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..59527774440da4ec944a7f2f311c65c6ba5a1999 100644
--- a/base/memory/singleton_unittest.cc
+++ b/base/memory/singleton_unittest.cc
@@ -110,6 +110,26 @@ struct CallbackSingletonWithStaticTrait::Trait
   }
 };
 
+template <class Type>
+class AlignedTestSingleton {
+ public:
+  static AlignedTestSingleton* GetInstance() {
+    return Singleton<AlignedTestSingleton,
+        StaticMemorySingletonTraits<AlignedTestSingleton> >::get();
+  }
+
+  Type type_;
+};
+
+class ALIGNED(32) Aligned32Type {
+ public:
+  Aligned32Type() {
+    memset(data_, 32, sizeof(data_));
+  }
+ private:
+  int32 data_[32 / 4];
+};
+
 
 void SingletonNoLeak(CallbackFunc CallOnQuit) {
   CallbackSingletonWithNoLeakTrait::GetInstance()->callback_ = CallOnQuit;
@@ -250,3 +270,21 @@ TEST_F(SingletonTest, Basic) {
   // The leaky singleton shouldn't leak since SingletonLeak has not been called.
   VerifiesCallbacksNotCalled();
 }
+
+TEST_F(SingletonTest, Alignment) {
+  AlignedTestSingleton<Aligned32Type>* singleton1_align32 =
+      AlignedTestSingleton<Aligned32Type>::GetInstance();
+  AlignedTestSingleton<int>* singleton2_align4 =
+      AlignedTestSingleton<int>::GetInstance();
+  AlignedTestSingleton<Aligned32Type>* singleton3_align32 =
+      AlignedTestSingleton<Aligned32Type>::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_align32->type_);
+  EXPECT_EQ(intptr_t(0), singleton1_addr & 31);
+  EXPECT_EQ(intptr_t(0), singleton2_addr & 3);
+  EXPECT_EQ(intptr_t(0), singleton3_addr & 31);

[Jeffrey Yasskin (google), 2012/02/15 22:27:19]

Isn't a better test to check that singleton1_addr == singleton3_addr?

[jbates, 2012/02/15 22:51:33]

Yes! In fact, I had a nightmare about how broken this test is and fully plan to
fix it :)

+}