Move Singleton and related structs to namespace base

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:
@@ skipping 18 matching lines @@
 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
 // we can implement the more complicated pieces out of line in the .cc file.
 BASE_EXPORT subtle::AtomicWord WaitForInstance(subtle::AtomicWord* instance);
 
+class DeleteTraceLogForTesting;

[danakj, 2015/09/03 17:37:44]

Why expose this in the header?

+
 }  // namespace internal
-}  // namespace base
 
-// TODO(joth): Move more of this file into namespace base
 
 // Default traits for Singleton<Type>. Calls operator new and operator delete on
 // the object. Registers automatic deletion at process exit.
 // Overload if you need arguments or another memory allocation function.
 template<typename Type>
 struct DefaultSingletonTraits {
   // Allocates the object.
   static Type* New() {
     // The parenthesis is very important here; it forces POD type
     // initialization.
@@ skipping 50 matching lines @@
 // this is also used in e.g. Chrome Frame, where you have to allow for the
 // possibility of loading briefly into someone else's process space, and
 // so leaking is not an option, as that would sabotage the state of your host
 // process once you've unloaded.
 template <typename Type>
 struct StaticMemorySingletonTraits {
   // WARNING: User has to deal with get() in the singleton class
   // this is traits for returning NULL.
   static Type* New() {
     // Only constructs once and returns pointer; otherwise returns NULL.
-    if (base::subtle::NoBarrier_AtomicExchange(&dead_, 1))
+    if (subtle::NoBarrier_AtomicExchange(&dead_, 1))
       return NULL;
 
     return new(buffer_.void_data()) Type();
   }
 
   static void Delete(Type* p) {
     if (p != NULL)
       p->Type::~Type();
   }
 
   static const bool kRegisterAtExit = true;
   static const bool kAllowedToAccessOnNonjoinableThread = true;
 
   // Exposed for unittesting.
-  static void Resurrect() {
-    base::subtle::NoBarrier_Store(&dead_, 0);
-  }
+  static void Resurrect() { subtle::NoBarrier_Store(&dead_, 0); }
 
  private:
-  static base::AlignedMemory<sizeof(Type), ALIGNOF(Type)> buffer_;
+  static AlignedMemory<sizeof(Type), ALIGNOF(Type)> buffer_;
   // Signal the object was already deleted, so it is not revived.
-  static base::subtle::Atomic32 dead_;
+  static subtle::Atomic32 dead_;
 };
 
-template <typename Type> base::AlignedMemory<sizeof(Type), ALIGNOF(Type)>
+template <typename Type>
+AlignedMemory<sizeof(Type), ALIGNOF(Type)>
     StaticMemorySingletonTraits<Type>::buffer_;
-template <typename Type> base::subtle::Atomic32
-    StaticMemorySingletonTraits<Type>::dead_ = 0;
+template <typename Type>
+subtle::Atomic32 StaticMemorySingletonTraits<Type>::dead_ = 0;
 
 // The Singleton<Type, Traits, DifferentiatingType> class manages a single
 // instance of Type which will be created on first use and will be destroyed at
 // normal process exit). The Trait::Delete function will not be called on
 // abnormal process exit.
 //
 // DifferentiatingType is used as a key to differentiate two different
 // singletons having the same memory allocation functions but serving a
 // different purpose. This is mainly used for Locks serving different purposes.
 //
@@ skipping 31 matching lines @@
 // instantiated.
 //
 // This class is itself thread-safe. The underlying Type must of course be
 // thread-safe if you want to use it concurrently. Two parameters may be tuned
 // depending on the user's requirements.
 //
 // Glossary:
 //   RAE = kRegisterAtExit
 //
 // On every platform, if Traits::RAE is true, the singleton will be destroyed at
-// process exit. More precisely it uses base::AtExitManager which requires an
+// process exit. More precisely it uses AtExitManager which requires an
 // object of this type to be instantiated. AtExitManager mimics the semantics
 // of atexit() such as LIFO order but under Windows is safer to call. For more
 // information see at_exit.h.
 //
 // If Traits::RAE is false, the singleton will not be freed at process exit,
 // thus the singleton will be leaked if it is ever accessed. Traits::RAE
 // shouldn't be false unless absolutely necessary. Remember that the heap where
 // the object is allocated may be destroyed by the CRT anyway.
 //
 // Caveats:
 // (a) Every call to get(), operator->() and operator*() incurs some overhead
 //     (16ns on my P4/2.8GHz) to check whether the object has already been
 //     initialized.  You may wish to cache the result of get(); it will not
 //     change.
 //
 // (b) Your factory function must never throw an exception. This class is not
 //     exception-safe.
 //
+
 template <typename Type,
           typename Traits = DefaultSingletonTraits<Type>,
           typename DifferentiatingType = Type>
 class Singleton {
  private:
   // Classes using the Singleton<T> pattern should declare a GetInstance()
   // method and call Singleton::get() from within that.
   friend Type* Type::GetInstance();
 
   // Allow TraceLog tests to test tracing after OnExit.
-  friend class DeleteTraceLogForTesting;
+  friend class internal::DeleteTraceLogForTesting;
 
   // This class is safe to be constructed and copy-constructed since it has no
   // member.
 
   // Return a pointer to the one true instance of the class.
   static Type* get() {
 #ifndef NDEBUG
     // Avoid making TLS lookup on release builds.
     if (!Traits::kAllowedToAccessOnNonjoinableThread)
-      base::ThreadRestrictions::AssertSingletonAllowed();
+      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) {
+    subtle::AtomicWord value = subtle::Acquire_Load(&instance_);
+    if (value != 0 && value != internal::kBeingCreatedMarker) {
       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) {
+    if (subtle::Acquire_CompareAndSwap(&instance_, 0,
+                                       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();
 
       // Releases the visibility over instance_ to the readers.
-      base::subtle::Release_Store(
-          &instance_, reinterpret_cast<base::subtle::AtomicWord>(newval));
+      subtle::Release_Store(&instance_,
+                            reinterpret_cast<subtle::AtomicWord>(newval));
 
       if (newval != NULL && Traits::kRegisterAtExit)
-        base::AtExitManager::RegisterCallback(OnExit, NULL);
+        AtExitManager::RegisterCallback(OnExit, NULL);
 
       return newval;
     }
 
     // We hit a race. Wait for the other thread to complete it.
-    value = base::internal::WaitForInstance(&instance_);
+    value = internal::WaitForInstance(&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_)));
+    Traits::Delete(reinterpret_cast<Type*>(subtle::NoBarrier_Load(&instance_)));
     instance_ = 0;
   }
-  static base::subtle::AtomicWord instance_;
+  static subtle::AtomicWord instance_;
 };
 
 template <typename Type, typename Traits, typename DifferentiatingType>
-base::subtle::AtomicWord Singleton<Type, Traits, DifferentiatingType>::
-    instance_ = 0;
+subtle::AtomicWord Singleton<Type, Traits, DifferentiatingType>::instance_ = 0;
+
+}  // namespace base
 
 #endif  // BASE_MEMORY_SINGLETON_H_