1 /* Copyright (c) 2007-2023. The SimGrid Team. All rights reserved. */
3 /* This program is free software; you can redistribute it and/or modify it
4 * under the terms of the license (GNU LGPL) which comes with this package. */
6 #ifndef SIMGRID_MC_UDPOR_MAXIMAL_SUBSETS_ITERATOR_HPP
7 #define SIMGRID_MC_UDPOR_MAXIMAL_SUBSETS_ITERATOR_HPP
9 #include "src/mc/explo/udpor/Configuration.hpp"
11 #include <boost/iterator/iterator_facade.hpp>
14 #include <unordered_map>
16 namespace simgrid::mc::udpor {
19 * @brief An iterator over the tree of sets of (non-empty) maximal events that
20 * can be generated from a given configuration
22 * This iterator traverses all possible sets of maximal events that
23 * can be formed from a configuration, each of which satisfy a predicate.
25 * Iteration over the maximal events of a configuration is an important
26 * step in computing the extension set of a configuration for an action
27 * whose identity is not "exploitable" (i.e. one whose type information cannot
28 * help us narrow down our search).
30 struct maximal_subsets_iterator
31 : public boost::iterator_facade<maximal_subsets_iterator, const EventSet, boost::forward_traversal_tag> {
33 // A function which answers the question "do I need to consider maximal sets
34 // that contain this node?"
35 using node_filter_function = std::function<bool(const UnfoldingEvent*)>;
36 using topological_order_position = std::vector<const UnfoldingEvent*>::const_iterator;
38 maximal_subsets_iterator() = default;
39 explicit maximal_subsets_iterator(const Configuration& config) : maximal_subsets_iterator(config, std::nullopt) {}
40 maximal_subsets_iterator(const Configuration& config, std::optional<node_filter_function> filter);
43 const std::optional<std::reference_wrapper<const Configuration>> config = std::nullopt;
44 std::vector<const UnfoldingEvent*> topological_ordering;
46 // The boolean is a bit of an annoyance, but it works. Effectively,
47 // there's no way to distinguish between "we're starting the search
48 // after the empty set" and "we've finished the search" since the resulting
49 // maximal set and backtracking point stack will both be empty in both cases
50 bool has_started_searching = false;
51 std::optional<EventSet> current_maximal_set = std::nullopt;
52 std::stack<topological_order_position> backtrack_points = std::stack<topological_order_position>();
55 * @brief A small class which provides functionality for managing
56 * the "counts" as the iterator proceeds forward in time
58 * As an instance of the `maximal_subsets_iterator` traverses
59 * the configuration, it keeps track of how many events
60 * further down in the causality tree have been signaled as in-conflict
61 * with events that are its current maximal event set (i.e.
62 * its `current_maximal_set`)
66 using topological_order_position = maximal_subsets_iterator::topological_order_position;
68 void mark_included_in_maximal_set(const UnfoldingEvent*);
69 void mark_removed_from_maximal_set(const UnfoldingEvent*);
70 topological_order_position find_next_candidate_event(topological_order_position first,
71 topological_order_position last) const;
74 std::unordered_map<const UnfoldingEvent*, unsigned> event_counts;
76 /// @brief Whether or not the given event, according to the
77 /// bookkeeping that has been done thus far, can be added to the
78 /// current candidate maximal set
79 bool is_candidate_event(const UnfoldingEvent*) const;
82 void add_element_to_current_maximal_set(const UnfoldingEvent*);
83 void remove_element_from_current_maximal_set(const UnfoldingEvent*);
86 * @brief Moves to the next node in the topological ordering
87 * by continuing the search in the tree of maximal event sets
88 * from where we currently believe we are in the tree
90 * At each stage of the iteration, the iterator points to
91 * a maximal event set that can be thought of as `R` + `A`:
96 * where `R` is some set of events and `A` is another event.
98 * The iterator first tries expansion from `R` + `A`. If it finds
99 * node `B` to expand, this means that there is a node in the tree of
100 * maximal event sets of `C` (the configuration traversed) such that
101 * `R` + `A` + `B` needs to be checked.
103 * If no such node is found, then the iterator must check `R` +
104 * some other node AFTER `A`. The new set of possibilities potentially
105 * includes some of `A`'s dependencies, so their counts are decremented
106 * prior to searching.
108 * @note: This method is a mutating method: it manipulates the
109 * iterator such that the iterator refers to the next maximal
110 * set sans the element returned. The `increment()` function performs
111 * the rest of the work needed to actually complete the transition
113 * @returns an iterator poiting to the event that should next
114 * be added to the set of maximal events if such an event exists,
115 * or to the end of the topological ordering if no such event exists
117 topological_order_position continue_traversal_of_maximal_events_tree();
119 // boost::iterator_facade<...> interface to implement
121 bool equal(const maximal_subsets_iterator& other) const { return current_maximal_set == other.current_maximal_set; }
122 const EventSet& dereference() const
124 static const EventSet empty_set = EventSet();
125 if (current_maximal_set.has_value()) {
126 return current_maximal_set.value();
131 // Allows boost::iterator_facade<...> to function properly
132 friend class boost::iterator_core_access;
135 } // namespace simgrid::mc::udpor