text: // Copyright 2011 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.
  
  #ifndef V8_GLOBAL_HANDLES_H_
  #define V8_GLOBAL_HANDLES_H_
  
  #include "../include/v8-profiler.h"
  
  #include "list.h"
  
  namespace v8 {
  namespace internal {
  
  // Structure for tracking global handles.
  // A single list keeps all the allocated global handles.
  // Destroyed handles stay in the list but is added to the free list.
  // At GC the destroyed global handles are removed from the free list
  // and deallocated.
  
  // An object group is treated like a single JS object: if one of object in
  // the group is alive, all objects in the same group are considered alive.
  // An object group is used to simulate object relationship in a DOM tree.
  class ObjectGroup {
   public:
    static ObjectGroup* New(Object*** handles,
                            size_t length,
                            v8::RetainedObjectInfo* info) {
      ASSERT(length > 0);
      ObjectGroup* group = reinterpret_cast<ObjectGroup*>(
          malloc(OFFSET_OF(ObjectGroup, objects_[length])));
      group->length_ = length;
      group->info_ = info;
      CopyWords(group->objects_, handles, static_cast<int>(length));
      return group;
    }
  
    void Dispose() {
      if (info_ != NULL) info_->Dispose();
      free(this);
    }
  
    size_t length_;
    v8::RetainedObjectInfo* info_;
    Object** objects_[1];  // Variable sized array.
  
   private:
    void* operator new(size_t size);
    void operator delete(void* p);
    ~ObjectGroup();
    DISALLOW_IMPLICIT_CONSTRUCTORS(ObjectGroup);
  };
  
  
  // An implicit references group consists of two parts: a parent object and
  // a list of children objects.  If the parent is alive, all the children
  // are alive too.
  class ImplicitRefGroup {
   public:
    static ImplicitRefGroup* New(HeapObject** parent,
                                 Object*** children,
                                 size_t length) {
      ASSERT(length > 0);
      ImplicitRefGroup* group = reinterpret_cast<ImplicitRefGroup*>(
          malloc(OFFSET_OF(ImplicitRefGroup, children_[length])));
      group->parent_ = parent;
      group->length_ = length;
      CopyWords(group->children_, children, static_cast<int>(length));
      return group;
    }
  
    void Dispose() {
      free(this);
    }
  
    HeapObject** parent_;
    size_t length_;
    Object** children_[1];  // Variable sized array.
  
   private:
    void* operator new(size_t size);
    void operator delete(void* p);
    ~ImplicitRefGroup();
    DISALLOW_IMPLICIT_CONSTRUCTORS(ImplicitRefGroup);
  };
  
  
  typedef void (*WeakReferenceGuest)(Object* object, void* parameter);
  
  class GlobalHandles {
   public:
    ~GlobalHandles();
  
    // Creates a new global handle that is alive until Destroy is called.
    Handle<Object> Create(Object* value);
  
    // Destroy a global handle.
    void Destroy(Object** location);
  
    // Make the global handle weak and set the callback parameter for the
    // handle.  When the garbage collector recognizes that only weak global
    // handles point to an object the handles are cleared and the callback
    // function is invoked (for each handle) with the handle and corresponding
    // parameter as arguments.  Note: cleared means set to Smi::FromInt(0). The
    // reason is that Smi::FromInt(0) does not change during garage collection.
    void MakeWeak(Object** location,
                  void* parameter,
                  WeakReferenceCallback callback);
  
    static void SetWrapperClassId(Object** location, uint16_t class_id);
    static uint16_t GetWrapperClassId(Object** location);
  
    // Returns the current number of weak handles.
    int NumberOfWeakHandles() { return number_of_weak_handles_; }
  
    void RecordStats(HeapStats* stats);
  
    // Returns the current number of weak handles to global objects.
    // These handles are also included in NumberOfWeakHandles().
    int NumberOfGlobalObjectWeakHandles() {
      return number_of_global_object_weak_handles_;
    }
  
    // Returns the current number of handles to global objects.
    int NumberOfGlobalHandles() {
      return number_of_global_handles_;
    }
  
    // Clear the weakness of a global handle.
    void ClearWeakness(Object** location);
  
    // Clear the weakness of a global handle.
    void MarkIndependent(Object** location);
  
    // Mark the reference to this object externaly unreachable.
    void MarkPartiallyDependent(Object** location);
  
    static bool IsIndependent(Object** location);
  
    // Tells whether global handle is near death.
    static bool IsNearDeath(Object** location);
  
    // Tells whether global handle is weak.
    static bool IsWeak(Object** location);
  
    // Process pending weak handles.
    // Returns true if next major GC is likely to collect more garbage.
    bool PostGarbageCollectionProcessing(GarbageCollector collector,
                                         GCTracer* tracer);
  
    // Iterates over all strong handles.
    void IterateStrongRoots(ObjectVisitor* v);
  
    // Iterates over all handles.
    void IterateAllRoots(ObjectVisitor* v);
  
    // Iterates over all handles that have embedder-assigned class ID.
    void IterateAllRootsWithClassIds(ObjectVisitor* v);
  
    // Iterates over all weak roots in heap.
    void IterateWeakRoots(ObjectVisitor* v);
  
    // Iterates over weak roots that are bound to a given callback.
    void IterateWeakRoots(WeakReferenceGuest f,
                          WeakReferenceCallback callback);
  
    // Find all weak handles satisfying the callback predicate, mark
    // them as pending.
    void IdentifyWeakHandles(WeakSlotCallback f);
  
    // NOTE: Three ...NewSpace... functions below are used during
    // scavenge collections and iterate over sets of handles that are
    // guaranteed to contain all handles holding new space objects (but
    // may also include old space objects).
  
    // Iterates over strong and dependent handles. See the node above.
    void IterateNewSpaceStrongAndDependentRoots(ObjectVisitor* v);
  
    // Finds weak independent or partially independent handles satisfying
    // the callback predicate and marks them as pending. See the note above.
    void IdentifyNewSpaceWeakIndependentHandles(WeakSlotCallbackWithHeap f);
  
    // Iterates over weak independent or partially independent handles.
    // See the note above.
    void IterateNewSpaceWeakIndependentRoots(ObjectVisitor* v);
  
    // Iterate over objects in object groups that have at least one object
    // which requires visiting. The callback has to return true if objects
    // can be skipped and false otherwise.
    bool IterateObjectGroups(ObjectVisitor* v, WeakSlotCallbackWithHeap can_skip);
  
    // Add an object group.
    // Should be only used in GC callback function before a collection.
    // All groups are destroyed after a garbage collection.
    void AddObjectGroup(Object*** handles,
                        size_t length,
                        v8::RetainedObjectInfo* info);
  
    // Add an implicit references' group.
    // Should be only used in GC callback function before a collection.
    // All groups are destroyed after a mark-compact collection.
    void AddImplicitReferences(HeapObject** parent,
                               Object*** children,
                               size_t length);
  
    // Returns the object groups.
    List<ObjectGroup*>* object_groups() { return &object_groups_; }
  
    // Returns the implicit references' groups.
    List<ImplicitRefGroup*>* implicit_ref_groups() {
      return &implicit_ref_groups_;
    }
  
    // Remove bags, this should only happen after GC.
    void RemoveObjectGroups();
    void RemoveImplicitRefGroups();
  
    // Tear down the global handle structure.
    void TearDown();
  
    Isolate* isolate() { return isolate_; }
  
  #ifdef DEBUG
    void PrintStats();
    void Print();
  #endif
  
   private:
    explicit GlobalHandles(Isolate* isolate);
  
    // Internal node structures.
    class Node;
    class NodeBlock;
    class NodeIterator;
  
    Isolate* isolate_;
  
    // Field always containing the number of weak and near-death handles.
    int number_of_weak_handles_;
  
    // Field always containing the number of weak and near-death handles
    // to global objects.  These objects are also included in
    // number_of_weak_handles_.
    int number_of_global_object_weak_handles_;
  
    // Field always containing the number of handles to global objects.
    int number_of_global_handles_;
  
    // List of all allocated node blocks.
    NodeBlock* first_block_;
  
    // List of node blocks with used nodes.
    NodeBlock* first_used_block_;
  
    // Free list of nodes.
    Node* first_free_;
  
    // Contains all nodes holding new space objects. Note: when the list
    // is accessed, some of the objects may have been promoted already.
    List<Node*> new_space_nodes_;
  
    int post_gc_processing_count_;
  
    List<ObjectGroup*> object_groups_;
    List<ImplicitRefGroup*> implicit_ref_groups_;
  
    friend class Isolate;
  
    DISALLOW_COPY_AND_ASSIGN(GlobalHandles);
  };
  
  
  } }  // namespace v8::internal
  
  #endif  // V8_GLOBAL_HANDLES_H_
  