src/global-handles.cc - platform/external/v8 - Git at Google

 // Copyright 2009 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
 //       with the distribution.
 //     * Neither the name of Google Inc. nor the names of its
 //       contributors may be used to endorse or promote products derived
 //       from this software without specific prior written permission.
 //
 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

 #include "v8.h"

 #include "api.h"
 #include "global-handles.h"

 #include "vm-state-inl.h"

 namespace v8 {
 namespace internal {


 ObjectGroup::~ObjectGroup() {
   if (info_ != NULL) info_->Dispose();
 }


 class GlobalHandles::Node : public Malloced {
  public:

   void Initialize(Object* object) {
     // Set the initial value of the handle.
     object_ = object;
     class_id_ = v8::HeapProfiler::kPersistentHandleNoClassId;
     state_  = NORMAL;
     parameter_or_next_free_.parameter = NULL;
     callback_ = NULL;
   }

   Node() {
     state_ = DESTROYED;
   }

   explicit Node(Object* object) {
     Initialize(object);
     // Initialize link structure.
     next_ = NULL;
   }

   ~Node() {
     if (state_ != DESTROYED) Destroy(Isolate::Current()->global_handles());
 #ifdef DEBUG
     // Zap the values for eager trapping.
     object_ = NULL;
     next_ = NULL;
     parameter_or_next_free_.next_free = NULL;
 #endif
   }

   void Destroy(GlobalHandles* global_handles) {
     if (state_ == WEAK || IsNearDeath()) {
       global_handles->number_of_weak_handles_--;
       if (object_->IsJSGlobalObject()) {
         global_handles->number_of_global_object_weak_handles_--;
       }
     }
     state_ = DESTROYED;
   }

   // Accessors for next_.
   Node* next() { return next_; }
   void set_next(Node* value) { next_ = value; }
   Node** next_addr() { return &next_; }

   // Accessors for next free node in the free list.
   Node* next_free() {
     ASSERT(state_ == DESTROYED);
     return parameter_or_next_free_.next_free;
   }
   void set_next_free(Node* value) {
     ASSERT(state_ == DESTROYED);
     parameter_or_next_free_.next_free = value;
   }

   // Returns a link from the handle.
   static Node* FromLocation(Object** location) {
     ASSERT(OFFSET_OF(Node, object_) == 0);
     return reinterpret_cast<Node*>(location);
   }

   // Returns the handle.
   Handle<Object> handle() { return Handle<Object>(&object_); }

   // Make this handle weak.
   void MakeWeak(GlobalHandles* global_handles, void* parameter,
                 WeakReferenceCallback callback) {
     LOG(global_handles->isolate(),
         HandleEvent("GlobalHandle::MakeWeak", handle().location()));
     ASSERT(state_ != DESTROYED);
     if (state_ != WEAK && !IsNearDeath()) {
       global_handles->number_of_weak_handles_++;
       if (object_->IsJSGlobalObject()) {
         global_handles->number_of_global_object_weak_handles_++;
       }
     }
     state_ = WEAK;
     set_parameter(parameter);
     callback_ = callback;
   }

   void ClearWeakness(GlobalHandles* global_handles) {
     LOG(global_handles->isolate(),
         HandleEvent("GlobalHandle::ClearWeakness", handle().location()));
     ASSERT(state_ != DESTROYED);
     if (state_ == WEAK || IsNearDeath()) {
       global_handles->number_of_weak_handles_--;
       if (object_->IsJSGlobalObject()) {
         global_handles->number_of_global_object_weak_handles_--;
       }
     }
     state_ = NORMAL;
     set_parameter(NULL);
   }

   bool IsNearDeath() {
     // Check for PENDING to ensure correct answer when processing callbacks.
     return state_ == PENDING || state_ == NEAR_DEATH;
   }

   bool IsWeak() {
     return state_ == WEAK;
   }

   bool CanBeRetainer() {
     return state_ != DESTROYED && state_ != NEAR_DEATH;
   }

   void SetWrapperClassId(uint16_t class_id) {
     class_id_ = class_id;
   }

   // Returns the id for this weak handle.
   void set_parameter(void* parameter) {
     ASSERT(state_ != DESTROYED);
     parameter_or_next_free_.parameter = parameter;
   }
   void* parameter() {
     ASSERT(state_ != DESTROYED);
     return parameter_or_next_free_.parameter;
   }

   // Returns the callback for this weak handle.
   WeakReferenceCallback callback() { return callback_; }

   bool PostGarbageCollectionProcessing(Isolate* isolate,
                                        GlobalHandles* global_handles) {
     if (state_ != Node::PENDING) return false;
     LOG(isolate, HandleEvent("GlobalHandle::Processing", handle().location()));
     WeakReferenceCallback func = callback();
     if (func == NULL) {
       Destroy(global_handles);
       return false;
     }
     void* par = parameter();
     state_ = NEAR_DEATH;
     set_parameter(NULL);

     v8::Persistent<v8::Object> object = ToApi<v8::Object>(handle());
     {
       // Forbid reuse of destroyed nodes as they might be already deallocated.
       // It's fine though to reuse nodes that were destroyed in weak callback
       // as those cannot be deallocated until we are back from the callback.
       global_handles->set_first_free(NULL);
       if (global_handles->first_deallocated()) {
         global_handles->first_deallocated()->set_next(global_handles->head());
       }
       // Check that we are not passing a finalized external string to
       // the callback.
       ASSERT(!object_->IsExternalAsciiString() ||
              ExternalAsciiString::cast(object_)->resource() != NULL);
       ASSERT(!object_->IsExternalTwoByteString() ||
              ExternalTwoByteString::cast(object_)->resource() != NULL);
       // Leaving V8.
       VMState state(isolate, EXTERNAL);
       func(object, par);
     }
     // Absense of explicit cleanup or revival of weak handle
     // in most of the cases would lead to memory leak.
     ASSERT(state_ != NEAR_DEATH);
     return true;
   }

   // Place the handle address first to avoid offset computation.
   Object* object_;  // Storage for object pointer.

   uint16_t class_id_;

   // Transition diagram:
   // NORMAL <-> WEAK -> PENDING -> NEAR_DEATH -> { NORMAL, WEAK, DESTROYED }
   enum State {
     NORMAL,      // Normal global handle.
     WEAK,        // Flagged as weak but not yet finalized.
     PENDING,     // Has been recognized as only reachable by weak handles.
     NEAR_DEATH,  // Callback has informed the handle is near death.
     DESTROYED
   };
   State state_ : 4;  // Need one more bit for MSVC as it treats enums as signed.

  private:
   // Handle specific callback.
   WeakReferenceCallback callback_;
   // Provided data for callback.  In DESTROYED state, this is used for
   // the free list link.
   union {
     void* parameter;
     Node* next_free;
   } parameter_or_next_free_;

   // Linkage for the list.
   Node* next_;

  public:
   TRACK_MEMORY("GlobalHandles::Node")
 };


 class GlobalHandles::Pool {
   public:
     Pool() {
       current_ = new Chunk();
       current_->previous = NULL;
       next_ = current_->nodes;
       limit_ = current_->nodes + kNodesPerChunk;
     }

     ~Pool() {
       if (current_ != NULL) {
         Release();
       }
     }

     Node* Allocate() {
       if (next_ < limit_) {
         return next_++;
       }
       return SlowAllocate();
     }

     void Release() {
       Chunk* current = current_;
       ASSERT(current != NULL);  // At least a single block must by allocated
       do {
         Chunk* previous = current->previous;
         delete current;
         current = previous;
       } while (current != NULL);
       current_ = NULL;
       next_ = limit_ = NULL;
     }

   private:
     static const int kNodesPerChunk = (1 << 12) - 1;
     struct Chunk : public Malloced {
       Chunk* previous;
       Node nodes[kNodesPerChunk];
     };

     Node* SlowAllocate() {
       Chunk* chunk = new Chunk();
       chunk->previous = current_;
       current_ = chunk;

       Node* new_nodes = current_->nodes;
       next_ = new_nodes + 1;
       limit_ = new_nodes + kNodesPerChunk;
       return new_nodes;
     }

     Chunk* current_;
     Node* next_;
     Node* limit_;
 };


 GlobalHandles::GlobalHandles(Isolate* isolate)
     : isolate_(isolate),
       number_of_weak_handles_(0),
       number_of_global_object_weak_handles_(0),
       head_(NULL),
       first_free_(NULL),
       first_deallocated_(NULL),
       pool_(new Pool()),
       post_gc_processing_count_(0),
       object_groups_(4) {
 }


 GlobalHandles::~GlobalHandles() {
   delete pool_;
   pool_ = 0;
 }


 Handle<Object> GlobalHandles::Create(Object* value) {
   isolate_->counters()->global_handles()->Increment();
   Node* result;
   if (first_free()) {
     // Take the first node in the free list.
     result = first_free();
     set_first_free(result->next_free());
   } else if (first_deallocated()) {
     // Next try deallocated list
     result = first_deallocated();
     set_first_deallocated(result->next_free());
     ASSERT(result->next() == head());
     set_head(result);
   } else {
     // Allocate a new node.
     result = pool_->Allocate();
     result->set_next(head());
     set_head(result);
   }
   result->Initialize(value);
   return result->handle();
 }


 void GlobalHandles::Destroy(Object** location) {
   isolate_->counters()->global_handles()->Decrement();
   if (location == NULL) return;
   Node* node = Node::FromLocation(location);
   node->Destroy(this);
   // Link the destroyed.
   node->set_next_free(first_free());
   set_first_free(node);
 }


 void GlobalHandles::MakeWeak(Object** location, void* parameter,
                              WeakReferenceCallback callback) {
   ASSERT(callback != NULL);
   Node::FromLocation(location)->MakeWeak(this, parameter, callback);
 }


 void GlobalHandles::ClearWeakness(Object** location) {
   Node::FromLocation(location)->ClearWeakness(this);
 }


 bool GlobalHandles::IsNearDeath(Object** location) {
   return Node::FromLocation(location)->IsNearDeath();
 }


 bool GlobalHandles::IsWeak(Object** location) {
   return Node::FromLocation(location)->IsWeak();
 }


 void GlobalHandles::SetWrapperClassId(Object** location, uint16_t class_id) {
   Node::FromLocation(location)->SetWrapperClassId(class_id);
 }


 void GlobalHandles::IterateWeakRoots(ObjectVisitor* v) {
   // Traversal of GC roots in the global handle list that are marked as
   // WEAK or PENDING.
   for (Node* current = head_; current != NULL; current = current->next()) {
     if (current->state_ == Node::WEAK
       || current->state_ == Node::PENDING
       || current->state_ == Node::NEAR_DEATH) {
       v->VisitPointer(&current->object_);
     }
   }
 }


 void GlobalHandles::IterateWeakRoots(WeakReferenceGuest f,
                                      WeakReferenceCallback callback) {
   for (Node* current = head_; current != NULL; current = current->next()) {
     if (current->IsWeak() && current->callback() == callback) {
       f(current->object_, current->parameter());
     }
   }
 }


 void GlobalHandles::IdentifyWeakHandles(WeakSlotCallback f) {
   for (Node* current = head_; current != NULL; current = current->next()) {
     if (current->state_ == Node::WEAK) {
       if (f(&current->object_)) {
         current->state_ = Node::PENDING;
         LOG(isolate_,
             HandleEvent("GlobalHandle::Pending", current->handle().location()));
       }
     }
   }
 }


 bool GlobalHandles::PostGarbageCollectionProcessing() {
   // Process weak global handle callbacks. This must be done after the
   // GC is completely done, because the callbacks may invoke arbitrary
   // API functions.
   // At the same time deallocate all DESTROYED nodes.
   ASSERT(isolate_->heap()->gc_state() == Heap::NOT_IN_GC);
   const int initial_post_gc_processing_count = ++post_gc_processing_count_;
   bool next_gc_likely_to_collect_more = false;
   Node** p = &head_;
   while (*p != NULL) {
     if ((*p)->PostGarbageCollectionProcessing(isolate_, this)) {
       if (initial_post_gc_processing_count != post_gc_processing_count_) {
         // Weak callback triggered another GC and another round of
         // PostGarbageCollection processing.  The current node might
         // have been deleted in that round, so we need to bail out (or
         // restart the processing).
         break;
       }
     }
     if ((*p)->state_ == Node::DESTROYED) {
       // Delete the link.
       Node* node = *p;
       *p = node->next();  // Update the link.
       if (first_deallocated()) {
         first_deallocated()->set_next(node);
       }
       node->set_next_free(first_deallocated());
       set_first_deallocated(node);
       next_gc_likely_to_collect_more = true;
     } else {
       p = (*p)->next_addr();
     }
   }
   set_first_free(NULL);
   if (first_deallocated()) {
     first_deallocated()->set_next(head());
   }

   return next_gc_likely_to_collect_more;
 }


 void GlobalHandles::IterateStrongRoots(ObjectVisitor* v) {
   // Traversal of global handles marked as NORMAL.
   for (Node* current = head_; current != NULL; current = current->next()) {
     if (current->state_ == Node::NORMAL) {
       v->VisitPointer(&current->object_);
     }
   }
 }


 void GlobalHandles::IterateAllRoots(ObjectVisitor* v) {
   for (Node* current = head_; current != NULL; current = current->next()) {
     if (current->state_ != Node::DESTROYED) {
       v->VisitPointer(&current->object_);
     }
   }
 }


 void GlobalHandles::IterateAllRootsWithClassIds(ObjectVisitor* v) {
   for (Node* current = head_; current != NULL; current = current->next()) {
     if (current->class_id_ != v8::HeapProfiler::kPersistentHandleNoClassId &&
         current->CanBeRetainer()) {
       v->VisitEmbedderReference(&current->object_, current->class_id_);
     }
   }
 }


 void GlobalHandles::TearDown() {
   // Reset all the lists.
   set_head(NULL);
   set_first_free(NULL);
   set_first_deallocated(NULL);
   pool_->Release();
 }


 void GlobalHandles::RecordStats(HeapStats* stats) {
   *stats->global_handle_count = 0;
   *stats->weak_global_handle_count = 0;
   *stats->pending_global_handle_count = 0;
   *stats->near_death_global_handle_count = 0;
   *stats->destroyed_global_handle_count = 0;
   for (Node* current = head_; current != NULL; current = current->next()) {
     *stats->global_handle_count += 1;
     if (current->state_ == Node::WEAK) {
       *stats->weak_global_handle_count += 1;
     } else if (current->state_ == Node::PENDING) {
       *stats->pending_global_handle_count += 1;
     } else if (current->state_ == Node::NEAR_DEATH) {
       *stats->near_death_global_handle_count += 1;
     } else if (current->state_ == Node::DESTROYED) {
       *stats->destroyed_global_handle_count += 1;
     }
   }
 }

 #ifdef DEBUG

 void GlobalHandles::PrintStats() {
   int total = 0;
   int weak = 0;
   int pending = 0;
   int near_death = 0;
   int destroyed = 0;

   for (Node* current = head_; current != NULL; current = current->next()) {
     total++;
     if (current->state_ == Node::WEAK) weak++;
     if (current->state_ == Node::PENDING) pending++;
     if (current->state_ == Node::NEAR_DEATH) near_death++;
     if (current->state_ == Node::DESTROYED) destroyed++;
   }

   PrintF("Global Handle Statistics:\n");
   PrintF("  allocated memory = %" V8_PTR_PREFIX "dB\n", sizeof(Node) * total);
   PrintF("  # weak       = %d\n", weak);
   PrintF("  # pending    = %d\n", pending);
   PrintF("  # near_death = %d\n", near_death);
   PrintF("  # destroyed  = %d\n", destroyed);
   PrintF("  # total      = %d\n", total);
 }

 void GlobalHandles::Print() {
   PrintF("Global handles:\n");
   for (Node* current = head_; current != NULL; current = current->next()) {
     PrintF("  handle %p to %p (weak=%d)\n",
            reinterpret_cast<void*>(current->handle().location()),
            reinterpret_cast<void*>(*current->handle()),
            current->state_ == Node::WEAK);
   }
 }

 #endif


 void GlobalHandles::AddObjectGroup(Object*** handles,
                                    size_t length,
                                    v8::RetainedObjectInfo* info) {
   if (length == 0) {
     if (info != NULL) info->Dispose();
     return;
   }
   object_groups_.Add(ObjectGroup::New(handles, length, info));
 }


 void GlobalHandles::AddImplicitReferences(HeapObject** parent,
                                           Object*** children,
                                           size_t length) {
   if (length == 0) return;
   implicit_ref_groups_.Add(ImplicitRefGroup::New(parent, children, length));
 }


 void GlobalHandles::RemoveObjectGroups() {
   for (int i = 0; i < object_groups_.length(); i++) {
     object_groups_.at(i)->Dispose();
   }
   object_groups_.Clear();
 }


 void GlobalHandles::RemoveImplicitRefGroups() {
   for (int i = 0; i < implicit_ref_groups_.length(); i++) {
     implicit_ref_groups_.at(i)->Dispose();
   }
   implicit_ref_groups_.Clear();
 }


 } }  // namespace v8::internal
	// Copyright 2009 the V8 project authors. All rights reserved.
	// Redistribution and use in source and binary forms, with or without
	// modification, are permitted provided that the following conditions are
	// met:
	//
	// * Redistributions of source code must retain the above copyright
	// notice, this list of conditions and the following disclaimer.
	// * Redistributions in binary form must reproduce the above
	// copyright notice, this list of conditions and the following
	// disclaimer in the documentation and/or other materials provided
	// with the distribution.
	// * Neither the name of Google Inc. nor the names of its
	// contributors may be used to endorse or promote products derived
	// from this software without specific prior written permission.
	//
	// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
	// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
	// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
	// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
	// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
	// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
	// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
	// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
	// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
	// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
	// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

	#include "v8.h"

	#include "api.h"
	#include "global-handles.h"

	#include "vm-state-inl.h"

	namespace v8 {
	namespace internal {


	ObjectGroup::~ObjectGroup() {
	if (info_ != NULL) info_->Dispose();
	}


	class GlobalHandles::Node : public Malloced {
	public:

	void Initialize(Object* object) {
	// Set the initial value of the handle.
	object_ = object;
	class_id_ = v8::HeapProfiler::kPersistentHandleNoClassId;
	state_ = NORMAL;
	parameter_or_next_free_.parameter = NULL;
	callback_ = NULL;
	}

	Node() {
	state_ = DESTROYED;
	}

	explicit Node(Object* object) {
	Initialize(object);
	// Initialize link structure.
	next_ = NULL;
	}

	~Node() {
	if (state_ != DESTROYED) Destroy(Isolate::Current()->global_handles());
	#ifdef DEBUG
	// Zap the values for eager trapping.
	object_ = NULL;
	next_ = NULL;
	parameter_or_next_free_.next_free = NULL;
	#endif
	}

	void Destroy(GlobalHandles* global_handles) {
	if (state_ == WEAK \|\| IsNearDeath()) {
	global_handles->number_of_weak_handles_--;
	if (object_->IsJSGlobalObject()) {
	global_handles->number_of_global_object_weak_handles_--;
	}
	}
	state_ = DESTROYED;
	}

	// Accessors for next_.
	Node* next() { return next_; }
	void set_next(Node* value) { next_ = value; }
	Node** next_addr() { return &next_; }

	// Accessors for next free node in the free list.
	Node* next_free() {
	ASSERT(state_ == DESTROYED);
	return parameter_or_next_free_.next_free;
	}
	void set_next_free(Node* value) {
	ASSERT(state_ == DESTROYED);
	parameter_or_next_free_.next_free = value;
	}

	// Returns a link from the handle.
	static Node* FromLocation(Object** location) {
	ASSERT(OFFSET_OF(Node, object_) == 0);
	return reinterpret_cast<Node*>(location);
	}

	// Returns the handle.
	Handle<Object> handle() { return Handle<Object>(&object_); }

	// Make this handle weak.
	void MakeWeak(GlobalHandles* global_handles, void* parameter,
	WeakReferenceCallback callback) {
	LOG(global_handles->isolate(),
	HandleEvent("GlobalHandle::MakeWeak", handle().location()));
	ASSERT(state_ != DESTROYED);
	if (state_ != WEAK && !IsNearDeath()) {
	global_handles->number_of_weak_handles_++;
	if (object_->IsJSGlobalObject()) {
	global_handles->number_of_global_object_weak_handles_++;
	}
	}
	state_ = WEAK;
	set_parameter(parameter);
	callback_ = callback;
	}

	void ClearWeakness(GlobalHandles* global_handles) {
	LOG(global_handles->isolate(),
	HandleEvent("GlobalHandle::ClearWeakness", handle().location()));
	ASSERT(state_ != DESTROYED);
	if (state_ == WEAK \|\| IsNearDeath()) {
	global_handles->number_of_weak_handles_--;
	if (object_->IsJSGlobalObject()) {
	global_handles->number_of_global_object_weak_handles_--;
	}
	}
	state_ = NORMAL;
	set_parameter(NULL);
	}

	bool IsNearDeath() {
	// Check for PENDING to ensure correct answer when processing callbacks.
	return state_ == PENDING \|\| state_ == NEAR_DEATH;
	}

	bool IsWeak() {
	return state_ == WEAK;
	}

	bool CanBeRetainer() {
	return state_ != DESTROYED && state_ != NEAR_DEATH;
	}

	void SetWrapperClassId(uint16_t class_id) {
	class_id_ = class_id;
	}

	// Returns the id for this weak handle.
	void set_parameter(void* parameter) {
	ASSERT(state_ != DESTROYED);
	parameter_or_next_free_.parameter = parameter;
	}
	void* parameter() {
	ASSERT(state_ != DESTROYED);
	return parameter_or_next_free_.parameter;
	}

	// Returns the callback for this weak handle.
	WeakReferenceCallback callback() { return callback_; }

	bool PostGarbageCollectionProcessing(Isolate* isolate,
	GlobalHandles* global_handles) {
	if (state_ != Node::PENDING) return false;
	LOG(isolate, HandleEvent("GlobalHandle::Processing", handle().location()));
	WeakReferenceCallback func = callback();
	if (func == NULL) {
	Destroy(global_handles);
	return false;
	}
	void* par = parameter();
	state_ = NEAR_DEATH;
	set_parameter(NULL);

	v8::Persistent<v8::Object> object = ToApi<v8::Object>(handle());
	{
	// Forbid reuse of destroyed nodes as they might be already deallocated.
	// It's fine though to reuse nodes that were destroyed in weak callback
	// as those cannot be deallocated until we are back from the callback.
	global_handles->set_first_free(NULL);
	if (global_handles->first_deallocated()) {
	global_handles->first_deallocated()->set_next(global_handles->head());
	}
	// Check that we are not passing a finalized external string to
	// the callback.
	ASSERT(!object_->IsExternalAsciiString() \|\|
	ExternalAsciiString::cast(object_)->resource() != NULL);
	ASSERT(!object_->IsExternalTwoByteString() \|\|
	ExternalTwoByteString::cast(object_)->resource() != NULL);
	// Leaving V8.
	VMState state(isolate, EXTERNAL);
	func(object, par);
	}
	// Absense of explicit cleanup or revival of weak handle
	// in most of the cases would lead to memory leak.
	ASSERT(state_ != NEAR_DEATH);
	return true;
	}

	// Place the handle address first to avoid offset computation.
	Object* object_; // Storage for object pointer.

	uint16_t class_id_;

	// Transition diagram:
	// NORMAL <-> WEAK -> PENDING -> NEAR_DEATH -> { NORMAL, WEAK, DESTROYED }
	enum State {
	NORMAL, // Normal global handle.
	WEAK, // Flagged as weak but not yet finalized.
	PENDING, // Has been recognized as only reachable by weak handles.
	NEAR_DEATH, // Callback has informed the handle is near death.
	DESTROYED
	};
	State state_ : 4; // Need one more bit for MSVC as it treats enums as signed.

	private:
	// Handle specific callback.
	WeakReferenceCallback callback_;
	// Provided data for callback. In DESTROYED state, this is used for
	// the free list link.
	union {
	void* parameter;
	Node* next_free;
	} parameter_or_next_free_;

	// Linkage for the list.
	Node* next_;

	public:
	TRACK_MEMORY("GlobalHandles::Node")
	};


	class GlobalHandles::Pool {
	public:
	Pool() {
	current_ = new Chunk();
	current_->previous = NULL;
	next_ = current_->nodes;
	limit_ = current_->nodes + kNodesPerChunk;
	}

	~Pool() {
	if (current_ != NULL) {
	Release();
	}
	}

	Node* Allocate() {
	if (next_ < limit_) {
	return next_++;
	}
	return SlowAllocate();
	}

	void Release() {
	Chunk* current = current_;
	ASSERT(current != NULL); // At least a single block must by allocated
	do {
	Chunk* previous = current->previous;
	delete current;
	current = previous;
	} while (current != NULL);
	current_ = NULL;
	next_ = limit_ = NULL;
	}

	private:
	static const int kNodesPerChunk = (1 << 12) - 1;
	struct Chunk : public Malloced {
	Chunk* previous;
	Node nodes[kNodesPerChunk];
	};

	Node* SlowAllocate() {
	Chunk* chunk = new Chunk();
	chunk->previous = current_;
	current_ = chunk;

	Node* new_nodes = current_->nodes;
	next_ = new_nodes + 1;
	limit_ = new_nodes + kNodesPerChunk;
	return new_nodes;
	}

	Chunk* current_;
	Node* next_;
	Node* limit_;
	};


	GlobalHandles::GlobalHandles(Isolate* isolate)
	: isolate_(isolate),
	number_of_weak_handles_(0),
	number_of_global_object_weak_handles_(0),
	head_(NULL),
	first_free_(NULL),
	first_deallocated_(NULL),
	pool_(new Pool()),
	post_gc_processing_count_(0),
	object_groups_(4) {
	}


	GlobalHandles::~GlobalHandles() {
	delete pool_;
	pool_ = 0;
	}


	Handle<Object> GlobalHandles::Create(Object* value) {
	isolate_->counters()->global_handles()->Increment();
	Node* result;
	if (first_free()) {
	// Take the first node in the free list.
	result = first_free();
	set_first_free(result->next_free());
	} else if (first_deallocated()) {
	// Next try deallocated list
	result = first_deallocated();
	set_first_deallocated(result->next_free());
	ASSERT(result->next() == head());
	set_head(result);
	} else {
	// Allocate a new node.
	result = pool_->Allocate();
	result->set_next(head());
	set_head(result);
	}
	result->Initialize(value);
	return result->handle();
	}


	void GlobalHandles::Destroy(Object** location) {
	isolate_->counters()->global_handles()->Decrement();
	if (location == NULL) return;
	Node* node = Node::FromLocation(location);
	node->Destroy(this);
	// Link the destroyed.
	node->set_next_free(first_free());
	set_first_free(node);
	}


	void GlobalHandles::MakeWeak(Object** location, void* parameter,
	WeakReferenceCallback callback) {
	ASSERT(callback != NULL);
	Node::FromLocation(location)->MakeWeak(this, parameter, callback);
	}


	void GlobalHandles::ClearWeakness(Object** location) {
	Node::FromLocation(location)->ClearWeakness(this);
	}


	bool GlobalHandles::IsNearDeath(Object** location) {
	return Node::FromLocation(location)->IsNearDeath();
	}


	bool GlobalHandles::IsWeak(Object** location) {
	return Node::FromLocation(location)->IsWeak();
	}


	void GlobalHandles::SetWrapperClassId(Object** location, uint16_t class_id) {
	Node::FromLocation(location)->SetWrapperClassId(class_id);
	}


	void GlobalHandles::IterateWeakRoots(ObjectVisitor* v) {
	// Traversal of GC roots in the global handle list that are marked as
	// WEAK or PENDING.
	for (Node* current = head_; current != NULL; current = current->next()) {
	if (current->state_ == Node::WEAK
	\|\| current->state_ == Node::PENDING
	\|\| current->state_ == Node::NEAR_DEATH) {
	v->VisitPointer(&current->object_);
	}
	}
	}


	void GlobalHandles::IterateWeakRoots(WeakReferenceGuest f,
	WeakReferenceCallback callback) {
	for (Node* current = head_; current != NULL; current = current->next()) {
	if (current->IsWeak() && current->callback() == callback) {
	f(current->object_, current->parameter());
	}
	}
	}


	void GlobalHandles::IdentifyWeakHandles(WeakSlotCallback f) {
	for (Node* current = head_; current != NULL; current = current->next()) {
	if (current->state_ == Node::WEAK) {
	if (f(&current->object_)) {
	current->state_ = Node::PENDING;
	LOG(isolate_,
	HandleEvent("GlobalHandle::Pending", current->handle().location()));
	}
	}
	}
	}


	bool GlobalHandles::PostGarbageCollectionProcessing() {
	// Process weak global handle callbacks. This must be done after the
	// GC is completely done, because the callbacks may invoke arbitrary
	// API functions.
	// At the same time deallocate all DESTROYED nodes.
	ASSERT(isolate_->heap()->gc_state() == Heap::NOT_IN_GC);
	const int initial_post_gc_processing_count = ++post_gc_processing_count_;
	bool next_gc_likely_to_collect_more = false;
	Node** p = &head_;
	while (*p != NULL) {
	if ((*p)->PostGarbageCollectionProcessing(isolate_, this)) {
	if (initial_post_gc_processing_count != post_gc_processing_count_) {
	// Weak callback triggered another GC and another round of
	// PostGarbageCollection processing. The current node might
	// have been deleted in that round, so we need to bail out (or
	// restart the processing).
	break;
	}
	}
	if ((*p)->state_ == Node::DESTROYED) {
	// Delete the link.
	Node* node = *p;
	*p = node->next(); // Update the link.
	if (first_deallocated()) {
	first_deallocated()->set_next(node);
	}
	node->set_next_free(first_deallocated());
	set_first_deallocated(node);
	next_gc_likely_to_collect_more = true;
	} else {
	p = (*p)->next_addr();
	}
	}
	set_first_free(NULL);
	if (first_deallocated()) {
	first_deallocated()->set_next(head());
	}

	return next_gc_likely_to_collect_more;
	}


	void GlobalHandles::IterateStrongRoots(ObjectVisitor* v) {
	// Traversal of global handles marked as NORMAL.
	for (Node* current = head_; current != NULL; current = current->next()) {
	if (current->state_ == Node::NORMAL) {
	v->VisitPointer(&current->object_);
	}
	}
	}


	void GlobalHandles::IterateAllRoots(ObjectVisitor* v) {
	for (Node* current = head_; current != NULL; current = current->next()) {
	if (current->state_ != Node::DESTROYED) {
	v->VisitPointer(&current->object_);
	}
	}
	}


	void GlobalHandles::IterateAllRootsWithClassIds(ObjectVisitor* v) {
	for (Node* current = head_; current != NULL; current = current->next()) {
	if (current->class_id_ != v8::HeapProfiler::kPersistentHandleNoClassId &&
	current->CanBeRetainer()) {
	v->VisitEmbedderReference(&current->object_, current->class_id_);
	}
	}
	}


	void GlobalHandles::TearDown() {
	// Reset all the lists.
	set_head(NULL);
	set_first_free(NULL);
	set_first_deallocated(NULL);
	pool_->Release();
	}


	void GlobalHandles::RecordStats(HeapStats* stats) {
	*stats->global_handle_count = 0;
	*stats->weak_global_handle_count = 0;
	*stats->pending_global_handle_count = 0;
	*stats->near_death_global_handle_count = 0;
	*stats->destroyed_global_handle_count = 0;
	for (Node* current = head_; current != NULL; current = current->next()) {
	*stats->global_handle_count += 1;
	if (current->state_ == Node::WEAK) {
	*stats->weak_global_handle_count += 1;
	} else if (current->state_ == Node::PENDING) {
	*stats->pending_global_handle_count += 1;
	} else if (current->state_ == Node::NEAR_DEATH) {
	*stats->near_death_global_handle_count += 1;
	} else if (current->state_ == Node::DESTROYED) {
	*stats->destroyed_global_handle_count += 1;
	}
	}
	}

	#ifdef DEBUG

	void GlobalHandles::PrintStats() {
	int total = 0;
	int weak = 0;
	int pending = 0;
	int near_death = 0;
	int destroyed = 0;

	for (Node* current = head_; current != NULL; current = current->next()) {
	total++;
	if (current->state_ == Node::WEAK) weak++;
	if (current->state_ == Node::PENDING) pending++;
	if (current->state_ == Node::NEAR_DEATH) near_death++;
	if (current->state_ == Node::DESTROYED) destroyed++;
	}

	PrintF("Global Handle Statistics:\n");
	PrintF(" allocated memory = %" V8_PTR_PREFIX "dB\n", sizeof(Node) * total);
	PrintF(" # weak = %d\n", weak);
	PrintF(" # pending = %d\n", pending);
	PrintF(" # near_death = %d\n", near_death);
	PrintF(" # destroyed = %d\n", destroyed);
	PrintF(" # total = %d\n", total);
	}

	void GlobalHandles::Print() {
	PrintF("Global handles:\n");
	for (Node* current = head_; current != NULL; current = current->next()) {
	PrintF(" handle %p to %p (weak=%d)\n",
	reinterpret_cast<void*>(current->handle().location()),
	reinterpret_cast<void>(current->handle()),
	current->state_ == Node::WEAK);
	}
	}

	#endif



	void GlobalHandles::AddObjectGroup(Object*** handles,
	size_t length,
	v8::RetainedObjectInfo* info) {
	if (length == 0) {
	if (info != NULL) info->Dispose();
	return;
	}
	object_groups_.Add(ObjectGroup::New(handles, length, info));
	}


	void GlobalHandles::AddImplicitReferences(HeapObject** parent,
	Object*** children,
	size_t length) {
	if (length == 0) return;
	implicit_ref_groups_.Add(ImplicitRefGroup::New(parent, children, length));
	}


	void GlobalHandles::RemoveObjectGroups() {
	for (int i = 0; i < object_groups_.length(); i++) {
	object_groups_.at(i)->Dispose();
	}
	object_groups_.Clear();
	}


	void GlobalHandles::RemoveImplicitRefGroups() {
	for (int i = 0; i < implicit_ref_groups_.length(); i++) {
	implicit_ref_groups_.at(i)->Dispose();
	}
	implicit_ref_groups_.Clear();
	}


	} } // namespace v8::internal