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// 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_
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