Remove static function pointer from LazyInstance

base/lazy_instance.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.
 
 // 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 31 matching lines @@
 #include "base/base_export.h"
 #include "base/basictypes.h"
 #include "base/logging.h"
 #include "base/third_party/dynamic_annotations/dynamic_annotations.h"
 #include "base/threading/thread_restrictions.h"
 
 namespace base {
 
 template <typename Type>
 struct DefaultLazyInstanceTraits {
+  static const bool kRegisterOnExit = true;
   static const bool kAllowedToAccessOnNonjoinableThread = false;
 
   static Type* New(void* instance) {
     DCHECK_EQ(reinterpret_cast<uintptr_t>(instance) % sizeof(instance), 0u)
         << ": Bad boy, the buffer passed to placement new is not aligned!\n"
         "This may break some stuff like SSE-based optimizations assuming the "
         "<Type> objects are word aligned.";
     // Use placement new to initialize our instance in our preallocated space.
     // The parenthesis is very important here to force POD type initialization.
     return new (instance) Type();
   }
-  static void Delete(void* instance) {
+  static void Delete(Type* instance) {
     // Explicitly call the destructor.
-    reinterpret_cast<Type*>(instance)->~Type();
+    instance->~Type();
   }
 };
 
 template <typename Type>
 struct LeakyLazyInstanceTraits {
+  static const bool kRegisterOnExit = false;
   static const bool kAllowedToAccessOnNonjoinableThread = true;
 
   static Type* New(void* instance) {
     return DefaultLazyInstanceTraits<Type>::New(instance);
   }
-  // Rather than define an empty Delete function, we make Delete itself
-  // a null pointer.  This allows us to completely sidestep registering
-  // this object with an AtExitManager, which allows you to use
-  // LeakyLazyInstanceTraits in contexts where you don't have an
-  // AtExitManager.
-  static void (*Delete)(void* instance);
+  static void Delete(Type* instance) {
+  }
 };
 
-template <typename Type>
-void (*LeakyLazyInstanceTraits<Type>::Delete)(void* instance) = NULL;
-
 // We pull out some of the functionality into a non-templated base, so that we
 // can implement the more complicated pieces out of line in the .cc file.
 class BASE_EXPORT LazyInstanceHelper {
  protected:
   enum {
     STATE_EMPTY    = 0,
     STATE_CREATING = 1,
     STATE_CREATED  = 2
   };
 
@@ skipping 48 matching lines @@
     // Since a thread sees state_ != STATE_CREATED at most once,
     // the load is taken out of NeedsInstance() as a fast-path.
     // The load has acquire memory ordering as a thread which sees
     // state_ == STATE_CREATED needs to acquire visibility over
     // the associated data (buf_). Pairing Release_Store is in
     // CompleteInstance().
     if ((base::subtle::Acquire_Load(&state_) != STATE_CREATED) &&
         NeedsInstance()) {
       // Create the instance in the space provided by |buf_|.
       instance_ = Traits::New(buf_);
-      // Traits::Delete will be null for LeakyLazyInstanceTraits
-      void (*dtor)(void*) = Traits::Delete;
-      CompleteInstance(this, (dtor == NULL) ? NULL : OnExit);
+      CompleteInstance(this, Traits::kRegisterOnExit ? OnExit : NULL);
     }
 
     // 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_;
   }
 
   bool operator==(Type* p) {
     switch (base::subtle::NoBarrier_Load(&state_)) {
       case STATE_EMPTY:
         return p == NULL;
       case STATE_CREATING:
         return static_cast<int8*>(static_cast<void*>(p)) == buf_;
       case STATE_CREATED:
         return p == instance_;
       default:
         return false;
     }
   }
 
  private:
   // Adapter function for use with AtExit.  This should be called single
-  // threaded, so don't use atomic operations.

[joth, 2011/10/25 14:22:57]

this comment looked incorrect, as it is using an atomic operation
(Release_Store). I made a rough-stab at correcting it.

[willchan no longer on Chromium, 2011/10/25 15:57:25]

I think what's happening here is we *shouldn't* need the atomic. But when we
have bugs with non-joinable threads we get races here. This helps shut up TSAN,
although the code will still probably crash :P Meh. I don't have any opinion
about changing this comment since I'm not sure how to fix it correctly.

+  // threaded, so don't synchronize across threads.
   // 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);
   }
 
   Type *instance_;
   int8 buf_[sizeof(Type)];  // Preallocate the space for the Type instance.
 
   DISALLOW_COPY_AND_ASSIGN(LazyInstance);
 };
 
 }  // namespace base
 
 #endif  // BASE_LAZY_INSTANCE_H_