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

base/memory/weak_ptr.h

Index: base/memory/weak_ptr.h
diff --git a/base/memory/weak_ptr.h b/base/memory/weak_ptr.h
index abda1af2eaa7e0abf54a9a79bd0d9f7a4a526538..792dc0f35a41a87ad9c1c0e185a453c260c05db6 100644
--- a/base/memory/weak_ptr.h
+++ b/base/memory/weak_ptr.h
@@ -69,7 +69,7 @@ class BASE_EXPORT WeakReference {
   // via base::WeakPtr::~WeakPtr().
   class Flag : public RefCountedThreadSafe<Flag> {
    public:
-    explicit Flag(Flag** handle);
+    explicit Flag();
 
     void Invalidate();
     bool IsValid() const;
@@ -82,11 +82,11 @@ class BASE_EXPORT WeakReference {
     ~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;
@@ -103,7 +103,7 @@ class BASE_EXPORT WeakReferenceOwner {
   WeakReference GetRef() const;
 
   bool HasRefs() const {
-    return flag_ != NULL;
+    return flag_.get() && !flag_->HasOneRef();
   }
 
   void Invalidate();
@@ -114,7 +114,7 @@ class BASE_EXPORT WeakReferenceOwner {
   }
 
  private:
-  mutable WeakReference::Flag* flag_;
+  mutable scoped_refptr<WeakReference::Flag> flag_;
 };
 
 // This class simplifies the implementation of WeakPtr's type conversion