f3eade2f62
Drop the AGPL license in favor of a source-available license. See the blog post [1] for details. [1] https://www.scylladb.com/2024/12/18/why-were-moving-to-a-source-available-license/
102 lines
3.1 KiB
C++
102 lines
3.1 KiB
C++
/*
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* Copyright (C) 2016-present ScyllaDB
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*/
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/*
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* SPDX-License-Identifier: LicenseRef-ScyllaDB-Source-Available-1.0
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*/
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#pragma once
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#include <any>
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#include <boost/signals2/connection.hpp>
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#include <boost/signals2/signal_type.hpp>
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#include <boost/signals2/dummy_mutex.hpp>
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#include <seastar/util/noncopyable_function.hh>
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#include <seastar/core/shared_ptr.hh>
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#include <seastar/core/sstring.hh>
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using namespace seastar;
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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 signal_type _s;
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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, std::string_view 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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operator bool() const {
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return _enabled;
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}
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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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[[nodiscard("the listener_registration returned by when_enabled must be kept alive "
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"in order to keep the callback registered")]]
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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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