1 /*
   2  * Copyright (c) 2002, 2020, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "classfile/classLoaderData.inline.hpp"
  27 #include "classfile/classLoaderDataGraph.hpp"
  28 #include "classfile/moduleEntry.hpp"
  29 #include "classfile/systemDictionary.hpp"
  30 #include "gc/shared/collectedHeap.hpp"
  31 #include "logging/log.hpp"
  32 #include "logging/logTag.hpp"
  33 #include "memory/heapInspection.hpp"
  34 #include "memory/resourceArea.hpp"
  35 #include "memory/universe.hpp"
  36 #include "oops/oop.inline.hpp"
  37 #include "oops/reflectionAccessorImplKlassHelper.hpp"
  38 #include "runtime/os.hpp"
  39 #include "utilities/globalDefinitions.hpp"
  40 #include "utilities/macros.hpp"
  41 #include "utilities/stack.inline.hpp"
  42 
  43 // HeapInspection
  44 
  45 inline KlassInfoEntry::~KlassInfoEntry() {
  46   if (_subclasses != NULL) {
  47     delete _subclasses;
  48   }
  49 }
  50 
  51 inline void KlassInfoEntry::add_subclass(KlassInfoEntry* cie) {
  52   if (_subclasses == NULL) {
  53     _subclasses = new  (ResourceObj::C_HEAP, mtInternal) GrowableArray<KlassInfoEntry*>(4, true);
  54   }
  55   _subclasses->append(cie);
  56 }
  57 
  58 int KlassInfoEntry::compare(KlassInfoEntry* e1, KlassInfoEntry* e2) {
  59   if(e1->_instance_words > e2->_instance_words) {
  60     return -1;
  61   } else if(e1->_instance_words < e2->_instance_words) {
  62     return 1;
  63   }
  64   // Sort alphabetically, note 'Z' < '[' < 'a', but it's better to group
  65   // the array classes before all the instance classes.
  66   ResourceMark rm;
  67   const char* name1 = e1->klass()->external_name();
  68   const char* name2 = e2->klass()->external_name();
  69   bool d1 = (name1[0] == JVM_SIGNATURE_ARRAY);
  70   bool d2 = (name2[0] == JVM_SIGNATURE_ARRAY);
  71   if (d1 && !d2) {
  72     return -1;
  73   } else if (d2 && !d1) {
  74     return 1;
  75   } else {
  76     return strcmp(name1, name2);
  77   }
  78 }
  79 
  80 const char* KlassInfoEntry::name() const {
  81   const char* name;
  82   if (_klass->name() != NULL) {
  83     name = _klass->external_name();
  84   } else {
  85     if (_klass == Universe::boolArrayKlassObj())         name = "<boolArrayKlass>";         else
  86     if (_klass == Universe::charArrayKlassObj())         name = "<charArrayKlass>";         else
  87     if (_klass == Universe::floatArrayKlassObj())        name = "<floatArrayKlass>";        else
  88     if (_klass == Universe::doubleArrayKlassObj())       name = "<doubleArrayKlass>";       else
  89     if (_klass == Universe::byteArrayKlassObj())         name = "<byteArrayKlass>";         else
  90     if (_klass == Universe::shortArrayKlassObj())        name = "<shortArrayKlass>";        else
  91     if (_klass == Universe::intArrayKlassObj())          name = "<intArrayKlass>";          else
  92     if (_klass == Universe::longArrayKlassObj())         name = "<longArrayKlass>";         else
  93       name = "<no name>";
  94   }
  95   return name;
  96 }
  97 
  98 void KlassInfoEntry::print_on(outputStream* st) const {
  99   ResourceMark rm;
 100 
 101   // simplify the formatting (ILP32 vs LP64) - always cast the numbers to 64-bit
 102   ModuleEntry* module = _klass->module();
 103   if (module->is_named()) {
 104     st->print_cr(INT64_FORMAT_W(13) "  " UINT64_FORMAT_W(13) "  %s (%s%s%s)",
 105                  (int64_t)_instance_count,
 106                  (uint64_t)_instance_words * HeapWordSize,
 107                  name(),
 108                  module->name()->as_C_string(),
 109                  module->version() != NULL ? "@" : "",
 110                  module->version() != NULL ? module->version()->as_C_string() : "");
 111   } else {
 112     st->print_cr(INT64_FORMAT_W(13) "  " UINT64_FORMAT_W(13) "  %s",
 113                  (int64_t)_instance_count,
 114                  (uint64_t)_instance_words * HeapWordSize,
 115                  name());
 116   }
 117 }
 118 
 119 KlassInfoEntry* KlassInfoBucket::lookup(Klass* const k) {
 120   // Can happen if k is an archived class that we haven't loaded yet.
 121   if (k->java_mirror_no_keepalive() == NULL) {
 122     return NULL;
 123   }
 124 
 125   KlassInfoEntry* elt = _list;
 126   while (elt != NULL) {
 127     if (elt->is_equal(k)) {
 128       return elt;
 129     }
 130     elt = elt->next();
 131   }
 132   elt = new (std::nothrow) KlassInfoEntry(k, list());
 133   // We may be out of space to allocate the new entry.
 134   if (elt != NULL) {
 135     set_list(elt);
 136   }
 137   return elt;
 138 }
 139 
 140 void KlassInfoBucket::iterate(KlassInfoClosure* cic) {
 141   KlassInfoEntry* elt = _list;
 142   while (elt != NULL) {
 143     cic->do_cinfo(elt);
 144     elt = elt->next();
 145   }
 146 }
 147 
 148 void KlassInfoBucket::empty() {
 149   KlassInfoEntry* elt = _list;
 150   _list = NULL;
 151   while (elt != NULL) {
 152     KlassInfoEntry* next = elt->next();
 153     delete elt;
 154     elt = next;
 155   }
 156 }
 157 
 158 class KlassInfoTable::AllClassesFinder : public LockedClassesDo {
 159   KlassInfoTable *_table;
 160 public:
 161   AllClassesFinder(KlassInfoTable* table) : _table(table) {}
 162   virtual void do_klass(Klass* k) {
 163     // This has the SIDE EFFECT of creating a KlassInfoEntry
 164     // for <k>, if one doesn't exist yet.
 165     _table->lookup(k);
 166   }
 167 };
 168 
 169 
 170 KlassInfoTable::KlassInfoTable(bool add_all_classes) {
 171   _size_of_instances_in_words = 0;
 172   _ref = (HeapWord*) Universe::boolArrayKlassObj();
 173   _buckets =
 174     (KlassInfoBucket*)  AllocateHeap(sizeof(KlassInfoBucket) * _num_buckets,
 175        mtInternal, CURRENT_PC, AllocFailStrategy::RETURN_NULL);
 176   if (_buckets != NULL) {
 177     for (int index = 0; index < _num_buckets; index++) {
 178       _buckets[index].initialize();
 179     }
 180     if (add_all_classes) {
 181       AllClassesFinder finder(this);
 182       ClassLoaderDataGraph::classes_do(&finder);
 183     }
 184   }
 185 }
 186 
 187 KlassInfoTable::~KlassInfoTable() {
 188   if (_buckets != NULL) {
 189     for (int index = 0; index < _num_buckets; index++) {
 190       _buckets[index].empty();
 191     }
 192     FREE_C_HEAP_ARRAY(KlassInfoBucket, _buckets);
 193     _buckets = NULL;
 194   }
 195 }
 196 
 197 uint KlassInfoTable::hash(const Klass* p) {
 198   return (uint)(((uintptr_t)p - (uintptr_t)_ref) >> 2);
 199 }
 200 
 201 KlassInfoEntry* KlassInfoTable::lookup(Klass* k) {
 202   uint         idx = hash(k) % _num_buckets;
 203   assert(_buckets != NULL, "Allocation failure should have been caught");
 204   KlassInfoEntry*  e   = _buckets[idx].lookup(k);
 205   // Lookup may fail if this is a new klass for which we
 206   // could not allocate space for an new entry, or if it's
 207   // an archived class that we haven't loaded yet.
 208   assert(e == NULL || k == e->klass(), "must be equal");
 209   return e;
 210 }
 211 
 212 // Return false if the entry could not be recorded on account
 213 // of running out of space required to create a new entry.
 214 bool KlassInfoTable::record_instance(const oop obj) {
 215   Klass*        k = obj->klass();
 216   KlassInfoEntry* elt = lookup(k);
 217   // elt may be NULL if it's a new klass for which we
 218   // could not allocate space for a new entry in the hashtable.
 219   if (elt != NULL) {
 220     elt->set_count(elt->count() + 1);
 221     elt->set_words(elt->words() + obj->size());
 222     _size_of_instances_in_words += obj->size();
 223     return true;
 224   } else {
 225     return false;
 226   }
 227 }
 228 
 229 void KlassInfoTable::iterate(KlassInfoClosure* cic) {
 230   assert(_buckets != NULL, "Allocation failure should have been caught");
 231   for (int index = 0; index < _num_buckets; index++) {
 232     _buckets[index].iterate(cic);
 233   }
 234 }
 235 
 236 size_t KlassInfoTable::size_of_instances_in_words() const {
 237   return _size_of_instances_in_words;
 238 }
 239 
 240 // Return false if the entry could not be recorded on account
 241 // of running out of space required to create a new entry.
 242 bool KlassInfoTable::merge_entry(const KlassInfoEntry* cie) {
 243   Klass*        k = cie->klass();
 244   KlassInfoEntry* elt = lookup(k);
 245   // elt may be NULL if it's a new klass for which we
 246   // could not allocate space for a new entry in the hashtable.
 247   if (elt != NULL) {
 248     elt->set_count(elt->count() + cie->count());
 249     elt->set_words(elt->words() + cie->words());
 250     _size_of_instances_in_words += cie->words();
 251     return true;
 252   } else {
 253     return false;
 254   }
 255 }
 256 
 257 class KlassInfoTableMergeClosure : public KlassInfoClosure {
 258 private:
 259   KlassInfoTable* _dest;
 260   bool _success;
 261 public:
 262   KlassInfoTableMergeClosure(KlassInfoTable* table) : _dest(table), _success(true) {}
 263   void do_cinfo(KlassInfoEntry* cie) {
 264     _success &= _dest->merge_entry(cie);
 265   }
 266   bool is_success() { return _success; }
 267 };
 268 
 269 // merge from table
 270 bool KlassInfoTable::merge(KlassInfoTable* table) {
 271   KlassInfoTableMergeClosure closure(this);
 272   table->iterate(&closure);
 273   return closure.is_success();
 274 }
 275 
 276 int KlassInfoHisto::sort_helper(KlassInfoEntry** e1, KlassInfoEntry** e2) {
 277   return (*e1)->compare(*e1,*e2);
 278 }
 279 
 280 KlassInfoHisto::KlassInfoHisto(KlassInfoTable* cit) :
 281   _cit(cit) {
 282   _elements = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<KlassInfoEntry*>(_histo_initial_size, true);
 283 }
 284 
 285 KlassInfoHisto::~KlassInfoHisto() {
 286   delete _elements;
 287 }
 288 
 289 void KlassInfoHisto::add(KlassInfoEntry* cie) {
 290   elements()->append(cie);
 291 }
 292 
 293 void KlassInfoHisto::sort() {
 294   elements()->sort(KlassInfoHisto::sort_helper);
 295 }
 296 
 297 void KlassInfoHisto::print_elements(outputStream* st) const {
 298   // simplify the formatting (ILP32 vs LP64) - store the sum in 64-bit
 299   int64_t total = 0;
 300   uint64_t totalw = 0;
 301   for(int i=0; i < elements()->length(); i++) {
 302     st->print("%4d: ", i+1);
 303     elements()->at(i)->print_on(st);
 304     total += elements()->at(i)->count();
 305     totalw += elements()->at(i)->words();
 306   }
 307   st->print_cr("Total " INT64_FORMAT_W(13) "  " UINT64_FORMAT_W(13),
 308                total, totalw * HeapWordSize);
 309 }
 310 
 311 class HierarchyClosure : public KlassInfoClosure {
 312 private:
 313   GrowableArray<KlassInfoEntry*> *_elements;
 314 public:
 315   HierarchyClosure(GrowableArray<KlassInfoEntry*> *_elements) : _elements(_elements) {}
 316 
 317   void do_cinfo(KlassInfoEntry* cie) {
 318     // ignore array classes
 319     if (cie->klass()->is_instance_klass()) {
 320       _elements->append(cie);
 321     }
 322   }
 323 };
 324 
 325 void KlassHierarchy::print_class_hierarchy(outputStream* st, bool print_interfaces,
 326                                            bool print_subclasses, char* classname) {
 327   ResourceMark rm;
 328   Stack <KlassInfoEntry*, mtClass> class_stack;
 329   GrowableArray<KlassInfoEntry*> elements;
 330 
 331   // Add all classes to the KlassInfoTable, which allows for quick lookup.
 332   // A KlassInfoEntry will be created for each class.
 333   KlassInfoTable cit(true);
 334   if (cit.allocation_failed()) {
 335     st->print_cr("ERROR: Ran out of C-heap; hierarchy not generated");
 336     return;
 337   }
 338 
 339   // Add all created KlassInfoEntry instances to the elements array for easy
 340   // iteration, and to allow each KlassInfoEntry instance to have a unique index.
 341   HierarchyClosure hc(&elements);
 342   cit.iterate(&hc);
 343 
 344   for(int i = 0; i < elements.length(); i++) {
 345     KlassInfoEntry* cie = elements.at(i);
 346     Klass* super = cie->klass()->super();
 347 
 348     // Set the index for the class.
 349     cie->set_index(i + 1);
 350 
 351     // Add the class to the subclass array of its superclass.
 352     if (super != NULL) {
 353       KlassInfoEntry* super_cie = cit.lookup(super);
 354       assert(super_cie != NULL, "could not lookup superclass");
 355       super_cie->add_subclass(cie);
 356     }
 357   }
 358 
 359   // Set the do_print flag for each class that should be printed.
 360   for(int i = 0; i < elements.length(); i++) {
 361     KlassInfoEntry* cie = elements.at(i);
 362     if (classname == NULL) {
 363       // We are printing all classes.
 364       cie->set_do_print(true);
 365     } else {
 366       // We are only printing the hierarchy of a specific class.
 367       if (strcmp(classname, cie->klass()->external_name()) == 0) {
 368         KlassHierarchy::set_do_print_for_class_hierarchy(cie, &cit, print_subclasses);
 369       }
 370     }
 371   }
 372 
 373   // Now we do a depth first traversal of the class hierachry. The class_stack will
 374   // maintain the list of classes we still need to process. Start things off
 375   // by priming it with java.lang.Object.
 376   KlassInfoEntry* jlo_cie = cit.lookup(SystemDictionary::Object_klass());
 377   assert(jlo_cie != NULL, "could not lookup java.lang.Object");
 378   class_stack.push(jlo_cie);
 379 
 380   // Repeatedly pop the top item off the stack, print its class info,
 381   // and push all of its subclasses on to the stack. Do this until there
 382   // are no classes left on the stack.
 383   while (!class_stack.is_empty()) {
 384     KlassInfoEntry* curr_cie = class_stack.pop();
 385     if (curr_cie->do_print()) {
 386       print_class(st, curr_cie, print_interfaces);
 387       if (curr_cie->subclasses() != NULL) {
 388         // Current class has subclasses, so push all of them onto the stack.
 389         for (int i = 0; i < curr_cie->subclasses()->length(); i++) {
 390           KlassInfoEntry* cie = curr_cie->subclasses()->at(i);
 391           if (cie->do_print()) {
 392             class_stack.push(cie);
 393           }
 394         }
 395       }
 396     }
 397   }
 398 
 399   st->flush();
 400 }
 401 
 402 // Sets the do_print flag for every superclass and subclass of the specified class.
 403 void KlassHierarchy::set_do_print_for_class_hierarchy(KlassInfoEntry* cie, KlassInfoTable* cit,
 404                                                       bool print_subclasses) {
 405   // Set do_print for all superclasses of this class.
 406   Klass* super = ((InstanceKlass*)cie->klass())->java_super();
 407   while (super != NULL) {
 408     KlassInfoEntry* super_cie = cit->lookup(super);
 409     super_cie->set_do_print(true);
 410     super = super->super();
 411   }
 412 
 413   // Set do_print for this class and all of its subclasses.
 414   Stack <KlassInfoEntry*, mtClass> class_stack;
 415   class_stack.push(cie);
 416   while (!class_stack.is_empty()) {
 417     KlassInfoEntry* curr_cie = class_stack.pop();
 418     curr_cie->set_do_print(true);
 419     if (print_subclasses && curr_cie->subclasses() != NULL) {
 420       // Current class has subclasses, so push all of them onto the stack.
 421       for (int i = 0; i < curr_cie->subclasses()->length(); i++) {
 422         KlassInfoEntry* cie = curr_cie->subclasses()->at(i);
 423         class_stack.push(cie);
 424       }
 425     }
 426   }
 427 }
 428 
 429 static void print_indent(outputStream* st, int indent) {
 430   while (indent != 0) {
 431     st->print("|");
 432     indent--;
 433     if (indent != 0) {
 434       st->print("  ");
 435     }
 436   }
 437 }
 438 
 439 // Print the class name and its unique ClassLoader identifer.
 440 static void print_classname(outputStream* st, Klass* klass) {
 441   oop loader_oop = klass->class_loader_data()->class_loader();
 442   st->print("%s/", klass->external_name());
 443   if (loader_oop == NULL) {
 444     st->print("null");
 445   } else {
 446     st->print(INTPTR_FORMAT, p2i(klass->class_loader_data()));
 447   }
 448 }
 449 
 450 static void print_interface(outputStream* st, InstanceKlass* intf_klass, const char* intf_type, int indent) {
 451   print_indent(st, indent);
 452   st->print("  implements ");
 453   print_classname(st, intf_klass);
 454   st->print(" (%s intf)\n", intf_type);
 455 }
 456 
 457 void KlassHierarchy::print_class(outputStream* st, KlassInfoEntry* cie, bool print_interfaces) {
 458   ResourceMark rm;
 459   InstanceKlass* klass = (InstanceKlass*)cie->klass();
 460   int indent = 0;
 461 
 462   // Print indentation with proper indicators of superclass.
 463   Klass* super = klass->super();
 464   while (super != NULL) {
 465     super = super->super();
 466     indent++;
 467   }
 468   print_indent(st, indent);
 469   if (indent != 0) st->print("--");
 470 
 471   // Print the class name, its unique ClassLoader identifer, and if it is an interface.
 472   print_classname(st, klass);
 473   if (klass->is_interface()) {
 474     st->print(" (intf)");
 475   }
 476   // Special treatment for generated core reflection accessor classes: print invocation target.
 477   if (ReflectionAccessorImplKlassHelper::is_generated_accessor(klass)) {
 478     st->print(" (invokes: ");
 479     ReflectionAccessorImplKlassHelper::print_invocation_target(st, klass);
 480     st->print(")");
 481   }
 482   st->print("\n");
 483 
 484   // Print any interfaces the class has.
 485   if (print_interfaces) {
 486     Array<InstanceKlass*>* local_intfs = klass->local_interfaces();
 487     Array<InstanceKlass*>* trans_intfs = klass->transitive_interfaces();
 488     for (int i = 0; i < local_intfs->length(); i++) {
 489       print_interface(st, local_intfs->at(i), "declared", indent);
 490     }
 491     for (int i = 0; i < trans_intfs->length(); i++) {
 492       InstanceKlass* trans_interface = trans_intfs->at(i);
 493       // Only print transitive interfaces if they are not also declared.
 494       if (!local_intfs->contains(trans_interface)) {
 495         print_interface(st, trans_interface, "inherited", indent);
 496       }
 497     }
 498   }
 499 }
 500 
 501 void KlassInfoHisto::print_histo_on(outputStream* st) {
 502   st->print_cr(" num     #instances         #bytes  class name (module)");
 503   st->print_cr("-------------------------------------------------------");
 504   print_elements(st);
 505 }
 506 
 507 class HistoClosure : public KlassInfoClosure {
 508  private:
 509   KlassInfoHisto* _cih;
 510  public:
 511   HistoClosure(KlassInfoHisto* cih) : _cih(cih) {}
 512 
 513   void do_cinfo(KlassInfoEntry* cie) {
 514     _cih->add(cie);
 515   }
 516 };
 517 
 518 class RecordInstanceClosure : public ObjectClosure {
 519  private:
 520   KlassInfoTable* _cit;
 521   size_t _missed_count;
 522   BoolObjectClosure* _filter;
 523  public:
 524   RecordInstanceClosure(KlassInfoTable* cit, BoolObjectClosure* filter) :
 525     _cit(cit), _missed_count(0), _filter(filter) {}
 526 
 527   void do_object(oop obj) {
 528     if (should_visit(obj)) {
 529       if (!_cit->record_instance(obj)) {
 530         _missed_count++;
 531       }
 532     }
 533   }
 534 
 535   size_t missed_count() { return _missed_count; }
 536 
 537  private:
 538   bool should_visit(oop obj) {
 539     return _filter == NULL || _filter->do_object_b(obj);
 540   }
 541 };
 542 
 543 void ParHeapInspectTask::work(uint worker_id) {
 544   size_t missed_count = 0;
 545   if (!_success) {
 546     // other worker has failed on parallel iteration.
 547     return;
 548   }
 549 
 550   KlassInfoTable cit(false);
 551   if (!cit.allocation_failed()) {
 552     RecordInstanceClosure ric(&cit, _filter);
 553     do_object_iterate_parallel(&ric, worker_id);
 554     missed_count = ric.missed_count();
 555   } else {
 556     // fail to allocate memory, stop parallel mode.
 557     _success = false;
 558     return;
 559   }
 560   {
 561     MutexLocker x(&_mutex);
 562 
 563     if (!_shared_cit->merge(&cit)) {
 564       _success = false;
 565       return;
 566     }
 567     *_shared_missed_count += missed_count;
 568   }
 569 }
 570 
 571 size_t HeapInspection::populate_table(KlassInfoTable* cit, BoolObjectClosure *filter, size_t parallel_thread_num) {
 572   ResourceMark rm;
 573   size_t missed_count = 0;
 574   bool do_serial = (parallel_thread_num == 1);
 575   // try parallel first.
 576   if (parallel_thread_num > 1) {
 577     bool succ = Universe::heap()->run_par_heap_inspect_task(cit, filter, &missed_count, parallel_thread_num);
 578     if (succ) {
 579      do_serial = false;
 580     } else {
 581       // heap does not support parallel iteration, or parallel task fail because of native memory oom.
 582       // use object_iterate.
 583       do_serial = true;
 584       missed_count = 0;
 585     }
 586   }
 587 
 588   if (do_serial) {
 589     RecordInstanceClosure ric(cit, filter);
 590     Universe::heap()->object_iterate(&ric);
 591     missed_count = ric.missed_count();
 592   }
 593   return missed_count;
 594 }
 595 
 596 void HeapInspection::heap_inspection(outputStream* st, size_t parallel_thread_num) {
 597   ResourceMark rm;
 598 
 599   KlassInfoTable cit(false);
 600   if (!cit.allocation_failed()) {
 601     size_t missed_count = 0;;
 602     // populate table with object allocation info
 603     missed_count = populate_table(&cit, NULL, parallel_thread_num);
 604     if (missed_count != 0) {
 605       log_info(gc, classhisto)("WARNING: Ran out of C-heap; undercounted " SIZE_FORMAT
 606                                " total instances in data below",
 607                                missed_count);
 608     }
 609 
 610     // Sort and print klass instance info
 611     KlassInfoHisto histo(&cit);
 612     HistoClosure hc(&histo);
 613 
 614     cit.iterate(&hc);
 615 
 616     histo.sort();
 617     histo.print_histo_on(st);
 618   } else {
 619     st->print_cr("ERROR: Ran out of C-heap; histogram not generated");
 620   }
 621   st->flush();
 622 }
 623 
 624 class FindInstanceClosure : public ObjectClosure {
 625  private:
 626   Klass* _klass;
 627   GrowableArray<oop>* _result;
 628 
 629  public:
 630   FindInstanceClosure(Klass* k, GrowableArray<oop>* result) : _klass(k), _result(result) {};
 631 
 632   void do_object(oop obj) {
 633     if (obj->is_a(_klass)) {
 634       // obj was read with AS_NO_KEEPALIVE, or equivalent.
 635       // The object needs to be kept alive when it is published.
 636       Universe::heap()->keep_alive(obj);
 637 
 638       _result->append(obj);
 639     }
 640   }
 641 };
 642 
 643 void HeapInspection::find_instances_at_safepoint(Klass* k, GrowableArray<oop>* result) {
 644   assert(SafepointSynchronize::is_at_safepoint(), "all threads are stopped");
 645   assert(Heap_lock->is_locked(), "should have the Heap_lock");
 646 
 647   // Ensure that the heap is parsable
 648   Universe::heap()->ensure_parsability(false);  // no need to retire TALBs
 649 
 650   // Iterate over objects in the heap
 651   FindInstanceClosure fic(k, result);
 652   Universe::heap()->object_iterate(&fic);
 653 }