From cd924d6e5efdf80f66283ac66987f2b339c381cf Mon Sep 17 00:00:00 2001
From: "jbates@chromium.org"
 <jbates@chromium.org@0039d316-1c4b-4281-b951-d872f2087c98>
Date: Thu, 23 Feb 2012 17:52:20 +0000
Subject: Add ALIGNAS and ALIGNOF macros to ensure proper alignment of
 StaticMemorySingletonTraits

BUG=95006

Review URL: https://chromiumcodereview.appspot.com/9186057

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@123270 0039d316-1c4b-4281-b951-d872f2087c98
---
 base/lazy_instance.h | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

(limited to 'base/lazy_instance.h')

diff --git a/base/lazy_instance.h b/base/lazy_instance.h
index 5ddc002..c428feb 100644
--- a/base/lazy_instance.h
+++ b/base/lazy_instance.h
@@ -42,6 +42,7 @@
 #include "base/base_export.h"
 #include "base/basictypes.h"
 #include "base/logging.h"
+#include "base/memory/aligned_memory.h"
 #include "base/third_party/dynamic_annotations/dynamic_annotations.h"
 #include "base/threading/thread_restrictions.h"
 
@@ -59,7 +60,7 @@ struct DefaultLazyInstanceTraits {
   static const bool kAllowedToAccessOnNonjoinableThread = false;
 
   static Type* New(void* instance) {
-    DCHECK_EQ(reinterpret_cast<uintptr_t>(instance) % sizeof(instance), 0u)
+    DCHECK_EQ(reinterpret_cast<uintptr_t>(instance) & (ALIGNOF(Type) - 1), 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.";
@@ -155,7 +156,8 @@ class LazyInstance {
     if (!(value & kLazyInstanceCreatedMask) &&
         internal::NeedsLazyInstance(&private_instance_)) {
       // Create the instance in the space provided by |private_buf_|.
-      value = reinterpret_cast<subtle::AtomicWord>(Traits::New(private_buf_));
+      value = reinterpret_cast<subtle::AtomicWord>(
+          Traits::New(private_buf_.void_data()));
       internal::CompleteLazyInstance(&private_instance_, value, this,
                                      Traits::kRegisterOnExit ? OnExit : NULL);
     }
@@ -174,20 +176,19 @@ class LazyInstance {
       case 0:
         return p == NULL;
       case internal::kLazyInstanceStateCreating:
-        return static_cast<int8*>(static_cast<void*>(p)) == private_buf_;
+        return static_cast<void*>(p) == private_buf_.void_data();
       default:
         return p == instance();
     }
   }
 
   // Effectively private: member data is only public to allow the linker to
-  // statically initialize it. DO NOT USE FROM OUTSIDE THIS CLASS.
+  // statically initialize it and to maintain a POD class. DO NOT USE FROM
+  // OUTSIDE THIS CLASS.
 
-  // Note this must use AtomicWord, not Atomic32, to ensure correct alignment
-  // of |private_buf_| on 64 bit architectures. (This member must be first to
-  // allow the syntax used in LAZY_INSTANCE_INITIALIZER to work correctly.)
   subtle::AtomicWord private_instance_;
-  int8 private_buf_[sizeof(Type)];  // Preallocated space for the Type instance.
+  // Preallocated space for the Type instance.
+  base::AlignedMemory<sizeof(Type), ALIGNOF(Type)> private_buf_;
 
  private:
   Type* instance() {
@@ -201,7 +202,7 @@ class LazyInstance {
     LazyInstance<Type, Traits>* me =
         reinterpret_cast<LazyInstance<Type, Traits>*>(lazy_instance);
     Traits::Delete(me->instance());
-    subtle::Release_Store(&me->private_instance_, 0);
+    subtle::NoBarrier_Store(&me->private_instance_, 0);
   }
 };
 
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