Implement weak persistent handles in the Dart API.

runtime/vm/dart_api_state.h

 // Copyright (c) 2011, 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 "vm/dart_api_impl.h"
@@ skipping 63 matching lines @@
 
 // A distinguished callback which indicates that a persistent handle
 // should not be deleted from the dart api.
 void ProtectedHandleCallback();
 
 
 // Implementation of persistent handles which are handed out through the
 // dart API.
 class PersistentHandle {
  public:
-  enum {
+  enum Kind {
     StrongReference = 0,
     WeakReference,
   };
 
+  // Adaptor for visiting handles with matching reference kind.
+  class Visitor : public HandleVisitor {
+   public:
+    explicit Visitor(ObjectPointerVisitor* visitor, Kind kind) {

[Ivan Posva, 2011/12/19 22:41:36]

explicit not needed here.

[cshapiro, 2011/12/20 00:58:57]

Right, done.

+      ASSERT(visitor != NULL);
+      kind_ = kind;
+      object_pointer_visitor_ = visitor;
+    }
+
+    void Visit(uword* addr) {
+      PersistentHandle* handle = reinterpret_cast<PersistentHandle*>(addr);
+      if (handle->kind() == kind_) {
+        object_pointer_visitor_->VisitPointer(&handle->raw_);
+      }
+    }
+
+    ~Visitor() {}
+
+   private:
+    Kind kind_;
+    ObjectPointerVisitor* object_pointer_visitor_;
+
+    DISALLOW_COPY_AND_ASSIGN(Visitor);
+  };
+
   // Accessors.
   RawObject* raw() const { return raw_; }
   void set_raw(const LocalHandle& ref) { raw_ = ref.raw(); }
   void set_raw(const Object& object) { raw_ = object.raw(); }
   static intptr_t raw_offset() { return OFFSET_OF(PersistentHandle, raw_); }
   void* callback() const { return callback_; }
   void set_callback(void* value) { callback_ = value; }
-  intptr_t type() const { return type_; }
-  void set_type(intptr_t value) { type_ = value; }
+  Kind kind() const { return kind_; }
+  void set_kind(Kind value) { kind_ = value; }
 
   // Some handles are protected from being freed via the external dart api.
   bool IsProtected() {
     return callback() == &ProtectedHandleCallback;
   }
 
  private:
   friend class PersistentHandles;
 
   PersistentHandle() { }
   ~PersistentHandle() { }
 
   // Overload the callback_ field as a next pointer when adding freed
   // handles to the free list.
   PersistentHandle* Next() {
     return reinterpret_cast<PersistentHandle*>(callback_);
   }
   void SetNext(PersistentHandle* free_list) {
     callback_ = reinterpret_cast<void*>(free_list);
   }
   void FreeHandle(PersistentHandle* free_list) {
     raw_ = NULL;
     SetNext(free_list);
   }
 
   RawObject* raw_;
   void* callback_;
-  intptr_t type_;
+  void* peer_;
+  Kind kind_;
   DISALLOW_ALLOCATION();  // Allocated through AllocateHandle methods.
   DISALLOW_COPY_AND_ASSIGN(PersistentHandle);
 };
 
 
 // Local handles repository structure.
 static const int kLocalHandleSizeInWords = sizeof(LocalHandle) / kWordSize;
 static const int kLocalHandlesPerChunk = 64;
 static const int kOffsetOfRawPtrInLocalHandle = 0;
 class LocalHandles : Handles<kLocalHandleSizeInWords,
@@ skipping 56 matching lines @@
   PersistentHandle* free_list() const { return free_list_; }
   void set_free_list(PersistentHandle* value) { free_list_ = value; }
 
   // Visit all object pointers stored in the various handles.
   void VisitObjectPointers(ObjectPointerVisitor* visitor) {
     Handles<kPersistentHandleSizeInWords,
             kPersistentHandlesPerChunk,
             kOffsetOfRawPtrInPersistentHandle>::VisitObjectPointers(visitor);
   }
 
+  // Visits the object pointers in strong persistent handles.
+  void VisitStrongObjectPointers(ObjectPointerVisitor* visitor) {
+    PersistentHandle::Visitor strong_visitor(visitor,
+                                             PersistentHandle::StrongReference);
+    Handles<kPersistentHandleSizeInWords,
+            kPersistentHandlesPerChunk,
+            kOffsetOfRawPtrInPersistentHandle>::Visit(&strong_visitor);
+  }
+
+  // Visits the object pointers in weak persistent handles.
+  void VisitWeakObjectPointers(ObjectPointerVisitor* visitor) {
+    PersistentHandle::Visitor weak_visitor(visitor,
+                                           PersistentHandle::WeakReference);
+    Handles<kPersistentHandleSizeInWords,
+            kPersistentHandlesPerChunk,
+            kOffsetOfRawPtrInPersistentHandle>::Visit(&weak_visitor);
+  }
+
   // Allocates a persistent handle, these have to be destroyed explicitly
   // by calling FreeHandle.
   PersistentHandle* AllocateHandle() {
     PersistentHandle* handle;
     if (free_list_ != NULL) {
       handle = free_list_;
       free_list_ = handle->Next();
     } else {
       handle = reinterpret_cast<PersistentHandle*>(AllocateScopedHandle());
     }
     handle->set_callback(NULL);
-    handle->set_type(PersistentHandle::StrongReference);
+    handle->set_kind(PersistentHandle::StrongReference);
     return handle;
   }
 
   void FreeHandle(PersistentHandle* handle) {
     handle->FreeHandle(free_list());
     set_free_list(handle);
   }
 
   // Validate if passed in handle is a Persistent Handle.
   bool IsValidHandle(Dart_Handle object) const {
@@ skipping 70 matching lines @@
   PersistentHandles& persistent_handles() { return persistent_handles_; }
 
   void UnwindScopes(uword sp) {
     while (top_scope_ != NULL && top_scope_->stack_marker() < sp) {
       ApiLocalScope* scope = top_scope_;
       top_scope_ = top_scope_->previous();
       delete scope;
     }
   }
 
-  void VisitObjectPointers(ObjectPointerVisitor* visitor) {
+  void VisitStrongObjectPointers(ObjectPointerVisitor* visitor) {
     ApiLocalScope* scope = top_scope_;
     while (scope != NULL) {
       scope->local_handles()->VisitObjectPointers(visitor);
       scope = scope->previous();
     }
-    persistent_handles().VisitObjectPointers(visitor);
+
+    persistent_handles().VisitStrongObjectPointers(visitor);
+  }
+
+  void VisitWeakObjectPointers(ObjectPointerVisitor* visitor) {
+    persistent_handles().VisitWeakObjectPointers(visitor);
+  }
+
+  void VisitObjectPointers(ObjectPointerVisitor* visitor) {
+    VisitStrongObjectPointers(visitor);
+    VisitWeakObjectPointers(visitor);
   }
 
   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 66 matching lines @@
   PersistentHandle* null_;
   PersistentHandle* true_;
   PersistentHandle* false_;
 
   DISALLOW_COPY_AND_ASSIGN(ApiState);
 };
 
 }  // namespace dart
 
 #endif  // VM_DART_API_STATE_H_