1  /*
   2  * Copyright (c) 2012, 2023, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 // A ClassLoaderData identifies the full set of class types that a class
  26 // loader's name resolution strategy produces for a given configuration of the
  27 // class loader.
  28 // Class types in the ClassLoaderData may be defined by from class file binaries
  29 // provided by the class loader, or from other class loader it interacts with
  30 // according to its name resolution strategy.
  31 //
  32 // Class loaders that implement a deterministic name resolution strategy
  33 // (including with respect to their delegation behavior), such as the boot, the
  34 // platform, and the system loaders of the JDK's built-in class loader
  35 // hierarchy, always produce the same linkset for a given configuration.
  36 //
  37 // ClassLoaderData carries information related to a linkset (e.g.,
  38 // metaspace holding its klass definitions).
  39 // The System Dictionary and related data structures (e.g., placeholder table,
  40 // loader constraints table) as well as the runtime representation of classes
  41 // only reference ClassLoaderData.
  42 //
  43 // Instances of java.lang.ClassLoader holds a pointer to a ClassLoaderData that
  44 // that represent the loader's "linking domain" in the JVM.
  45 //
  46 // The bootstrap loader (represented by null) also has a ClassLoaderData,
  47 // the singleton class the_null_class_loader_data().
  48 
  49 #include "precompiled.hpp"
  50 #include "classfile/classLoaderData.inline.hpp"
  51 #include "classfile/classLoaderDataGraph.inline.hpp"
  52 #include "classfile/dictionary.hpp"
  53 #include "classfile/javaClasses.inline.hpp"
  54 #include "classfile/moduleEntry.hpp"
  55 #include "classfile/packageEntry.hpp"
  56 #include "classfile/symbolTable.hpp"
  57 #include "classfile/systemDictionary.hpp"
  58 #include "classfile/systemDictionaryShared.hpp"
  59 #include "classfile/vmClasses.hpp"
  60 #include "logging/log.hpp"
  61 #include "logging/logStream.hpp"
  62 #include "memory/allocation.inline.hpp"
  63 #include "memory/classLoaderMetaspace.hpp"
  64 #include "memory/metadataFactory.hpp"
  65 #include "memory/metaspace.hpp"
  66 #include "memory/resourceArea.hpp"
  67 #include "memory/universe.hpp"
  68 #include "oops/access.inline.hpp"
  69 #include "oops/klass.inline.hpp"
  70 #include "oops/oop.inline.hpp"
  71 #include "oops/oopHandle.inline.hpp"
  72 #include "oops/verifyOopClosure.hpp"
  73 #include "oops/weakHandle.inline.hpp"
  74 #include "runtime/arguments.hpp"
  75 #include "runtime/atomic.hpp"
  76 #include "runtime/handles.inline.hpp"
  77 #include "runtime/mutex.hpp"
  78 #include "runtime/safepoint.hpp"
  79 #include "utilities/growableArray.hpp"
  80 #include "utilities/macros.hpp"
  81 #include "utilities/ostream.hpp"
  82 
  83 ClassLoaderData * ClassLoaderData::_the_null_class_loader_data = nullptr;
  84 
  85 void ClassLoaderData::init_null_class_loader_data() {
  86   assert(_the_null_class_loader_data == nullptr, "cannot initialize twice");
  87   assert(ClassLoaderDataGraph::_head == nullptr, "cannot initialize twice");
  88 
  89   _the_null_class_loader_data = new ClassLoaderData(Handle(), false);
  90   ClassLoaderDataGraph::_head = _the_null_class_loader_data;
  91   assert(_the_null_class_loader_data->is_the_null_class_loader_data(), "Must be");
  92 
  93   LogTarget(Trace, class, loader, data) lt;
  94   if (lt.is_enabled()) {
  95     ResourceMark rm;
  96     LogStream ls(lt);
  97     ls.print("create ");
  98     _the_null_class_loader_data->print_value_on(&ls);
  99     ls.cr();
 100   }
 101 }
 102 
 103 // Obtain and set the class loader's name within the ClassLoaderData so
 104 // it will be available for error messages, logging, JFR, etc.  The name
 105 // and klass are available after the class_loader oop is no longer alive,
 106 // during unloading.
 107 void ClassLoaderData::initialize_name(Handle class_loader) {
 108   ResourceMark rm;
 109 
 110   // Obtain the class loader's name.  If the class loader's name was not
 111   // explicitly set during construction, the CLD's _name field will be null.
 112   oop cl_name = java_lang_ClassLoader::name(class_loader());
 113   if (cl_name != nullptr) {
 114     const char* cl_instance_name = java_lang_String::as_utf8_string(cl_name);
 115 
 116     if (cl_instance_name != nullptr && cl_instance_name[0] != '\0') {
 117       _name = SymbolTable::new_symbol(cl_instance_name);
 118     }
 119   }
 120 
 121   // Obtain the class loader's name and identity hash.  If the class loader's
 122   // name was not explicitly set during construction, the class loader's name and id
 123   // will be set to the qualified class name of the class loader along with its
 124   // identity hash.
 125   // If for some reason the ClassLoader's constructor has not been run, instead of
 126   // leaving the _name_and_id field null, fall back to the external qualified class
 127   // name.  Thus CLD's _name_and_id field should never have a null value.
 128   oop cl_name_and_id = java_lang_ClassLoader::nameAndId(class_loader());
 129   const char* cl_instance_name_and_id =
 130                   (cl_name_and_id == nullptr) ? _class_loader_klass->external_name() :
 131                                              java_lang_String::as_utf8_string(cl_name_and_id);
 132   assert(cl_instance_name_and_id != nullptr && cl_instance_name_and_id[0] != '\0', "class loader has no name and id");
 133   _name_and_id = SymbolTable::new_symbol(cl_instance_name_and_id);
 134 }
 135 
 136 ClassLoaderData::ClassLoaderData(Handle h_class_loader, bool has_class_mirror_holder) :
 137   _metaspace(nullptr),
 138   _metaspace_lock(new Mutex(Mutex::nosafepoint-2, "MetaspaceAllocation_lock")),
 139   _unloading(false), _has_class_mirror_holder(has_class_mirror_holder),
 140   _modified_oops(true),
 141   // A non-strong hidden class loader data doesn't have anything to keep
 142   // it from being unloaded during parsing of the non-strong hidden class.
 143   // The null-class-loader should always be kept alive.
 144   _keep_alive((has_class_mirror_holder || h_class_loader.is_null()) ? 1 : 0),
 145   _claim(0),
 146   _handles(),
 147   _klasses(nullptr), _packages(nullptr), _modules(nullptr), _unnamed_module(nullptr), _dictionary(nullptr),
 148   _jmethod_ids(nullptr),
 149   _deallocate_list(nullptr),
 150   _next(nullptr),
 151   _unloading_next(nullptr),
 152   _class_loader_klass(nullptr), _name(nullptr), _name_and_id(nullptr) {
 153 
 154   if (!h_class_loader.is_null()) {
 155     _class_loader = _handles.add(h_class_loader());
 156     _class_loader_klass = h_class_loader->klass();
 157     initialize_name(h_class_loader);
 158   }
 159 
 160   if (!has_class_mirror_holder) {
 161     // The holder is initialized later for non-strong hidden classes,
 162     // and before calling anything that call class_loader().
 163     initialize_holder(h_class_loader);
 164 
 165     // A ClassLoaderData created solely for a non-strong hidden class should never
 166     // have a ModuleEntryTable or PackageEntryTable created for it.
 167     _packages = new PackageEntryTable();
 168     if (h_class_loader.is_null()) {
 169       // Create unnamed module for boot loader
 170       _unnamed_module = ModuleEntry::create_boot_unnamed_module(this);
 171     } else {
 172       // Create unnamed module for all other loaders
 173       _unnamed_module = ModuleEntry::create_unnamed_module(this);
 174     }
 175     _dictionary = create_dictionary();
 176   }
 177 
 178   NOT_PRODUCT(_dependency_count = 0); // number of class loader dependencies
 179 
 180   JFR_ONLY(INIT_ID(this);)
 181 }
 182 
 183 ClassLoaderData::ChunkedHandleList::~ChunkedHandleList() {
 184   Chunk* c = _head;
 185   while (c != nullptr) {
 186     Chunk* next = c->_next;
 187     delete c;
 188     c = next;
 189   }
 190 }
 191 
 192 OopHandle ClassLoaderData::ChunkedHandleList::add(oop o) {
 193   if (_head == nullptr || _head->_size == Chunk::CAPACITY) {
 194     Chunk* next = new Chunk(_head);
 195     Atomic::release_store(&_head, next);
 196   }
 197   oop* handle = &_head->_data[_head->_size];
 198   NativeAccess<IS_DEST_UNINITIALIZED>::oop_store(handle, o);
 199   Atomic::release_store(&_head->_size, _head->_size + 1);
 200   return OopHandle(handle);
 201 }
 202 
 203 int ClassLoaderData::ChunkedHandleList::count() const {
 204   int count = 0;
 205   Chunk* chunk = _head;
 206   while (chunk != nullptr) {
 207     count += chunk->_size;
 208     chunk = chunk->_next;
 209   }
 210   return count;
 211 }
 212 
 213 inline void ClassLoaderData::ChunkedHandleList::oops_do_chunk(OopClosure* f, Chunk* c, const juint size) {
 214   for (juint i = 0; i < size; i++) {
 215     f->do_oop(&c->_data[i]);
 216   }
 217 }
 218 
 219 void ClassLoaderData::ChunkedHandleList::oops_do(OopClosure* f) {
 220   Chunk* head = Atomic::load_acquire(&_head);
 221   if (head != nullptr) {
 222     // Must be careful when reading size of head
 223     oops_do_chunk(f, head, Atomic::load_acquire(&head->_size));
 224     for (Chunk* c = head->_next; c != nullptr; c = c->_next) {
 225       oops_do_chunk(f, c, c->_size);
 226     }
 227   }
 228 }
 229 
 230 class VerifyContainsOopClosure : public OopClosure {
 231   oop  _target;
 232   bool _found;
 233 
 234  public:
 235   VerifyContainsOopClosure(oop target) : _target(target), _found(false) {}
 236 
 237   void do_oop(oop* p) {
 238     if (p != nullptr && NativeAccess<AS_NO_KEEPALIVE>::oop_load(p) == _target) {
 239       _found = true;
 240     }
 241   }
 242 
 243   void do_oop(narrowOop* p) {
 244     // The ChunkedHandleList should not contain any narrowOop
 245     ShouldNotReachHere();
 246   }
 247 
 248   bool found() const {
 249     return _found;
 250   }
 251 };
 252 
 253 bool ClassLoaderData::ChunkedHandleList::contains(oop p) {
 254   VerifyContainsOopClosure cl(p);
 255   oops_do(&cl);
 256   return cl.found();
 257 }
 258 
 259 #ifndef PRODUCT
 260 bool ClassLoaderData::ChunkedHandleList::owner_of(oop* oop_handle) {
 261   Chunk* chunk = _head;
 262   while (chunk != nullptr) {
 263     if (&(chunk->_data[0]) <= oop_handle && oop_handle < &(chunk->_data[chunk->_size])) {
 264       return true;
 265     }
 266     chunk = chunk->_next;
 267   }
 268   return false;
 269 }
 270 #endif // PRODUCT
 271 
 272 void ClassLoaderData::clear_claim(int claim) {
 273   for (;;) {
 274     int old_claim = Atomic::load(&_claim);
 275     if ((old_claim & claim) == 0) {
 276       return;
 277     }
 278     int new_claim = old_claim & ~claim;
 279     if (Atomic::cmpxchg(&_claim, old_claim, new_claim) == old_claim) {
 280       return;
 281     }
 282   }
 283 }
 284 
 285 #ifdef ASSERT
 286 void ClassLoaderData::verify_not_claimed(int claim) {
 287   assert((_claim & claim) == 0, "Found claim: %d bits in _claim: %d", claim, _claim);
 288 }
 289 #endif
 290 
 291 bool ClassLoaderData::try_claim(int claim) {
 292   for (;;) {
 293     int old_claim = Atomic::load(&_claim);
 294     if ((old_claim & claim) == claim) {
 295       return false;
 296     }
 297     int new_claim = old_claim | claim;
 298     if (Atomic::cmpxchg(&_claim, old_claim, new_claim) == old_claim) {
 299       return true;
 300     }
 301   }
 302 }
 303 
 304 void ClassLoaderData::demote_strong_roots() {
 305   // The oop handle area contains strong roots that the GC traces from. We are about
 306   // to demote them to strong native oops that the GC does *not* trace from. Conceptually,
 307   // we are retiring a rather normal strong root, and creating a strong non-root handle,
 308   // which happens to reuse the same address as the normal strong root had.
 309   // Unless we invoke the right barriers, the GC might not notice that a strong root
 310   // has been pulled from the system, and is left unprocessed by the GC. There can be
 311   // several consequences:
 312   // 1. A concurrently marking snapshot-at-the-beginning GC might assume that the contents
 313   //    of all strong roots get processed by the GC in order to keep them alive. Without
 314   //    barriers, some objects might not be kept alive.
 315   // 2. A concurrently relocating GC might assume that after moving an object, a subsequent
 316   //    tracing from all roots can fix all the pointers in the system, which doesn't play
 317   //    well with roots racingly being pulled.
 318   // 3. A concurrent GC using colored pointers, might assume that tracing the object graph
 319   //    from roots results in all pointers getting some particular color, which also doesn't
 320   //    play well with roots being pulled out from the system concurrently.
 321 
 322   class TransitionRootsOopClosure : public OopClosure {
 323   public:
 324     virtual void do_oop(oop* p) {
 325       // By loading the strong root with the access API, we can use the right barriers to
 326       // store the oop as a strong non-root handle, that happens to reuse the same memory
 327       // address as the strong root. The barriered store ensures that:
 328       // 1. The concurrent SATB marking properties are satisfied as the store will keep
 329       //    the oop alive.
 330       // 2. The concurrent object movement properties are satisfied as we store the address
 331       //    of the new location of the object, if any.
 332       // 3. The colors if any will be stored as the new good colors.
 333       oop obj = NativeAccess<>::oop_load(p); // Load the strong root
 334       NativeAccess<>::oop_store(p, obj); // Store the strong non-root
 335     }
 336 
 337     virtual void do_oop(narrowOop* p) {
 338       ShouldNotReachHere();
 339     }
 340   } cl;
 341   oops_do(&cl, ClassLoaderData::_claim_none, false /* clear_mod_oops */);
 342 }
 343 
 344 // Non-strong hidden classes have their own ClassLoaderData that is marked to keep alive
 345 // while the class is being parsed, and if the class appears on the module fixup list.
 346 // Due to the uniqueness that no other class shares the hidden class' name or
 347 // ClassLoaderData, no other non-GC thread has knowledge of the hidden class while
 348 // it is being defined, therefore _keep_alive is not volatile or atomic.
 349 void ClassLoaderData::inc_keep_alive() {
 350   if (has_class_mirror_holder()) {
 351     assert(_keep_alive > 0, "Invalid keep alive increment count");
 352     _keep_alive++;
 353   }
 354 }
 355 
 356 void ClassLoaderData::dec_keep_alive() {
 357   if (has_class_mirror_holder()) {
 358     assert(_keep_alive > 0, "Invalid keep alive decrement count");
 359     if (_keep_alive == 1) {
 360       // When the keep_alive counter is 1, the oop handle area is a strong root,
 361       // acting as input to the GC tracing. Such strong roots are part of the
 362       // snapshot-at-the-beginning, and can not just be pulled out from the
 363       // system when concurrent GCs are running at the same time, without
 364       // invoking the right barriers.
 365       demote_strong_roots();
 366     }
 367     _keep_alive--;
 368   }
 369 }
 370 
 371 void ClassLoaderData::oops_do(OopClosure* f, int claim_value, bool clear_mod_oops) {
 372   if (claim_value != ClassLoaderData::_claim_none && !try_claim(claim_value)) {
 373     return;
 374   }
 375 
 376   // Only clear modified_oops after the ClassLoaderData is claimed.
 377   if (clear_mod_oops) {
 378     clear_modified_oops();
 379   }
 380 
 381   _handles.oops_do(f);
 382 }
 383 
 384 void ClassLoaderData::classes_do(KlassClosure* klass_closure) {
 385   // Lock-free access requires load_acquire
 386   for (Klass* k = Atomic::load_acquire(&_klasses); k != nullptr; k = k->next_link()) {
 387     klass_closure->do_klass(k);
 388     assert(k != k->next_link(), "no loops!");
 389   }
 390 }
 391 
 392 void ClassLoaderData::classes_do(void f(Klass * const)) {
 393   // Lock-free access requires load_acquire
 394   for (Klass* k = Atomic::load_acquire(&_klasses); k != nullptr; k = k->next_link()) {
 395     f(k);
 396     assert(k != k->next_link(), "no loops!");
 397   }
 398 }
 399 
 400 void ClassLoaderData::methods_do(void f(Method*)) {
 401   // Lock-free access requires load_acquire
 402   for (Klass* k = Atomic::load_acquire(&_klasses); k != nullptr; k = k->next_link()) {
 403     if (k->is_instance_klass() && InstanceKlass::cast(k)->is_loaded()) {
 404       InstanceKlass::cast(k)->methods_do(f);
 405     }
 406   }
 407 }
 408 
 409 void ClassLoaderData::loaded_classes_do(KlassClosure* klass_closure) {
 410   // To call this, one must have the MultiArray_lock held, but the _klasses list still has lock free reads.
 411   assert_locked_or_safepoint(MultiArray_lock);
 412 
 413   // Lock-free access requires load_acquire
 414   for (Klass* k = Atomic::load_acquire(&_klasses); k != nullptr; k = k->next_link()) {
 415     // Filter out InstanceKlasses (or their ObjArrayKlasses) that have not entered the
 416     // loaded state.
 417     if (k->is_instance_klass()) {
 418       if (!InstanceKlass::cast(k)->is_loaded()) {
 419         continue;
 420       }
 421     } else if (k->is_shared() && k->is_objArray_klass()) {
 422       Klass* bottom = ObjArrayKlass::cast(k)->bottom_klass();
 423       if (bottom->is_instance_klass() && !InstanceKlass::cast(bottom)->is_loaded()) {
 424         // This could happen if <bottom> is a shared class that has been restored
 425         // but is not yet marked as loaded. All archived array classes of the
 426         // bottom class are already restored and placed in the _klasses list.
 427         continue;
 428       }
 429     }
 430 
 431 #ifdef ASSERT
 432     oop m = k->java_mirror();
 433     assert(m != nullptr, "nullptr mirror");
 434     assert(m->is_a(vmClasses::Class_klass()), "invalid mirror");
 435 #endif
 436     klass_closure->do_klass(k);
 437   }
 438 }
 439 
 440 void ClassLoaderData::classes_do(void f(InstanceKlass*)) {
 441   // Lock-free access requires load_acquire
 442   for (Klass* k = Atomic::load_acquire(&_klasses); k != nullptr; k = k->next_link()) {
 443     if (k->is_instance_klass()) {
 444       f(InstanceKlass::cast(k));
 445     }
 446     assert(k != k->next_link(), "no loops!");
 447   }
 448 }
 449 
 450 void ClassLoaderData::modules_do(void f(ModuleEntry*)) {
 451   assert_locked_or_safepoint(Module_lock);
 452   if (_unnamed_module != nullptr) {
 453     f(_unnamed_module);
 454   }
 455   if (_modules != nullptr) {
 456     _modules->modules_do(f);
 457   }
 458 }
 459 
 460 void ClassLoaderData::packages_do(void f(PackageEntry*)) {
 461   assert_locked_or_safepoint(Module_lock);
 462   if (_packages != nullptr) {
 463     _packages->packages_do(f);
 464   }
 465 }
 466 
 467 void ClassLoaderData::record_dependency(const Klass* k) {
 468   assert(k != nullptr, "invariant");
 469 
 470   ClassLoaderData * const from_cld = this;
 471   ClassLoaderData * const to_cld = k->class_loader_data();
 472 
 473   // Do not need to record dependency if the dependency is to a class whose
 474   // class loader data is never freed.  (i.e. the dependency's class loader
 475   // is one of the three builtin class loaders and the dependency's class
 476   // loader data has a ClassLoader holder, not a Class holder.)
 477   if (to_cld->is_permanent_class_loader_data()) {
 478     return;
 479   }
 480 
 481   oop to;
 482   if (to_cld->has_class_mirror_holder()) {
 483     // Just return if a non-strong hidden class class is attempting to record a dependency
 484     // to itself.  (Note that every non-strong hidden class has its own unique class
 485     // loader data.)
 486     if (to_cld == from_cld) {
 487       return;
 488     }
 489     // Hidden class dependencies are through the mirror.
 490     to = k->java_mirror();
 491   } else {
 492     to = to_cld->class_loader();
 493     oop from = from_cld->class_loader();
 494 
 495     // Just return if this dependency is to a class with the same or a parent
 496     // class_loader.
 497     if (from == to || java_lang_ClassLoader::isAncestor(from, to)) {
 498       return; // this class loader is in the parent list, no need to add it.
 499     }
 500   }
 501 
 502   // It's a dependency we won't find through GC, add it.
 503   if (!_handles.contains(to)) {
 504     NOT_PRODUCT(Atomic::inc(&_dependency_count));
 505     LogTarget(Trace, class, loader, data) lt;
 506     if (lt.is_enabled()) {
 507       ResourceMark rm;
 508       LogStream ls(lt);
 509       ls.print("adding dependency from ");
 510       print_value_on(&ls);
 511       ls.print(" to ");
 512       to_cld->print_value_on(&ls);
 513       ls.cr();
 514     }
 515     Handle dependency(Thread::current(), to);
 516     add_handle(dependency);
 517     // Added a potentially young gen oop to the ClassLoaderData
 518     record_modified_oops();
 519   }
 520 }
 521 
 522 void ClassLoaderData::add_class(Klass* k, bool publicize /* true */) {
 523   {
 524     MutexLocker ml(metaspace_lock(), Mutex::_no_safepoint_check_flag);
 525     Klass* old_value = _klasses;
 526     k->set_next_link(old_value);
 527     // Link the new item into the list, making sure the linked class is stable
 528     // since the list can be walked without a lock
 529     Atomic::release_store(&_klasses, k);
 530     if (k->is_array_klass()) {
 531       ClassLoaderDataGraph::inc_array_classes(1);
 532     } else {
 533       ClassLoaderDataGraph::inc_instance_classes(1);
 534     }
 535   }
 536 
 537   if (publicize) {
 538     LogTarget(Trace, class, loader, data) lt;
 539     if (lt.is_enabled()) {
 540       ResourceMark rm;
 541       LogStream ls(lt);
 542       ls.print("Adding k: " PTR_FORMAT " %s to ", p2i(k), k->external_name());
 543       print_value_on(&ls);
 544       ls.cr();
 545     }
 546   }
 547 }
 548 
 549 void ClassLoaderData::initialize_holder(Handle loader_or_mirror) {
 550   if (loader_or_mirror() != nullptr) {
 551     assert(_holder.is_null(), "never replace holders");
 552     _holder = WeakHandle(Universe::vm_weak(), loader_or_mirror);
 553   }
 554 }
 555 
 556 // Remove a klass from the _klasses list for scratch_class during redefinition
 557 // or parsed class in the case of an error.
 558 void ClassLoaderData::remove_class(Klass* scratch_class) {
 559   assert_locked_or_safepoint(ClassLoaderDataGraph_lock);
 560 
 561   Klass* prev = nullptr;
 562   for (Klass* k = _klasses; k != nullptr; k = k->next_link()) {
 563     if (k == scratch_class) {
 564       if (prev == nullptr) {
 565         _klasses = k->next_link();
 566       } else {
 567         Klass* next = k->next_link();
 568         prev->set_next_link(next);
 569       }
 570 
 571       if (k->is_array_klass()) {
 572         ClassLoaderDataGraph::dec_array_classes(1);
 573       } else {
 574         ClassLoaderDataGraph::dec_instance_classes(1);
 575       }
 576 
 577       return;
 578     }
 579     prev = k;
 580     assert(k != k->next_link(), "no loops!");
 581   }
 582   ShouldNotReachHere();   // should have found this class!!
 583 }
 584 
 585 void ClassLoaderData::unload() {
 586   _unloading = true;
 587 
 588   LogTarget(Trace, class, loader, data) lt;
 589   if (lt.is_enabled()) {
 590     ResourceMark rm;
 591     LogStream ls(lt);
 592     ls.print("unload");
 593     print_value_on(&ls);
 594     ls.cr();
 595   }
 596 
 597   // Some items on the _deallocate_list need to free their C heap structures
 598   // if they are not already on the _klasses list.
 599   free_deallocate_list_C_heap_structures();
 600 
 601   // Clean up class dependencies and tell serviceability tools
 602   // these classes are unloading.  Must be called
 603   // after erroneous classes are released.
 604   classes_do(InstanceKlass::unload_class);
 605 
 606   // Method::clear_jmethod_ids only sets the jmethod_ids to null without
 607   // releasing the memory for related JNIMethodBlocks and JNIMethodBlockNodes.
 608   // This is done intentionally because native code (e.g. JVMTI agent) holding
 609   // jmethod_ids may access them after the associated classes and class loader
 610   // are unloaded. The Java Native Interface Specification says "method ID
 611   // does not prevent the VM from unloading the class from which the ID has
 612   // been derived. After the class is unloaded, the method or field ID becomes
 613   // invalid". In real world usages, the native code may rely on jmethod_ids
 614   // being null after class unloading. Hence, it is unsafe to free the memory
 615   // from the VM side without knowing when native code is going to stop using
 616   // them.
 617   if (_jmethod_ids != nullptr) {
 618     Method::clear_jmethod_ids(this);
 619   }
 620 }
 621 
 622 ModuleEntryTable* ClassLoaderData::modules() {
 623   // Lazily create the module entry table at first request.
 624   // Lock-free access requires load_acquire.
 625   ModuleEntryTable* modules = Atomic::load_acquire(&_modules);
 626   if (modules == nullptr) {
 627     MutexLocker m1(Module_lock);
 628     // Check if _modules got allocated while we were waiting for this lock.
 629     if ((modules = _modules) == nullptr) {
 630       modules = new ModuleEntryTable();
 631 
 632       {
 633         MutexLocker m1(metaspace_lock(), Mutex::_no_safepoint_check_flag);
 634         // Ensure _modules is stable, since it is examined without a lock
 635         Atomic::release_store(&_modules, modules);
 636       }
 637     }
 638   }
 639   return modules;
 640 }
 641 
 642 const int _boot_loader_dictionary_size    = 1009;
 643 const int _default_loader_dictionary_size = 107;
 644 
 645 Dictionary* ClassLoaderData::create_dictionary() {
 646   assert(!has_class_mirror_holder(), "class mirror holder cld does not have a dictionary");
 647   int size;
 648   if (_the_null_class_loader_data == nullptr) {
 649     size = _boot_loader_dictionary_size;
 650   } else if (class_loader()->is_a(vmClasses::reflect_DelegatingClassLoader_klass())) {
 651     size = 1;  // there's only one class in relection class loader and no initiated classes
 652   } else if (is_system_class_loader_data()) {
 653     size = _boot_loader_dictionary_size;
 654   } else {
 655     size = _default_loader_dictionary_size;
 656   }
 657   return new Dictionary(this, size);
 658 }
 659 
 660 // Tell the GC to keep this klass alive. Needed while iterating ClassLoaderDataGraph,
 661 // and any runtime code that uses klasses.
 662 oop ClassLoaderData::holder() const {
 663   // A klass that was previously considered dead can be looked up in the
 664   // CLD/SD, and its _java_mirror or _class_loader can be stored in a root
 665   // or a reachable object making it alive again. The SATB part of G1 needs
 666   // to get notified about this potential resurrection, otherwise the marking
 667   // might not find the object.
 668   if (!_holder.is_null()) {  // null class_loader
 669     return _holder.resolve();
 670   } else {
 671     return nullptr;
 672   }
 673 }
 674 
 675 // Let the GC read the holder without keeping it alive.
 676 oop ClassLoaderData::holder_no_keepalive() const {
 677   if (!_holder.is_null()) {  // null class_loader
 678     return _holder.peek();
 679   } else {
 680     return nullptr;
 681   }
 682 }
 683 
 684 // Unloading support
 685 bool ClassLoaderData::is_alive() const {
 686   bool alive = keep_alive()         // null class loader and incomplete non-strong hidden class.
 687       || (_holder.peek() != nullptr);  // and not cleaned by the GC weak handle processing.
 688 
 689   return alive;
 690 }
 691 
 692 class ReleaseKlassClosure: public KlassClosure {
 693 private:
 694   size_t  _instance_class_released;
 695   size_t  _array_class_released;
 696 public:
 697   ReleaseKlassClosure() : _instance_class_released(0), _array_class_released(0) { }
 698 
 699   size_t instance_class_released() const { return _instance_class_released; }
 700   size_t array_class_released()    const { return _array_class_released;    }
 701 
 702   void do_klass(Klass* k) {
 703     if (k->is_array_klass()) {
 704       _array_class_released ++;
 705     } else {
 706       assert(k->is_instance_klass(), "Must be");
 707       _instance_class_released ++;
 708     }
 709     k->release_C_heap_structures();
 710   }
 711 };
 712 
 713 ClassLoaderData::~ClassLoaderData() {
 714   // Release C heap structures for all the classes.
 715   ReleaseKlassClosure cl;
 716   classes_do(&cl);
 717 
 718   ClassLoaderDataGraph::dec_array_classes(cl.array_class_released());
 719   ClassLoaderDataGraph::dec_instance_classes(cl.instance_class_released());
 720 
 721   // Release the WeakHandle
 722   _holder.release(Universe::vm_weak());
 723 
 724   // Release C heap allocated hashtable for all the packages.
 725   if (_packages != nullptr) {
 726     // Destroy the table itself
 727     delete _packages;
 728     _packages = nullptr;
 729   }
 730 
 731   // Release C heap allocated hashtable for all the modules.
 732   if (_modules != nullptr) {
 733     // Destroy the table itself
 734     delete _modules;
 735     _modules = nullptr;
 736   }
 737 
 738   // Release C heap allocated hashtable for the dictionary
 739   if (_dictionary != nullptr) {
 740     // Destroy the table itself
 741     delete _dictionary;
 742     _dictionary = nullptr;
 743   }
 744 
 745   if (_unnamed_module != nullptr) {
 746     delete _unnamed_module;
 747     _unnamed_module = nullptr;
 748   }
 749 
 750   // release the metaspace
 751   ClassLoaderMetaspace *m = _metaspace;
 752   if (m != nullptr) {
 753     _metaspace = nullptr;
 754     delete m;
 755   }
 756 
 757   // Delete lock
 758   delete _metaspace_lock;
 759 
 760   // Delete free list
 761   if (_deallocate_list != nullptr) {
 762     delete _deallocate_list;
 763   }
 764 
 765   // Decrement refcounts of Symbols if created.
 766   if (_name != nullptr) {
 767     _name->decrement_refcount();
 768   }
 769   if (_name_and_id != nullptr) {
 770     _name_and_id->decrement_refcount();
 771   }
 772 }
 773 
 774 // Returns true if this class loader data is for the app class loader
 775 // or a user defined system class loader.  (Note that the class loader
 776 // data may have a Class holder.)
 777 bool ClassLoaderData::is_system_class_loader_data() const {
 778   return SystemDictionary::is_system_class_loader(class_loader());
 779 }
 780 
 781 // Returns true if this class loader data is for the platform class loader.
 782 // (Note that the class loader data may have a Class holder.)
 783 bool ClassLoaderData::is_platform_class_loader_data() const {
 784   return SystemDictionary::is_platform_class_loader(class_loader());
 785 }
 786 
 787 // Returns true if the class loader for this class loader data is one of
 788 // the 3 builtin (boot application/system or platform) class loaders,
 789 // including a user-defined system class loader.  Note that if the class
 790 // loader data is for a non-strong hidden class then it may
 791 // get freed by a GC even if its class loader is one of these loaders.
 792 bool ClassLoaderData::is_builtin_class_loader_data() const {
 793   return (is_boot_class_loader_data() ||
 794           SystemDictionary::is_system_class_loader(class_loader()) ||
 795           SystemDictionary::is_platform_class_loader(class_loader()));
 796 }
 797 
 798 // Returns true if this class loader data is a class loader data
 799 // that is not ever freed by a GC.  It must be the CLD for one of the builtin
 800 // class loaders and not the CLD for a non-strong hidden class.
 801 bool ClassLoaderData::is_permanent_class_loader_data() const {
 802   return is_builtin_class_loader_data() && !has_class_mirror_holder();
 803 }
 804 
 805 ClassLoaderMetaspace* ClassLoaderData::metaspace_non_null() {
 806   // If the metaspace has not been allocated, create a new one.  Might want
 807   // to create smaller arena for Reflection class loaders also.
 808   // The reason for the delayed allocation is because some class loaders are
 809   // simply for delegating with no metadata of their own.
 810   // Lock-free access requires load_acquire.
 811   ClassLoaderMetaspace* metaspace = Atomic::load_acquire(&_metaspace);
 812   if (metaspace == nullptr) {
 813     MutexLocker ml(_metaspace_lock,  Mutex::_no_safepoint_check_flag);
 814     // Check if _metaspace got allocated while we were waiting for this lock.
 815     if ((metaspace = _metaspace) == nullptr) {
 816       if (this == the_null_class_loader_data()) {
 817         assert (class_loader() == nullptr, "Must be");
 818         metaspace = new ClassLoaderMetaspace(_metaspace_lock, Metaspace::BootMetaspaceType);
 819       } else if (has_class_mirror_holder()) {
 820         metaspace = new ClassLoaderMetaspace(_metaspace_lock, Metaspace::ClassMirrorHolderMetaspaceType);
 821       } else if (class_loader()->is_a(vmClasses::reflect_DelegatingClassLoader_klass())) {
 822         metaspace = new ClassLoaderMetaspace(_metaspace_lock, Metaspace::ReflectionMetaspaceType);
 823       } else {
 824         metaspace = new ClassLoaderMetaspace(_metaspace_lock, Metaspace::StandardMetaspaceType);
 825       }
 826       // Ensure _metaspace is stable, since it is examined without a lock
 827       Atomic::release_store(&_metaspace, metaspace);
 828     }
 829   }
 830   return metaspace;
 831 }
 832 
 833 OopHandle ClassLoaderData::add_handle(Handle h) {
 834   MutexLocker ml(metaspace_lock(),  Mutex::_no_safepoint_check_flag);
 835   record_modified_oops();
 836   return _handles.add(h());
 837 }
 838 
 839 void ClassLoaderData::remove_handle(OopHandle h) {
 840   assert(!is_unloading(), "Do not remove a handle for a CLD that is unloading");
 841   oop* ptr = h.ptr_raw();
 842   if (ptr != nullptr) {
 843     assert(_handles.owner_of(ptr), "Got unexpected handle " PTR_FORMAT, p2i(ptr));
 844     NativeAccess<>::oop_store(ptr, oop(nullptr));
 845   }
 846 }
 847 
 848 void ClassLoaderData::init_handle_locked(OopHandle& dest, Handle h) {
 849   MutexLocker ml(metaspace_lock(),  Mutex::_no_safepoint_check_flag);
 850   if (dest.resolve() != nullptr) {
 851     return;
 852   } else {
 853     record_modified_oops();
 854     dest = _handles.add(h());
 855   }
 856 }
 857 
 858 // Add this metadata pointer to be freed when it's safe.  This is only during
 859 // a safepoint which checks if handles point to this metadata field.
 860 void ClassLoaderData::add_to_deallocate_list(Metadata* m) {
 861   // Metadata in shared region isn't deleted.
 862   if (!m->is_shared()) {
 863     MutexLocker ml(metaspace_lock(),  Mutex::_no_safepoint_check_flag);
 864     if (_deallocate_list == nullptr) {
 865       _deallocate_list = new (mtClass) GrowableArray<Metadata*>(100, mtClass);
 866     }
 867     _deallocate_list->append_if_missing(m);
 868     ResourceMark rm;
 869     log_debug(class, loader, data)("deallocate added for %s", m->print_value_string());
 870     ClassLoaderDataGraph::set_should_clean_deallocate_lists();
 871   }
 872 }
 873 
 874 // Deallocate free metadata on the free list.  How useful the PermGen was!
 875 void ClassLoaderData::free_deallocate_list() {
 876   // This must be called at a safepoint because it depends on metadata walking at
 877   // safepoint cleanup time.
 878   assert(SafepointSynchronize::is_at_safepoint(), "only called at safepoint");
 879   assert(!is_unloading(), "only called for ClassLoaderData that are not unloading");
 880   if (_deallocate_list == nullptr) {
 881     return;
 882   }
 883   // Go backwards because this removes entries that are freed.
 884   for (int i = _deallocate_list->length() - 1; i >= 0; i--) {
 885     Metadata* m = _deallocate_list->at(i);
 886     if (!m->on_stack()) {
 887       _deallocate_list->remove_at(i);
 888       // There are only three types of metadata that we deallocate directly.
 889       // Cast them so they can be used by the template function.
 890       if (m->is_method()) {
 891         MetadataFactory::free_metadata(this, (Method*)m);
 892       } else if (m->is_constantPool()) {
 893         MetadataFactory::free_metadata(this, (ConstantPool*)m);
 894       } else if (m->is_klass()) {
 895         MetadataFactory::free_metadata(this, (InstanceKlass*)m);
 896       } else {
 897         ShouldNotReachHere();
 898       }
 899     } else {
 900       // Metadata is alive.
 901       // If scratch_class is on stack then it shouldn't be on this list!
 902       assert(!m->is_klass() || !((InstanceKlass*)m)->is_scratch_class(),
 903              "scratch classes on this list should be dead");
 904       // Also should assert that other metadata on the list was found in handles.
 905       // Some cleaning remains.
 906       ClassLoaderDataGraph::set_should_clean_deallocate_lists();
 907     }
 908   }
 909 }
 910 
 911 // This is distinct from free_deallocate_list.  For class loader data that are
 912 // unloading, this frees the C heap memory for items on the list, and unlinks
 913 // scratch or error classes so that unloading events aren't triggered for these
 914 // classes. The metadata is removed with the unloading metaspace.
 915 // There isn't C heap memory allocated for methods, so nothing is done for them.
 916 void ClassLoaderData::free_deallocate_list_C_heap_structures() {
 917   assert_locked_or_safepoint(ClassLoaderDataGraph_lock);
 918   assert(is_unloading(), "only called for ClassLoaderData that are unloading");
 919   if (_deallocate_list == nullptr) {
 920     return;
 921   }
 922   // Go backwards because this removes entries that are freed.
 923   for (int i = _deallocate_list->length() - 1; i >= 0; i--) {
 924     Metadata* m = _deallocate_list->at(i);
 925     _deallocate_list->remove_at(i);
 926     if (m->is_constantPool()) {
 927       ((ConstantPool*)m)->release_C_heap_structures();
 928     } else if (m->is_klass()) {
 929       InstanceKlass* ik = (InstanceKlass*)m;
 930       // also releases ik->constants() C heap memory
 931       ik->release_C_heap_structures();
 932       // Remove the class so unloading events aren't triggered for
 933       // this class (scratch or error class) in do_unloading().
 934       remove_class(ik);
 935       // But still have to remove it from the dumptime_table.
 936       SystemDictionaryShared::handle_class_unloading(ik);
 937     }
 938   }
 939 }
 940 
 941 // Caller needs ResourceMark
 942 // If the class loader's _name has not been explicitly set, the class loader's
 943 // qualified class name is returned.
 944 const char* ClassLoaderData::loader_name() const {
 945    if (_class_loader_klass == nullptr) {
 946      return BOOTSTRAP_LOADER_NAME;
 947    } else if (_name != nullptr) {
 948      return _name->as_C_string();
 949    } else {
 950      return _class_loader_klass->external_name();
 951    }
 952 }
 953 
 954 // Caller needs ResourceMark
 955 // Format of the _name_and_id is as follows:
 956 //   If the defining loader has a name explicitly set then '<loader-name>' @<id>
 957 //   If the defining loader has no name then <qualified-class-name> @<id>
 958 //   If built-in loader, then omit '@<id>' as there is only one instance.
 959 const char* ClassLoaderData::loader_name_and_id() const {
 960   if (_class_loader_klass == nullptr) {
 961     return "'" BOOTSTRAP_LOADER_NAME "'";
 962   } else if (_name_and_id != nullptr) {
 963     return _name_and_id->as_C_string();
 964   } else {
 965     // May be called in a race before _name_and_id is initialized.
 966     return _class_loader_klass->external_name();
 967   }
 968 }
 969 
 970 void ClassLoaderData::print_value_on(outputStream* out) const {
 971   if (!is_unloading() && class_loader() != nullptr) {
 972     out->print("loader data: " INTPTR_FORMAT " for instance ", p2i(this));
 973     class_loader()->print_value_on(out);  // includes loader_name_and_id() and address of class loader instance
 974   } else {
 975     // loader data: 0xsomeaddr of 'bootstrap'
 976     out->print("loader data: " INTPTR_FORMAT " of %s", p2i(this), loader_name_and_id());
 977   }
 978   if (_has_class_mirror_holder) {
 979     out->print(" has a class holder");
 980   }
 981 }
 982 
 983 void ClassLoaderData::print_value() const { print_value_on(tty); }
 984 
 985 #ifndef PRODUCT
 986 class PrintKlassClosure: public KlassClosure {
 987   outputStream* _out;
 988 public:
 989   PrintKlassClosure(outputStream* out): _out(out) { }
 990 
 991   void do_klass(Klass* k) {
 992     ResourceMark rm;
 993     _out->print("%s,", k->external_name());
 994   }
 995 };
 996 
 997 void ClassLoaderData::print_on(outputStream* out) const {
 998   ResourceMark rm;
 999   out->print_cr("ClassLoaderData(" INTPTR_FORMAT ")", p2i(this));
1000   out->print_cr(" - name                %s", loader_name_and_id());
1001   if (!_holder.is_null()) {
1002     out->print   (" - holder              ");
1003     _holder.print_on(out);
1004     out->print_cr("");
1005   }
1006   out->print_cr(" - class loader        " INTPTR_FORMAT, p2i(_class_loader.ptr_raw()));
1007   out->print_cr(" - metaspace           " INTPTR_FORMAT, p2i(_metaspace));
1008   out->print_cr(" - unloading           %s", _unloading ? "true" : "false");
1009   out->print_cr(" - class mirror holder %s", _has_class_mirror_holder ? "true" : "false");
1010   out->print_cr(" - modified oops       %s", _modified_oops ? "true" : "false");
1011   out->print_cr(" - keep alive          %d", _keep_alive);
1012   out->print   (" - claim               ");
1013   switch(_claim) {
1014     case _claim_none:                       out->print_cr("none"); break;
1015     case _claim_finalizable:                out->print_cr("finalizable"); break;
1016     case _claim_strong:                     out->print_cr("strong"); break;
1017     case _claim_stw_fullgc_mark:            out->print_cr("stw full gc mark"); break;
1018     case _claim_stw_fullgc_adjust:          out->print_cr("stw full gc adjust"); break;
1019     case _claim_other:                      out->print_cr("other"); break;
1020     case _claim_other | _claim_finalizable: out->print_cr("other and finalizable"); break;
1021     case _claim_other | _claim_strong:      out->print_cr("other and strong"); break;
1022     default:                                ShouldNotReachHere();
1023   }
1024   out->print_cr(" - handles             %d", _handles.count());
1025   out->print_cr(" - dependency count    %d", _dependency_count);
1026   out->print   (" - klasses             { ");
1027   if (Verbose) {
1028     PrintKlassClosure closure(out);
1029     ((ClassLoaderData*)this)->classes_do(&closure);
1030   } else {
1031      out->print("...");
1032   }
1033   out->print_cr(" }");
1034   out->print_cr(" - packages            " INTPTR_FORMAT, p2i(_packages));
1035   out->print_cr(" - module              " INTPTR_FORMAT, p2i(_modules));
1036   out->print_cr(" - unnamed module      " INTPTR_FORMAT, p2i(_unnamed_module));
1037   if (_dictionary != nullptr) {
1038     out->print   (" - dictionary          " INTPTR_FORMAT " ", p2i(_dictionary));
1039     _dictionary->print_size(out);
1040   } else {
1041     out->print_cr(" - dictionary          " INTPTR_FORMAT, p2i(_dictionary));
1042   }
1043   if (_jmethod_ids != nullptr) {
1044     out->print   (" - jmethod count       ");
1045     Method::print_jmethod_ids_count(this, out);
1046     out->print_cr("");
1047   }
1048   out->print_cr(" - deallocate list     " INTPTR_FORMAT, p2i(_deallocate_list));
1049   out->print_cr(" - next CLD            " INTPTR_FORMAT, p2i(_next));
1050 }
1051 #endif // PRODUCT
1052 
1053 void ClassLoaderData::print() const { print_on(tty); }
1054 
1055 class VerifyHandleOops : public OopClosure {
1056   VerifyOopClosure vc;
1057  public:
1058   virtual void do_oop(oop* p) {
1059     if (p != nullptr && *p != nullptr) {
1060       oop o = *p;
1061       if (!java_lang_Class::is_instance(o)) {
1062         // is_instance will assert for an invalid oop.
1063         // Walk the resolved_references array and other assorted oops in the
1064         // CLD::_handles field.  The mirror oops are followed by other heap roots.
1065         o->oop_iterate(&vc);
1066       }
1067     }
1068   }
1069   virtual void do_oop(narrowOop* o) { ShouldNotReachHere(); }
1070 };
1071 
1072 void ClassLoaderData::verify() {
1073   assert_locked_or_safepoint(_metaspace_lock);
1074   oop cl = class_loader();
1075 
1076   guarantee(this == class_loader_data(cl) || has_class_mirror_holder(), "Must be the same");
1077   guarantee(cl != nullptr || this == ClassLoaderData::the_null_class_loader_data() || has_class_mirror_holder(), "must be");
1078 
1079   // Verify the integrity of the allocated space.
1080 #ifdef ASSERT
1081   if (metaspace_or_null() != nullptr) {
1082     metaspace_or_null()->verify();
1083   }
1084 #endif
1085 
1086   for (Klass* k = _klasses; k != nullptr; k = k->next_link()) {
1087     guarantee(k->class_loader_data() == this, "Must be the same");
1088     k->verify();
1089     assert(k != k->next_link(), "no loops!");
1090   }
1091 
1092   if (_modules != nullptr) {
1093     _modules->verify();
1094   }
1095 
1096   if (_deallocate_list != nullptr) {
1097     for (int i = _deallocate_list->length() - 1; i >= 0; i--) {
1098       Metadata* m = _deallocate_list->at(i);
1099       if (m->is_klass()) {
1100         ((Klass*)m)->verify();
1101       }
1102     }
1103   }
1104 
1105   // Check the oops in the handles area
1106   VerifyHandleOops vho;
1107   oops_do(&vho, _claim_none, false);
1108 }
1109 
1110 bool ClassLoaderData::contains_klass(Klass* klass) {
1111   // Lock-free access requires load_acquire
1112   for (Klass* k = Atomic::load_acquire(&_klasses); k != nullptr; k = k->next_link()) {
1113     if (k == klass) return true;
1114   }
1115   return false;
1116 }