2bd76f8fc5
This class is an atomic view update backlog representation, safe to update from multiple shards. Signed-off-by: Duarte Nunes <duarte@scylladb.com>
71 lines
2.1 KiB
C++
71 lines
2.1 KiB
C++
/*
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* Copyright (C) 2018 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 "db/view/view_update_backlog.hh"
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#include <seastar/core/cacheline.hh>
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#include <seastar/core/lowres_clock.hh>
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#include <atomic>
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#include <chrono>
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#include <new>
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namespace db::view {
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/**
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* An atomic view update backlog representation, safe to update from multiple shards.
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* It is legal for a stale current max value to be returned.
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*/
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class node_update_backlog {
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using clock = seastar::lowres_clock;
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struct per_shard_backlog {
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// Multiply by 2 to defeat the prefetcher
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alignas(seastar::cache_line_size * 2) std::atomic<update_backlog> backlog = update_backlog::no_backlog();
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update_backlog load() const {
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return backlog.load(std::memory_order_relaxed);
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}
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};
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std::vector<per_shard_backlog> _backlogs;
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std::chrono::milliseconds _interval;
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std::atomic<clock::time_point> _last_update;
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std::atomic<update_backlog> _max;
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public:
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explicit node_update_backlog(size_t shards, std::chrono::milliseconds interval)
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: _backlogs(shards)
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, _interval(interval)
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, _last_update(clock::now() - _interval)
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, _max(update_backlog::no_backlog()) {
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}
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update_backlog add_fetch(unsigned shard, update_backlog backlog);
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// Exposed for testing only.
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update_backlog load() const {
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return _max.load(std::memory_order_relaxed);
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}
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};
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}
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