f3eade2f62
Drop the AGPL license in favor of a source-available license. See the blog post [1] for details. [1] https://www.scylladb.com/2024/12/18/why-were-moving-to-a-source-available-license/
127 lines
2.8 KiB
C++
127 lines
2.8 KiB
C++
/*
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* Copyright (C) 2015-present ScyllaDB
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*/
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/*
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* SPDX-License-Identifier: LicenseRef-ScyllaDB-Source-Available-1.0
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*/
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#pragma once
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#include "utils/allocation_strategy.hh"
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template<typename T>
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requires std::is_nothrow_move_constructible_v<T>
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class managed;
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//
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// Similar to std::unique_ptr<>, but for LSA-allocated objects. Remains
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// valid across deferring points. See make_managed().
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//
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// std::unique_ptr<> can't be used with LSA-allocated objects because
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// it assumes that the object doesn't move after being allocated. This
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// is not true for LSA, which moves objects during compaction.
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//
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// Also works for objects allocated using standard allocators, though
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// there the extra space overhead of a pointer is not justified.
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// It still make sense to use it in places which are meant to work
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// with either kind of allocator.
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//
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template<typename T>
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struct managed_ref {
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managed<T>* _ptr;
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managed_ref() : _ptr(nullptr) {}
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managed_ref(const managed_ref&) = delete;
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managed_ref(managed_ref&& other) noexcept
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: _ptr(other._ptr)
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{
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other._ptr = nullptr;
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if (_ptr) {
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_ptr->_backref = &_ptr;
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}
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}
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~managed_ref() {
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if (_ptr) {
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current_allocator().destroy(_ptr);
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}
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}
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managed_ref& operator=(managed_ref&& o) {
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this->~managed_ref();
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new (this) managed_ref(std::move(o));
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return *this;
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}
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T* get() {
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return _ptr ? &_ptr->_value : nullptr;
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}
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const T* get() const {
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return _ptr ? &_ptr->_value : nullptr;
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}
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T& operator*() {
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return _ptr->_value;
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}
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const T& operator*() const {
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return _ptr->_value;
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}
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T* operator->() {
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return &_ptr->_value;
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}
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const T* operator->() const {
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return &_ptr->_value;
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}
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explicit operator bool() const {
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return _ptr != nullptr;
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}
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size_t external_memory_usage() const {
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return _ptr ? current_allocator().object_memory_size_in_allocator(_ptr) : 0;
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}
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};
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template<typename T>
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requires std::is_nothrow_move_constructible_v<T>
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class managed {
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managed<T>** _backref;
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T _value;
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template<typename T_>
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friend struct managed_ref;
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public:
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managed(managed<T>** backref, T&& v) noexcept
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: _backref(backref)
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, _value(std::move(v))
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{
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*_backref = this;
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}
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managed(managed&& other) noexcept
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: _backref(other._backref)
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, _value(std::move(other._value))
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{
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*_backref = this;
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}
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};
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//
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// Allocates T using given AllocationStrategy and returns a managed_ref owning the
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// allocated object.
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//
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template<typename T, typename... Args>
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managed_ref<T>
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make_managed(Args&&... args) {
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managed_ref<T> ref;
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current_allocator().construct<managed<T>>(&ref._ptr, T(std::forward<Args>(args)...));
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return ref;
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}
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