Make WeakPtr thread-safe, i.e. allow cross-thread copying of WeakPtr

base/memory/weak_ptr.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Weak pointers help in cases where you have many objects referring back to a
 // shared object and you wish for the lifetime of the shared object to not be
 // bound to the lifetime of the referrers.  In other words, this is useful when
 // reference counting is not a good fit.
 //
 // A common alternative to weak pointers is to have the shared object hold a
@@ skipping 51 matching lines @@
 namespace internal {
 // These classes are part of the WeakPtr implementation.
 // DO NOT USE THESE CLASSES DIRECTLY YOURSELF.
 
 class BASE_EXPORT WeakReference {
  public:
   // While Flag is bound to a specific thread, it may be deleted from another
   // via base::WeakPtr::~WeakPtr().
   class Flag : public RefCountedThreadSafe<Flag> {
    public:
-    explicit Flag(Flag** handle);
+    explicit Flag();
 
     void Invalidate();
     bool IsValid() const;
 
     void DetachFromThread() { thread_checker_.DetachFromThread(); }
 
    private:
     friend class base::RefCountedThreadSafe<Flag>;
 
     ~Flag();
 
     ThreadChecker thread_checker_;
-    Flag** handle_;
+    bool valid_;

[darin (slow to review), 2011/08/18 18:29:06]

nit: valid_ -> is_valid_

   };
 
   WeakReference();
-  WeakReference(Flag* flag);
+  WeakReference(scoped_refptr<Flag> flag);

[darin (slow to review), 2011/08/18 18:29:06]

nit: WeakReference(const scoped_refptr<Flag>& flag);

[willchan no longer on Chromium, 2011/08/18 19:14:12]

While I'm glad you seem to have this preference here (I share this preference),
I think chromium-dev disagreed. We should be using Flag* here instead. See
http://groups.google.com/a/chromium.org/group/chromium-dev/browse_thread/thre....

   ~WeakReference();
 
   bool is_valid() const;
 
  private:
   scoped_refptr<Flag> flag_;
 };
 
 class BASE_EXPORT WeakReferenceOwner {
  public:
   WeakReferenceOwner();
   ~WeakReferenceOwner();
 
   WeakReference GetRef() const;
 
   bool HasRefs() const {
-    return flag_ != NULL;
+    return flag_.get() && !flag_->HasOneRef();
   }
 
   void Invalidate();
 
   // Indicates that this object will be used on another thread from now on.
   void DetachFromThread() {
     if (flag_) flag_->DetachFromThread();
   }
 
  private:
-  mutable WeakReference::Flag* flag_;
+  mutable scoped_refptr<WeakReference::Flag> flag_;
 };
 
 // This class simplifies the implementation of WeakPtr's type conversion
 // constructor by avoiding the need for a public accessor for ref_.  A
 // WeakPtr<T> cannot access the private members of WeakPtr<U>, so this
 // base class gives us a way to access ref_ in a protected fashion.
 class BASE_EXPORT WeakPtrBase {
  public:
   WeakPtrBase();
   ~WeakPtrBase();
@@ skipping 118 matching lines @@
 
  private:
   internal::WeakReferenceOwner weak_reference_owner_;
   T* ptr_;
   DISALLOW_IMPLICIT_CONSTRUCTORS(WeakPtrFactory);
 };
 
 }  // namespace base
 
 #endif  // BASE_MEMORY_WEAK_PTR_H_