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6db002163f
It can be invoked with a lambda without the ceremony of creating a class deriving from gms::feature::listener. The reutrned registration object controls listener's scope.
112 lines
3.7 KiB
C++
112 lines
3.7 KiB
C++
/*
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* Copyright (C) 2016 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 <boost/signals2.hpp>
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#include <boost/signals2/dummy_mutex.hpp>
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#include <seastar/core/shared_future.hh>
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#include <seastar/util/noncopyable_function.hh>
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namespace bs2 = boost::signals2;
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namespace gms {
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class feature_service;
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/**
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* A gossip feature tracks whether all the nodes the current one is
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* aware of support the specified feature.
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*
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* A feature should only be created once the gossiper is available.
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*/
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class feature final {
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using signal_type = bs2::signal_type<void (), bs2::keywords::mutex_type<bs2::dummy_mutex>>::type;
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feature_service* _service = nullptr;
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sstring _name;
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bool _enabled = false;
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mutable shared_promise<> _pr;
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mutable signal_type _s;
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friend class gossiper;
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public:
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using listener_registration = std::any;
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class listener {
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friend class feature;
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bs2::scoped_connection _conn;
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signal_type::slot_type _slot;
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const signal_type::slot_type& get_slot() const { return _slot; }
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void set_connection(bs2::scoped_connection&& conn) { _conn = std::move(conn); }
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void callback() {
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_conn.disconnect();
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on_enabled();
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}
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protected:
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bool _started = false;
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public:
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listener() : _slot(signal_type::slot_type(&listener::callback, this)) {}
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listener(const listener&) = delete;
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listener(listener&&) = delete;
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listener& operator=(const listener&) = delete;
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listener& operator=(listener&&) = delete;
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// Has to run inside seastar::async context
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virtual void on_enabled() = 0;
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};
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explicit feature(feature_service& service, sstring name, bool enabled = false);
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feature() = default;
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~feature();
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feature(const feature& other) = delete;
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// Has to run inside seastar::async context
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void enable();
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feature& operator=(feature&& other);
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const sstring& name() const {
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return _name;
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}
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explicit operator bool() const {
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return _enabled;
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}
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friend inline std::ostream& operator<<(std::ostream& os, const feature& f) {
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return os << "{ gossip feature = " << f._name << " }";
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}
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future<> when_enabled() const { return _pr.get_shared_future(); }
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void when_enabled(listener& callback) const {
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callback.set_connection(_s.connect(callback.get_slot()));
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if (_enabled) {
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_s();
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}
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}
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// Will call the callback functor when this feature is enabled, unless
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// the returned listener_registration is destroyed earlier.
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listener_registration when_enabled(seastar::noncopyable_function<void()> callback) const {
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struct wrapper : public listener {
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seastar::noncopyable_function<void()> _func;
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wrapper(seastar::noncopyable_function<void()> func) : _func(std::move(func)) {}
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void on_enabled() override { _func(); }
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};
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auto holder = make_lw_shared<wrapper>(std::move(callback));
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when_enabled(*holder);
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return holder;
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}
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};
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} // namespace gms
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