diff options
Diffstat (limited to 'libs')
| -rw-r--r-- | libs/kstd/include/kstd/bits/shared_ptr.hpp | 320 |
1 files changed, 286 insertions, 34 deletions
diff --git a/libs/kstd/include/kstd/bits/shared_ptr.hpp b/libs/kstd/include/kstd/bits/shared_ptr.hpp index 6bce83f..674807d 100644 --- a/libs/kstd/include/kstd/bits/shared_ptr.hpp +++ b/libs/kstd/include/kstd/bits/shared_ptr.hpp @@ -10,10 +10,200 @@ namespace kstd { + /** + * @brief Control block for shared_ptr and weak_ptr. This control block contains the reference counts for shared + * ownership and weak ownership. The shared_count tracks the number of shared_ptr instances that own the managed + * object, while the weak_count tracks the number of weak_ptr instances that reference the managed object. + * The weak_count is needed to determine when it is safe to delete the shared_control_block itself + */ + struct shared_control_block + { + std::atomic<std::size_t> shared_count; + std::atomic<std::size_t> weak_count; + + explicit shared_control_block(std::size_t shared = 1, std::size_t weak = 0) + : shared_count(shared) + , weak_count(weak) + {} + }; + template<typename T> struct shared_ptr; /** + * @brief weak_ptr is a smart pointer that holds a non-owning weak reference to an object that is managed by + * shared_ptr. It must be converted to shared_ptr in to be able to access the referenced object. A weak_ptr is created + * as a copy of a shared_ptr, or as a copy of another weak_ptr. A weak_ptr is typically used to break circular + * references between shared_ptr to avoid memory leaks. A weak_ptr does not contribute to the reference count of the + * object, and it does not manage the lifetime of the object. If the object managed by shared_ptr is destroyed, the + * weak_ptr becomes expired and cannot be used to access the object anymore. + */ + template<typename T> + struct weak_ptr + { + template<typename U> + friend struct shared_ptr; + + /** + * @brief Constructs a null weak_ptr. + */ + weak_ptr() noexcept + : pointer(nullptr) + , control(nullptr) + {} + + template<typename U> + requires(std::is_convertible_v<U *, T *>) + weak_ptr(shared_ptr<U> const & other) + : pointer(other.pointer) + , control(other.control) + { + if (control != nullptr) + { + ++(control->weak_count); + } + } + + /** + * @brief Copy constructor. Constructs a weak_ptr which shares ownership of the object managed by other. + */ + weak_ptr(weak_ptr const & other) + : pointer(other.pointer) + , control(other.control) + { + if (control != nullptr) + { + ++(control->weak_count); + } + } + + /** + * @brief Move constructor. Constructs a weak_ptr which takes ownership of the object managed by other. + */ + weak_ptr(weak_ptr && other) noexcept + : pointer(other.pointer) + , control(other.control) + { + other.pointer = nullptr; + other.control = nullptr; + } + + /** + * @brief Assignment operator. Assigns the weak_ptr to another weak_ptr. + */ + auto operator=(weak_ptr const & other) -> weak_ptr & + { + if (this != &other) + { + cleanup(); + pointer = other.pointer; + control = other.control; + if (control != nullptr) + { + ++(control->weak_count); + } + } + + return *this; + } + + /** + * @brief Move assignment operator. Move-assigns a weak_ptr from other. + */ + auto operator=(weak_ptr && other) noexcept -> weak_ptr & + { + if (this != &other) + { + cleanup(); + pointer = other.pointer; + control = other.control; + other.pointer = nullptr; + other.control = nullptr; + } + + return *this; + } + + /** + * @brief Destructor. Cleans up resources if necessary. + */ + ~weak_ptr() + { + cleanup(); + } + + /** + * @brief Returns a shared_ptr that shares ownership of the managed object if the managed object still exists, or an + * empty shared_ptr otherwise. + */ + [[nodiscard]] auto lock() const -> shared_ptr<T> + { + return shared_ptr<T>(*this); + } + + private: + auto cleanup() -> void + { + if (control != nullptr) + { + if (--(control->weak_count) == 0 && control->shared_count == 0) + { + delete control; + } + } + } + + T * pointer; + shared_control_block * control; + }; + + /** + * @brief enable_shared_from_this is a base class that allows an object that is currently managed by a shared_ptr to + * create additional shared_ptr instances that share ownership of the same object. This is usefl when you want to + * create shared_ptr instances in a member function of the object. + * + * @tparam T The type of the managed object. + */ + template<typename T> + struct enable_shared_from_this + { + template<typename U> + friend struct shared_ptr; + + friend T; + + public: + /** + * @brief Returns a shared_ptr that shares ownership of *this. + */ + auto shared_from_this() -> shared_ptr<T> + { + return shared_ptr<T>(weak_this); + } + + /** + * @brief Returns a shared_ptr that shares ownership of *this. + */ + auto shared_from_this() const -> shared_ptr<T const> + { + return shared_ptr<T const>(weak_this); + } + + private: + enable_shared_from_this() = default; + enable_shared_from_this(enable_shared_from_this const &) = default; + auto operator=(enable_shared_from_this const &) -> enable_shared_from_this & = default; + ~enable_shared_from_this() = default; + + void internal_assign_ptr(shared_ptr<T> const & ptr) const + { + weak_this = ptr; + } + + mutable weak_ptr<T> weak_this{}; ///< Weak pointer to the object, used for shared_from_this functionality. + }; + + /** * @brief Shared_pointer is a smart pointer that retains shared ownership of an object through a pointer. Several * shared_ptr objects may own the same object. The object is destroyed and its memory deallocated when either of * the following happens: the last remaining shared_ptr owning the object is destroyed; the last remaining @@ -31,12 +221,23 @@ namespace kstd template<typename U> friend struct shared_ptr; + template<typename U> + friend struct weak_ptr; + + /** + * @brief Construct an empty shared_ptr. + */ + shared_ptr() noexcept + : pointer(nullptr) + , control(nullptr) + {} + /** * @brief Construct an empty shared_ptr from nullptr. */ shared_ptr(std::nullptr_t) noexcept : pointer(nullptr) - , ref_count(nullptr) + , control(nullptr) {} /** @@ -44,11 +245,33 @@ namespace kstd * * @param pointer A pointer to an object to manage (default is nullptr). */ - explicit shared_ptr(T * pointer = nullptr) + template<typename U> + requires(std::is_convertible_v<U *, T *>) + explicit shared_ptr(U * pointer = nullptr) : pointer(pointer) - , ref_count(pointer != nullptr ? new std::atomic<std::size_t>(1) : nullptr) + , control(pointer != nullptr ? new shared_control_block() : nullptr) + { + assign_enable_shared_from_this(pointer); + } + + /** + * @brief Constructor a shared_ptr from a weak_ptr. If other is not expired, constructs a shared_ptr which shares + * ownership of the object managed by other. Otherwise, constructs an empty shared_ptr. + * + * @param other The weak_ptr to construct from. + */ + template<typename U> + requires(std::is_convertible_v<U *, T *>) + explicit shared_ptr(weak_ptr<U> const & other) + : pointer(nullptr) + , control(nullptr) { - // Nothing to do. + if (other.control != nullptr && other.control->shared_count != 0) + { + pointer = other.pointer; + control = other.control; + ++(control->shared_count); + } } /** @@ -58,11 +281,11 @@ namespace kstd */ shared_ptr(shared_ptr const & other) : pointer(other.pointer) - , ref_count(other.ref_count) + , control(other.control) { - if (ref_count != nullptr) + if (control != nullptr) { - ++(*ref_count); + ++(control->shared_count); } } @@ -76,11 +299,11 @@ namespace kstd requires(std::is_convertible_v<U *, T *>) shared_ptr(shared_ptr<U> const & other) : pointer(other.pointer) - , ref_count(other.ref_count) + , control(other.control) { - if (ref_count != nullptr) + if (control != nullptr) { - ++(*ref_count); + ++(control->shared_count); } } @@ -91,10 +314,10 @@ namespace kstd */ shared_ptr(shared_ptr && other) noexcept : pointer(other.pointer) - , ref_count(other.ref_count) + , control(other.control) { other.pointer = nullptr; - other.ref_count = nullptr; + other.control = nullptr; } /** @@ -107,10 +330,10 @@ namespace kstd requires(std::is_convertible_v<U *, T *>) shared_ptr(shared_ptr<U> && other) noexcept : pointer(other.pointer) - , ref_count(other.ref_count) + , control(other.control) { other.pointer = nullptr; - other.ref_count = nullptr; + other.control = nullptr; } /** @@ -127,11 +350,11 @@ namespace kstd { cleanup(); pointer = other.pointer; - ref_count = other.ref_count; + control = other.control; - if (ref_count != nullptr) + if (control != nullptr) { - ++(*ref_count); + ++(control->shared_count); } } @@ -151,11 +374,11 @@ namespace kstd { cleanup(); pointer = other.pointer; - ref_count = other.ref_count; + control = other.control; - if (ref_count != nullptr) + if (control != nullptr) { - ++(*ref_count); + ++(control->shared_count); } return *this; @@ -174,9 +397,9 @@ namespace kstd { cleanup(); pointer = other.pointer; - ref_count = other.ref_count; + control = other.control; other.pointer = nullptr; - other.ref_count = nullptr; + other.control = nullptr; } return *this; @@ -195,9 +418,9 @@ namespace kstd { cleanup(); pointer = other.pointer; - ref_count = other.ref_count; + control = other.control; other.pointer = nullptr; - other.ref_count = nullptr; + other.control = nullptr; return *this; } @@ -209,7 +432,7 @@ namespace kstd { cleanup(); pointer = nullptr; - ref_count = nullptr; + control = nullptr; return *this; } @@ -230,7 +453,8 @@ namespace kstd { cleanup(); pointer = ptr; - ref_count = ptr != nullptr ? new std::atomic<std::size_t>(1) : nullptr; + control = ptr != nullptr ? new shared_control_block() : nullptr; + assign_enable_shared_from_this(ptr); } /** @@ -242,7 +466,7 @@ namespace kstd void swap(shared_ptr & other) { std::swap(pointer, other.pointer); - std::swap(ref_count, other.ref_count); + std::swap(control, other.control); } /** @@ -288,9 +512,9 @@ namespace kstd */ [[nodiscard]] auto use_count() const -> std::size_t { - if (ref_count != nullptr) + if (control != nullptr) { - return *ref_count; + return control->shared_count; } return 0; @@ -329,19 +553,47 @@ namespace kstd private: /** + * @brief If the candidate type inherits from enable_shared_from_this, assigns the internal weak pointer to this + * shared_ptr. This weak_ptr is used to implement shared_from_this functionality for the candidate type. If the + * candidate type does not inherit from enable_shared_from_this, this function does nothing. + * + * @tparam U The candidate type to check for enable_shared_from_this inheritance. + * @param candidate The candidate object to assign the internal weak pointer for. + */ + template<typename U> + auto assign_enable_shared_from_this(U * candidate) -> void + { + if constexpr (requires(U * p, shared_ptr<T> const & sp) { p->internal_assign_ptr(sp); }) + { + if (candidate != nullptr) + { + candidate->internal_assign_ptr(*this); + } + } + } + + /** * @brief Releases ownership and deletes the object if this was the last reference to the owned managed object. */ auto cleanup() -> void { - if (ref_count != nullptr && --(*ref_count) == 0) + if (control != nullptr) { - delete pointer; - delete ref_count; + if (--(control->shared_count) == 0) + { + delete pointer; + pointer = nullptr; + + if (control->weak_count == 0) + { + delete control; + } + } } } - T * pointer; ///< The managed object. - std::atomic<std::size_t> * ref_count; ///< Reference count. + T * pointer; ///< The managed object. + shared_control_block * control; ///< Shared control block. }; /** |