7b10cc8079
this change was created in the same spirit ofebff5f5d. despite that we include Seastar as a submodule, Seastar is not a part of scylla project. so we'd better include its headers using brackets.ebff5f5daddressed this cosmetic issue a while back. but probably clangd's header-insertion helped some of contributor to insert the missing headers with `"`. so this style of `include` returned to the tree with these new changes. unfortunately, clangd does not allow us to configure the style of `include` at the time of writing. Signed-off-by: Kefu Chai <kefu.chai@scylladb.com> Closes scylladb/scylladb#19406
68 lines
2.0 KiB
C++
68 lines
2.0 KiB
C++
/*
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* Copyright (C) 2024-present ScyllaDB
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*/
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/*
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* SPDX-License-Identifier: AGPL-3.0-or-later
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*/
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#include <stdexcept>
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#include <vector>
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#include <map>
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#include <seastar/core/future.hh>
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#include <seastar/coroutine/maybe_yield.hh>
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#include "utils/stall_free.hh"
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namespace utils {
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/**
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* Topological sort a DAG using Kahn's algorithm.
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*
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* @param vertices Contains all vertices of the graph
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* @param adjacency_map Entry {k, v} means there is an k->v edge in the graph
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* @return a vector of topologically sorted vertices.
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If there is an edge k->v, then vertex k will be before vertex v.
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* @throws std::runtime_error when a graph has any cycle.
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*/
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template<typename T, typename Compare = std::less<T>>
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seastar::future<std::vector<T>> topological_sort(const std::vector<T>& vertices, const std::multimap<T, T, Compare>& adjacency_map) {
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std::map<T, size_t, Compare> ref_count_map; // Contains counters how many edges point (reference) to a vertex
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std::vector<T> sorted;
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sorted.reserve(vertices.size());
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for (auto& edge: adjacency_map) {
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ref_count_map[edge.second]++;
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}
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// Push to result vertices which reference counter == 0
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for (auto& v: vertices) {
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if (!ref_count_map.contains(v)) {
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sorted.emplace_back(v);
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}
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}
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// Iterate over already sorted vertices,
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// decrease counter of vertices to which sorted vertices points,
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// push to the end of `sorted` vector vertices which counter == 0.
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for (size_t i = 0; i < sorted.size(); i++) {
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auto [it_begin, it_end] = adjacency_map.equal_range(sorted[i]);
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while (it_begin != it_end) {
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auto d = it_begin->second;
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if (--ref_count_map[d] == 0) {
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sorted.push_back(d);
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}
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++it_begin;
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}
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co_await seastar::coroutine::maybe_yield();
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}
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co_await utils::clear_gently(ref_count_map);
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if (sorted.size() != vertices.size()) {
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throw std::runtime_error("Detected cycle in the graph.");
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}
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co_return sorted;
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}
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}
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