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An observable is used to decouple an information producer from a consumer
(in the same way as a callback), while allowing multiple consumers (called
observers) to coexist and to manage their lifetime separately.
Two classes are introduced:
observable: a producer class; when an observable is invoked all observers
receive the information
observer: a consumer class; receives information from a observable
Modelled after boost::signals2, with the following changes
- all signals return void; information is passed from the producer to
the consumer but not back
- thread-unsafe
- modern C++ without preprocessor hacks
- connection lifetime is always managed rather than leaked by default
- renamed to avoid the funky "slot" name
Message-Id: <20180709172726.5079-1-avi@scylladb.com>
133 lines
3.7 KiB
C++
133 lines
3.7 KiB
C++
/*
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* Copyright (C) 2018 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 <functional>
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#include <vector>
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#include <boost/range/algorithm/replace.hpp>
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#include <boost/range/algorithm/remove.hpp>
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namespace utils {
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template <typename... Args>
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class observable {
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public:
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class observer;
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private:
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std::vector<observer*> _observers;
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public:
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class observer {
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friend class observable;
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observable* _observable;
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std::function<void (Args...)> _callback;
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private:
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void moved(observer* from) {
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if (_observable) {
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_observable->moved(from, this);
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}
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}
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public:
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observer(observable* o, std::function<void (Args...)> callback) noexcept
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: _observable(o), _callback(std::move(callback)) {
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}
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observer(observer&& o) noexcept
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: _observable(std::exchange(o._observable, nullptr))
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, _callback(std::move(o._callback)) {
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moved(&o);
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}
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observer& operator=(observer&& o) noexcept {
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if (this != &o) {
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disconnect();
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_observable = std::exchange(o._observable, nullptr);
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_callback = std::move(o._callback);
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moved(&o);
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}
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return *this;
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}
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~observer() {
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disconnect();
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}
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void disconnect() {
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if (_observable) {
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_observable->destroyed(this);
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}
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}
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};
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friend class observer;
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private:
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void destroyed(observer* dead) {
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_observers.erase(boost::remove(_observers, dead), _observers.end());
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}
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void moved(observer* from, observer* to) {
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boost::replace(_observers, from, to);
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}
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void update_observers(observable* ob) {
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for (auto&& c : _observers) {
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c->_observable = ob;
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}
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}
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public:
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observable() = default;
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observable(observable&& o) noexcept
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: _observers(std::move(o._observers)) {
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update_observers(this);
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}
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observable& operator=(observable&& o) noexcept {
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if (this != &o) {
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update_observers(nullptr);
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_observers = std::move(o._observers);
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update_observers(this);
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}
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return *this;
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}
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~observable() {
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update_observers(nullptr);
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}
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// Send args to all connected observers
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void operator()(Args... args) const {
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std::exception_ptr e;
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for (auto&& ob : _observers) {
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try {
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ob->_callback(args...);
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} catch (...) {
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if (!e) {
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e = std::current_exception();
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}
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}
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}
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if (e) {
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std::rethrow_exception(std::move(e));
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}
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}
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// Adds an observer to an observable
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observer observe(std::function<void (Args...)> callback) {
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observer ob(this, std::move(callback));
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_observers.push_back(&ob);
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return ob;
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}
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};
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template <typename... Args>
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using observer = typename observable<Args...>::observer;
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}
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