111 lines
3.2 KiB
C++
111 lines
3.2 KiB
C++
/*
|
|
* Copyright (C) 2020 ScyllaDB
|
|
*/
|
|
|
|
/*
|
|
* This file is part of Scylla.
|
|
*
|
|
* Scylla is free software: you can redistribute it and/or modify
|
|
* it under the terms of the GNU Affero General Public License as published by
|
|
* the Free Software Foundation, either version 3 of the License, or
|
|
* (at your option) any later version.
|
|
*
|
|
* Scylla is distributed in the hope that it will be useful,
|
|
* but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
|
* GNU General Public License for more details.
|
|
*
|
|
* You should have received a copy of the GNU General Public License
|
|
* along with Scylla. If not, see <http://www.gnu.org/licenses/>.
|
|
*/
|
|
|
|
#pragma once
|
|
|
|
#include <boost/intrusive/parent_from_member.hpp>
|
|
|
|
// A movable pointer-like object paired with exactly one other object of the same type.
|
|
// The two objects which are paired with each other point at each other.
|
|
// The relationship is symmetrical.
|
|
//
|
|
// A pair of such objects can be used for implementing bi-directional traversal in data structures.
|
|
//
|
|
// Moving this object automatically updates the other reference, so the references remain
|
|
// consistent when the containing objects are managed by LSA.
|
|
//
|
|
// get()
|
|
// ------------------>
|
|
// ----------- -----------
|
|
// | entangled |~~~~~~~~~~~| entangled |
|
|
// ----------- -----------
|
|
// <------------------
|
|
// get()
|
|
//
|
|
class entangled final {
|
|
entangled* _ref = nullptr;
|
|
private:
|
|
struct init_tag {};
|
|
entangled(init_tag, entangled& other) {
|
|
assert(!other._ref);
|
|
_ref = &other;
|
|
other._ref = this;
|
|
}
|
|
public:
|
|
// Creates a new object which is paired with a given "other".
|
|
// The other is also paired with this object afterwards.
|
|
// The other must not be paired before the call.
|
|
static entangled make_paired_with(entangled& other) {
|
|
return entangled(init_tag(), other);
|
|
}
|
|
|
|
// Creates an unpaired object.
|
|
entangled() = default;
|
|
entangled(const entangled&) = delete;
|
|
|
|
entangled(entangled&& other) noexcept
|
|
: _ref(other._ref)
|
|
{
|
|
if (_ref) {
|
|
_ref->_ref = this;
|
|
}
|
|
other._ref = nullptr;
|
|
}
|
|
|
|
~entangled() {
|
|
if (_ref) {
|
|
_ref->_ref = nullptr;
|
|
}
|
|
}
|
|
|
|
entangled& operator=(entangled&& other) noexcept {
|
|
if (_ref) {
|
|
_ref->_ref = nullptr;
|
|
}
|
|
_ref = other._ref;
|
|
if (_ref) {
|
|
_ref->_ref = this;
|
|
}
|
|
other._ref = nullptr;
|
|
return *this;
|
|
}
|
|
|
|
entangled* get() { return _ref; }
|
|
const entangled* get() const { return _ref; }
|
|
explicit operator bool() const { return _ref != nullptr; }
|
|
|
|
template<typename T>
|
|
T* get(entangled T::* paired_member) {
|
|
if (!_ref) {
|
|
return nullptr;
|
|
}
|
|
return boost::intrusive::get_parent_from_member(get(), paired_member);
|
|
}
|
|
|
|
template<typename T>
|
|
const T* get(entangled T::* paired_member) const {
|
|
if (!_ref) {
|
|
return nullptr;
|
|
}
|
|
return boost::intrusive::get_parent_from_member(get(), paired_member);
|
|
}
|
|
};
|