Revert "Pull chromium at 2c3ffb2355a27c32f45e508ef861416b820c823b"

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_
 
 #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;
 
 // We pull out some of the functionality into a non-templated function, so that
@@ skipping 193 matching lines @@
 #ifndef NDEBUG
     // Avoid making TLS lookup on release builds.
     if (!Traits::kAllowedToAccessOnNonjoinableThread)
       base::ThreadRestrictions::AssertSingletonAllowed();
 #endif
 
     // The load has acquire memory ordering as the thread which reads the
     // instance_ pointer must acquire visibility over the singleton data.
     base::subtle::AtomicWord value = base::subtle::Acquire_Load(&instance_);
     if (value != 0 && value != base::internal::kBeingCreatedMarker) {
+      // See the corresponding HAPPENS_BEFORE below.
+      ANNOTATE_HAPPENS_AFTER(&instance_);
       return reinterpret_cast<Type*>(value);
     }
 
     // Object isn't created yet, maybe we will get to create it, let's try...
     if (base::subtle::Acquire_CompareAndSwap(
           &instance_, 0, base::internal::kBeingCreatedMarker) == 0) {
       // instance_ was NULL and is now kBeingCreatedMarker.  Only one thread
       // will ever get here.  Threads might be spinning on us, and they will
       // stop right after we do this store.
       Type* newval = Traits::New();
 
+      // This annotation helps race detectors recognize correct lock-less
+      // synchronization between different threads calling get().
+      // See the corresponding HAPPENS_AFTER below and above.
+      ANNOTATE_HAPPENS_BEFORE(&instance_);
       // Releases the visibility over instance_ to the readers.
       base::subtle::Release_Store(
           &instance_, reinterpret_cast<base::subtle::AtomicWord>(newval));
 
       if (newval != NULL && Traits::kRegisterAtExit)
         base::AtExitManager::RegisterCallback(OnExit, NULL);
 
       return newval;
     }
 
     // We hit a race. Wait for the other thread to complete it.
     value = base::internal::WaitForInstance(&instance_);
 
+    // See the corresponding HAPPENS_BEFORE above.
+    ANNOTATE_HAPPENS_AFTER(&instance_);
     return reinterpret_cast<Type*>(value);
   }
 
   // Adapter function for use with AtExit().  This should be called single
   // threaded, so don't use atomic operations.
   // Calling OnExit while singleton is in use by other threads is a mistake.
   static void OnExit(void* /*unused*/) {
     // AtExit should only ever be register after the singleton instance was
     // created.  We should only ever get here with a valid instance_ pointer.
     Traits::Delete(
         reinterpret_cast<Type*>(base::subtle::NoBarrier_Load(&instance_)));
     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_