Phantom references support internal fields

src/global-handles.cc

 // Copyright 2009 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 
 #include "src/api.h"
 #include "src/global-handles.h"
 
 #include "src/vm-state-inl.h"
@@ skipping 15 matching lines @@
 
 class GlobalHandles::Node {
  public:
   // State transition diagram:
   // FREE -> NORMAL <-> WEAK -> PENDING -> NEAR_DEATH -> { NORMAL, WEAK, FREE }
   enum State {
     FREE = 0,
     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.
+    NEAR_DEATH, // Callback has informed the handle is near death.
+    NUMBER_OF_NODE_STATES
+  };
+
+  enum WeaknessType {
+    NORMAL_WEAK,   // Embedder gets a handle to the dying object.
+    PHANTOM_WEAK,  // Embedder gets the parameter they passed in earlier.
+    INTERNAL_FIELDS_WEAK  // Embedded gets 1 or 2 internal fields from dying object.
   };
 
   // Maps handle location (slot) to the containing node.
   static Node* FromLocation(Object** location) {
     DCHECK(OFFSET_OF(Node, object_) == 0);
     return reinterpret_cast<Node*>(location);
   }
 
   Node() {
     DCHECK(OFFSET_OF(Node, class_id_) == Internals::kNodeClassIdOffset);
@@ skipping 38 matching lines @@
     object_ = object;
     class_id_ = v8::HeapProfiler::kPersistentHandleNoClassId;
     set_independent(false);
     set_partially_dependent(false);
     set_state(NORMAL);
     parameter_or_next_free_.parameter = NULL;
     weak_callback_ = NULL;
     IncreaseBlockUses();
   }
 
+  void Zap() {
+    DCHECK(state() != FREE);
+    // Zap the values for eager trapping.
+    object_ = reinterpret_cast<Object*>(kGlobalHandleZapValue);
+  }
+
   void Release() {
     DCHECK(state() != FREE);
     set_state(FREE);
     // Zap the values for eager trapping.
     object_ = reinterpret_cast<Object*>(kGlobalHandleZapValue);
     class_id_ = v8::HeapProfiler::kPersistentHandleNoClassId;
     set_independent(false);
     set_partially_dependent(false);
     weak_callback_ = NULL;
     DecreaseBlockUses();
@@ skipping 34 matching lines @@
     flags_ = IsPartiallyDependent::update(flags_, v);
   }
 
   bool is_in_new_space_list() {
     return IsInNewSpaceList::decode(flags_);
   }
   void set_in_new_space_list(bool v) {
     flags_ = IsInNewSpaceList::update(flags_, v);
   }
 
-  bool is_zapped_during_weak_callback() {
-    return IsZappedDuringWeakCallback::decode(flags_);
+  WeaknessType weakness_type() const {
+    return NodeWeaknessType::decode(flags_);
   }
-  void set_is_zapped_during_weak_callback(bool v) {
-    flags_ = IsZappedDuringWeakCallback::update(flags_, v);
+  void set_weakness_type(WeaknessType t) {
+    flags_ = NodeWeaknessType::update(flags_, t);
   }
 
   bool IsNearDeath() const {
     // Check for PENDING to ensure correct answer when processing callbacks.
     return state() == PENDING || state() == NEAR_DEATH;
   }
 
   bool IsWeak() const { return state() == WEAK; }
 
   bool IsRetainer() const { return state() != FREE; }
@@ skipping 23 matching lines @@
   }
   void clear_partially_dependent() { set_partially_dependent(false); }
 
   // Callback accessor.
   // TODO(svenpanne) Re-enable or nuke later.
   // WeakReferenceCallback callback() { return callback_; }
 
   // Callback parameter accessors.
   void set_parameter(void* parameter) {
     DCHECK(state() != FREE);
+    DCHECK(weakness_type() == NORMAL_WEAK || weakness_type() == PHANTOM_WEAK);
     parameter_or_next_free_.parameter = parameter;
   }
   void* parameter() const {
     DCHECK(state() != FREE);
     return parameter_or_next_free_.parameter;
   }
 
+  void set_internal_fields(int internal_field_index1, int internal_field_index2) {
+    DCHECK(weakness_type() == INTERNAL_FIELDS_WEAK);
+    parameter_or_next_free_.internal_field_indeces.internal_field1 = internal_field_index1;
+    parameter_or_next_free_.internal_field_indeces.internal_field2 = internal_field_index2;
+  }
+
+  int internal_field1() const {
+    DCHECK(weakness_type() == INTERNAL_FIELDS_WEAK);
+    return parameter_or_next_free_.internal_field_indeces.internal_field1;
+  }
+
+  int internal_field2() const {
+    DCHECK(weakness_type() == INTERNAL_FIELDS_WEAK);
+    return parameter_or_next_free_.internal_field_indeces.internal_field2;
+  }
+
   // Accessors for next free node in the free list.
   Node* next_free() {
     DCHECK(state() == FREE);
     return parameter_or_next_free_.next_free;
   }
   void set_next_free(Node* value) {
     DCHECK(state() == FREE);
     parameter_or_next_free_.next_free = value;
   }
 
-  void MakeWeak(void* parameter, WeakCallback weak_callback,
-                bool is_zapped_during_weak_callback = false) {
+  void MakeWeak(void* parameter, WeakCallback weak_callback) {
     DCHECK(weak_callback != NULL);
     DCHECK(state() != FREE);
     CHECK(object_ != NULL);
     set_state(WEAK);
+    set_weakness_type(Node::NORMAL_WEAK);
     set_parameter(parameter);
-    set_is_zapped_during_weak_callback(is_zapped_during_weak_callback);
     weak_callback_ = weak_callback;
   }
 
+  void MakePhantom(void* parameter, PhantomCallback phantom_callback,
+                   int internal_field_index1, int internal_field_index2) {
+    //FIXME: Where to put the indeces...
+    DCHECK(phantom_callback != NULL);
+    DCHECK(state() != FREE);
+    CHECK(object_ != NULL);
+    set_state(WEAK);
+    if (parameter != NULL) {
+      DCHECK(internal_field_index1 == v8::Object::kNoInternalFieldIndex);
+      DCHECK(internal_field_index2 == v8::Object::kNoInternalFieldIndex);
+      set_weakness_type(Node::PHANTOM_WEAK);
+      set_parameter(parameter);
+    } else {
+      set_weakness_type(Node::INTERNAL_FIELDS_WEAK);
+      set_internal_fields(internal_field_index1, internal_field_index2);
+    }
+    weak_callback_ = reinterpret_cast<WeakCallback>(phantom_callback);
+  }
+
   void* ClearWeakness() {
     DCHECK(state() != FREE);
     void* p = parameter();
     set_state(NORMAL);
     set_parameter(NULL);
     return p;
   }
 
   bool PostGarbageCollectionProcessing(Isolate* isolate) {
     if (state() != Node::PENDING) return false;
     if (weak_callback_ == NULL) {
       Release();
       return false;
     }
-    void* param = parameter();
     set_state(NEAR_DEATH);
-    set_parameter(NULL);
 
-    Object** object = location();
     {
       // Check that we are not passing a finalized external string to
       // the callback.
       DCHECK(!object_->IsExternalOneByteString() ||
              ExternalOneByteString::cast(object_)->resource() != NULL);
       DCHECK(!object_->IsExternalTwoByteString() ||
              ExternalTwoByteString::cast(object_)->resource() != NULL);
       // Leaving V8.
       VMState<EXTERNAL> vmstate(isolate);
       HandleScope handle_scope(isolate);
-      if (is_zapped_during_weak_callback()) {
-        // Phantom weak pointer case.
-        DCHECK(*object == Smi::FromInt(kPhantomReferenceZap));
-        // Make data with a null handle.
-        v8::WeakCallbackData<v8::Value, void> data(
-            reinterpret_cast<v8::Isolate*>(isolate), v8::Local<v8::Object>(),
-            param);
-        weak_callback_(data);
-        if (state() != FREE) {
-          // Callback does not have to clear the global handle if it is a
-          // phantom handle.
-          Release();
-        }
-      } else {
+      if (weakness_type() == Node::NORMAL_WEAK) {
+        Object** object = location();
         Handle<Object> handle(*object, isolate);
         v8::WeakCallbackData<v8::Value, void> data(
             reinterpret_cast<v8::Isolate*>(isolate), v8::Utils::ToLocal(handle),
-            param);
+            parameter());
+        set_parameter(NULL);
         weak_callback_(data);
+      } else {
+        v8::PhantomCallbackData<void>::Callback callback =
+            reinterpret_cast<v8::PhantomCallbackData<void>::Callback>(weak_callback_);
+        if (weakness_type() == Node::PHANTOM_WEAK) {
+          // Phantom weak pointer case.
+          DCHECK(*location() == Smi::FromInt(kPhantomReferenceZap));
+          // Make data with a null handle.
+          v8::PhantomCallbackData<void> data(
+              reinterpret_cast<v8::Isolate*>(isolate), parameter());
+          callback(data);
+          if (state() != FREE) {
+            // Callback does not have to clear the global handle if it is a
+            // phantom handle.
+            Release();
+          }
+          set_parameter(NULL);
+        } else {
+          DCHECK(weakness_type() == Node::INTERNAL_FIELDS_WEAK);
+          // Phantom weak pointer case, passing internal fields instead of parameter.
+          Handle<Object> handle(object(), isolate);
+          Handle<JSObject> jsobject = Handle<JSObject>::cast(handle);
+          v8::PhantomCallbackData<void> data(
+              reinterpret_cast<v8::Isolate*>(isolate),
+              jsobject->GetInternalField(internal_field1()),
+              jsobject->GetInternalField(internal_field2()));
+          // In the future, we want to delay the callback. In that case we will zap
+          // when we queue up, to stop the C++ side accessing the dead V8 object,
+          // but we will call Release only after the callback (allowing the node
+          // to be reused).
+          Zap();
+          callback(data);
+          Release();
+          set_internal_fields(v8::Object::kNoInternalFieldIndex, v8::Object::kNoInternalFieldIndex);
+        }
       }
     }
     // Absence of explicit cleanup or revival of weak handle
     // in most of the cases would lead to memory leak.
     CHECK(state() != NEAR_DEATH);
     return true;
   }
 
   inline GlobalHandles* GetGlobalHandles();
 
@@ skipping 10 matching lines @@
   // Note: the most aligned fields should go first.
 
   // Wrapper class ID.
   uint16_t class_id_;
 
   // Index in the containing handle block.
   uint8_t index_;
 
   // This stores three flags (independent, partially_dependent and
   // in_new_space_list) and a State.
-  class NodeState : public BitField<State, 0, 4> {};
-  class IsIndependent : public BitField<bool, 4, 1> {};
-  class IsPartiallyDependent : public BitField<bool, 5, 1> {};
-  class IsInNewSpaceList : public BitField<bool, 6, 1> {};
-  class IsZappedDuringWeakCallback : public BitField<bool, 7, 1> {};
+  class NodeState : public BitField<State, 0, 3> {};
+  class IsIndependent : public BitField<bool, 3, 1> {};
+  class IsPartiallyDependent : public BitField<bool, 4, 1> {};
+  class IsInNewSpaceList : public BitField<bool, 5, 1> {};
+  class NodeWeaknessType : public BitField<WeaknessType, 6, 2> {};
 
   uint8_t flags_;
 
   // Handle specific callback - might be a weak reference in disguise.
   WeakCallback weak_callback_;
 
   // Provided data for callback.  In FREE state, this is used for
   // the free list link.
   union {
     void* parameter;
+    struct {
+      uint16_t internal_field1;
+      uint16_t internal_field2;
+    } internal_field_indeces;
     Node* next_free;
   } parameter_or_next_free_;
 
   DISALLOW_COPY_AND_ASSIGN(Node);
 };
 
 
 class GlobalHandles::NodeBlock {
  public:
   static const int kSize = 256;
@@ skipping 165 matching lines @@
   return Node::FromLocation(location)->GetGlobalHandles()->Create(*location);
 }
 
 
 void GlobalHandles::Destroy(Object** location) {
   if (location != NULL) Node::FromLocation(location)->Release();
 }
 
 
 void GlobalHandles::MakeWeak(Object** location, void* parameter,
-                             WeakCallback weak_callback, PhantomState phantom) {
-  Node::FromLocation(location)
-      ->MakeWeak(parameter, weak_callback, phantom == Phantom);
+                             WeakCallback weak_callback) {
+  Node::FromLocation(location)->MakeWeak(parameter, weak_callback);
 }
 
 
+void GlobalHandles::MakePhantom(Object** location, void* parameter,
+                                PhantomCallback phantom_callback,
+                                int internal_field_index1,
+                                int internal_field_index2) {
+  Node::FromLocation(location)
+      ->MakePhantom(parameter, phantom_callback, internal_field_index1, internal_field_index2);
+}
+
+
 void* GlobalHandles::ClearWeakness(Object** location) {
   return Node::FromLocation(location)->ClearWeakness();
 }
 
 
 void GlobalHandles::MarkIndependent(Object** location) {
   Node::FromLocation(location)->MarkIndependent();
 }
 
 
@@ skipping 14 matching lines @@
 
 bool GlobalHandles::IsWeak(Object** location) {
   return Node::FromLocation(location)->IsWeak();
 }
 
 
 void GlobalHandles::IterateWeakRoots(ObjectVisitor* v) {
   for (NodeIterator it(this); !it.done(); it.Advance()) {
     Node* node = it.node();
     if (node->IsWeakRetainer()) {
-      if (node->state() == Node::PENDING &&
-          node->is_zapped_during_weak_callback()) {
-        *(node->location()) = Smi::FromInt(kPhantomReferenceZap);
+      // Weakness type can be normal, phantom or internal fields.
+      // For normal weakness we mark through the handle so that
+      // the object and things reachable from it are available
+      // to the callback.
+      // In the case of phantom we can zap the object handle now
+      // and we won't need it, so we don't need to mark through it.
+      // In the internal fields case we will need the internal
+      // fields, so we can't zap the handle, but we don't need to
+      // mark through it, because it will die in this GC round.
+        v->VisitPointer(node->location());
+      if (node->state() == Node::PENDING) {
+        if (node->weakness_type() == Node::PHANTOM_WEAK) {
+          *(node->location()) = Smi::FromInt(kPhantomReferenceZap);

[jochen (gone - plz use gerrit), 2014/11/24 12:27:53]

if you zap the handle here, how can you get to object() when you read out the
internal fields?

[Erik Corry, 2014/11/24 12:38:26]

For the INTERNAL_FIELDS case we don't zap here.

+        } else if (node->weakness_type() == Node::NORMAL_WEAK) {
+          v->VisitPointer(node->location());
+        }
       } else {
         v->VisitPointer(node->location());
       }
     }
   }
 }
 
 
 void GlobalHandles::IdentifyWeakHandles(WeakSlotCallback f) {
   for (NodeIterator it(this); !it.done(); it.Advance()) {
@@ skipping 28 matching lines @@
   }
 }
 
 
 void GlobalHandles::IterateNewSpaceWeakIndependentRoots(ObjectVisitor* v) {
   for (int i = 0; i < new_space_nodes_.length(); ++i) {
     Node* node = new_space_nodes_[i];
     DCHECK(node->is_in_new_space_list());
     if ((node->is_independent() || node->is_partially_dependent()) &&
         node->IsWeakRetainer()) {
-      if (node->is_zapped_during_weak_callback()) {
+      if (node->weakness_type() == Node::PHANTOM_WEAK) {
         *(node->location()) = Smi::FromInt(kPhantomReferenceZap);
+      } else if (node->weakness_type() == Node::NORMAL_WEAK) {
+        v->VisitPointer(node->location());
       } else {
-        v->VisitPointer(node->location());
+        // For this case we don't need to trace through, but we don't
+        // zap yet.
+        DCHECK(node->weakness_type() == Node::INTERNAL_FIELDS_WEAK);
       }
     }
   }
 }
 
 
 bool GlobalHandles::IterateObjectGroups(ObjectVisitor* v,
                                         WeakSlotCallbackWithHeap can_skip) {
   ComputeObjectGroupsAndImplicitReferences();
   int last = 0;
@@ skipping 475 matching lines @@
   DCHECK_EQ(isolate->heap()->the_hole_value(), blocks_[block][offset]);
   blocks_[block][offset] = object;
   if (isolate->heap()->InNewSpace(object)) {
     new_space_indices_.Add(size_);
   }
   *index = size_++;
 }
 
 
 } }  // namespace v8::internal