Make members of Singleton<T> private and only visible to the singleton type.

base/lazy_instance.h

 // Copyright (c) 2008 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.
 
 // The LazyInstance<Type, Traits> class manages a single instance of Type,
 // which will be lazily created on the first time it's accessed.  This class is
 // useful for places you would normally use a function-level static, but you
 // need to have guaranteed thread-safety.  The Type constructor will only ever
 // be called once, even if two threads are racing to create the object.  Get()
 // and Pointer() will always return the same, completely initialized instance.
@@ skipping 109 matching lines @@
 
   Type* Pointer() {
     if (!Traits::kAllowedToAccessOnNonjoinableThread)
       base::ThreadRestrictions::AssertSingletonAllowed();
 
     // We will hopefully have fast access when the instance is already created.
     if ((base::subtle::NoBarrier_Load(&state_) != STATE_CREATED) &&
         NeedsInstance()) {
       // Create the instance in the space provided by |buf_|.
       instance_ = Traits::New(buf_);
-      CompleteInstance(instance_, Traits::Delete);
+      if (Traits::Delete != NULL)  // Will be null for LeakyLazyInstannceTraits

[M-A Ruel, 2010/12/13 17:30:51]

LeakyLazyInstanceTraits

+        CompleteInstance(this, OnExit);
     }
 
     // This annotation helps race detectors recognize correct lock-less
     // synchronization between different threads calling Pointer().
     // We suggest dynamic race detection tool that "Traits::New" above
     // and CompleteInstance(...) happens before "return instance_" below.
     // See the corresponding HAPPENS_BEFORE in CompleteInstance(...).
     ANNOTATE_HAPPENS_AFTER(&state_);
     return instance_;
   }
 
  private:
+  // Adapter function for use with AtExit.  This should be called single
+  // threaded, so don't use atomic operations.
+  // Calling OnExit while the instance is in use by other threads is a mistake.
+  static void OnExit(void* lazy_instance) {
+    LazyInstance<Type, Traits>* me =
+        reinterpret_cast<LazyInstance<Type, Traits>*>(lazy_instance);
+    Traits::Delete(me->instance_);
+    me->instance_ = NULL;
+    base::subtle::Release_Store(&me->state_, STATE_EMPTY);
+  }
+
   int8 buf_[sizeof(Type)];  // Preallocate the space for the Type instance.
   Type *instance_;
 
   DISALLOW_COPY_AND_ASSIGN(LazyInstance);
 };
 
 }  // namespace base
 
 #endif  // BASE_LAZY_INSTANCE_H_