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/
96 lines
2.8 KiB
C++
96 lines
2.8 KiB
C++
/*
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* Copyright (C) 2020-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 <seastar/core/lowres_clock.hh>
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#include <unordered_map>
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#include <list>
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namespace utils {
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// A map with the track of least recent visited entries.
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template <class Key, class Val, class Clock = seastar::lowres_clock>
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class recent_entries_map {
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struct recent_entry {
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Key _key;
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Val _value;
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typename Clock::time_point _last_visit;
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template<typename... Args>
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recent_entry(const Key& k, Args&&... args)
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: _key(k)
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, _value(std::forward<Args>(args)...)
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, _last_visit(Clock::now())
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{}
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recent_entry(const recent_entry&) = delete;
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recent_entry& operator=(const recent_entry&) = delete;
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};
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using recent_entries = std::list<recent_entry>;
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using entries_map = std::unordered_map<Key, typename recent_entries::iterator>;
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private:
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recent_entries _recent_entries;
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entries_map _entries_map;
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private:
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void touch(typename recent_entries::const_iterator it) {
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_recent_entries.splice(_recent_entries.begin(), _recent_entries, it);
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recent_entry& entry = *_recent_entries.begin();
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entry._last_visit = Clock::now();
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}
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public:
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// Returns the size of the map.
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size_t size() const {
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return _entries_map.size();
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}
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// Returns the recent_entry with the given key, or constructs new one
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// if the corresponding key is not present in the map.
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template<typename... Args>
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Val& try_get_recent_entry(const Key& k, Args&&... args) {
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if (auto it = _entries_map.find(k); it != _entries_map.end()) {
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touch(it->second);
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recent_entry& entry = *it->second;
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return entry._value;
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}
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_recent_entries.emplace_front(k, std::forward<Args>(args)...);
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auto it = _recent_entries.begin();
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_entries_map.emplace(k, it);
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return it->_value;
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}
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// Removes the recent_entry with the given key.
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void remove_recent_entry(const Key& k) {
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if (auto it = _entries_map.find(k); it != _entries_map.end()) {
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_recent_entries.erase(it->second);
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_entries_map.erase(it);
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}
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}
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// Removes recent_entries not younger than the specified interval.
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void remove_least_recent_entries(std::chrono::milliseconds interval) {
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const auto now = Clock::now();
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auto it = std::find_if(_recent_entries.begin(), _recent_entries.end(), [now, interval](const recent_entry& entry) {
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return now - entry._last_visit >= interval;
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});
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for (; it != _recent_entries.end(); ) {
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_entries_map.erase(it->_key);
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it = _recent_entries.erase(it);
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}
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}
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};
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} // end of namespace utils
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