1 /* Copyright (c) 2007-2023. The SimGrid Team.
2 * All rights reserved. */
4 /* This program is free software; you can redistribute it and/or modify it
5 * under the terms of the license (GNU LGPL) which comes with this package. */
7 #ifndef SIMGRID_MC_UDPOR_CHECKER_HPP
8 #define SIMGRID_MC_UDPOR_CHECKER_HPP
10 #include "src/mc/explo/Exploration.hpp"
11 #include "src/mc/explo/udpor/Configuration.hpp"
12 #include "src/mc/explo/udpor/EventSet.hpp"
13 #include "src/mc/explo/udpor/Unfolding.hpp"
14 #include "src/mc/explo/udpor/UnfoldingEvent.hpp"
15 #include "src/mc/mc_record.hpp"
20 namespace simgrid::mc::udpor {
23 * @brief Performs exploration of a concurrent system via the
26 * The `UdporChecker` implementation is based primarily off three papers,
27 * herein referred to as [1], [2], and [3] respectively, as well as the
28 * current implementation of `tiny_simgrid`:
30 * 1. "Unfolding-based Partial Order Reduction" by Rodriguez et al.
31 * 2. Quasi-Optimal Partial Order Reduction by Nguyen et al.
32 * 3. The Anh Pham's Thesis "Exploration efficace de l'espace ..."
34 class XBT_PRIVATE UdporChecker : public Exploration {
36 explicit UdporChecker(const std::vector<char*>& args);
39 RecordTrace get_record_trace() override;
40 std::vector<std::string> get_textual_trace() override;
42 inline std::unique_ptr<State> get_current_state() { return std::make_unique<State>(get_remote_app()); }
46 * @brief The "relevant" portions of the unfolding that must be kept around to ensure that
47 * UDPOR properly searches the state space
49 * The set `U` is a global variable which is maintained by UDPOR
50 * to keep track of "just enough" information about the unfolding
51 * to compute *alternatives* (see the paper for more details).
53 * @invariant: When a new event is created by UDPOR, it is inserted into
54 * this set. All new events that are created by UDPOR have causes that
55 * also exist in U and are valid for the duration of the search.
57 * If an event is discarded instead of moved from set `U` to set `G`,
58 * the event and its contents will be discarded.
63 * @brief The "irrelevant" portions of the unfolding that do not need to be kept
64 * around to ensure that UDPOR functions correctly
66 * The set `G` is another global variable maintained by the UDPOR algorithm which
67 * is used to keep track of all events which used to be important to UDPOR
71 /// @brief UDPOR's current "view" of the program it is exploring
72 Unfolding unfolding = Unfolding();
74 using ExtensionFunction = std::function<EventSet(const Configuration&, const Transition&)>;
77 * @brief A collection of specialized functions which can incrementally
78 * compute the extension of a configuration based on the action taken
80 std::unordered_map<Transition::Type, ExtensionFunction> incremental_extension_functions =
81 std::unordered_map<Transition::Type, ExtensionFunction>();
84 * @brief Explores the unfolding of the concurrent system
85 * represented by the ModelChecker instance "mcmodel_checker"
87 * This function performs the actual search following the
88 * UDPOR algorithm according to [1].
90 * @param C the current configuration from which UDPOR will be used
91 * to explore expansions of the concurrent system being modeled
92 * @param D the set of events that should not be considered by UDPOR
93 * while performing its searches, in order to avoid sleep-set blocked
94 * executions. See [1] for more details
95 * @param A the set of events to "guide" UDPOR in the correct direction
96 * when it returns back to a node in the unfolding and must decide among
97 * events to select from `ex(C)`. See [1] for more details
98 * @param stateC the state of the program after having executed `C`,
99 * viz. `state(C)` using the notation of [1]
101 * TODO: Add the optimization where we can check if e == e_prior
102 * to prevent repeated work when computing ex(C)
104 void explore(const Configuration& C, EventSet D, EventSet A, std::unique_ptr<State> stateC, EventSet prev_exC);
107 * @brief Identifies the next event from the unfolding of the concurrent system
108 * that should next be explored as an extension of a configuration with
109 * enabled events `enC`
111 * @param A The set of events `A` maintained by the UDPOR algorithm to help
112 * determine how events should be selected. See the original paper [1] for more details
114 * @param enC The set `enC` of enabled events from the extension set `exC` used
115 * by the UDPOR algorithm to select new events to search. See the original
116 * paper [1] for more details
118 const UnfoldingEvent* select_next_unfolding_event(const EventSet& A, const EventSet& enC);
121 * @brief Computes the sets `ex(C)` and `en(C)` of the given configuration
122 * `C` as an incremental computation from the the previous computation of `ex(C)`
124 * A central component to UDPOR is the computation of the set `ex(C)`. The
125 * extension set `ex(C)` of a configuration `C` is defined as the set of events
126 * outside of `C` whose full dependency chain is contained in `C` (see [1]
129 * In general, computing `ex(C)` is very expensive. In paper [3], The Anh Pham
130 * shows a method of incremental computation of the set `ex(C)` under the
131 * conclusions afforded under the computation model in consideration, of which
132 * SimGrid is apart, which allow for `ex(C)` to be computed much more efficiently.
133 * Intuitively, the idea is to take advantage of the fact that you can avoid a lot
134 * of repeated computation by exploiting the aforementioned properties (in [3]) in
135 * what is effectively a dynamic programming optimization. See [3] for more details
137 * @param C the configuration based on which the two sets `ex(C)` and `en(C)` are
139 * @param stateC the state of the program after having executed C (viz. `state(C)`)
140 * @param prev_exC the previous value of `ex(C)`, viz. that which was computed for
141 * the configuration `C' := C - {e}`
142 * @returns a tuple containing the pair of sets `ex(C)` and `en(C)` respectively
144 std::tuple<EventSet, EventSet> compute_extension(const Configuration& C, const State& stateC,
145 const EventSet& prev_exC) const;
147 EventSet compute_extension_by_enumeration(const Configuration& C, const Transition& action) const;
152 EventSet compute_partial_alternative(const EventSet& D, const Configuration& C, const unsigned k) const;
157 void move_to_stateCe(State& stateC, const UnfoldingEvent& e);
160 * @brief Creates a new snapshot of the state of the progam undergoing
163 * @returns the handle used to uniquely identify this state later in the
164 * exploration of the unfolding. You provide this handle to an event in the
165 * unfolding to regenerate past states
167 std::unique_ptr<State> record_current_state();
172 void restore_program_state_to(const State& stateC);
177 void clean_up_explore(const UnfoldingEvent* e, const Configuration& C, const EventSet& D);
179 } // namespace simgrid::mc::udpor