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https://github.com/scylladb/scylladb.git
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74 lines
2.3 KiB
C++
74 lines
2.3 KiB
C++
/*
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* Copyright (C) 2017 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 <seastar/core/semaphore.hh>
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#include <seastar/core/future.hh>
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#include <seastar/core/shared_future.hh>
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// An async action wrapper which ensures that at most one action
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// is running at any time.
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class serialized_action {
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public:
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template <typename... T>
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using future = seastar::future<T...>;
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private:
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std::function<future<>()> _func;
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seastar::shared_future<> _pending;
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seastar::semaphore _sem;
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public:
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serialized_action(std::function<future<>()> func)
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: _func(std::move(func))
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, _sem(1)
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{ }
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serialized_action(serialized_action&&) = delete;
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serialized_action(const serialized_action&) = delete;
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// Makes sure that a new action will be started after this call and
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// returns a future which resolves when that action completes.
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// At most one action can run at any given moment.
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// A single action is started on behalf of all earlier triggers.
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future<> trigger() {
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if (_pending.valid()) {
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return _pending;
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}
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seastar::shared_promise<> pr;
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_pending = pr.get_shared_future();
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return with_semaphore(_sem, 1, [this, pr = std::move(pr)]() mutable {
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_pending = {};
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return futurize_apply(_func).then_wrapped([pr = std::move(pr)](auto&& f) mutable {
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if (f.failed()) {
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pr.set_exception(f.get_exception());
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} else {
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pr.set_value();
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}
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});
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});
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}
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// Waits for all invocations initiated in the past.
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future<> join() {
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return get_units(_sem, 1).discard_result();
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}
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};
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