jdk8-mips64-public/hotspot: src/share/vm/prims/jvmtiTagMap.cpp@93b6525e3b82 (annotated)

src/share/vm/prims/jvmtiTagMap.cpp@93b6525e3b82 (annotated)

src/share/vm/prims/jvmtiTagMap.cpp

Tue, 08 Apr 2008 12:23:15 -0400

author: sgoldman
date: Tue, 08 Apr 2008 12:23:15 -0400
changeset 542: 93b6525e3b82
parent 435: a61af66fc99e
child 548: ba764ed4b6f2
permissions: -rw-r--r--

6603919: Stackwalking crash on x86 -server with Sun Studio's collect -j on
Summary: Rewrite frame::safe_for_sender and friends to be safe for collector/analyzer
Reviewed-by: dcubed, kvn

 /*
  * Copyright 2003-2007 Sun Microsystems, Inc.  All Rights Reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
  * under the terms of the GNU General Public License version 2 only, as
  * published by the Free Software Foundation.
  *
  * This code is distributed in the hope that it will be useful, but WITHOUT
  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  * version 2 for more details (a copy is included in the LICENSE file that
  * accompanied this code).
  *
  * You should have received a copy of the GNU General Public License version
  * 2 along with this work; if not, write to the Free Software Foundation,
  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  *
  * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
  * CA 95054 USA or visit www.sun.com if you need additional information or
  * have any questions.
  *
  */
 # include "incls/_precompiled.incl"
 # include "incls/_jvmtiTagMap.cpp.incl"
 // JvmtiTagHashmapEntry
 //
 // Each entry encapsulates a JNI weak reference to the tagged object
 // and the tag value. In addition an entry includes a next pointer which
 // is used to chain entries together.
 class JvmtiTagHashmapEntry : public CHeapObj {
  private:
   friend class JvmtiTagMap;
   jweak _object;                        // JNI weak ref to tagged object
   jlong _tag;                           // the tag
   JvmtiTagHashmapEntry* _next;          // next on the list
   inline void init(jweak object, jlong tag) {
     _object = object;
     _tag = tag;
     _next = NULL;
   }
   // constructor
   JvmtiTagHashmapEntry(jweak object, jlong tag)         { init(object, tag); }
  public:
   // accessor methods
   inline jweak object() const                           { return _object; }
   inline jlong tag() const                              { return _tag; }
   inline void set_tag(jlong tag) {
     assert(tag != 0, "can't be zero");
     _tag = tag;
   }
   inline JvmtiTagHashmapEntry* next() const             { return _next; }
   inline void set_next(JvmtiTagHashmapEntry* next)      { _next = next; }
 };
 // JvmtiTagHashmap
 //
 // A hashmap is essentially a table of pointers to entries. Entries
 // are hashed to a location, or position in the table, and then
 // chained from that location. The "key" for hashing is address of
 // the object, or oop. The "value" is the JNI weak reference to the
 // object and the tag value. Keys are not stored with the entry.
 // Instead the weak reference is resolved to obtain the key.
 //
 // A hashmap maintains a count of the number entries in the hashmap
 // and resizes if the number of entries exceeds a given threshold.
 // The threshold is specified as a percentage of the size - for
 // example a threshold of 0.75 will trigger the hashmap to resize
 // if the number of entries is >75% of table size.
 //
 // A hashmap provides functions for adding, removing, and finding
 // entries. It also provides a function to iterate over all entries
 // in the hashmap.
 class JvmtiTagHashmap : public CHeapObj {
  private:
   friend class JvmtiTagMap;
   enum {
     small_trace_threshold  = 10000,                  // threshold for tracing
     medium_trace_threshold = 100000,
     large_trace_threshold  = 1000000,
     initial_trace_threshold = small_trace_threshold
   };
   static int _sizes[];                  // array of possible hashmap sizes
   int _size;                            // actual size of the table
   int _size_index;                      // index into size table
   int _entry_count;                     // number of entries in the hashmap
   float _load_factor;                   // load factor as a % of the size
   int _resize_threshold;                // computed threshold to trigger resizing.
   bool _resizing_enabled;               // indicates if hashmap can resize
   int _trace_threshold;                 // threshold for trace messages
   JvmtiTagHashmapEntry** _table;        // the table of entries.
   // private accessors
   int resize_threshold() const                  { return _resize_threshold; }
   int trace_threshold() const                   { return _trace_threshold; }
   // initialize the hashmap
   void init(int size_index=0, float load_factor=4.0f) {
     int initial_size =  _sizes[size_index];
     _size_index = size_index;
     _size = initial_size;
     _entry_count = 0;
     if (TraceJVMTIObjectTagging) {
       _trace_threshold = initial_trace_threshold;
     } else {
       _trace_threshold = -1;
     }
     _load_factor = load_factor;
     _resize_threshold = (int)(_load_factor * _size);
     _resizing_enabled = true;
     size_t s = initial_size * sizeof(JvmtiTagHashmapEntry*);
     _table = (JvmtiTagHashmapEntry**)os::malloc(s);
     if (_table == NULL) {
       vm_exit_out_of_memory(s, "unable to allocate initial hashtable for jvmti object tags");
     }
     for (int i=0; i<initial_size; i++) {
       _table[i] = NULL;
     }
   }
   // hash a given key (oop) with the specified size
   static unsigned int hash(oop key, int size) {
     // shift right to get better distribution (as these bits will be zero
     // with aligned addresses)
     unsigned int addr = (unsigned int)((intptr_t)key);
 #ifdef _LP64
     return (addr >> 3) % size;
 #else
     return (addr >> 2) % size;
 #endif
   }
   // hash a given key (oop)
   unsigned int hash(oop key) {
     return hash(key, _size);
   }
   // resize the hashmap - allocates a large table and re-hashes
   // all entries into the new table.
   void resize() {
     int new_size_index = _size_index+1;
     int new_size = _sizes[new_size_index];
     if (new_size < 0) {
       // hashmap already at maximum capacity
       return;
     }
     // allocate new table
     size_t s = new_size * sizeof(JvmtiTagHashmapEntry*);
     JvmtiTagHashmapEntry** new_table = (JvmtiTagHashmapEntry**)os::malloc(s);
     if (new_table == NULL) {
       warning("unable to allocate larger hashtable for jvmti object tags");
       set_resizing_enabled(false);
       return;
     }
     // initialize new table
     int i;
     for (i=0; i<new_size; i++) {
       new_table[i] = NULL;
     }
     // rehash all entries into the new table
     for (i=0; i<_size; i++) {
       JvmtiTagHashmapEntry* entry = _table[i];
       while (entry != NULL) {
         JvmtiTagHashmapEntry* next = entry->next();
         oop key = JNIHandles::resolve(entry->object());
         assert(key != NULL, "jni weak reference cleared!!");
         unsigned int h = hash(key, new_size);
         JvmtiTagHashmapEntry* anchor = new_table[h];
         if (anchor == NULL) {
           new_table[h] = entry;
           entry->set_next(NULL);
         } else {
           entry->set_next(anchor);
           new_table[h] = entry;
         }
         entry = next;
       }
     }
     // free old table and update settings.
     os::free((void*)_table);
     _table = new_table;
     _size_index = new_size_index;
     _size = new_size;
     // compute new resize threshold
     _resize_threshold = (int)(_load_factor * _size);
   }
   // internal remove function - remove an entry at a given position in the
   // table.
   inline void remove(JvmtiTagHashmapEntry* prev, int pos, JvmtiTagHashmapEntry* entry) {
     assert(pos >= 0 && pos < _size, "out of range");
     if (prev == NULL) {
       _table[pos] = entry->next();
     } else {
       prev->set_next(entry->next());
     }
     assert(_entry_count > 0, "checking");
     _entry_count--;
   }
   // resizing switch
   bool is_resizing_enabled() const          { return _resizing_enabled; }
   void set_resizing_enabled(bool enable)    { _resizing_enabled = enable; }
   // debugging
   void print_memory_usage();
   void compute_next_trace_threshold();
  public:
   // create a JvmtiTagHashmap of a preferred size and optionally a load factor.
   // The preferred size is rounded down to an actual size.
   JvmtiTagHashmap(int size, float load_factor=0.0f) {
     int i=0;
     while (_sizes[i] < size) {
       if (_sizes[i] < 0) {
         assert(i > 0, "sanity check");
         i--;
         break;
       }
       i++;
     }
     // if a load factor is specified then use it, otherwise use default
     if (load_factor > 0.01f) {
       init(i, load_factor);
     } else {
       init(i);
     }
   }
   // create a JvmtiTagHashmap with default settings
   JvmtiTagHashmap() {
     init();
   }
   // release table when JvmtiTagHashmap destroyed
   ~JvmtiTagHashmap() {
     if (_table != NULL) {
       os::free((void*)_table);
       _table = NULL;
     }
   }
   // accessors
   int size() const                              { return _size; }
   JvmtiTagHashmapEntry** table() const          { return _table; }
   int entry_count() const                       { return _entry_count; }
   // find an entry in the hashmap, returns NULL if not found.
   inline JvmtiTagHashmapEntry* find(oop key) {
     unsigned int h = hash(key);
     JvmtiTagHashmapEntry* entry = _table[h];
     while (entry != NULL) {
       oop orig_key = JNIHandles::resolve(entry->object());
       assert(orig_key != NULL, "jni weak reference cleared!!");
       if (key == orig_key) {
         break;
       }
       entry = entry->next();
     }
     return entry;
   }
   // add a new entry to hashmap
   inline void add(oop key, JvmtiTagHashmapEntry* entry) {
     assert(key != NULL, "checking");
     assert(find(key) == NULL, "duplicate detected");
     unsigned int h = hash(key);
     JvmtiTagHashmapEntry* anchor = _table[h];
     if (anchor == NULL) {
       _table[h] = entry;
       entry->set_next(NULL);
     } else {
       entry->set_next(anchor);
       _table[h] = entry;
     }
     _entry_count++;
     if (trace_threshold() > 0 && entry_count() >= trace_threshold()) {
       assert(TraceJVMTIObjectTagging, "should only get here when tracing");
       print_memory_usage();
       compute_next_trace_threshold();
     }
     // if the number of entries exceed the threshold then resize
     if (entry_count() > resize_threshold() && is_resizing_enabled()) {
       resize();
     }
   }
   // remove an entry with the given key.
   inline JvmtiTagHashmapEntry* remove(oop key) {
     unsigned int h = hash(key);
     JvmtiTagHashmapEntry* entry = _table[h];
     JvmtiTagHashmapEntry* prev = NULL;
     while (entry != NULL) {
       oop orig_key = JNIHandles::resolve(entry->object());
       assert(orig_key != NULL, "jni weak reference cleared!!");
       if (key == orig_key) {
         break;
       }
       prev = entry;
       entry = entry->next();
     }
     if (entry != NULL) {
       remove(prev, h, entry);
     }
     return entry;
   }
   // iterate over all entries in the hashmap
   void entry_iterate(JvmtiTagHashmapEntryClosure* closure);
 };
 // possible hashmap sizes - odd primes that roughly double in size.
 // To avoid excessive resizing the odd primes from 4801-76831 and
 // 76831-307261 have been removed. The list must be terminated by -1.
 int JvmtiTagHashmap::_sizes[] =  { 4801, 76831, 307261, 614563, 1228891,
     2457733, 4915219, 9830479, 19660831, 39321619, 78643219, -1 };
 // A supporting class for iterating over all entries in Hashmap
 class JvmtiTagHashmapEntryClosure {
  public:
   virtual void do_entry(JvmtiTagHashmapEntry* entry) = 0;
 };
 // iterate over all entries in the hashmap
 void JvmtiTagHashmap::entry_iterate(JvmtiTagHashmapEntryClosure* closure) {
   for (int i=0; i<_size; i++) {
     JvmtiTagHashmapEntry* entry = _table[i];
     JvmtiTagHashmapEntry* prev = NULL;
     while (entry != NULL) {
       // obtain the next entry before invoking do_entry - this is
       // necessary because do_entry may remove the entry from the
       // hashmap.
       JvmtiTagHashmapEntry* next = entry->next();
       closure->do_entry(entry);
       entry = next;
      }
   }
 }
 // debugging
 void JvmtiTagHashmap::print_memory_usage() {
   intptr_t p = (intptr_t)this;
   tty->print("[JvmtiTagHashmap @ " INTPTR_FORMAT, p);
   // table + entries in KB
   int hashmap_usage = (size()*sizeof(JvmtiTagHashmapEntry*) +
     entry_count()*sizeof(JvmtiTagHashmapEntry))/K;
   int weak_globals_usage = (int)(JNIHandles::weak_global_handle_memory_usage()/K);
   tty->print_cr(", %d entries (%d KB) <JNI weak globals: %d KB>]",
     entry_count(), hashmap_usage, weak_globals_usage);
 }
 // compute threshold for the next trace message
 void JvmtiTagHashmap::compute_next_trace_threshold() {
   if (trace_threshold() < medium_trace_threshold) {
     _trace_threshold += small_trace_threshold;
   } else {
     if (trace_threshold() < large_trace_threshold) {
       _trace_threshold += medium_trace_threshold;
     } else {
       _trace_threshold += large_trace_threshold;
     }
   }
 }
 // memory region for young generation
 MemRegion JvmtiTagMap::_young_gen;
 // get the memory region used for the young generation
 void JvmtiTagMap::get_young_generation() {
   if (Universe::heap()->kind() == CollectedHeap::GenCollectedHeap) {
     GenCollectedHeap* gch = GenCollectedHeap::heap();
     _young_gen = gch->get_gen(0)->reserved();
   } else {
 #ifndef SERIALGC
     ParallelScavengeHeap* psh = ParallelScavengeHeap::heap();
     _young_gen= psh->young_gen()->reserved();
 #else  // SERIALGC
     fatal("SerialGC only supported in this configuration.");
 #endif // SERIALGC
   }
 }
 // returns true if oop is in the young generation
 inline bool JvmtiTagMap::is_in_young(oop o) {
   assert(_young_gen.start() != NULL, "checking");
   void* p = (void*)o;
   bool in_young = _young_gen.contains(p);
   return in_young;
 }
 // returns the appropriate hashmap for a given object
 inline JvmtiTagHashmap* JvmtiTagMap::hashmap_for(oop o) {
   if (is_in_young(o)) {
     return _hashmap[0];
   } else {
     return _hashmap[1];
   }
 }
 // create a JvmtiTagMap
 JvmtiTagMap::JvmtiTagMap(JvmtiEnv* env) :
   _env(env),
   _lock(Mutex::nonleaf+2, "JvmtiTagMap._lock", false),
   _free_entries(NULL),
   _free_entries_count(0)
 {
   assert(JvmtiThreadState_lock->is_locked(), "sanity check");
   assert(((JvmtiEnvBase *)env)->tag_map() == NULL, "tag map already exists for environment");
   // create the hashmaps
   for (int i=0; i<n_hashmaps; i++) {
     _hashmap[i] = new JvmtiTagHashmap();
   }
   // get the memory region used by the young generation
   get_young_generation();
   // finally add us to the environment
   ((JvmtiEnvBase *)env)->set_tag_map(this);
 }
 // destroy a JvmtiTagMap
 JvmtiTagMap::~JvmtiTagMap() {
   // no lock acquired as we assume the enclosing environment is
   // also being destroryed.
   ((JvmtiEnvBase *)_env)->set_tag_map(NULL);
   // iterate over the hashmaps and destroy each of the entries
   for (int i=0; i<n_hashmaps; i++) {
     JvmtiTagHashmap* hashmap = _hashmap[i];
     JvmtiTagHashmapEntry** table = hashmap->table();
     for (int j=0; j<hashmap->size(); j++) {
       JvmtiTagHashmapEntry *entry = table[j];
       while (entry != NULL) {
         JvmtiTagHashmapEntry* next = entry->next();
         jweak ref = entry->object();
         JNIHandles::destroy_weak_global(ref);
         delete entry;
         entry = next;
       }
     }
     // finally destroy the hashmap
     delete hashmap;
   }
   // remove any entries on the free list
   JvmtiTagHashmapEntry* entry = _free_entries;
   while (entry != NULL) {
     JvmtiTagHashmapEntry* next = entry->next();
     delete entry;
     entry = next;
   }
 }
 // create a hashmap entry
 // - if there's an entry on the (per-environment) free list then this
 // is returned. Otherwise an new entry is allocated.
 JvmtiTagHashmapEntry* JvmtiTagMap::create_entry(jweak ref, jlong tag) {
   assert(Thread::current()->is_VM_thread() || is_locked(), "checking");
   JvmtiTagHashmapEntry* entry;
   if (_free_entries == NULL) {
     entry = new JvmtiTagHashmapEntry(ref, tag);
   } else {
     assert(_free_entries_count > 0, "mismatched _free_entries_count");
     _free_entries_count--;
     entry = _free_entries;
     _free_entries = entry->next();
     entry->init(ref, tag);
   }
   return entry;
 }
 // destroy an entry by returning it to the free list
 void JvmtiTagMap::destroy_entry(JvmtiTagHashmapEntry* entry) {
   assert(SafepointSynchronize::is_at_safepoint() || is_locked(), "checking");
   // limit the size of the free list
   if (_free_entries_count >= max_free_entries) {
     delete entry;
   } else {
     entry->set_next(_free_entries);
     _free_entries = entry;
     _free_entries_count++;
   }
 }
 // returns the tag map for the given environments. If the tag map
 // doesn't exist then it is created.
 JvmtiTagMap* JvmtiTagMap::tag_map_for(JvmtiEnv* env) {
   JvmtiTagMap* tag_map = ((JvmtiEnvBase *)env)->tag_map();
   if (tag_map == NULL) {
     MutexLocker mu(JvmtiThreadState_lock);
     tag_map = ((JvmtiEnvBase *)env)->tag_map();
     if (tag_map == NULL) {
       tag_map = new JvmtiTagMap(env);
     }
   } else {
     CHECK_UNHANDLED_OOPS_ONLY(Thread::current()->clear_unhandled_oops());
   }
   return tag_map;
 }
 // iterate over all entries in the tag map.
 void JvmtiTagMap::entry_iterate(JvmtiTagHashmapEntryClosure* closure) {
   for (int i=0; i<n_hashmaps; i++) {
     JvmtiTagHashmap* hashmap = _hashmap[i];
     hashmap->entry_iterate(closure);
   }
 }
 // returns true if the hashmaps are empty
 bool JvmtiTagMap::is_empty() {
   assert(SafepointSynchronize::is_at_safepoint() || is_locked(), "checking");
   assert(n_hashmaps == 2, "not implemented");
   return ((_hashmap[0]->entry_count() == 0) && (_hashmap[1]->entry_count() == 0));
 }
 // Return the tag value for an object, or 0 if the object is
 // not tagged
 //
 static inline jlong tag_for(JvmtiTagMap* tag_map, oop o) {
   JvmtiTagHashmapEntry* entry = tag_map->hashmap_for(o)->find(o);
   if (entry == NULL) {
     return 0;
   } else {
     return entry->tag();
   }
 }
 // If the object is a java.lang.Class then return the klassOop,
 // otherwise return the original object
 static inline oop klassOop_if_java_lang_Class(oop o) {
   if (o->klass() == SystemDictionary::class_klass()) {
     if (!java_lang_Class::is_primitive(o)) {
       o = (oop)java_lang_Class::as_klassOop(o);
       assert(o != NULL, "class for non-primitive mirror must exist");
     }
   }
   return o;
 }
 // A CallbackWrapper is a support class for querying and tagging an object
 // around a callback to a profiler. The constructor does pre-callback
 // work to get the tag value, klass tag value, ... and the destructor
 // does the post-callback work of tagging or untagging the object.
 //
 // {
 //   CallbackWrapper wrapper(tag_map, o);
 //
 //   (*callback)(wrapper.klass_tag(), wrapper.obj_size(), wrapper.obj_tag_p(), ...)
 //
 // } // wrapper goes out of scope here which results in the destructor
 //      checking to see if the object has been tagged, untagged, or the
 //      tag value has changed.
 //
 class CallbackWrapper : public StackObj {
  private:
   JvmtiTagMap* _tag_map;
   JvmtiTagHashmap* _hashmap;
   JvmtiTagHashmapEntry* _entry;
   oop _o;
   jlong _obj_size;
   jlong _obj_tag;
   klassOop _klass;         // the object's class
   jlong _klass_tag;
  protected:
   JvmtiTagMap* tag_map() const      { return _tag_map; }
   // invoked post-callback to tag, untag, or update the tag of an object
   void inline post_callback_tag_update(oop o, JvmtiTagHashmap* hashmap,
                                        JvmtiTagHashmapEntry* entry, jlong obj_tag);
  public:
   CallbackWrapper(JvmtiTagMap* tag_map, oop o) {
     assert(Thread::current()->is_VM_thread() || tag_map->is_locked(),
            "MT unsafe or must be VM thread");
     // for Classes the klassOop is tagged
     _o = klassOop_if_java_lang_Class(o);
     // object size
     _obj_size = _o->size() * wordSize;
     // record the context
     _tag_map = tag_map;
     _hashmap = tag_map->hashmap_for(_o);
     _entry = _hashmap->find(_o);
     // get object tag
     _obj_tag = (_entry == NULL) ? 0 : _entry->tag();
     // get the class and the class's tag value
     if (_o == o) {
       _klass = _o->klass();
     } else {
       // if the object represents a runtime class then use the
       // tag for java.lang.Class
       _klass = SystemDictionary::class_klass();
     }
     _klass_tag = tag_for(tag_map, _klass);
   }
   ~CallbackWrapper() {
     post_callback_tag_update(_o, _hashmap, _entry, _obj_tag);
   }
   inline jlong* obj_tag_p()                     { return &_obj_tag; }
   inline jlong obj_size() const                 { return _obj_size; }
   inline jlong obj_tag() const                  { return _obj_tag; }
   inline klassOop klass() const                 { return _klass; }
   inline jlong klass_tag() const                { return _klass_tag; }
 };
 // callback post-callback to tag, untag, or update the tag of an object
 void inline CallbackWrapper::post_callback_tag_update(oop o,
                                                       JvmtiTagHashmap* hashmap,
                                                       JvmtiTagHashmapEntry* entry,
                                                       jlong obj_tag) {
   if (entry == NULL) {
     if (obj_tag != 0) {
       // callback has tagged the object
       assert(Thread::current()->is_VM_thread(), "must be VMThread");
       HandleMark hm;
       Handle h(o);
       jweak ref = JNIHandles::make_weak_global(h);
       entry = tag_map()->create_entry(ref, obj_tag);
       hashmap->add(o, entry);
     }
   } else {
     // object was previously tagged - the callback may have untagged
     // the object or changed the tag value
     if (obj_tag == 0) {
       jweak ref = entry->object();
       JvmtiTagHashmapEntry* entry_removed = hashmap->remove(o);
       assert(entry_removed == entry, "checking");
       tag_map()->destroy_entry(entry);
       JNIHandles::destroy_weak_global(ref);
     } else {
       if (obj_tag != entry->tag()) {
          entry->set_tag(obj_tag);
       }
     }
   }
 }
 // An extended CallbackWrapper used when reporting an object reference
 // to the agent.
 //
 // {
 //   TwoOopCallbackWrapper wrapper(tag_map, referrer, o);
 //
 //   (*callback)(wrapper.klass_tag(),
 //               wrapper.obj_size(),
 //               wrapper.obj_tag_p()
 //               wrapper.referrer_tag_p(), ...)
 //
 // } // wrapper goes out of scope here which results in the destructor
 //      checking to see if the referrer object has been tagged, untagged,
 //      or the tag value has changed.
 //
 class TwoOopCallbackWrapper : public CallbackWrapper {
  private:
   bool _is_reference_to_self;
   JvmtiTagHashmap* _referrer_hashmap;
   JvmtiTagHashmapEntry* _referrer_entry;
   oop _referrer;
   jlong _referrer_obj_tag;
   jlong _referrer_klass_tag;
   jlong* _referrer_tag_p;
   bool is_reference_to_self() const             { return _is_reference_to_self; }
  public:
   TwoOopCallbackWrapper(JvmtiTagMap* tag_map, oop referrer, oop o) :
     CallbackWrapper(tag_map, o)
   {
     // self reference needs to be handled in a special way
     _is_reference_to_self = (referrer == o);
     if (_is_reference_to_self) {
       _referrer_klass_tag = klass_tag();
       _referrer_tag_p = obj_tag_p();
     } else {
       // for Classes the klassOop is tagged
       _referrer = klassOop_if_java_lang_Class(referrer);
       // record the context
       _referrer_hashmap = tag_map->hashmap_for(_referrer);
       _referrer_entry = _referrer_hashmap->find(_referrer);
       // get object tag
       _referrer_obj_tag = (_referrer_entry == NULL) ? 0 : _referrer_entry->tag();
       _referrer_tag_p = &_referrer_obj_tag;
       // get referrer class tag.
       klassOop k = (_referrer == referrer) ?  // Check if referrer is a class...
           _referrer->klass()                  // No, just get its class
          : SystemDictionary::class_klass();   // Yes, its class is Class
       _referrer_klass_tag = tag_for(tag_map, k);
     }
   }
   ~TwoOopCallbackWrapper() {
     if (!is_reference_to_self()){
       post_callback_tag_update(_referrer,
                                _referrer_hashmap,
                                _referrer_entry,
                                _referrer_obj_tag);
     }
   }
   // address of referrer tag
   // (for a self reference this will return the same thing as obj_tag_p())
   inline jlong* referrer_tag_p()        { return _referrer_tag_p; }
   // referrer's class tag
   inline jlong referrer_klass_tag()     { return _referrer_klass_tag; }
 };
 // tag an object
 //
 // This function is performance critical. If many threads attempt to tag objects
 // around the same time then it's possible that the Mutex associated with the
 // tag map will be a hot lock. Eliminating this lock will not eliminate the issue
 // because creating a JNI weak reference requires acquiring a global lock also.
 void JvmtiTagMap::set_tag(jobject object, jlong tag) {
   MutexLocker ml(lock());
   // resolve the object
   oop o = JNIHandles::resolve_non_null(object);
   // for Classes we tag the klassOop
   o = klassOop_if_java_lang_Class(o);
   // see if the object is already tagged
   JvmtiTagHashmap* hashmap = hashmap_for(o);
   JvmtiTagHashmapEntry* entry = hashmap->find(o);
   // if the object is not already tagged then we tag it
   if (entry == NULL) {
     if (tag != 0) {
       HandleMark hm;
       Handle h(o);
       jweak ref = JNIHandles::make_weak_global(h);
       // the object may have moved because make_weak_global may
       // have blocked - thus it is necessary resolve the handle
       // and re-hash the object.
       o = h();
       entry = create_entry(ref, tag);
       hashmap_for(o)->add(o, entry);
     } else {
       // no-op
     }
   } else {
     // if the object is already tagged then we either update
     // the tag (if a new tag value has been provided)
     // or remove the object if the new tag value is 0.
     // Removing the object requires that we also delete the JNI
     // weak ref to the object.
     if (tag == 0) {
       jweak ref = entry->object();
       hashmap->remove(o);
       destroy_entry(entry);
       JNIHandles::destroy_weak_global(ref);
     } else {
       entry->set_tag(tag);
     }
   }
 }
 // get the tag for an object
 jlong JvmtiTagMap::get_tag(jobject object) {
   MutexLocker ml(lock());
   // resolve the object
   oop o = JNIHandles::resolve_non_null(object);
   // for Classes get the tag from the klassOop
   return tag_for(this, klassOop_if_java_lang_Class(o));
 }
 // Helper class used to describe the static or instance fields of a class.
 // For each field it holds the field index (as defined by the JVMTI specification),
 // the field type, and the offset.
 class ClassFieldDescriptor: public CHeapObj {
  private:
   int _field_index;
   int _field_offset;
   char _field_type;
  public:
   ClassFieldDescriptor(int index, char type, int offset) :
     _field_index(index), _field_type(type), _field_offset(offset) {
   }
   int field_index()  const  { return _field_index; }
   char field_type()  const  { return _field_type; }
   int field_offset() const  { return _field_offset; }
 };
 class ClassFieldMap: public CHeapObj {
  private:
   enum {
     initial_field_count = 5
   };
   // list of field descriptors
   GrowableArray<ClassFieldDescriptor*>* _fields;
   // constructor
   ClassFieldMap();
   // add a field
   void add(int index, char type, int offset);
   // returns the field count for the given class
   static int compute_field_count(instanceKlassHandle ikh);
  public:
   ~ClassFieldMap();
   // access
   int field_count()                     { return _fields->length(); }
   ClassFieldDescriptor* field_at(int i) { return _fields->at(i); }
   // functions to create maps of static or instance fields
   static ClassFieldMap* create_map_of_static_fields(klassOop k);
   static ClassFieldMap* create_map_of_instance_fields(oop obj);
 };
 ClassFieldMap::ClassFieldMap() {
   _fields = new (ResourceObj::C_HEAP) GrowableArray<ClassFieldDescriptor*>(initial_field_count, true);
 }
 ClassFieldMap::~ClassFieldMap() {
   for (int i=0; i<_fields->length(); i++) {
     delete _fields->at(i);
   }
   delete _fields;
 }
 void ClassFieldMap::add(int index, char type, int offset) {
   ClassFieldDescriptor* field = new ClassFieldDescriptor(index, type, offset);
   _fields->append(field);
 }
 // Returns a heap allocated ClassFieldMap to describe the static fields
 // of the given class.
 //
 ClassFieldMap* ClassFieldMap::create_map_of_static_fields(klassOop k) {
   HandleMark hm;
   instanceKlassHandle ikh = instanceKlassHandle(Thread::current(), k);
   // create the field map
   ClassFieldMap* field_map = new ClassFieldMap();
   FilteredFieldStream f(ikh, false, false);
   int max_field_index = f.field_count()-1;
   int index = 0;
   for (FilteredFieldStream fld(ikh, true, true); !fld.eos(); fld.next(), index++) {
     // ignore instance fields
     if (!fld.access_flags().is_static()) {
       continue;
     }
     field_map->add(max_field_index - index, fld.signature()->byte_at(0), fld.offset());
   }
   return field_map;
 }
 // Returns a heap allocated ClassFieldMap to describe the instance fields
 // of the given class. All instance fields are included (this means public
 // and private fields declared in superclasses and superinterfaces too).
 //
 ClassFieldMap* ClassFieldMap::create_map_of_instance_fields(oop obj) {
   HandleMark hm;
   instanceKlassHandle ikh = instanceKlassHandle(Thread::current(), obj->klass());
   // create the field map
   ClassFieldMap* field_map = new ClassFieldMap();
   FilteredFieldStream f(ikh, false, false);
   int max_field_index = f.field_count()-1;
   int index = 0;
   for (FilteredFieldStream fld(ikh, false, false); !fld.eos(); fld.next(), index++) {
     // ignore static fields
     if (fld.access_flags().is_static()) {
       continue;
     }
     field_map->add(max_field_index - index, fld.signature()->byte_at(0), fld.offset());
   }
   return field_map;
 }
 // Helper class used to cache a ClassFileMap for the instance fields of
 // a cache. A JvmtiCachedClassFieldMap can be cached by an instanceKlass during
 // heap iteration and avoid creating a field map for each object in the heap
 // (only need to create the map when the first instance of a class is encountered).
 //
 class JvmtiCachedClassFieldMap : public CHeapObj {
  private:
    enum {
      initial_class_count = 200
    };
   ClassFieldMap* _field_map;
   ClassFieldMap* field_map() const          { return _field_map; }
   JvmtiCachedClassFieldMap(ClassFieldMap* field_map);
   ~JvmtiCachedClassFieldMap();
   static GrowableArray<instanceKlass*>* _class_list;
   static void add_to_class_list(instanceKlass* ik);
  public:
   // returns the field map for a given object (returning map cached
   // by instanceKlass if possible
   static ClassFieldMap* get_map_of_instance_fields(oop obj);
   // removes the field map from all instanceKlasses - should be
   // called before VM operation completes
   static void clear_cache();
   // returns the number of ClassFieldMap cached by instanceKlasses
   static int cached_field_map_count();
 };
 GrowableArray<instanceKlass*>* JvmtiCachedClassFieldMap::_class_list;
 JvmtiCachedClassFieldMap::JvmtiCachedClassFieldMap(ClassFieldMap* field_map) {
   _field_map = field_map;
 }
 JvmtiCachedClassFieldMap::~JvmtiCachedClassFieldMap() {
   if (_field_map != NULL) {
     delete _field_map;
   }
 }
 // Marker class to ensure that the class file map cache is only used in a defined
 // scope.
 class ClassFieldMapCacheMark : public StackObj {
  private:
    static bool _is_active;
  public:
    ClassFieldMapCacheMark() {
      assert(Thread::current()->is_VM_thread(), "must be VMThread");
      assert(JvmtiCachedClassFieldMap::cached_field_map_count() == 0, "cache not empty");
      assert(!_is_active, "ClassFieldMapCacheMark cannot be nested");
      _is_active = true;
    }
    ~ClassFieldMapCacheMark() {
      JvmtiCachedClassFieldMap::clear_cache();
      _is_active = false;
    }
    static bool is_active() { return _is_active; }
 };
 bool ClassFieldMapCacheMark::_is_active;
 // record that the given instanceKlass is caching a field map
 void JvmtiCachedClassFieldMap::add_to_class_list(instanceKlass* ik) {
   if (_class_list == NULL) {
     _class_list = new (ResourceObj::C_HEAP) GrowableArray<instanceKlass*>(initial_class_count, true);
   }
   _class_list->push(ik);
 }
 // returns the instance field map for the given object
 // (returns field map cached by the instanceKlass if possible)
 ClassFieldMap* JvmtiCachedClassFieldMap::get_map_of_instance_fields(oop obj) {
   assert(Thread::current()->is_VM_thread(), "must be VMThread");
   assert(ClassFieldMapCacheMark::is_active(), "ClassFieldMapCacheMark not active");
   klassOop k = obj->klass();
   instanceKlass* ik = instanceKlass::cast(k);
   // return cached map if possible
   JvmtiCachedClassFieldMap* cached_map = ik->jvmti_cached_class_field_map();
   if (cached_map != NULL) {
     assert(cached_map->field_map() != NULL, "missing field list");
     return cached_map->field_map();
   } else {
     ClassFieldMap* field_map = ClassFieldMap::create_map_of_instance_fields(obj);
     cached_map = new JvmtiCachedClassFieldMap(field_map);
     ik->set_jvmti_cached_class_field_map(cached_map);
     add_to_class_list(ik);
     return field_map;
   }
 }
 // remove the fields maps cached from all instanceKlasses
 void JvmtiCachedClassFieldMap::clear_cache() {
   assert(Thread::current()->is_VM_thread(), "must be VMThread");
   if (_class_list != NULL) {
     for (int i = 0; i < _class_list->length(); i++) {
       instanceKlass* ik = _class_list->at(i);
       JvmtiCachedClassFieldMap* cached_map = ik->jvmti_cached_class_field_map();
       assert(cached_map != NULL, "should not be NULL");
       ik->set_jvmti_cached_class_field_map(NULL);
       delete cached_map;  // deletes the encapsulated field map
     }
     delete _class_list;
     _class_list = NULL;
   }
 }
 // returns the number of ClassFieldMap cached by instanceKlasses
 int JvmtiCachedClassFieldMap::cached_field_map_count() {
   return (_class_list == NULL) ? 0 : _class_list->length();
 }
 // helper function to indicate if an object is filtered by its tag or class tag
 static inline bool is_filtered_by_heap_filter(jlong obj_tag,
                                               jlong klass_tag,
                                               int heap_filter) {
   // apply the heap filter
   if (obj_tag != 0) {
     // filter out tagged objects
     if (heap_filter & JVMTI_HEAP_FILTER_TAGGED) return true;
   } else {
     // filter out untagged objects
     if (heap_filter & JVMTI_HEAP_FILTER_UNTAGGED) return true;
   }
   if (klass_tag != 0) {
     // filter out objects with tagged classes
     if (heap_filter & JVMTI_HEAP_FILTER_CLASS_TAGGED) return true;
   } else {
     // filter out objects with untagged classes.
     if (heap_filter & JVMTI_HEAP_FILTER_CLASS_UNTAGGED) return true;
   }
   return false;
 }
 // helper function to indicate if an object is filtered by a klass filter
 static inline bool is_filtered_by_klass_filter(oop obj, KlassHandle klass_filter) {
   if (!klass_filter.is_null()) {
     if (obj->klass() != klass_filter()) {
       return true;
     }
   }
   return false;
 }
 // helper function to tell if a field is a primitive field or not
 static inline bool is_primitive_field_type(char type) {
   return (type != 'L' && type != '[');
 }
 // helper function to copy the value from location addr to jvalue.
 static inline void copy_to_jvalue(jvalue *v, address addr, jvmtiPrimitiveType value_type) {
   switch (value_type) {
     case JVMTI_PRIMITIVE_TYPE_BOOLEAN : { v->z = *(jboolean*)addr; break; }
     case JVMTI_PRIMITIVE_TYPE_BYTE    : { v->b = *(jbyte*)addr;    break; }
     case JVMTI_PRIMITIVE_TYPE_CHAR    : { v->c = *(jchar*)addr;    break; }
     case JVMTI_PRIMITIVE_TYPE_SHORT   : { v->s = *(jshort*)addr;   break; }
     case JVMTI_PRIMITIVE_TYPE_INT     : { v->i = *(jint*)addr;     break; }
     case JVMTI_PRIMITIVE_TYPE_LONG    : { v->j = *(jlong*)addr;    break; }
     case JVMTI_PRIMITIVE_TYPE_FLOAT   : { v->f = *(jfloat*)addr;   break; }
     case JVMTI_PRIMITIVE_TYPE_DOUBLE  : { v->d = *(jdouble*)addr;  break; }
     default: ShouldNotReachHere();
   }
 }
 // helper function to invoke string primitive value callback
 // returns visit control flags
 static jint invoke_string_value_callback(jvmtiStringPrimitiveValueCallback cb,
                                          CallbackWrapper* wrapper,
                                          oop str,
                                          void* user_data)
 {
   assert(str->klass() == SystemDictionary::string_klass(), "not a string");
   // get the string value and length
   // (string value may be offset from the base)
   int s_len = java_lang_String::length(str);
   typeArrayOop s_value = java_lang_String::value(str);
   int s_offset = java_lang_String::offset(str);
   jchar* value;
   if (s_len > 0) {
     value = s_value->char_at_addr(s_offset);
   } else {
     value = (jchar*) s_value->base(T_CHAR);
   }
   // invoke the callback
   return (*cb)(wrapper->klass_tag(),
                wrapper->obj_size(),
                wrapper->obj_tag_p(),
                value,
                (jint)s_len,
                user_data);
 }
 // helper function to invoke string primitive value callback
 // returns visit control flags
 static jint invoke_array_primitive_value_callback(jvmtiArrayPrimitiveValueCallback cb,
                                                   CallbackWrapper* wrapper,
                                                   oop obj,
                                                   void* user_data)
 {
   assert(obj->is_typeArray(), "not a primitive array");
   // get base address of first element
   typeArrayOop array = typeArrayOop(obj);
   BasicType type = typeArrayKlass::cast(array->klass())->element_type();
   void* elements = array->base(type);
   // jvmtiPrimitiveType is defined so this mapping is always correct
   jvmtiPrimitiveType elem_type = (jvmtiPrimitiveType)type2char(type);
   return (*cb)(wrapper->klass_tag(),
                wrapper->obj_size(),
                wrapper->obj_tag_p(),
                (jint)array->length(),
                elem_type,
                elements,
                user_data);
 }
 // helper function to invoke the primitive field callback for all static fields
 // of a given class
 static jint invoke_primitive_field_callback_for_static_fields
   (CallbackWrapper* wrapper,
    oop obj,
    jvmtiPrimitiveFieldCallback cb,
    void* user_data)
 {
   // for static fields only the index will be set
   static jvmtiHeapReferenceInfo reference_info = { 0 };
   assert(obj->klass() == SystemDictionary::class_klass(), "not a class");
   if (java_lang_Class::is_primitive(obj)) {
     return 0;
   }
   klassOop k = java_lang_Class::as_klassOop(obj);
   Klass* klass = k->klass_part();
   // ignore classes for object and type arrays
   if (!klass->oop_is_instance()) {
     return 0;
   }
   // ignore classes which aren't linked yet
   instanceKlass* ik = instanceKlass::cast(k);
   if (!ik->is_linked()) {
     return 0;
   }
   // get the field map
   ClassFieldMap* field_map = ClassFieldMap::create_map_of_static_fields(k);
   // invoke the callback for each static primitive field
   for (int i=0; i<field_map->field_count(); i++) {
     ClassFieldDescriptor* field = field_map->field_at(i);
     // ignore non-primitive fields
     char type = field->field_type();
     if (!is_primitive_field_type(type)) {
       continue;
     }
     // one-to-one mapping
     jvmtiPrimitiveType value_type = (jvmtiPrimitiveType)type;
     // get offset and field value
     int offset = field->field_offset();
     address addr = (address)k + offset;
     jvalue value;
     copy_to_jvalue(&value, addr, value_type);
     // field index
     reference_info.field.index = field->field_index();
     // invoke the callback
     jint res = (*cb)(JVMTI_HEAP_REFERENCE_STATIC_FIELD,
                      &reference_info,
                      wrapper->klass_tag(),
                      wrapper->obj_tag_p(),
                      value,
                      value_type,
                      user_data);
     if (res & JVMTI_VISIT_ABORT) {
       delete field_map;
       return res;
     }
   }
   delete field_map;
   return 0;
 }
 // helper function to invoke the primitive field callback for all instance fields
 // of a given object
 static jint invoke_primitive_field_callback_for_instance_fields(
   CallbackWrapper* wrapper,
   oop obj,
   jvmtiPrimitiveFieldCallback cb,
   void* user_data)
 {
   // for instance fields only the index will be set
   static jvmtiHeapReferenceInfo reference_info = { 0 };
   // get the map of the instance fields
   ClassFieldMap* fields = JvmtiCachedClassFieldMap::get_map_of_instance_fields(obj);
   // invoke the callback for each instance primitive field
   for (int i=0; i<fields->field_count(); i++) {
     ClassFieldDescriptor* field = fields->field_at(i);
     // ignore non-primitive fields
     char type = field->field_type();
     if (!is_primitive_field_type(type)) {
       continue;
     }
     // one-to-one mapping
     jvmtiPrimitiveType value_type = (jvmtiPrimitiveType)type;
     // get offset and field value
     int offset = field->field_offset();
     address addr = (address)obj + offset;
     jvalue value;
     copy_to_jvalue(&value, addr, value_type);
     // field index
     reference_info.field.index = field->field_index();
     // invoke the callback
     jint res = (*cb)(JVMTI_HEAP_REFERENCE_FIELD,
                      &reference_info,
                      wrapper->klass_tag(),
                      wrapper->obj_tag_p(),
                      value,
                      value_type,
                      user_data);
     if (res & JVMTI_VISIT_ABORT) {
       return res;
     }
   }
   return 0;
 }
 // VM operation to iterate over all objects in the heap (both reachable
 // and unreachable)
 class VM_HeapIterateOperation: public VM_Operation {
  private:
   ObjectClosure* _blk;
  public:
   VM_HeapIterateOperation(ObjectClosure* blk) { _blk = blk; }
   VMOp_Type type() const { return VMOp_HeapIterateOperation; }
   void doit() {
     // allows class files maps to be cached during iteration
     ClassFieldMapCacheMark cm;
     // make sure that heap is parsable (fills TLABs with filler objects)
     Universe::heap()->ensure_parsability(false);  // no need to retire TLABs
     // Verify heap before iteration - if the heap gets corrupted then
     // JVMTI's IterateOverHeap will crash.
     if (VerifyBeforeIteration) {
       Universe::verify();
     }
     // do the iteration
     Universe::heap()->object_iterate(_blk);
     // when sharing is enabled we must iterate over the shared spaces
     if (UseSharedSpaces) {
       GenCollectedHeap* gch = GenCollectedHeap::heap();
       CompactingPermGenGen* gen = (CompactingPermGenGen*)gch->perm_gen();
       gen->ro_space()->object_iterate(_blk);
       gen->rw_space()->object_iterate(_blk);
     }
   }
 };
 // An ObjectClosure used to support the deprecated IterateOverHeap and
 // IterateOverInstancesOfClass functions
 class IterateOverHeapObjectClosure: public ObjectClosure {
  private:
   JvmtiTagMap* _tag_map;
   KlassHandle _klass;
   jvmtiHeapObjectFilter _object_filter;
   jvmtiHeapObjectCallback _heap_object_callback;
   const void* _user_data;
   // accessors
   JvmtiTagMap* tag_map() const                    { return _tag_map; }
   jvmtiHeapObjectFilter object_filter() const     { return _object_filter; }
   jvmtiHeapObjectCallback object_callback() const { return _heap_object_callback; }
   KlassHandle klass() const                       { return _klass; }
   const void* user_data() const                   { return _user_data; }
   // indicates if iteration has been aborted
   bool _iteration_aborted;
   bool is_iteration_aborted() const               { return _iteration_aborted; }
   void set_iteration_aborted(bool aborted)        { _iteration_aborted = aborted; }
  public:
   IterateOverHeapObjectClosure(JvmtiTagMap* tag_map,
                                KlassHandle klass,
                                jvmtiHeapObjectFilter object_filter,
                                jvmtiHeapObjectCallback heap_object_callback,
                                const void* user_data) :
     _tag_map(tag_map),
     _klass(klass),
     _object_filter(object_filter),
     _heap_object_callback(heap_object_callback),
     _user_data(user_data),
     _iteration_aborted(false)
   {
   }
   void do_object(oop o);
 };
 // invoked for each object in the heap
 void IterateOverHeapObjectClosure::do_object(oop o) {
   // check if iteration has been halted
   if (is_iteration_aborted()) return;
   // ignore any objects that aren't visible to profiler
   if (!ServiceUtil::visible_oop(o)) return;
   // instanceof check when filtering by klass
   if (!klass().is_null() && !o->is_a(klass()())) {
     return;
   }
   // prepare for the calllback
   CallbackWrapper wrapper(tag_map(), o);
   // if the object is tagged and we're only interested in untagged objects
   // then don't invoke the callback. Similiarly, if the object is untagged
   // and we're only interested in tagged objects we skip the callback.
   if (wrapper.obj_tag() != 0) {
     if (object_filter() == JVMTI_HEAP_OBJECT_UNTAGGED) return;
   } else {
     if (object_filter() == JVMTI_HEAP_OBJECT_TAGGED) return;
   }
   // invoke the agent's callback
   jvmtiIterationControl control = (*object_callback())(wrapper.klass_tag(),
                                                        wrapper.obj_size(),
                                                        wrapper.obj_tag_p(),
                                                        (void*)user_data());
   if (control == JVMTI_ITERATION_ABORT) {
     set_iteration_aborted(true);
   }
 }
 // An ObjectClosure used to support the IterateThroughHeap function
 class IterateThroughHeapObjectClosure: public ObjectClosure {
  private:
   JvmtiTagMap* _tag_map;
   KlassHandle _klass;
   int _heap_filter;
   const jvmtiHeapCallbacks* _callbacks;
   const void* _user_data;
   // accessor functions
   JvmtiTagMap* tag_map() const                     { return _tag_map; }
   int heap_filter() const                          { return _heap_filter; }
   const jvmtiHeapCallbacks* callbacks() const      { return _callbacks; }
   KlassHandle klass() const                        { return _klass; }
   const void* user_data() const                    { return _user_data; }
   // indicates if the iteration has been aborted
   bool _iteration_aborted;
   bool is_iteration_aborted() const                { return _iteration_aborted; }
   // used to check the visit control flags. If the abort flag is set
   // then we set the iteration aborted flag so that the iteration completes
   // without processing any further objects
   bool check_flags_for_abort(jint flags) {
     bool is_abort = (flags & JVMTI_VISIT_ABORT) != 0;
     if (is_abort) {
       _iteration_aborted = true;
     }
     return is_abort;
   }
  public:
   IterateThroughHeapObjectClosure(JvmtiTagMap* tag_map,
                                   KlassHandle klass,
                                   int heap_filter,
                                   const jvmtiHeapCallbacks* heap_callbacks,
                                   const void* user_data) :
     _tag_map(tag_map),
     _klass(klass),
     _heap_filter(heap_filter),
     _callbacks(heap_callbacks),
     _user_data(user_data),
     _iteration_aborted(false)
   {
   }
   void do_object(oop o);
 };
 // invoked for each object in the heap
 void IterateThroughHeapObjectClosure::do_object(oop obj) {
   // check if iteration has been halted
   if (is_iteration_aborted()) return;
   // ignore any objects that aren't visible to profiler
   if (!ServiceUtil::visible_oop(obj)) return;
   // apply class filter
   if (is_filtered_by_klass_filter(obj, klass())) return;
   // prepare for callback
   CallbackWrapper wrapper(tag_map(), obj);
   // check if filtered by the heap filter
   if (is_filtered_by_heap_filter(wrapper.obj_tag(), wrapper.klass_tag(), heap_filter())) {
     return;
   }
   // for arrays we need the length, otherwise -1
   bool is_array = obj->is_array();
   int len = is_array ? arrayOop(obj)->length() : -1;
   // invoke the object callback (if callback is provided)
   if (callbacks()->heap_iteration_callback != NULL) {
     jvmtiHeapIterationCallback cb = callbacks()->heap_iteration_callback;
     jint res = (*cb)(wrapper.klass_tag(),
                      wrapper.obj_size(),
                      wrapper.obj_tag_p(),
                      (jint)len,
                      (void*)user_data());
     if (check_flags_for_abort(res)) return;
   }
   // for objects and classes we report primitive fields if callback provided
   if (callbacks()->primitive_field_callback != NULL && obj->is_instance()) {
     jint res;
     jvmtiPrimitiveFieldCallback cb = callbacks()->primitive_field_callback;
     if (obj->klass() == SystemDictionary::class_klass()) {
       res = invoke_primitive_field_callback_for_static_fields(&wrapper,
                                                                     obj,
                                                                     cb,
                                                                     (void*)user_data());
     } else {
       res = invoke_primitive_field_callback_for_instance_fields(&wrapper,
                                                                       obj,
                                                                       cb,
                                                                       (void*)user_data());
     }
     if (check_flags_for_abort(res)) return;
   }
   // string callback
   if (!is_array &&
       callbacks()->string_primitive_value_callback != NULL &&
       obj->klass() == SystemDictionary::string_klass()) {
     jint res = invoke_string_value_callback(
                 callbacks()->string_primitive_value_callback,
                 &wrapper,
                 obj,
                 (void*)user_data() );
     if (check_flags_for_abort(res)) return;
   }
   // array callback
   if (is_array &&
       callbacks()->array_primitive_value_callback != NULL &&
       obj->is_typeArray()) {
     jint res = invoke_array_primitive_value_callback(
                callbacks()->array_primitive_value_callback,
                &wrapper,
                obj,
                (void*)user_data() );
     if (check_flags_for_abort(res)) return;
   }
 };
 // Deprecated function to iterate over all objects in the heap
 void JvmtiTagMap::iterate_over_heap(jvmtiHeapObjectFilter object_filter,
                                     KlassHandle klass,
                                     jvmtiHeapObjectCallback heap_object_callback,
                                     const void* user_data)
 {
   MutexLocker ml(Heap_lock);
   IterateOverHeapObjectClosure blk(this,
                                    klass,
                                    object_filter,
                                    heap_object_callback,
                                    user_data);
   VM_HeapIterateOperation op(&blk);
   VMThread::execute(&op);
 }
 // Iterates over all objects in the heap
 void JvmtiTagMap::iterate_through_heap(jint heap_filter,
                                        KlassHandle klass,
                                        const jvmtiHeapCallbacks* callbacks,
                                        const void* user_data)
 {
   MutexLocker ml(Heap_lock);
   IterateThroughHeapObjectClosure blk(this,
                                       klass,
                                       heap_filter,
                                       callbacks,
                                       user_data);
   VM_HeapIterateOperation op(&blk);
   VMThread::execute(&op);
 }
 // support class for get_objects_with_tags
 class TagObjectCollector : public JvmtiTagHashmapEntryClosure {
  private:
   JvmtiEnv* _env;
   jlong* _tags;
   jint _tag_count;
   GrowableArray<jobject>* _object_results;  // collected objects (JNI weak refs)
   GrowableArray<uint64_t>* _tag_results;    // collected tags
  public:
   TagObjectCollector(JvmtiEnv* env, const jlong* tags, jint tag_count) {
     _env = env;
     _tags = (jlong*)tags;
     _tag_count = tag_count;
     _object_results = new (ResourceObj::C_HEAP) GrowableArray<jobject>(1,true);
     _tag_results = new (ResourceObj::C_HEAP) GrowableArray<uint64_t>(1,true);
   }
   ~TagObjectCollector() {
     delete _object_results;
     delete _tag_results;
   }
   // for each tagged object check if the tag value matches
   // - if it matches then we create a JNI local reference to the object
   // and record the reference and tag value.
   //
   void do_entry(JvmtiTagHashmapEntry* entry) {
     for (int i=0; i<_tag_count; i++) {
       if (_tags[i] == entry->tag()) {
         oop o = JNIHandles::resolve(entry->object());
         assert(o != NULL && o != JNIHandles::deleted_handle(), "sanity check");
         // the mirror is tagged
         if (o->is_klass()) {
           klassOop k = (klassOop)o;
           o = Klass::cast(k)->java_mirror();
         }
         jobject ref = JNIHandles::make_local(JavaThread::current(), o);
         _object_results->append(ref);
         _tag_results->append((uint64_t)entry->tag());
       }
     }
   }
   // return the results from the collection
   //
   jvmtiError result(jint* count_ptr, jobject** object_result_ptr, jlong** tag_result_ptr) {
     jvmtiError error;
     int count = _object_results->length();
     assert(count >= 0, "sanity check");
     // if object_result_ptr is not NULL then allocate the result and copy
     // in the object references.
     if (object_result_ptr != NULL) {
       error = _env->Allocate(count * sizeof(jobject), (unsigned char**)object_result_ptr);
       if (error != JVMTI_ERROR_NONE) {
         return error;
       }
       for (int i=0; i<count; i++) {
         (*object_result_ptr)[i] = _object_results->at(i);
       }
     }
     // if tag_result_ptr is not NULL then allocate the result and copy
     // in the tag values.
     if (tag_result_ptr != NULL) {
       error = _env->Allocate(count * sizeof(jlong), (unsigned char**)tag_result_ptr);
       if (error != JVMTI_ERROR_NONE) {
         if (object_result_ptr != NULL) {
           _env->Deallocate((unsigned char*)object_result_ptr);
         }
         return error;
       }
       for (int i=0; i<count; i++) {
         (*tag_result_ptr)[i] = (jlong)_tag_results->at(i);
       }
     }
     *count_ptr = count;
     return JVMTI_ERROR_NONE;
   }
 };
 // return the list of objects with the specified tags
 jvmtiError JvmtiTagMap::get_objects_with_tags(const jlong* tags,
   jint count, jint* count_ptr, jobject** object_result_ptr, jlong** tag_result_ptr) {
   TagObjectCollector collector(env(), tags, count);
   {
     // iterate over all tagged objects
     MutexLocker ml(lock());
     entry_iterate(&collector);
   }
   return collector.result(count_ptr, object_result_ptr, tag_result_ptr);
 }
 // ObjectMarker is used to support the marking objects when walking the
 // heap.
 //
 // This implementation uses the existing mark bits in an object for
 // marking. Objects that are marked must later have their headers restored.
 // As most objects are unlocked and don't have their identity hash computed
 // we don't have to save their headers. Instead we save the headers that
 // are "interesting". Later when the headers are restored this implementation
 // restores all headers to their initial value and then restores the few
 // objects that had interesting headers.
 //
 // Future work: This implementation currently uses growable arrays to save
 // the oop and header of interesting objects. As an optimization we could
 // use the same technique as the GC and make use of the unused area
 // between top() and end().
 //
 // An ObjectClosure used to restore the mark bits of an object
 class RestoreMarksClosure : public ObjectClosure {
  public:
   void do_object(oop o) {
     if (o != NULL) {
       markOop mark = o->mark();
       if (mark->is_marked()) {
         o->init_mark();
       }
     }
   }
 };
 // ObjectMarker provides the mark and visited functions
 class ObjectMarker : AllStatic {
  private:
   // saved headers
   static GrowableArray<oop>* _saved_oop_stack;
   static GrowableArray<markOop>* _saved_mark_stack;
  public:
   static void init();                       // initialize
   static void done();                       // clean-up
   static inline void mark(oop o);           // mark an object
   static inline bool visited(oop o);        // check if object has been visited
 };
 GrowableArray<oop>* ObjectMarker::_saved_oop_stack = NULL;
 GrowableArray<markOop>* ObjectMarker::_saved_mark_stack = NULL;
 // initialize ObjectMarker - prepares for object marking
 void ObjectMarker::init() {
   assert(Thread::current()->is_VM_thread(), "must be VMThread");
   // prepare heap for iteration
   Universe::heap()->ensure_parsability(false);  // no need to retire TLABs
   // create stacks for interesting headers
   _saved_mark_stack = new (ResourceObj::C_HEAP) GrowableArray<markOop>(4000, true);
   _saved_oop_stack = new (ResourceObj::C_HEAP) GrowableArray<oop>(4000, true);
   if (UseBiasedLocking) {
     BiasedLocking::preserve_marks();
   }
 }
 // Object marking is done so restore object headers
 void ObjectMarker::done() {
   // iterate over all objects and restore the mark bits to
   // their initial value
   RestoreMarksClosure blk;
   Universe::heap()->object_iterate(&blk);
   // When sharing is enabled we need to restore the headers of the objects
   // in the readwrite space too.
   if (UseSharedSpaces) {
     GenCollectedHeap* gch = GenCollectedHeap::heap();
     CompactingPermGenGen* gen = (CompactingPermGenGen*)gch->perm_gen();
     gen->rw_space()->object_iterate(&blk);
   }
   // now restore the interesting headers
   for (int i = 0; i < _saved_oop_stack->length(); i++) {
     oop o = _saved_oop_stack->at(i);
     markOop mark = _saved_mark_stack->at(i);
     o->set_mark(mark);
   }
   if (UseBiasedLocking) {
     BiasedLocking::restore_marks();
   }
   // free the stacks
   delete _saved_oop_stack;
   delete _saved_mark_stack;
 }
 // mark an object
 inline void ObjectMarker::mark(oop o) {
   assert(Universe::heap()->is_in(o), "sanity check");
   assert(!o->mark()->is_marked(), "should only mark an object once");
   // object's mark word
   markOop mark = o->mark();
   if (mark->must_be_preserved(o)) {
     _saved_mark_stack->push(mark);
     _saved_oop_stack->push(o);
   }
   // mark the object
   o->set_mark(markOopDesc::prototype()->set_marked());
 }
 // return true if object is marked
 inline bool ObjectMarker::visited(oop o) {
   return o->mark()->is_marked();
 }
 // Stack allocated class to help ensure that ObjectMarker is used
 // correctly. Constructor initializes ObjectMarker, destructor calls
 // ObjectMarker's done() function to restore object headers.
 class ObjectMarkerController : public StackObj {
  public:
   ObjectMarkerController() {
     ObjectMarker::init();
   }
   ~ObjectMarkerController() {
     ObjectMarker::done();
   }
 };
 // helper to map a jvmtiHeapReferenceKind to an old style jvmtiHeapRootKind
 // (not performance critical as only used for roots)
 static jvmtiHeapRootKind toJvmtiHeapRootKind(jvmtiHeapReferenceKind kind) {
   switch (kind) {
     case JVMTI_HEAP_REFERENCE_JNI_GLOBAL:   return JVMTI_HEAP_ROOT_JNI_GLOBAL;
     case JVMTI_HEAP_REFERENCE_SYSTEM_CLASS: return JVMTI_HEAP_ROOT_SYSTEM_CLASS;
     case JVMTI_HEAP_REFERENCE_MONITOR:      return JVMTI_HEAP_ROOT_MONITOR;
     case JVMTI_HEAP_REFERENCE_STACK_LOCAL:  return JVMTI_HEAP_ROOT_STACK_LOCAL;
     case JVMTI_HEAP_REFERENCE_JNI_LOCAL:    return JVMTI_HEAP_ROOT_JNI_LOCAL;
     case JVMTI_HEAP_REFERENCE_THREAD:       return JVMTI_HEAP_ROOT_THREAD;
     case JVMTI_HEAP_REFERENCE_OTHER:        return JVMTI_HEAP_ROOT_OTHER;
     default: ShouldNotReachHere();          return JVMTI_HEAP_ROOT_OTHER;
   }
 }
 // Base class for all heap walk contexts. The base class maintains a flag
 // to indicate if the context is valid or not.
 class HeapWalkContext VALUE_OBJ_CLASS_SPEC {
  private:
   bool _valid;
  public:
   HeapWalkContext(bool valid)                   { _valid = valid; }
   void invalidate()                             { _valid = false; }
   bool is_valid() const                         { return _valid; }
 };
 // A basic heap walk context for the deprecated heap walking functions.
 // The context for a basic heap walk are the callbacks and fields used by
 // the referrer caching scheme.
 class BasicHeapWalkContext: public HeapWalkContext {
  private:
   jvmtiHeapRootCallback _heap_root_callback;
   jvmtiStackReferenceCallback _stack_ref_callback;
   jvmtiObjectReferenceCallback _object_ref_callback;
   // used for caching
   oop _last_referrer;
   jlong _last_referrer_tag;
  public:
   BasicHeapWalkContext() : HeapWalkContext(false) { }
   BasicHeapWalkContext(jvmtiHeapRootCallback heap_root_callback,
                        jvmtiStackReferenceCallback stack_ref_callback,
                        jvmtiObjectReferenceCallback object_ref_callback) :
     HeapWalkContext(true),
     _heap_root_callback(heap_root_callback),
     _stack_ref_callback(stack_ref_callback),
     _object_ref_callback(object_ref_callback),
     _last_referrer(NULL),
     _last_referrer_tag(0) {
   }
   // accessors
   jvmtiHeapRootCallback heap_root_callback() const         { return _heap_root_callback; }
   jvmtiStackReferenceCallback stack_ref_callback() const   { return _stack_ref_callback; }
   jvmtiObjectReferenceCallback object_ref_callback() const { return _object_ref_callback;  }
   oop last_referrer() const               { return _last_referrer; }
   void set_last_referrer(oop referrer)    { _last_referrer = referrer; }
   jlong last_referrer_tag() const         { return _last_referrer_tag; }
   void set_last_referrer_tag(jlong value) { _last_referrer_tag = value; }
 };
 // The advanced heap walk context for the FollowReferences functions.
 // The context is the callbacks, and the fields used for filtering.
 class AdvancedHeapWalkContext: public HeapWalkContext {
  private:
   jint _heap_filter;
   KlassHandle _klass_filter;
   const jvmtiHeapCallbacks* _heap_callbacks;
  public:
   AdvancedHeapWalkContext() : HeapWalkContext(false) { }
   AdvancedHeapWalkContext(jint heap_filter,
                            KlassHandle klass_filter,
                            const jvmtiHeapCallbacks* heap_callbacks) :
     HeapWalkContext(true),
     _heap_filter(heap_filter),
     _klass_filter(klass_filter),
     _heap_callbacks(heap_callbacks) {
   }
   // accessors
   jint heap_filter() const         { return _heap_filter; }
   KlassHandle klass_filter() const { return _klass_filter; }
   const jvmtiHeapReferenceCallback heap_reference_callback() const {
     return _heap_callbacks->heap_reference_callback;
   };
   const jvmtiPrimitiveFieldCallback primitive_field_callback() const {
     return _heap_callbacks->primitive_field_callback;
   }
   const jvmtiArrayPrimitiveValueCallback array_primitive_value_callback() const {
     return _heap_callbacks->array_primitive_value_callback;
   }
   const jvmtiStringPrimitiveValueCallback string_primitive_value_callback() const {
     return _heap_callbacks->string_primitive_value_callback;
   }
 };
 // The CallbackInvoker is a class with static functions that the heap walk can call
 // into to invoke callbacks. It works in one of two modes. The "basic" mode is
 // used for the deprecated IterateOverReachableObjects functions. The "advanced"
 // mode is for the newer FollowReferences function which supports a lot of
 // additional callbacks.
 class CallbackInvoker : AllStatic {
  private:
   // heap walk styles
   enum { basic, advanced };
   static int _heap_walk_type;
   static bool is_basic_heap_walk()           { return _heap_walk_type == basic; }
   static bool is_advanced_heap_walk()        { return _heap_walk_type == advanced; }
   // context for basic style heap walk
   static BasicHeapWalkContext _basic_context;
   static BasicHeapWalkContext* basic_context() {
     assert(_basic_context.is_valid(), "invalid");
     return &_basic_context;
   }
   // context for advanced style heap walk
   static AdvancedHeapWalkContext _advanced_context;
   static AdvancedHeapWalkContext* advanced_context() {
     assert(_advanced_context.is_valid(), "invalid");
     return &_advanced_context;
   }
   // context needed for all heap walks
   static JvmtiTagMap* _tag_map;
   static const void* _user_data;
   static GrowableArray<oop>* _visit_stack;
   // accessors
   static JvmtiTagMap* tag_map()                        { return _tag_map; }
   static const void* user_data()                       { return _user_data; }
   static GrowableArray<oop>* visit_stack()             { return _visit_stack; }
   // if the object hasn't been visited then push it onto the visit stack
   // so that it will be visited later
   static inline bool check_for_visit(oop obj) {
     if (!ObjectMarker::visited(obj)) visit_stack()->push(obj);
     return true;
   }
   // invoke basic style callbacks
   static inline bool invoke_basic_heap_root_callback
     (jvmtiHeapRootKind root_kind, oop obj);
   static inline bool invoke_basic_stack_ref_callback
     (jvmtiHeapRootKind root_kind, jlong thread_tag, jint depth, jmethodID method,
      int slot, oop obj);
   static inline bool invoke_basic_object_reference_callback
     (jvmtiObjectReferenceKind ref_kind, oop referrer, oop referree, jint index);
   // invoke advanced style callbacks
   static inline bool invoke_advanced_heap_root_callback
     (jvmtiHeapReferenceKind ref_kind, oop obj);
   static inline bool invoke_advanced_stack_ref_callback
     (jvmtiHeapReferenceKind ref_kind, jlong thread_tag, jlong tid, int depth,
      jmethodID method, jlocation bci, jint slot, oop obj);
   static inline bool invoke_advanced_object_reference_callback
     (jvmtiHeapReferenceKind ref_kind, oop referrer, oop referree, jint index);
   // used to report the value of primitive fields
   static inline bool report_primitive_field
     (jvmtiHeapReferenceKind ref_kind, oop obj, jint index, address addr, char type);
  public:
   // initialize for basic mode
   static void initialize_for_basic_heap_walk(JvmtiTagMap* tag_map,
                                              GrowableArray<oop>* visit_stack,
                                              const void* user_data,
                                              BasicHeapWalkContext context);
   // initialize for advanced mode
   static void initialize_for_advanced_heap_walk(JvmtiTagMap* tag_map,
                                                 GrowableArray<oop>* visit_stack,
                                                 const void* user_data,
                                                 AdvancedHeapWalkContext context);
    // functions to report roots
   static inline bool report_simple_root(jvmtiHeapReferenceKind kind, oop o);
   static inline bool report_jni_local_root(jlong thread_tag, jlong tid, jint depth,
     jmethodID m, oop o);
   static inline bool report_stack_ref_root(jlong thread_tag, jlong tid, jint depth,
     jmethodID method, jlocation bci, jint slot, oop o);
   // functions to report references
   static inline bool report_array_element_reference(oop referrer, oop referree, jint index);
   static inline bool report_class_reference(oop referrer, oop referree);
   static inline bool report_class_loader_reference(oop referrer, oop referree);
   static inline bool report_signers_reference(oop referrer, oop referree);
   static inline bool report_protection_domain_reference(oop referrer, oop referree);
   static inline bool report_superclass_reference(oop referrer, oop referree);
   static inline bool report_interface_reference(oop referrer, oop referree);
   static inline bool report_static_field_reference(oop referrer, oop referree, jint slot);
   static inline bool report_field_reference(oop referrer, oop referree, jint slot);
   static inline bool report_constant_pool_reference(oop referrer, oop referree, jint index);
   static inline bool report_primitive_array_values(oop array);
   static inline bool report_string_value(oop str);
   static inline bool report_primitive_instance_field(oop o, jint index, address value, char type);
   static inline bool report_primitive_static_field(oop o, jint index, address value, char type);
 };
 // statics
 int CallbackInvoker::_heap_walk_type;
 BasicHeapWalkContext CallbackInvoker::_basic_context;
 AdvancedHeapWalkContext CallbackInvoker::_advanced_context;
 JvmtiTagMap* CallbackInvoker::_tag_map;
 const void* CallbackInvoker::_user_data;
 GrowableArray<oop>* CallbackInvoker::_visit_stack;
 // initialize for basic heap walk (IterateOverReachableObjects et al)
 void CallbackInvoker::initialize_for_basic_heap_walk(JvmtiTagMap* tag_map,
                                                      GrowableArray<oop>* visit_stack,
                                                      const void* user_data,
                                                      BasicHeapWalkContext context) {
   _tag_map = tag_map;
   _visit_stack = visit_stack;
   _user_data = user_data;
   _basic_context = context;
   _advanced_context.invalidate();       // will trigger assertion if used
   _heap_walk_type = basic;
 }
 // initialize for advanced heap walk (FollowReferences)
 void CallbackInvoker::initialize_for_advanced_heap_walk(JvmtiTagMap* tag_map,
                                                         GrowableArray<oop>* visit_stack,
                                                         const void* user_data,
                                                         AdvancedHeapWalkContext context) {
   _tag_map = tag_map;
   _visit_stack = visit_stack;
   _user_data = user_data;
   _advanced_context = context;
   _basic_context.invalidate();      // will trigger assertion if used
   _heap_walk_type = advanced;
 }
 // invoke basic style heap root callback
 inline bool CallbackInvoker::invoke_basic_heap_root_callback(jvmtiHeapRootKind root_kind, oop obj) {
   assert(ServiceUtil::visible_oop(obj), "checking");
   // if we heap roots should be reported
   jvmtiHeapRootCallback cb = basic_context()->heap_root_callback();
   if (cb == NULL) {
     return check_for_visit(obj);
   }
   CallbackWrapper wrapper(tag_map(), obj);
   jvmtiIterationControl control = (*cb)(root_kind,
                                         wrapper.klass_tag(),
                                         wrapper.obj_size(),
                                         wrapper.obj_tag_p(),
                                         (void*)user_data());
   // push root to visit stack when following references
   if (control == JVMTI_ITERATION_CONTINUE &&
       basic_context()->object_ref_callback() != NULL) {
     visit_stack()->push(obj);
   }
   return control != JVMTI_ITERATION_ABORT;
 }
 // invoke basic style stack ref callback
 inline bool CallbackInvoker::invoke_basic_stack_ref_callback(jvmtiHeapRootKind root_kind,
                                                              jlong thread_tag,
                                                              jint depth,
                                                              jmethodID method,
                                                              jint slot,
                                                              oop obj) {
   assert(ServiceUtil::visible_oop(obj), "checking");
   // if we stack refs should be reported
   jvmtiStackReferenceCallback cb = basic_context()->stack_ref_callback();
   if (cb == NULL) {
     return check_for_visit(obj);
   }
   CallbackWrapper wrapper(tag_map(), obj);
   jvmtiIterationControl control = (*cb)(root_kind,
                                         wrapper.klass_tag(),
                                         wrapper.obj_size(),
                                         wrapper.obj_tag_p(),
                                         thread_tag,
                                         depth,
                                         method,
                                         slot,
                                         (void*)user_data());
   // push root to visit stack when following references
   if (control == JVMTI_ITERATION_CONTINUE &&
       basic_context()->object_ref_callback() != NULL) {
     visit_stack()->push(obj);
   }
   return control != JVMTI_ITERATION_ABORT;
 }
 // invoke basic style object reference callback
 inline bool CallbackInvoker::invoke_basic_object_reference_callback(jvmtiObjectReferenceKind ref_kind,
                                                                     oop referrer,
                                                                     oop referree,
                                                                     jint index) {
   assert(ServiceUtil::visible_oop(referrer), "checking");
   assert(ServiceUtil::visible_oop(referree), "checking");
   BasicHeapWalkContext* context = basic_context();
   // callback requires the referrer's tag. If it's the same referrer
   // as the last call then we use the cached value.
   jlong referrer_tag;
   if (referrer == context->last_referrer()) {
     referrer_tag = context->last_referrer_tag();
   } else {
     referrer_tag = tag_for(tag_map(), klassOop_if_java_lang_Class(referrer));
   }
   // do the callback
   CallbackWrapper wrapper(tag_map(), referree);
   jvmtiObjectReferenceCallback cb = context->object_ref_callback();
   jvmtiIterationControl control = (*cb)(ref_kind,
                                         wrapper.klass_tag(),
                                         wrapper.obj_size(),
                                         wrapper.obj_tag_p(),
                                         referrer_tag,
                                         index,
                                         (void*)user_data());
   // record referrer and referrer tag. For self-references record the
   // tag value from the callback as this might differ from referrer_tag.
   context->set_last_referrer(referrer);
   if (referrer == referree) {
     context->set_last_referrer_tag(*wrapper.obj_tag_p());
   } else {
     context->set_last_referrer_tag(referrer_tag);
   }
   if (control == JVMTI_ITERATION_CONTINUE) {
     return check_for_visit(referree);
   } else {
     return control != JVMTI_ITERATION_ABORT;
   }
 }
 // invoke advanced style heap root callback
 inline bool CallbackInvoker::invoke_advanced_heap_root_callback(jvmtiHeapReferenceKind ref_kind,
                                                                 oop obj) {
   assert(ServiceUtil::visible_oop(obj), "checking");
   AdvancedHeapWalkContext* context = advanced_context();
   // check that callback is provided
   jvmtiHeapReferenceCallback cb = context->heap_reference_callback();
   if (cb == NULL) {
     return check_for_visit(obj);
   }
   // apply class filter
   if (is_filtered_by_klass_filter(obj, context->klass_filter())) {
     return check_for_visit(obj);
   }
   // setup the callback wrapper
   CallbackWrapper wrapper(tag_map(), obj);
   // apply tag filter
   if (is_filtered_by_heap_filter(wrapper.obj_tag(),
                                  wrapper.klass_tag(),
                                  context->heap_filter())) {
     return check_for_visit(obj);
   }
   // for arrays we need the length, otherwise -1
   jint len = (jint)(obj->is_array() ? arrayOop(obj)->length() : -1);
   // invoke the callback
   jint res  = (*cb)(ref_kind,
                     NULL, // referrer info
                     wrapper.klass_tag(),
 ,    // referrer_class_tag is 0 for heap root
                     wrapper.obj_size(),
                     wrapper.obj_tag_p(),
                     NULL, // referrer_tag_p
                     len,
                     (void*)user_data());
   if (res & JVMTI_VISIT_ABORT) {
     return false;// referrer class tag
   }
   if (res & JVMTI_VISIT_OBJECTS) {
     check_for_visit(obj);
   }
   return true;
 }
 // report a reference from a thread stack to an object
 inline bool CallbackInvoker::invoke_advanced_stack_ref_callback(jvmtiHeapReferenceKind ref_kind,
                                                                 jlong thread_tag,
                                                                 jlong tid,
                                                                 int depth,
                                                                 jmethodID method,
                                                                 jlocation bci,
                                                                 jint slot,
                                                                 oop obj) {
   assert(ServiceUtil::visible_oop(obj), "checking");
   AdvancedHeapWalkContext* context = advanced_context();
   // check that callback is provider
   jvmtiHeapReferenceCallback cb = context->heap_reference_callback();
   if (cb == NULL) {
     return check_for_visit(obj);
   }
   // apply class filter
   if (is_filtered_by_klass_filter(obj, context->klass_filter())) {
     return check_for_visit(obj);
   }
   // setup the callback wrapper
   CallbackWrapper wrapper(tag_map(), obj);
   // apply tag filter
   if (is_filtered_by_heap_filter(wrapper.obj_tag(),
                                  wrapper.klass_tag(),
                                  context->heap_filter())) {
     return check_for_visit(obj);
   }
   // setup the referrer info
   jvmtiHeapReferenceInfo reference_info;
   reference_info.stack_local.thread_tag = thread_tag;
   reference_info.stack_local.thread_id = tid;
   reference_info.stack_local.depth = depth;
   reference_info.stack_local.method = method;
   reference_info.stack_local.location = bci;
   reference_info.stack_local.slot = slot;
   // for arrays we need the length, otherwise -1
   jint len = (jint)(obj->is_array() ? arrayOop(obj)->length() : -1);
   // call into the agent
   int res = (*cb)(ref_kind,
                   &reference_info,
                   wrapper.klass_tag(),
 ,    // referrer_class_tag is 0 for heap root (stack)
                   wrapper.obj_size(),
                   wrapper.obj_tag_p(),
                   NULL, // referrer_tag is 0 for root
                   len,
                   (void*)user_data());
   if (res & JVMTI_VISIT_ABORT) {
     return false;
   }
   if (res & JVMTI_VISIT_OBJECTS) {
     check_for_visit(obj);
   }
   return true;
 }
 // This mask is used to pass reference_info to a jvmtiHeapReferenceCallback
 // only for ref_kinds defined by the JVM TI spec. Otherwise, NULL is passed.
 #define REF_INFO_MASK  ((1 << JVMTI_HEAP_REFERENCE_FIELD)         \
                       | (1 << JVMTI_HEAP_REFERENCE_STATIC_FIELD)  \
                       | (1 << JVMTI_HEAP_REFERENCE_ARRAY_ELEMENT) \
                       | (1 << JVMTI_HEAP_REFERENCE_CONSTANT_POOL) \
                       | (1 << JVMTI_HEAP_REFERENCE_STACK_LOCAL)   \
                       | (1 << JVMTI_HEAP_REFERENCE_JNI_LOCAL))
 // invoke the object reference callback to report a reference
 inline bool CallbackInvoker::invoke_advanced_object_reference_callback(jvmtiHeapReferenceKind ref_kind,
                                                                        oop referrer,
                                                                        oop obj,
                                                                        jint index)
 {
   // field index is only valid field in reference_info
   static jvmtiHeapReferenceInfo reference_info = { 0 };
   assert(ServiceUtil::visible_oop(referrer), "checking");
   assert(ServiceUtil::visible_oop(obj), "checking");
   AdvancedHeapWalkContext* context = advanced_context();
   // check that callback is provider
   jvmtiHeapReferenceCallback cb = context->heap_reference_callback();
   if (cb == NULL) {
     return check_for_visit(obj);
   }
   // apply class filter
   if (is_filtered_by_klass_filter(obj, context->klass_filter())) {
     return check_for_visit(obj);
   }
   // setup the callback wrapper
   TwoOopCallbackWrapper wrapper(tag_map(), referrer, obj);
   // apply tag filter
   if (is_filtered_by_heap_filter(wrapper.obj_tag(),
                                  wrapper.klass_tag(),
                                  context->heap_filter())) {
     return check_for_visit(obj);
   }
   // field index is only valid field in reference_info
   reference_info.field.index = index;
   // for arrays we need the length, otherwise -1
   jint len = (jint)(obj->is_array() ? arrayOop(obj)->length() : -1);
   // invoke the callback
   int res = (*cb)(ref_kind,
                   (REF_INFO_MASK & (1 << ref_kind)) ? &reference_info : NULL,
                   wrapper.klass_tag(),
                   wrapper.referrer_klass_tag(),
                   wrapper.obj_size(),
                   wrapper.obj_tag_p(),
                   wrapper.referrer_tag_p(),
                   len,
                   (void*)user_data());
   if (res & JVMTI_VISIT_ABORT) {
     return false;
   }
   if (res & JVMTI_VISIT_OBJECTS) {
     check_for_visit(obj);
   }
   return true;
 }
 // report a "simple root"
 inline bool CallbackInvoker::report_simple_root(jvmtiHeapReferenceKind kind, oop obj) {
   assert(kind != JVMTI_HEAP_REFERENCE_STACK_LOCAL &&
          kind != JVMTI_HEAP_REFERENCE_JNI_LOCAL, "not a simple root");
   assert(ServiceUtil::visible_oop(obj), "checking");
   if (is_basic_heap_walk()) {
     // map to old style root kind
     jvmtiHeapRootKind root_kind = toJvmtiHeapRootKind(kind);
     return invoke_basic_heap_root_callback(root_kind, obj);
   } else {
     assert(is_advanced_heap_walk(), "wrong heap walk type");
     return invoke_advanced_heap_root_callback(kind, obj);
   }
 }
 // invoke the primitive array values
 inline bool CallbackInvoker::report_primitive_array_values(oop obj) {
   assert(obj->is_typeArray(), "not a primitive array");
   AdvancedHeapWalkContext* context = advanced_context();
   assert(context->array_primitive_value_callback() != NULL, "no callback");
   // apply class filter
   if (is_filtered_by_klass_filter(obj, context->klass_filter())) {
     return true;
   }
   CallbackWrapper wrapper(tag_map(), obj);
   // apply tag filter
   if (is_filtered_by_heap_filter(wrapper.obj_tag(),
                                  wrapper.klass_tag(),
                                  context->heap_filter())) {
     return true;
   }
   // invoke the callback
   int res = invoke_array_primitive_value_callback(context->array_primitive_value_callback(),
                                                   &wrapper,
                                                   obj,
                                                   (void*)user_data());
   return (!(res & JVMTI_VISIT_ABORT));
 }
 // invoke the string value callback
 inline bool CallbackInvoker::report_string_value(oop str) {
   assert(str->klass() == SystemDictionary::string_klass(), "not a string");
   AdvancedHeapWalkContext* context = advanced_context();
   assert(context->string_primitive_value_callback() != NULL, "no callback");
   // apply class filter
   if (is_filtered_by_klass_filter(str, context->klass_filter())) {
     return true;
   }
   CallbackWrapper wrapper(tag_map(), str);
   // apply tag filter
   if (is_filtered_by_heap_filter(wrapper.obj_tag(),
                                  wrapper.klass_tag(),
                                  context->heap_filter())) {
     return true;
   }
   // invoke the callback
   int res = invoke_string_value_callback(context->string_primitive_value_callback(),
                                          &wrapper,
                                          str,
                                          (void*)user_data());
   return (!(res & JVMTI_VISIT_ABORT));
 }
 // invoke the primitive field callback
 inline bool CallbackInvoker::report_primitive_field(jvmtiHeapReferenceKind ref_kind,
                                                     oop obj,
                                                     jint index,
                                                     address addr,
                                                     char type)
 {
   // for primitive fields only the index will be set
   static jvmtiHeapReferenceInfo reference_info = { 0 };
   AdvancedHeapWalkContext* context = advanced_context();
   assert(context->primitive_field_callback() != NULL, "no callback");
   // apply class filter
   if (is_filtered_by_klass_filter(obj, context->klass_filter())) {
     return true;
   }
   CallbackWrapper wrapper(tag_map(), obj);
   // apply tag filter
   if (is_filtered_by_heap_filter(wrapper.obj_tag(),
                                  wrapper.klass_tag(),
                                  context->heap_filter())) {
     return true;
   }
   // the field index in the referrer
   reference_info.field.index = index;
   // map the type
   jvmtiPrimitiveType value_type = (jvmtiPrimitiveType)type;
   // setup the jvalue
   jvalue value;
   copy_to_jvalue(&value, addr, value_type);
   jvmtiPrimitiveFieldCallback cb = context->primitive_field_callback();
   int res = (*cb)(ref_kind,
                   &reference_info,
                   wrapper.klass_tag(),
                   wrapper.obj_tag_p(),
                   value,
                   value_type,
                   (void*)user_data());
   return (!(res & JVMTI_VISIT_ABORT));
 }
 // instance field
 inline bool CallbackInvoker::report_primitive_instance_field(oop obj,
                                                              jint index,
                                                              address value,
                                                              char type) {
   return report_primitive_field(JVMTI_HEAP_REFERENCE_FIELD,
                                 obj,
                                 index,
                                 value,
                                 type);
 }
 // static field
 inline bool CallbackInvoker::report_primitive_static_field(oop obj,
                                                            jint index,
                                                            address value,
                                                            char type) {
   return report_primitive_field(JVMTI_HEAP_REFERENCE_STATIC_FIELD,
                                 obj,
                                 index,
                                 value,
                                 type);
 }
 // report a JNI local (root object) to the profiler
 inline bool CallbackInvoker::report_jni_local_root(jlong thread_tag, jlong tid, jint depth, jmethodID m, oop obj) {
   if (is_basic_heap_walk()) {
     return invoke_basic_stack_ref_callback(JVMTI_HEAP_ROOT_JNI_LOCAL,
                                            thread_tag,
                                            depth,
                                            m,
                                            -1,
                                            obj);
   } else {
     return invoke_advanced_stack_ref_callback(JVMTI_HEAP_REFERENCE_JNI_LOCAL,
                                               thread_tag, tid,
                                               depth,
                                               m,
                                               (jlocation)-1,
                                               -1,
                                               obj);
   }
 }
 // report a local (stack reference, root object)
 inline bool CallbackInvoker::report_stack_ref_root(jlong thread_tag,
                                                    jlong tid,
                                                    jint depth,
                                                    jmethodID method,
                                                    jlocation bci,
                                                    jint slot,
                                                    oop obj) {
   if (is_basic_heap_walk()) {
     return invoke_basic_stack_ref_callback(JVMTI_HEAP_ROOT_STACK_LOCAL,
                                            thread_tag,
                                            depth,
                                            method,
                                            slot,
                                            obj);
   } else {
     return invoke_advanced_stack_ref_callback(JVMTI_HEAP_REFERENCE_STACK_LOCAL,
                                               thread_tag,
                                               tid,
                                               depth,
                                               method,
                                               bci,
                                               slot,
                                               obj);
   }
 }
 // report an object referencing a class.
 inline bool CallbackInvoker::report_class_reference(oop referrer, oop referree) {
   if (is_basic_heap_walk()) {
     return invoke_basic_object_reference_callback(JVMTI_REFERENCE_CLASS, referrer, referree, -1);
   } else {
     return invoke_advanced_object_reference_callback(JVMTI_HEAP_REFERENCE_CLASS, referrer, referree, -1);
   }
 }
 // report a class referencing its class loader.
 inline bool CallbackInvoker::report_class_loader_reference(oop referrer, oop referree) {
   if (is_basic_heap_walk()) {
     return invoke_basic_object_reference_callback(JVMTI_REFERENCE_CLASS_LOADER, referrer, referree, -1);
   } else {
     return invoke_advanced_object_reference_callback(JVMTI_HEAP_REFERENCE_CLASS_LOADER, referrer, referree, -1);
   }
 }
 // report a class referencing its signers.
 inline bool CallbackInvoker::report_signers_reference(oop referrer, oop referree) {
   if (is_basic_heap_walk()) {
     return invoke_basic_object_reference_callback(JVMTI_REFERENCE_SIGNERS, referrer, referree, -1);
   } else {
     return invoke_advanced_object_reference_callback(JVMTI_HEAP_REFERENCE_SIGNERS, referrer, referree, -1);
   }
 }
 // report a class referencing its protection domain..
 inline bool CallbackInvoker::report_protection_domain_reference(oop referrer, oop referree) {
   if (is_basic_heap_walk()) {
     return invoke_basic_object_reference_callback(JVMTI_REFERENCE_PROTECTION_DOMAIN, referrer, referree, -1);
   } else {
     return invoke_advanced_object_reference_callback(JVMTI_HEAP_REFERENCE_PROTECTION_DOMAIN, referrer, referree, -1);
   }
 }
 // report a class referencing its superclass.
 inline bool CallbackInvoker::report_superclass_reference(oop referrer, oop referree) {
   if (is_basic_heap_walk()) {
     // Send this to be consistent with past implementation
     return invoke_basic_object_reference_callback(JVMTI_REFERENCE_CLASS, referrer, referree, -1);
   } else {
     return invoke_advanced_object_reference_callback(JVMTI_HEAP_REFERENCE_SUPERCLASS, referrer, referree, -1);
   }
 }
 // report a class referencing one of its interfaces.
 inline bool CallbackInvoker::report_interface_reference(oop referrer, oop referree) {
   if (is_basic_heap_walk()) {
     return invoke_basic_object_reference_callback(JVMTI_REFERENCE_INTERFACE, referrer, referree, -1);
   } else {
     return invoke_advanced_object_reference_callback(JVMTI_HEAP_REFERENCE_INTERFACE, referrer, referree, -1);
   }
 }
 // report a class referencing one of its static fields.
 inline bool CallbackInvoker::report_static_field_reference(oop referrer, oop referree, jint slot) {
   if (is_basic_heap_walk()) {
     return invoke_basic_object_reference_callback(JVMTI_REFERENCE_STATIC_FIELD, referrer, referree, slot);
   } else {
     return invoke_advanced_object_reference_callback(JVMTI_HEAP_REFERENCE_STATIC_FIELD, referrer, referree, slot);
   }
 }
 // report an array referencing an element object
 inline bool CallbackInvoker::report_array_element_reference(oop referrer, oop referree, jint index) {
   if (is_basic_heap_walk()) {
     return invoke_basic_object_reference_callback(JVMTI_REFERENCE_ARRAY_ELEMENT, referrer, referree, index);
   } else {
     return invoke_advanced_object_reference_callback(JVMTI_HEAP_REFERENCE_ARRAY_ELEMENT, referrer, referree, index);
   }
 }
 // report an object referencing an instance field object
 inline bool CallbackInvoker::report_field_reference(oop referrer, oop referree, jint slot) {
   if (is_basic_heap_walk()) {
     return invoke_basic_object_reference_callback(JVMTI_REFERENCE_FIELD, referrer, referree, slot);
   } else {
     return invoke_advanced_object_reference_callback(JVMTI_HEAP_REFERENCE_FIELD, referrer, referree, slot);
   }
 }
 // report an array referencing an element object
 inline bool CallbackInvoker::report_constant_pool_reference(oop referrer, oop referree, jint index) {
   if (is_basic_heap_walk()) {
     return invoke_basic_object_reference_callback(JVMTI_REFERENCE_CONSTANT_POOL, referrer, referree, index);
   } else {
     return invoke_advanced_object_reference_callback(JVMTI_HEAP_REFERENCE_CONSTANT_POOL, referrer, referree, index);
   }
 }
 // A supporting closure used to process simple roots
 class SimpleRootsClosure : public OopClosure {
  private:
   jvmtiHeapReferenceKind _kind;
   bool _continue;
   jvmtiHeapReferenceKind root_kind()    { return _kind; }
  public:
   void set_kind(jvmtiHeapReferenceKind kind) {
     _kind = kind;
     _continue = true;
   }
   inline bool stopped() {
     return !_continue;
   }
   void do_oop(oop* obj_p) {
     // iteration has terminated
     if (stopped()) {
       return;
     }
     // ignore null or deleted handles
     oop o = *obj_p;
     if (o == NULL || o == JNIHandles::deleted_handle()) {
       return;
     }
     jvmtiHeapReferenceKind kind = root_kind();
     // many roots are Klasses so we use the java mirror
     if (o->is_klass()) {
       klassOop k = (klassOop)o;
       o = Klass::cast(k)->java_mirror();
     } else {
       // SystemDictionary::always_strong_oops_do reports the application
       // class loader as a root. We want this root to be reported as
       // a root kind of "OTHER" rather than "SYSTEM_CLASS".
       if (o->is_instance() && root_kind() == JVMTI_HEAP_REFERENCE_SYSTEM_CLASS) {
         kind = JVMTI_HEAP_REFERENCE_OTHER;
       }
     }
     // some objects are ignored - in the case of simple
     // roots it's mostly symbolOops that we are skipping
     // here.
     if (!ServiceUtil::visible_oop(o)) {
       return;
     }
     // invoke the callback
     _continue = CallbackInvoker::report_simple_root(kind, o);
   }
 };
 // A supporting closure used to process JNI locals
 class JNILocalRootsClosure : public OopClosure {
  private:
   jlong _thread_tag;
   jlong _tid;
   jint _depth;
   jmethodID _method;
   bool _continue;
  public:
   void set_context(jlong thread_tag, jlong tid, jint depth, jmethodID method) {
     _thread_tag = thread_tag;
     _tid = tid;
     _depth = depth;
     _method = method;
     _continue = true;
   }
   inline bool stopped() {
     return !_continue;
   }
   void do_oop(oop* obj_p) {
     // iteration has terminated
     if (stopped()) {
       return;
     }
     // ignore null or deleted handles
     oop o = *obj_p;
     if (o == NULL || o == JNIHandles::deleted_handle()) {
       return;
     }
     if (!ServiceUtil::visible_oop(o)) {
       return;
     }
     // invoke the callback
     _continue = CallbackInvoker::report_jni_local_root(_thread_tag, _tid, _depth, _method, o);
   }
 };
 // A VM operation to iterate over objects that are reachable from
 // a set of roots or an initial object.
 //
 // For VM_HeapWalkOperation the set of roots used is :-
 //
 // - All JNI global references
 // - All inflated monitors
 // - All classes loaded by the boot class loader (or all classes
 //     in the event that class unloading is disabled)
 // - All java threads
 // - For each java thread then all locals and JNI local references
 //      on the thread's execution stack
 // - All visible/explainable objects from Universes::oops_do
 //
 class VM_HeapWalkOperation: public VM_Operation {
  private:
   enum {
     initial_visit_stack_size = 4000
   };
   bool _is_advanced_heap_walk;                      // indicates FollowReferences
   JvmtiTagMap* _tag_map;
   Handle _initial_object;
   GrowableArray<oop>* _visit_stack;                 // the visit stack
   bool _collecting_heap_roots;                      // are we collecting roots
   bool _following_object_refs;                      // are we following object references
   bool _reporting_primitive_fields;                 // optional reporting
   bool _reporting_primitive_array_values;
   bool _reporting_string_values;
   GrowableArray<oop>* create_visit_stack() {
     return new (ResourceObj::C_HEAP) GrowableArray<oop>(initial_visit_stack_size, true);
   }
   // accessors
   bool is_advanced_heap_walk() const               { return _is_advanced_heap_walk; }
   JvmtiTagMap* tag_map() const                     { return _tag_map; }
   Handle initial_object() const                    { return _initial_object; }
   bool is_following_references() const             { return _following_object_refs; }
   bool is_reporting_primitive_fields()  const      { return _reporting_primitive_fields; }
   bool is_reporting_primitive_array_values() const { return _reporting_primitive_array_values; }
   bool is_reporting_string_values() const          { return _reporting_string_values; }
   GrowableArray<oop>* visit_stack() const          { return _visit_stack; }
   // iterate over the various object types
   inline bool iterate_over_array(oop o);
   inline bool iterate_over_type_array(oop o);
   inline bool iterate_over_class(klassOop o);
   inline bool iterate_over_object(oop o);
   // root collection
   inline bool collect_simple_roots();
   inline bool collect_stack_roots();
   inline bool collect_stack_roots(JavaThread* java_thread, JNILocalRootsClosure* blk);
   // visit an object
   inline bool visit(oop o);
  public:
   VM_HeapWalkOperation(JvmtiTagMap* tag_map,
                        Handle initial_object,
                        BasicHeapWalkContext callbacks,
                        const void* user_data);
   VM_HeapWalkOperation(JvmtiTagMap* tag_map,
                        Handle initial_object,
                        AdvancedHeapWalkContext callbacks,
                        const void* user_data);
   ~VM_HeapWalkOperation();
   VMOp_Type type() const { return VMOp_HeapWalkOperation; }
   void doit();
 };
 VM_HeapWalkOperation::VM_HeapWalkOperation(JvmtiTagMap* tag_map,
                                            Handle initial_object,
                                            BasicHeapWalkContext callbacks,
                                            const void* user_data) {
   _is_advanced_heap_walk = false;
   _tag_map = tag_map;
   _initial_object = initial_object;
   _following_object_refs = (callbacks.object_ref_callback() != NULL);
   _reporting_primitive_fields = false;
   _reporting_primitive_array_values = false;
   _reporting_string_values = false;
   _visit_stack = create_visit_stack();
   CallbackInvoker::initialize_for_basic_heap_walk(tag_map, _visit_stack, user_data, callbacks);
 }
 VM_HeapWalkOperation::VM_HeapWalkOperation(JvmtiTagMap* tag_map,
                                            Handle initial_object,
                                            AdvancedHeapWalkContext callbacks,
                                            const void* user_data) {
   _is_advanced_heap_walk = true;
   _tag_map = tag_map;
   _initial_object = initial_object;
   _following_object_refs = true;
   _reporting_primitive_fields = (callbacks.primitive_field_callback() != NULL);;
   _reporting_primitive_array_values = (callbacks.array_primitive_value_callback() != NULL);;
   _reporting_string_values = (callbacks.string_primitive_value_callback() != NULL);;
   _visit_stack = create_visit_stack();
   CallbackInvoker::initialize_for_advanced_heap_walk(tag_map, _visit_stack, user_data, callbacks);
 }
 VM_HeapWalkOperation::~VM_HeapWalkOperation() {
   if (_following_object_refs) {
     assert(_visit_stack != NULL, "checking");
     delete _visit_stack;
     _visit_stack = NULL;
   }
 }
 // an array references its class and has a reference to
 // each element in the array
 inline bool VM_HeapWalkOperation::iterate_over_array(oop o) {
   objArrayOop array = objArrayOop(o);
   if (array->klass() == Universe::systemObjArrayKlassObj()) {
     // filtered out
     return true;
   }
   // array reference to its class
   oop mirror = objArrayKlass::cast(array->klass())->java_mirror();
   if (!CallbackInvoker::report_class_reference(o, mirror)) {
     return false;
   }
   // iterate over the array and report each reference to a
   // non-null element
   for (int index=0; index<array->length(); index++) {
     oop elem = array->obj_at(index);
     if (elem == NULL) {
       continue;
     }
     // report the array reference o[index] = elem
     if (!CallbackInvoker::report_array_element_reference(o, elem, index)) {
       return false;
     }
   }
   return true;
 }
 // a type array references its class
 inline bool VM_HeapWalkOperation::iterate_over_type_array(oop o) {
   klassOop k = o->klass();
   oop mirror = Klass::cast(k)->java_mirror();
   if (!CallbackInvoker::report_class_reference(o, mirror)) {
     return false;
   }
   // report the array contents if required
   if (is_reporting_primitive_array_values()) {
     if (!CallbackInvoker::report_primitive_array_values(o)) {
       return false;
     }
   }
   return true;
 }
 // verify that a static oop field is in range
 static inline bool verify_static_oop(instanceKlass* ik, oop* obj_p) {
   oop* start = ik->start_of_static_fields();
   oop* end = start + ik->static_oop_field_size();
   assert(end >= start, "sanity check");
   if (obj_p >= start && obj_p < end) {
     return true;
   } else {
     return false;
   }
 }
 // a class references its super class, interfaces, class loader, ...
 // and finally its static fields
 inline bool VM_HeapWalkOperation::iterate_over_class(klassOop k) {
   int i;
   Klass* klass = klassOop(k)->klass_part();
   if (klass->oop_is_instance()) {
     instanceKlass* ik = instanceKlass::cast(k);
     // ignore the class if it's has been initialized yet
     if (!ik->is_linked()) {
       return true;
     }
     // get the java mirror
     oop mirror = klass->java_mirror();
     // super (only if something more interesting than java.lang.Object)
     klassOop java_super = ik->java_super();
     if (java_super != NULL && java_super != SystemDictionary::object_klass()) {
       oop super = Klass::cast(java_super)->java_mirror();
       if (!CallbackInvoker::report_superclass_reference(mirror, super)) {
         return false;
       }
     }
     // class loader
     oop cl = ik->class_loader();
     if (cl != NULL) {
       if (!CallbackInvoker::report_class_loader_reference(mirror, cl)) {
         return false;
       }
     }
     // protection domain
     oop pd = ik->protection_domain();
     if (pd != NULL) {
       if (!CallbackInvoker::report_protection_domain_reference(mirror, pd)) {
         return false;
       }
     }
     // signers
     oop signers = ik->signers();
     if (signers != NULL) {
       if (!CallbackInvoker::report_signers_reference(mirror, signers)) {
         return false;
       }
     }
     // references from the constant pool
     {
       const constantPoolOop pool = ik->constants();
       for (int i = 1; i < pool->length(); i++) {
         constantTag tag = pool->tag_at(i).value();
         if (tag.is_string() || tag.is_klass()) {
           oop entry;
           if (tag.is_string()) {
             entry = pool->resolved_string_at(i);
             assert(java_lang_String::is_instance(entry), "must be string");
           } else {
             entry = Klass::cast(pool->resolved_klass_at(i))->java_mirror();
           }
           if (!CallbackInvoker::report_constant_pool_reference(mirror, entry, (jint)i)) {
             return false;
           }
         }
       }
     }
     // interfaces
     // (These will already have been reported as references from the constant pool
     //  but are specified by IterateOverReachableObjects and must be reported).
     objArrayOop interfaces = ik->local_interfaces();
     for (i = 0; i < interfaces->length(); i++) {
       oop interf = Klass::cast((klassOop)interfaces->obj_at(i))->java_mirror();
       if (interf == NULL) {
         continue;
       }
       if (!CallbackInvoker::report_interface_reference(mirror, interf)) {
         return false;
       }
     }
     // iterate over the static fields
     ClassFieldMap* field_map = ClassFieldMap::create_map_of_static_fields(k);
     for (i=0; i<field_map->field_count(); i++) {
       ClassFieldDescriptor* field = field_map->field_at(i);
       char type = field->field_type();
       if (!is_primitive_field_type(type)) {
         address addr = (address)k + field->field_offset();
         oop* f = (oop*)addr;
         assert(verify_static_oop(ik, f), "sanity check");
         oop fld_o = *f;
         if (fld_o != NULL) {
           int slot = field->field_index();
           if (!CallbackInvoker::report_static_field_reference(mirror, fld_o, slot)) {
             delete field_map;
             return false;
           }
         }
       } else {
          if (is_reporting_primitive_fields()) {
            address addr = (address)k + field->field_offset();
            int slot = field->field_index();
            if (!CallbackInvoker::report_primitive_static_field(mirror, slot, addr, type)) {
              delete field_map;
              return false;
           }
         }
       }
     }
     delete field_map;
     return true;
   }
   return true;
 }
 // an object references a class and its instance fields
 // (static fields are ignored here as we report these as
 // references from the class).
 inline bool VM_HeapWalkOperation::iterate_over_object(oop o) {
   // reference to the class
   if (!CallbackInvoker::report_class_reference(o, Klass::cast(o->klass())->java_mirror())) {
     return false;
   }
   // iterate over instance fields
   ClassFieldMap* field_map = JvmtiCachedClassFieldMap::get_map_of_instance_fields(o);
   for (int i=0; i<field_map->field_count(); i++) {
     ClassFieldDescriptor* field = field_map->field_at(i);
     char type = field->field_type();
     if (!is_primitive_field_type(type)) {
       address addr = (address)o + field->field_offset();
       oop* f = (oop*)addr;
       oop fld_o = *f;
       if (fld_o != NULL) {
         // reflection code may have a reference to a klassOop.
         // - see sun.reflect.UnsafeStaticFieldAccessorImpl and sun.misc.Unsafe
         if (fld_o->is_klass()) {
           klassOop k = (klassOop)fld_o;
           fld_o = Klass::cast(k)->java_mirror();
         }
         int slot = field->field_index();
         if (!CallbackInvoker::report_field_reference(o, fld_o, slot)) {
           return false;
         }
       }
     } else {
       if (is_reporting_primitive_fields()) {
         // primitive instance field
         address addr = (address)o + field->field_offset();
         int slot = field->field_index();
         if (!CallbackInvoker::report_primitive_instance_field(o, slot, addr, type)) {
           return false;
         }
       }
     }
   }
   // if the object is a java.lang.String
   if (is_reporting_string_values() &&
       o->klass() == SystemDictionary::string_klass()) {
     if (!CallbackInvoker::report_string_value(o)) {
       return false;
     }
   }
   return true;
 }
 // collects all simple (non-stack) roots.
 // if there's a heap root callback provided then the callback is
 // invoked for each simple root.
 // if an object reference callback is provided then all simple
 // roots are pushed onto the marking stack so that they can be
 // processed later
 //
 inline bool VM_HeapWalkOperation::collect_simple_roots() {
   SimpleRootsClosure blk;
   // JNI globals
   blk.set_kind(JVMTI_HEAP_REFERENCE_JNI_GLOBAL);
   JNIHandles::oops_do(&blk);
   if (blk.stopped()) {
     return false;
   }
   // Preloaded classes and loader from the system dictionary
   blk.set_kind(JVMTI_HEAP_REFERENCE_SYSTEM_CLASS);
   SystemDictionary::always_strong_oops_do(&blk);
   if (blk.stopped()) {
     return false;
   }
   // Inflated monitors
   blk.set_kind(JVMTI_HEAP_REFERENCE_MONITOR);
   ObjectSynchronizer::oops_do(&blk);
   if (blk.stopped()) {
     return false;
   }
   // Threads
   for (JavaThread* thread = Threads::first(); thread != NULL ; thread = thread->next()) {
     oop threadObj = thread->threadObj();
     if (threadObj != NULL && !thread->is_exiting() && !thread->is_hidden_from_external_view()) {
       bool cont = CallbackInvoker::report_simple_root(JVMTI_HEAP_REFERENCE_THREAD, threadObj);
       if (!cont) {
         return false;
       }
     }
   }
   // Other kinds of roots maintained by HotSpot
   // Many of these won't be visible but others (such as instances of important
   // exceptions) will be visible.
   blk.set_kind(JVMTI_HEAP_REFERENCE_OTHER);
   Universe::oops_do(&blk);
   return true;
 }
 // Walk the stack of a given thread and find all references (locals
 // and JNI calls) and report these as stack references
 inline bool VM_HeapWalkOperation::collect_stack_roots(JavaThread* java_thread,
                                                       JNILocalRootsClosure* blk)
 {
   oop threadObj = java_thread->threadObj();
   assert(threadObj != NULL, "sanity check");
   // only need to get the thread's tag once per thread
   jlong thread_tag = tag_for(_tag_map, threadObj);
   // also need the thread id
   jlong tid = java_lang_Thread::thread_id(threadObj);
   if (java_thread->has_last_Java_frame()) {
     // vframes are resource allocated
     Thread* current_thread = Thread::current();
     ResourceMark rm(current_thread);
     HandleMark hm(current_thread);
     RegisterMap reg_map(java_thread);
     frame f = java_thread->last_frame();
     vframe* vf = vframe::new_vframe(&f, &reg_map, java_thread);
     bool is_top_frame = true;
     int depth = 0;
     frame* last_entry_frame = NULL;
     while (vf != NULL) {
       if (vf->is_java_frame()) {
         // java frame (interpreted, compiled, ...)
         javaVFrame *jvf = javaVFrame::cast(vf);
         // the jmethodID
         jmethodID method = jvf->method()->jmethod_id();
         if (!(jvf->method()->is_native())) {
           jlocation bci = (jlocation)jvf->bci();
           StackValueCollection* locals = jvf->locals();
           for (int slot=0; slot<locals->size(); slot++) {
             if (locals->at(slot)->type() == T_OBJECT) {
               oop o = locals->obj_at(slot)();
               if (o == NULL) {
                 continue;
               }
               // stack reference
               if (!CallbackInvoker::report_stack_ref_root(thread_tag, tid, depth, method,
                                                    bci, slot, o)) {
                 return false;
               }
             }
           }
         } else {
           blk->set_context(thread_tag, tid, depth, method);
           if (is_top_frame) {
             // JNI locals for the top frame.
             java_thread->active_handles()->oops_do(blk);
           } else {
             if (last_entry_frame != NULL) {
               // JNI locals for the entry frame
               assert(last_entry_frame->is_entry_frame(), "checking");
               last_entry_frame->entry_frame_call_wrapper()->handles()->oops_do(blk);
             }
           }
         }
         last_entry_frame = NULL;
         depth++;
       } else {
         // externalVFrame - for an entry frame then we report the JNI locals
         // when we find the corresponding javaVFrame
         frame* fr = vf->frame_pointer();
         assert(fr != NULL, "sanity check");
         if (fr->is_entry_frame()) {
           last_entry_frame = fr;
         }
       }
       vf = vf->sender();
       is_top_frame = false;
     }
   } else {
     // no last java frame but there may be JNI locals
     blk->set_context(thread_tag, tid, 0, (jmethodID)NULL);
     java_thread->active_handles()->oops_do(blk);
   }
   return true;
 }
 // collects all stack roots - for each thread it walks the execution
 // stack to find all references and local JNI refs.
 inline bool VM_HeapWalkOperation::collect_stack_roots() {
   JNILocalRootsClosure blk;
   for (JavaThread* thread = Threads::first(); thread != NULL ; thread = thread->next()) {
     oop threadObj = thread->threadObj();
     if (threadObj != NULL && !thread->is_exiting() && !thread->is_hidden_from_external_view()) {
       if (!collect_stack_roots(thread, &blk)) {
         return false;
       }
     }
   }
   return true;
 }
 // visit an object
 // first mark the object as visited
 // second get all the outbound references from this object (in other words, all
 // the objects referenced by this object).
 //
 bool VM_HeapWalkOperation::visit(oop o) {
   // mark object as visited
   assert(!ObjectMarker::visited(o), "can't visit same object more than once");
   ObjectMarker::mark(o);
   // instance
   if (o->is_instance()) {
     if (o->klass() == SystemDictionary::class_klass()) {
       o = klassOop_if_java_lang_Class(o);
       if (o->is_klass()) {
         // a java.lang.Class
         return iterate_over_class(klassOop(o));
       }
     } else {
       return iterate_over_object(o);
     }
   }
   // object array
   if (o->is_objArray()) {
     return iterate_over_array(o);
   }
   // type array
   if (o->is_typeArray()) {
     return iterate_over_type_array(o);
   }
   return true;
 }
 void VM_HeapWalkOperation::doit() {
   ResourceMark rm;
   ObjectMarkerController marker;
   ClassFieldMapCacheMark cm;
   assert(visit_stack()->is_empty(), "visit stack must be empty");
   // the heap walk starts with an initial object or the heap roots
   if (initial_object().is_null()) {
     if (!collect_simple_roots()) return;
     if (!collect_stack_roots()) return;
   } else {
     visit_stack()->push(initial_object()());
   }
   // object references required
   if (is_following_references()) {
     // visit each object until all reachable objects have been
     // visited or the callback asked to terminate the iteration.
     while (!visit_stack()->is_empty()) {
       oop o = visit_stack()->pop();
       if (!ObjectMarker::visited(o)) {
         if (!visit(o)) {
           break;
         }
       }
     }
   }
 }
 // iterate over all objects that are reachable from a set of roots
 void JvmtiTagMap::iterate_over_reachable_objects(jvmtiHeapRootCallback heap_root_callback,
                                                  jvmtiStackReferenceCallback stack_ref_callback,
                                                  jvmtiObjectReferenceCallback object_ref_callback,
                                                  const void* user_data) {
   MutexLocker ml(Heap_lock);
   BasicHeapWalkContext context(heap_root_callback, stack_ref_callback, object_ref_callback);
   VM_HeapWalkOperation op(this, Handle(), context, user_data);
   VMThread::execute(&op);
 }
 // iterate over all objects that are reachable from a given object
 void JvmtiTagMap::iterate_over_objects_reachable_from_object(jobject object,
                                                              jvmtiObjectReferenceCallback object_ref_callback,
                                                              const void* user_data) {
   oop obj = JNIHandles::resolve(object);
   Handle initial_object(Thread::current(), obj);
   MutexLocker ml(Heap_lock);
   BasicHeapWalkContext context(NULL, NULL, object_ref_callback);
   VM_HeapWalkOperation op(this, initial_object, context, user_data);
   VMThread::execute(&op);
 }
 // follow references from an initial object or the GC roots
 void JvmtiTagMap::follow_references(jint heap_filter,
                                     KlassHandle klass,
                                     jobject object,
                                     const jvmtiHeapCallbacks* callbacks,
                                     const void* user_data)
 {
   oop obj = JNIHandles::resolve(object);
   Handle initial_object(Thread::current(), obj);
   MutexLocker ml(Heap_lock);
   AdvancedHeapWalkContext context(heap_filter, klass, callbacks);
   VM_HeapWalkOperation op(this, initial_object, context, user_data);
   VMThread::execute(&op);
 }
 // called post-GC
 // - for each JVMTI environment with an object tag map, call its rehash
 // function to re-sync with the new object locations.
 void JvmtiTagMap::gc_epilogue(bool full) {
   assert(SafepointSynchronize::is_at_safepoint(), "must be executed at a safepoint");
   if (JvmtiEnv::environments_might_exist()) {
     // re-obtain the memory region for the young generation (might
     // changed due to adaptive resizing policy)
     get_young_generation();
     JvmtiEnvIterator it;
     for (JvmtiEnvBase* env = it.first(); env != NULL; env = it.next(env)) {
       JvmtiTagMap* tag_map = env->tag_map();
       if (tag_map != NULL && !tag_map->is_empty()) {
         TraceTime t(full ? "JVMTI Full Rehash " : "JVMTI Rehash ", TraceJVMTIObjectTagging);
         if (full) {
           tag_map->rehash(0, n_hashmaps);
         } else {
           tag_map->rehash(0, 0);        // tag map for young gen only
         }
       }
     }
   }
 }
 // CMS has completed referencing processing so we may have JNI weak refs
 // to objects in the CMS generation that have been GC'ed.
 void JvmtiTagMap::cms_ref_processing_epilogue() {
   assert(SafepointSynchronize::is_at_safepoint(), "must be executed at a safepoint");
   assert(UseConcMarkSweepGC, "should only be used with CMS");
   if (JvmtiEnv::environments_might_exist()) {
     JvmtiEnvIterator it;
     for (JvmtiEnvBase* env = it.first(); env != NULL; env = it.next(env)) {
       JvmtiTagMap* tag_map = ((JvmtiEnvBase *)env)->tag_map();
       if (tag_map != NULL && !tag_map->is_empty()) {
         TraceTime t("JVMTI Rehash (CMS) ", TraceJVMTIObjectTagging);
         tag_map->rehash(1, n_hashmaps);    // assume CMS not used in young gen
       }
     }
   }
 }
 // For each entry in the hashmaps 'start' to 'end' :
 //
 // 1. resolve the JNI weak reference
 //
 // 2. If it resolves to NULL it means the object has been freed so the entry
 //    is removed, the weak reference destroyed, and the object free event is
 //    posted (if enabled).
 //
 // 3. If the weak reference resolves to an object then we re-hash the object
 //    to see if it has moved or has been promoted (from the young to the old
 //    generation for example).
 //
 void JvmtiTagMap::rehash(int start, int end) {
   // does this environment have the OBJECT_FREE event enabled
   bool post_object_free = env()->is_enabled(JVMTI_EVENT_OBJECT_FREE);
   // counters used for trace message
   int freed = 0;
   int moved = 0;
   int promoted = 0;
   // we assume there are two hashmaps - one for the young generation
   // and the other for all other spaces.
   assert(n_hashmaps == 2, "not implemented");
   JvmtiTagHashmap* young_hashmap = _hashmap[0];
   JvmtiTagHashmap* other_hashmap = _hashmap[1];
   // reenable sizing (if disabled)
   young_hashmap->set_resizing_enabled(true);
   other_hashmap->set_resizing_enabled(true);
   // when re-hashing the hashmap corresponding to the young generation we
   // collect the entries corresponding to objects that have been promoted.
   JvmtiTagHashmapEntry* promoted_entries = NULL;
   if (end >= n_hashmaps) {
     end = n_hashmaps - 1;
   }
   for (int i=start; i <= end; i++) {
     JvmtiTagHashmap* hashmap = _hashmap[i];
     // if the hashmap is empty then we can skip it
     if (hashmap->_entry_count == 0) {
       continue;
     }
     // now iterate through each entry in the table
     JvmtiTagHashmapEntry** table = hashmap->table();
     int size = hashmap->size();
     for (int pos=0; pos<size; pos++) {
       JvmtiTagHashmapEntry* entry = table[pos];
       JvmtiTagHashmapEntry* prev = NULL;
       while (entry != NULL) {
         JvmtiTagHashmapEntry* next = entry->next();
         jweak ref = entry->object();
         oop oop = JNIHandles::resolve(ref);
         // has object been GC'ed
         if (oop == NULL) {
           // grab the tag
           jlong tag = entry->tag();
           guarantee(tag != 0, "checking");
           // remove GC'ed entry from hashmap and return the
           // entry to the free list
           hashmap->remove(prev, pos, entry);
           destroy_entry(entry);
           // destroy the weak ref
           JNIHandles::destroy_weak_global(ref);
           // post the event to the profiler
           if (post_object_free) {
             JvmtiExport::post_object_free(env(), tag);
           }
           freed++;
           entry = next;
           continue;
         }
         // if this is the young hashmap then the object is either promoted
         // or moved.
         // if this is the other hashmap then the object is moved.
         bool same_gen;
         if (i == 0) {
           assert(hashmap == young_hashmap, "checking");
           same_gen = is_in_young(oop);
         } else {
           same_gen = true;
         }
         if (same_gen) {
           // if the object has moved then re-hash it and move its
           // entry to its new location.
           unsigned int new_pos = JvmtiTagHashmap::hash(oop, size);
           if (new_pos != (unsigned int)pos) {
             if (prev == NULL) {
               table[pos] = next;
             } else {
               prev->set_next(next);
             }
             entry->set_next(table[new_pos]);
             table[new_pos] = entry;
             moved++;
           } else {
             // object didn't move
             prev = entry;
           }
         } else {
           // object has been promoted so remove the entry from the
           // young hashmap
           assert(hashmap == young_hashmap, "checking");
           hashmap->remove(prev, pos, entry);
           // move the entry to the promoted list
           entry->set_next(promoted_entries);
           promoted_entries = entry;
         }
         entry = next;
       }
     }
   }
   // add the entries, corresponding to the promoted objects, to the
   // other hashmap.
   JvmtiTagHashmapEntry* entry = promoted_entries;
   while (entry != NULL) {
     oop o = JNIHandles::resolve(entry->object());
     assert(hashmap_for(o) == other_hashmap, "checking");
     JvmtiTagHashmapEntry* next = entry->next();
     other_hashmap->add(o, entry);
     entry = next;
     promoted++;
   }
   // stats
   if (TraceJVMTIObjectTagging) {
     int total_moves = promoted + moved;
     int post_total = 0;
     for (int i=0; i<n_hashmaps; i++) {
       post_total += _hashmap[i]->_entry_count;
     }
     int pre_total = post_total + freed;
     tty->print("(%d->%d, %d freed, %d promoted, %d total moves)",
         pre_total, post_total, freed, promoted, total_moves);
   }
 }

Mercurial > jdk8-mips64-public > hotspot / annotate

src/share/vm/prims/jvmtiTagMap.cpp@93b6525e3b82 (annotated)

src/share/vm/prims/jvmtiTagMap.cpp