1 /*
   2  * Copyright (c) 2012, 2015, 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 // extension, 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.hpp"
  51 #include "classfile/classLoaderData.inline.hpp"
  52 #include "classfile/javaClasses.hpp"
  53 #include "classfile/metadataOnStackMark.hpp"
  54 #include "classfile/systemDictionary.hpp"
  55 #include "code/codeCache.hpp"
  56 #include "gc/shared/gcLocker.hpp"
  57 #include "memory/metadataFactory.hpp"
  58 #include "memory/metaspaceShared.hpp"
  59 #include "memory/oopFactory.hpp"
  60 #include "oops/objArrayOop.inline.hpp"
  61 #include "oops/oop.inline.hpp"
  62 #include "runtime/atomic.inline.hpp"
  63 #include "runtime/jniHandles.hpp"
  64 #include "runtime/mutex.hpp"
  65 #include "runtime/safepoint.hpp"
  66 #include "runtime/synchronizer.hpp"
  67 #include "utilities/growableArray.hpp"
  68 #include "utilities/macros.hpp"
  69 #include "utilities/ostream.hpp"
  70 #if INCLUDE_TRACE
  71 #include "trace/tracing.hpp"
  72 #endif
  73 
  74 ClassLoaderData * ClassLoaderData::_the_null_class_loader_data = NULL;
  75 
  76 ClassLoaderData::ClassLoaderData(Handle h_class_loader, bool is_anonymous, Dependencies dependencies) :
  77   _class_loader(h_class_loader()),
  78   _is_anonymous(is_anonymous),
  79   // An anonymous class loader data doesn't have anything to keep
  80   // it from being unloaded during parsing of the anonymous class.
  81   // The null-class-loader should always be kept alive.
  82   _keep_alive(is_anonymous || h_class_loader.is_null()),
  83   _metaspace(NULL), _unloading(false), _klasses(NULL),
  84   _claimed(0), _jmethod_ids(NULL), _handles(NULL), _deallocate_list(NULL),
  85   _next(NULL), _dependencies(dependencies), _shared_class_loader_id(-1),
  86   _metaspace_lock(new Mutex(Monitor::leaf+1, "Metaspace allocation lock", true,
  87                             Monitor::_safepoint_check_never)) {
  88     // empty
  89 }
  90 
  91 void ClassLoaderData::init_dependencies(TRAPS) {
  92   assert(!Universe::is_fully_initialized(), "should only be called when initializing");
  93   assert(is_the_null_class_loader_data(), "should only call this for the null class loader");
  94   _dependencies.init(CHECK);
  95 }
  96 
  97 void ClassLoaderData::Dependencies::init(TRAPS) {
  98   // Create empty dependencies array to add to. CMS requires this to be
  99   // an oop so that it can track additions via card marks.  We think.
 100   _list_head = oopFactory::new_objectArray(2, CHECK);
 101 }
 102 
 103 bool ClassLoaderData::claim() {
 104   if (_claimed == 1) {
 105     return false;
 106   }
 107 
 108   return (int) Atomic::cmpxchg(1, &_claimed, 0) == 0;
 109 }
 110 
 111 void ClassLoaderData::oops_do(OopClosure* f, KlassClosure* klass_closure, bool must_claim) {
 112   if (must_claim && !claim()) {
 113     return;
 114   }
 115 
 116   f->do_oop(&_class_loader);
 117   _dependencies.oops_do(f);
 118   _handles->oops_do(f);
 119   if (klass_closure != NULL) {
 120     classes_do(klass_closure);
 121   }
 122 }
 123 
 124 void ClassLoaderData::Dependencies::oops_do(OopClosure* f) {
 125   f->do_oop((oop*)&_list_head);
 126 }
 127 
 128 void ClassLoaderData::classes_do(KlassClosure* klass_closure) {
 129   for (Klass* k = _klasses; k != NULL; k = k->next_link()) {
 130     klass_closure->do_klass(k);
 131     assert(k != k->next_link(), "no loops!");
 132   }
 133 }
 134 
 135 void ClassLoaderData::classes_do(void f(Klass * const)) {
 136   for (Klass* k = _klasses; k != NULL; k = k->next_link()) {
 137     f(k);
 138   }
 139 }
 140 
 141 void ClassLoaderData::methods_do(void f(Method*)) {
 142   for (Klass* k = _klasses; k != NULL; k = k->next_link()) {
 143     if (k->is_instance_klass()) {
 144       InstanceKlass::cast(k)->methods_do(f);
 145     }
 146   }
 147 }
 148 
 149 void ClassLoaderData::loaded_classes_do(KlassClosure* klass_closure) {
 150   // Lock to avoid classes being modified/added/removed during iteration
 151   MutexLockerEx ml(metaspace_lock(),  Mutex::_no_safepoint_check_flag);
 152   for (Klass* k = _klasses; k != NULL; k = k->next_link()) {
 153     // Do not filter ArrayKlass oops here...
 154     if (k->is_array_klass() || (k->is_instance_klass() && InstanceKlass::cast(k)->is_loaded())) {
 155       klass_closure->do_klass(k);
 156     }
 157   }
 158 }
 159 
 160 void ClassLoaderData::classes_do(void f(InstanceKlass*)) {
 161   for (Klass* k = _klasses; k != NULL; k = k->next_link()) {
 162     if (k->is_instance_klass()) {
 163       f(InstanceKlass::cast(k));
 164     }
 165     assert(k != k->next_link(), "no loops!");
 166   }
 167 }
 168 
 169 void ClassLoaderData::record_dependency(const Klass* k, TRAPS) {
 170   assert(k != NULL, "invariant");
 171 
 172   ClassLoaderData * const from_cld = this;
 173   ClassLoaderData * const to_cld = k->class_loader_data();
 174 
 175   // Dependency to the null class loader data doesn't need to be recorded
 176   // because the null class loader data never goes away.
 177   if (to_cld->is_the_null_class_loader_data()) {
 178     return;
 179   }
 180 
 181   oop to;
 182   if (to_cld->is_anonymous()) {
 183     // Anonymous class dependencies are through the mirror.
 184     to = k->java_mirror();
 185   } else {
 186     to = to_cld->class_loader();
 187 
 188     // If from_cld is anonymous, even if it's class_loader is a parent of 'to'
 189     // we still have to add it.  The class_loader won't keep from_cld alive.
 190     if (!from_cld->is_anonymous()) {
 191       // Check that this dependency isn't from the same or parent class_loader
 192       oop from = from_cld->class_loader();
 193 
 194       oop curr = from;
 195       while (curr != NULL) {
 196         if (curr == to) {
 197           return; // this class loader is in the parent list, no need to add it.
 198         }
 199         curr = java_lang_ClassLoader::parent(curr);
 200       }
 201     }
 202   }
 203 
 204   // It's a dependency we won't find through GC, add it. This is relatively rare
 205   // Must handle over GC point.
 206   Handle dependency(THREAD, to);
 207   from_cld->_dependencies.add(dependency, CHECK);
 208 }
 209 
 210 
 211 void ClassLoaderData::Dependencies::add(Handle dependency, TRAPS) {
 212   // Check first if this dependency is already in the list.
 213   // Save a pointer to the last to add to under the lock.
 214   objArrayOop ok = _list_head;
 215   objArrayOop last = NULL;
 216   while (ok != NULL) {
 217     last = ok;
 218     if (ok->obj_at(0) == dependency()) {
 219       // Don't need to add it
 220       return;
 221     }
 222     ok = (objArrayOop)ok->obj_at(1);
 223   }
 224 
 225   // Must handle over GC points
 226   assert (last != NULL, "dependencies should be initialized");
 227   objArrayHandle last_handle(THREAD, last);
 228 
 229   // Create a new dependency node with fields for (class_loader or mirror, next)
 230   objArrayOop deps = oopFactory::new_objectArray(2, CHECK);
 231   deps->obj_at_put(0, dependency());
 232 
 233   // Must handle over GC points
 234   objArrayHandle new_dependency(THREAD, deps);
 235 
 236   // Add the dependency under lock
 237   locked_add(last_handle, new_dependency, THREAD);
 238 }
 239 
 240 void ClassLoaderData::Dependencies::locked_add(objArrayHandle last_handle,
 241                                                objArrayHandle new_dependency,
 242                                                Thread* THREAD) {
 243 
 244   // Have to lock and put the new dependency on the end of the dependency
 245   // array so the card mark for CMS sees that this dependency is new.
 246   // Can probably do this lock free with some effort.
 247   ObjectLocker ol(Handle(THREAD, _list_head), THREAD);
 248 
 249   oop loader_or_mirror = new_dependency->obj_at(0);
 250 
 251   // Since the dependencies are only added, add to the end.
 252   objArrayOop end = last_handle();
 253   objArrayOop last = NULL;
 254   while (end != NULL) {
 255     last = end;
 256     // check again if another thread added it to the end.
 257     if (end->obj_at(0) == loader_or_mirror) {
 258       // Don't need to add it
 259       return;
 260     }
 261     end = (objArrayOop)end->obj_at(1);
 262   }
 263   assert (last != NULL, "dependencies should be initialized");
 264   // fill in the first element with the oop in new_dependency.
 265   if (last->obj_at(0) == NULL) {
 266     last->obj_at_put(0, new_dependency->obj_at(0));
 267   } else {
 268     last->obj_at_put(1, new_dependency());
 269   }
 270 }
 271 
 272 void ClassLoaderDataGraph::clear_claimed_marks() {
 273   for (ClassLoaderData* cld = _head; cld != NULL; cld = cld->next()) {
 274     cld->clear_claimed();
 275   }
 276 }
 277 
 278 void ClassLoaderData::add_class(Klass* k, bool publicize /* true */) {
 279   {
 280     MutexLockerEx ml(metaspace_lock(), Mutex::_no_safepoint_check_flag);
 281     Klass* old_value = _klasses;
 282     k->set_next_link(old_value);
 283     // Make sure linked class is stable, since the class list is walked without a lock
 284     OrderAccess::storestore();
 285     // link the new item into the list
 286     _klasses = k;
 287   }
 288 
 289   if (publicize && TraceClassLoaderData && Verbose && k->class_loader_data() != NULL) {
 290     ResourceMark rm;
 291     tty->print_cr("[TraceClassLoaderData] Adding k: " PTR_FORMAT " %s to CLD: "
 292                   PTR_FORMAT " loader: " PTR_FORMAT " %s",
 293                   p2i(k),
 294                   k->external_name(),
 295                   p2i(k->class_loader_data()),
 296                   p2i((void *)k->class_loader()),
 297                   loader_name());
 298   }
 299 }
 300 
 301 // This is called by InstanceKlass::deallocate_contents() to remove the
 302 // scratch_class for redefine classes.  We need a lock because there it may not
 303 // be called at a safepoint if there's an error.
 304 void ClassLoaderData::remove_class(Klass* scratch_class) {
 305   MutexLockerEx ml(metaspace_lock(),  Mutex::_no_safepoint_check_flag);
 306   Klass* prev = NULL;
 307   for (Klass* k = _klasses; k != NULL; k = k->next_link()) {
 308     if (k == scratch_class) {
 309       if (prev == NULL) {
 310         _klasses = k->next_link();
 311       } else {
 312         Klass* next = k->next_link();
 313         prev->set_next_link(next);
 314       }
 315       return;
 316     }
 317     prev = k;
 318     assert(k != k->next_link(), "no loops!");
 319   }
 320   ShouldNotReachHere();   // should have found this class!!
 321 }
 322 
 323 void ClassLoaderData::unload() {
 324   _unloading = true;
 325 
 326   // Tell serviceability tools these classes are unloading
 327   classes_do(InstanceKlass::notify_unload_class);
 328 
 329   if (TraceClassLoaderData) {
 330     ResourceMark rm;
 331     tty->print("[ClassLoaderData: unload loader data " INTPTR_FORMAT, p2i(this));
 332     tty->print(" for instance " INTPTR_FORMAT " of %s", p2i((void *)class_loader()),
 333                loader_name());
 334     if (is_anonymous()) {
 335       tty->print(" for anonymous class  " INTPTR_FORMAT " ", p2i(_klasses));
 336     }
 337     tty->print_cr("]");
 338   }
 339 }
 340 
 341 oop ClassLoaderData::keep_alive_object() const {
 342   assert(!keep_alive(), "Don't use with CLDs that are artificially kept alive");
 343   return is_anonymous() ? _klasses->java_mirror() : class_loader();
 344 }
 345 
 346 bool ClassLoaderData::is_alive(BoolObjectClosure* is_alive_closure) const {
 347   bool alive = keep_alive() // null class loader and incomplete anonymous klasses.
 348       || is_alive_closure->do_object_b(keep_alive_object());
 349 
 350   return alive;
 351 }
 352 
 353 
 354 ClassLoaderData::~ClassLoaderData() {
 355   // Release C heap structures for all the classes.
 356   classes_do(InstanceKlass::release_C_heap_structures);
 357 
 358   Metaspace *m = _metaspace;
 359   if (m != NULL) {
 360     _metaspace = NULL;
 361     // release the metaspace
 362     delete m;
 363     // release the handles
 364     if (_handles != NULL) {
 365       JNIHandleBlock::release_block(_handles);
 366       _handles = NULL;
 367     }
 368   }
 369 
 370   // Clear all the JNI handles for methods
 371   // These aren't deallocated and are going to look like a leak, but that's
 372   // needed because we can't really get rid of jmethodIDs because we don't
 373   // know when native code is going to stop using them.  The spec says that
 374   // they're "invalid" but existing programs likely rely on their being
 375   // NULL after class unloading.
 376   if (_jmethod_ids != NULL) {
 377     Method::clear_jmethod_ids(this);
 378   }
 379   // Delete lock
 380   delete _metaspace_lock;
 381 
 382   // Delete free list
 383   if (_deallocate_list != NULL) {
 384     delete _deallocate_list;
 385   }
 386 }
 387 
 388 /**
 389  * Returns true if this class loader data is for the extension class loader.
 390  */
 391 bool ClassLoaderData::is_ext_class_loader_data() const {
 392   return SystemDictionary::is_ext_class_loader(class_loader());
 393 }
 394 
 395 Metaspace* ClassLoaderData::metaspace_non_null() {
 396   assert(!DumpSharedSpaces, "wrong metaspace!");
 397   // If the metaspace has not been allocated, create a new one.  Might want
 398   // to create smaller arena for Reflection class loaders also.
 399   // The reason for the delayed allocation is because some class loaders are
 400   // simply for delegating with no metadata of their own.
 401   if (_metaspace == NULL) {
 402     MutexLockerEx ml(metaspace_lock(),  Mutex::_no_safepoint_check_flag);
 403     // Check again if metaspace has been allocated while we were getting this lock.
 404     if (_metaspace != NULL) {
 405       return _metaspace;
 406     }
 407     if (this == the_null_class_loader_data()) {
 408       assert (class_loader() == NULL, "Must be");
 409       set_metaspace(new Metaspace(_metaspace_lock, Metaspace::BootMetaspaceType));
 410     } else if (is_anonymous()) {
 411       if (TraceClassLoaderData && Verbose && class_loader() != NULL) {
 412         tty->print_cr("is_anonymous: %s", class_loader()->klass()->internal_name());
 413       }
 414       set_metaspace(new Metaspace(_metaspace_lock, Metaspace::AnonymousMetaspaceType));
 415     } else if (class_loader()->is_a(SystemDictionary::reflect_DelegatingClassLoader_klass())) {
 416       if (TraceClassLoaderData && Verbose && class_loader() != NULL) {
 417         tty->print_cr("is_reflection: %s", class_loader()->klass()->internal_name());
 418       }
 419       set_metaspace(new Metaspace(_metaspace_lock, Metaspace::ReflectionMetaspaceType));
 420     } else {
 421       set_metaspace(new Metaspace(_metaspace_lock, Metaspace::StandardMetaspaceType));
 422     }
 423   }
 424   return _metaspace;
 425 }
 426 
 427 JNIHandleBlock* ClassLoaderData::handles() const           { return _handles; }
 428 void ClassLoaderData::set_handles(JNIHandleBlock* handles) { _handles = handles; }
 429 
 430 jobject ClassLoaderData::add_handle(Handle h) {
 431   MutexLockerEx ml(metaspace_lock(),  Mutex::_no_safepoint_check_flag);
 432   if (handles() == NULL) {
 433     set_handles(JNIHandleBlock::allocate_block());
 434   }
 435   return handles()->allocate_handle(h());
 436 }
 437 
 438 // Add this metadata pointer to be freed when it's safe.  This is only during
 439 // class unloading because Handles might point to this metadata field.
 440 void ClassLoaderData::add_to_deallocate_list(Metadata* m) {
 441   // Metadata in shared region isn't deleted.
 442   if (!m->is_shared()) {
 443     MutexLockerEx ml(metaspace_lock(),  Mutex::_no_safepoint_check_flag);
 444     if (_deallocate_list == NULL) {
 445       _deallocate_list = new (ResourceObj::C_HEAP, mtClass) GrowableArray<Metadata*>(100, true);
 446     }
 447     _deallocate_list->append_if_missing(m);
 448   }
 449 }
 450 
 451 // Deallocate free metadata on the free list.  How useful the PermGen was!
 452 void ClassLoaderData::free_deallocate_list() {
 453   // Don't need lock, at safepoint
 454   assert(SafepointSynchronize::is_at_safepoint(), "only called at safepoint");
 455   if (_deallocate_list == NULL) {
 456     return;
 457   }
 458   // Go backwards because this removes entries that are freed.
 459   for (int i = _deallocate_list->length() - 1; i >= 0; i--) {
 460     Metadata* m = _deallocate_list->at(i);
 461     if (!m->on_stack()) {
 462       _deallocate_list->remove_at(i);
 463       // There are only three types of metadata that we deallocate directly.
 464       // Cast them so they can be used by the template function.
 465       if (m->is_method()) {
 466         MetadataFactory::free_metadata(this, (Method*)m);
 467       } else if (m->is_constantPool()) {
 468         MetadataFactory::free_metadata(this, (ConstantPool*)m);
 469       } else if (m->is_klass()) {
 470         MetadataFactory::free_metadata(this, (InstanceKlass*)m);
 471       } else {
 472         ShouldNotReachHere();
 473       }
 474     } else {
 475       // Metadata is alive.
 476       // If scratch_class is on stack then it shouldn't be on this list!
 477       assert(!m->is_klass() || !((InstanceKlass*)m)->is_scratch_class(),
 478              "scratch classes on this list should be dead");
 479       // Also should assert that other metadata on the list was found in handles.
 480     }
 481   }
 482 }
 483 
 484 // These anonymous class loaders are to contain classes used for JSR292
 485 ClassLoaderData* ClassLoaderData::anonymous_class_loader_data(oop loader, TRAPS) {
 486   // Add a new class loader data to the graph.
 487   return ClassLoaderDataGraph::add(loader, true, THREAD);
 488 }
 489 
 490 const char* ClassLoaderData::loader_name() {
 491   // Handles null class loader
 492   return SystemDictionary::loader_name(class_loader());
 493 }
 494 
 495 #ifndef PRODUCT
 496 // Define to dump klasses
 497 #undef CLD_DUMP_KLASSES
 498 
 499 void ClassLoaderData::dump(outputStream * const out) {
 500   ResourceMark rm;
 501   out->print("ClassLoaderData CLD: " PTR_FORMAT ", loader: " PTR_FORMAT ", loader_klass: " PTR_FORMAT " %s {",
 502       p2i(this), p2i((void *)class_loader()),
 503       p2i(class_loader() != NULL ? class_loader()->klass() : NULL), loader_name());
 504   if (claimed()) out->print(" claimed ");
 505   if (is_unloading()) out->print(" unloading ");
 506   out->print(" handles " INTPTR_FORMAT, p2i(handles()));
 507   out->cr();
 508   if (metaspace_or_null() != NULL) {
 509     out->print_cr("metaspace: " INTPTR_FORMAT, p2i(metaspace_or_null()));
 510     metaspace_or_null()->dump(out);
 511   } else {
 512     out->print_cr("metaspace: NULL");
 513   }
 514 
 515 #ifdef CLD_DUMP_KLASSES
 516   if (Verbose) {
 517     ResourceMark rm;
 518     Klass* k = _klasses;
 519     while (k != NULL) {
 520       out->print_cr("klass " PTR_FORMAT ", %s, CT: %d, MUT: %d", k, k->name()->as_C_string(),
 521           k->has_modified_oops(), k->has_accumulated_modified_oops());
 522       assert(k != k->next_link(), "no loops!");
 523       k = k->next_link();
 524     }
 525   }
 526 #endif  // CLD_DUMP_KLASSES
 527 #undef CLD_DUMP_KLASSES
 528   if (_jmethod_ids != NULL) {
 529     Method::print_jmethod_ids(this, out);
 530   }
 531   out->print_cr("}");
 532 }
 533 #endif // PRODUCT
 534 
 535 void ClassLoaderData::verify() {
 536   oop cl = class_loader();
 537 
 538   guarantee(this == class_loader_data(cl) || is_anonymous(), "Must be the same");
 539   guarantee(cl != NULL || this == ClassLoaderData::the_null_class_loader_data() || is_anonymous(), "must be");
 540 
 541   // Verify the integrity of the allocated space.
 542   if (metaspace_or_null() != NULL) {
 543     metaspace_or_null()->verify();
 544   }
 545 
 546   for (Klass* k = _klasses; k != NULL; k = k->next_link()) {
 547     guarantee(k->class_loader_data() == this, "Must be the same");
 548     k->verify();
 549     assert(k != k->next_link(), "no loops!");
 550   }
 551 }
 552 
 553 bool ClassLoaderData::contains_klass(Klass* klass) {
 554   for (Klass* k = _klasses; k != NULL; k = k->next_link()) {
 555     if (k == klass) return true;
 556   }
 557   return false;
 558 }
 559 
 560 
 561 // GC root of class loader data created.
 562 ClassLoaderData* ClassLoaderDataGraph::_head = NULL;
 563 ClassLoaderData* ClassLoaderDataGraph::_unloading = NULL;
 564 ClassLoaderData* ClassLoaderDataGraph::_saved_unloading = NULL;
 565 ClassLoaderData* ClassLoaderDataGraph::_saved_head = NULL;
 566 
 567 bool ClassLoaderDataGraph::_should_purge = false;
 568 bool ClassLoaderDataGraph::_metaspace_oom = false;
 569 
 570 // Add a new class loader data node to the list.  Assign the newly created
 571 // ClassLoaderData into the java/lang/ClassLoader object as a hidden field
 572 ClassLoaderData* ClassLoaderDataGraph::add(Handle loader, bool is_anonymous, TRAPS) {
 573   // We need to allocate all the oops for the ClassLoaderData before allocating the
 574   // actual ClassLoaderData object.
 575   ClassLoaderData::Dependencies dependencies(CHECK_NULL);
 576 
 577   NoSafepointVerifier no_safepoints; // we mustn't GC until we've installed the
 578                                      // ClassLoaderData in the graph since the CLD
 579                                      // contains unhandled oops
 580 
 581   ClassLoaderData* cld = new ClassLoaderData(loader, is_anonymous, dependencies);
 582 
 583 
 584   if (!is_anonymous) {
 585     ClassLoaderData** cld_addr = java_lang_ClassLoader::loader_data_addr(loader());
 586     // First, Atomically set it
 587     ClassLoaderData* old = (ClassLoaderData*) Atomic::cmpxchg_ptr(cld, cld_addr, NULL);
 588     if (old != NULL) {
 589       delete cld;
 590       // Returns the data.
 591       return old;
 592     }
 593   }
 594 
 595   // We won the race, and therefore the task of adding the data to the list of
 596   // class loader data
 597   ClassLoaderData** list_head = &_head;
 598   ClassLoaderData* next = _head;
 599 
 600   do {
 601     cld->set_next(next);
 602     ClassLoaderData* exchanged = (ClassLoaderData*)Atomic::cmpxchg_ptr(cld, list_head, next);
 603     if (exchanged == next) {
 604       if (TraceClassLoaderData) {
 605         ResourceMark rm;
 606         tty->print("[ClassLoaderData: ");
 607         tty->print("create class loader data " INTPTR_FORMAT, p2i(cld));
 608         tty->print(" for instance " INTPTR_FORMAT " of %s", p2i((void *)cld->class_loader()),
 609                    cld->loader_name());
 610         tty->print_cr("]");
 611       }
 612       return cld;
 613     }
 614     next = exchanged;
 615   } while (true);
 616 
 617 }
 618 
 619 void ClassLoaderDataGraph::oops_do(OopClosure* f, KlassClosure* klass_closure, bool must_claim) {
 620   for (ClassLoaderData* cld = _head; cld != NULL; cld = cld->next()) {
 621     cld->oops_do(f, klass_closure, must_claim);
 622   }
 623 }
 624 
 625 void ClassLoaderDataGraph::keep_alive_oops_do(OopClosure* f, KlassClosure* klass_closure, bool must_claim) {
 626   for (ClassLoaderData* cld = _head; cld != NULL; cld = cld->next()) {
 627     if (cld->keep_alive()) {
 628       cld->oops_do(f, klass_closure, must_claim);
 629     }
 630   }
 631 }
 632 
 633 void ClassLoaderDataGraph::always_strong_oops_do(OopClosure* f, KlassClosure* klass_closure, bool must_claim) {
 634   if (ClassUnloading) {
 635     keep_alive_oops_do(f, klass_closure, must_claim);
 636   } else {
 637     oops_do(f, klass_closure, must_claim);
 638   }
 639 }
 640 
 641 void ClassLoaderDataGraph::cld_do(CLDClosure* cl) {
 642   for (ClassLoaderData* cld = _head; cl != NULL && cld != NULL; cld = cld->next()) {
 643     cl->do_cld(cld);
 644   }
 645 }
 646 
 647 void ClassLoaderDataGraph::roots_cld_do(CLDClosure* strong, CLDClosure* weak) {
 648   for (ClassLoaderData* cld = _head;  cld != NULL; cld = cld->_next) {
 649     CLDClosure* closure = cld->keep_alive() ? strong : weak;
 650     if (closure != NULL) {
 651       closure->do_cld(cld);
 652     }
 653   }
 654 }
 655 
 656 void ClassLoaderDataGraph::keep_alive_cld_do(CLDClosure* cl) {
 657   roots_cld_do(cl, NULL);
 658 }
 659 
 660 void ClassLoaderDataGraph::always_strong_cld_do(CLDClosure* cl) {
 661   if (ClassUnloading) {
 662     keep_alive_cld_do(cl);
 663   } else {
 664     cld_do(cl);
 665   }
 666 }
 667 
 668 void ClassLoaderDataGraph::classes_do(KlassClosure* klass_closure) {
 669   for (ClassLoaderData* cld = _head; cld != NULL; cld = cld->next()) {
 670     cld->classes_do(klass_closure);
 671   }
 672 }
 673 
 674 void ClassLoaderDataGraph::classes_do(void f(Klass* const)) {
 675   for (ClassLoaderData* cld = _head; cld != NULL; cld = cld->next()) {
 676     cld->classes_do(f);
 677   }
 678 }
 679 
 680 void ClassLoaderDataGraph::methods_do(void f(Method*)) {
 681   for (ClassLoaderData* cld = _head; cld != NULL; cld = cld->next()) {
 682     cld->methods_do(f);
 683   }
 684 }
 685 
 686 void ClassLoaderDataGraph::loaded_classes_do(KlassClosure* klass_closure) {
 687   for (ClassLoaderData* cld = _head; cld != NULL; cld = cld->next()) {
 688     cld->loaded_classes_do(klass_closure);
 689   }
 690 }
 691 
 692 void ClassLoaderDataGraph::classes_unloading_do(void f(Klass* const)) {
 693   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint!");
 694   // Only walk the head until any clds not purged from prior unloading
 695   // (CMS doesn't purge right away).
 696   for (ClassLoaderData* cld = _unloading; cld != _saved_unloading; cld = cld->next()) {
 697     cld->classes_do(f);
 698   }
 699 }
 700 
 701 GrowableArray<ClassLoaderData*>* ClassLoaderDataGraph::new_clds() {
 702   assert(_head == NULL || _saved_head != NULL, "remember_new_clds(true) not called?");
 703 
 704   GrowableArray<ClassLoaderData*>* array = new GrowableArray<ClassLoaderData*>();
 705 
 706   // The CLDs in [_head, _saved_head] were all added during last call to remember_new_clds(true);
 707   ClassLoaderData* curr = _head;
 708   while (curr != _saved_head) {
 709     if (!curr->claimed()) {
 710       array->push(curr);
 711 
 712       if (TraceClassLoaderData) {
 713         tty->print("[ClassLoaderData] found new CLD: ");
 714         curr->print_value_on(tty);
 715         tty->cr();
 716       }
 717     }
 718 
 719     curr = curr->_next;
 720   }
 721 
 722   return array;
 723 }
 724 
 725 bool ClassLoaderDataGraph::unload_list_contains(const void* x) {
 726   assert(SafepointSynchronize::is_at_safepoint(), "only safe to call at safepoint");
 727   for (ClassLoaderData* cld = _unloading; cld != NULL; cld = cld->next()) {
 728     if (cld->metaspace_or_null() != NULL && cld->metaspace_or_null()->contains(x)) {
 729       return true;
 730     }
 731   }
 732   return false;
 733 }
 734 
 735 #ifndef PRODUCT
 736 bool ClassLoaderDataGraph::contains_loader_data(ClassLoaderData* loader_data) {
 737   for (ClassLoaderData* data = _head; data != NULL; data = data->next()) {
 738     if (loader_data == data) {
 739       return true;
 740     }
 741   }
 742 
 743   return false;
 744 }
 745 #endif // PRODUCT
 746 
 747 
 748 // Move class loader data from main list to the unloaded list for unloading
 749 // and deallocation later.
 750 bool ClassLoaderDataGraph::do_unloading(BoolObjectClosure* is_alive_closure,
 751                                         bool clean_previous_versions) {
 752 
 753   ClassLoaderData* data = _head;
 754   ClassLoaderData* prev = NULL;
 755   bool seen_dead_loader = false;
 756 
 757   // Mark metadata seen on the stack only so we can delete unneeded entries.
 758   // Only walk all metadata, including the expensive code cache walk, for Full GC
 759   // and only if class redefinition and if there's previous versions of
 760   // Klasses to delete.
 761   bool walk_all_metadata = clean_previous_versions &&
 762                            JvmtiExport::has_redefined_a_class() &&
 763                            InstanceKlass::has_previous_versions();
 764   MetadataOnStackMark md_on_stack(walk_all_metadata);
 765 
 766   // Save previous _unloading pointer for CMS which may add to unloading list before
 767   // purging and we don't want to rewalk the previously unloaded class loader data.
 768   _saved_unloading = _unloading;
 769 
 770   data = _head;
 771   while (data != NULL) {
 772     if (data->is_alive(is_alive_closure)) {
 773       // clean metaspace
 774       if (walk_all_metadata) {
 775         data->classes_do(InstanceKlass::purge_previous_versions);
 776       }
 777       data->free_deallocate_list();
 778       prev = data;
 779       data = data->next();
 780       continue;
 781     }
 782     seen_dead_loader = true;
 783     ClassLoaderData* dead = data;
 784     dead->unload();
 785     data = data->next();
 786     // Remove from loader list.
 787     // This class loader data will no longer be found
 788     // in the ClassLoaderDataGraph.
 789     if (prev != NULL) {
 790       prev->set_next(data);
 791     } else {
 792       assert(dead == _head, "sanity check");
 793       _head = data;
 794     }
 795     dead->set_next(_unloading);
 796     _unloading = dead;
 797   }
 798 
 799   if (seen_dead_loader) {
 800     post_class_unload_events();
 801   }
 802 
 803   return seen_dead_loader;
 804 }
 805 
 806 void ClassLoaderDataGraph::purge() {
 807   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint!");
 808   ClassLoaderData* list = _unloading;
 809   _unloading = NULL;
 810   ClassLoaderData* next = list;
 811   bool classes_unloaded = false;
 812   while (next != NULL) {
 813     ClassLoaderData* purge_me = next;
 814     next = purge_me->next();
 815     delete purge_me;
 816     classes_unloaded = true;
 817   }
 818   if (classes_unloaded) {
 819     Metaspace::purge();
 820     set_metaspace_oom(false);
 821   }
 822 }
 823 
 824 void ClassLoaderDataGraph::post_class_unload_events(void) {
 825 #if INCLUDE_TRACE
 826   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint!");
 827   if (Tracing::enabled()) {
 828     if (Tracing::is_event_enabled(TraceClassUnloadEvent)) {
 829       assert(_unloading != NULL, "need class loader data unload list!");
 830       _class_unload_time = Ticks::now();
 831       classes_unloading_do(&class_unload_event);
 832     }
 833     Tracing::on_unloading_classes();
 834   }
 835 #endif
 836 }
 837 
 838 // CDS support
 839 
 840 // Global metaspaces for writing information to the shared archive.  When
 841 // application CDS is supported, we may need one per metaspace, so this
 842 // sort of looks like it.
 843 Metaspace* ClassLoaderData::_ro_metaspace = NULL;
 844 Metaspace* ClassLoaderData::_rw_metaspace = NULL;
 845 static bool _shared_metaspaces_initialized = false;
 846 
 847 // Initialize shared metaspaces (change to call from somewhere not lazily)
 848 void ClassLoaderData::initialize_shared_metaspaces() {
 849   assert(DumpSharedSpaces, "only use this for dumping shared spaces");
 850   assert(this == ClassLoaderData::the_null_class_loader_data(),
 851          "only supported for null loader data for now");
 852   assert (!_shared_metaspaces_initialized, "only initialize once");
 853   MutexLockerEx ml(metaspace_lock(),  Mutex::_no_safepoint_check_flag);
 854   _ro_metaspace = new Metaspace(_metaspace_lock, Metaspace::ROMetaspaceType);
 855   _rw_metaspace = new Metaspace(_metaspace_lock, Metaspace::ReadWriteMetaspaceType);
 856   _shared_metaspaces_initialized = true;
 857 }
 858 
 859 Metaspace* ClassLoaderData::ro_metaspace() {
 860   assert(_ro_metaspace != NULL, "should already be initialized");
 861   return _ro_metaspace;
 862 }
 863 
 864 Metaspace* ClassLoaderData::rw_metaspace() {
 865   assert(_rw_metaspace != NULL, "should already be initialized");
 866   return _rw_metaspace;
 867 }
 868 
 869 ClassLoaderDataGraphKlassIteratorAtomic::ClassLoaderDataGraphKlassIteratorAtomic()
 870     : _next_klass(NULL) {
 871   ClassLoaderData* cld = ClassLoaderDataGraph::_head;
 872   Klass* klass = NULL;
 873 
 874   // Find the first klass in the CLDG.
 875   while (cld != NULL) {
 876     klass = cld->_klasses;
 877     if (klass != NULL) {
 878       _next_klass = klass;
 879       return;
 880     }
 881     cld = cld->next();
 882   }
 883 }
 884 
 885 Klass* ClassLoaderDataGraphKlassIteratorAtomic::next_klass_in_cldg(Klass* klass) {
 886   Klass* next = klass->next_link();
 887   if (next != NULL) {
 888     return next;
 889   }
 890 
 891   // No more klasses in the current CLD. Time to find a new CLD.
 892   ClassLoaderData* cld = klass->class_loader_data();
 893   while (next == NULL) {
 894     cld = cld->next();
 895     if (cld == NULL) {
 896       break;
 897     }
 898     next = cld->_klasses;
 899   }
 900 
 901   return next;
 902 }
 903 
 904 Klass* ClassLoaderDataGraphKlassIteratorAtomic::next_klass() {
 905   Klass* head = _next_klass;
 906 
 907   while (head != NULL) {
 908     Klass* next = next_klass_in_cldg(head);
 909 
 910     Klass* old_head = (Klass*)Atomic::cmpxchg_ptr(next, &_next_klass, head);
 911 
 912     if (old_head == head) {
 913       return head; // Won the CAS.
 914     }
 915 
 916     head = old_head;
 917   }
 918 
 919   // Nothing more for the iterator to hand out.
 920   assert(head == NULL, "head is " PTR_FORMAT ", expected not null:", p2i(head));
 921   return NULL;
 922 }
 923 
 924 ClassLoaderDataGraphMetaspaceIterator::ClassLoaderDataGraphMetaspaceIterator() {
 925   _data = ClassLoaderDataGraph::_head;
 926 }
 927 
 928 ClassLoaderDataGraphMetaspaceIterator::~ClassLoaderDataGraphMetaspaceIterator() {}
 929 
 930 #ifndef PRODUCT
 931 // callable from debugger
 932 extern "C" int print_loader_data_graph() {
 933   ClassLoaderDataGraph::dump_on(tty);
 934   return 0;
 935 }
 936 
 937 void ClassLoaderDataGraph::verify() {
 938   for (ClassLoaderData* data = _head; data != NULL; data = data->next()) {
 939     data->verify();
 940   }
 941 }
 942 
 943 void ClassLoaderDataGraph::dump_on(outputStream * const out) {
 944   for (ClassLoaderData* data = _head; data != NULL; data = data->next()) {
 945     data->dump(out);
 946   }
 947   MetaspaceAux::dump(out);
 948 }
 949 #endif // PRODUCT
 950 
 951 void ClassLoaderData::print_value_on(outputStream* out) const {
 952   if (class_loader() == NULL) {
 953     out->print("NULL class_loader");
 954   } else {
 955     out->print("class loader " INTPTR_FORMAT, p2i(this));
 956     class_loader()->print_value_on(out);
 957   }
 958 }
 959 
 960 #if INCLUDE_TRACE
 961 
 962 Ticks ClassLoaderDataGraph::_class_unload_time;
 963 
 964 void ClassLoaderDataGraph::class_unload_event(Klass* const k) {
 965 
 966   // post class unload event
 967   EventClassUnload event(UNTIMED);
 968   event.set_endtime(_class_unload_time);
 969   event.set_unloadedClass(k);
 970   oop defining_class_loader = k->class_loader();
 971   event.set_definingClassLoader(defining_class_loader != NULL ?
 972                                 defining_class_loader->klass() : (Klass*)NULL);
 973   event.commit();
 974 }
 975 
 976 #endif // INCLUDE_TRACE