third_party/blink/renderer/platform/wtf/vector_traits.h

/*
 * Copyright (C) 2006, 2007, 2008 Apple Inc. All rights reserved.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public License
 * along with this library; see the file COPYING.LIB.  If not, write to
 * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
 * Boston, MA 02110-1301, USA.
 *
 */

#ifndef THIRD_PARTY_BLINK_RENDERER_PLATFORM_WTF_VECTOR_TRAITS_H_
#define THIRD_PARTY_BLINK_RENDERER_PLATFORM_WTF_VECTOR_TRAITS_H_

#include <memory>
#include <type_traits>
#include <utility>
#include "base/memory/scoped_refptr.h"
#include "third_party/blink/renderer/platform/wtf/allocator/allocator.h"
#include "third_party/blink/renderer/platform/wtf/type_traits.h"

namespace WTF {

template <typename T>
struct VectorTraitsBase {
  static const bool kNeedsDestruction =
      !std::is_trivially_destructible<T>::value;

  static constexpr bool kCanInitializeWithMemset =
      std::is_trivially_default_constructible<T>::value;
  // true iff memset(slot, 0, size) constructs an unused slot value that is
  // valid for Oilpan to trace and if the value needs destruction, its
  // destructor can be invoked over. The zero'ed value representing an unused
  // slot in the vector's backing storage; it does not have to be equal to
  // what its constructor(s) would create, only be valid for those two uses.
  static constexpr bool kCanClearUnusedSlotsWithMemset =
      std::is_trivially_destructible<T>::value &&
      (!IsTraceable<T>::value || (std::is_trivially_constructible<T>::value &&
                                  std::is_trivially_copyable<T>::value));

  static constexpr bool kCanMoveWithMemcpy =
      std::is_trivially_move_assignable<T>::value;
  static constexpr bool kCanCopyWithMemcpy =
      std::is_trivially_copy_assignable<T>::value;
  static constexpr bool kCanFillWithMemset =
      std::is_default_constructible<T>::value && (sizeof(T) == sizeof(char));
  static constexpr bool kCanCompareWithMemcmp =
      std::is_scalar<T>::value;  // Types without padding.

  // Supports swapping elements using regular std::swap semantics.
  static const bool kCanSwapUsingCopyOrMove = true;

  template <typename U = void>
  struct IsTraceableInCollection {
    static const bool value = IsTraceable<T>::value;
  };

  // Vectors do not support deleting values.
  static constexpr bool kCanHaveDeletedValue = false;
  static bool IsDeletedValue(const T& value) { return false; }

  // The kCanTraceConcurrently value is used by Oilpan concurrent marking.
  // Only type for which VectorTraits<T>::kCanTraceConcurrently is true can
  // be traced on a concurrent thread.
  static constexpr bool kCanTraceConcurrently = false;
};

template <typename T>
struct VectorTraits : VectorTraitsBase<T> {};

// Classes marked with SimpleVectorTraits will use memmov, memcpy, memcmp
// instead of constructors, copy operators, etc for initialization, move and
// comparison.
template <typename T>
struct SimpleClassVectorTraits : VectorTraitsBase<T> {
  static const bool kCanInitializeWithMemset = true;
  static const bool kCanClearUnusedSlotsWithMemset = true;
  static const bool kCanMoveWithMemcpy = true;
  static const bool kCanCompareWithMemcmp = true;
};

// We know std::unique_ptr and RefPtr are simple enough that initializing to 0
// and moving with memcpy (and then not destructing the original) will totally
// work.
template <typename P>
struct VectorTraits<scoped_refptr<P>>
    : SimpleClassVectorTraits<scoped_refptr<P>> {
  // scoped_refptr cannot be copied using memcpy as the internals (e.g. ref
  // count) depend on properly constructing the object.
  static const bool kCanCopyWithMemcpy = false;
};

template <typename P>
struct VectorTraits<std::unique_ptr<P>>
    : SimpleClassVectorTraits<std::unique_ptr<P>> {
  // std::unique_ptr -> std::unique_ptr has a very particular structure that
  // tricks the normal type traits into thinking that the class is "trivially
  // copyable".
  static const bool kCanCopyWithMemcpy = false;
};
static_assert(VectorTraits<scoped_refptr<int>>::kCanInitializeWithMemset,
              "inefficient RefPtr Vector");
static_assert(VectorTraits<scoped_refptr<int>>::kCanMoveWithMemcpy,
              "inefficient RefPtr Vector");
static_assert(VectorTraits<scoped_refptr<int>>::kCanCompareWithMemcmp,
              "inefficient RefPtr Vector");
static_assert(VectorTraits<std::unique_ptr<int>>::kCanInitializeWithMemset,
              "inefficient std::unique_ptr Vector");
static_assert(VectorTraits<std::unique_ptr<int>>::kCanMoveWithMemcpy,
              "inefficient std::unique_ptr Vector");
static_assert(VectorTraits<std::unique_ptr<int>>::kCanCompareWithMemcmp,
              "inefficient std::unique_ptr Vector");

template <typename First, typename Second>
struct VectorTraits<std::pair<First, Second>> {
  typedef VectorTraits<First> FirstTraits;
  typedef VectorTraits<Second> SecondTraits;

  static_assert(!IsWeak<First>::value,
                "Weak references are not allowed in Vector");
  static_assert(!IsWeak<Second>::value,
                "Weak references are not allowed in Vector");

  static const bool kNeedsDestruction =
      FirstTraits::kNeedsDestruction || SecondTraits::kNeedsDestruction;
  static const bool kCanInitializeWithMemset =
      FirstTraits::kCanInitializeWithMemset &&
      SecondTraits::kCanInitializeWithMemset;
  static const bool kCanMoveWithMemcpy =
      FirstTraits::kCanMoveWithMemcpy && SecondTraits::kCanMoveWithMemcpy;
  static const bool kCanCopyWithMemcpy =
      FirstTraits::kCanCopyWithMemcpy && SecondTraits::kCanCopyWithMemcpy;
  static const bool kCanFillWithMemset = false;
  static const bool kCanCompareWithMemcmp =
      FirstTraits::kCanCompareWithMemcmp && SecondTraits::kCanCompareWithMemcmp;
  static const bool kCanClearUnusedSlotsWithMemset =
      FirstTraits::kCanClearUnusedSlotsWithMemset &&
      SecondTraits::kCanClearUnusedSlotsWithMemset;
  // Supports swapping elements using regular std::swap semantics.
  static const bool kCanSwapUsingCopyOrMove = true;
  template <typename U = void>
  struct IsTraceableInCollection {
    static const bool value =
        IsTraceableInCollectionTrait<FirstTraits>::value ||
        IsTraceableInCollectionTrait<SecondTraits>::value;
  };

  // Vectors do not support deleting values.
  static constexpr bool kCanHaveDeletedValue = false;
  static bool IsDeletedValue(std::pair<First, Second> value) { return false; }

  static constexpr bool kCanTraceConcurrently = false;
};

}  // namespace WTF

#define WTF_ALLOW_MOVE_INIT_AND_COMPARE_WITH_MEM_FUNCTIONS(ClassName)         \
  namespace WTF {                                                             \
  static_assert(!std::is_trivially_default_constructible<ClassName>::value || \
                    !std::is_trivially_move_assignable<ClassName>::value ||   \
                    !std::is_scalar<ClassName>::value,                        \
                "macro not needed");                                          \
  template <>                                                                 \
  struct VectorTraits<ClassName> : SimpleClassVectorTraits<ClassName> {};     \
  }

#define WTF_ALLOW_MOVE_AND_INIT_WITH_MEM_FUNCTIONS(ClassName)                 \
  namespace WTF {                                                             \
  static_assert(!std::is_trivially_default_constructible<ClassName>::value || \
                    !std::is_trivially_move_assignable<ClassName>::value,     \
                "macro not needed");                                          \
  template <>                                                                 \
  struct VectorTraits<ClassName> : VectorTraitsBase<ClassName> {              \
    static const bool kCanInitializeWithMemset = true;                        \
    static const bool kCanClearUnusedSlotsWithMemset = true;                  \
    static const bool kCanMoveWithMemcpy = true;                              \
  };                                                                          \
  }

#define WTF_ALLOW_INIT_WITH_MEM_FUNCTIONS(ClassName)                        \
  namespace WTF {                                                           \
  static_assert(!std::is_trivially_default_constructible<ClassName>::value, \
                "macro not needed");                                        \
  template <>                                                               \
  struct VectorTraits<ClassName> : VectorTraitsBase<ClassName> {            \
    static const bool kCanInitializeWithMemset = true;                      \
    static const bool kCanClearUnusedSlotsWithMemset = true;                \
  };                                                                        \
  }

#define WTF_ALLOW_CLEAR_UNUSED_SLOTS_WITH_MEM_FUNCTIONS(ClassName)          \
  namespace WTF {                                                           \
  static_assert(!std::is_trivially_default_constructible<ClassName>::value, \
                "macro not needed");                                        \
  template <>                                                               \
  struct VectorTraits<ClassName> : VectorTraitsBase<ClassName> {            \
    static const bool kCanClearUnusedSlotsWithMemset = true;                \
  };                                                                        \
  }

using WTF::VectorTraits;
using WTF::SimpleClassVectorTraits;

#endif  // THIRD_PARTY_BLINK_RENDERER_PLATFORM_WTF_VECTOR_TRAITS_H_