Add ALIGNAS and ALIGNOF macros to ensure proper alignment of StaticMemorySingletonTraits

base/memory/singleton.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.
 
 // PLEASE READ: Do you really need a singleton?
 //
 // Singletons make it hard to determine the lifetime of an object, which can
 // lead to buggy code and spurious crashes.
 //
 // Instead of adding another singleton into the mix, try to identify either:
 //   a) An existing singleton that can manage your object's lifetime
 //   b) Locations where you can deterministically create the object and pass
 //      into other objects
 //
 // If you absolutely need a singleton, please keep them as trivial as possible
 // and ideally a leaf dependency. Singletons get problematic when they attempt
 // to do too much in their destructor or have circular dependencies.
 
 #ifndef BASE_MEMORY_SINGLETON_H_
 #define BASE_MEMORY_SINGLETON_H_
 #pragma once
 
 #include "base/at_exit.h"
 #include "base/atomicops.h"
 #include "base/base_export.h"
+#include "base/memory/aligned_memory.h"
 #include "base/third_party/dynamic_annotations/dynamic_annotations.h"
 #include "base/threading/thread_restrictions.h"
 
 namespace base {
 namespace internal {
 
 // Our AtomicWord doubles as a spinlock, where a value of
 // kBeingCreatedMarker means the spinlock is being held for creation.
 static const subtle::AtomicWord kBeingCreatedMarker = 1;
 
@@ skipping 63 matching lines @@
 // a callback the system will invoke when logging levels change. Note that
 // this is also used in e.g. Chrome Frame, where you have to allow for the
 // possibility of loading briefly into someone else's process space, and
 // so leaking is not an option, as that would sabotage the state of your host
 // process once you've unloaded.
 template <typename Type>
 struct StaticMemorySingletonTraits {
   // WARNING: User has to deal with get() in the singleton class
   // this is traits for returning NULL.
   static Type* New() {
+    // Only constructs once and returns pointer; otherwise returns NULL.
     if (base::subtle::NoBarrier_AtomicExchange(&dead_, 1))
       return NULL;
-    Type* ptr = reinterpret_cast<Type*>(buffer_);
 
-    // We are protected by a memory barrier.
-    new(ptr) Type();
-    return ptr;
+    return new(buffer_.void_data()) Type();
   }
 
   static void Delete(Type* p) {
-    base::subtle::NoBarrier_Store(&dead_, 1);
-    base::subtle::MemoryBarrier();
     if (p != NULL)
       p->Type::~Type();
   }
 
   static const bool kRegisterAtExit = true;
   static const bool kAllowedToAccessOnNonjoinableThread = true;
 
   // Exposed for unittesting.
   static void Resurrect() {
     base::subtle::NoBarrier_Store(&dead_, 0);
   }
 
  private:
-  static const size_t kBufferSize = (sizeof(Type) +
-                                     sizeof(intptr_t) - 1) / sizeof(intptr_t);
-  static intptr_t buffer_[kBufferSize];
-
+  static base::AlignedMemory<sizeof(Type), ALIGNOF(Type)> buffer_;
   // Signal the object was already deleted, so it is not revived.
   static base::subtle::Atomic32 dead_;
 };
 
-template <typename Type> intptr_t
-    StaticMemorySingletonTraits<Type>::buffer_[kBufferSize];
+template <typename Type> base::AlignedMemory<sizeof(Type), ALIGNOF(Type)>
+    StaticMemorySingletonTraits<Type>::buffer_;
 template <typename Type> base::subtle::Atomic32
     StaticMemorySingletonTraits<Type>::dead_ = 0;
 
 // The Singleton<Type, Traits, DifferentiatingType> class manages a single
 // instance of Type which will be created on first use and will be destroyed at
 // normal process exit). The Trait::Delete function will not be called on
 // abnormal process exit.
 //
 // DifferentiatingType is used as a key to differentiate two different
 // singletons having the same memory allocation functions but serving a
@@ skipping 128 matching lines @@
     instance_ = 0;
   }
   static base::subtle::AtomicWord instance_;
 };
 
 template <typename Type, typename Traits, typename DifferentiatingType>
 base::subtle::AtomicWord Singleton<Type, Traits, DifferentiatingType>::
     instance_ = 0;
 
 #endif  // BASE_MEMORY_SINGLETON_H_