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f8156702de
~2076 files used "Copyright (C) YYYY-present ScyllaDB" while ~88 files used "Copyright (C) YYYY ScyllaDB". This inconsistency leads to unnecessary code review discussions and gradual spread of the less common format. Standardize all ScyllaDB copyright headers to use -present. Fixes SCYLLADB-1984 Closes scylladb/scylladb#29876
55 lines
1.5 KiB
C++
55 lines
1.5 KiB
C++
/*
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* Copyright (C) 2021-present ScyllaDB
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*/
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/*
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* SPDX-License-Identifier: LicenseRef-ScyllaDB-Source-Available-1.1
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*/
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#pragma once
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#include <functional>
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#include <seastar/core/shared_future.hh>
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#include <stdexcept>
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/// Invokes a factory to produce an object, but sequentially: only one fiber at a time may be executing the
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/// factory. Any other fiber requesting the object will wait for the existing factory invocation to finish, then
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/// copy the result.
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///
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/// TODO: Move to Seastar.
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template<typename T>
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class sequential_producer {
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public:
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using factory_t = std::function<seastar::future<T>()>;
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using time_point = seastar::shared_future<T>::time_point;
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private:
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factory_t _factory;
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seastar::shared_future<T> _churning; ///< Resolves when the previous _factory call completes.
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public:
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sequential_producer(factory_t&& f) : _factory(std::move(f))
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{
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clear();
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}
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seastar::future<T> operator()(time_point timeout = time_point::max()) {
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if (_churning.available()) {
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_churning = _factory();
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}
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return _churning.get_future(timeout);
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}
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seastar::future<T> operator()(seastar::abort_source& as) {
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if (_churning.available()) {
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_churning = _factory();
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}
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return _churning.get_future(as);
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}
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void clear() {
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_churning = seastar::make_exception_future<T>(
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std::logic_error("initial future used in sequential_producer"));
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}
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};
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