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f3fc81751f
Currently, the serialized_action error is set to a shared_promise, but is not returned to the caller, unless there is an already outstanding action. Note that setting the exception to the promise when noone collected it via the shared_future caused 'Exceptional future ignored' warning to be issued, as seen in #7352. Fixes #7352 Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
98 lines
3.1 KiB
C++
98 lines
3.1 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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#include <seastar/util/later.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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private:
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future<> do_trigger() {
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_pending = {};
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return futurize_invoke(_func);
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}
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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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//
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// When action is not currently running, it is started immediately if !later or
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// at some point in time soon after current fiber defers when later is true.
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future<> trigger(bool later = false) {
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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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future<> ret = _pending;
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// run in background, synchronize using `ret`
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(void)_sem.wait().then([this, later] () mutable {
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if (later) {
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return seastar::later().then([this] () mutable {
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return do_trigger();
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});
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}
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return do_trigger();
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}).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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return ret.finally([this] {
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_sem.signal();
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});
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}
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// Like trigger(), but defers invocation of the action to allow for batching
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// more requests.
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future<> trigger_later() {
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return trigger(true);
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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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