Move atomic ops and related files to base library

src/lazy-instance.h

-// Copyright 2012 the V8 project authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-// The LazyInstance<Type, Traits> class manages a single instance of Type,
-// which will be lazily created on the first time it's accessed.  This class is
-// useful for places you would normally use a function-level static, but you
-// need to have guaranteed thread-safety.  The Type constructor will only ever
-// be called once, even if two threads are racing to create the object.  Get()
-// and Pointer() will always return the same, completely initialized instance.
-//
-// LazyInstance is completely thread safe, assuming that you create it safely.
-// The class was designed to be POD initialized, so it shouldn't require a
-// static constructor.  It really only makes sense to declare a LazyInstance as
-// a global variable using the LAZY_INSTANCE_INITIALIZER initializer.
-//
-// LazyInstance is similar to Singleton, except it does not have the singleton
-// property.  You can have multiple LazyInstance's of the same type, and each
-// will manage a unique instance.  It also preallocates the space for Type, as
-// to avoid allocating the Type instance on the heap.  This may help with the
-// performance of creating the instance, and reducing heap fragmentation.  This
-// requires that Type be a complete type so we can determine the size. See
-// notes for advanced users below for more explanations.
-//
-// Example usage:
-//   static LazyInstance<MyClass>::type my_instance = LAZY_INSTANCE_INITIALIZER;
-//   void SomeMethod() {
-//     my_instance.Get().SomeMethod();  // MyClass::SomeMethod()
-//
-//     MyClass* ptr = my_instance.Pointer();
-//     ptr->DoDoDo();  // MyClass::DoDoDo
-//   }
-//
-// Additionally you can override the way your instance is constructed by
-// providing your own trait:
-// Example usage:
-//   struct MyCreateTrait {
-//     static void Construct(MyClass* allocated_ptr) {
-//       new (allocated_ptr) MyClass(/* extra parameters... */);
-//     }
-//   };
-//   static LazyInstance<MyClass, MyCreateTrait>::type my_instance =
-//      LAZY_INSTANCE_INITIALIZER;
-//
-// WARNINGS:
-// - This implementation of LazyInstance IS THREAD-SAFE by default. See
-//   SingleThreadInitOnceTrait if you don't care about thread safety.
-// - Lazy initialization comes with a cost. Make sure that you don't use it on
-//   critical path. Consider adding your initialization code to a function
-//   which is explicitly called once.
-//
-// Notes for advanced users:
-// LazyInstance can actually be used in two different ways:
-//
-// - "Static mode" which is the default mode since it is the most efficient
-//   (no extra heap allocation). In this mode, the instance is statically
-//   allocated (stored in the global data section at compile time).
-//   The macro LAZY_STATIC_INSTANCE_INITIALIZER (= LAZY_INSTANCE_INITIALIZER)
-//   must be used to initialize static lazy instances.
-//
-// - "Dynamic mode". In this mode, the instance is dynamically allocated and
-//   constructed (using new) by default. This mode is useful if you have to
-//   deal with some code already allocating the instance for you (e.g.
-//   OS::Mutex() which returns a new private OS-dependent subclass of Mutex).
-//   The macro LAZY_DYNAMIC_INSTANCE_INITIALIZER must be used to initialize
-//   dynamic lazy instances.
-
-#ifndef V8_LAZY_INSTANCE_H_
-#define V8_LAZY_INSTANCE_H_
-
-#include "src/base/macros.h"
-#include "src/once.h"
-
-namespace v8 {
-namespace internal {
-
-#define LAZY_STATIC_INSTANCE_INITIALIZER { V8_ONCE_INIT, { {} } }
-#define LAZY_DYNAMIC_INSTANCE_INITIALIZER { V8_ONCE_INIT, 0 }
-
-// Default to static mode.
-#define LAZY_INSTANCE_INITIALIZER LAZY_STATIC_INSTANCE_INITIALIZER
-
-
-template <typename T>
-struct LeakyInstanceTrait {
-  static void Destroy(T* /* instance */) {}
-};
-
-
-// Traits that define how an instance is allocated and accessed.
-
-
-template <typename T>
-struct StaticallyAllocatedInstanceTrait {
-  // 16-byte alignment fallback to be on the safe side here.
-  struct V8_ALIGNAS(T, 16) StorageType {
-    char x[sizeof(T)];
-  };
-
-  STATIC_ASSERT(V8_ALIGNOF(StorageType) >= V8_ALIGNOF(T));
-
-  static T* MutableInstance(StorageType* storage) {
-    return reinterpret_cast<T*>(storage);
-  }
-
-  template <typename ConstructTrait>
-  static void InitStorageUsingTrait(StorageType* storage) {
-    ConstructTrait::Construct(MutableInstance(storage));
-  }
-};
-
-
-template <typename T>
-struct DynamicallyAllocatedInstanceTrait {
-  typedef T* StorageType;
-
-  static T* MutableInstance(StorageType* storage) {
-    return *storage;
-  }
-
-  template <typename CreateTrait>
-  static void InitStorageUsingTrait(StorageType* storage) {
-    *storage = CreateTrait::Create();
-  }
-};
-
-
-template <typename T>
-struct DefaultConstructTrait {
-  // Constructs the provided object which was already allocated.
-  static void Construct(T* allocated_ptr) {
-    new(allocated_ptr) T();
-  }
-};
-
-
-template <typename T>
-struct DefaultCreateTrait {
-  static T* Create() {
-    return new T();
-  }
-};
-
-
-struct ThreadSafeInitOnceTrait {
-  template <typename Function, typename Storage>
-  static void Init(OnceType* once, Function function, Storage storage) {
-    CallOnce(once, function, storage);
-  }
-};
-
-
-// Initialization trait for users who don't care about thread-safety.
-struct SingleThreadInitOnceTrait {
-  template <typename Function, typename Storage>
-  static void Init(OnceType* once, Function function, Storage storage) {
-    if (*once == ONCE_STATE_UNINITIALIZED) {
-      function(storage);
-      *once = ONCE_STATE_DONE;
-    }
-  }
-};
-
-
-// TODO(pliard): Handle instances destruction (using global destructors).
-template <typename T, typename AllocationTrait, typename CreateTrait,
-          typename InitOnceTrait, typename DestroyTrait  /* not used yet. */>
-struct LazyInstanceImpl {
- public:
-  typedef typename AllocationTrait::StorageType StorageType;
-
- private:
-  static void InitInstance(StorageType* storage) {
-    AllocationTrait::template InitStorageUsingTrait<CreateTrait>(storage);
-  }
-
-  void Init() const {
-    InitOnceTrait::Init(
-        &once_,
-        // Casts to void* are needed here to avoid breaking strict aliasing
-        // rules.
-        reinterpret_cast<void(*)(void*)>(&InitInstance),  // NOLINT
-        reinterpret_cast<void*>(&storage_));
-  }
-
- public:
-  T* Pointer() {
-    Init();
-    return AllocationTrait::MutableInstance(&storage_);
-  }
-
-  const T& Get() const {
-    Init();
-    return *AllocationTrait::MutableInstance(&storage_);
-  }
-
-  mutable OnceType once_;
-  // Note that the previous field, OnceType, is an AtomicWord which guarantees
-  // 4-byte alignment of the storage field below. If compiling with GCC (>4.2),
-  // the LAZY_ALIGN macro above will guarantee correctness for any alignment.
-  mutable StorageType storage_;
-};
-
-
-template <typename T,
-          typename CreateTrait = DefaultConstructTrait<T>,
-          typename InitOnceTrait = ThreadSafeInitOnceTrait,
-          typename DestroyTrait = LeakyInstanceTrait<T> >
-struct LazyStaticInstance {
-  typedef LazyInstanceImpl<T, StaticallyAllocatedInstanceTrait<T>,
-      CreateTrait, InitOnceTrait, DestroyTrait> type;
-};
-
-
-template <typename T,
-          typename CreateTrait = DefaultConstructTrait<T>,
-          typename InitOnceTrait = ThreadSafeInitOnceTrait,
-          typename DestroyTrait = LeakyInstanceTrait<T> >
-struct LazyInstance {
-  // A LazyInstance is a LazyStaticInstance.
-  typedef typename LazyStaticInstance<T, CreateTrait, InitOnceTrait,
-      DestroyTrait>::type type;
-};
-
-
-template <typename T,
-          typename CreateTrait = DefaultCreateTrait<T>,
-          typename InitOnceTrait = ThreadSafeInitOnceTrait,
-          typename DestroyTrait = LeakyInstanceTrait<T> >
-struct LazyDynamicInstance {
-  typedef LazyInstanceImpl<T, DynamicallyAllocatedInstanceTrait<T>,
-      CreateTrait, InitOnceTrait, DestroyTrait> type;
-};
-
-} }  // namespace v8::internal
-
-#endif  // V8_LAZY_INSTANCE_H_