1 /*
   2  * Copyright (c) 2012, 2013, 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/systemDictionary.hpp"
  54 #include "code/codeCache.hpp"
  55 #include "memory/metadataFactory.hpp"
  56 #include "memory/metaspaceShared.hpp"
  57 #include "prims/jvmtiRedefineClasses.hpp"
  58 #include "runtime/jniHandles.hpp"
  59 #include "runtime/mutex.hpp"
  60 #include "runtime/safepoint.hpp"
  61 #include "runtime/synchronizer.hpp"
  62 #include "utilities/growableArray.hpp"
  63 #include "utilities/ostream.hpp"
  64 
  65 ClassLoaderData * ClassLoaderData::_the_null_class_loader_data = NULL;
  66 
  67 ClassLoaderData::ClassLoaderData(Handle h_class_loader, bool is_anonymous) :
  68   _class_loader(h_class_loader()),
  69   _is_anonymous(is_anonymous), _keep_alive(is_anonymous), // initially
  70   _metaspace(NULL), _unloading(false), _klasses(NULL),
  71   _claimed(0), _jmethod_ids(NULL), _handles(NULL), _deallocate_list(NULL),
  72   _next(NULL), _dependencies(NULL),
  73   _metaspace_lock(new Mutex(Monitor::leaf+1, "Metaspace allocation lock", true)) {
  74     // empty
  75 }
  76 
  77 void ClassLoaderData::init_dependencies(TRAPS) {
  78   // Create empty dependencies array to add to. CMS requires this to be
  79   // an oop so that it can track additions via card marks.  We think.
  80   _dependencies = (oop)oopFactory::new_objectArray(2, CHECK);
  81 }
  82 
  83 bool ClassLoaderData::claim() {
  84   if (_claimed == 1) {
  85     return false;
  86   }
  87 
  88   return (int) Atomic::cmpxchg(1, &_claimed, 0) == 0;
  89 }
  90 
  91 void ClassLoaderData::oops_do(OopClosure* f, KlassClosure* klass_closure, bool must_claim) {
  92   if (must_claim && !claim()) {
  93     return;
  94   }
  95 
  96   f->do_oop(&_class_loader);
  97   f->do_oop(&_dependencies);
  98   _handles->oops_do(f);
  99   if (klass_closure != NULL) {
 100     classes_do(klass_closure);
 101   }
 102 }
 103 
 104 void ClassLoaderData::classes_do(KlassClosure* klass_closure) {
 105   for (Klass* k = _klasses; k != NULL; k = k->next_link()) {
 106     klass_closure->do_klass(k);
 107   }
 108 }
 109 
 110 void ClassLoaderData::classes_do(void f(InstanceKlass*)) {
 111   for (Klass* k = _klasses; k != NULL; k = k->next_link()) {
 112     if (k->oop_is_instance()) {
 113       f(InstanceKlass::cast(k));
 114     }
 115   }
 116 }
 117 
 118 void ClassLoaderData::record_dependency(Klass* k, TRAPS) {
 119   ClassLoaderData * const from_cld = this;
 120   ClassLoaderData * const to_cld = k->class_loader_data();
 121 
 122   // Dependency to the null class loader data doesn't need to be recorded
 123   // because the null class loader data never goes away.
 124   if (to_cld->is_the_null_class_loader_data()) {
 125     return;
 126   }
 127 
 128   oop to;
 129   if (to_cld->is_anonymous()) {
 130     // Anonymous class dependencies are through the mirror.
 131     to = k->java_mirror();
 132   } else {
 133     to = to_cld->class_loader();
 134 
 135     // If from_cld is anonymous, even if it's class_loader is a parent of 'to'
 136     // we still have to add it.  The class_loader won't keep from_cld alive.
 137     if (!from_cld->is_anonymous()) {
 138       // Check that this dependency isn't from the same or parent class_loader
 139       oop from = from_cld->class_loader();
 140 
 141       oop curr = from;
 142       while (curr != NULL) {
 143         if (curr == to) {
 144           return; // this class loader is in the parent list, no need to add it.
 145         }
 146         curr = java_lang_ClassLoader::parent(curr);
 147       }
 148     }
 149   }
 150 
 151   // It's a dependency we won't find through GC, add it. This is relatively rare
 152   // Must handle over GC point.
 153   Handle dependency(THREAD, to);
 154   from_cld->add_dependency(dependency, CHECK);
 155 }
 156 
 157 
 158 void ClassLoaderData::add_dependency(Handle dependency, TRAPS) {
 159   // Check first if this dependency is already in the list.
 160   // Save a pointer to the last to add to under the lock.
 161   objArrayOop ok = (objArrayOop)_dependencies;
 162   objArrayOop last = NULL;
 163   while (ok != NULL) {
 164     last = ok;
 165     if (ok->obj_at(0) == dependency()) {
 166       // Don't need to add it
 167       return;
 168     }
 169     ok = (objArrayOop)ok->obj_at(1);
 170   }
 171 
 172   // Must handle over GC points
 173   assert (last != NULL, "dependencies should be initialized");
 174   objArrayHandle last_handle(THREAD, last);
 175 
 176   // Create a new dependency node with fields for (class_loader or mirror, next)
 177   objArrayOop deps = oopFactory::new_objectArray(2, CHECK);
 178   deps->obj_at_put(0, dependency());
 179 
 180   // Must handle over GC points
 181   objArrayHandle new_dependency(THREAD, deps);
 182 
 183   // Add the dependency under lock
 184   locked_add_dependency(last_handle, new_dependency);
 185 }
 186 
 187 void ClassLoaderData::locked_add_dependency(objArrayHandle last_handle,
 188                                             objArrayHandle new_dependency) {
 189 
 190   // Have to lock and put the new dependency on the end of the dependency
 191   // array so the card mark for CMS sees that this dependency is new.
 192   // Can probably do this lock free with some effort.
 193   MutexLockerEx ml(metaspace_lock(),  Mutex::_no_safepoint_check_flag);
 194 
 195   oop loader_or_mirror = new_dependency->obj_at(0);
 196 
 197   // Since the dependencies are only added, add to the end.
 198   objArrayOop end = last_handle();
 199   objArrayOop last = NULL;
 200   while (end != NULL) {
 201     last = end;
 202     // check again if another thread added it to the end.
 203     if (end->obj_at(0) == loader_or_mirror) {
 204       // Don't need to add it
 205       return;
 206     }
 207     end = (objArrayOop)end->obj_at(1);
 208   }
 209   assert (last != NULL, "dependencies should be initialized");
 210   // fill in the first element with the oop in new_dependency.
 211   if (last->obj_at(0) == NULL) {
 212     last->obj_at_put(0, new_dependency->obj_at(0));
 213   } else {
 214     last->obj_at_put(1, new_dependency());
 215   }
 216 }
 217 
 218 void ClassLoaderDataGraph::clear_claimed_marks() {
 219   for (ClassLoaderData* cld = _head; cld != NULL; cld = cld->next()) {
 220     cld->clear_claimed();
 221   }
 222 }
 223 
 224 void ClassLoaderData::add_class(Klass* k) {
 225   MutexLockerEx ml(metaspace_lock(),  Mutex::_no_safepoint_check_flag);
 226   Klass* old_value = _klasses;
 227   k->set_next_link(old_value);
 228   // link the new item into the list
 229   _klasses = k;
 230 
 231   if (TraceClassLoaderData && Verbose && k->class_loader_data() != NULL) {
 232     ResourceMark rm;
 233     tty->print_cr("[TraceClassLoaderData] Adding k: " PTR_FORMAT " %s to CLD: "
 234                   PTR_FORMAT " loader: " PTR_FORMAT " %s",
 235                   k,
 236                   k->external_name(),
 237                   k->class_loader_data(),
 238                   k->class_loader(),
 239                   loader_name());
 240   }
 241 }
 242 
 243 // This is called by InstanceKlass::deallocate_contents() to remove the
 244 // scratch_class for redefine classes.  We need a lock because there it may not
 245 // be called at a safepoint if there's an error.
 246 void ClassLoaderData::remove_class(Klass* scratch_class) {
 247   MutexLockerEx ml(metaspace_lock(),  Mutex::_no_safepoint_check_flag);
 248   Klass* prev = NULL;
 249   for (Klass* k = _klasses; k != NULL; k = k->next_link()) {
 250     if (k == scratch_class) {
 251       if (prev == NULL) {
 252         _klasses = k->next_link();
 253       } else {
 254         Klass* next = k->next_link();
 255         prev->set_next_link(next);
 256       }
 257       return;
 258     }
 259     prev = k;
 260   }
 261   ShouldNotReachHere();   // should have found this class!!
 262 }
 263 
 264 void ClassLoaderData::unload() {
 265   _unloading = true;
 266 
 267   if (TraceClassLoaderData) {
 268     ResourceMark rm;
 269     tty->print("[ClassLoaderData: unload loader data "PTR_FORMAT, this);
 270     tty->print(" for instance "PTR_FORMAT" of %s", class_loader(),
 271                loader_name());
 272     if (is_anonymous()) {
 273       tty->print(" for anonymous class  "PTR_FORMAT " ", _klasses);
 274     }
 275     tty->print_cr("]");
 276   }
 277 }
 278 
 279 bool ClassLoaderData::is_alive(BoolObjectClosure* is_alive_closure) const {
 280   bool alive =
 281     is_anonymous() ?
 282        is_alive_closure->do_object_b(_klasses->java_mirror()) :
 283        class_loader() == NULL || is_alive_closure->do_object_b(class_loader());
 284   assert(!alive || claimed(), "must be claimed");
 285   return alive;
 286 }
 287 
 288 
 289 ClassLoaderData::~ClassLoaderData() {
 290   Metaspace *m = _metaspace;
 291   if (m != NULL) {
 292     _metaspace = NULL;
 293     // release the metaspace
 294     delete m;
 295     // release the handles
 296     if (_handles != NULL) {
 297       JNIHandleBlock::release_block(_handles);
 298       _handles = NULL;
 299     }
 300   }
 301 
 302   // Clear all the JNI handles for methods
 303   // These aren't deallocated and are going to look like a leak, but that's
 304   // needed because we can't really get rid of jmethodIDs because we don't
 305   // know when native code is going to stop using them.  The spec says that
 306   // they're "invalid" but existing programs likely rely on their being
 307   // NULL after class unloading.
 308   if (_jmethod_ids != NULL) {
 309     Method::clear_jmethod_ids(this);
 310   }
 311   // Delete lock
 312   delete _metaspace_lock;
 313 
 314   // Delete free list
 315   if (_deallocate_list != NULL) {
 316     delete _deallocate_list;
 317   }
 318 }
 319 
 320 Metaspace* ClassLoaderData::metaspace_non_null() {
 321   assert(!DumpSharedSpaces, "wrong metaspace!");
 322   // If the metaspace has not been allocated, create a new one.  Might want
 323   // to create smaller arena for Reflection class loaders also.
 324   // The reason for the delayed allocation is because some class loaders are
 325   // simply for delegating with no metadata of their own.
 326   if (_metaspace == NULL) {
 327     MutexLockerEx ml(metaspace_lock(),  Mutex::_no_safepoint_check_flag);
 328     // Check again if metaspace has been allocated while we were getting this lock.
 329     if (_metaspace != NULL) {
 330       return _metaspace;
 331     }
 332     if (this == the_null_class_loader_data()) {
 333       assert (class_loader() == NULL, "Must be");
 334       set_metaspace(new Metaspace(_metaspace_lock, Metaspace::BootMetaspaceType));
 335     } else if (is_anonymous()) {
 336       if (TraceClassLoaderData && Verbose && class_loader() != NULL) {
 337         tty->print_cr("is_anonymous: %s", class_loader()->klass()->internal_name());
 338       }
 339       set_metaspace(new Metaspace(_metaspace_lock, Metaspace::AnonymousMetaspaceType));
 340     } else if (class_loader()->is_a(SystemDictionary::reflect_DelegatingClassLoader_klass())) {
 341       if (TraceClassLoaderData && Verbose && class_loader() != NULL) {
 342         tty->print_cr("is_reflection: %s", class_loader()->klass()->internal_name());
 343       }
 344       set_metaspace(new Metaspace(_metaspace_lock, Metaspace::ReflectionMetaspaceType));
 345     } else {
 346       set_metaspace(new Metaspace(_metaspace_lock, Metaspace::StandardMetaspaceType));
 347     }
 348   }
 349   return _metaspace;
 350 }
 351 
 352 JNIHandleBlock* ClassLoaderData::handles() const           { return _handles; }
 353 void ClassLoaderData::set_handles(JNIHandleBlock* handles) { _handles = handles; }
 354 
 355 jobject ClassLoaderData::add_handle(Handle h) {
 356   MutexLockerEx ml(metaspace_lock(),  Mutex::_no_safepoint_check_flag);
 357   if (handles() == NULL) {
 358     set_handles(JNIHandleBlock::allocate_block());
 359   }
 360   return handles()->allocate_handle(h());
 361 }
 362 
 363 // Add this metadata pointer to be freed when it's safe.  This is only during
 364 // class unloading because Handles might point to this metadata field.
 365 void ClassLoaderData::add_to_deallocate_list(Metadata* m) {
 366   // Metadata in shared region isn't deleted.
 367   if (!m->is_shared()) {
 368     MutexLockerEx ml(metaspace_lock(),  Mutex::_no_safepoint_check_flag);
 369     if (_deallocate_list == NULL) {
 370       _deallocate_list = new (ResourceObj::C_HEAP, mtClass) GrowableArray<Metadata*>(100, true);
 371     }
 372     _deallocate_list->append_if_missing(m);
 373   }
 374 }
 375 
 376 // Deallocate free metadata on the free list.  How useful the PermGen was!
 377 void ClassLoaderData::free_deallocate_list() {
 378   // Don't need lock, at safepoint
 379   assert(SafepointSynchronize::is_at_safepoint(), "only called at safepoint");
 380   if (_deallocate_list == NULL) {
 381     return;
 382   }
 383   // Go backwards because this removes entries that are freed.
 384   for (int i = _deallocate_list->length() - 1; i >= 0; i--) {
 385     Metadata* m = _deallocate_list->at(i);
 386     if (!m->on_stack()) {
 387       _deallocate_list->remove_at(i);
 388       // There are only three types of metadata that we deallocate directly.
 389       // Cast them so they can be used by the template function.
 390       if (m->is_method()) {
 391         MetadataFactory::free_metadata(this, (Method*)m);
 392       } else if (m->is_constantPool()) {
 393         MetadataFactory::free_metadata(this, (ConstantPool*)m);
 394       } else if (m->is_klass()) {
 395         MetadataFactory::free_metadata(this, (InstanceKlass*)m);
 396       } else {
 397         ShouldNotReachHere();
 398       }
 399     }
 400   }
 401 }
 402 
 403 // These anonymous class loaders are to contain classes used for JSR292
 404 ClassLoaderData* ClassLoaderData::anonymous_class_loader_data(oop loader, TRAPS) {
 405   // Add a new class loader data to the graph.
 406   return ClassLoaderDataGraph::add(NULL, loader, CHECK_NULL);
 407 }
 408 
 409 const char* ClassLoaderData::loader_name() {
 410   // Handles null class loader
 411   return SystemDictionary::loader_name(class_loader());
 412 }
 413 
 414 #ifndef PRODUCT
 415 // Define to dump klasses
 416 #undef CLD_DUMP_KLASSES
 417 
 418 void ClassLoaderData::dump(outputStream * const out) {
 419   ResourceMark rm;
 420   out->print("ClassLoaderData CLD: "PTR_FORMAT", loader: "PTR_FORMAT", loader_klass: "PTR_FORMAT" %s {",
 421       this, class_loader(),
 422       class_loader() != NULL ? class_loader()->klass() : NULL, loader_name());
 423   if (claimed()) out->print(" claimed ");
 424   if (is_unloading()) out->print(" unloading ");
 425   out->print(" handles " INTPTR_FORMAT, handles());
 426   out->cr();
 427   if (metaspace_or_null() != NULL) {
 428     out->print_cr("metaspace: " PTR_FORMAT, metaspace_or_null());
 429     metaspace_or_null()->dump(out);
 430   } else {
 431     out->print_cr("metaspace: NULL");
 432   }
 433 
 434 #ifdef CLD_DUMP_KLASSES
 435   if (Verbose) {
 436     ResourceMark rm;
 437     Klass* k = _klasses;
 438     while (k != NULL) {
 439       out->print_cr("klass "PTR_FORMAT", %s, CT: %d, MUT: %d", k, k->name()->as_C_string(),
 440           k->has_modified_oops(), k->has_accumulated_modified_oops());
 441       k = k->next_link();
 442     }
 443   }
 444 #endif  // CLD_DUMP_KLASSES
 445 #undef CLD_DUMP_KLASSES
 446   if (_jmethod_ids != NULL) {
 447     Method::print_jmethod_ids(this, out);
 448   }
 449   out->print_cr("}");
 450 }
 451 #endif // PRODUCT
 452 
 453 void ClassLoaderData::verify() {
 454   oop cl = class_loader();
 455 
 456   guarantee(this == class_loader_data(cl) || is_anonymous(), "Must be the same");
 457   guarantee(cl != NULL || this == ClassLoaderData::the_null_class_loader_data() || is_anonymous(), "must be");
 458 
 459   // Verify the integrity of the allocated space.
 460   if (metaspace_or_null() != NULL) {
 461     metaspace_or_null()->verify();
 462   }
 463 
 464   for (Klass* k = _klasses; k != NULL; k = k->next_link()) {
 465     guarantee(k->class_loader_data() == this, "Must be the same");
 466     k->verify();
 467   }
 468 }
 469 
 470 
 471 // GC root of class loader data created.
 472 ClassLoaderData* ClassLoaderDataGraph::_head = NULL;
 473 ClassLoaderData* ClassLoaderDataGraph::_unloading = NULL;
 474 ClassLoaderData* ClassLoaderDataGraph::_saved_head = NULL;
 475 
 476 
 477 // Add a new class loader data node to the list.  Assign the newly created
 478 // ClassLoaderData into the java/lang/ClassLoader object as a hidden field
 479 ClassLoaderData* ClassLoaderDataGraph::add(ClassLoaderData** cld_addr, Handle loader, TRAPS) {
 480   // Not assigned a class loader data yet.
 481   // Create one.
 482   ClassLoaderData* *list_head = &_head;
 483   ClassLoaderData* next = _head;
 484 
 485   bool is_anonymous = (cld_addr == NULL);
 486   ClassLoaderData* cld = new ClassLoaderData(loader, is_anonymous);
 487 
 488   if (cld_addr != NULL) {
 489     // First, Atomically set it
 490     ClassLoaderData* old = (ClassLoaderData*) Atomic::cmpxchg_ptr(cld, cld_addr, NULL);
 491     if (old != NULL) {
 492       delete cld;
 493       // Returns the data.
 494       return old;
 495     }
 496   }
 497 
 498   // We won the race, and therefore the task of adding the data to the list of
 499   // class loader data
 500   do {
 501     cld->set_next(next);
 502     ClassLoaderData* exchanged = (ClassLoaderData*)Atomic::cmpxchg_ptr(cld, list_head, next);
 503     if (exchanged == next) {
 504       if (TraceClassLoaderData) {
 505         ResourceMark rm;
 506         tty->print("[ClassLoaderData: ");
 507         tty->print("create class loader data "PTR_FORMAT, cld);
 508         tty->print(" for instance "PTR_FORMAT" of %s", cld->class_loader(),
 509                    cld->loader_name());
 510         tty->print_cr("]");
 511       }
 512       // Create dependencies after the CLD is added to the list.  Otherwise,
 513       // the GC GC will not find the CLD and the _class_loader field will
 514       // not be updated.
 515       cld->init_dependencies(CHECK_NULL);
 516       return cld;
 517     }
 518     next = exchanged;
 519   } while (true);
 520 
 521 }
 522 
 523 void ClassLoaderDataGraph::oops_do(OopClosure* f, KlassClosure* klass_closure, bool must_claim) {
 524   for (ClassLoaderData* cld = _head; cld != NULL; cld = cld->next()) {
 525     cld->oops_do(f, klass_closure, must_claim);
 526   }
 527 }
 528 
 529 void ClassLoaderDataGraph::keep_alive_oops_do(OopClosure* f, KlassClosure* klass_closure, bool must_claim) {
 530   for (ClassLoaderData* cld = _head; cld != NULL; cld = cld->next()) {
 531     if (cld->keep_alive()) {
 532       cld->oops_do(f, klass_closure, must_claim);
 533     }
 534   }
 535 }
 536 
 537 void ClassLoaderDataGraph::always_strong_oops_do(OopClosure* f, KlassClosure* klass_closure, bool must_claim) {
 538   if (ClassUnloading) {
 539     ClassLoaderData::the_null_class_loader_data()->oops_do(f, klass_closure, must_claim);
 540     // keep any special CLDs alive.
 541     ClassLoaderDataGraph::keep_alive_oops_do(f, klass_closure, must_claim);
 542   } else {
 543     ClassLoaderDataGraph::oops_do(f, klass_closure, must_claim);
 544   }
 545 }
 546 
 547 void ClassLoaderDataGraph::classes_do(KlassClosure* klass_closure) {
 548   for (ClassLoaderData* cld = _head; cld != NULL; cld = cld->next()) {
 549     cld->classes_do(klass_closure);
 550   }
 551 }
 552 
 553 GrowableArray<ClassLoaderData*>* ClassLoaderDataGraph::new_clds() {
 554   assert(_head == NULL || _saved_head != NULL, "remember_new_clds(true) not called?");
 555 
 556   GrowableArray<ClassLoaderData*>* array = new GrowableArray<ClassLoaderData*>();
 557 
 558   // The CLDs in [_head, _saved_head] were all added during last call to remember_new_clds(true);
 559   ClassLoaderData* curr = _head;
 560   while (curr != _saved_head) {
 561     if (!curr->claimed()) {
 562       array->push(curr);
 563 
 564       if (TraceClassLoaderData) {
 565         tty->print("[ClassLoaderData] found new CLD: ");
 566         curr->print_value_on(tty);
 567         tty->cr();
 568       }
 569     }
 570 
 571     curr = curr->_next;
 572   }
 573 
 574   return array;
 575 }
 576 
 577 #ifndef PRODUCT
 578 // for debugging and hsfind(x)
 579 bool ClassLoaderDataGraph::contains(address x) {
 580   // I think we need the _metaspace_lock taken here because the class loader
 581   // data graph could be changing while we are walking it (new entries added,
 582   // new entries being unloaded, etc).
 583   if (DumpSharedSpaces) {
 584     // There are only two metaspaces to worry about.
 585     ClassLoaderData* ncld = ClassLoaderData::the_null_class_loader_data();
 586     return (ncld->ro_metaspace()->contains(x) || ncld->rw_metaspace()->contains(x));
 587   }
 588 
 589   if (UseSharedSpaces && MetaspaceShared::is_in_shared_space(x)) {
 590     return true;
 591   }
 592 
 593   for (ClassLoaderData* cld = _head; cld != NULL; cld = cld->next()) {
 594     if (cld->metaspace_or_null() != NULL && cld->metaspace_or_null()->contains(x)) {
 595       return true;
 596     }
 597   }
 598 
 599   // Could also be on an unloading list which is okay, ie. still allocated
 600   // for a little while.
 601   for (ClassLoaderData* ucld = _unloading; ucld != NULL; ucld = ucld->next()) {
 602     if (ucld->metaspace_or_null() != NULL && ucld->metaspace_or_null()->contains(x)) {
 603       return true;
 604     }
 605   }
 606   return false;
 607 }
 608 
 609 bool ClassLoaderDataGraph::contains_loader_data(ClassLoaderData* loader_data) {
 610   for (ClassLoaderData* data = _head; data != NULL; data = data->next()) {
 611     if (loader_data == data) {
 612       return true;
 613     }
 614   }
 615 
 616   return false;
 617 }
 618 #endif // PRODUCT
 619 
 620 
 621 // Move class loader data from main list to the unloaded list for unloading
 622 // and deallocation later.
 623 bool ClassLoaderDataGraph::do_unloading(BoolObjectClosure* is_alive_closure) {
 624   ClassLoaderData* data = _head;
 625   ClassLoaderData* prev = NULL;
 626   bool seen_dead_loader = false;
 627   // mark metadata seen on the stack and code cache so we can delete
 628   // unneeded entries.
 629   bool has_redefined_a_class = JvmtiExport::has_redefined_a_class();
 630   MetadataOnStackMark md_on_stack;
 631   while (data != NULL) {
 632     if (data->keep_alive() || data->is_alive(is_alive_closure)) {
 633       if (has_redefined_a_class) {
 634         data->classes_do(InstanceKlass::purge_previous_versions);
 635       }
 636       data->free_deallocate_list();
 637       prev = data;
 638       data = data->next();
 639       continue;
 640     }
 641     seen_dead_loader = true;
 642     ClassLoaderData* dead = data;
 643     dead->unload();
 644     data = data->next();
 645     // Remove from loader list.
 646     if (prev != NULL) {
 647       prev->set_next(data);
 648     } else {
 649       assert(dead == _head, "sanity check");
 650       _head = data;
 651     }
 652     dead->set_next(_unloading);
 653     _unloading = dead;
 654   }
 655   return seen_dead_loader;
 656 }
 657 
 658 void ClassLoaderDataGraph::purge() {
 659   ClassLoaderData* list = _unloading;
 660   _unloading = NULL;
 661   ClassLoaderData* next = list;
 662   while (next != NULL) {
 663     ClassLoaderData* purge_me = next;
 664     next = purge_me->next();
 665     delete purge_me;
 666   }
 667 }
 668 
 669 // CDS support
 670 
 671 // Global metaspaces for writing information to the shared archive.  When
 672 // application CDS is supported, we may need one per metaspace, so this
 673 // sort of looks like it.
 674 Metaspace* ClassLoaderData::_ro_metaspace = NULL;
 675 Metaspace* ClassLoaderData::_rw_metaspace = NULL;
 676 static bool _shared_metaspaces_initialized = false;
 677 
 678 // Initialize shared metaspaces (change to call from somewhere not lazily)
 679 void ClassLoaderData::initialize_shared_metaspaces() {
 680   assert(DumpSharedSpaces, "only use this for dumping shared spaces");
 681   assert(this == ClassLoaderData::the_null_class_loader_data(),
 682          "only supported for null loader data for now");
 683   assert (!_shared_metaspaces_initialized, "only initialize once");
 684   MutexLockerEx ml(metaspace_lock(),  Mutex::_no_safepoint_check_flag);
 685   _ro_metaspace = new Metaspace(_metaspace_lock, Metaspace::ROMetaspaceType);
 686   _rw_metaspace = new Metaspace(_metaspace_lock, Metaspace::ReadWriteMetaspaceType);
 687   _shared_metaspaces_initialized = true;
 688 }
 689 
 690 Metaspace* ClassLoaderData::ro_metaspace() {
 691   assert(_ro_metaspace != NULL, "should already be initialized");
 692   return _ro_metaspace;
 693 }
 694 
 695 Metaspace* ClassLoaderData::rw_metaspace() {
 696   assert(_rw_metaspace != NULL, "should already be initialized");
 697   return _rw_metaspace;
 698 }
 699 
 700 
 701 ClassLoaderDataGraphMetaspaceIterator::ClassLoaderDataGraphMetaspaceIterator() {
 702   _data = ClassLoaderDataGraph::_head;
 703 }
 704 
 705 ClassLoaderDataGraphMetaspaceIterator::~ClassLoaderDataGraphMetaspaceIterator() {}
 706 
 707 #ifndef PRODUCT
 708 // callable from debugger
 709 extern "C" int print_loader_data_graph() {
 710   ClassLoaderDataGraph::dump_on(tty);
 711   return 0;
 712 }
 713 
 714 void ClassLoaderDataGraph::verify() {
 715   for (ClassLoaderData* data = _head; data != NULL; data = data->next()) {
 716     data->verify();
 717   }
 718 }
 719 
 720 void ClassLoaderDataGraph::dump_on(outputStream * const out) {
 721   for (ClassLoaderData* data = _head; data != NULL; data = data->next()) {
 722     data->dump(out);
 723   }
 724   MetaspaceAux::dump(out);
 725 }
 726 #endif // PRODUCT
 727 
 728 void ClassLoaderData::print_value_on(outputStream* out) const {
 729   if (class_loader() == NULL) {
 730     out->print("NULL class_loader");
 731   } else {
 732     out->print("class loader "PTR_FORMAT, this);
 733     class_loader()->print_value_on(out);
 734   }
 735 }