// Copyright 2020 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. #ifndef INCLUDE_CPPGC_CUSTOM_SPACE_H_ #define INCLUDE_CPPGC_CUSTOM_SPACE_H_ #include <stddef.h> namespace cppgc { /** * Index identifying a custom space. */ struct CustomSpaceIndex { constexpr CustomSpaceIndex(size_t value) : value(value) {} // NOLINT size_t value; }; /** * Top-level base class for custom spaces. Users must inherit from CustomSpace * below. */ class CustomSpaceBase { public: virtual ~CustomSpaceBase() = default; virtual CustomSpaceIndex GetCustomSpaceIndex() const = 0; virtual bool IsCompactable() const = 0; }; /** * Base class custom spaces should directly inherit from. The class inheriting * from `CustomSpace` must define `kSpaceIndex` as unique space index. These * indices need for form a sequence starting at 0. * * Example: * \code * class CustomSpace1 : public CustomSpace<CustomSpace1> { * public: * static constexpr CustomSpaceIndex kSpaceIndex = 0; * }; * class CustomSpace2 : public CustomSpace<CustomSpace2> { * public: * static constexpr CustomSpaceIndex kSpaceIndex = 1; * }; * \endcode */ template <typename ConcreteCustomSpace> class CustomSpace : public CustomSpaceBase { public: /** * Compaction is only supported on spaces that manually manage slots * recording. */ static constexpr bool kSupportsCompaction = false; CustomSpaceIndex GetCustomSpaceIndex() const final { return ConcreteCustomSpace::kSpaceIndex; } bool IsCompactable() const final { return ConcreteCustomSpace::kSupportsCompaction; } }; /** * User-overridable trait that allows pinning types to custom spaces. */ template <typename T, typename = void> struct SpaceTrait { using Space = void; }; namespace internal { template <typename CustomSpace> struct IsAllocatedOnCompactableSpaceImpl { static constexpr bool value = CustomSpace::kSupportsCompaction; }; template <> struct IsAllocatedOnCompactableSpaceImpl<void> { // Non-custom spaces are by default not compactable. static constexpr bool value = false; }; template <typename T> struct IsAllocatedOnCompactableSpace { public: static constexpr bool value = IsAllocatedOnCompactableSpaceImpl<typename SpaceTrait<T>::Space>::value; }; } // namespace internal } // namespace cppgc #endif // INCLUDE_CPPGC_CUSTOM_SPACE_H_