Let WeakPtrFactory operations fail once its dtor is called

base/memory/weak_ptr.h

 // Copyright (c) 2012 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.
 //
 // Thread-safety notes:
@@ skipping 214 matching lines @@
 // control how it exposes weak pointers to itself.  This is helpful if you only
 // need weak pointers within the implementation of a class.  This class is also
 // useful when working with primitive types.  For example, you could have a
 // WeakPtrFactory<bool> that is used to pass around a weak reference to a bool.
 template <class T>
 class WeakPtrFactory {
  public:
   explicit WeakPtrFactory(T* ptr) : ptr_(ptr) {
   }
 
+  ~WeakPtrFactory() {
+    ptr_ = NULL;
+  }
+
   WeakPtr<T> GetWeakPtr() {
+    CHECK(ptr_);

[darin (slow to review), 2012/05/18 17:45:13]

I think it is a bit bloaty to inline this into every callsite.  If you want to
null-check ptr_ in release builds, then we should find a way to de-inline.

     return WeakPtr<T>(weak_reference_owner_.GetRef(), ptr_);
   }
 
   // Call this method to invalidate all existing weak pointers.
   void InvalidateWeakPtrs() {
+    CHECK(ptr_);
     weak_reference_owner_.Invalidate();
   }
 
   // Call this method to determine if any weak pointers exist.
   bool HasWeakPtrs() const {
+    CHECK(ptr_);
     return weak_reference_owner_.HasRefs();
   }
 
   // Indicates that this object will be used on another thread from now on.
   void DetachFromThread() {
+    CHECK(ptr_);
     weak_reference_owner_.DetachFromThread();
   }
 
  private:
   internal::WeakReferenceOwner weak_reference_owner_;
   T* ptr_;
   DISALLOW_IMPLICIT_CONSTRUCTORS(WeakPtrFactory);
 };
 
 }  // namespace base
 
 #endif  // BASE_MEMORY_WEAK_PTR_H_