fcb8d040e8
Instead of lengthy blurbs, switch to single-line, machine-readable standardized (https://spdx.dev) license identifiers. The Linux kernel switched long ago, so there is strong precedent. Three cases are handled: AGPL-only, Apache-only, and dual licensed. For the latter case, I chose (AGPL-3.0-or-later and Apache-2.0), reasoning that our changes are extensive enough to apply our license. The changes we applied mechanically with a script, except to licenses/README.md. Closes #9937
98 lines
2.5 KiB
C++
98 lines
2.5 KiB
C++
/*
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* Copyright (C) 2020 ScyllaDB
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*/
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/*
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* SPDX-License-Identifier: AGPL-3.0-or-later
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*/
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#pragma once
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#include <boost/intrusive/parent_from_member.hpp>
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// A movable pointer-like object paired with exactly one other object of the same type.
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// The two objects which are paired with each other point at each other.
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// The relationship is symmetrical.
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//
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// A pair of such objects can be used for implementing bi-directional traversal in data structures.
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//
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// Moving this object automatically updates the other reference, so the references remain
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// consistent when the containing objects are managed by LSA.
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//
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// get()
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// ------------------>
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// ----------- -----------
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// | entangled |~~~~~~~~~~~| entangled |
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// ----------- -----------
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// <------------------
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// get()
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//
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class entangled final {
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entangled* _ref = nullptr;
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private:
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struct init_tag {};
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entangled(init_tag, entangled& other) {
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assert(!other._ref);
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_ref = &other;
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other._ref = this;
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}
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public:
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// Creates a new object which is paired with a given "other".
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// The other is also paired with this object afterwards.
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// The other must not be paired before the call.
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static entangled make_paired_with(entangled& other) {
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return entangled(init_tag(), other);
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}
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// Creates an unpaired object.
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entangled() = default;
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entangled(const entangled&) = delete;
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entangled(entangled&& other) noexcept
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: _ref(other._ref)
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{
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if (_ref) {
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_ref->_ref = this;
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}
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other._ref = nullptr;
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}
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~entangled() {
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if (_ref) {
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_ref->_ref = nullptr;
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}
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}
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entangled& operator=(entangled&& other) noexcept {
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if (_ref) {
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_ref->_ref = nullptr;
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}
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_ref = other._ref;
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if (_ref) {
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_ref->_ref = this;
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}
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other._ref = nullptr;
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return *this;
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}
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entangled* get() { return _ref; }
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const entangled* get() const { return _ref; }
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explicit operator bool() const { return _ref != nullptr; }
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template<typename T>
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T* get(entangled T::* paired_member) {
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if (!_ref) {
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return nullptr;
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}
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return boost::intrusive::get_parent_from_member(get(), paired_member);
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}
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template<typename T>
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const T* get(entangled T::* paired_member) const {
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if (!_ref) {
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return nullptr;
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}
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return boost::intrusive::get_parent_from_member(get(), paired_member);
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}
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};
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