Add ALIGNAS and ALIGNOF macros to ensure proper alignment of StaticMemorySingletonTraits

base/memory/aligned_memory.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.
+
+// AlignedMemory is a POD type that gives you a portable way to specify static
+// or local stack data of a given alignment and size. For example, if you need
+// static storage for a class, but you want manual control over when the object
+// is constructed and destructed (you don't want static initialization and
+// destruction), use AlignedMemory:
+//
+//   static AlignedMemory<sizeof(MyClass), ALIGNOF(MyClass)> my_class;
+//
+//   // ... at runtime:
+//   new(my_class.void_data()) MyClass();
+//
+//   // ... use it:
+//   MyClass* mc = my_class.data_as<MyClass>();
+//
+//   // ... later, to destruct my_class:
+//   my_class.data_as<MyClass>()->MyClass::~MyClass();
+
+#ifndef BASE_MEMORY_ALIGNED_MEMORY_H_
+#define BASE_MEMORY_ALIGNED_MEMORY_H_
+#pragma once
+
+#include "base/basictypes.h"
+#include "base/compiler_specific.h"
+#include "base/logging.h"
+
+namespace base {
+
+// AlignedMemory is specialized for all supported alignments.
+// Make sure we get a compiler error if someone uses an unsupported alignment.
+template <size_t Size, size_t ByteAlignment>
+struct AlignedMemory {};
+
+#define BASE_DECL_ALIGNED_MEMORY(byte_alignment) \
+    template <size_t Size> \
+    class AlignedMemory<Size, byte_alignment> { \
+     public: \
+      ALIGNAS(byte_alignment) uint8 data_[Size]; \
+      void* void_data() { return reinterpret_cast<void*>(data_); } \
+      const void* void_data() const { \
+        return reinterpret_cast<const void*>(data_); \
+      } \
+      template<typename Type> \
+      Type* data_as() { return reinterpret_cast<Type*>(void_data()); } \
+      template<typename Type> \
+      const Type* data_as() const { \
+        return reinterpret_cast<const Type*>(void_data()); \
+      } \
+     private: \
+      void* operator new(size_t); \
+      void operator delete(void*); \
+    }
+
+// Specialization for all alignments is required because MSVC (as of VS 2008)
+// does not understand ALIGNAS(ALIGNOF(Type)) or ALIGNAS(template_param).
+// Greater than 4096 alignment is not supported by some compilers, so 4096 is
+// the maximum specified here.
+BASE_DECL_ALIGNED_MEMORY(1);
+BASE_DECL_ALIGNED_MEMORY(2);
+BASE_DECL_ALIGNED_MEMORY(4);
+BASE_DECL_ALIGNED_MEMORY(8);
+BASE_DECL_ALIGNED_MEMORY(16);
+BASE_DECL_ALIGNED_MEMORY(32);
+BASE_DECL_ALIGNED_MEMORY(64);
+BASE_DECL_ALIGNED_MEMORY(128);
+BASE_DECL_ALIGNED_MEMORY(256);
+BASE_DECL_ALIGNED_MEMORY(512);
+BASE_DECL_ALIGNED_MEMORY(1024);
+BASE_DECL_ALIGNED_MEMORY(2048);
+BASE_DECL_ALIGNED_MEMORY(4096);
+
+}  // base
+
+#endif  // BASE_MEMORY_ALIGNED_MEMORY_H_