1 /*
   2  * Copyright (c) 2003, 2025, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "classfile/classLoaderDataGraph.hpp"
  26 #include "classfile/javaClasses.inline.hpp"
  27 #include "classfile/symbolTable.hpp"
  28 #include "classfile/vmClasses.hpp"
  29 #include "classfile/vmSymbols.hpp"
  30 #include "gc/shared/collectedHeap.hpp"
  31 #include "jvmtifiles/jvmtiEnv.hpp"
  32 #include "logging/log.hpp"
  33 #include "memory/allocation.inline.hpp"
  34 #include "memory/resourceArea.hpp"
  35 #include "memory/universe.hpp"
  36 #include "oops/access.inline.hpp"
  37 #include "oops/arrayOop.hpp"
  38 #include "oops/constantPool.inline.hpp"
  39 #include "oops/fieldStreams.inline.hpp"
  40 #include "oops/instanceMirrorKlass.hpp"
  41 #include "oops/klass.inline.hpp"
  42 #include "oops/objArrayKlass.hpp"
  43 #include "oops/objArrayOop.inline.hpp"
  44 #include "oops/oop.inline.hpp"
  45 #include "oops/typeArrayOop.inline.hpp"
  46 #include "prims/jvmtiEventController.inline.hpp"
  47 #include "prims/jvmtiExport.hpp"
  48 #include "prims/jvmtiImpl.hpp"
  49 #include "prims/jvmtiTagMap.hpp"
  50 #include "prims/jvmtiTagMapTable.hpp"
  51 #include "prims/jvmtiThreadState.hpp"
  52 #include "runtime/continuationWrapper.inline.hpp"
  53 #include "runtime/deoptimization.hpp"
  54 #include "runtime/frame.inline.hpp"
  55 #include "runtime/handles.inline.hpp"
  56 #include "runtime/interfaceSupport.inline.hpp"
  57 #include "runtime/javaCalls.hpp"
  58 #include "runtime/javaThread.inline.hpp"
  59 #include "runtime/jniHandles.inline.hpp"
  60 #include "runtime/mutex.hpp"
  61 #include "runtime/mutexLocker.hpp"
  62 #include "runtime/safepoint.hpp"
  63 #include "runtime/threadSMR.hpp"
  64 #include "runtime/timerTrace.hpp"
  65 #include "runtime/vframe.hpp"
  66 #include "runtime/vmOperations.hpp"
  67 #include "runtime/vmThread.hpp"
  68 #include "utilities/macros.hpp"
  69 #include "utilities/objectBitSet.inline.hpp"
  70 
  71 typedef ObjectBitSet<mtServiceability> JVMTIBitSet;
  72 
  73 bool JvmtiTagMap::_has_object_free_events = false;
  74 
  75 // create a JvmtiTagMap
  76 JvmtiTagMap::JvmtiTagMap(JvmtiEnv* env) :
  77   _env(env),
  78   _lock(Mutex::nosafepoint, "JvmtiTagMap_lock"),
  79   _needs_cleaning(false),
  80   _posting_events(false) {
  81 
  82   assert(JvmtiThreadState_lock->is_locked(), "sanity check");
  83   assert(((JvmtiEnvBase *)env)->tag_map() == nullptr, "tag map already exists for environment");
  84 
  85   _hashmap = new JvmtiTagMapTable();
  86 
  87   // finally add us to the environment
  88   ((JvmtiEnvBase *)env)->release_set_tag_map(this);
  89 }
  90 
  91 // destroy a JvmtiTagMap
  92 JvmtiTagMap::~JvmtiTagMap() {
  93 
  94   // no lock acquired as we assume the enclosing environment is
  95   // also being destroyed.
  96   ((JvmtiEnvBase *)_env)->set_tag_map(nullptr);
  97 
  98   // finally destroy the hashmap
  99   delete _hashmap;
 100   _hashmap = nullptr;
 101 }
 102 
 103 // Called by env_dispose() to reclaim memory before deallocation.
 104 // Remove all the entries but keep the empty table intact.
 105 // This needs the table lock.
 106 void JvmtiTagMap::clear() {
 107   MutexLocker ml(lock(), Mutex::_no_safepoint_check_flag);
 108   _hashmap->clear();
 109 }
 110 
 111 // returns the tag map for the given environments. If the tag map
 112 // doesn't exist then it is created.
 113 JvmtiTagMap* JvmtiTagMap::tag_map_for(JvmtiEnv* env) {
 114   JvmtiTagMap* tag_map = ((JvmtiEnvBase*)env)->tag_map_acquire();
 115   if (tag_map == nullptr) {
 116     MutexLocker mu(JvmtiThreadState_lock);
 117     tag_map = ((JvmtiEnvBase*)env)->tag_map();
 118     if (tag_map == nullptr) {
 119       tag_map = new JvmtiTagMap(env);
 120     }
 121   } else {
 122     DEBUG_ONLY(JavaThread::current()->check_possible_safepoint());
 123   }
 124   return tag_map;
 125 }
 126 
 127 // iterate over all entries in the tag map.
 128 void JvmtiTagMap::entry_iterate(JvmtiTagMapKeyClosure* closure) {
 129   hashmap()->entry_iterate(closure);
 130 }
 131 
 132 // returns true if the hashmaps are empty
 133 bool JvmtiTagMap::is_empty() {
 134   assert(SafepointSynchronize::is_at_safepoint() || is_locked(), "checking");
 135   return hashmap()->is_empty();
 136 }
 137 
 138 // This checks for posting before operations that use
 139 // this tagmap table.
 140 void JvmtiTagMap::check_hashmap(GrowableArray<jlong>* objects) {
 141   assert(is_locked(), "checking");
 142 
 143   if (is_empty()) { return; }
 144 
 145   if (_needs_cleaning &&
 146       objects != nullptr &&
 147       env()->is_enabled(JVMTI_EVENT_OBJECT_FREE)) {
 148     remove_dead_entries_locked(objects);
 149   }
 150 }
 151 
 152 // This checks for posting and is called from the heap walks.
 153 void JvmtiTagMap::check_hashmaps_for_heapwalk(GrowableArray<jlong>* objects) {
 154   assert(SafepointSynchronize::is_at_safepoint(), "called from safepoints");
 155 
 156   // Verify that the tag map tables are valid and unconditionally post events
 157   // that are expected to be posted before gc_notification.
 158   JvmtiEnvIterator it;
 159   for (JvmtiEnv* env = it.first(); env != nullptr; env = it.next(env)) {
 160     JvmtiTagMap* tag_map = env->tag_map_acquire();
 161     if (tag_map != nullptr) {
 162       // The ZDriver may be walking the hashmaps concurrently so this lock is needed.
 163       MutexLocker ml(tag_map->lock(), Mutex::_no_safepoint_check_flag);
 164       tag_map->check_hashmap(objects);
 165     }
 166   }
 167 }
 168 
 169 // Return the tag value for an object, or 0 if the object is
 170 // not tagged
 171 //
 172 static inline jlong tag_for(JvmtiTagMap* tag_map, oop o) {
 173   return tag_map->hashmap()->find(o);
 174 }
 175 
 176 // A CallbackWrapper is a support class for querying and tagging an object
 177 // around a callback to a profiler. The constructor does pre-callback
 178 // work to get the tag value, klass tag value, ... and the destructor
 179 // does the post-callback work of tagging or untagging the object.
 180 //
 181 // {
 182 //   CallbackWrapper wrapper(tag_map, o);
 183 //
 184 //   (*callback)(wrapper.klass_tag(), wrapper.obj_size(), wrapper.obj_tag_p(), ...)
 185 //
 186 // }
 187 // wrapper goes out of scope here which results in the destructor
 188 // checking to see if the object has been tagged, untagged, or the
 189 // tag value has changed.
 190 //
 191 class CallbackWrapper : public StackObj {
 192  private:
 193   JvmtiTagMap* _tag_map;
 194   JvmtiTagMapTable* _hashmap;
 195   oop _o;
 196   jlong _obj_size;
 197   jlong _obj_tag;
 198   jlong _klass_tag;
 199 
 200  protected:
 201   JvmtiTagMap* tag_map() const { return _tag_map; }
 202 
 203   // invoked post-callback to tag, untag, or update the tag of an object
 204   void inline post_callback_tag_update(oop o, JvmtiTagMapTable* hashmap,
 205                                        jlong obj_tag);
 206  public:
 207   CallbackWrapper(JvmtiTagMap* tag_map, oop o) {
 208     assert(Thread::current()->is_VM_thread() || tag_map->is_locked(),
 209            "MT unsafe or must be VM thread");
 210 
 211     // object to tag
 212     _o = o;
 213 
 214     // object size
 215     _obj_size = (jlong)_o->size() * wordSize;
 216 
 217     // record the context
 218     _tag_map = tag_map;
 219     _hashmap = tag_map->hashmap();
 220 
 221     // get object tag
 222     _obj_tag = _hashmap->find(_o);
 223 
 224     // get the class and the class's tag value
 225     assert(vmClasses::Class_klass()->is_mirror_instance_klass(), "Is not?");
 226 
 227     _klass_tag = tag_for(tag_map, _o->klass()->java_mirror());
 228   }
 229 
 230   ~CallbackWrapper() {
 231     post_callback_tag_update(_o, _hashmap, _obj_tag);
 232   }
 233 
 234   inline jlong* obj_tag_p()                     { return &_obj_tag; }
 235   inline jlong obj_size() const                 { return _obj_size; }
 236   inline jlong obj_tag() const                  { return _obj_tag; }
 237   inline jlong klass_tag() const                { return _klass_tag; }
 238 };
 239 
 240 // callback post-callback to tag, untag, or update the tag of an object
 241 void inline CallbackWrapper::post_callback_tag_update(oop o,
 242                                                       JvmtiTagMapTable* hashmap,
 243                                                       jlong obj_tag) {
 244   if (obj_tag == 0) {
 245     // callback has untagged the object, remove the entry if present
 246     hashmap->remove(o);
 247   } else {
 248     // object was previously tagged or not present - the callback may have
 249     // changed the tag value
 250     assert(Thread::current()->is_VM_thread(), "must be VMThread");
 251     hashmap->add(o, obj_tag);
 252   }
 253 }
 254 
 255 // An extended CallbackWrapper used when reporting an object reference
 256 // to the agent.
 257 //
 258 // {
 259 //   TwoOopCallbackWrapper wrapper(tag_map, referrer, o);
 260 //
 261 //   (*callback)(wrapper.klass_tag(),
 262 //               wrapper.obj_size(),
 263 //               wrapper.obj_tag_p()
 264 //               wrapper.referrer_tag_p(), ...)
 265 //
 266 // }
 267 // wrapper goes out of scope here which results in the destructor
 268 // checking to see if the referrer object has been tagged, untagged,
 269 // or the tag value has changed.
 270 //
 271 class TwoOopCallbackWrapper : public CallbackWrapper {
 272  private:
 273   bool _is_reference_to_self;
 274   JvmtiTagMapTable* _referrer_hashmap;
 275   oop _referrer;
 276   jlong _referrer_obj_tag;
 277   jlong _referrer_klass_tag;
 278   jlong* _referrer_tag_p;
 279 
 280   bool is_reference_to_self() const             { return _is_reference_to_self; }
 281 
 282  public:
 283   TwoOopCallbackWrapper(JvmtiTagMap* tag_map, oop referrer, oop o) :
 284     CallbackWrapper(tag_map, o)
 285   {
 286     // self reference needs to be handled in a special way
 287     _is_reference_to_self = (referrer == o);
 288 
 289     if (_is_reference_to_self) {
 290       _referrer_klass_tag = klass_tag();
 291       _referrer_tag_p = obj_tag_p();
 292     } else {
 293       _referrer = referrer;
 294       // record the context
 295       _referrer_hashmap = tag_map->hashmap();
 296 
 297       // get object tag
 298       _referrer_obj_tag = _referrer_hashmap->find(_referrer);
 299 
 300       _referrer_tag_p = &_referrer_obj_tag;
 301 
 302       // get referrer class tag.
 303       _referrer_klass_tag = tag_for(tag_map, _referrer->klass()->java_mirror());
 304     }
 305   }
 306 
 307   ~TwoOopCallbackWrapper() {
 308     if (!is_reference_to_self()) {
 309       post_callback_tag_update(_referrer,
 310                                _referrer_hashmap,
 311                                _referrer_obj_tag);
 312     }
 313   }
 314 
 315   // address of referrer tag
 316   // (for a self reference this will return the same thing as obj_tag_p())
 317   inline jlong* referrer_tag_p() { return _referrer_tag_p; }
 318 
 319   // referrer's class tag
 320   inline jlong referrer_klass_tag() { return _referrer_klass_tag; }
 321 };
 322 
 323 // tag an object
 324 //
 325 // This function is performance critical. If many threads attempt to tag objects
 326 // around the same time then it's possible that the Mutex associated with the
 327 // tag map will be a hot lock.
 328 void JvmtiTagMap::set_tag(jobject object, jlong tag) {
 329   MutexLocker ml(lock(), Mutex::_no_safepoint_check_flag);
 330 
 331   // SetTag should not post events because the JavaThread has to
 332   // transition to native for the callback and this cannot stop for
 333   // safepoints with the hashmap lock held.
 334   check_hashmap(nullptr);  /* don't collect dead objects */
 335 
 336   // resolve the object
 337   oop o = JNIHandles::resolve_non_null(object);
 338 
 339   // see if the object is already tagged
 340   JvmtiTagMapTable* hashmap = _hashmap;
 341 
 342   if (tag == 0) {
 343     // remove the entry if present
 344     hashmap->remove(o);
 345   } else {
 346     // if the object is already tagged or not present then we add/update
 347     // the tag
 348     hashmap->add(o, tag);
 349   }
 350 }
 351 
 352 // get the tag for an object
 353 jlong JvmtiTagMap::get_tag(jobject object) {
 354   MutexLocker ml(lock(), Mutex::_no_safepoint_check_flag);
 355 
 356   // GetTag should not post events because the JavaThread has to
 357   // transition to native for the callback and this cannot stop for
 358   // safepoints with the hashmap lock held.
 359   check_hashmap(nullptr); /* don't collect dead objects */
 360 
 361   // resolve the object
 362   oop o = JNIHandles::resolve_non_null(object);
 363 
 364   return tag_for(this, o);
 365 }
 366 
 367 
 368 // Helper class used to describe the static or instance fields of a class.
 369 // For each field it holds the field index (as defined by the JVMTI specification),
 370 // the field type, and the offset.
 371 
 372 class ClassFieldDescriptor: public CHeapObj<mtInternal> {
 373  private:
 374   int _field_index;
 375   int _field_offset;
 376   char _field_type;
 377  public:
 378   ClassFieldDescriptor(int index, char type, int offset) :
 379     _field_index(index), _field_offset(offset), _field_type(type) {
 380   }
 381   int field_index()  const  { return _field_index; }
 382   char field_type()  const  { return _field_type; }
 383   int field_offset() const  { return _field_offset; }
 384 };
 385 
 386 class ClassFieldMap: public CHeapObj<mtInternal> {
 387  private:
 388   enum {
 389     initial_field_count = 5
 390   };
 391 
 392   // list of field descriptors
 393   GrowableArray<ClassFieldDescriptor*>* _fields;
 394 
 395   // constructor
 396   ClassFieldMap();
 397 
 398   // calculates number of fields in all interfaces
 399   static int interfaces_field_count(InstanceKlass* ik);
 400 
 401   // add a field
 402   void add(int index, char type, int offset);
 403 
 404  public:
 405   ~ClassFieldMap();
 406 
 407   // access
 408   int field_count()                     { return _fields->length(); }
 409   ClassFieldDescriptor* field_at(int i) { return _fields->at(i); }
 410 
 411   // functions to create maps of static or instance fields
 412   static ClassFieldMap* create_map_of_static_fields(Klass* k);
 413   static ClassFieldMap* create_map_of_instance_fields(oop obj);
 414 };
 415 
 416 ClassFieldMap::ClassFieldMap() {
 417   _fields = new (mtServiceability)
 418     GrowableArray<ClassFieldDescriptor*>(initial_field_count, mtServiceability);
 419 }
 420 
 421 ClassFieldMap::~ClassFieldMap() {
 422   for (int i=0; i<_fields->length(); i++) {
 423     delete _fields->at(i);
 424   }
 425   delete _fields;
 426 }
 427 
 428 int ClassFieldMap::interfaces_field_count(InstanceKlass* ik) {
 429   const Array<InstanceKlass*>* interfaces = ik->transitive_interfaces();
 430   int count = 0;
 431   for (int i = 0; i < interfaces->length(); i++) {
 432     count += interfaces->at(i)->java_fields_count();
 433 
 434   }
 435   return count;
 436 }
 437 
 438 void ClassFieldMap::add(int index, char type, int offset) {
 439   ClassFieldDescriptor* field = new ClassFieldDescriptor(index, type, offset);
 440   _fields->append(field);
 441 }
 442 
 443 // Returns a heap allocated ClassFieldMap to describe the static fields
 444 // of the given class.
 445 ClassFieldMap* ClassFieldMap::create_map_of_static_fields(Klass* k) {
 446   InstanceKlass* ik = InstanceKlass::cast(k);
 447 
 448   // create the field map
 449   ClassFieldMap* field_map = new ClassFieldMap();
 450 
 451   // Static fields of interfaces and superclasses are reported as references from the interfaces/superclasses.
 452   // Need to calculate start index of this class fields: number of fields in all interfaces and superclasses.
 453   int index = interfaces_field_count(ik);
 454   for (InstanceKlass* super_klass = ik->super(); super_klass != nullptr; super_klass = super_klass->super()) {
 455     index += super_klass->java_fields_count();
 456   }
 457 
 458   for (JavaFieldStream fld(ik); !fld.done(); fld.next(), index++) {
 459     // ignore instance fields
 460     if (!fld.access_flags().is_static()) {
 461       continue;
 462     }
 463     field_map->add(index, fld.signature()->char_at(0), fld.offset());
 464   }
 465 
 466   return field_map;
 467 }
 468 
 469 // Returns a heap allocated ClassFieldMap to describe the instance fields
 470 // of the given class. All instance fields are included (this means public
 471 // and private fields declared in superclasses too).
 472 ClassFieldMap* ClassFieldMap::create_map_of_instance_fields(oop obj) {
 473   InstanceKlass* ik = InstanceKlass::cast(obj->klass());
 474 
 475   // create the field map
 476   ClassFieldMap* field_map = new ClassFieldMap();
 477 
 478   // fields of the superclasses are reported first, so need to know total field number to calculate field indices
 479   int total_field_number = interfaces_field_count(ik);
 480   for (InstanceKlass* klass = ik; klass != nullptr; klass = klass->super()) {
 481     total_field_number += klass->java_fields_count();
 482   }
 483 
 484   for (InstanceKlass* klass = ik; klass != nullptr; klass = klass->super()) {
 485     JavaFieldStream fld(klass);
 486     int start_index = total_field_number - klass->java_fields_count();
 487     for (int index = 0; !fld.done(); fld.next(), index++) {
 488       // ignore static fields
 489       if (fld.access_flags().is_static()) {
 490         continue;
 491       }
 492       field_map->add(start_index + index, fld.signature()->char_at(0), fld.offset());
 493     }
 494     // update total_field_number for superclass (decrease by the field count in the current class)
 495     total_field_number = start_index;
 496   }
 497 
 498   return field_map;
 499 }
 500 
 501 // Helper class used to cache a ClassFileMap for the instance fields of
 502 // a cache. A JvmtiCachedClassFieldMap can be cached by an InstanceKlass during
 503 // heap iteration and avoid creating a field map for each object in the heap
 504 // (only need to create the map when the first instance of a class is encountered).
 505 //
 506 class JvmtiCachedClassFieldMap : public CHeapObj<mtInternal> {
 507  private:
 508   enum {
 509      initial_class_count = 200
 510   };
 511   ClassFieldMap* _field_map;
 512 
 513   ClassFieldMap* field_map() const { return _field_map; }
 514 
 515   JvmtiCachedClassFieldMap(ClassFieldMap* field_map);
 516   ~JvmtiCachedClassFieldMap();
 517 
 518   static GrowableArray<InstanceKlass*>* _class_list;
 519   static void add_to_class_list(InstanceKlass* ik);
 520 
 521  public:
 522   // returns the field map for a given object (returning map cached
 523   // by InstanceKlass if possible
 524   static ClassFieldMap* get_map_of_instance_fields(oop obj);
 525 
 526   // removes the field map from all instanceKlasses - should be
 527   // called before VM operation completes
 528   static void clear_cache();
 529 
 530   // returns the number of ClassFieldMap cached by instanceKlasses
 531   static int cached_field_map_count();
 532 };
 533 
 534 GrowableArray<InstanceKlass*>* JvmtiCachedClassFieldMap::_class_list;
 535 
 536 JvmtiCachedClassFieldMap::JvmtiCachedClassFieldMap(ClassFieldMap* field_map) {
 537   _field_map = field_map;
 538 }
 539 
 540 JvmtiCachedClassFieldMap::~JvmtiCachedClassFieldMap() {
 541   if (_field_map != nullptr) {
 542     delete _field_map;
 543   }
 544 }
 545 
 546 // Marker class to ensure that the class file map cache is only used in a defined
 547 // scope.
 548 class ClassFieldMapCacheMark : public StackObj {
 549  private:
 550    static bool _is_active;
 551  public:
 552    ClassFieldMapCacheMark() {
 553      assert(Thread::current()->is_VM_thread(), "must be VMThread");
 554      assert(JvmtiCachedClassFieldMap::cached_field_map_count() == 0, "cache not empty");
 555      assert(!_is_active, "ClassFieldMapCacheMark cannot be nested");
 556      _is_active = true;
 557    }
 558    ~ClassFieldMapCacheMark() {
 559      JvmtiCachedClassFieldMap::clear_cache();
 560      _is_active = false;
 561    }
 562    static bool is_active() { return _is_active; }
 563 };
 564 
 565 bool ClassFieldMapCacheMark::_is_active;
 566 
 567 // record that the given InstanceKlass is caching a field map
 568 void JvmtiCachedClassFieldMap::add_to_class_list(InstanceKlass* ik) {
 569   if (_class_list == nullptr) {
 570     _class_list = new (mtServiceability)
 571       GrowableArray<InstanceKlass*>(initial_class_count, mtServiceability);
 572   }
 573   _class_list->push(ik);
 574 }
 575 
 576 // returns the instance field map for the given object
 577 // (returns field map cached by the InstanceKlass if possible)
 578 ClassFieldMap* JvmtiCachedClassFieldMap::get_map_of_instance_fields(oop obj) {
 579   assert(Thread::current()->is_VM_thread(), "must be VMThread");
 580   assert(ClassFieldMapCacheMark::is_active(), "ClassFieldMapCacheMark not active");
 581 
 582   Klass* k = obj->klass();
 583   InstanceKlass* ik = InstanceKlass::cast(k);
 584 
 585   // return cached map if possible
 586   JvmtiCachedClassFieldMap* cached_map = ik->jvmti_cached_class_field_map();
 587   if (cached_map != nullptr) {
 588     assert(cached_map->field_map() != nullptr, "missing field list");
 589     return cached_map->field_map();
 590   } else {
 591     ClassFieldMap* field_map = ClassFieldMap::create_map_of_instance_fields(obj);
 592     cached_map = new JvmtiCachedClassFieldMap(field_map);
 593     ik->set_jvmti_cached_class_field_map(cached_map);
 594     add_to_class_list(ik);
 595     return field_map;
 596   }
 597 }
 598 
 599 // remove the fields maps cached from all instanceKlasses
 600 void JvmtiCachedClassFieldMap::clear_cache() {
 601   assert(Thread::current()->is_VM_thread(), "must be VMThread");
 602   if (_class_list != nullptr) {
 603     for (int i = 0; i < _class_list->length(); i++) {
 604       InstanceKlass* ik = _class_list->at(i);
 605       JvmtiCachedClassFieldMap* cached_map = ik->jvmti_cached_class_field_map();
 606       assert(cached_map != nullptr, "should not be null");
 607       ik->set_jvmti_cached_class_field_map(nullptr);
 608       delete cached_map;  // deletes the encapsulated field map
 609     }
 610     delete _class_list;
 611     _class_list = nullptr;
 612   }
 613 }
 614 
 615 // returns the number of ClassFieldMap cached by instanceKlasses
 616 int JvmtiCachedClassFieldMap::cached_field_map_count() {
 617   return (_class_list == nullptr) ? 0 : _class_list->length();
 618 }
 619 
 620 // helper function to indicate if an object is filtered by its tag or class tag
 621 static inline bool is_filtered_by_heap_filter(jlong obj_tag,
 622                                               jlong klass_tag,
 623                                               int heap_filter) {
 624   // apply the heap filter
 625   if (obj_tag != 0) {
 626     // filter out tagged objects
 627     if (heap_filter & JVMTI_HEAP_FILTER_TAGGED) return true;
 628   } else {
 629     // filter out untagged objects
 630     if (heap_filter & JVMTI_HEAP_FILTER_UNTAGGED) return true;
 631   }
 632   if (klass_tag != 0) {
 633     // filter out objects with tagged classes
 634     if (heap_filter & JVMTI_HEAP_FILTER_CLASS_TAGGED) return true;
 635   } else {
 636     // filter out objects with untagged classes.
 637     if (heap_filter & JVMTI_HEAP_FILTER_CLASS_UNTAGGED) return true;
 638   }
 639   return false;
 640 }
 641 
 642 // helper function to indicate if an object is filtered by a klass filter
 643 static inline bool is_filtered_by_klass_filter(oop obj, Klass* klass_filter) {
 644   if (klass_filter != nullptr) {
 645     if (obj->klass() != klass_filter) {
 646       return true;
 647     }
 648   }
 649   return false;
 650 }
 651 
 652 // helper function to tell if a field is a primitive field or not
 653 static inline bool is_primitive_field_type(char type) {
 654   return (type != JVM_SIGNATURE_CLASS && type != JVM_SIGNATURE_ARRAY);
 655 }
 656 
 657 // helper function to copy the value from location addr to jvalue.
 658 static inline void copy_to_jvalue(jvalue *v, address addr, jvmtiPrimitiveType value_type) {
 659   switch (value_type) {
 660     case JVMTI_PRIMITIVE_TYPE_BOOLEAN : { v->z = *(jboolean*)addr; break; }
 661     case JVMTI_PRIMITIVE_TYPE_BYTE    : { v->b = *(jbyte*)addr;    break; }
 662     case JVMTI_PRIMITIVE_TYPE_CHAR    : { v->c = *(jchar*)addr;    break; }
 663     case JVMTI_PRIMITIVE_TYPE_SHORT   : { v->s = *(jshort*)addr;   break; }
 664     case JVMTI_PRIMITIVE_TYPE_INT     : { v->i = *(jint*)addr;     break; }
 665     case JVMTI_PRIMITIVE_TYPE_LONG    : { v->j = *(jlong*)addr;    break; }
 666     case JVMTI_PRIMITIVE_TYPE_FLOAT   : { v->f = *(jfloat*)addr;   break; }
 667     case JVMTI_PRIMITIVE_TYPE_DOUBLE  : { v->d = *(jdouble*)addr;  break; }
 668     default: ShouldNotReachHere();
 669   }
 670 }
 671 
 672 // helper function to invoke string primitive value callback
 673 // returns visit control flags
 674 static jint invoke_string_value_callback(jvmtiStringPrimitiveValueCallback cb,
 675                                          CallbackWrapper* wrapper,
 676                                          oop str,
 677                                          void* user_data)
 678 {
 679   assert(str->klass() == vmClasses::String_klass(), "not a string");
 680 
 681   typeArrayOop s_value = java_lang_String::value(str);
 682 
 683   // JDK-6584008: the value field may be null if a String instance is
 684   // partially constructed.
 685   if (s_value == nullptr) {
 686     return 0;
 687   }
 688   // get the string value and length
 689   // (string value may be offset from the base)
 690   int s_len = java_lang_String::length(str);
 691   bool is_latin1 = java_lang_String::is_latin1(str);
 692   jchar* value;
 693   if (s_len > 0) {
 694     if (!is_latin1) {
 695       value = s_value->char_at_addr(0);
 696     } else {
 697       // Inflate latin1 encoded string to UTF16
 698       jchar* buf = NEW_C_HEAP_ARRAY(jchar, s_len, mtInternal);
 699       for (int i = 0; i < s_len; i++) {
 700         buf[i] = ((jchar) s_value->byte_at(i)) & 0xff;
 701       }
 702       value = &buf[0];
 703     }
 704   } else {
 705     // Don't use char_at_addr(0) if length is 0
 706     value = (jchar*) s_value->base(T_CHAR);
 707   }
 708 
 709   // invoke the callback
 710   jint res = (*cb)(wrapper->klass_tag(),
 711                    wrapper->obj_size(),
 712                    wrapper->obj_tag_p(),
 713                    value,
 714                    (jint)s_len,
 715                    user_data);
 716 
 717   if (is_latin1 && s_len > 0) {
 718     FREE_C_HEAP_ARRAY(jchar, value);
 719   }
 720   return res;
 721 }
 722 
 723 // helper function to invoke string primitive value callback
 724 // returns visit control flags
 725 static jint invoke_array_primitive_value_callback(jvmtiArrayPrimitiveValueCallback cb,
 726                                                   CallbackWrapper* wrapper,
 727                                                   oop obj,
 728                                                   void* user_data)
 729 {
 730   assert(obj->is_typeArray(), "not a primitive array");
 731 
 732   // get base address of first element
 733   typeArrayOop array = typeArrayOop(obj);
 734   BasicType type = TypeArrayKlass::cast(array->klass())->element_type();
 735   void* elements = array->base(type);
 736 
 737   // jvmtiPrimitiveType is defined so this mapping is always correct
 738   jvmtiPrimitiveType elem_type = (jvmtiPrimitiveType)type2char(type);
 739 
 740   return (*cb)(wrapper->klass_tag(),
 741                wrapper->obj_size(),
 742                wrapper->obj_tag_p(),
 743                (jint)array->length(),
 744                elem_type,
 745                elements,
 746                user_data);
 747 }
 748 
 749 // helper function to invoke the primitive field callback for all static fields
 750 // of a given class
 751 static jint invoke_primitive_field_callback_for_static_fields
 752   (CallbackWrapper* wrapper,
 753    oop obj,
 754    jvmtiPrimitiveFieldCallback cb,
 755    void* user_data)
 756 {
 757   // for static fields only the index will be set
 758   static jvmtiHeapReferenceInfo reference_info = { 0 };
 759 
 760   assert(obj->klass() == vmClasses::Class_klass(), "not a class");
 761   if (java_lang_Class::is_primitive(obj)) {
 762     return 0;
 763   }
 764   Klass* klass = java_lang_Class::as_Klass(obj);
 765 
 766   // ignore classes for object and type arrays
 767   if (!klass->is_instance_klass()) {
 768     return 0;
 769   }
 770 
 771   // ignore classes which aren't linked yet
 772   InstanceKlass* ik = InstanceKlass::cast(klass);
 773   if (!ik->is_linked()) {
 774     return 0;
 775   }
 776 
 777   // get the field map
 778   ClassFieldMap* field_map = ClassFieldMap::create_map_of_static_fields(klass);
 779 
 780   // invoke the callback for each static primitive field
 781   for (int i=0; i<field_map->field_count(); i++) {
 782     ClassFieldDescriptor* field = field_map->field_at(i);
 783 
 784     // ignore non-primitive fields
 785     char type = field->field_type();
 786     if (!is_primitive_field_type(type)) {
 787       continue;
 788     }
 789     // one-to-one mapping
 790     jvmtiPrimitiveType value_type = (jvmtiPrimitiveType)type;
 791 
 792     // get offset and field value
 793     int offset = field->field_offset();
 794     address addr = cast_from_oop<address>(klass->java_mirror()) + offset;
 795     jvalue value;
 796     copy_to_jvalue(&value, addr, value_type);
 797 
 798     // field index
 799     reference_info.field.index = field->field_index();
 800 
 801     // invoke the callback
 802     jint res = (*cb)(JVMTI_HEAP_REFERENCE_STATIC_FIELD,
 803                      &reference_info,
 804                      wrapper->klass_tag(),
 805                      wrapper->obj_tag_p(),
 806                      value,
 807                      value_type,
 808                      user_data);
 809     if (res & JVMTI_VISIT_ABORT) {
 810       delete field_map;
 811       return res;
 812     }
 813   }
 814 
 815   delete field_map;
 816   return 0;
 817 }
 818 
 819 // helper function to invoke the primitive field callback for all instance fields
 820 // of a given object
 821 static jint invoke_primitive_field_callback_for_instance_fields(
 822   CallbackWrapper* wrapper,
 823   oop obj,
 824   jvmtiPrimitiveFieldCallback cb,
 825   void* user_data)
 826 {
 827   // for instance fields only the index will be set
 828   static jvmtiHeapReferenceInfo reference_info = { 0 };
 829 
 830   // get the map of the instance fields
 831   ClassFieldMap* fields = JvmtiCachedClassFieldMap::get_map_of_instance_fields(obj);
 832 
 833   // invoke the callback for each instance primitive field
 834   for (int i=0; i<fields->field_count(); i++) {
 835     ClassFieldDescriptor* field = fields->field_at(i);
 836 
 837     // ignore non-primitive fields
 838     char type = field->field_type();
 839     if (!is_primitive_field_type(type)) {
 840       continue;
 841     }
 842     // one-to-one mapping
 843     jvmtiPrimitiveType value_type = (jvmtiPrimitiveType)type;
 844 
 845     // get offset and field value
 846     int offset = field->field_offset();
 847     address addr = cast_from_oop<address>(obj) + offset;
 848     jvalue value;
 849     copy_to_jvalue(&value, addr, value_type);
 850 
 851     // field index
 852     reference_info.field.index = field->field_index();
 853 
 854     // invoke the callback
 855     jint res = (*cb)(JVMTI_HEAP_REFERENCE_FIELD,
 856                      &reference_info,
 857                      wrapper->klass_tag(),
 858                      wrapper->obj_tag_p(),
 859                      value,
 860                      value_type,
 861                      user_data);
 862     if (res & JVMTI_VISIT_ABORT) {
 863       return res;
 864     }
 865   }
 866   return 0;
 867 }
 868 
 869 
 870 // VM operation to iterate over all objects in the heap (both reachable
 871 // and unreachable)
 872 class VM_HeapIterateOperation: public VM_Operation {
 873  private:
 874   ObjectClosure* _blk;
 875   GrowableArray<jlong>* const _dead_objects;
 876  public:
 877   VM_HeapIterateOperation(ObjectClosure* blk, GrowableArray<jlong>* objects) :
 878     _blk(blk), _dead_objects(objects) { }
 879 
 880   VMOp_Type type() const { return VMOp_HeapIterateOperation; }
 881   void doit() {
 882     // allows class files maps to be cached during iteration
 883     ClassFieldMapCacheMark cm;
 884 
 885     JvmtiTagMap::check_hashmaps_for_heapwalk(_dead_objects);
 886 
 887     // make sure that heap is parsable (fills TLABs with filler objects)
 888     Universe::heap()->ensure_parsability(false);  // no need to retire TLABs
 889 
 890     // Verify heap before iteration - if the heap gets corrupted then
 891     // JVMTI's IterateOverHeap will crash.
 892     if (VerifyBeforeIteration) {
 893       Universe::verify();
 894     }
 895 
 896     // do the iteration
 897     Universe::heap()->object_iterate(_blk);
 898   }
 899 };
 900 
 901 
 902 // An ObjectClosure used to support the deprecated IterateOverHeap and
 903 // IterateOverInstancesOfClass functions
 904 class IterateOverHeapObjectClosure: public ObjectClosure {
 905  private:
 906   JvmtiTagMap* _tag_map;
 907   Klass* _klass;
 908   jvmtiHeapObjectFilter _object_filter;
 909   jvmtiHeapObjectCallback _heap_object_callback;
 910   const void* _user_data;
 911 
 912   // accessors
 913   JvmtiTagMap* tag_map() const                    { return _tag_map; }
 914   jvmtiHeapObjectFilter object_filter() const     { return _object_filter; }
 915   jvmtiHeapObjectCallback object_callback() const { return _heap_object_callback; }
 916   Klass* klass() const                            { return _klass; }
 917   const void* user_data() const                   { return _user_data; }
 918 
 919   // indicates if iteration has been aborted
 920   bool _iteration_aborted;
 921   bool is_iteration_aborted() const               { return _iteration_aborted; }
 922   void set_iteration_aborted(bool aborted)        { _iteration_aborted = aborted; }
 923 
 924  public:
 925   IterateOverHeapObjectClosure(JvmtiTagMap* tag_map,
 926                                Klass* klass,
 927                                jvmtiHeapObjectFilter object_filter,
 928                                jvmtiHeapObjectCallback heap_object_callback,
 929                                const void* user_data) :
 930     _tag_map(tag_map),
 931     _klass(klass),
 932     _object_filter(object_filter),
 933     _heap_object_callback(heap_object_callback),
 934     _user_data(user_data),
 935     _iteration_aborted(false)
 936   {
 937   }
 938 
 939   void do_object(oop o);
 940 };
 941 
 942 // invoked for each object in the heap
 943 void IterateOverHeapObjectClosure::do_object(oop o) {
 944   assert(o != nullptr, "Heap iteration should never produce null!");
 945   // check if iteration has been halted
 946   if (is_iteration_aborted()) return;
 947 
 948   // instanceof check when filtering by klass
 949   if (klass() != nullptr && !o->is_a(klass())) {
 950     return;
 951   }
 952 
 953   // skip if object is a dormant shared object whose mirror hasn't been loaded
 954   if (o->klass()->java_mirror() == nullptr) {
 955     log_debug(aot, heap)("skipped dormant archived object " INTPTR_FORMAT " (%s)", p2i(o),
 956                          o->klass()->external_name());
 957     return;
 958   }
 959 
 960   // prepare for the calllback
 961   CallbackWrapper wrapper(tag_map(), o);
 962 
 963   // if the object is tagged and we're only interested in untagged objects
 964   // then don't invoke the callback. Similarly, if the object is untagged
 965   // and we're only interested in tagged objects we skip the callback.
 966   if (wrapper.obj_tag() != 0) {
 967     if (object_filter() == JVMTI_HEAP_OBJECT_UNTAGGED) return;
 968   } else {
 969     if (object_filter() == JVMTI_HEAP_OBJECT_TAGGED) return;
 970   }
 971 
 972   // invoke the agent's callback
 973   jvmtiIterationControl control = (*object_callback())(wrapper.klass_tag(),
 974                                                        wrapper.obj_size(),
 975                                                        wrapper.obj_tag_p(),
 976                                                        (void*)user_data());
 977   if (control == JVMTI_ITERATION_ABORT) {
 978     set_iteration_aborted(true);
 979   }
 980 }
 981 
 982 // An ObjectClosure used to support the IterateThroughHeap function
 983 class IterateThroughHeapObjectClosure: public ObjectClosure {
 984  private:
 985   JvmtiTagMap* _tag_map;
 986   Klass* _klass;
 987   int _heap_filter;
 988   const jvmtiHeapCallbacks* _callbacks;
 989   const void* _user_data;
 990 
 991   // accessor functions
 992   JvmtiTagMap* tag_map() const                     { return _tag_map; }
 993   int heap_filter() const                          { return _heap_filter; }
 994   const jvmtiHeapCallbacks* callbacks() const      { return _callbacks; }
 995   Klass* klass() const                             { return _klass; }
 996   const void* user_data() const                    { return _user_data; }
 997 
 998   // indicates if the iteration has been aborted
 999   bool _iteration_aborted;
1000   bool is_iteration_aborted() const                { return _iteration_aborted; }
1001 
1002   // used to check the visit control flags. If the abort flag is set
1003   // then we set the iteration aborted flag so that the iteration completes
1004   // without processing any further objects
1005   bool check_flags_for_abort(jint flags) {
1006     bool is_abort = (flags & JVMTI_VISIT_ABORT) != 0;
1007     if (is_abort) {
1008       _iteration_aborted = true;
1009     }
1010     return is_abort;
1011   }
1012 
1013  public:
1014   IterateThroughHeapObjectClosure(JvmtiTagMap* tag_map,
1015                                   Klass* klass,
1016                                   int heap_filter,
1017                                   const jvmtiHeapCallbacks* heap_callbacks,
1018                                   const void* user_data) :
1019     _tag_map(tag_map),
1020     _klass(klass),
1021     _heap_filter(heap_filter),
1022     _callbacks(heap_callbacks),
1023     _user_data(user_data),
1024     _iteration_aborted(false)
1025   {
1026   }
1027 
1028   void do_object(oop o);
1029 };
1030 
1031 // invoked for each object in the heap
1032 void IterateThroughHeapObjectClosure::do_object(oop obj) {
1033   assert(obj != nullptr, "Heap iteration should never produce null!");
1034   // check if iteration has been halted
1035   if (is_iteration_aborted()) return;
1036 
1037   // apply class filter
1038   if (is_filtered_by_klass_filter(obj, klass())) return;
1039 
1040   // skip if object is a dormant shared object whose mirror hasn't been loaded
1041   if (obj->klass()->java_mirror() == nullptr) {
1042     log_debug(aot, heap)("skipped dormant archived object " INTPTR_FORMAT " (%s)", p2i(obj),
1043                          obj->klass()->external_name());
1044     return;
1045   }
1046 
1047   // prepare for callback
1048   CallbackWrapper wrapper(tag_map(), obj);
1049 
1050   // check if filtered by the heap filter
1051   if (is_filtered_by_heap_filter(wrapper.obj_tag(), wrapper.klass_tag(), heap_filter())) {
1052     return;
1053   }
1054 
1055   // for arrays we need the length, otherwise -1
1056   bool is_array = obj->is_array();
1057   int len = is_array ? arrayOop(obj)->length() : -1;
1058 
1059   // invoke the object callback (if callback is provided)
1060   if (callbacks()->heap_iteration_callback != nullptr) {
1061     jvmtiHeapIterationCallback cb = callbacks()->heap_iteration_callback;
1062     jint res = (*cb)(wrapper.klass_tag(),
1063                      wrapper.obj_size(),
1064                      wrapper.obj_tag_p(),
1065                      (jint)len,
1066                      (void*)user_data());
1067     if (check_flags_for_abort(res)) return;
1068   }
1069 
1070   // for objects and classes we report primitive fields if callback provided
1071   if (callbacks()->primitive_field_callback != nullptr && obj->is_instance()) {
1072     jint res;
1073     jvmtiPrimitiveFieldCallback cb = callbacks()->primitive_field_callback;
1074     if (obj->klass() == vmClasses::Class_klass()) {
1075       res = invoke_primitive_field_callback_for_static_fields(&wrapper,
1076                                                                     obj,
1077                                                                     cb,
1078                                                                     (void*)user_data());
1079     } else {
1080       res = invoke_primitive_field_callback_for_instance_fields(&wrapper,
1081                                                                       obj,
1082                                                                       cb,
1083                                                                       (void*)user_data());
1084     }
1085     if (check_flags_for_abort(res)) return;
1086   }
1087 
1088   // string callback
1089   if (!is_array &&
1090       callbacks()->string_primitive_value_callback != nullptr &&
1091       obj->klass() == vmClasses::String_klass()) {
1092     jint res = invoke_string_value_callback(
1093                 callbacks()->string_primitive_value_callback,
1094                 &wrapper,
1095                 obj,
1096                 (void*)user_data() );
1097     if (check_flags_for_abort(res)) return;
1098   }
1099 
1100   // array callback
1101   if (is_array &&
1102       callbacks()->array_primitive_value_callback != nullptr &&
1103       obj->is_typeArray()) {
1104     jint res = invoke_array_primitive_value_callback(
1105                callbacks()->array_primitive_value_callback,
1106                &wrapper,
1107                obj,
1108                (void*)user_data() );
1109     if (check_flags_for_abort(res)) return;
1110   }
1111 };
1112 
1113 
1114 // Deprecated function to iterate over all objects in the heap
1115 void JvmtiTagMap::iterate_over_heap(jvmtiHeapObjectFilter object_filter,
1116                                     Klass* klass,
1117                                     jvmtiHeapObjectCallback heap_object_callback,
1118                                     const void* user_data)
1119 {
1120   // EA based optimizations on tagged objects are already reverted.
1121   EscapeBarrier eb(object_filter == JVMTI_HEAP_OBJECT_UNTAGGED ||
1122                    object_filter == JVMTI_HEAP_OBJECT_EITHER,
1123                    JavaThread::current());
1124   eb.deoptimize_objects_all_threads();
1125   Arena dead_object_arena(mtServiceability);
1126   GrowableArray <jlong> dead_objects(&dead_object_arena, 10, 0, 0);
1127   {
1128     MutexLocker ml(Heap_lock);
1129     IterateOverHeapObjectClosure blk(this,
1130                                      klass,
1131                                      object_filter,
1132                                      heap_object_callback,
1133                                      user_data);
1134     VM_HeapIterateOperation op(&blk, &dead_objects);
1135     VMThread::execute(&op);
1136   }
1137   // Post events outside of Heap_lock
1138   post_dead_objects(&dead_objects);
1139 }
1140 
1141 
1142 // Iterates over all objects in the heap
1143 void JvmtiTagMap::iterate_through_heap(jint heap_filter,
1144                                        Klass* klass,
1145                                        const jvmtiHeapCallbacks* callbacks,
1146                                        const void* user_data)
1147 {
1148   // EA based optimizations on tagged objects are already reverted.
1149   EscapeBarrier eb(!(heap_filter & JVMTI_HEAP_FILTER_UNTAGGED), JavaThread::current());
1150   eb.deoptimize_objects_all_threads();
1151 
1152   Arena dead_object_arena(mtServiceability);
1153   GrowableArray<jlong> dead_objects(&dead_object_arena, 10, 0, 0);
1154   {
1155     MutexLocker ml(Heap_lock);
1156     IterateThroughHeapObjectClosure blk(this,
1157                                         klass,
1158                                         heap_filter,
1159                                         callbacks,
1160                                         user_data);
1161     VM_HeapIterateOperation op(&blk, &dead_objects);
1162     VMThread::execute(&op);
1163   }
1164   // Post events outside of Heap_lock
1165   post_dead_objects(&dead_objects);
1166 }
1167 
1168 void JvmtiTagMap::remove_dead_entries_locked(GrowableArray<jlong>* objects) {
1169   assert(is_locked(), "precondition");
1170   if (_needs_cleaning) {
1171     // Recheck whether to post object free events under the lock.
1172     if (!env()->is_enabled(JVMTI_EVENT_OBJECT_FREE)) {
1173       objects = nullptr;
1174     }
1175     log_info(jvmti, table)("TagMap table needs cleaning%s",
1176                            ((objects != nullptr) ? " and posting" : ""));
1177     hashmap()->remove_dead_entries(objects);
1178     _needs_cleaning = false;
1179   }
1180 }
1181 
1182 void JvmtiTagMap::remove_dead_entries(GrowableArray<jlong>* objects) {
1183   MutexLocker ml(lock(), Mutex::_no_safepoint_check_flag);
1184   remove_dead_entries_locked(objects);
1185 }
1186 
1187 void JvmtiTagMap::post_dead_objects(GrowableArray<jlong>* const objects) {
1188   assert(Thread::current()->is_Java_thread(), "Must post from JavaThread");
1189   if (objects != nullptr && objects->length() > 0) {
1190     JvmtiExport::post_object_free(env(), objects);
1191     log_info(jvmti, table)("%d free object posted", objects->length());
1192   }
1193 }
1194 
1195 void JvmtiTagMap::remove_and_post_dead_objects() {
1196   ResourceMark rm;
1197   GrowableArray<jlong> objects;
1198   remove_dead_entries(&objects);
1199   post_dead_objects(&objects);
1200 }
1201 
1202 void JvmtiTagMap::flush_object_free_events() {
1203   assert_not_at_safepoint();
1204   if (env()->is_enabled(JVMTI_EVENT_OBJECT_FREE)) {
1205     {
1206       MonitorLocker ml(lock(), Mutex::_no_safepoint_check_flag);
1207       // If another thread is posting events, let it finish
1208       while (_posting_events) {
1209         ml.wait();
1210       }
1211 
1212       if (!_needs_cleaning || is_empty()) {
1213         _needs_cleaning = false;
1214         return;
1215       }
1216       _posting_events = true;
1217     } // Drop the lock so we can do the cleaning on the VM thread.
1218     // Needs both cleaning and event posting (up to some other thread
1219     // getting there first after we dropped the lock).
1220     remove_and_post_dead_objects();
1221     {
1222       MonitorLocker ml(lock(), Mutex::_no_safepoint_check_flag);
1223       _posting_events = false;
1224       ml.notify_all();
1225     }
1226   } else {
1227     remove_dead_entries(nullptr);
1228   }
1229 }
1230 
1231 // support class for get_objects_with_tags
1232 
1233 class TagObjectCollector : public JvmtiTagMapKeyClosure {
1234  private:
1235   JvmtiEnv* _env;
1236   JavaThread* _thread;
1237   jlong* _tags;
1238   jint _tag_count;
1239   bool _some_dead_found;
1240 
1241   GrowableArray<jobject>* _object_results;  // collected objects (JNI weak refs)
1242   GrowableArray<uint64_t>* _tag_results;    // collected tags
1243 
1244  public:
1245   TagObjectCollector(JvmtiEnv* env, const jlong* tags, jint tag_count) :
1246     _env(env),
1247     _thread(JavaThread::current()),
1248     _tags((jlong*)tags),
1249     _tag_count(tag_count),
1250     _some_dead_found(false),
1251     _object_results(new (mtServiceability) GrowableArray<jobject>(1, mtServiceability)),
1252     _tag_results(new (mtServiceability) GrowableArray<uint64_t>(1, mtServiceability)) { }
1253 
1254   ~TagObjectCollector() {
1255     delete _object_results;
1256     delete _tag_results;
1257   }
1258 
1259   bool some_dead_found() const { return _some_dead_found; }
1260 
1261   // for each tagged object check if the tag value matches
1262   // - if it matches then we create a JNI local reference to the object
1263   // and record the reference and tag value.
1264   // Always return true so the iteration continues.
1265   bool do_entry(JvmtiTagMapKey& key, jlong& value) {
1266     for (int i = 0; i < _tag_count; i++) {
1267       if (_tags[i] == value) {
1268         // The reference in this tag map could be the only (implicitly weak)
1269         // reference to that object. If we hand it out, we need to keep it live wrt
1270         // SATB marking similar to other j.l.ref.Reference referents. This is
1271         // achieved by using a phantom load in the object() accessor.
1272         oop o = key.object();
1273         if (o == nullptr) {
1274           _some_dead_found = true;
1275           // skip this whole entry
1276           return true;
1277         }
1278         assert(o != nullptr && Universe::heap()->is_in(o), "sanity check");
1279         jobject ref = JNIHandles::make_local(_thread, o);
1280         _object_results->append(ref);
1281         _tag_results->append(value);
1282       }
1283     }
1284     return true;
1285   }
1286 
1287   // return the results from the collection
1288   //
1289   jvmtiError result(jint* count_ptr, jobject** object_result_ptr, jlong** tag_result_ptr) {
1290     jvmtiError error;
1291     int count = _object_results->length();
1292     assert(count >= 0, "sanity check");
1293 
1294     // if object_result_ptr is not null then allocate the result and copy
1295     // in the object references.
1296     if (object_result_ptr != nullptr) {
1297       error = _env->Allocate(count * sizeof(jobject), (unsigned char**)object_result_ptr);
1298       if (error != JVMTI_ERROR_NONE) {
1299         return error;
1300       }
1301       for (int i=0; i<count; i++) {
1302         (*object_result_ptr)[i] = _object_results->at(i);
1303       }
1304     }
1305 
1306     // if tag_result_ptr is not null then allocate the result and copy
1307     // in the tag values.
1308     if (tag_result_ptr != nullptr) {
1309       error = _env->Allocate(count * sizeof(jlong), (unsigned char**)tag_result_ptr);
1310       if (error != JVMTI_ERROR_NONE) {
1311         if (object_result_ptr != nullptr) {
1312           _env->Deallocate((unsigned char*)object_result_ptr);
1313         }
1314         return error;
1315       }
1316       for (int i=0; i<count; i++) {
1317         (*tag_result_ptr)[i] = (jlong)_tag_results->at(i);
1318       }
1319     }
1320 
1321     *count_ptr = count;
1322     return JVMTI_ERROR_NONE;
1323   }
1324 };
1325 
1326 // return the list of objects with the specified tags
1327 jvmtiError JvmtiTagMap::get_objects_with_tags(const jlong* tags,
1328   jint count, jint* count_ptr, jobject** object_result_ptr, jlong** tag_result_ptr) {
1329 
1330   TagObjectCollector collector(env(), tags, count);
1331   {
1332     // iterate over all tagged objects
1333     MutexLocker ml(lock(), Mutex::_no_safepoint_check_flag);
1334     // Can't post ObjectFree events here from a JavaThread, so this
1335     // will race with the gc_notification thread in the tiny
1336     // window where the object is not marked but hasn't been notified that
1337     // it is collected yet.
1338     entry_iterate(&collector);
1339   }
1340   return collector.result(count_ptr, object_result_ptr, tag_result_ptr);
1341 }
1342 
1343 // helper to map a jvmtiHeapReferenceKind to an old style jvmtiHeapRootKind
1344 // (not performance critical as only used for roots)
1345 static jvmtiHeapRootKind toJvmtiHeapRootKind(jvmtiHeapReferenceKind kind) {
1346   switch (kind) {
1347     case JVMTI_HEAP_REFERENCE_JNI_GLOBAL:   return JVMTI_HEAP_ROOT_JNI_GLOBAL;
1348     case JVMTI_HEAP_REFERENCE_SYSTEM_CLASS: return JVMTI_HEAP_ROOT_SYSTEM_CLASS;
1349     case JVMTI_HEAP_REFERENCE_STACK_LOCAL:  return JVMTI_HEAP_ROOT_STACK_LOCAL;
1350     case JVMTI_HEAP_REFERENCE_JNI_LOCAL:    return JVMTI_HEAP_ROOT_JNI_LOCAL;
1351     case JVMTI_HEAP_REFERENCE_THREAD:       return JVMTI_HEAP_ROOT_THREAD;
1352     case JVMTI_HEAP_REFERENCE_OTHER:        return JVMTI_HEAP_ROOT_OTHER;
1353     default: ShouldNotReachHere();          return JVMTI_HEAP_ROOT_OTHER;
1354   }
1355 }
1356 
1357 // Base class for all heap walk contexts. The base class maintains a flag
1358 // to indicate if the context is valid or not.
1359 class HeapWalkContext {
1360  private:
1361   bool _valid;
1362  public:
1363   HeapWalkContext(bool valid)                   { _valid = valid; }
1364   void invalidate()                             { _valid = false; }
1365   bool is_valid() const                         { return _valid; }
1366 };
1367 
1368 // A basic heap walk context for the deprecated heap walking functions.
1369 // The context for a basic heap walk are the callbacks and fields used by
1370 // the referrer caching scheme.
1371 class BasicHeapWalkContext: public HeapWalkContext {
1372  private:
1373   jvmtiHeapRootCallback _heap_root_callback;
1374   jvmtiStackReferenceCallback _stack_ref_callback;
1375   jvmtiObjectReferenceCallback _object_ref_callback;
1376 
1377   // used for caching
1378   oop _last_referrer;
1379   jlong _last_referrer_tag;
1380 
1381  public:
1382   BasicHeapWalkContext() : HeapWalkContext(false) { }
1383 
1384   BasicHeapWalkContext(jvmtiHeapRootCallback heap_root_callback,
1385                        jvmtiStackReferenceCallback stack_ref_callback,
1386                        jvmtiObjectReferenceCallback object_ref_callback) :
1387     HeapWalkContext(true),
1388     _heap_root_callback(heap_root_callback),
1389     _stack_ref_callback(stack_ref_callback),
1390     _object_ref_callback(object_ref_callback),
1391     _last_referrer(nullptr),
1392     _last_referrer_tag(0) {
1393   }
1394 
1395   // accessors
1396   jvmtiHeapRootCallback heap_root_callback() const         { return _heap_root_callback; }
1397   jvmtiStackReferenceCallback stack_ref_callback() const   { return _stack_ref_callback; }
1398   jvmtiObjectReferenceCallback object_ref_callback() const { return _object_ref_callback;  }
1399 
1400   oop last_referrer() const               { return _last_referrer; }
1401   void set_last_referrer(oop referrer)    { _last_referrer = referrer; }
1402   jlong last_referrer_tag() const         { return _last_referrer_tag; }
1403   void set_last_referrer_tag(jlong value) { _last_referrer_tag = value; }
1404 };
1405 
1406 // The advanced heap walk context for the FollowReferences functions.
1407 // The context is the callbacks, and the fields used for filtering.
1408 class AdvancedHeapWalkContext: public HeapWalkContext {
1409  private:
1410   jint _heap_filter;
1411   Klass* _klass_filter;
1412   const jvmtiHeapCallbacks* _heap_callbacks;
1413 
1414  public:
1415   AdvancedHeapWalkContext() : HeapWalkContext(false) { }
1416 
1417   AdvancedHeapWalkContext(jint heap_filter,
1418                            Klass* klass_filter,
1419                            const jvmtiHeapCallbacks* heap_callbacks) :
1420     HeapWalkContext(true),
1421     _heap_filter(heap_filter),
1422     _klass_filter(klass_filter),
1423     _heap_callbacks(heap_callbacks) {
1424   }
1425 
1426   // accessors
1427   jint heap_filter() const         { return _heap_filter; }
1428   Klass* klass_filter() const      { return _klass_filter; }
1429 
1430   jvmtiHeapReferenceCallback heap_reference_callback() const {
1431     return _heap_callbacks->heap_reference_callback;
1432   };
1433   jvmtiPrimitiveFieldCallback primitive_field_callback() const {
1434     return _heap_callbacks->primitive_field_callback;
1435   }
1436   jvmtiArrayPrimitiveValueCallback array_primitive_value_callback() const {
1437     return _heap_callbacks->array_primitive_value_callback;
1438   }
1439   jvmtiStringPrimitiveValueCallback string_primitive_value_callback() const {
1440     return _heap_callbacks->string_primitive_value_callback;
1441   }
1442 };
1443 
1444 // The CallbackInvoker is a class with static functions that the heap walk can call
1445 // into to invoke callbacks. It works in one of two modes. The "basic" mode is
1446 // used for the deprecated IterateOverReachableObjects functions. The "advanced"
1447 // mode is for the newer FollowReferences function which supports a lot of
1448 // additional callbacks.
1449 class CallbackInvoker : AllStatic {
1450  private:
1451   // heap walk styles
1452   enum { basic, advanced };
1453   static int _heap_walk_type;
1454   static bool is_basic_heap_walk()           { return _heap_walk_type == basic; }
1455   static bool is_advanced_heap_walk()        { return _heap_walk_type == advanced; }
1456 
1457   // context for basic style heap walk
1458   static BasicHeapWalkContext _basic_context;
1459   static BasicHeapWalkContext* basic_context() {
1460     assert(_basic_context.is_valid(), "invalid");
1461     return &_basic_context;
1462   }
1463 
1464   // context for advanced style heap walk
1465   static AdvancedHeapWalkContext _advanced_context;
1466   static AdvancedHeapWalkContext* advanced_context() {
1467     assert(_advanced_context.is_valid(), "invalid");
1468     return &_advanced_context;
1469   }
1470 
1471   // context needed for all heap walks
1472   static JvmtiTagMap* _tag_map;
1473   static const void* _user_data;
1474   static GrowableArray<oop>* _visit_stack;
1475   static JVMTIBitSet* _bitset;
1476 
1477   // accessors
1478   static JvmtiTagMap* tag_map()                        { return _tag_map; }
1479   static const void* user_data()                       { return _user_data; }
1480   static GrowableArray<oop>* visit_stack()             { return _visit_stack; }
1481 
1482   // if the object hasn't been visited then push it onto the visit stack
1483   // so that it will be visited later
1484   static inline bool check_for_visit(oop obj) {
1485     if (!_bitset->is_marked(obj)) visit_stack()->push(obj);
1486     return true;
1487   }
1488 
1489   // invoke basic style callbacks
1490   static inline bool invoke_basic_heap_root_callback
1491     (jvmtiHeapRootKind root_kind, oop obj);
1492   static inline bool invoke_basic_stack_ref_callback
1493     (jvmtiHeapRootKind root_kind, jlong thread_tag, jint depth, jmethodID method,
1494      int slot, oop obj);
1495   static inline bool invoke_basic_object_reference_callback
1496     (jvmtiObjectReferenceKind ref_kind, oop referrer, oop referree, jint index);
1497 
1498   // invoke advanced style callbacks
1499   static inline bool invoke_advanced_heap_root_callback
1500     (jvmtiHeapReferenceKind ref_kind, oop obj);
1501   static inline bool invoke_advanced_stack_ref_callback
1502     (jvmtiHeapReferenceKind ref_kind, jlong thread_tag, jlong tid, int depth,
1503      jmethodID method, jlocation bci, jint slot, oop obj);
1504   static inline bool invoke_advanced_object_reference_callback
1505     (jvmtiHeapReferenceKind ref_kind, oop referrer, oop referree, jint index);
1506 
1507   // used to report the value of primitive fields
1508   static inline bool report_primitive_field
1509     (jvmtiHeapReferenceKind ref_kind, oop obj, jint index, address addr, char type);
1510 
1511  public:
1512   // initialize for basic mode
1513   static void initialize_for_basic_heap_walk(JvmtiTagMap* tag_map,
1514                                              GrowableArray<oop>* visit_stack,
1515                                              const void* user_data,
1516                                              BasicHeapWalkContext context,
1517                                              JVMTIBitSet* bitset);
1518 
1519   // initialize for advanced mode
1520   static void initialize_for_advanced_heap_walk(JvmtiTagMap* tag_map,
1521                                                 GrowableArray<oop>* visit_stack,
1522                                                 const void* user_data,
1523                                                 AdvancedHeapWalkContext context,
1524                                                 JVMTIBitSet* bitset);
1525 
1526    // functions to report roots
1527   static inline bool report_simple_root(jvmtiHeapReferenceKind kind, oop o);
1528   static inline bool report_jni_local_root(jlong thread_tag, jlong tid, jint depth,
1529     jmethodID m, oop o);
1530   static inline bool report_stack_ref_root(jlong thread_tag, jlong tid, jint depth,
1531     jmethodID method, jlocation bci, jint slot, oop o);
1532 
1533   // functions to report references
1534   static inline bool report_array_element_reference(oop referrer, oop referree, jint index);
1535   static inline bool report_class_reference(oop referrer, oop referree);
1536   static inline bool report_class_loader_reference(oop referrer, oop referree);
1537   static inline bool report_signers_reference(oop referrer, oop referree);
1538   static inline bool report_protection_domain_reference(oop referrer, oop referree);
1539   static inline bool report_superclass_reference(oop referrer, oop referree);
1540   static inline bool report_interface_reference(oop referrer, oop referree);
1541   static inline bool report_static_field_reference(oop referrer, oop referree, jint slot);
1542   static inline bool report_field_reference(oop referrer, oop referree, jint slot);
1543   static inline bool report_constant_pool_reference(oop referrer, oop referree, jint index);
1544   static inline bool report_primitive_array_values(oop array);
1545   static inline bool report_string_value(oop str);
1546   static inline bool report_primitive_instance_field(oop o, jint index, address value, char type);
1547   static inline bool report_primitive_static_field(oop o, jint index, address value, char type);
1548 };
1549 
1550 // statics
1551 int CallbackInvoker::_heap_walk_type;
1552 BasicHeapWalkContext CallbackInvoker::_basic_context;
1553 AdvancedHeapWalkContext CallbackInvoker::_advanced_context;
1554 JvmtiTagMap* CallbackInvoker::_tag_map;
1555 const void* CallbackInvoker::_user_data;
1556 GrowableArray<oop>* CallbackInvoker::_visit_stack;
1557 JVMTIBitSet* CallbackInvoker::_bitset;
1558 
1559 // initialize for basic heap walk (IterateOverReachableObjects et al)
1560 void CallbackInvoker::initialize_for_basic_heap_walk(JvmtiTagMap* tag_map,
1561                                                      GrowableArray<oop>* visit_stack,
1562                                                      const void* user_data,
1563                                                      BasicHeapWalkContext context,
1564                                                      JVMTIBitSet* bitset) {
1565   _tag_map = tag_map;
1566   _visit_stack = visit_stack;
1567   _user_data = user_data;
1568   _basic_context = context;
1569   _advanced_context.invalidate();       // will trigger assertion if used
1570   _heap_walk_type = basic;
1571   _bitset = bitset;
1572 }
1573 
1574 // initialize for advanced heap walk (FollowReferences)
1575 void CallbackInvoker::initialize_for_advanced_heap_walk(JvmtiTagMap* tag_map,
1576                                                         GrowableArray<oop>* visit_stack,
1577                                                         const void* user_data,
1578                                                         AdvancedHeapWalkContext context,
1579                                                         JVMTIBitSet* bitset) {
1580   _tag_map = tag_map;
1581   _visit_stack = visit_stack;
1582   _user_data = user_data;
1583   _advanced_context = context;
1584   _basic_context.invalidate();      // will trigger assertion if used
1585   _heap_walk_type = advanced;
1586   _bitset = bitset;
1587 }
1588 
1589 
1590 // invoke basic style heap root callback
1591 inline bool CallbackInvoker::invoke_basic_heap_root_callback(jvmtiHeapRootKind root_kind, oop obj) {
1592   // if we heap roots should be reported
1593   jvmtiHeapRootCallback cb = basic_context()->heap_root_callback();
1594   if (cb == nullptr) {
1595     return check_for_visit(obj);
1596   }
1597 
1598   CallbackWrapper wrapper(tag_map(), obj);
1599   jvmtiIterationControl control = (*cb)(root_kind,
1600                                         wrapper.klass_tag(),
1601                                         wrapper.obj_size(),
1602                                         wrapper.obj_tag_p(),
1603                                         (void*)user_data());
1604   // push root to visit stack when following references
1605   if (control == JVMTI_ITERATION_CONTINUE &&
1606       basic_context()->object_ref_callback() != nullptr) {
1607     visit_stack()->push(obj);
1608   }
1609   return control != JVMTI_ITERATION_ABORT;
1610 }
1611 
1612 // invoke basic style stack ref callback
1613 inline bool CallbackInvoker::invoke_basic_stack_ref_callback(jvmtiHeapRootKind root_kind,
1614                                                              jlong thread_tag,
1615                                                              jint depth,
1616                                                              jmethodID method,
1617                                                              int slot,
1618                                                              oop obj) {
1619   // if we stack refs should be reported
1620   jvmtiStackReferenceCallback cb = basic_context()->stack_ref_callback();
1621   if (cb == nullptr) {
1622     return check_for_visit(obj);
1623   }
1624 
1625   CallbackWrapper wrapper(tag_map(), obj);
1626   jvmtiIterationControl control = (*cb)(root_kind,
1627                                         wrapper.klass_tag(),
1628                                         wrapper.obj_size(),
1629                                         wrapper.obj_tag_p(),
1630                                         thread_tag,
1631                                         depth,
1632                                         method,
1633                                         slot,
1634                                         (void*)user_data());
1635   // push root to visit stack when following references
1636   if (control == JVMTI_ITERATION_CONTINUE &&
1637       basic_context()->object_ref_callback() != nullptr) {
1638     visit_stack()->push(obj);
1639   }
1640   return control != JVMTI_ITERATION_ABORT;
1641 }
1642 
1643 // invoke basic style object reference callback
1644 inline bool CallbackInvoker::invoke_basic_object_reference_callback(jvmtiObjectReferenceKind ref_kind,
1645                                                                     oop referrer,
1646                                                                     oop referree,
1647                                                                     jint index) {
1648 
1649   BasicHeapWalkContext* context = basic_context();
1650 
1651   // callback requires the referrer's tag. If it's the same referrer
1652   // as the last call then we use the cached value.
1653   jlong referrer_tag;
1654   if (referrer == context->last_referrer()) {
1655     referrer_tag = context->last_referrer_tag();
1656   } else {
1657     referrer_tag = tag_for(tag_map(), referrer);
1658   }
1659 
1660   // do the callback
1661   CallbackWrapper wrapper(tag_map(), referree);
1662   jvmtiObjectReferenceCallback cb = context->object_ref_callback();
1663   jvmtiIterationControl control = (*cb)(ref_kind,
1664                                         wrapper.klass_tag(),
1665                                         wrapper.obj_size(),
1666                                         wrapper.obj_tag_p(),
1667                                         referrer_tag,
1668                                         index,
1669                                         (void*)user_data());
1670 
1671   // record referrer and referrer tag. For self-references record the
1672   // tag value from the callback as this might differ from referrer_tag.
1673   context->set_last_referrer(referrer);
1674   if (referrer == referree) {
1675     context->set_last_referrer_tag(*wrapper.obj_tag_p());
1676   } else {
1677     context->set_last_referrer_tag(referrer_tag);
1678   }
1679 
1680   if (control == JVMTI_ITERATION_CONTINUE) {
1681     return check_for_visit(referree);
1682   } else {
1683     return control != JVMTI_ITERATION_ABORT;
1684   }
1685 }
1686 
1687 // invoke advanced style heap root callback
1688 inline bool CallbackInvoker::invoke_advanced_heap_root_callback(jvmtiHeapReferenceKind ref_kind,
1689                                                                 oop obj) {
1690   AdvancedHeapWalkContext* context = advanced_context();
1691 
1692   // check that callback is provided
1693   jvmtiHeapReferenceCallback cb = context->heap_reference_callback();
1694   if (cb == nullptr) {
1695     return check_for_visit(obj);
1696   }
1697 
1698   // apply class filter
1699   if (is_filtered_by_klass_filter(obj, context->klass_filter())) {
1700     return check_for_visit(obj);
1701   }
1702 
1703   // setup the callback wrapper
1704   CallbackWrapper wrapper(tag_map(), obj);
1705 
1706   // apply tag filter
1707   if (is_filtered_by_heap_filter(wrapper.obj_tag(),
1708                                  wrapper.klass_tag(),
1709                                  context->heap_filter())) {
1710     return check_for_visit(obj);
1711   }
1712 
1713   // for arrays we need the length, otherwise -1
1714   jint len = (jint)(obj->is_array() ? arrayOop(obj)->length() : -1);
1715 
1716   // invoke the callback
1717   jint res  = (*cb)(ref_kind,
1718                     nullptr, // referrer info
1719                     wrapper.klass_tag(),
1720                     0,    // referrer_class_tag is 0 for heap root
1721                     wrapper.obj_size(),
1722                     wrapper.obj_tag_p(),
1723                     nullptr, // referrer_tag_p
1724                     len,
1725                     (void*)user_data());
1726   if (res & JVMTI_VISIT_ABORT) {
1727     return false;// referrer class tag
1728   }
1729   if (res & JVMTI_VISIT_OBJECTS) {
1730     check_for_visit(obj);
1731   }
1732   return true;
1733 }
1734 
1735 // report a reference from a thread stack to an object
1736 inline bool CallbackInvoker::invoke_advanced_stack_ref_callback(jvmtiHeapReferenceKind ref_kind,
1737                                                                 jlong thread_tag,
1738                                                                 jlong tid,
1739                                                                 int depth,
1740                                                                 jmethodID method,
1741                                                                 jlocation bci,
1742                                                                 jint slot,
1743                                                                 oop obj) {
1744   AdvancedHeapWalkContext* context = advanced_context();
1745 
1746   // check that callback is provider
1747   jvmtiHeapReferenceCallback cb = context->heap_reference_callback();
1748   if (cb == nullptr) {
1749     return check_for_visit(obj);
1750   }
1751 
1752   // apply class filter
1753   if (is_filtered_by_klass_filter(obj, context->klass_filter())) {
1754     return check_for_visit(obj);
1755   }
1756 
1757   // setup the callback wrapper
1758   CallbackWrapper wrapper(tag_map(), obj);
1759 
1760   // apply tag filter
1761   if (is_filtered_by_heap_filter(wrapper.obj_tag(),
1762                                  wrapper.klass_tag(),
1763                                  context->heap_filter())) {
1764     return check_for_visit(obj);
1765   }
1766 
1767   // setup the referrer info
1768   jvmtiHeapReferenceInfo reference_info;
1769   reference_info.stack_local.thread_tag = thread_tag;
1770   reference_info.stack_local.thread_id = tid;
1771   reference_info.stack_local.depth = depth;
1772   reference_info.stack_local.method = method;
1773   reference_info.stack_local.location = bci;
1774   reference_info.stack_local.slot = slot;
1775 
1776   // for arrays we need the length, otherwise -1
1777   jint len = (jint)(obj->is_array() ? arrayOop(obj)->length() : -1);
1778 
1779   // call into the agent
1780   int res = (*cb)(ref_kind,
1781                   &reference_info,
1782                   wrapper.klass_tag(),
1783                   0,    // referrer_class_tag is 0 for heap root (stack)
1784                   wrapper.obj_size(),
1785                   wrapper.obj_tag_p(),
1786                   nullptr, // referrer_tag is 0 for root
1787                   len,
1788                   (void*)user_data());
1789 
1790   if (res & JVMTI_VISIT_ABORT) {
1791     return false;
1792   }
1793   if (res & JVMTI_VISIT_OBJECTS) {
1794     check_for_visit(obj);
1795   }
1796   return true;
1797 }
1798 
1799 // This mask is used to pass reference_info to a jvmtiHeapReferenceCallback
1800 // only for ref_kinds defined by the JVM TI spec. Otherwise, null is passed.
1801 #define REF_INFO_MASK  ((1 << JVMTI_HEAP_REFERENCE_FIELD)         \
1802                       | (1 << JVMTI_HEAP_REFERENCE_STATIC_FIELD)  \
1803                       | (1 << JVMTI_HEAP_REFERENCE_ARRAY_ELEMENT) \
1804                       | (1 << JVMTI_HEAP_REFERENCE_CONSTANT_POOL) \
1805                       | (1 << JVMTI_HEAP_REFERENCE_STACK_LOCAL)   \
1806                       | (1 << JVMTI_HEAP_REFERENCE_JNI_LOCAL))
1807 
1808 // invoke the object reference callback to report a reference
1809 inline bool CallbackInvoker::invoke_advanced_object_reference_callback(jvmtiHeapReferenceKind ref_kind,
1810                                                                        oop referrer,
1811                                                                        oop obj,
1812                                                                        jint index)
1813 {
1814   // field index is only valid field in reference_info
1815   static jvmtiHeapReferenceInfo reference_info = { 0 };
1816 
1817   AdvancedHeapWalkContext* context = advanced_context();
1818 
1819   // check that callback is provider
1820   jvmtiHeapReferenceCallback cb = context->heap_reference_callback();
1821   if (cb == nullptr) {
1822     return check_for_visit(obj);
1823   }
1824 
1825   // apply class filter
1826   if (is_filtered_by_klass_filter(obj, context->klass_filter())) {
1827     return check_for_visit(obj);
1828   }
1829 
1830   // setup the callback wrapper
1831   TwoOopCallbackWrapper wrapper(tag_map(), referrer, obj);
1832 
1833   // apply tag filter
1834   if (is_filtered_by_heap_filter(wrapper.obj_tag(),
1835                                  wrapper.klass_tag(),
1836                                  context->heap_filter())) {
1837     return check_for_visit(obj);
1838   }
1839 
1840   // field index is only valid field in reference_info
1841   reference_info.field.index = index;
1842 
1843   // for arrays we need the length, otherwise -1
1844   jint len = (jint)(obj->is_array() ? arrayOop(obj)->length() : -1);
1845 
1846   // invoke the callback
1847   int res = (*cb)(ref_kind,
1848                   (REF_INFO_MASK & (1 << ref_kind)) ? &reference_info : nullptr,
1849                   wrapper.klass_tag(),
1850                   wrapper.referrer_klass_tag(),
1851                   wrapper.obj_size(),
1852                   wrapper.obj_tag_p(),
1853                   wrapper.referrer_tag_p(),
1854                   len,
1855                   (void*)user_data());
1856 
1857   if (res & JVMTI_VISIT_ABORT) {
1858     return false;
1859   }
1860   if (res & JVMTI_VISIT_OBJECTS) {
1861     check_for_visit(obj);
1862   }
1863   return true;
1864 }
1865 
1866 // report a "simple root"
1867 inline bool CallbackInvoker::report_simple_root(jvmtiHeapReferenceKind kind, oop obj) {
1868   assert(kind != JVMTI_HEAP_REFERENCE_STACK_LOCAL &&
1869          kind != JVMTI_HEAP_REFERENCE_JNI_LOCAL, "not a simple root");
1870 
1871   if (is_basic_heap_walk()) {
1872     // map to old style root kind
1873     jvmtiHeapRootKind root_kind = toJvmtiHeapRootKind(kind);
1874     return invoke_basic_heap_root_callback(root_kind, obj);
1875   } else {
1876     assert(is_advanced_heap_walk(), "wrong heap walk type");
1877     return invoke_advanced_heap_root_callback(kind, obj);
1878   }
1879 }
1880 
1881 
1882 // invoke the primitive array values
1883 inline bool CallbackInvoker::report_primitive_array_values(oop obj) {
1884   assert(obj->is_typeArray(), "not a primitive array");
1885 
1886   AdvancedHeapWalkContext* context = advanced_context();
1887   assert(context->array_primitive_value_callback() != nullptr, "no callback");
1888 
1889   // apply class filter
1890   if (is_filtered_by_klass_filter(obj, context->klass_filter())) {
1891     return true;
1892   }
1893 
1894   CallbackWrapper wrapper(tag_map(), obj);
1895 
1896   // apply tag filter
1897   if (is_filtered_by_heap_filter(wrapper.obj_tag(),
1898                                  wrapper.klass_tag(),
1899                                  context->heap_filter())) {
1900     return true;
1901   }
1902 
1903   // invoke the callback
1904   int res = invoke_array_primitive_value_callback(context->array_primitive_value_callback(),
1905                                                   &wrapper,
1906                                                   obj,
1907                                                   (void*)user_data());
1908   return (!(res & JVMTI_VISIT_ABORT));
1909 }
1910 
1911 // invoke the string value callback
1912 inline bool CallbackInvoker::report_string_value(oop str) {
1913   assert(str->klass() == vmClasses::String_klass(), "not a string");
1914 
1915   AdvancedHeapWalkContext* context = advanced_context();
1916   assert(context->string_primitive_value_callback() != nullptr, "no callback");
1917 
1918   // apply class filter
1919   if (is_filtered_by_klass_filter(str, context->klass_filter())) {
1920     return true;
1921   }
1922 
1923   CallbackWrapper wrapper(tag_map(), str);
1924 
1925   // apply tag filter
1926   if (is_filtered_by_heap_filter(wrapper.obj_tag(),
1927                                  wrapper.klass_tag(),
1928                                  context->heap_filter())) {
1929     return true;
1930   }
1931 
1932   // invoke the callback
1933   int res = invoke_string_value_callback(context->string_primitive_value_callback(),
1934                                          &wrapper,
1935                                          str,
1936                                          (void*)user_data());
1937   return (!(res & JVMTI_VISIT_ABORT));
1938 }
1939 
1940 // invoke the primitive field callback
1941 inline bool CallbackInvoker::report_primitive_field(jvmtiHeapReferenceKind ref_kind,
1942                                                     oop obj,
1943                                                     jint index,
1944                                                     address addr,
1945                                                     char type)
1946 {
1947   // for primitive fields only the index will be set
1948   static jvmtiHeapReferenceInfo reference_info = { 0 };
1949 
1950   AdvancedHeapWalkContext* context = advanced_context();
1951   assert(context->primitive_field_callback() != nullptr, "no callback");
1952 
1953   // apply class filter
1954   if (is_filtered_by_klass_filter(obj, context->klass_filter())) {
1955     return true;
1956   }
1957 
1958   CallbackWrapper wrapper(tag_map(), obj);
1959 
1960   // apply tag filter
1961   if (is_filtered_by_heap_filter(wrapper.obj_tag(),
1962                                  wrapper.klass_tag(),
1963                                  context->heap_filter())) {
1964     return true;
1965   }
1966 
1967   // the field index in the referrer
1968   reference_info.field.index = index;
1969 
1970   // map the type
1971   jvmtiPrimitiveType value_type = (jvmtiPrimitiveType)type;
1972 
1973   // setup the jvalue
1974   jvalue value;
1975   copy_to_jvalue(&value, addr, value_type);
1976 
1977   jvmtiPrimitiveFieldCallback cb = context->primitive_field_callback();
1978   int res = (*cb)(ref_kind,
1979                   &reference_info,
1980                   wrapper.klass_tag(),
1981                   wrapper.obj_tag_p(),
1982                   value,
1983                   value_type,
1984                   (void*)user_data());
1985   return (!(res & JVMTI_VISIT_ABORT));
1986 }
1987 
1988 
1989 // instance field
1990 inline bool CallbackInvoker::report_primitive_instance_field(oop obj,
1991                                                              jint index,
1992                                                              address value,
1993                                                              char type) {
1994   return report_primitive_field(JVMTI_HEAP_REFERENCE_FIELD,
1995                                 obj,
1996                                 index,
1997                                 value,
1998                                 type);
1999 }
2000 
2001 // static field
2002 inline bool CallbackInvoker::report_primitive_static_field(oop obj,
2003                                                            jint index,
2004                                                            address value,
2005                                                            char type) {
2006   return report_primitive_field(JVMTI_HEAP_REFERENCE_STATIC_FIELD,
2007                                 obj,
2008                                 index,
2009                                 value,
2010                                 type);
2011 }
2012 
2013 // report a JNI local (root object) to the profiler
2014 inline bool CallbackInvoker::report_jni_local_root(jlong thread_tag, jlong tid, jint depth, jmethodID m, oop obj) {
2015   if (is_basic_heap_walk()) {
2016     return invoke_basic_stack_ref_callback(JVMTI_HEAP_ROOT_JNI_LOCAL,
2017                                            thread_tag,
2018                                            depth,
2019                                            m,
2020                                            -1,
2021                                            obj);
2022   } else {
2023     return invoke_advanced_stack_ref_callback(JVMTI_HEAP_REFERENCE_JNI_LOCAL,
2024                                               thread_tag, tid,
2025                                               depth,
2026                                               m,
2027                                               (jlocation)-1,
2028                                               -1,
2029                                               obj);
2030   }
2031 }
2032 
2033 
2034 // report a local (stack reference, root object)
2035 inline bool CallbackInvoker::report_stack_ref_root(jlong thread_tag,
2036                                                    jlong tid,
2037                                                    jint depth,
2038                                                    jmethodID method,
2039                                                    jlocation bci,
2040                                                    jint slot,
2041                                                    oop obj) {
2042   if (is_basic_heap_walk()) {
2043     return invoke_basic_stack_ref_callback(JVMTI_HEAP_ROOT_STACK_LOCAL,
2044                                            thread_tag,
2045                                            depth,
2046                                            method,
2047                                            slot,
2048                                            obj);
2049   } else {
2050     return invoke_advanced_stack_ref_callback(JVMTI_HEAP_REFERENCE_STACK_LOCAL,
2051                                               thread_tag,
2052                                               tid,
2053                                               depth,
2054                                               method,
2055                                               bci,
2056                                               slot,
2057                                               obj);
2058   }
2059 }
2060 
2061 // report an object referencing a class.
2062 inline bool CallbackInvoker::report_class_reference(oop referrer, oop referree) {
2063   if (is_basic_heap_walk()) {
2064     return invoke_basic_object_reference_callback(JVMTI_REFERENCE_CLASS, referrer, referree, -1);
2065   } else {
2066     return invoke_advanced_object_reference_callback(JVMTI_HEAP_REFERENCE_CLASS, referrer, referree, -1);
2067   }
2068 }
2069 
2070 // report a class referencing its class loader.
2071 inline bool CallbackInvoker::report_class_loader_reference(oop referrer, oop referree) {
2072   if (is_basic_heap_walk()) {
2073     return invoke_basic_object_reference_callback(JVMTI_REFERENCE_CLASS_LOADER, referrer, referree, -1);
2074   } else {
2075     return invoke_advanced_object_reference_callback(JVMTI_HEAP_REFERENCE_CLASS_LOADER, referrer, referree, -1);
2076   }
2077 }
2078 
2079 // report a class referencing its signers.
2080 inline bool CallbackInvoker::report_signers_reference(oop referrer, oop referree) {
2081   if (is_basic_heap_walk()) {
2082     return invoke_basic_object_reference_callback(JVMTI_REFERENCE_SIGNERS, referrer, referree, -1);
2083   } else {
2084     return invoke_advanced_object_reference_callback(JVMTI_HEAP_REFERENCE_SIGNERS, referrer, referree, -1);
2085   }
2086 }
2087 
2088 // report a class referencing its protection domain..
2089 inline bool CallbackInvoker::report_protection_domain_reference(oop referrer, oop referree) {
2090   if (is_basic_heap_walk()) {
2091     return invoke_basic_object_reference_callback(JVMTI_REFERENCE_PROTECTION_DOMAIN, referrer, referree, -1);
2092   } else {
2093     return invoke_advanced_object_reference_callback(JVMTI_HEAP_REFERENCE_PROTECTION_DOMAIN, referrer, referree, -1);
2094   }
2095 }
2096 
2097 // report a class referencing its superclass.
2098 inline bool CallbackInvoker::report_superclass_reference(oop referrer, oop referree) {
2099   if (is_basic_heap_walk()) {
2100     // Send this to be consistent with past implementation
2101     return invoke_basic_object_reference_callback(JVMTI_REFERENCE_CLASS, referrer, referree, -1);
2102   } else {
2103     return invoke_advanced_object_reference_callback(JVMTI_HEAP_REFERENCE_SUPERCLASS, referrer, referree, -1);
2104   }
2105 }
2106 
2107 // report a class referencing one of its interfaces.
2108 inline bool CallbackInvoker::report_interface_reference(oop referrer, oop referree) {
2109   if (is_basic_heap_walk()) {
2110     return invoke_basic_object_reference_callback(JVMTI_REFERENCE_INTERFACE, referrer, referree, -1);
2111   } else {
2112     return invoke_advanced_object_reference_callback(JVMTI_HEAP_REFERENCE_INTERFACE, referrer, referree, -1);
2113   }
2114 }
2115 
2116 // report a class referencing one of its static fields.
2117 inline bool CallbackInvoker::report_static_field_reference(oop referrer, oop referree, jint slot) {
2118   if (is_basic_heap_walk()) {
2119     return invoke_basic_object_reference_callback(JVMTI_REFERENCE_STATIC_FIELD, referrer, referree, slot);
2120   } else {
2121     return invoke_advanced_object_reference_callback(JVMTI_HEAP_REFERENCE_STATIC_FIELD, referrer, referree, slot);
2122   }
2123 }
2124 
2125 // report an array referencing an element object
2126 inline bool CallbackInvoker::report_array_element_reference(oop referrer, oop referree, jint index) {
2127   if (is_basic_heap_walk()) {
2128     return invoke_basic_object_reference_callback(JVMTI_REFERENCE_ARRAY_ELEMENT, referrer, referree, index);
2129   } else {
2130     return invoke_advanced_object_reference_callback(JVMTI_HEAP_REFERENCE_ARRAY_ELEMENT, referrer, referree, index);
2131   }
2132 }
2133 
2134 // report an object referencing an instance field object
2135 inline bool CallbackInvoker::report_field_reference(oop referrer, oop referree, jint slot) {
2136   if (is_basic_heap_walk()) {
2137     return invoke_basic_object_reference_callback(JVMTI_REFERENCE_FIELD, referrer, referree, slot);
2138   } else {
2139     return invoke_advanced_object_reference_callback(JVMTI_HEAP_REFERENCE_FIELD, referrer, referree, slot);
2140   }
2141 }
2142 
2143 // report an array referencing an element object
2144 inline bool CallbackInvoker::report_constant_pool_reference(oop referrer, oop referree, jint index) {
2145   if (is_basic_heap_walk()) {
2146     return invoke_basic_object_reference_callback(JVMTI_REFERENCE_CONSTANT_POOL, referrer, referree, index);
2147   } else {
2148     return invoke_advanced_object_reference_callback(JVMTI_HEAP_REFERENCE_CONSTANT_POOL, referrer, referree, index);
2149   }
2150 }
2151 
2152 // A supporting closure used to process simple roots
2153 class SimpleRootsClosure : public OopClosure {
2154  private:
2155   jvmtiHeapReferenceKind _kind;
2156   bool _continue;
2157 
2158   jvmtiHeapReferenceKind root_kind()    { return _kind; }
2159 
2160  public:
2161   void set_kind(jvmtiHeapReferenceKind kind) {
2162     _kind = kind;
2163     _continue = true;
2164   }
2165 
2166   inline bool stopped() {
2167     return !_continue;
2168   }
2169 
2170   void do_oop(oop* obj_p) {
2171     // iteration has terminated
2172     if (stopped()) {
2173       return;
2174     }
2175 
2176     oop o = NativeAccess<AS_NO_KEEPALIVE>::oop_load(obj_p);
2177     // ignore null
2178     if (o == nullptr) {
2179       return;
2180     }
2181 
2182     assert(Universe::heap()->is_in(o), "should be impossible");
2183 
2184     jvmtiHeapReferenceKind kind = root_kind();
2185 
2186     // invoke the callback
2187     _continue = CallbackInvoker::report_simple_root(kind, o);
2188 
2189   }
2190   virtual void do_oop(narrowOop* obj_p) { ShouldNotReachHere(); }
2191 };
2192 
2193 // A supporting closure used to process JNI locals
2194 class JNILocalRootsClosure : public OopClosure {
2195  private:
2196   jlong _thread_tag;
2197   jlong _tid;
2198   jint _depth;
2199   jmethodID _method;
2200   bool _continue;
2201  public:
2202   void set_context(jlong thread_tag, jlong tid, jint depth, jmethodID method) {
2203     _thread_tag = thread_tag;
2204     _tid = tid;
2205     _depth = depth;
2206     _method = method;
2207     _continue = true;
2208   }
2209 
2210   inline bool stopped() {
2211     return !_continue;
2212   }
2213 
2214   void do_oop(oop* obj_p) {
2215     // iteration has terminated
2216     if (stopped()) {
2217       return;
2218     }
2219 
2220     oop o = *obj_p;
2221     // ignore null
2222     if (o == nullptr) {
2223       return;
2224     }
2225 
2226     // invoke the callback
2227     _continue = CallbackInvoker::report_jni_local_root(_thread_tag, _tid, _depth, _method, o);
2228   }
2229   virtual void do_oop(narrowOop* obj_p) { ShouldNotReachHere(); }
2230 };
2231 
2232 // Helper class to collect/report stack references.
2233 class StackRefCollector {
2234 private:
2235   JvmtiTagMap* _tag_map;
2236   JNILocalRootsClosure* _blk;
2237   // java_thread is needed only to report JNI local on top native frame;
2238   // I.e. it's required only for platform/carrier threads or mounted virtual threads.
2239   JavaThread* _java_thread;
2240 
2241   oop _threadObj;
2242   jlong _thread_tag;
2243   jlong _tid;
2244 
2245   bool _is_top_frame;
2246   int _depth;
2247   frame* _last_entry_frame;
2248 
2249   bool report_java_stack_refs(StackValueCollection* values, jmethodID method, jlocation bci, jint slot_offset);
2250   bool report_native_stack_refs(jmethodID method);
2251 
2252 public:
2253   StackRefCollector(JvmtiTagMap* tag_map, JNILocalRootsClosure* blk, JavaThread* java_thread)
2254     : _tag_map(tag_map), _blk(blk), _java_thread(java_thread),
2255       _threadObj(nullptr), _thread_tag(0), _tid(0),
2256       _is_top_frame(true), _depth(0), _last_entry_frame(nullptr)
2257   {
2258   }
2259 
2260   bool set_thread(oop o);
2261   // Sets the thread and reports the reference to it with the specified kind.
2262   bool set_thread(jvmtiHeapReferenceKind kind, oop o);
2263 
2264   bool do_frame(vframe* vf);
2265   // Handles frames until vf->sender() is null.
2266   bool process_frames(vframe* vf);
2267 };
2268 
2269 bool StackRefCollector::set_thread(oop o) {
2270   _threadObj = o;
2271   _thread_tag = tag_for(_tag_map, _threadObj);
2272   _tid = java_lang_Thread::thread_id(_threadObj);
2273 
2274   _is_top_frame = true;
2275   _depth = 0;
2276   _last_entry_frame = nullptr;
2277 
2278   return true;
2279 }
2280 
2281 bool StackRefCollector::set_thread(jvmtiHeapReferenceKind kind, oop o) {
2282   return set_thread(o)
2283          && CallbackInvoker::report_simple_root(kind, _threadObj);
2284 }
2285 
2286 bool StackRefCollector::report_java_stack_refs(StackValueCollection* values, jmethodID method, jlocation bci, jint slot_offset) {
2287   for (int index = 0; index < values->size(); index++) {
2288     if (values->at(index)->type() == T_OBJECT) {
2289       oop obj = values->obj_at(index)();
2290       if (obj == nullptr) {
2291         continue;
2292       }
2293       // stack reference
2294       if (!CallbackInvoker::report_stack_ref_root(_thread_tag, _tid, _depth, method,
2295                                                   bci, slot_offset + index, obj)) {
2296         return false;
2297       }
2298     }
2299   }
2300   return true;
2301 }
2302 
2303 bool StackRefCollector::report_native_stack_refs(jmethodID method) {
2304   _blk->set_context(_thread_tag, _tid, _depth, method);
2305   if (_is_top_frame) {
2306     // JNI locals for the top frame.
2307     if (_java_thread != nullptr) {
2308       _java_thread->active_handles()->oops_do(_blk);
2309       if (_blk->stopped()) {
2310         return false;
2311       }
2312     }
2313   } else {
2314     if (_last_entry_frame != nullptr) {
2315       // JNI locals for the entry frame.
2316       assert(_last_entry_frame->is_entry_frame(), "checking");
2317       _last_entry_frame->entry_frame_call_wrapper()->handles()->oops_do(_blk);
2318       if (_blk->stopped()) {
2319         return false;
2320       }
2321     }
2322   }
2323   return true;
2324 }
2325 
2326 bool StackRefCollector::do_frame(vframe* vf) {
2327   if (vf->is_java_frame()) {
2328     // java frame (interpreted, compiled, ...)
2329     javaVFrame* jvf = javaVFrame::cast(vf);
2330 
2331     jmethodID method = jvf->method()->jmethod_id();
2332 
2333     if (!(jvf->method()->is_native())) {
2334       jlocation bci = (jlocation)jvf->bci();
2335       StackValueCollection* locals = jvf->locals();
2336       if (!report_java_stack_refs(locals, method, bci, 0)) {
2337         return false;
2338       }
2339       if (!report_java_stack_refs(jvf->expressions(), method, bci, locals->size())) {
2340         return false;
2341       }
2342 
2343       // Follow oops from compiled nmethod.
2344       if (jvf->cb() != nullptr && jvf->cb()->is_nmethod()) {
2345         _blk->set_context(_thread_tag, _tid, _depth, method);
2346         // Need to apply load barriers for unmounted vthreads.
2347         nmethod* nm = jvf->cb()->as_nmethod();
2348         nm->run_nmethod_entry_barrier();
2349         nm->oops_do(_blk);
2350         if (_blk->stopped()) {
2351           return false;
2352         }
2353       }
2354     } else {
2355       // native frame
2356       if (!report_native_stack_refs(method)) {
2357         return false;
2358       }
2359     }
2360     _last_entry_frame = nullptr;
2361     _depth++;
2362   } else {
2363     // externalVFrame - for an entry frame then we report the JNI locals
2364     // when we find the corresponding javaVFrame
2365     frame* fr = vf->frame_pointer();
2366     assert(fr != nullptr, "sanity check");
2367     if (fr->is_entry_frame()) {
2368       _last_entry_frame = fr;
2369     }
2370   }
2371 
2372   _is_top_frame = false;
2373 
2374   return true;
2375 }
2376 
2377 bool StackRefCollector::process_frames(vframe* vf) {
2378   while (vf != nullptr) {
2379     if (!do_frame(vf)) {
2380       return false;
2381     }
2382     vf = vf->sender();
2383   }
2384   return true;
2385 }
2386 
2387 
2388 // A VM operation to iterate over objects that are reachable from
2389 // a set of roots or an initial object.
2390 //
2391 // For VM_HeapWalkOperation the set of roots used is :-
2392 //
2393 // - All JNI global references
2394 // - All inflated monitors
2395 // - All classes loaded by the boot class loader (or all classes
2396 //     in the event that class unloading is disabled)
2397 // - All java threads
2398 // - For each java thread then all locals and JNI local references
2399 //      on the thread's execution stack
2400 // - All visible/explainable objects from Universes::oops_do
2401 //
2402 class VM_HeapWalkOperation: public VM_Operation {
2403  private:
2404   enum {
2405     initial_visit_stack_size = 4000
2406   };
2407 
2408   bool _is_advanced_heap_walk;                      // indicates FollowReferences
2409   JvmtiTagMap* _tag_map;
2410   Handle _initial_object;
2411   GrowableArray<oop>* _visit_stack;                 // the visit stack
2412 
2413   JVMTIBitSet _bitset;
2414 
2415   // Dead object tags in JvmtiTagMap
2416   GrowableArray<jlong>* _dead_objects;
2417 
2418   bool _following_object_refs;                      // are we following object references
2419 
2420   bool _reporting_primitive_fields;                 // optional reporting
2421   bool _reporting_primitive_array_values;
2422   bool _reporting_string_values;
2423 
2424   GrowableArray<oop>* create_visit_stack() {
2425     return new (mtServiceability) GrowableArray<oop>(initial_visit_stack_size, mtServiceability);
2426   }
2427 
2428   // accessors
2429   bool is_advanced_heap_walk() const               { return _is_advanced_heap_walk; }
2430   JvmtiTagMap* tag_map() const                     { return _tag_map; }
2431   Handle initial_object() const                    { return _initial_object; }
2432 
2433   bool is_following_references() const             { return _following_object_refs; }
2434 
2435   bool is_reporting_primitive_fields()  const      { return _reporting_primitive_fields; }
2436   bool is_reporting_primitive_array_values() const { return _reporting_primitive_array_values; }
2437   bool is_reporting_string_values() const          { return _reporting_string_values; }
2438 
2439   GrowableArray<oop>* visit_stack() const          { return _visit_stack; }
2440 
2441   // iterate over the various object types
2442   inline bool iterate_over_array(oop o);
2443   inline bool iterate_over_type_array(oop o);
2444   inline bool iterate_over_class(oop o);
2445   inline bool iterate_over_object(oop o);
2446 
2447   // root collection
2448   inline bool collect_simple_roots();
2449   inline bool collect_stack_roots();
2450   inline bool collect_stack_refs(JavaThread* java_thread, JNILocalRootsClosure* blk);
2451   inline bool collect_vthread_stack_refs(oop vt);
2452 
2453   // visit an object
2454   inline bool visit(oop o);
2455 
2456  public:
2457   VM_HeapWalkOperation(JvmtiTagMap* tag_map,
2458                        Handle initial_object,
2459                        BasicHeapWalkContext callbacks,
2460                        const void* user_data,
2461                        GrowableArray<jlong>* objects);
2462 
2463   VM_HeapWalkOperation(JvmtiTagMap* tag_map,
2464                        Handle initial_object,
2465                        AdvancedHeapWalkContext callbacks,
2466                        const void* user_data,
2467                        GrowableArray<jlong>* objects);
2468 
2469   ~VM_HeapWalkOperation();
2470 
2471   VMOp_Type type() const { return VMOp_HeapWalkOperation; }
2472   void doit();
2473 };
2474 
2475 
2476 VM_HeapWalkOperation::VM_HeapWalkOperation(JvmtiTagMap* tag_map,
2477                                            Handle initial_object,
2478                                            BasicHeapWalkContext callbacks,
2479                                            const void* user_data,
2480                                            GrowableArray<jlong>* objects) {
2481   _is_advanced_heap_walk = false;
2482   _tag_map = tag_map;
2483   _initial_object = initial_object;
2484   _following_object_refs = (callbacks.object_ref_callback() != nullptr);
2485   _reporting_primitive_fields = false;
2486   _reporting_primitive_array_values = false;
2487   _reporting_string_values = false;
2488   _visit_stack = create_visit_stack();
2489   _dead_objects = objects;
2490 
2491   CallbackInvoker::initialize_for_basic_heap_walk(tag_map, _visit_stack, user_data, callbacks, &_bitset);
2492 }
2493 
2494 VM_HeapWalkOperation::VM_HeapWalkOperation(JvmtiTagMap* tag_map,
2495                                            Handle initial_object,
2496                                            AdvancedHeapWalkContext callbacks,
2497                                            const void* user_data,
2498                                            GrowableArray<jlong>* objects) {
2499   _is_advanced_heap_walk = true;
2500   _tag_map = tag_map;
2501   _initial_object = initial_object;
2502   _following_object_refs = true;
2503   _reporting_primitive_fields = (callbacks.primitive_field_callback() != nullptr);;
2504   _reporting_primitive_array_values = (callbacks.array_primitive_value_callback() != nullptr);;
2505   _reporting_string_values = (callbacks.string_primitive_value_callback() != nullptr);;
2506   _visit_stack = create_visit_stack();
2507   _dead_objects = objects;
2508   CallbackInvoker::initialize_for_advanced_heap_walk(tag_map, _visit_stack, user_data, callbacks, &_bitset);
2509 }
2510 
2511 VM_HeapWalkOperation::~VM_HeapWalkOperation() {
2512   if (_following_object_refs) {
2513     assert(_visit_stack != nullptr, "checking");
2514     delete _visit_stack;
2515     _visit_stack = nullptr;
2516   }
2517 }
2518 
2519 // an array references its class and has a reference to
2520 // each element in the array
2521 inline bool VM_HeapWalkOperation::iterate_over_array(oop o) {
2522   objArrayOop array = objArrayOop(o);
2523 
2524   // array reference to its class
2525   oop mirror = ObjArrayKlass::cast(array->klass())->java_mirror();
2526   if (!CallbackInvoker::report_class_reference(o, mirror)) {
2527     return false;
2528   }
2529 
2530   // iterate over the array and report each reference to a
2531   // non-null element
2532   for (int index=0; index<array->length(); index++) {
2533     oop elem = array->obj_at(index);
2534     if (elem == nullptr) {
2535       continue;
2536     }
2537 
2538     // report the array reference o[index] = elem
2539     if (!CallbackInvoker::report_array_element_reference(o, elem, index)) {
2540       return false;
2541     }
2542   }
2543   return true;
2544 }
2545 
2546 // a type array references its class
2547 inline bool VM_HeapWalkOperation::iterate_over_type_array(oop o) {
2548   Klass* k = o->klass();
2549   oop mirror = k->java_mirror();
2550   if (!CallbackInvoker::report_class_reference(o, mirror)) {
2551     return false;
2552   }
2553 
2554   // report the array contents if required
2555   if (is_reporting_primitive_array_values()) {
2556     if (!CallbackInvoker::report_primitive_array_values(o)) {
2557       return false;
2558     }
2559   }
2560   return true;
2561 }
2562 
2563 #ifdef ASSERT
2564 // verify that a static oop field is in range
2565 static inline bool verify_static_oop(InstanceKlass* ik,
2566                                      oop mirror, int offset) {
2567   address obj_p = cast_from_oop<address>(mirror) + offset;
2568   address start = (address)InstanceMirrorKlass::start_of_static_fields(mirror);
2569   address end = start + (java_lang_Class::static_oop_field_count(mirror) * heapOopSize);
2570   assert(end >= start, "sanity check");
2571 
2572   if (obj_p >= start && obj_p < end) {
2573     return true;
2574   } else {
2575     return false;
2576   }
2577 }
2578 #endif // #ifdef ASSERT
2579 
2580 // a class references its super class, interfaces, class loader, ...
2581 // and finally its static fields
2582 inline bool VM_HeapWalkOperation::iterate_over_class(oop java_class) {
2583   int i;
2584   Klass* klass = java_lang_Class::as_Klass(java_class);
2585 
2586   if (klass->is_instance_klass()) {
2587     InstanceKlass* ik = InstanceKlass::cast(klass);
2588 
2589     // Ignore the class if it hasn't been initialized yet
2590     if (!ik->is_linked()) {
2591       return true;
2592     }
2593 
2594     // get the java mirror
2595     oop mirror = klass->java_mirror();
2596 
2597     // super (only if something more interesting than java.lang.Object)
2598     InstanceKlass* super_klass = ik->super();
2599     if (super_klass != nullptr && super_klass != vmClasses::Object_klass()) {
2600       oop super_oop = super_klass->java_mirror();
2601       if (!CallbackInvoker::report_superclass_reference(mirror, super_oop)) {
2602         return false;
2603       }
2604     }
2605 
2606     // class loader
2607     oop cl = ik->class_loader();
2608     if (cl != nullptr) {
2609       if (!CallbackInvoker::report_class_loader_reference(mirror, cl)) {
2610         return false;
2611       }
2612     }
2613 
2614     // protection domain
2615     oop pd = ik->protection_domain();
2616     if (pd != nullptr) {
2617       if (!CallbackInvoker::report_protection_domain_reference(mirror, pd)) {
2618         return false;
2619       }
2620     }
2621 
2622     // signers
2623     oop signers = ik->signers();
2624     if (signers != nullptr) {
2625       if (!CallbackInvoker::report_signers_reference(mirror, signers)) {
2626         return false;
2627       }
2628     }
2629 
2630     // references from the constant pool
2631     {
2632       ConstantPool* pool = ik->constants();
2633       for (int i = 1; i < pool->length(); i++) {
2634         constantTag tag = pool->tag_at(i).value();
2635         if (tag.is_string() || tag.is_klass() || tag.is_unresolved_klass()) {
2636           oop entry;
2637           if (tag.is_string()) {
2638             entry = pool->resolved_string_at(i);
2639             // If the entry is non-null it is resolved.
2640             if (entry == nullptr) {
2641               continue;
2642             }
2643           } else if (tag.is_klass()) {
2644             entry = pool->resolved_klass_at(i)->java_mirror();
2645           } else {
2646             // Code generated by JIT compilers might not resolve constant
2647             // pool entries.  Treat them as resolved if they are loaded.
2648             assert(tag.is_unresolved_klass(), "must be");
2649             constantPoolHandle cp(Thread::current(), pool);
2650             Klass* klass = ConstantPool::klass_at_if_loaded(cp, i);
2651             if (klass == nullptr) {
2652               continue;
2653             }
2654             entry = klass->java_mirror();
2655           }
2656           if (!CallbackInvoker::report_constant_pool_reference(mirror, entry, (jint)i)) {
2657             return false;
2658           }
2659         }
2660       }
2661     }
2662 
2663     // interfaces
2664     // (These will already have been reported as references from the constant pool
2665     //  but are specified by IterateOverReachableObjects and must be reported).
2666     Array<InstanceKlass*>* interfaces = ik->local_interfaces();
2667     for (i = 0; i < interfaces->length(); i++) {
2668       oop interf = interfaces->at(i)->java_mirror();
2669       if (interf == nullptr) {
2670         continue;
2671       }
2672       if (!CallbackInvoker::report_interface_reference(mirror, interf)) {
2673         return false;
2674       }
2675     }
2676 
2677     // iterate over the static fields
2678 
2679     ClassFieldMap* field_map = ClassFieldMap::create_map_of_static_fields(klass);
2680     for (i=0; i<field_map->field_count(); i++) {
2681       ClassFieldDescriptor* field = field_map->field_at(i);
2682       char type = field->field_type();
2683       if (!is_primitive_field_type(type)) {
2684         oop fld_o = mirror->obj_field(field->field_offset());
2685         assert(verify_static_oop(ik, mirror, field->field_offset()), "sanity check");
2686         if (fld_o != nullptr) {
2687           int slot = field->field_index();
2688           if (!CallbackInvoker::report_static_field_reference(mirror, fld_o, slot)) {
2689             delete field_map;
2690             return false;
2691           }
2692         }
2693       } else {
2694          if (is_reporting_primitive_fields()) {
2695            address addr = cast_from_oop<address>(mirror) + field->field_offset();
2696            int slot = field->field_index();
2697            if (!CallbackInvoker::report_primitive_static_field(mirror, slot, addr, type)) {
2698              delete field_map;
2699              return false;
2700           }
2701         }
2702       }
2703     }
2704     delete field_map;
2705 
2706     return true;
2707   }
2708 
2709   return true;
2710 }
2711 
2712 // an object references a class and its instance fields
2713 // (static fields are ignored here as we report these as
2714 // references from the class).
2715 inline bool VM_HeapWalkOperation::iterate_over_object(oop o) {
2716   // reference to the class
2717   if (!CallbackInvoker::report_class_reference(o, o->klass()->java_mirror())) {
2718     return false;
2719   }
2720 
2721   // iterate over instance fields
2722   ClassFieldMap* field_map = JvmtiCachedClassFieldMap::get_map_of_instance_fields(o);
2723   for (int i=0; i<field_map->field_count(); i++) {
2724     ClassFieldDescriptor* field = field_map->field_at(i);
2725     char type = field->field_type();
2726     if (!is_primitive_field_type(type)) {
2727       oop fld_o = o->obj_field_access<AS_NO_KEEPALIVE | ON_UNKNOWN_OOP_REF>(field->field_offset());
2728       // ignore any objects that aren't visible to profiler
2729       if (fld_o != nullptr) {
2730         assert(Universe::heap()->is_in(fld_o), "unsafe code should not "
2731                "have references to Klass* anymore");
2732         int slot = field->field_index();
2733         if (!CallbackInvoker::report_field_reference(o, fld_o, slot)) {
2734           return false;
2735         }
2736       }
2737     } else {
2738       if (is_reporting_primitive_fields()) {
2739         // primitive instance field
2740         address addr = cast_from_oop<address>(o) + field->field_offset();
2741         int slot = field->field_index();
2742         if (!CallbackInvoker::report_primitive_instance_field(o, slot, addr, type)) {
2743           return false;
2744         }
2745       }
2746     }
2747   }
2748 
2749   // if the object is a java.lang.String
2750   if (is_reporting_string_values() &&
2751       o->klass() == vmClasses::String_klass()) {
2752     if (!CallbackInvoker::report_string_value(o)) {
2753       return false;
2754     }
2755   }
2756   return true;
2757 }
2758 
2759 
2760 // Collects all simple (non-stack) roots except for threads;
2761 // threads are handled in collect_stack_roots() as an optimization.
2762 // if there's a heap root callback provided then the callback is
2763 // invoked for each simple root.
2764 // if an object reference callback is provided then all simple
2765 // roots are pushed onto the marking stack so that they can be
2766 // processed later
2767 //
2768 inline bool VM_HeapWalkOperation::collect_simple_roots() {
2769   SimpleRootsClosure blk;
2770 
2771   // JNI globals
2772   blk.set_kind(JVMTI_HEAP_REFERENCE_JNI_GLOBAL);
2773   JNIHandles::oops_do(&blk);
2774   if (blk.stopped()) {
2775     return false;
2776   }
2777 
2778   // Preloaded classes and loader from the system dictionary
2779   blk.set_kind(JVMTI_HEAP_REFERENCE_SYSTEM_CLASS);
2780   CLDToOopClosure cld_closure(&blk, ClassLoaderData::_claim_none);
2781   ClassLoaderDataGraph::always_strong_cld_do(&cld_closure);
2782   if (blk.stopped()) {
2783     return false;
2784   }
2785 
2786   // threads are now handled in collect_stack_roots()
2787 
2788   // Other kinds of roots maintained by HotSpot
2789   // Many of these won't be visible but others (such as instances of important
2790   // exceptions) will be visible.
2791   blk.set_kind(JVMTI_HEAP_REFERENCE_OTHER);
2792   Universe::vm_global()->oops_do(&blk);
2793   if (blk.stopped()) {
2794     return false;
2795   }
2796 
2797   return true;
2798 }
2799 
2800 // Reports the thread as JVMTI_HEAP_REFERENCE_THREAD,
2801 // walks the stack of the thread, finds all references (locals
2802 // and JNI calls) and reports these as stack references.
2803 inline bool VM_HeapWalkOperation::collect_stack_refs(JavaThread* java_thread,
2804                                                      JNILocalRootsClosure* blk)
2805 {
2806   oop threadObj = java_thread->threadObj();
2807   oop mounted_vt = java_thread->is_vthread_mounted() ? java_thread->vthread() : nullptr;
2808   if (mounted_vt != nullptr && !JvmtiEnvBase::is_vthread_alive(mounted_vt)) {
2809     mounted_vt = nullptr;
2810   }
2811   assert(threadObj != nullptr, "sanity check");
2812 
2813   StackRefCollector stack_collector(tag_map(), blk, java_thread);
2814 
2815   if (!java_thread->has_last_Java_frame()) {
2816     if (!stack_collector.set_thread(JVMTI_HEAP_REFERENCE_THREAD, threadObj)) {
2817       return false;
2818     }
2819     // no last java frame but there may be JNI locals
2820     blk->set_context(tag_for(_tag_map, threadObj), java_lang_Thread::thread_id(threadObj), 0, (jmethodID)nullptr);
2821     java_thread->active_handles()->oops_do(blk);
2822     return !blk->stopped();
2823   }
2824   // vframes are resource allocated
2825   Thread* current_thread = Thread::current();
2826   ResourceMark rm(current_thread);
2827   HandleMark hm(current_thread);
2828 
2829   RegisterMap reg_map(java_thread,
2830                       RegisterMap::UpdateMap::include,
2831                       RegisterMap::ProcessFrames::include,
2832                       RegisterMap::WalkContinuation::include);
2833 
2834   // first handle mounted vthread (if any)
2835   if (mounted_vt != nullptr) {
2836     frame f = java_thread->last_frame();
2837     vframe* vf = vframe::new_vframe(&f, &reg_map, java_thread);
2838     // report virtual thread as JVMTI_HEAP_REFERENCE_OTHER
2839     if (!stack_collector.set_thread(JVMTI_HEAP_REFERENCE_OTHER, mounted_vt)) {
2840       return false;
2841     }
2842     // split virtual thread and carrier thread stacks by vthread entry ("enterSpecial") frame,
2843     // consider vthread entry frame as the last vthread stack frame
2844     while (vf != nullptr) {
2845       if (!stack_collector.do_frame(vf)) {
2846         return false;
2847       }
2848       if (vf->is_vthread_entry()) {
2849         break;
2850       }
2851       vf = vf->sender();
2852     }
2853   }
2854   // Platform or carrier thread.
2855   vframe* vf = JvmtiEnvBase::get_cthread_last_java_vframe(java_thread, &reg_map);
2856   if (!stack_collector.set_thread(JVMTI_HEAP_REFERENCE_THREAD, threadObj)) {
2857     return false;
2858   }
2859   return stack_collector.process_frames(vf);
2860 }
2861 
2862 
2863 // Collects the simple roots for all threads and collects all
2864 // stack roots - for each thread it walks the execution
2865 // stack to find all references and local JNI refs.
2866 inline bool VM_HeapWalkOperation::collect_stack_roots() {
2867   JNILocalRootsClosure blk;
2868   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thread = jtiwh.next(); ) {
2869     oop threadObj = thread->threadObj();
2870     if (threadObj != nullptr && !thread->is_exiting() && !thread->is_hidden_from_external_view()) {
2871       if (!collect_stack_refs(thread, &blk)) {
2872         return false;
2873       }
2874     }
2875   }
2876   return true;
2877 }
2878 
2879 // Reports stack references for the unmounted virtual thread.
2880 inline bool VM_HeapWalkOperation::collect_vthread_stack_refs(oop vt) {
2881   if (!JvmtiEnvBase::is_vthread_alive(vt)) {
2882     return true;
2883   }
2884   ContinuationWrapper cont(java_lang_VirtualThread::continuation(vt));
2885   if (cont.is_empty()) {
2886     return true;
2887   }
2888   assert(!cont.is_mounted(), "sanity check");
2889 
2890   stackChunkOop chunk = cont.last_nonempty_chunk();
2891   if (chunk == nullptr || chunk->is_empty()) {
2892     return true;
2893   }
2894 
2895   // vframes are resource allocated
2896   Thread* current_thread = Thread::current();
2897   ResourceMark rm(current_thread);
2898   HandleMark hm(current_thread);
2899 
2900   RegisterMap reg_map(cont.continuation(), RegisterMap::UpdateMap::include);
2901 
2902   JNILocalRootsClosure blk;
2903   // JavaThread is not required for unmounted virtual threads
2904   StackRefCollector stack_collector(tag_map(), &blk, nullptr);
2905   // reference to the vthread is already reported
2906   if (!stack_collector.set_thread(vt)) {
2907     return false;
2908   }
2909 
2910   frame fr = chunk->top_frame(&reg_map);
2911   vframe* vf = vframe::new_vframe(&fr, &reg_map, nullptr);
2912   return stack_collector.process_frames(vf);
2913 }
2914 
2915 // visit an object
2916 // first mark the object as visited
2917 // second get all the outbound references from this object (in other words, all
2918 // the objects referenced by this object).
2919 //
2920 bool VM_HeapWalkOperation::visit(oop o) {
2921   // mark object as visited
2922   assert(!_bitset.is_marked(o), "can't visit same object more than once");
2923   _bitset.mark_obj(o);
2924 
2925   // instance
2926   if (o->is_instance()) {
2927     if (o->klass() == vmClasses::Class_klass()) {
2928       if (!java_lang_Class::is_primitive(o)) {
2929         // a java.lang.Class
2930         return iterate_over_class(o);
2931       }
2932     } else {
2933       // we report stack references only when initial object is not specified
2934       // (in the case we start from heap roots which include platform thread stack references)
2935       if (initial_object().is_null() && java_lang_VirtualThread::is_subclass(o->klass())) {
2936         if (!collect_vthread_stack_refs(o)) {
2937           return false;
2938         }
2939       }
2940       return iterate_over_object(o);
2941     }
2942   }
2943 
2944   // object array
2945   if (o->is_objArray()) {
2946     return iterate_over_array(o);
2947   }
2948 
2949   // type array
2950   if (o->is_typeArray()) {
2951     return iterate_over_type_array(o);
2952   }
2953 
2954   return true;
2955 }
2956 
2957 void VM_HeapWalkOperation::doit() {
2958   ResourceMark rm;
2959   ClassFieldMapCacheMark cm;
2960 
2961   JvmtiTagMap::check_hashmaps_for_heapwalk(_dead_objects);
2962 
2963   assert(visit_stack()->is_empty(), "visit stack must be empty");
2964 
2965   // the heap walk starts with an initial object or the heap roots
2966   if (initial_object().is_null()) {
2967     // can result in a big performance boost for an agent that is
2968     // focused on analyzing references in the thread stacks.
2969     if (!collect_stack_roots()) return;
2970 
2971     if (!collect_simple_roots()) return;
2972   } else {
2973     visit_stack()->push(initial_object()());
2974   }
2975 
2976   // object references required
2977   if (is_following_references()) {
2978 
2979     // visit each object until all reachable objects have been
2980     // visited or the callback asked to terminate the iteration.
2981     while (!visit_stack()->is_empty()) {
2982       oop o = visit_stack()->pop();
2983       if (!_bitset.is_marked(o)) {
2984         if (!visit(o)) {
2985           break;
2986         }
2987       }
2988     }
2989   }
2990 }
2991 
2992 // iterate over all objects that are reachable from a set of roots
2993 void JvmtiTagMap::iterate_over_reachable_objects(jvmtiHeapRootCallback heap_root_callback,
2994                                                  jvmtiStackReferenceCallback stack_ref_callback,
2995                                                  jvmtiObjectReferenceCallback object_ref_callback,
2996                                                  const void* user_data) {
2997   // VTMS transitions must be disabled before the EscapeBarrier.
2998   JvmtiVTMSTransitionDisabler disabler;
2999 
3000   JavaThread* jt = JavaThread::current();
3001   EscapeBarrier eb(true, jt);
3002   eb.deoptimize_objects_all_threads();
3003   Arena dead_object_arena(mtServiceability);
3004   GrowableArray<jlong> dead_objects(&dead_object_arena, 10, 0, 0);
3005 
3006   {
3007     MutexLocker ml(Heap_lock);
3008     BasicHeapWalkContext context(heap_root_callback, stack_ref_callback, object_ref_callback);
3009     VM_HeapWalkOperation op(this, Handle(), context, user_data, &dead_objects);
3010     VMThread::execute(&op);
3011   }
3012   // Post events outside of Heap_lock
3013   post_dead_objects(&dead_objects);
3014 }
3015 
3016 // iterate over all objects that are reachable from a given object
3017 void JvmtiTagMap::iterate_over_objects_reachable_from_object(jobject object,
3018                                                              jvmtiObjectReferenceCallback object_ref_callback,
3019                                                              const void* user_data) {
3020   oop obj = JNIHandles::resolve(object);
3021   Handle initial_object(Thread::current(), obj);
3022 
3023   Arena dead_object_arena(mtServiceability);
3024   GrowableArray<jlong> dead_objects(&dead_object_arena, 10, 0, 0);
3025 
3026   JvmtiVTMSTransitionDisabler disabler;
3027 
3028   {
3029     MutexLocker ml(Heap_lock);
3030     BasicHeapWalkContext context(nullptr, nullptr, object_ref_callback);
3031     VM_HeapWalkOperation op(this, initial_object, context, user_data, &dead_objects);
3032     VMThread::execute(&op);
3033   }
3034   // Post events outside of Heap_lock
3035   post_dead_objects(&dead_objects);
3036 }
3037 
3038 // follow references from an initial object or the GC roots
3039 void JvmtiTagMap::follow_references(jint heap_filter,
3040                                     Klass* klass,
3041                                     jobject object,
3042                                     const jvmtiHeapCallbacks* callbacks,
3043                                     const void* user_data)
3044 {
3045   // VTMS transitions must be disabled before the EscapeBarrier.
3046   JvmtiVTMSTransitionDisabler disabler;
3047 
3048   oop obj = JNIHandles::resolve(object);
3049   JavaThread* jt = JavaThread::current();
3050   Handle initial_object(jt, obj);
3051   // EA based optimizations that are tagged or reachable from initial_object are already reverted.
3052   EscapeBarrier eb(initial_object.is_null() &&
3053                    !(heap_filter & JVMTI_HEAP_FILTER_UNTAGGED),
3054                    jt);
3055   eb.deoptimize_objects_all_threads();
3056 
3057   Arena dead_object_arena(mtServiceability);
3058   GrowableArray<jlong> dead_objects(&dead_object_arena, 10, 0, 0);
3059 
3060   {
3061     MutexLocker ml(Heap_lock);
3062     AdvancedHeapWalkContext context(heap_filter, klass, callbacks);
3063     VM_HeapWalkOperation op(this, initial_object, context, user_data, &dead_objects);
3064     VMThread::execute(&op);
3065   }
3066   // Post events outside of Heap_lock
3067   post_dead_objects(&dead_objects);
3068 }
3069 
3070 // Verify gc_notification follows set_needs_cleaning.
3071 DEBUG_ONLY(static bool notified_needs_cleaning = false;)
3072 
3073 void JvmtiTagMap::set_needs_cleaning() {
3074   assert(SafepointSynchronize::is_at_safepoint(), "called in gc pause");
3075   assert(Thread::current()->is_VM_thread(), "should be the VM thread");
3076   // Can't assert !notified_needs_cleaning; a partial GC might be upgraded
3077   // to a full GC and do this twice without intervening gc_notification.
3078   DEBUG_ONLY(notified_needs_cleaning = true;)
3079 
3080   JvmtiEnvIterator it;
3081   for (JvmtiEnv* env = it.first(); env != nullptr; env = it.next(env)) {
3082     JvmtiTagMap* tag_map = env->tag_map_acquire();
3083     if (tag_map != nullptr) {
3084       tag_map->_needs_cleaning = !tag_map->is_empty();
3085     }
3086   }
3087 }
3088 
3089 void JvmtiTagMap::gc_notification(size_t num_dead_entries) {
3090   assert(notified_needs_cleaning, "missing GC notification");
3091   DEBUG_ONLY(notified_needs_cleaning = false;)
3092 
3093   // Notify ServiceThread if there's work to do.
3094   {
3095     MonitorLocker ml(Service_lock, Mutex::_no_safepoint_check_flag);
3096     _has_object_free_events = (num_dead_entries != 0);
3097     if (_has_object_free_events) ml.notify_all();
3098   }
3099 
3100   // If no dead entries then cancel cleaning requests.
3101   if (num_dead_entries == 0) {
3102     JvmtiEnvIterator it;
3103     for (JvmtiEnv* env = it.first(); env != nullptr; env = it.next(env)) {
3104       JvmtiTagMap* tag_map = env->tag_map_acquire();
3105       if (tag_map != nullptr) {
3106         MutexLocker ml (tag_map->lock(), Mutex::_no_safepoint_check_flag);
3107         tag_map->_needs_cleaning = false;
3108       }
3109     }
3110   }
3111 }
3112 
3113 // Used by ServiceThread to discover there is work to do.
3114 bool JvmtiTagMap::has_object_free_events_and_reset() {
3115   assert_lock_strong(Service_lock);
3116   bool result = _has_object_free_events;
3117   _has_object_free_events = false;
3118   return result;
3119 }
3120 
3121 // Used by ServiceThread to clean up tagmaps.
3122 void JvmtiTagMap::flush_all_object_free_events() {
3123   JavaThread* thread = JavaThread::current();
3124   JvmtiEnvIterator it;
3125   for (JvmtiEnv* env = it.first(); env != nullptr; env = it.next(env)) {
3126     JvmtiTagMap* tag_map = env->tag_map_acquire();
3127     if (tag_map != nullptr) {
3128       tag_map->flush_object_free_events();
3129       ThreadBlockInVM tbiv(thread); // Be safepoint-polite while looping.
3130     }
3131   }
3132 }