Add ALIGNAS and ALIGNOF macros to ensure proper alignment of StaticMemorySingletonTraits

base/memory/singleton_unittest.cc

Index: base/memory/singleton_unittest.cc
diff --git a/base/memory/singleton_unittest.cc b/base/memory/singleton_unittest.cc
index 068148ff76b75e5e25f9f02ff1ddc802e93591d8..8619d8828e7049b3c024554d15d7f7a93c83498e 100644
--- a/base/memory/singleton_unittest.cc
+++ b/base/memory/singleton_unittest.cc
@@ -110,6 +110,17 @@ struct CallbackSingletonWithStaticTrait::Trait
   }
 };
 
+template <class Type>
+class AlignedTestSingleton {
+ public:
+  static AlignedTestSingleton* GetInstance() {
+    return Singleton<AlignedTestSingleton,
+        StaticMemorySingletonTraits<AlignedTestSingleton> >::get();
+  }
+
+  Type type_;
+};
+
 
 void SingletonNoLeak(CallbackFunc CallOnQuit) {
   CallbackSingletonWithNoLeakTrait::GetInstance()->callback_ = CallOnQuit;
@@ -250,3 +261,36 @@ TEST_F(SingletonTest, Basic) {
   // The leaky singleton shouldn't leak since SingletonLeak has not been called.
   VerifiesCallbacksNotCalled();
 }
+
+TEST_F(SingletonTest, Alignment) {
+  using base::RawAlignedMemory;
+  AlignedTestSingleton<RawAlignedMemory<32, 32> >* singleton1_align32 =
+      AlignedTestSingleton<RawAlignedMemory<32, 32> >::GetInstance();
+  AlignedTestSingleton<int>* singleton2_align4 =
+      AlignedTestSingleton<int>::GetInstance();
+  AlignedTestSingleton<RawAlignedMemory<64, 64> >* singleton3_align64 =
+      AlignedTestSingleton<RawAlignedMemory<64, 64> >::GetInstance();
+  AlignedTestSingleton<char>* singleton4_align1 =
+      AlignedTestSingleton<char>::GetInstance();
+  AlignedTestSingleton<RawAlignedMemory<128, 128> >* singleton5_align128 =
+      AlignedTestSingleton<RawAlignedMemory<128, 128> >::GetInstance();
+  AlignedTestSingleton<RawAlignedMemory<4096, 4096> >* singleton6_align4096 =
+      AlignedTestSingleton<RawAlignedMemory<4096, 4096> >::GetInstance();
+  intptr_t singleton1_addr =
+      reinterpret_cast<intptr_t>(&singleton1_align32->type_);
+  intptr_t singleton2_addr =
+      reinterpret_cast<intptr_t>(&singleton2_align4->type_);
+  intptr_t singleton3_addr =
+      reinterpret_cast<intptr_t>(&singleton3_align64->type_);
+  (void)singleton4_align1;
+  intptr_t singleton5_addr =
+      reinterpret_cast<intptr_t>(&singleton5_align128->type_);
+  intptr_t singleton6_addr =
+      reinterpret_cast<intptr_t>(&singleton6_align4096->type_);
+  EXPECT_EQ(intptr_t(0), singleton1_addr & 31);

[Sigurður Ásgeirsson, 2012/02/22 15:31:32]

this test would IMHO be more readable if you'd pull the declarations, casts and
tests together into groups. Some running commentary would be good for the reader
as well.

[jbates, 2012/02/22 19:37:15]

Done.

+  EXPECT_EQ(intptr_t(0), singleton2_addr & 3);
+  EXPECT_EQ(intptr_t(0), singleton3_addr & 63);
+  // singleton4_addr is 1-byte aligned, don't care what the pointer is.
+  EXPECT_EQ(intptr_t(0), singleton5_addr & 127);
+  EXPECT_EQ(intptr_t(0), singleton6_addr & 4095);
+}