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_ODPOR_EXECUTION_HPP
7 #define SIMGRID_MC_ODPOR_EXECUTION_HPP
9 #include "src/mc/api/ClockVector.hpp"
10 #include "src/mc/explo/odpor/odpor_forward.hpp"
11 #include "src/mc/transition/Transition.hpp"
15 #include <unordered_set>
18 namespace simgrid::mc::odpor {
21 * @brief The occurrence of a transition in an execution
23 * An execution is set of *events*, where each element represents
24 * the occurrence or execution of the `i`th step of a particular
28 std::pair<const Transition*, ClockVector> contents_;
32 Event(Event&&) = default;
33 Event(const Event&) = default;
34 Event& operator=(const Event&) = default;
35 explicit Event(std::pair<const Transition*, ClockVector> pair) : contents_(std::move(pair)) {}
37 const Transition* get_transition() const { return std::get<0>(contents_); }
38 const ClockVector& get_clock_vector() const { return std::get<1>(contents_); }
42 * @brief An ordered sequence of transitions which describe
43 * the evolution of a process undergoing model checking
45 * An execution conceptually is just a string of actors
46 * ids (e.g. "1.2.3.1.2.2.1.1"), where the `i`th occurrence
47 * of actor id `j` corresponds to the `i`th action executed
48 * by the actor with id `j` (viz. the `i`th step of actor `j`).
49 * Executions can stand alone on their own or can extend
50 * the execution of other sequences
52 * Executions are conceived based on the following papers:
53 * 1. "Source Sets: A Foundation for Optimal Dynamic Partial Order Reduction"
56 * In addition to representing an actual steps taken,
57 * an execution keeps track of the "happens-before"
58 * relation among the transitions in the execution
59 * by following the procedure outlined in section 4 of the
60 * original DPOR paper with clock vectors.
61 * As new transitions are added to the execution, clock vectors are
62 * computed as appropriate and associated with the corresponding position
63 * in the execution. This allows us to determine “happens-before” in
64 * constant-time between points in the execution (called events
65 * [which is unfortunately the same name used in UDPOR for a slightly
66 * different concept]), albeit for an up-front cost of traversing the
67 * execution stack. The happens-before relation is important in many
68 * places in SDPOR and ODPOR.
70 * @note: For more nuanced happens-before relations, clock
71 * vectors may not always suffice. Clock vectors work
72 * well with transition-based dependencies like that used in
73 * SimGrid; but to have a more refined independence relation,
74 * an event-based dependency approach is needed. See the section 2
75 * in the ODPOR paper [1] concerning event-based dependencies and
76 * how the happens-before relation can be refined in a
77 * computation model much like that of SimGrid. In fact, the same issue
78 * arrises with UDPOR with context-sensitive dependencies:
79 * the two concepts are analogous if not identical
84 * @brief The actual steps that are taken by the process
85 * during exploration, relative to the
87 std::vector<Event> contents_;
89 Execution(std::vector<Event>&& contents) : contents_(std::move(contents)) {}
92 using Handle = decltype(contents_)::const_iterator;
93 using EventHandle = uint32_t;
95 Execution() = default;
96 Execution(const Execution&) = default;
97 Execution& operator=(Execution const&) = default;
98 Execution(Execution&&) = default;
100 size_t size() const { return this->contents_.size(); }
101 bool empty() const { return this->contents_.empty(); }
102 auto begin() const { return this->contents_.begin(); }
103 auto end() const { return this->contents_.end(); }
106 * @brief Computes the "core" portion the SDPOR algorithm,
107 * viz. the intersection of the backtracking set and the
108 * set of initials with respect to the *last* event added
111 * The "core" portion of the SDPOR algorithm is found on
112 * lines 6-9 of the pseudocode:
114 * 6 | let E' := pre(E, e)
115 * 7 | let v := notdep(e, E).p
116 * 8 | if I_[E'](v) ∩ backtrack(E') = empty then
117 * 9 | --> add some q in I_[E'](v) to backtrack(E')
119 * This method computes all of the lines simultaneously,
120 * returning some actor `q` if it passes line 8 and exists.
121 * The event `e` and the set `backtrack(E')` are the provided
122 * arguments to the method.
124 * @param e the event with respect to which to determine
125 * whether a backtrack point needs to be added for the
126 * prefix corresponding to the execution prior to `e`
128 * @param backtrack_set The set of actors which should
129 * not be considered for selection as an SDPOR initial.
130 * While this set need not necessarily correspond to the
131 * backtrack set `backtrack(E')`, doing so provides what
132 * is expected for SDPOR
134 * See the SDPOR algorithm pseudocode in [1] for more
135 * details for the context of the function.
137 * @invariant: This method assumes that events `e` and
138 * `e' := get_latest_event_handle()` are in a *reversible* race
139 * as is explicitly the case in SDPOR
141 * @returns an actor not contained in `disqualified` which
142 * can serve as an initial to reverse the race between `e`
145 std::optional<aid_t> get_first_sdpor_initial_from(EventHandle e, std::unordered_set<aid_t> backtrack_set) const;
147 bool is_initial_after_execution(const PartialExecution& w, aid_t p) const;
148 bool is_independent_with_execution(const PartialExecution& w, const Transition* next_E_p) const;
151 * @brief For a given sequence of actors `v` and a sequence of transitions `w`,
152 * computes the sequence, if any, that should be inserted as a child a WakeupTree for
155 std::optional<PartialExecution> get_shortest_odpor_sq_subset_insertion(const PartialExecution& v,
156 const PartialExecution& w) const;
159 * @brief Determines the event associated with
160 * the given handle `handle`
162 const Event& get_event_with_handle(EventHandle handle) const { return contents_[handle]; }
165 * @brief Determines the actor associated with
166 * the given event handle `handle`
168 aid_t get_actor_with_handle(EventHandle handle) const { return get_event_with_handle(handle).get_transition()->aid_; }
171 * @brief Returns a set of events which are in
172 * "immediate conflict" (according to the definition given
173 * in the ODPOR paper) with the given event
175 * Two events `e` and `e'` in an execution `E` are said to
178 * 1. `proc(e) != proc(e')`; that is, the events correspond to
179 * the execution of different actors
180 * 2. `e -->_E e'` and there is no `e''` in `E` such that
181 * `e -->_E e''` and `e'' -->_E e'`; that is, the two events
182 * "happen-before" one another in `E` and no other event in
183 * `E` "happens-between" `e` and `e'`
185 * @param handle the event with respect to which races are
187 * @returns a set of event handles from which race with `handle`
189 std::unordered_set<EventHandle> get_racing_events_of(EventHandle handle) const;
192 * @brief Returns a handle to the newest event of the execution,
193 * if such an event exists
195 std::optional<EventHandle> get_latest_event_handle() const
197 return contents_.empty() ? std::nullopt : std::optional<EventHandle>{static_cast<EventHandle>(size() - 1)};
201 * @brief Computes `pre(e, E)` as described in ODPOR [1]
203 * The execution `pre(e, E)` for an event `e` in an
204 * execution `E` is the contiguous prefix of events
205 * `E' <= E` up to by excluding the event `e` itself.
206 * The prefix intuitively represents the "history" of
207 * causes that permitted event `e` to exist (roughly
210 Execution get_prefix_up_to(EventHandle) const;
213 * @brief Whether the event represented by `e1`
214 * "happens-before" the event represented by
215 * `e2` in the context of this execution
217 * In the terminology of the ODPOR paper,
218 * this function computes
222 * where `E` is this execution
224 * @note: The happens-before relation computed by this
225 * execution is "coarse" in the sense that context-sensitive
226 * independence is not exploited. To include such context-sensitive
227 * dependencies requires a new method of keeping track of
228 * the happens-before procedure, which is nontrivial...
230 bool happens_before(EventHandle e1, EventHandle e2) const;
233 * @brief Extends the execution by one more step
235 * Intutively, pushing a transition `t` onto execution `E`
236 * is equivalent to making the execution become (using the
237 * notation of [1]) `E.proc(t)` where `proc(t)` is the
238 * actor which executed transition `t`.
240 void push_transition(const Transition*);
243 } // namespace simgrid::mc::odpor