_NULL);
 186   return result.get_oop();
 187 }
 188 
 189 // Helper function
 190 inline ClassLoaderData* class_loader_data(Handle class_loader) {
 191   return ClassLoaderData::class_loader_data(class_loader());
 192 }
 193 
 194 ClassLoaderData* SystemDictionary::register_loader(Handle class_loader, bool create_mirror_cld) {
 195   if (create_mirror_cld) {
 196     // Add a new class loader data to the graph.
 197     return ClassLoaderDataGraph::add(class_loader, true);
 198   } else {
 199     return (class_loader() == nullptr) ? ClassLoaderData::the_null_class_loader_data() :
 200                                       ClassLoaderDataGraph::find_or_create(class_loader);
 201   }
 202 }
 203 
 204 void SystemDictionary::set_system_loader(ClassLoaderData *cld) {
 205   assert(_java_system_loader.is_empty(), "already set!");
 206   _java_system_loader = cld->class_loader_handle();
 207 
 208 }
 209 
 210 void SystemDictionary::set_platform_loader(ClassLoaderData *cld) {
 211   assert(_java_platform_loader.is_empty(), "already set!");
 212   _java_platform_loader = cld->class_loader_handle();
 213 }
 214 
 215 // ----------------------------------------------------------------------------
 216 // Parallel class loading check
 217 
 218 static bool is_parallelCapable(Handle class_loader) {
 219   if (class_loader.is_null()) return true;
 220   return java_lang_ClassLoader::parallelCapable(class_loader());
 221 }
 222 // ----------------------------------------------------------------------------
 223 // ParallelDefineClass flag does not apply to bootclass loader
 224 static bool is_parallelDefine(Handle class_loader) {
 225    if (class_loader.is_null()) return false;
 226    if (AllowParallelDefineClass && java_lang_ClassLoader::parallelCapable(class_loader())) {
 227      return true;
 228    }
 229    return false;
 230 }
 231 
 232 // Returns true if the passed class loader is the builtin application class loader
 233 // or a custom system class loader. A customer system class loader can be
 234 // specified via -Djava.system.class.loader.
 235 bool SystemDictionary::is_system_class_loader(oop class_loader) {
 236   if (class_loader == nullptr) {
 237     return false;
 238   }
 239   return (class_loader->klass() == vmClasses::jdk_internal_loader_ClassLoaders_AppClassLoader_klass() ||
 240          class_loader == _java_system_loader.peek());
 241 }
 242 
 243 // Returns true if the passed class loader is the platform class loader.
 244 bool SystemDictionary::is_platform_class_loader(oop class_loader) {
 245   if (class_loader == nullptr) {
 246     return false;
 247   }
 248   return (class_loader->klass() == vmClasses::jdk_internal_loader_ClassLoaders_PlatformClassLoader_klass());
 249 }
 250 
 251 Handle SystemDictionary::get_loader_lock_or_null(Handle class_loader) {
 252   // If class_loader is null or parallelCapable, the JVM doesn't acquire a lock while loading.
 253   if (is_parallelCapable(class_loader)) {
 254     return Handle();
 255   } else {
 256     return class_loader;
 257   }
 258 }
 259 
 260 // ----------------------------------------------------------------------------
 261 // Resolving of classes
 262 
 263 Symbol* SystemDictionary::class_name_symbol(const char* name, Symbol* exception, TRAPS) {
 264   if (name == nullptr) {
 265     THROW_MSG_NULL(exception, "No class name given");
 266   }
 267   size_t name_len = strlen(name);
 268   if (name_len > static_cast<size_t>(Symbol::max_length())) {
 269     // It's impossible to create this class;  the name cannot fit
 270     // into the constant pool. If necessary report an abridged name
 271     // in the exception message.
 272     if (name_len > static_cast<size_t>(MaxStringPrintSize)) {
 273       Exceptions::fthrow(THREAD_AND_LOCATION, exception,
 274                          "Class name exceeds maximum length of %d: %.*s ... (%zu characters omitted) ... %.*s",
 275                          Symbol::max_length(),
 276                          MaxStringPrintSize / 2,
 277                          name,
 278                          name_len - 2 * (MaxStringPrintSize / 2), // allows for odd value
 279                          MaxStringPrintSize / 2,
 280                          name + name_len - MaxStringPrintSize / 2);
 281     }
 282     else {
 283       Exceptions::fthrow(THREAD_AND_LOCATION, exception,
 284                          "Class name exceeds maximum length of %d: %s",
 285                          Symbol::max_length(),
 286                          name);
 287     }
 288     return nullptr;
 289   }
 290   // Callers should ensure that the name is never an illegal UTF8 string.
 291   assert(UTF8::is_legal_utf8((const unsigned char*)name, name_len, false),
 292          "Class name is not a valid utf8 string.");
 293 
 294   // Make a new symbol for the class name.
 295   return SymbolTable::new_symbol(name);
 296 }
 297 
 298 #ifdef ASSERT
 299 // Used to verify that class loading succeeded in adding k to the dictionary.
 300 static void verify_dictionary_entry(Symbol* class_name, InstanceKlass* k) {
 301   MutexLocker mu(SystemDictionary_lock);
 302   ClassLoaderData* loader_data = k->class_loader_data();
 303   Dictionary* dictionary = loader_data->dictionary();
 304   assert(class_name == k->name(), "Must be the same");
 305   InstanceKlass* kk = dictionary->find_class(JavaThread::current(), class_name);
 306   assert(kk == k, "should be present in dictionary");
 307 }
 308 #endif
 309 
 310 static void handle_resolution_exception(Symbol* class_name, bool throw_error, TRAPS) {
 311   if (HAS_PENDING_EXCEPTION) {
 312     // If we have a pending exception we forward it to the caller, unless throw_error is true,
 313     // in which case we have to check whether the pending exception is a ClassNotFoundException,
 314     // and convert it to a NoClassDefFoundError and chain the original ClassNotFoundException.
 315     if (throw_error && PENDING_EXCEPTION->is_a(vmClasses::ClassNotFoundException_klass())) {
 316       ResourceMark rm(THREAD);
 317       Handle e(THREAD, PENDING_EXCEPTION);
 318       CLEAR_PENDING_EXCEPTION;
 319       THROW_MSG_CAUSE(vmSymbols::java_lang_NoClassDefFoundError(), class_name->as_C_string(), e);
 320     } else {
 321       return; // the caller will throw the incoming exception
 322     }
 323   }
 324   // If the class is not found, ie, caller has checked that klass is null, throw the appropriate
 325   // error or exception depending on the value of throw_error.
 326   ResourceMark rm(THREAD);
 327   if (throw_error) {
 328     THROW_MSG(vmSymbols::java_lang_NoClassDefFoundError(), class_name->as_C_string());
 329   } else {
 330     THROW_MSG(vmSymbols::java_lang_ClassNotFoundException(), class_name->as_C_string());
 331   }
 332 }
 333 
 334 // Forwards to resolve_or_null
 335 
 336 Klass* SystemDictionary::resolve_or_fail(Symbol* class_name, Handle class_loader,
 337                                          bool throw_error, TRAPS) {
 338   Klass* klass = resolve_or_null(class_name, class_loader, THREAD);
 339   // Check for pending exception or null klass, and throw exception
 340   if (HAS_PENDING_EXCEPTION || klass == nullptr) {
 341     handle_resolution_exception(class_name, throw_error, CHECK_NULL);
 342   }
 343   return klass;
 344 }
 345 
 346 // Forwards to resolve_array_class_or_null or resolve_instance_class_or_null
 347 
 348 Klass* SystemDictionary::resolve_or_null(Symbol* class_name, Handle class_loader, TRAPS) {
 349   if (Signature::is_array(class_name)) {
 350     return resolve_array_class_or_null(class_name, class_loader, THREAD);
 351   } else {
 352     assert(class_name != nullptr && !Signature::is_array(class_name), "must be");
 353     if (Signature::has_envelope(class_name)) {
 354       ResourceMark rm(THREAD);
 355       // Ignore wrapping L and ; (and Q and ; for value types).
 356       TempNewSymbol name = SymbolTable::new_symbol(class_name->as_C_string() + 1,
 357                                                    class_name->utf8_length() - 2);
 358       return resolve_instance_class_or_null(name, class_loader, THREAD);
 359     } else {
 360       return resolve_instance_class_or_null(class_name, class_loader, THREAD);
 361     }
 362   }
 363 }
 364 
 365 // Forwards to resolve_instance_class_or_null
 366 
 367 Klass* SystemDictionary::resolve_array_class_or_null(Symbol* class_name,
 368                                                      Handle class_loader,
 369                                                      TRAPS) {
 370   assert(Signature::is_array(class_name), "must be array");
 371   ResourceMark rm(THREAD);
 372   SignatureStream ss(class_name, false);
 373   int ndims = ss.skip_array_prefix();  // skip all '['s
 374   Klass* k = nullptr;
 375   BasicType t = ss.type();
 376   if (ss.has_envelope()) {
 377     Symbol* obj_class = ss.as_symbol();
 378     k = SystemDictionary::resolve_instance_class_or_null(obj_class,
 379                                                          class_loader,
 380                                                          CHECK_NULL);
 381     if (k != nullptr) {
 382       k = k->array_klass(ndims, CHECK_NULL);
 383     }
 384   } else {
 385     k = Universe::typeArrayKlass(t);
 386     k = k->array_klass(ndims, CHECK_NULL);
 387   }
 388   return k;
 389 }
 390 
 391 static inline void log_circularity_error(Symbol* name, PlaceholderEntry* probe) {
 392   LogTarget(Debug, class, load, placeholders) lt;
 393   if (lt.is_enabled()) {
 394     ResourceMark rm;
 395     LogStream ls(lt);
 396     ls.print("ClassCircularityError detected for placeholder entry %s", name->as_C_string());
 397     probe->print_on(&ls);
 398     ls.cr();
 399   }
 400 }
 401 
 402 // Must be called for any superclass or superinterface resolution
 403 // during class definition to allow class circularity checking
 404 // superinterface callers:
 405 //    parse_interfaces - from defineClass
 406 // superclass callers:
 407 //   ClassFileParser - from defineClass
 408 //   load_shared_class - while loading a class from shared archive
 409 //   resolve_instance_class_or_null:
 410 //     via: handle_parallel_super_load
 411 //      when resolving a class that has an existing placeholder with
 412 //      a saved superclass [i.e. a defineClass is currently in progress]
 413 //      If another thread is trying to resolve the class, it must do
 414 //      superclass checks on its own thread to catch class circularity and
 415 //      to avoid deadlock.
 416 //
 417 // resolve_with_circularity_detection adds a DETECT_CIRCULARITY placeholder to the placeholder table before calling
 418 // resolve_instance_class_or_null. ClassCircularityError is detected when a DETECT_CIRCULARITY or LOAD_INSTANCE
 419 // placeholder for the same thread, class, classloader is found.
 420 // This can be seen with logging option: -Xlog:class+load+placeholders=debug.
 421 //
 422 InstanceKlass* SystemDictionary::resolve_with_circularity_detection(Symbol* class_name,
 423                                                                     Symbol* next_name,
 424                                                                     Handle class_loader,
 425                                                                     bool is_superclass,
 426                                                                     TRAPS) {
 427 
 428   assert(next_name != nullptr, "null superclass for resolving");
 429   assert(!Signature::is_array(next_name), "invalid superclass name");
 430 
 431   ClassLoaderData* loader_data = class_loader_data(class_loader);
 432 
 433   if (is_superclass) {
 434     InstanceKlass* klassk = loader_data->dictionary()->find_class(THREAD, class_name);
 435     if (klassk != nullptr) {
 436       // We can come here for two reasons:
 437       // (a) RedefineClasses -- the class is already loaded
 438       // (b) Rarely, the class might have been loaded by a parallel thread
 439       // We can do a quick check against the already assigned superclass's name and loader.
 440       InstanceKlass* superk = klassk->java_super();
 441       if (superk != nullptr &&
 442           superk->name() == next_name &&
 443           superk->class_loader() == class_loader()) {
 444         return superk;
 445       }
 446     }
 447   }
 448 
 449   // can't throw error holding a lock
 450   bool throw_circularity_error = false;
 451   {
 452     MutexLocker mu(THREAD, SystemDictionary_lock);
 453 
 454     // Must check ClassCircularity before resolving next_name (superclass or interface).
 455     PlaceholderEntry* probe = PlaceholderTable::get_entry(class_name, loader_data);
 456     if (probe != nullptr && probe->check_seen_thread(THREAD, PlaceholderTable::DETECT_CIRCULARITY)) {
 457         log_circularity_error(class_name, probe);
 458         throw_circularity_error = true;
 459     }
 460 
 461     // Make sure there's a placeholder for the class_name before resolving.
 462     // This is used as a claim that this thread is currently loading superclass/classloader
 463     // and for ClassCircularity checks.
 464     if (!throw_circularity_error) {
 465       // Be careful not to exit resolve_with_circularity_detection without removing this placeholder.
 466       PlaceholderEntry* newprobe = PlaceholderTable::find_and_add(class_name,
 467                                                                   loader_data,
 468                                                                   PlaceholderTable::DETECT_CIRCULARITY,
 469                                                                   next_name, THREAD);
 470     }
 471   }
 472 
 473   if (throw_circularity_error) {
 474       ResourceMark rm(THREAD);
 475       THROW_MSG_NULL(vmSymbols::java_lang_ClassCircularityError(), class_name->as_C_string());
 476   }
 477 
 478   // Resolve the superclass or superinterface, check results on return
 479   InstanceKlass* superk =
 480     SystemDictionary::resolve_instance_class_or_null(next_name,
 481                                                      class_loader,
 482                                                      THREAD);
 483 
 484   // Clean up placeholder entry.
 485   {
 486     MutexLocker mu(THREAD, SystemDictionary_lock);
 487     PlaceholderTable::find_and_remove(class_name, loader_data, PlaceholderTable::DETECT_CIRCULARITY, THREAD);
 488     SystemDictionary_lock->notify_all();
 489   }
 490 
 491   // Check for pending exception or null superk, and throw exception
 492   if (HAS_PENDING_EXCEPTION || superk == nullptr) {
 493     handle_resolution_exception(next_name, true, CHECK_NULL);
 494   }
 495 
 496   return superk;
 497 }
 498 
 499 // If the class in is in the placeholder table, class loading is in progress.
 500 // For cases where the application changes threads to load classes, it
 501 // is critical to ClassCircularity detection that we try loading
 502 // the superclass on the new thread internally, so we do parallel
 503 // superclass loading here.  This avoids deadlock for ClassCircularity
 504 // detection for parallelCapable class loaders that lock on a per-class lock.
 505 static void handle_parallel_super_load(Symbol* name,
 506                                        Symbol* superclassname,
 507                                        Handle class_loader,
 508                                        TRAPS) {
 509 
 510   // The result superk is not used; resolve_with_circularity_detection is called for circularity check only.
 511   // This passes false to is_superclass to skip doing the unlikely optimization.
 512   Klass* superk = SystemDictionary::resolve_with_circularity_detection(name,
 513                                                                        superclassname,
 514                                                                        class_loader,
 515                                                                        false,
 516                                                                        CHECK);
 517 }
 518 
 519 // Bootstrap and non-parallel capable class loaders use the LOAD_INSTANCE placeholder to
 520 // wait for parallel class loading and/or to check for circularity error for Xcomp when loading.
 521 static bool needs_load_placeholder(Handle class_loader) {
 522   return class_loader.is_null() || !is_parallelCapable(class_loader);
 523 }
 524 
 525 // Check for other threads loading this class either to throw CCE or wait in the case of the boot loader.
 526 static InstanceKlass* handle_parallel_loading(JavaThread* current,
 527                                               Symbol* name,
 528                                               ClassLoaderData* loader_data,
 529                                               bool must_wait_for_class_loading,
 530                                               bool* throw_circularity_error) {
 531   PlaceholderEntry* oldprobe = PlaceholderTable::get_entry(name, loader_data);
 532   if (oldprobe != nullptr) {
 533     // -Xcomp calls load_signature_classes which might result in loading
 534     // a class that's already in the process of loading, so we detect CCE here also.
 535     // Only need check_seen_thread once, not on each loop
 536     if (oldprobe->check_seen_thread(current, PlaceholderTable::LOAD_INSTANCE)) {
 537       log_circularity_error(name, oldprobe);
 538       *throw_circularity_error = true;
 539       return nullptr;
 540     } else if (must_wait_for_class_loading) {
 541       // Wait until the first thread has finished loading this class. Also wait until all the
 542       // threads trying to load its superclass have removed their placeholders.
 543       while (oldprobe != nullptr &&
 544              (oldprobe->instance_load_in_progress() || oldprobe->circularity_detection_in_progress())) {
 545 
 546         // LOAD_INSTANCE placeholders are used to implement parallel capable class loading
 547         // for the bootclass loader.
 548         SystemDictionary_lock->wait();
 549 
 550         // Check if classloading completed while we were waiting
 551         InstanceKlass* check = loader_data->dictionary()->find_class(current, name);
 552         if (check != nullptr) {
 553           // Klass is already loaded, so just return it
 554           return check;
 555         }
 556         // check if other thread failed to load and cleaned up
 557         oldprobe = PlaceholderTable::get_entry(name, loader_data);
 558       }
 559     }
 560   }
 561   return nullptr;
 562 }
 563 
 564 void SystemDictionary::post_class_load_event(EventClassLoad* event, const InstanceKlass* k, const ClassLoaderData* init_cld) {
 565   assert(event != nullptr, "invariant");
 566   assert(k != nullptr, "invariant");
 567   event->set_loadedClass(k);
 568   event->set_definingClassLoader(k->class_loader_data());
 569   event->set_initiatingClassLoader(init_cld);
 570   event->commit();
 571 }
 572 
 573 // SystemDictionary::resolve_instance_class_or_null is the main function for class name resolution.
 574 // After checking if the InstanceKlass already exists, it checks for ClassCircularityError and
 575 // whether the thread must wait for loading in parallel.  It eventually calls load_instance_class,
 576 // which will load the class via the bootstrap loader or call ClassLoader.loadClass().
 577 // This can return null, an exception or an InstanceKlass.
 578 InstanceKlass* SystemDictionary::resolve_instance_class_or_null(Symbol* name,
 579                                                                 Handle class_loader,
 580                                                                 TRAPS) {
 581   // name must be in the form of "java/lang/Object" -- cannot be "Ljava/lang/Object;"
 582   DEBUG_ONLY(ResourceMark rm(THREAD));
 583   assert(name != nullptr && !Signature::is_array(name) &&
 584          !Signature::has_envelope(name), "invalid class name: %s", name == nullptr ? "nullptr" : name->as_C_string());
 585 
 586   EventClassLoad class_load_start_event;
 587 
 588   HandleMark hm(THREAD);
 589 
 590   ClassLoaderData* loader_data = register_loader(class_loader);
 591   Dictionary* dictionary = loader_data->dictionary();
 592 
 593   // Do lookup to see if class already exists.
 594   InstanceKlass* probe = dictionary->find_class(THREAD, name);
 595   if (probe != nullptr) return probe;
 596 
 597   // Non-bootstrap class loaders will call out to class loader and
 598   // define via jvm/jni_DefineClass which will acquire the
 599   // class loader object lock to protect against multiple threads
 600   // defining the class in parallel by accident.
 601   // This lock must be acquired here so the waiter will find
 602   // any successful result in the SystemDictionary and not attempt
 603   // the define.
 604   // ParallelCapable class loaders and the bootstrap classloader
 605   // do not acquire lock here.
 606   Handle lockObject = get_loader_lock_or_null(class_loader);
 607   ObjectLocker ol(lockObject, THREAD);
 608 
 609   bool circularity_detection_in_progress  = false;
 610   InstanceKlass* loaded_class = nullptr;
 611   SymbolHandle superclassname; // Keep alive while loading in parallel thread.
 612 
 613   guarantee(THREAD->can_call_java(),
 614          "can not load classes with compiler thread: class=%s, classloader=%s",
 615          name->as_C_string(),
 616          class_loader.is_null() ? "null" : class_loader->klass()->name()->as_C_string());
 617 
 618   // Check again (after locking) if the class already exists in SystemDictionary
 619   {
 620     MutexLocker mu(THREAD, SystemDictionary_lock);
 621     InstanceKlass* check = dictionary->find_class(THREAD, name);
 622     if (check != nullptr) {
 623       // InstanceKlass is already loaded, but we still need to check protection domain below.
 624       loaded_class = check;
 625     } else {
 626       PlaceholderEntry* placeholder = PlaceholderTable::get_entry(name, loader_data);
 627       if (placeholder != nullptr && placeholder->circularity_detection_in_progress()) {
 628          circularity_detection_in_progress = true;
 629          superclassname = placeholder->next_klass_name();
 630          assert(superclassname != nullptr, "superclass has to have a name");
 631       }
 632     }
 633   }
 634 
 635   // If the class is in the placeholder table with super_class set,
 636   // handle superclass loading in progress.
 637   if (circularity_detection_in_progress) {
 638     handle_parallel_super_load(name, superclassname,
 639                                class_loader,
 640                                CHECK_NULL);
 641   }
 642 
 643   bool throw_circularity_error = false;
 644   if (loaded_class == nullptr) {
 645     bool load_placeholder_added = false;
 646 
 647     // Add placeholder entry to record loading instance class
 648     // case 1. Bootstrap classloader
 649     //    This classloader supports parallelism at the classloader level
 650     //    but only allows a single thread to load a class/classloader pair.
 651     //    The LOAD_INSTANCE placeholder is the mechanism for mutual exclusion.
 652     // case 2. parallelCapable user level classloaders
 653     //    These class loaders lock a per-class object lock when ClassLoader.loadClass()
 654     //    is called. A LOAD_INSTANCE placeholder isn't used for mutual exclusion.
 655     // case 3. traditional classloaders that rely on the classloader object lock
 656     //    There should be no need for need for LOAD_INSTANCE for mutual exclusion,
 657     //    except the LOAD_INSTANCE placeholder is used to detect CCE for -Xcomp.
 658     //    TODO: should also be used to detect CCE for parallel capable class loaders but it's not.
 659     {
 660       MutexLocker mu(THREAD, SystemDictionary_lock);
 661       if (needs_load_placeholder(class_loader)) {
 662         loaded_class = handle_parallel_loading(THREAD,
 663                                                name,
 664                                                loader_data,
 665                                                class_loader.is_null(),
 666                                                &throw_circularity_error);
 667       }
 668 
 669       // Recheck if the class has been loaded for all class loader cases and
 670       // add a LOAD_INSTANCE placeholder while holding the SystemDictionary_lock.
 671       if (!throw_circularity_error && loaded_class == nullptr) {
 672         InstanceKlass* check = dictionary->find_class(THREAD, name);
 673         if (check != nullptr) {
 674           loaded_class = check;
 675         } else if (needs_load_placeholder(class_loader)) {
 676           // Add the LOAD_INSTANCE token. Threads will wait on loading to complete for this thread.
 677           PlaceholderEntry* newprobe = PlaceholderTable::find_and_add(name, loader_data,
 678                                                                       PlaceholderTable::LOAD_INSTANCE,
 679                                                                       nullptr,
 680                                                                       THREAD);
 681           load_placeholder_added = true;
 682         }
 683       }
 684     }
 685 
 686     // Must throw error outside of owning lock
 687     if (throw_circularity_error) {
 688       assert(!HAS_PENDING_EXCEPTION && !load_placeholder_added, "circularity error cleanup");
 689       ResourceMark rm(THREAD);
 690       THROW_MSG_NULL(vmSymbols::java_lang_ClassCircularityError(), name->as_C_string());
 691     }
 692 
 693     // Be careful when modifying this code: once you have run
 694     // PlaceholderTable::find_and_add(PlaceholderTable::LOAD_INSTANCE),
 695     // you need to find_and_remove it before returning.
 696     // So be careful to not exit with a CHECK_ macro between these calls.
 697 
 698     if (loaded_class == nullptr) {
 699       // Do actual loading
 700       loaded_class = load_instance_class(name, class_loader, THREAD);
 701     }
 702 
 703     if (load_placeholder_added) {
 704       // clean up placeholder entries for LOAD_INSTANCE success or error
 705       // This brackets the SystemDictionary updates for both defining
 706       // and initiating loaders
 707       MutexLocker mu(THREAD, SystemDictionary_lock);
 708       PlaceholderTable::find_and_remove(name, loader_data, PlaceholderTable::LOAD_INSTANCE, THREAD);
 709       SystemDictionary_lock->notify_all();
 710     }
 711   }
 712 
 713   if (HAS_PENDING_EXCEPTION || loaded_class == nullptr) {
 714     return nullptr;
 715   }
 716 
 717   if (class_load_start_event.should_commit()) {
 718     post_class_load_event(&class_load_start_event, loaded_class, loader_data);
 719   }
 720 
 721   // Make sure we have the right class in the dictionary
 722   DEBUG_ONLY(verify_dictionary_entry(name, loaded_class));
 723 
 724   return loaded_class;
 725 }
 726 
 727 
 728 // This routine does not lock the system dictionary.
 729 //
 730 // Since readers don't hold a lock, we must make sure that system
 731 // dictionary entries are added to in a safe way (all links must
 732 // be updated in an MT-safe manner). All entries are removed during class
 733 // unloading, when this class loader is no longer referenced.
 734 //
 735 // Callers should be aware that an entry could be added just after
 736 // Dictionary is read here, so the caller will not see
 737 // the new entry.
 738 
 739 InstanceKlass* SystemDictionary::find_instance_klass(Thread* current,
 740                                                      Symbol* class_name,
 741                                                      Handle class_loader) {
 742 
 743   ClassLoaderData* loader_data = ClassLoaderData::class_loader_data_or_null(class_loader());
 744   if (loader_data == nullptr) {
 745     // If the ClassLoaderData has not been setup,
 746     // then the class loader has no entries in the dictionary.
 747     return nullptr;
 748   }
 749 
 750   Dictionary* dictionary = loader_data->dictionary();
 751   return dictionary->find_class(current, class_name);
 752 }
 753 
 754 // Look for a loaded instance or array klass by name.  Do not do any loading.
 755 // return null in case of error.
 756 Klass* SystemDictionary::find_instance_or_array_klass(Thread* current,
 757                                                       Symbol* class_name,
 758                                                       Handle class_loader) {
 759   Klass* k = nullptr;
 760   assert(class_name != nullptr, "class name must be non nullptr");
 761 
 762   if (Signature::is_array(class_name)) {
 763     // The name refers to an array.  Parse the name.
 764     // dimension and object_key in FieldArrayInfo are assigned as a
 765     // side-effect of this call
 766     SignatureStream ss(class_name, false);
 767     int ndims = ss.skip_array_prefix();  // skip all '['s
 768     BasicType t = ss.type();
 769     if (t != T_OBJECT) {
 770       k = Universe::typeArrayKlass(t);
 771     } else {
 772       k = SystemDictionary::find_instance_klass(current, ss.as_symbol(), class_loader);
 773     }
 774     if (k != nullptr) {
 775       k = k->array_klass_or_null(ndims);
 776     }
 777   } else {
 778     k = find_instance_klass(current, class_name, class_loader);
 779   }
 780   return k;
 781 }
 782 
 783 // Note: this method is much like resolve_class_from_stream, but
 784 // does not publish the classes in the SystemDictionary.
 785 // Handles Lookup.defineClass hidden.
 786 InstanceKlass* SystemDictionary::resolve_hidden_class_from_stream(
 787                                                      ClassFileStream* st,
 788                                                      Symbol* class_name,
 789                                                      Handle class_loader,
 790                                                      const ClassLoadInfo& cl_info,
 791                                                      TRAPS) {
 792 
 793   EventClassLoad class_load_start_event;
 794   ClassLoaderData* loader_data;
 795 
 796   // - for hidden classes that are not strong: create a new CLD that has a class holder and
 797   //                                           whose loader is the Lookup class's loader.
 798   // - for hidden class: add the class to the Lookup class's loader's CLD.
 799   assert (cl_info.is_hidden(), "only used for hidden classes");
 800   bool create_mirror_cld = !cl_info.is_strong_hidden();
 801   loader_data = register_loader(class_loader, create_mirror_cld);
 802 
 803   assert(st != nullptr, "invariant");
 804 
 805   // Parse stream and create a klass.
 806   InstanceKlass* k = KlassFactory::create_from_stream(st,
 807                                                       class_name,
 808                                                       loader_data,
 809                                                       cl_info,
 810                                                       CHECK_NULL);
 811   assert(k != nullptr, "no klass created");
 812 
 813   // Hidden classes that are not strong must update ClassLoaderData holder
 814   // so that they can be unloaded when the mirror is no longer referenced.
 815   if (!cl_info.is_strong_hidden()) {
 816     k->class_loader_data()->initialize_holder(Handle(THREAD, k->java_mirror()));
 817   }
 818 
 819   // Add to class hierarchy, and do possible deoptimizations.
 820   k->add_to_hierarchy(THREAD);
 821   // But, do not add to dictionary.
 822 
 823   k->link_class(CHECK_NULL);
 824 
 825   // notify jvmti
 826   if (JvmtiExport::should_post_class_load()) {
 827     JvmtiExport::post_class_load(THREAD, k);
 828   }
 829   if (class_load_start_event.should_commit()) {
 830     post_class_load_event(&class_load_start_event, k, loader_data);
 831   }
 832 
 833   return k;
 834 }
 835 
 836 // Add a klass to the system from a stream (called by jni_DefineClass and
 837 // JVM_DefineClass).
 838 // Note: class_name can be null. In that case we do not know the name of
 839 // the class until we have parsed the stream.
 840 // This function either returns an InstanceKlass or throws an exception.  It does
 841 // not return null without a pending exception.
 842 InstanceKlass* SystemDictionary::resolve_class_from_stream(
 843                                                      ClassFileStream* st,
 844                                                      Symbol* class_name,
 845                                                      Handle class_loader,
 846                                                      const ClassLoadInfo& cl_info,
 847                                                      TRAPS) {
 848 
 849   HandleMark hm(THREAD);
 850 
 851   ClassLoaderData* loader_data = register_loader(class_loader);
 852 
 853   // Classloaders that support parallelism, e.g. bootstrap classloader,
 854   // do not acquire lock here
 855   Handle lockObject = get_loader_lock_or_null(class_loader);
 856   ObjectLocker ol(lockObject, THREAD);
 857 
 858   // Parse the stream and create a klass.
 859   // Note that we do this even though this klass might
 860   // already be present in the SystemDictionary, otherwise we would not
 861   // throw potential ClassFormatErrors.
 862  InstanceKlass* k = nullptr;
 863 
 864 #if INCLUDE_CDS
 865   if (!CDSConfig::is_dumping_static_archive()) {
 866     k = SystemDictionaryShared::lookup_from_stream(class_name,
 867                                                    class_loader,
 868                                                    cl_info.protection_domain(),
 869                                                    st,
 870                                                    CHECK_NULL);
 871   }
 872 #endif
 873 
 874   if (k == nullptr) {
 875     k = KlassFactory::create_from_stream(st, class_name, loader_data, cl_info, CHECK_NULL);
 876   }
 877 
 878   assert(k != nullptr, "no klass created");
 879   Symbol* h_name = k->name();
 880   assert(class_name == nullptr || class_name == h_name, "name mismatch");
 881 
 882   // Add class just loaded
 883   // If a class loader supports parallel classloading, handle parallel define requests.
 884   // find_or_define_instance_class may return a different InstanceKlass,
 885   // in which case the old k would be deallocated
 886   if (is_parallelCapable(class_loader)) {
 887     k = find_or_define_instance_class(h_name, class_loader, k, CHECK_NULL);
 888   } else {
 889     define_instance_class(k, class_loader, THREAD);
 890 
 891     // If defining the class throws an exception register 'k' for cleanup.
 892     if (HAS_PENDING_EXCEPTION) {
 893       assert(k != nullptr, "Must have an instance klass here!");
 894       loader_data->add_to_deallocate_list(k);
 895       return nullptr;
 896     }
 897   }
 898 
 899   // Make sure we have an entry in the SystemDictionary on success
 900   DEBUG_ONLY(verify_dictionary_entry(h_name, k));
 901 
 902   return k;
 903 }
 904 
 905 InstanceKlass* SystemDictionary::resolve_from_stream(ClassFileStream* st,
 906                                                      Symbol* class_name,
 907                                                      Handle class_loader,
 908                                                      const ClassLoadInfo& cl_info,
 909                                                      TRAPS) {
 910   if (cl_info.is_hidden()) {
 911     return resolve_hidden_class_from_stream(st, class_name, class_loader, cl_info, CHECK_NULL);
 912   } else {
 913     return resolve_class_from_stream(st, class_name, class_loader, cl_info, CHECK_NULL);
 914   }
 915 }
 916 
 917 
 918 #if INCLUDE_CDS
 919 // Check if a shared class can be loaded by the specific classloader.
 920 bool SystemDictionary::is_shared_class_visible(Symbol* class_name,
 921                                                InstanceKlass* ik,
 922                                                PackageEntry* pkg_entry,
 923                                                Handle class_loader) {
 924   assert(!CDSConfig::module_patching_disables_cds(), "Cannot use CDS");
 925 
 926   // (1) Check if we are loading into the same loader as in dump time.
 927 
 928   if (ik->is_shared_boot_class()) {
 929     if (class_loader() != nullptr) {
 930       return false;
 931     }
 932   } else if (ik->is_shared_platform_class()) {
 933     if (class_loader() != java_platform_loader()) {
 934       return false;
 935     }
 936   } else if (ik->is_shared_app_class()) {
 937     if (class_loader() != java_system_loader()) {
 938       return false;
 939     }
 940   } else {
 941     // ik was loaded by a custom loader during dump time
 942     if (class_loader_data(class_loader)->is_builtin_class_loader_data()) {
 943       return false;
 944     } else {
 945       return true;
 946     }
 947   }
 948 
 949   // (2) Check if we are loading into the same module from the same location as in dump time.
 950 
 951   if (CDSConfig::is_using_optimized_module_handling()) {
 952     // Class visibility has not changed between dump time and run time, so a class
 953     // that was visible (and thus archived) during dump time is always visible during runtime.
 954     assert(SystemDictionary::is_shared_class_visible_impl(class_name, ik, pkg_entry, class_loader),
 955            "visibility cannot change between dump time and runtime");
 956     return true;
 957   }
 958   return is_shared_class_visible_impl(class_name, ik, pkg_entry, class_loader);
 959 }
 960 
 961 bool SystemDictionary::is_shared_class_visible_impl(Symbol* class_name,
 962                                                     InstanceKlass* ik,
 963                                                     PackageEntry* pkg_entry,
 964                                                     Handle class_loader) {
 965   int scp_index = ik->shared_classpath_index();
 966   assert(!ik->is_shared_unregistered_class(), "this function should be called for built-in classes only");
 967   assert(scp_index >= 0, "must be");
 968   const AOTClassLocation* cl = AOTClassLocationConfig::runtime()->class_location_at(scp_index);
 969   if (!Universe::is_module_initialized()) {
 970     assert(cl != nullptr, "must be");
 971     // At this point, no modules have been defined yet. KlassSubGraphInfo::check_allowed_klass()
 972     // has restricted the classes can be loaded at this step to be only:
 973     // [1] cs->is_modules_image(): classes in java.base, or,
 974     // [2] HeapShared::is_a_test_class_in_unnamed_module(ik): classes in bootstrap/unnamed module
 975     assert(cl->is_modules_image() || HeapShared::is_a_test_class_in_unnamed_module(ik),
 976            "only these classes can be loaded before the module system is initialized");
 977     assert(class_loader.is_null(), "sanity");
 978     return true;
 979   }
 980 
 981   if (pkg_entry == nullptr) {
 982     // We might have looked up pkg_entry before the module system was initialized.
 983     // Need to reload it now.
 984     TempNewSymbol pkg_name = ClassLoader::package_from_class_name(class_name);
 985     if (pkg_name != nullptr) {
 986       pkg_entry = class_loader_data(class_loader)->packages()->lookup_only(pkg_name);
 987     }
 988   }
 989 
 990   ModuleEntry* mod_entry = (pkg_entry == nullptr) ? nullptr : pkg_entry->module();
 991   bool should_be_in_named_module = (mod_entry != nullptr && mod_entry->is_named());
 992   bool was_archived_from_named_module = !cl->has_unnamed_module();
 993   bool visible;
 994 
 995   if (was_archived_from_named_module) {
 996     if (should_be_in_named_module) {
 997       // Is the module loaded from the same location as during dump time?
 998       visible = mod_entry->shared_path_index() == scp_index;
 999       if (visible) {
1000         assert(!CDSConfig::module_patching_disables_cds(), "Cannot use CDS");
1001       }
1002     } else {
1003       // During dump time, this class was in a named module, but at run time, this class should be
1004       // in an unnamed module.
1005       visible = false;
1006     }
1007   } else {
1008     if (should_be_in_named_module) {
1009       // During dump time, this class was in an unnamed, but at run time, this class should be
1010       // in a named module.
1011       visible = false;
1012     } else {
1013       visible = true;
1014     }
1015   }
1016 
1017   return visible;
1018 }
1019 
1020 bool SystemDictionary::check_shared_class_super_type(InstanceKlass* klass, InstanceKlass* super_type,
1021                                                      Handle class_loader, bool is_superclass, TRAPS) {
1022   assert(super_type->is_shared(), "must be");
1023 
1024   // Quick check if the super type has been already loaded.
1025   // + Don't do it for unregistered classes -- they can be unloaded so
1026   //   super_type->class_loader_data() could be stale.
1027   // + Don't check if loader data is null, ie. the super_type isn't fully loaded.
1028   if (!super_type->is_shared_unregistered_class() && super_type->class_loader_data() != nullptr) {
1029     // Check if the superclass is loaded by the current class_loader
1030     Symbol* name = super_type->name();
1031     InstanceKlass* check = find_instance_klass(THREAD, name, class_loader);
1032     if (check == super_type) {
1033       return true;
1034     }
1035   }
1036 
1037   Klass *found = resolve_with_circularity_detection(klass->name(), super_type->name(),
1038                                                     class_loader, is_superclass, CHECK_false);
1039   if (found == super_type) {
1040     return true;
1041   } else {
1042     // The dynamically resolved super type is not the same as the one we used during dump time,
1043     // so we cannot use the class.
1044     return false;
1045   }
1046 }
1047 
1048 bool SystemDictionary::check_shared_class_super_types(InstanceKlass* ik, Handle class_loader, TRAPS) {
1049   // Check the superclass and interfaces. They must be the same
1050   // as in dump time, because the layout of <ik> depends on
1051   // the specific layout of ik->super() and ik->local_interfaces().
1052   //
1053   // If unexpected superclass or interfaces are found, we cannot
1054   // load <ik> from the shared archive.
1055 
1056   if (ik->super() != nullptr) {
1057     bool check_super = check_shared_class_super_type(ik, InstanceKlass::cast(ik->super()),
1058                                                      class_loader, true,
1059                                                      CHECK_false);
1060     if (!check_super) {
1061       return false;
1062     }
1063   }
1064 
1065   Array<InstanceKlass*>* interfaces = ik->local_interfaces();
1066   int num_interfaces = interfaces->length();
1067   for (int index = 0; index < num_interfaces; index++) {
1068     bool check_interface = check_shared_class_super_type(ik, interfaces->at(index), class_loader, false,
1069                                                          CHECK_false);
1070     if (!check_interface) {
1071       return false;
1072     }
1073   }
1074 
1075   return true;
1076 }
1077 
1078 InstanceKlass* SystemDictionary::load_shared_class(InstanceKlass* ik,
1079                                                    Handle class_loader,
1080                                                    Handle protection_domain,
1081                                                    const ClassFileStream *cfs,
1082                                                    PackageEntry* pkg_entry,
1083                                                    TRAPS) {
1084   assert(ik != nullptr, "sanity");
1085   assert(ik->is_shared(), "sanity");
1086   assert(!ik->is_unshareable_info_restored(), "shared class can be restored only once");
1087   assert(Atomic::add(&ik->_shared_class_load_count, 1) == 1, "shared class loaded more than once");
1088   Symbol* class_name = ik->name();
1089 
1090   if (!is_shared_class_visible(class_name, ik, pkg_entry, class_loader)) {
1091     ik->set_shared_loading_failed();
1092     return nullptr;
1093   }
1094 
1095   bool check = check_shared_class_super_types(ik, class_loader, CHECK_NULL);
1096   if (!check) {
1097     ik->set_shared_loading_failed();
1098     return nullptr;
1099   }
1100 
1101   if (ik->has_inline_type_fields()) {
1102     for (AllFieldStream fs(ik); !fs.done(); fs.next()) {
1103       if (fs.access_flags().is_static()) continue;
1104       Symbol* sig = fs.signature();
1105       if (fs.is_null_free_inline_type()) {
1106         // Pre-load inline class
1107         TempNewSymbol name = Signature::strip_envelope(sig);
1108         log_info(class, preload)("Preloading class %s during loading of shared class %s. Cause: field type in LoadableDescriptors attribute", name->as_C_string(), ik->name()->as_C_string());
1109         Klass* real_k = SystemDictionary::resolve_with_circularity_detection_or_fail(ik->name(), name,
1110           class_loader, false, CHECK_NULL);
1111         Klass* k = ik->get_inline_type_field_klass_or_null(fs.index());
1112         if (real_k != k) {
1113           // oops, the app has substituted a different version of k!
1114           log_warning(class, preload)("Preloading of class %s during loading of shared class %s (cause: field type in LoadableDescriptors attribute) failed : %s",
1115                                       name->as_C_string(), ik->name()->as_C_string(), PENDING_EXCEPTION->klass()->name()->as_C_string());
1116           return nullptr;
1117         } else if (real_k != nullptr) {
1118             log_info(class, preload)("Preloading of class %s during loading of shared class %s (cause: field type in LoadableDescriptors attribute) succeeded",
1119                                      name->as_C_string(), ik->name()->as_C_string());
1120         }
1121       } else if (Signature::has_envelope(sig)) {
1122         TempNewSymbol name = Signature::strip_envelope(sig);
1123         if (name != ik->name() && ik->is_class_in_loadable_descriptors_attribute(sig)) {
1124           log_info(class, preload)("Preloading class %s during loading of shared class %s. Cause: field type in LoadableDescriptors attribute",
1125                                    name->as_C_string(), ik->name()->as_C_string());
1126           Klass* real_k = SystemDictionary::resolve_with_circularity_detection_or_fail(ik->name(), name,
1127             class_loader, false, THREAD);
1128           if (HAS_PENDING_EXCEPTION) {
1129             CLEAR_PENDING_EXCEPTION;
1130           }
1131           Klass* k = ik->get_inline_type_field_klass_or_null(fs.index());
1132           if (real_k != k) {
1133             // oops, the app has substituted a different version of k!
1134             log_warning(class, preload)("Preloading of class %s during loading of shared class %s (cause: field type in LoadableDescriptors attribute) failed : %s",
1135                                         name->as_C_string(), ik->name()->as_C_string(), PENDING_EXCEPTION->klass()->name()->as_C_string());
1136             return nullptr;
1137           } else if (real_k != nullptr) {
1138             log_info(class, preload)("Preloading of class %s during loading of shared class %s (cause: field type in LoadableDescriptors attribute) succeeded",
1139                                      name->as_C_string(), ik->name()->as_C_string());
1140           }
1141         }
1142       }
1143     }
1144   }
1145 
1146   InstanceKlass* new_ik = nullptr;
1147   // CFLH check is skipped for VM hidden classes (see KlassFactory::create_from_stream).
1148   // It will be skipped for shared VM hidden lambda proxy classes.
1149   if (!ik->is_hidden()) {
1150     new_ik = KlassFactory::check_shared_class_file_load_hook(
1151       ik, class_name, class_loader, protection_domain, cfs, CHECK_NULL);
1152   }
1153   if (new_ik != nullptr) {
1154     // The class is changed by CFLH. Return the new class. The shared class is
1155     // not used.
1156     return new_ik;
1157   }
1158 
1159   // Adjust methods to recover missing data.  They need addresses for
1160   // interpreter entry points and their default native method address
1161   // must be reset.
1162 
1163   // Shared classes are all currently loaded by either the bootstrap or
1164   // internal parallel class loaders, so this will never cause a deadlock
1165   // on a custom class loader lock.
1166   // Since this class is already locked with parallel capable class
1167   // loaders, including the bootstrap loader via the placeholder table,
1168   // this lock is currently a nop.
1169 
1170   ClassLoaderData* loader_data = class_loader_data(class_loader);
1171   {
1172     HandleMark hm(THREAD);
1173     Handle lockObject = get_loader_lock_or_null(class_loader);
1174     ObjectLocker ol(lockObject, THREAD);
1175     // prohibited package check assumes all classes loaded from archive call
1176     // restore_unshareable_info which calls ik->set_package()
1177     ik->restore_unshareable_info(loader_data, protection_domain, pkg_entry, CHECK_NULL);
1178   }
1179 
1180   load_shared_class_misc(ik, loader_data);
1181 
1182   return ik;
1183 }
1184 
1185 void SystemDictionary::load_shared_class_misc(InstanceKlass* ik, ClassLoaderData* loader_data) {
1186   ik->print_class_load_logging(loader_data, nullptr, nullptr);
1187 
1188   // For boot loader, ensure that GetSystemPackage knows that a class in this
1189   // package was loaded.
1190   if (loader_data->is_the_null_class_loader_data()) {
1191     s2 path_index = ik->shared_classpath_index();
1192     ik->set_classpath_index(path_index);
1193   }
1194 
1195   // notify a class loaded from shared object
1196   ClassLoadingService::notify_class_loaded(ik, true /* shared class */);
1197 
1198   if (CDSConfig::is_dumping_final_static_archive()) {
1199     SystemDictionaryShared::init_dumptime_info_from_preimage(ik);
1200   }
1201 }
1202 
1203 #endif // INCLUDE_CDS
1204 
1205 InstanceKlass* SystemDictionary::load_instance_class_impl(Symbol* class_name, Handle class_loader, TRAPS) {
1206 
1207   if (class_loader.is_null()) {
1208     ResourceMark rm(THREAD);
1209     PackageEntry* pkg_entry = nullptr;
1210     bool search_only_bootloader_append = false;
1211 
1212     // Find the package in the boot loader's package entry table.
1213     TempNewSymbol pkg_name = ClassLoader::package_from_class_name(class_name);
1214     if (pkg_name != nullptr) {
1215       pkg_entry = class_loader_data(class_loader)->packages()->lookup_only(pkg_name);
1216     }
1217 
1218     // Prior to attempting to load the class, enforce the boot loader's
1219     // visibility boundaries.
1220     if (!Universe::is_module_initialized()) {
1221       // During bootstrapping, prior to module initialization, any
1222       // class attempting to be loaded must be checked against the
1223       // java.base packages in the boot loader's PackageEntryTable.
1224       // No class outside of java.base is allowed to be loaded during
1225       // this bootstrapping window.
1226       if (pkg_entry == nullptr || pkg_entry->in_unnamed_module()) {
1227         // Class is either in the unnamed package or in
1228         // a named package within the unnamed module.  Either
1229         // case is outside of java.base, do not attempt to
1230         // load the class post java.base definition.  If
1231         // java.base has not been defined, let the class load
1232         // and its package will be checked later by
1233         // ModuleEntryTable::verify_javabase_packages.
1234         if (ModuleEntryTable::javabase_defined()) {
1235           return nullptr;
1236         }
1237       } else {
1238         // Check that the class' package is defined within java.base.
1239         ModuleEntry* mod_entry = pkg_entry->module();
1240         Symbol* mod_entry_name = mod_entry->name();
1241         if (mod_entry_name->fast_compare(vmSymbols::java_base()) != 0) {
1242           return nullptr;
1243         }
1244       }
1245     } else {
1246       // After the module system has been initialized, check if the class'
1247       // package is in a module defined to the boot loader.
1248       if (pkg_name == nullptr || pkg_entry == nullptr || pkg_entry->in_unnamed_module()) {
1249         // Class is either in the unnamed package, in a named package
1250         // within a module not defined to the boot loader or in a
1251         // a named package within the unnamed module.  In all cases,
1252         // limit visibility to search for the class only in the boot
1253         // loader's append path.
1254         if (!ClassLoader::has_bootclasspath_append()) {
1255            // If there is no bootclasspath append entry, no need to continue
1256            // searching.
1257            return nullptr;
1258         }
1259         search_only_bootloader_append = true;
1260       }
1261     }
1262 
1263     // Prior to bootstrapping's module initialization, never load a class outside
1264     // of the boot loader's module path
1265     assert(Universe::is_module_initialized() ||
1266            !search_only_bootloader_append,
1267            "Attempt to load a class outside of boot loader's module path");
1268 
1269     // Search for classes in the CDS archive.
1270     InstanceKlass* k = nullptr;
1271 
1272 #if INCLUDE_CDS
1273     if (CDSConfig::is_using_archive())
1274     {
1275       PerfTraceTime vmtimer(ClassLoader::perf_shared_classload_time());
1276       InstanceKlass* ik = SystemDictionaryShared::find_builtin_class(class_name);
1277       if (ik != nullptr && ik->is_shared_boot_class() && !ik->shared_loading_failed()) {
1278         SharedClassLoadingMark slm(THREAD, ik);
1279         k = load_shared_class(ik, class_loader, Handle(), nullptr,  pkg_entry, CHECK_NULL);
1280       }
1281     }
1282 #endif
1283 
1284     if (k == nullptr) {
1285       // Use VM class loader
1286       PerfTraceTime vmtimer(ClassLoader::perf_sys_classload_time());
1287       k = ClassLoader::load_class(class_name, pkg_entry, search_only_bootloader_append, CHECK_NULL);
1288     }
1289 
1290     // find_or_define_instance_class may return a different InstanceKlass
1291     if (k != nullptr) {
1292       CDS_ONLY(SharedClassLoadingMark slm(THREAD, k);)
1293       k = find_or_define_instance_class(class_name, class_loader, k, CHECK_NULL);
1294     }
1295     return k;
1296   } else {
1297     // Use user specified class loader to load class. Call loadClass operation on class_loader.
1298     ResourceMark rm(THREAD);
1299 
1300     JavaThread* jt = THREAD;
1301 
1302     PerfClassTraceTime vmtimer(ClassLoader::perf_app_classload_time(),
1303                                ClassLoader::perf_app_classload_selftime(),
1304                                ClassLoader::perf_app_classload_count(),
1305                                jt->get_thread_stat()->perf_recursion_counts_addr(),
1306                                jt->get_thread_stat()->perf_timers_addr(),
1307                                PerfClassTraceTime::CLASS_LOAD);
1308 
1309     // Translate to external class name format, i.e., convert '/' chars to '.'
1310     Handle string = java_lang_String::externalize_classname(class_name, CHECK_NULL);
1311 
1312     JavaValue result(T_OBJECT);
1313 
1314     InstanceKlass* spec_klass = vmClasses::ClassLoader_klass();
1315 
1316     // Call public unsynchronized loadClass(String) directly for all class loaders.
1317     // For parallelCapable class loaders, JDK >=7, loadClass(String, boolean) will
1318     // acquire a class-name based lock rather than the class loader object lock.
1319     // JDK < 7 already acquire the class loader lock in loadClass(String, boolean).
1320     JavaCalls::call_virtual(&result,
1321                             class_loader,
1322                             spec_klass,
1323                             vmSymbols::loadClass_name(),
1324                             vmSymbols::string_class_signature(),
1325                             string,
1326                             CHECK_NULL);
1327 
1328     assert(result.get_type() == T_OBJECT, "just checking");
1329     oop obj = result.get_oop();
1330 
1331     // Primitive classes return null since forName() can not be
1332     // used to obtain any of the Class objects representing primitives or void
1333     if ((obj != nullptr) && !(java_lang_Class::is_primitive(obj))) {
1334       InstanceKlass* k = InstanceKlass::cast(java_lang_Class::as_Klass(obj));
1335       // For user defined Java class loaders, check that the name returned is
1336       // the same as that requested.  This check is done for the bootstrap
1337       // loader when parsing the class file.
1338       if (class_name == k->name()) {
1339         return k;
1340       }
1341     }
1342     // Class is not found or has the wrong name, return null
1343     return nullptr;
1344   }
1345 }
1346 
1347 InstanceKlass* SystemDictionary::load_instance_class(Symbol* name,
1348                                                      Handle class_loader,
1349                                                      TRAPS) {
1350 
1351   InstanceKlass* loaded_class = load_instance_class_impl(name, class_loader, CHECK_NULL);
1352 
1353   // If everything was OK (no exceptions, no null return value), and
1354   // class_loader is NOT the defining loader, do a little more bookkeeping.
1355   if (loaded_class != nullptr &&
1356       loaded_class->class_loader() != class_loader()) {
1357 
1358     ClassLoaderData* loader_data = class_loader_data(class_loader);
1359     check_constraints(loaded_class, loader_data, false, CHECK_NULL);
1360 
1361     // Record dependency for non-parent delegation.
1362     // This recording keeps the defining class loader of the klass (loaded_class) found
1363     // from being unloaded while the initiating class loader is loaded
1364     // even if the reference to the defining class loader is dropped
1365     // before references to the initiating class loader.
1366     loader_data->record_dependency(loaded_class);
1367 
1368     update_dictionary(THREAD, loaded_class, loader_data);
1369 
1370     if (JvmtiExport::should_post_class_load()) {
1371       JvmtiExport::post_class_load(THREAD, loaded_class);
1372     }
1373   }
1374   return loaded_class;
1375 }
1376 
1377 static void post_class_define_event(InstanceKlass* k, const ClassLoaderData* def_cld) {
1378   EventClassDefine event;
1379   if (event.should_commit()) {
1380     event.set_definedClass(k);
1381     event.set_definingClassLoader(def_cld);
1382     event.commit();
1383   }
1384 }
1385 
1386 void SystemDictionary::define_instance_class(InstanceKlass* k, Handle class_loader, TRAPS) {
1387 
1388   ClassLoaderData* loader_data = k->class_loader_data();
1389   assert(loader_data->class_loader() == class_loader(), "they must be the same");
1390 
1391   // Bootstrap and other parallel classloaders don't acquire a lock,
1392   // they use placeholder token.
1393   // If a parallelCapable class loader calls define_instance_class instead of
1394   // find_or_define_instance_class to get here, we have a timing
1395   // hole with systemDictionary updates and check_constraints
1396   if (!is_parallelCapable(class_loader)) {
1397     assert(ObjectSynchronizer::current_thread_holds_lock(THREAD,
1398            get_loader_lock_or_null(class_loader)),
1399            "define called without lock");
1400   }
1401 
1402   // Check class-loading constraints. Throw exception if violation is detected.
1403   // Grabs and releases SystemDictionary_lock
1404   // The check_constraints/find_class call and update_dictionary sequence
1405   // must be "atomic" for a specific class/classloader pair so we never
1406   // define two different instanceKlasses for that class/classloader pair.
1407   // Existing classloaders will call define_instance_class with the
1408   // classloader lock held
1409   // Parallel classloaders will call find_or_define_instance_class
1410   // which will require a token to perform the define class
1411   check_constraints(k, loader_data, true, CHECK);
1412 
1413   // Register class just loaded with class loader (placed in ArrayList)
1414   // Note we do this before updating the dictionary, as this can
1415   // fail with an OutOfMemoryError (if it does, we will *not* put this
1416   // class in the dictionary and will not update the class hierarchy).
1417   // JVMTI FollowReferences needs to find the classes this way.
1418   if (k->class_loader() != nullptr) {
1419     methodHandle m(THREAD, Universe::loader_addClass_method());
1420     JavaValue result(T_VOID);
1421     JavaCallArguments args(class_loader);
1422     args.push_oop(Handle(THREAD, k->java_mirror()));
1423     JavaCalls::call(&result, m, &args, CHECK);
1424   }
1425 
1426   // Add to class hierarchy, and do possible deoptimizations.
1427   k->add_to_hierarchy(THREAD);
1428 
1429   // Add to systemDictionary - so other classes can see it.
1430   // Grabs and releases SystemDictionary_lock
1431   update_dictionary(THREAD, k, loader_data);
1432 
1433   // notify jvmti
1434   if (JvmtiExport::should_post_class_load()) {
1435     JvmtiExport::post_class_load(THREAD, k);
1436   }
1437   post_class_define_event(k, loader_data);
1438 }
1439 
1440 // Support parallel classloading
1441 // All parallel class loaders, including bootstrap classloader
1442 // lock a placeholder entry for this class/class_loader pair
1443 // to allow parallel defines of different classes for this class loader
1444 // With AllowParallelDefine flag==true, in case they do not synchronize around
1445 // FindLoadedClass/DefineClass, calls, we check for parallel
1446 // loading for them, wait if a defineClass is in progress
1447 // and return the initial requestor's results
1448 // This flag does not apply to the bootstrap classloader.
1449 // With AllowParallelDefine flag==false, call through to define_instance_class
1450 // which will throw LinkageError: duplicate class definition.
1451 // False is the requested default.
1452 // For better performance, the class loaders should synchronize
1453 // findClass(), i.e. FindLoadedClass/DefineClassIfAbsent or they
1454 // potentially waste time reading and parsing the bytestream.
1455 // Note: VM callers should ensure consistency of k/class_name,class_loader
1456 // Be careful when modifying this code: once you have run
1457 // PlaceholderTable::find_and_add(PlaceholderTable::DEFINE_CLASS),
1458 // you need to find_and_remove it before returning.
1459 // So be careful to not exit with a CHECK_ macro between these calls.
1460 InstanceKlass* SystemDictionary::find_or_define_helper(Symbol* class_name, Handle class_loader,
1461                                                        InstanceKlass* k, TRAPS) {
1462 
1463   Symbol* name_h = k->name();
1464   ClassLoaderData* loader_data = class_loader_data(class_loader);
1465   Dictionary* dictionary = loader_data->dictionary();
1466 
1467   // Hold SD lock around find_class and placeholder creation for DEFINE_CLASS
1468   {
1469     MutexLocker mu(THREAD, SystemDictionary_lock);
1470     // First check if class already defined
1471     if (is_parallelDefine(class_loader)) {
1472       InstanceKlass* check = dictionary->find_class(THREAD, name_h);
1473       if (check != nullptr) {
1474         return check;
1475       }
1476     }
1477 
1478     // Acquire define token for this class/classloader
1479     PlaceholderEntry* probe = PlaceholderTable::find_and_add(name_h, loader_data,
1480                                                              PlaceholderTable::DEFINE_CLASS, nullptr, THREAD);
1481     // Wait if another thread defining in parallel
1482     // All threads wait - even those that will throw duplicate class: otherwise
1483     // caller is surprised by LinkageError: duplicate, but findLoadedClass fails
1484     // if other thread has not finished updating dictionary
1485     while (probe->definer() != nullptr) {
1486       SystemDictionary_lock->wait();
1487     }
1488     // Only special cases allow parallel defines and can use other thread's results
1489     // Other cases fall through, and may run into duplicate defines
1490     // caught by finding an entry in the SystemDictionary
1491     if (is_parallelDefine(class_loader) && (probe->instance_klass() != nullptr)) {
1492       InstanceKlass* ik = probe->instance_klass();
1493       PlaceholderTable::find_and_remove(name_h, loader_data, PlaceholderTable::DEFINE_CLASS, THREAD);
1494       SystemDictionary_lock->notify_all();
1495 #ifdef ASSERT
1496       InstanceKlass* check = dictionary->find_class(THREAD, name_h);
1497       assert(check != nullptr, "definer missed recording success");
1498 #endif
1499       return ik;
1500     } else {
1501       // This thread will define the class (even if earlier thread tried and had an error)
1502       probe->set_definer(THREAD);
1503     }
1504   }
1505 
1506   define_instance_class(k, class_loader, THREAD);
1507 
1508   // definer must notify any waiting threads
1509   {
1510     MutexLocker mu(THREAD, SystemDictionary_lock);
1511     PlaceholderEntry* probe = PlaceholderTable::get_entry(name_h, loader_data);
1512     assert(probe != nullptr, "DEFINE_CLASS placeholder lost?");
1513     if (!HAS_PENDING_EXCEPTION) {
1514       probe->set_instance_klass(k);
1515     }
1516     probe->set_definer(nullptr);
1517     PlaceholderTable::find_and_remove(name_h, loader_data, PlaceholderTable::DEFINE_CLASS, THREAD);
1518     SystemDictionary_lock->notify_all();
1519   }
1520 
1521   return HAS_PENDING_EXCEPTION ? nullptr : k;
1522 }
1523 
1524 // If a class loader supports parallel classloading handle parallel define requests.
1525 // find_or_define_instance_class may return a different InstanceKlass
1526 InstanceKlass* SystemDictionary::find_or_define_instance_class(Symbol* class_name, Handle class_loader,
1527                                                                InstanceKlass* k, TRAPS) {
1528   InstanceKlass* defined_k = find_or_define_helper(class_name, class_loader, k, THREAD);
1529   // Clean up original InstanceKlass if duplicate or error
1530   if (!HAS_PENDING_EXCEPTION && defined_k != k) {
1531     // If a parallel capable class loader already defined this class, register 'k' for cleanup.
1532     assert(defined_k != nullptr, "Should have a klass if there's no exception");
1533     k->class_loader_data()->add_to_deallocate_list(k);
1534   } else if (HAS_PENDING_EXCEPTION) {
1535     // Remove this InstanceKlass from the LoaderConstraintTable if added.
1536     LoaderConstraintTable::remove_failed_loaded_klass(k, class_loader_data(class_loader));
1537     assert(defined_k == nullptr, "Should not have a klass if there's an exception");
1538     k->class_loader_data()->add_to_deallocate_list(k);
1539   }
1540   return defined_k;
1541 }
1542 
1543 
1544 // ----------------------------------------------------------------------------
1545 // GC support
1546 
1547 // Assumes classes in the SystemDictionary are only unloaded at a safepoint
1548 bool SystemDictionary::do_unloading(GCTimer* gc_timer) {
1549 
1550   bool unloading_occurred;
1551   bool is_concurrent = !SafepointSynchronize::is_at_safepoint();
1552   {
1553     GCTraceTime(Debug, gc, phases) t("ClassLoaderData", gc_timer);
1554     assert_locked_or_safepoint(ClassLoaderDataGraph_lock);  // caller locks.
1555     // First, mark for unload all ClassLoaderData referencing a dead class loader.
1556     unloading_occurred = ClassLoaderDataGraph::do_unloading();
1557     if (unloading_occurred) {
1558       ConditionalMutexLocker ml2(Module_lock, is_concurrent);
1559       JFR_ONLY(Jfr::on_unloading_classes();)
1560       MANAGEMENT_ONLY(FinalizerService::purge_unloaded();)
1561       ConditionalMutexLocker ml1(SystemDictionary_lock, is_concurrent);
1562       ClassLoaderDataGraph::clean_module_and_package_info();
1563       LoaderConstraintTable::purge_loader_constraints();
1564       ResolutionErrorTable::purge_resolution_errors();
1565     }
1566   }
1567 
1568   GCTraceTime(Debug, gc, phases) t("Trigger cleanups", gc_timer);
1569 
1570   if (unloading_occurred) {
1571     SymbolTable::trigger_cleanup();
1572 
1573     ConditionalMutexLocker ml(ClassInitError_lock, is_concurrent);
1574     InstanceKlass::clean_initialization_error_table();
1575   }
1576 
1577   return unloading_occurred;
1578 }
1579 
1580 void SystemDictionary::methods_do(void f(Method*)) {
1581   // Walk methods in loaded classes
1582 
1583   {
1584     MutexLocker ml(ClassLoaderDataGraph_lock);
1585     ClassLoaderDataGraph::methods_do(f);
1586   }
1587 
1588   auto doit = [&] (InvokeMethodKey key, Method* method) {
1589     if (method != nullptr) {
1590       f(method);
1591     }
1592   };
1593 
1594   {
1595     MutexLocker ml(InvokeMethodIntrinsicTable_lock);
1596     _invoke_method_intrinsic_table->iterate_all(doit);
1597   }
1598 
1599 }
1600 
1601 // ----------------------------------------------------------------------------
1602 // Initialization
1603 
1604 void SystemDictionary::initialize(TRAPS) {
1605   _invoke_method_intrinsic_table = new (mtClass) InvokeMethodIntrinsicTable();
1606   _invoke_method_type_table = new (mtClass) InvokeMethodTypeTable();
1607   ResolutionErrorTable::initialize();
1608   LoaderConstraintTable::initialize();
1609   PlaceholderTable::initialize();
1610 #if INCLUDE_CDS
1611   SystemDictionaryShared::initialize();
1612   if (CDSConfig::is_dumping_archive()) {
1613     AOTClassLocationConfig::dumptime_init(THREAD);
1614   }
1615 #endif
1616   // Resolve basic classes
1617   vmClasses::resolve_all(CHECK);
1618   // Resolve classes used by archived heap objects
1619   if (CDSConfig::is_using_archive()) {
1620     HeapShared::resolve_classes(THREAD);
1621   }
1622 }
1623 
1624 // Constraints on class loaders. The details of the algorithm can be
1625 // found in the OOPSLA'98 paper "Dynamic Class Loading in the Java
1626 // Virtual Machine" by Sheng Liang and Gilad Bracha.  The basic idea is
1627 // that the dictionary needs to maintain a set of constraints that
1628 // must be satisfied by all classes in the dictionary.
1629 // if defining is true, then LinkageError if already in dictionary
1630 // if initiating loader, then ok if InstanceKlass matches existing entry
1631 
1632 void SystemDictionary::check_constraints(InstanceKlass* k,
1633                                          ClassLoaderData* loader_data,
1634                                          bool defining,
1635                                          TRAPS) {
1636   ResourceMark rm(THREAD);
1637   stringStream ss;
1638   bool throwException = false;
1639 
1640   {
1641     Symbol* name = k->name();
1642 
1643     MutexLocker mu(THREAD, SystemDictionary_lock);
1644 
1645     InstanceKlass* check = loader_data->dictionary()->find_class(THREAD, name);
1646     if (check != nullptr) {
1647       // If different InstanceKlass - duplicate class definition,
1648       // else - ok, class loaded by a different thread in parallel.
1649       // We should only have found it if it was done loading and ok to use.
1650 
1651       if ((defining == true) || (k != check)) {
1652         throwException = true;
1653         ss.print("loader %s", loader_data->loader_name_and_id());
1654         ss.print(" attempted duplicate %s definition for %s. (%s)",
1655                  k->external_kind(), k->external_name(), k->class_in_module_of_loader(false, true));
1656       } else {
1657         return;
1658       }
1659     }
1660 
1661     if (throwException == false) {
1662       if (LoaderConstraintTable::check_or_update(k, loader_data, name) == false) {
1663         throwException = true;
1664         ss.print("loader constraint violation: loader %s", loader_data->loader_name_and_id());
1665         ss.print(" wants to load %s %s.",
1666                  k->external_kind(), k->external_name());
1667         Klass *existing_klass = LoaderConstraintTable::find_constrained_klass(name, loader_data);
1668         if (existing_klass != nullptr && existing_klass->class_loader_data() != loader_data) {
1669           ss.print(" A different %s with the same name was previously loaded by %s. (%s)",
1670                    existing_klass->external_kind(),
1671                    existing_klass->class_loader_data()->loader_name_and_id(),
1672                    existing_klass->class_in_module_of_loader(false, true));
1673         } else {
1674           ss.print(" (%s)", k->class_in_module_of_loader(false, true));
1675         }
1676       }
1677     }
1678   }
1679 
1680   // Throw error now if needed (cannot throw while holding
1681   // SystemDictionary_lock because of rank ordering)
1682   if (throwException == true) {
1683     THROW_MSG(vmSymbols::java_lang_LinkageError(), ss.as_string());
1684   }
1685 }
1686 
1687 // Update class loader data dictionary - done after check_constraint and add_to_hierarchy
1688 // have been called.
1689 void SystemDictionary::update_dictionary(JavaThread* current,
1690                                          InstanceKlass* k,
1691                                          ClassLoaderData* loader_data) {
1692   MonitorLocker mu1(SystemDictionary_lock);
1693 
1694   // Make a new dictionary entry.
1695   Symbol* name  = k->name();
1696   Dictionary* dictionary = loader_data->dictionary();
1697   InstanceKlass* sd_check = dictionary->find_class(current, name);
1698   if (sd_check == nullptr) {
1699     dictionary->add_klass(current, name, k);
1700   }
1701   mu1.notify_all();
1702 }
1703 
1704 #if INCLUDE_CDS
1705 // Indicate that loader_data has initiated the loading of class k, which
1706 // has already been defined by a parent loader.
1707 // This API should be used only by AOTLinkedClassBulkLoader
1708 void SystemDictionary::add_to_initiating_loader(JavaThread* current,
1709                                                 InstanceKlass* k,
1710                                                 ClassLoaderData* loader_data) {
1711   assert(CDSConfig::is_using_aot_linked_classes(), "must be");
1712   assert_locked_or_safepoint(SystemDictionary_lock);
1713   Symbol* name  = k->name();
1714   Dictionary* dictionary = loader_data->dictionary();
1715   assert(k->is_loaded(), "must be");
1716   assert(k->class_loader_data() != loader_data, "only for classes defined by a parent loader");
1717   assert(dictionary->find_class(current, name) == nullptr, "sanity");
1718   dictionary->add_klass(current, name, k);
1719 }
1720 #endif
1721 
1722 // Try to find a class name using the loader constraints.  The
1723 // loader constraints might know about a class that isn't fully loaded
1724 // yet and these will be ignored.
1725 Klass* SystemDictionary::find_constrained_instance_or_array_klass(
1726                     Thread* current, Symbol* class_name, Handle class_loader) {
1727 
1728   // First see if it has been loaded directly.
1729   Klass* klass = find_instance_or_array_klass(current, class_name, class_loader);
1730   if (klass != nullptr)
1731     return klass;
1732 
1733   // Now look to see if it has been loaded elsewhere, and is subject to
1734   // a loader constraint that would require this loader to return the
1735   // klass that is already loaded.
1736   if (Signature::is_array(class_name)) {
1737     // For array classes, their Klass*s are not kept in the
1738     // constraint table. The element Klass*s are.
1739     SignatureStream ss(class_name, false);
1740     int ndims = ss.skip_array_prefix();  // skip all '['s
1741     BasicType t = ss.type();
1742     if (t != T_OBJECT) {
1743       klass = Universe::typeArrayKlass(t);
1744     } else {
1745       MutexLocker mu(current, SystemDictionary_lock);
1746       klass = LoaderConstraintTable::find_constrained_klass(ss.as_symbol(), class_loader_data(class_loader));
1747     }
1748     // If element class already loaded, allocate array klass
1749     if (klass != nullptr) {
1750       klass = klass->array_klass_or_null(ndims);
1751     }
1752   } else {
1753     MutexLocker mu(current, SystemDictionary_lock);
1754     // Non-array classes are easy: simply check the constraint table.
1755     klass = LoaderConstraintTable::find_constrained_klass(class_name, class_loader_data(class_loader));
1756   }
1757 
1758   return klass;
1759 }
1760 
1761 bool SystemDictionary::add_loader_constraint(Symbol* class_name,
1762                                              Klass* klass_being_linked,
1763                                              Handle class_loader1,
1764                                              Handle class_loader2) {
1765   ClassLoaderData* loader_data1 = class_loader_data(class_loader1);
1766   ClassLoaderData* loader_data2 = class_loader_data(class_loader2);
1767 
1768   Symbol* constraint_name = nullptr;
1769 
1770   if (!Signature::is_array(class_name)) {
1771     constraint_name = class_name;
1772   } else {
1773     // For array classes, their Klass*s are not kept in the
1774     // constraint table. The element classes are.
1775     SignatureStream ss(class_name, false);
1776     ss.skip_array_prefix();  // skip all '['s
1777     if (!ss.has_envelope()) {
1778       return true;     // primitive types always pass
1779     }
1780     constraint_name = ss.as_symbol();
1781     // Increment refcount to keep constraint_name alive after
1782     // SignatureStream is destructed. It will be decremented below
1783     // before returning.
1784     constraint_name->increment_refcount();
1785   }
1786 
1787   Dictionary* dictionary1 = loader_data1->dictionary();
1788   Dictionary* dictionary2 = loader_data2->dictionary();
1789 
1790   JavaThread* current = JavaThread::current();
1791   {
1792     MutexLocker mu_s(SystemDictionary_lock);
1793     InstanceKlass* klass1 = dictionary1->find_class(current, constraint_name);
1794     InstanceKlass* klass2 = dictionary2->find_class(current, constraint_name);
1795     bool result = LoaderConstraintTable::add_entry(constraint_name, klass1, loader_data1,
1796                                                    klass2, loader_data2);
1797 #if INCLUDE_CDS
1798     if (CDSConfig::is_dumping_archive() && klass_being_linked != nullptr &&
1799         !klass_being_linked->is_shared()) {
1800          SystemDictionaryShared::record_linking_constraint(constraint_name,
1801                                      InstanceKlass::cast(klass_being_linked),
1802                                      class_loader1, class_loader2);
1803     }
1804 #endif // INCLUDE_CDS
1805     if (Signature::is_array(class_name)) {
1806       constraint_name->decrement_refcount();
1807     }
1808     return result;
1809   }
1810 }
1811 
1812 // Add entry to resolution error table to record the error when the first
1813 // attempt to resolve a reference to a class has failed.
1814 void SystemDictionary::add_resolution_error(const constantPoolHandle& pool, int which,
1815                                             Symbol* error, const char* message,
1816                                             Symbol* cause, const char* cause_msg) {
1817   {
1818     MutexLocker ml(Thread::current(), SystemDictionary_lock);
1819     ResolutionErrorEntry* entry = ResolutionErrorTable::find_entry(pool, which);
1820     if (entry == nullptr) {
1821       ResolutionErrorTable::add_entry(pool, which, error, message, cause, cause_msg);
1822     }
1823   }
1824 }
1825 
1826 // Delete a resolution error for RedefineClasses for a constant pool is going away
1827 void SystemDictionary::delete_resolution_error(ConstantPool* pool) {
1828   ResolutionErrorTable::delete_entry(pool);
1829 }
1830 
1831 // Lookup resolution error table. Returns error if found, otherwise null.
1832 Symbol* SystemDictionary::find_resolution_error(const constantPoolHandle& pool, int which,
1833                                                 const char** message,
1834                                                 Symbol** cause, const char** cause_msg) {
1835 
1836   {
1837     MutexLocker ml(Thread::current(), SystemDictionary_lock);
1838     ResolutionErrorEntry* entry = ResolutionErrorTable::find_entry(pool, which);
1839     if (entry != nullptr) {
1840       *message = entry->message();
1841       *cause = entry->cause();
1842       *cause_msg = entry->cause_msg();
1843       return entry->error();
1844     } else {
1845       return nullptr;
1846     }
1847   }
1848 }
1849 
1850 // Add an entry to resolution error table to record an error in resolving or
1851 // validating a nest host. This is used to construct informative error
1852 // messages when IllegalAccessError's occur. If an entry already exists it will
1853 // be updated with the nest host error message.
1854 
1855 void SystemDictionary::add_nest_host_error(const constantPoolHandle& pool,
1856                                            int which,
1857                                            const char* message) {
1858   {
1859     MutexLocker ml(Thread::current(), SystemDictionary_lock);
1860     ResolutionErrorEntry* entry = ResolutionErrorTable::find_entry(pool, which);
1861     if (entry != nullptr && entry->nest_host_error() == nullptr) {
1862       // An existing entry means we had a true resolution failure (LinkageError) with our nest host, but we
1863       // still want to add the error message for the higher-level access checks to report. We should
1864       // only reach here under the same error condition, so we can ignore the potential race with setting
1865       // the message. If we see it is already set then we can ignore it.
1866       entry->set_nest_host_error(message);
1867     } else {
1868       ResolutionErrorTable::add_entry(pool, which, message);
1869     }
1870   }
1871 }
1872 
1873 // Lookup any nest host error
1874 const char* SystemDictionary::find_nest_host_error(const constantPoolHandle& pool, int which) {
1875   {
1876     MutexLocker ml(Thread::current(), SystemDictionary_lock);
1877     ResolutionErrorEntry* entry = ResolutionErrorTable::find_entry(pool, which);
1878     if (entry != nullptr) {
1879       return entry->nest_host_error();
1880     } else {
1881       return nullptr;
1882     }
1883   }
1884 }
1885 
1886 // Signature constraints ensure that callers and callees agree about
1887 // the meaning of type names in their signatures.  This routine is the
1888 // intake for constraints.  It collects them from several places:
1889 //
1890 //  * LinkResolver::resolve_method (if check_access is true) requires
1891 //    that the resolving class (the caller) and the defining class of
1892 //    the resolved method (the callee) agree on each type in the
1893 //    method's signature.
1894 //
1895 //  * LinkResolver::resolve_interface_method performs exactly the same
1896 //    checks.
1897 //
1898 //  * LinkResolver::resolve_field requires that the constant pool
1899 //    attempting to link to a field agree with the field's defining
1900 //    class about the type of the field signature.
1901 //
1902 //  * klassVtable::initialize_vtable requires that, when a class
1903 //    overrides a vtable entry allocated by a superclass, that the
1904 //    overriding method (i.e., the callee) agree with the superclass
1905 //    on each type in the method's signature.
1906 //
1907 //  * klassItable::initialize_itable requires that, when a class fills
1908 //    in its itables, for each non-abstract method installed in an
1909 //    itable, the method (i.e., the callee) agree with the interface
1910 //    on each type in the method's signature.
1911 //
1912 // All those methods have a boolean (check_access, checkconstraints)
1913 // which turns off the checks.  This is used from specialized contexts
1914 // such as bootstrapping, dumping, and debugging.
1915 //
1916 // No direct constraint is placed between the class and its
1917 // supertypes.  Constraints are only placed along linked relations
1918 // between callers and callees.  When a method overrides or implements
1919 // an abstract method in a supertype (superclass or interface), the
1920 // constraints are placed as if the supertype were the caller to the
1921 // overriding method.  (This works well, since callers to the
1922 // supertype have already established agreement between themselves and
1923 // the supertype.)  As a result of all this, a class can disagree with
1924 // its supertype about the meaning of a type name, as long as that
1925 // class neither calls a relevant method of the supertype, nor is
1926 // called (perhaps via an override) from the supertype.
1927 //
1928 //
1929 // SystemDictionary::check_signature_loaders(sig, klass_being_linked, l1, l2)
1930 //
1931 // Make sure all class components (including arrays) in the given
1932 // signature will be resolved to the same class in both loaders.
1933 // Returns the name of the type that failed a loader constraint check, or
1934 // null if no constraint failed.  No exception except OOME is thrown.
1935 // Arrays are not added to the loader constraint table, their elements are.
1936 Symbol* SystemDictionary::check_signature_loaders(Symbol* signature,
1937                                                   Klass* klass_being_linked,
1938                                                   Handle loader1, Handle loader2,
1939                                                   bool is_method)  {
1940   // Nothing to do if loaders are the same.
1941   if (loader1() == loader2()) {
1942     return nullptr;
1943   }
1944 
1945   for (SignatureStream ss(signature, is_method); !ss.is_done(); ss.next()) {
1946     if (ss.is_reference()) {
1947       Symbol* sig = ss.as_symbol();
1948       // Note: In the future, if template-like types can take
1949       // arguments, we will want to recognize them and dig out class
1950       // names hiding inside the argument lists.
1951       if (!add_loader_constraint(sig, klass_being_linked, loader1, loader2)) {
1952         return sig;
1953       }
1954     }
1955   }
1956   return nullptr;
1957 }
1958 
1959 Method* SystemDictionary::find_method_handle_intrinsic(vmIntrinsicID iid,
1960                                                        Symbol* signature,
1961                                                        TRAPS) {
1962 
1963   const int iid_as_int = vmIntrinsics::as_int(iid);
1964   assert(MethodHandles::is_signature_polymorphic(iid) &&
1965          MethodHandles::is_signature_polymorphic_intrinsic(iid) &&
1966          iid != vmIntrinsics::_invokeGeneric,
1967          "must be a known MH intrinsic iid=%d: %s", iid_as_int, vmIntrinsics::name_at(iid));
1968 
1969   InvokeMethodKey key(signature, iid_as_int);
1970   Method** met = nullptr;
1971 
1972   // We only want one entry in the table for this (signature/id, method) pair but the code
1973   // to create the intrinsic method needs to be outside the lock.
1974   // The first thread claims the entry by adding the key and the other threads wait, until the
1975   // Method has been added as the value.
1976   {
1977     MonitorLocker ml(THREAD, InvokeMethodIntrinsicTable_lock);
1978     while (true) {
1979       bool created;
1980       met = _invoke_method_intrinsic_table->put_if_absent(key, &created);
1981       assert(met != nullptr, "either created or found");
1982       if (*met != nullptr) {
1983         return *met;
1984       } else if (created) {
1985         // The current thread won the race and will try to create the full entry.
1986         break;
1987       } else {
1988         // Another thread beat us to it, so wait for them to complete
1989         // and return *met; or if they hit an error we get another try.
1990         ml.wait();
1991         // Note it is not safe to read *met here as that entry could have
1992         // been deleted, so we must loop and try put_if_absent again.
1993       }
1994     }
1995   }
1996 
1997   methodHandle m = Method::make_method_handle_intrinsic(iid, signature, THREAD);
1998   bool throw_error = HAS_PENDING_EXCEPTION;
1999   if (!throw_error && (!Arguments::is_interpreter_only() || iid == vmIntrinsics::_linkToNative)) {
2000     // Generate a compiled form of the MH intrinsic
2001     // linkToNative doesn't have interpreter-specific implementation, so always has to go through compiled version.
2002     AdapterHandlerLibrary::create_native_wrapper(m);
2003     // Check if have the compiled code.
2004     throw_error = (!m->has_compiled_code());
2005   }
2006 
2007   {
2008     MonitorLocker ml(THREAD, InvokeMethodIntrinsicTable_lock);
2009     if (throw_error) {
2010       // Remove the entry and let another thread try, or get the same exception.
2011       bool removed = _invoke_method_intrinsic_table->remove(key);
2012       assert(removed, "must be the owner");
2013       ml.notify_all();
2014     } else {
2015       signature->make_permanent(); // The signature is never unloaded.
2016       assert(Arguments::is_interpreter_only() || (m->has_compiled_code() &&
2017              m->code()->entry_point() == m->from_compiled_entry()),
2018              "MH intrinsic invariant");
2019       *met = m(); // insert the element
2020       ml.notify_all();
2021       return m();
2022     }
2023   }
2024 
2025   // Throw OOM or the pending exception in the JavaThread
2026   if (throw_error && !HAS_PENDING_EXCEPTION) {
2027     THROW_MSG_NULL(vmSymbols::java_lang_OutOfMemoryError(),
2028                    "Out of space in CodeCache for method handle intrinsic");
2029   }
2030   return nullptr;
2031 }
2032 
2033 #if INCLUDE_CDS
2034 void SystemDictionary::get_all_method_handle_intrinsics(GrowableArray<Method*>* methods) {
2035   assert(SafepointSynchronize::is_at_safepoint(), "must be");
2036   auto do_method = [&] (InvokeMethodKey& key, Method*& m) {
2037     methods->append(m);
2038   };
2039   _invoke_method_intrinsic_table->iterate_all(do_method);
2040 }
2041 
2042 void SystemDictionary::restore_archived_method_handle_intrinsics() {
2043   if (UseSharedSpaces) {
2044     EXCEPTION_MARK;
2045     restore_archived_method_handle_intrinsics_impl(THREAD);
2046     if (HAS_PENDING_EXCEPTION) {
2047       // This is probably caused by OOM -- other parts of the CDS archive have direct pointers to
2048       // the archived method handle intrinsics, so we can't really recover from this failure.
2049       vm_exit_during_initialization(err_msg("Failed to restore archived method handle intrinsics. Try to increase heap size."));
2050     }
2051   }
2052 }
2053 
2054 void SystemDictionary::restore_archived_method_handle_intrinsics_impl(TRAPS) {
2055   Array<Method*>* list = MetaspaceShared::archived_method_handle_intrinsics();
2056   for (int i = 0; i < list->length(); i++) {
2057     methodHandle m(THREAD, list->at(i));
2058     Method::restore_archived_method_handle_intrinsic(m, CHECK);
2059     m->constants()->restore_unshareable_info(CHECK);
2060     if (!Arguments::is_interpreter_only() || m->intrinsic_id() == vmIntrinsics::_linkToNative) {
2061       AdapterHandlerLibrary::create_native_wrapper(m);
2062       if (!m->has_compiled_code()) {
2063         ResourceMark rm(THREAD);
2064         vm_exit_during_initialization(err_msg("Failed to initialize method %s", m->external_name()));
2065       }
2066     }
2067 
2068     // There's no need to grab the InvokeMethodIntrinsicTable_lock, as we are still very early in
2069     // VM start-up -- in init_globals2() -- so we are still running a single Java thread. It's not
2070     // possible to have a contention.
2071     const int iid_as_int = vmIntrinsics::as_int(m->intrinsic_id());
2072     InvokeMethodKey key(m->signature(), iid_as_int);
2073     bool created = _invoke_method_intrinsic_table->put(key, m());
2074     assert(created, "unexpected contention");
2075   }
2076 }
2077 #endif // INCLUDE_CDS
2078 
2079 // Helper for unpacking the return value from linkMethod and linkCallSite.
2080 static Method* unpack_method_and_appendix(Handle mname,
2081                                           Klass* accessing_klass,
2082                                           objArrayHandle appendix_box,
2083                                           Handle* appendix_result,
2084                                           TRAPS) {
2085   if (mname.not_null()) {
2086     Method* m = java_lang_invoke_MemberName::vmtarget(mname());
2087     if (m != nullptr) {
2088       oop appendix = appendix_box->obj_at(0);
2089       LogTarget(Info, methodhandles) lt;
2090       if (lt.develop_is_enabled()) {
2091         ResourceMark rm(THREAD);
2092         LogStream ls(lt);
2093         ls.print("Linked method=" INTPTR_FORMAT ": ", p2i(m));
2094         m->print_on(&ls);
2095         if (appendix != nullptr) { ls.print("appendix = "); appendix->print_on(&ls); }
2096         ls.cr();
2097       }
2098 
2099       (*appendix_result) = Handle(THREAD, appendix);
2100       // the target is stored in the cpCache and if a reference to this
2101       // MemberName is dropped we need a way to make sure the
2102       // class_loader containing this method is kept alive.
2103       methodHandle mh(THREAD, m); // record_dependency can safepoint.
2104       ClassLoaderData* this_key = accessing_klass->class_loader_data();
2105       this_key->record_dependency(m->method_holder());
2106       return mh();
2107     }
2108   }
2109   THROW_MSG_NULL(vmSymbols::java_lang_LinkageError(), "bad value from MethodHandleNatives");
2110 }
2111 
2112 Method* SystemDictionary::find_method_handle_invoker(Klass* klass,
2113                                                      Symbol* name,
2114                                                      Symbol* signature,
2115                                                      Klass* accessing_klass,
2116                                                      Handle* appendix_result,
2117                                                      TRAPS) {
2118   guarantee(THREAD->can_call_java(), "");
2119   Handle method_type =
2120     SystemDictionary::find_method_handle_type(signature, accessing_klass, CHECK_NULL);
2121 
2122   int ref_kind = JVM_REF_invokeVirtual;
2123   oop name_oop = StringTable::intern(name, CHECK_NULL);
2124   Handle name_str (THREAD, name_oop);
2125   objArrayHandle appendix_box = oopFactory::new_objArray_handle(vmClasses::Object_klass(), 1, CHECK_NULL);
2126   assert(appendix_box->obj_at(0) == nullptr, "");
2127 
2128   // This should not happen.  JDK code should take care of that.
2129   if (accessing_klass == nullptr || method_type.is_null()) {
2130     THROW_MSG_NULL(vmSymbols::java_lang_InternalError(), "bad invokehandle");
2131   }
2132 
2133   // call java.lang.invoke.MethodHandleNatives::linkMethod(... String, MethodType) -> MemberName
2134   JavaCallArguments args;
2135   args.push_oop(Handle(THREAD, accessing_klass->java_mirror()));
2136   args.push_int(ref_kind);
2137   args.push_oop(Handle(THREAD, klass->java_mirror()));
2138   args.push_oop(name_str);
2139   args.push_oop(method_type);
2140   args.push_oop(appendix_box);
2141   JavaValue result(T_OBJECT);
2142   JavaCalls::call_static(&result,
2143                          vmClasses::MethodHandleNatives_klass(),
2144                          vmSymbols::linkMethod_name(),
2145                          vmSymbols::linkMethod_signature(),
2146                          &args, CHECK_NULL);
2147   Handle mname(THREAD, result.get_oop());
2148   return unpack_method_and_appendix(mname, accessing_klass, appendix_box, appendix_result, THREAD);
2149 }
2150 
2151 // Decide if we can globally cache a lookup of this class, to be returned to any client that asks.
2152 // We must ensure that all class loaders everywhere will reach this class, for any client.
2153 // This is a safe bet for public classes in java.lang, such as Object and String.
2154 // We also include public classes in java.lang.invoke, because they appear frequently in system-level method types.
2155 // Out of an abundance of caution, we do not include any other classes, not even for packages like java.util.
2156 static bool is_always_visible_class(oop mirror) {
2157   Klass* klass = java_lang_Class::as_Klass(mirror);
2158   if (klass->is_objArray_klass()) {
2159     klass = ObjArrayKlass::cast(klass)->bottom_klass(); // check element type
2160   }
2161   if (klass->is_typeArray_klass()) {
2162     return true; // primitive array
2163   }
2164   assert(klass->is_instance_klass(), "%s", klass->external_name());
2165   return klass->is_public() &&
2166          (InstanceKlass::cast(klass)->is_same_class_package(vmClasses::Object_klass()) ||       // java.lang
2167           InstanceKlass::cast(klass)->is_same_class_package(vmClasses::MethodHandle_klass()));  // java.lang.invoke
2168 }
2169 
2170 // Find or construct the Java mirror (java.lang.Class instance) for
2171 // the given field type signature, as interpreted relative to the
2172 // given class loader.  Handles primitives, void, references, arrays,
2173 // and all other reflectable types, except method types.
2174 // N.B.  Code in reflection should use this entry point.
2175 Handle SystemDictionary::find_java_mirror_for_type(Symbol* signature,
2176                                                    Klass* accessing_klass,
2177                                                    SignatureStream::FailureMode failure_mode,
2178                                                    TRAPS) {
2179 
2180   Handle class_loader;
2181 
2182   // What we have here must be a valid field descriptor,
2183   // and all valid field descriptors are supported.
2184   // Produce the same java.lang.Class that reflection reports.
2185   if (accessing_klass != nullptr) {
2186     class_loader      = Handle(THREAD, accessing_klass->class_loader());
2187   }
2188   ResolvingSignatureStream ss(signature, class_loader, false);
2189   oop mirror_oop = ss.as_java_mirror(failure_mode, CHECK_NH);
2190   if (mirror_oop == nullptr) {
2191     return Handle();  // report failure this way
2192   }
2193   Handle mirror(THREAD, mirror_oop);
2194 
2195   if (accessing_klass != nullptr) {
2196     // Check accessibility, emulating ConstantPool::verify_constant_pool_resolve.
2197     Klass* sel_klass = java_lang_Class::as_Klass(mirror());
2198     if (sel_klass != nullptr) {
2199       LinkResolver::check_klass_accessibility(accessing_klass, sel_klass, CHECK_NH);
2200     }
2201   }
2202   return mirror;
2203 }
2204 
2205 
2206 // Ask Java code to find or construct a java.lang.invoke.MethodType for the given
2207 // signature, as interpreted relative to the given class loader.
2208 // Because of class loader constraints, all method handle usage must be
2209 // consistent with this loader.
2210 Handle SystemDictionary::find_method_handle_type(Symbol* signature,
2211                                                  Klass* accessing_klass,
2212                                                  TRAPS) {
2213   Handle empty;
2214   OopHandle* o;
2215   {
2216     MutexLocker ml(THREAD, InvokeMethodTypeTable_lock);
2217     o = _invoke_method_type_table->get(signature);
2218   }
2219 
2220   if (o != nullptr) {
2221     oop mt = o->resolve();
2222     assert(java_lang_invoke_MethodType::is_instance(mt), "");
2223     return Handle(THREAD, mt);
2224   } else if (!THREAD->can_call_java()) {
2225     warning("SystemDictionary::find_method_handle_type called from compiler thread");  // FIXME
2226     return Handle();  // do not attempt from within compiler, unless it was cached
2227   }
2228 
2229   Handle class_loader;
2230   if (accessing_klass != nullptr) {
2231     class_loader      = Handle(THREAD, accessing_klass->class_loader());
2232   }
2233   bool can_be_cached = true;
2234   int npts = ArgumentCount(signature).size();
2235   objArrayHandle pts = oopFactory::new_objArray_handle(vmClasses::Class_klass(), npts, CHECK_(empty));
2236   int arg = 0;
2237   Handle rt; // the return type from the signature
2238   ResourceMark rm(THREAD);
2239   for (SignatureStream ss(signature); !ss.is_done(); ss.next()) {
2240     oop mirror = nullptr;
2241     if (can_be_cached) {
2242       // Use neutral class loader to lookup candidate classes to be placed in the cache.
2243       mirror = ss.as_java_mirror(Handle(), SignatureStream::ReturnNull, CHECK_(empty));
2244       if (mirror == nullptr || (ss.is_reference() && !is_always_visible_class(mirror))) {
2245         // Fall back to accessing_klass context.
2246         can_be_cached = false;
2247       }
2248     }
2249     if (!can_be_cached) {
2250       // Resolve, throwing a real error if it doesn't work.
2251       mirror = ss.as_java_mirror(class_loader, SignatureStream::NCDFError, CHECK_(empty));
2252     }
2253     assert(mirror != nullptr, "%s", ss.as_symbol()->as_C_string());
2254     if (ss.at_return_type())
2255       rt = Handle(THREAD, mirror);
2256     else
2257       pts->obj_at_put(arg++, mirror);
2258 
2259     // Check accessibility.
2260     if (!java_lang_Class::is_primitive(mirror) && accessing_klass != nullptr) {
2261       Klass* sel_klass = java_lang_Class::as_Klass(mirror);
2262       mirror = nullptr;  // safety
2263       // Emulate ConstantPool::verify_constant_pool_resolve.
2264       LinkResolver::check_klass_accessibility(accessing_klass, sel_klass, CHECK_(empty));
2265     }
2266   }
2267   assert(arg == npts, "");
2268 
2269   // call java.lang.invoke.MethodHandleNatives::findMethodHandleType(Class rt, Class[] pts) -> MethodType
2270   JavaCallArguments args(Handle(THREAD, rt()));
2271   args.push_oop(pts);
2272   JavaValue result(T_OBJECT);
2273   JavaCalls::call_static(&result,
2274                          vmClasses::MethodHandleNatives_klass(),
2275                          vmSymbols::findMethodHandleType_name(),
2276                          vmSymbols::findMethodHandleType_signature(),
2277                          &args, CHECK_(empty));
2278   Handle method_type(THREAD, result.get_oop());
2279 
2280   if (can_be_cached) {
2281     // We can cache this MethodType inside the JVM.
2282     MutexLocker ml(THREAD, InvokeMethodTypeTable_lock);
2283     bool created = false;
2284     assert(method_type != nullptr, "unexpected null");
2285     OopHandle* h = _invoke_method_type_table->get(signature);
2286     if (h == nullptr) {
2287       signature->make_permanent(); // The signature is never unloaded.
2288       OopHandle elem = OopHandle(Universe::vm_global(), method_type());
2289       bool created = _invoke_method_type_table->put(signature, elem);
2290       assert(created, "better be created");
2291     }
2292   }
2293   // report back to the caller with the MethodType
2294   return method_type;
2295 }
2296 
2297 Handle SystemDictionary::find_field_handle_type(Symbol* signature,
2298                                                 Klass* accessing_klass,
2299                                                 TRAPS) {
2300   Handle empty;
2301   ResourceMark rm(THREAD);
2302   SignatureStream ss(signature, /*is_method=*/ false);
2303   if (!ss.is_done()) {
2304     Handle class_loader;
2305     if (accessing_klass != nullptr) {
2306       class_loader      = Handle(THREAD, accessing_klass->class_loader());
2307     }
2308     oop mirror = ss.as_java_mirror(class_loader, SignatureStream::NCDFError, CHECK_(empty));
2309     ss.next();
2310     if (ss.is_done()) {
2311       return Handle(THREAD, mirror);
2312     }
2313   }
2314   return empty;
2315 }
2316 
2317 // Ask Java code to find or construct a method handle constant.
2318 Handle SystemDictionary::link_method_handle_constant(Klass* caller,
2319                                                      int ref_kind, //e.g., JVM_REF_invokeVirtual
2320                                                      Klass* callee,
2321                                                      Symbol* name,
2322                                                      Symbol* signature,
2323                                                      TRAPS) {
2324   Handle empty;
2325   if (caller == nullptr) {
2326     THROW_MSG_(vmSymbols::java_lang_InternalError(), "bad MH constant", empty);
2327   }
2328   Handle name_str      = java_lang_String::create_from_symbol(name,      CHECK_(empty));
2329   Handle signature_str = java_lang_String::create_from_symbol(signature, CHECK_(empty));
2330 
2331   // Put symbolic info from the MH constant into freshly created MemberName and resolve it.
2332   Handle mname = vmClasses::MemberName_klass()->allocate_instance_handle(CHECK_(empty));
2333   java_lang_invoke_MemberName::set_clazz(mname(), callee->java_mirror());
2334   java_lang_invoke_MemberName::set_name (mname(), name_str());
2335   java_lang_invoke_MemberName::set_type (mname(), signature_str());
2336   java_lang_invoke_MemberName::set_flags(mname(), MethodHandles::ref_kind_to_flags(ref_kind));
2337 
2338   if (ref_kind == JVM_REF_invokeVirtual &&
2339       MethodHandles::is_signature_polymorphic_public_name(callee, name)) {
2340     // Skip resolution for public signature polymorphic methods such as
2341     // j.l.i.MethodHandle.invoke()/invokeExact() and those on VarHandle
2342     // They require appendix argument which MemberName resolution doesn't handle.
2343     // There's special logic on JDK side to handle them
2344     // (see MethodHandles.linkMethodHandleConstant() and MethodHandles.findVirtualForMH()).
2345   } else {
2346     MethodHandles::resolve_MemberName(mname, caller, 0, false /*speculative_resolve*/, CHECK_(empty));
2347   }
2348 
2349   // After method/field resolution succeeded, it's safe to resolve MH signature as well.
2350   Handle type = MethodHandles::resolve_MemberName_type(mname, caller, CHECK_(empty));
2351 
2352   // call java.lang.invoke.MethodHandleNatives::linkMethodHandleConstant(Class caller, int refKind, Class callee, String name, Object type) -> MethodHandle
2353   JavaCallArguments args;
2354   args.push_oop(Handle(THREAD, caller->java_mirror()));  // the referring class
2355   args.push_int(ref_kind);
2356   args.push_oop(Handle(THREAD, callee->java_mirror()));  // the target class
2357   args.push_oop(name_str);
2358   args.push_oop(type);
2359   JavaValue result(T_OBJECT);
2360   JavaCalls::call_static(&result,
2361                          vmClasses::MethodHandleNatives_klass(),
2362                          vmSymbols::linkMethodHandleConstant_name(),
2363                          vmSymbols::linkMethodHandleConstant_signature(),
2364                          &args, CHECK_(empty));
2365   return Handle(THREAD, result.get_oop());
2366 }
2367 
2368 // Ask Java to run a bootstrap method, in order to create a dynamic call site
2369 // while linking an invokedynamic op, or compute a constant for Dynamic_info CP entry
2370 // with linkage results being stored back into the bootstrap specifier.
2371 void SystemDictionary::invoke_bootstrap_method(BootstrapInfo& bootstrap_specifier, TRAPS) {
2372   // Resolve the bootstrap specifier, its name, type, and static arguments
2373   bootstrap_specifier.resolve_bsm(CHECK);
2374 
2375   // This should not happen.  JDK code should take care of that.
2376   if (bootstrap_specifier.caller() == nullptr || bootstrap_specifier.type_arg().is_null()) {
2377     THROW_MSG(vmSymbols::java_lang_InternalError(), "Invalid bootstrap method invocation with no caller or type argument");
2378   }
2379 
2380   bool is_indy = bootstrap_specifier.is_method_call();
2381   objArrayHandle appendix_box;
2382   if (is_indy) {
2383     // Some method calls may require an appendix argument.  Arrange to receive it.
2384     appendix_box = oopFactory::new_objArray_handle(vmClasses::Object_klass(), 1, CHECK);
2385     assert(appendix_box->obj_at(0) == nullptr, "");
2386   }
2387 
2388   // call condy: java.lang.invoke.MethodHandleNatives::linkDynamicConstant(caller, bsm, type, info)
2389   //       indy: java.lang.invoke.MethodHandleNatives::linkCallSite(caller, bsm, name, mtype, info, &appendix)
2390   JavaCallArguments args;
2391   args.push_oop(Handle(THREAD, bootstrap_specifier.caller_mirror()));
2392   args.push_oop(bootstrap_specifier.bsm());
2393   args.push_oop(bootstrap_specifier.name_arg());
2394   args.push_oop(bootstrap_specifier.type_arg());
2395   args.push_oop(bootstrap_specifier.arg_values());
2396   if (is_indy) {
2397     args.push_oop(appendix_box);
2398   }
2399   JavaValue result(T_OBJECT);
2400   JavaCalls::call_static(&result,
2401                          vmClasses::MethodHandleNatives_klass(),
2402                          is_indy ? vmSymbols::linkCallSite_name() : vmSymbols::linkDynamicConstant_name(),
2403                          is_indy ? vmSymbols::linkCallSite_signature() : vmSymbols::linkDynamicConstant_signature(),
2404                          &args, CHECK);
2405 
2406   Handle value(THREAD, result.get_oop());
2407   if (is_indy) {
2408     Handle appendix;
2409     Method* method = unpack_method_and_appendix(value,
2410                                                 bootstrap_specifier.caller(),
2411                                                 appendix_box,
2412                                                 &appendix, CHECK);
2413     methodHandle mh(THREAD, method);
2414     bootstrap_specifier.set_resolved_method(mh, appendix);
2415   } else {
2416     bootstrap_specifier.set_resolved_value(value);
2417   }
2418 
2419   // sanity check
2420   assert(bootstrap_specifier.is_resolved() ||
2421          (bootstrap_specifier.is_method_call() &&
2422           bootstrap_specifier.resolved_method().not_null()), "bootstrap method call failed");
2423 }
2424 
2425 
2426 bool SystemDictionary::is_nonpublic_Object_method(Method* m) {
2427   assert(m != nullptr, "Unexpected nullptr Method*");
2428   return !m->is_public() && m->method_holder() == vmClasses::Object_klass();
2429 }
2430 
2431 // ----------------------------------------------------------------------------
2432 
2433 void SystemDictionary::print_on(outputStream *st) {
2434   CDS_ONLY(SystemDictionaryShared::print_on(st));
2435   GCMutexLocker mu(SystemDictionary_lock);
2436 
2437   ClassLoaderDataGraph::print_dictionary(st);
2438 
2439   // Placeholders
2440   PlaceholderTable::print_on(st);
2441   st->cr();
2442 
2443   // loader constraints - print under SD_lock
2444   LoaderConstraintTable::print_on(st);
2445   st->cr();
2446 }
2447 
2448 void SystemDictionary::print() { print_on(tty); }
2449 
2450 void SystemDictionary::verify() {
2451 
2452   GCMutexLocker mu(SystemDictionary_lock);
2453 
2454   // Verify dictionary
2455   ClassLoaderDataGraph::verify_dictionary();
2456 
2457   // Verify constraint table
2458   LoaderConstraintTable::verify();
2459 }
2460 
2461 void SystemDictionary::dump(outputStream *st, bool verbose) {
2462   assert_locked_or_safepoint(SystemDictionary_lock);
2463   if (verbose) {
2464     print_on(st);
2465   } else {
2466     CDS_ONLY(SystemDictionaryShared::print_table_statistics(st));
2467     ClassLoaderDataGraph::print_table_statistics(st);
2468     LoaderConstraintTable::print_table_statistics(st);
2469   }
2470 }
2471 
2472 // Utility for dumping dictionaries.
2473 SystemDictionaryDCmd::SystemDictionaryDCmd(outputStream* output, bool heap) :
2474                                  DCmdWithParser(output, heap),
2475   _verbose("-verbose", "Dump the content of each dictionary entry for all class loaders",
2476            "BOOLEAN", false, "false") {
2477   _dcmdparser.add_dcmd_option(&_verbose);
2478 }
2479 
2480 void SystemDictionaryDCmd::execute(DCmdSource source, TRAPS) {
2481   VM_DumpHashtable dumper(output(), VM_DumpHashtable::DumpSysDict,
2482                          _verbose.value());
2483   VMThread::execute(&dumper);
2484 }