Use a tag bit for indicating prologue weak persistent handles, this avoids

runtime/vm/dart_api_state.h

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_DART_API_STATE_H_
 #define VM_DART_API_STATE_H_
 
 #include "include/dart_api.h"
 
 #include "platform/thread.h"
@@ skipping 153 matching lines @@
   PersistentHandle* Next() {
     return reinterpret_cast<PersistentHandle*>(raw_);
   }
   void SetNext(PersistentHandle* free_list) {
     raw_ = reinterpret_cast<RawObject*>(free_list);
     ASSERT(!raw_->IsHeapObject());
   }
   void FreeHandle(PersistentHandle* free_list) {
     SetNext(free_list);
   }
 

[Ivan Posva, 2014/03/03 21:00:19]

external and Cast might need to be added here.

[siva, 2014/03/04 00:24:48]

Done.

   RawObject* raw_;
   DISALLOW_ALLOCATION();  // Allocated through AllocateHandle methods.
   DISALLOW_COPY_AND_ASSIGN(PersistentHandle);
 };
 
 
 // Implementation of persistent handles which are handed out through the
 // dart API.
 class FinalizablePersistentHandle {
  public:
   // Accessors.
   RawObject* raw() const { return raw_; }
   void set_raw(RawObject* raw) { raw_ = raw; }
   void set_raw(const LocalHandle& ref) { raw_ = ref.raw(); }
   void set_raw(const Object& object) { raw_ = object.raw(); }
   RawObject** raw_addr() { return &raw_; }
   static intptr_t raw_offset() {
     return OFFSET_OF(FinalizablePersistentHandle, raw_);
   }
   void* peer() const { return peer_; }
   void set_peer(void* peer) { peer_ = peer; }
   Dart_WeakPersistentHandleFinalizer callback() const { return callback_; }
   void set_callback(Dart_WeakPersistentHandleFinalizer callback) {
     callback_ = callback;
   }
-
-  static void Finalize(FinalizablePersistentHandle* handle) {
+  static bool IsPrologueWeakPersistentHandle(Dart_WeakPersistentHandle handle) {
+    uword addr = reinterpret_cast<uword>(handle);
+    return (addr & kWeakPersistentTagMask) == kPrologueWeakPersistentTag;
+  }
+  static Dart_WeakPersistentHandle AsDartPrologueWeakPersistentHandle(

[Ivan Posva, 2014/03/03 21:00:19]

Make this a method such as external on FinalizablePersistentHandle?

[siva, 2014/03/04 00:24:48]

Done.

+      FinalizablePersistentHandle* handle) {
+    uword addr = reinterpret_cast<uword>(handle);
+    return reinterpret_cast<Dart_WeakPersistentHandle>(
+        addr | kPrologueWeakPersistentTag);
+  }
+  static Dart_WeakPersistentHandle AsDartWeakPersistentHandle(
+      FinalizablePersistentHandle* handle) {
+    return reinterpret_cast<Dart_WeakPersistentHandle>(handle);
+  }
+  static FinalizablePersistentHandle* AsFinalizablePersistentHandle(

[Ivan Posva, 2014/03/03 21:00:19]

How about renaming this as
FinalizablePersistentHandle::Cast(Dart_WeakPersistentHandle)?

[siva, 2014/03/04 00:24:48]

Done.

+      Dart_WeakPersistentHandle handle) {
+    uword addr = reinterpret_cast<uword>(handle);
+    return reinterpret_cast<FinalizablePersistentHandle*>(
+        addr & ~kWeakPersistentTagMask);
+  }
+  static void Finalize(FinalizablePersistentHandle* handle,
+                       bool is_prologue_weak) {
     Dart_WeakPersistentHandleFinalizer callback = handle->callback();
     if (callback != NULL) {
       void* peer = handle->peer();
       handle->Clear();
-      (*callback)(reinterpret_cast<Dart_WeakPersistentHandle>(handle), peer);
+      Dart_WeakPersistentHandle object =
+          is_prologue_weak ? AsDartPrologueWeakPersistentHandle(handle) :
+                             AsDartWeakPersistentHandle(handle);
+      (*callback)(object, peer);
     } else {
       handle->Clear();
     }
   }
 
  private:
+  enum {
+    kWeakPersistentTag = 0,
+    kPrologueWeakPersistentTag = 1,
+    kWeakPersistentTagSize = 1,
+    kWeakPersistentTagMask = 1,
+  };
+
   friend class FinalizablePersistentHandles;
 
   FinalizablePersistentHandle() : raw_(NULL), peer_(NULL), callback_(NULL) { }
   ~FinalizablePersistentHandle() { }
 
   // Overload the raw_ field as a next pointer when adding freed
   // handles to the free list.
   FinalizablePersistentHandle* Next() {
     return reinterpret_cast<FinalizablePersistentHandle*>(raw_);
   }
@@ skipping 173 matching lines @@
 static const int kOffsetOfRawPtrInFinalizablePersistentHandle = 0;
 class FinalizablePersistentHandles
     : Handles<kFinalizablePersistentHandleSizeInWords,
               kFinalizablePersistentHandlesPerChunk,
               kOffsetOfRawPtrInFinalizablePersistentHandle> {
  public:
   FinalizablePersistentHandles()
       : Handles<kFinalizablePersistentHandleSizeInWords,
                 kFinalizablePersistentHandlesPerChunk,
                 kOffsetOfRawPtrInFinalizablePersistentHandle>(),
-                                   free_list_(NULL) { }
+        free_list_(NULL) { }
   ~FinalizablePersistentHandles() {
     free_list_ = NULL;
   }
 
   // Accessors.
   FinalizablePersistentHandle* free_list() const { return free_list_; }
   void set_free_list(FinalizablePersistentHandle* value) { free_list_ = value; }
 
   // Visit all handles stored in the various handle blocks.
-  void VisitHandles(HandleVisitor* visitor) {
+  void VisitHandles(HandleVisitor* visitor, bool is_prologue_weak) {
     Handles<kFinalizablePersistentHandleSizeInWords,
             kFinalizablePersistentHandlesPerChunk,
-            kOffsetOfRawPtrInFinalizablePersistentHandle>::Visit(visitor);
+            kOffsetOfRawPtrInFinalizablePersistentHandle>::Visit(
+                visitor, is_prologue_weak);
   }
 
   // Visit all object pointers stored in the various handles.
   void VisitObjectPointers(ObjectPointerVisitor* visitor) {
     Handles<kFinalizablePersistentHandleSizeInWords,
             kFinalizablePersistentHandlesPerChunk,
             kOffsetOfRawPtrInFinalizablePersistentHandle>::VisitObjectPointers(
                 visitor);
   }
 
@@ skipping 42 matching lines @@
         values_(values), num_values_(values_length) {
   }
   ~WeakReferenceSet() {}
 
   WeakReferenceSet* next() const { return next_; }
 
   intptr_t num_keys() const { return num_keys_; }
   RawObject** get_key(intptr_t i) {
     ASSERT(i >= 0);
     ASSERT(i < num_keys_);
-    return (reinterpret_cast<FinalizablePersistentHandle*>(keys_[i]))->
-        raw_addr();
+    FinalizablePersistentHandle* ref =
+        FinalizablePersistentHandle::AsFinalizablePersistentHandle(keys_[i]);
+    return ref->raw_addr();
   }
 
   intptr_t num_values() const { return num_values_; }
   RawObject** get_value(intptr_t i) {
     ASSERT(i >= 0);
     ASSERT(i < num_values_);
-    return (reinterpret_cast<FinalizablePersistentHandle*>(values_[i]))->
-        raw_addr();
+    FinalizablePersistentHandle* ref =
+        FinalizablePersistentHandle::AsFinalizablePersistentHandle(values_[i]);
+    return ref->raw_addr();
   }
 
   static WeakReferenceSet* Pop(WeakReferenceSet** queue) {
     ASSERT(queue != NULL);
     WeakReferenceSet* head = *queue;
     if (head != NULL) {
       *queue = head->next();
       head->next_ = NULL;
     }
     return head;
@@ skipping 143 matching lines @@
       scope = scope->previous();
     }
     persistent_handles().VisitObjectPointers(visitor);
     if (visit_prologue_weak_handles) {
       prologue_weak_persistent_handles().VisitObjectPointers(visitor);
     }
   }
 
   void VisitWeakHandles(HandleVisitor* visitor,
                         bool visit_prologue_weak_handles) {
-    weak_persistent_handles().VisitHandles(visitor);
+    weak_persistent_handles().VisitHandles(visitor, false);
     if (visit_prologue_weak_handles) {
-      prologue_weak_persistent_handles().VisitHandles(visitor);
+      prologue_weak_persistent_handles().VisitHandles(visitor, true);
     }
   }
 
   bool IsValidLocalHandle(Dart_Handle object) const {
     ApiLocalScope* scope = top_scope_;
     while (scope != NULL) {
       if (scope->local_handles()->IsValidHandle(object)) {
         return true;
       }
       scope = scope->previous();
@@ skipping 114 matching lines @@
           ApiNativeScope::Current()->zone()) {}
   ApiGrowableArray()
       : BaseGrowableArray<T, ValueObject>(
           ApiNativeScope::Current()->zone()) {}
 };
 
 
 }  // namespace dart
 
 #endif  // VM_DART_API_STATE_H_