38a54df863
People keep tripping over the old copyrights and copy-pasting them to new files. Search and replace "Cloudius Systems" with "ScyllaDB". Message-Id: <1460013664-25966-1-git-send-email-penberg@scylladb.com>
128 lines
3.1 KiB
C++
128 lines
3.1 KiB
C++
/*
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* Copyright (C) 2015 ScyllaDB
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*/
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/*
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* This file is part of Scylla.
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*
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* Scylla is free software: you can redistribute it and/or modify
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* it under the terms of the GNU Affero General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* Scylla is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with Scylla. If not, see <http://www.gnu.org/licenses/>.
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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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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& 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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};
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template<typename 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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static_assert(std::is_nothrow_move_constructible<T>::value, "Throwing move constructor not supported");
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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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