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/mc_forward.hpp"
12 #include "src/mc/mc_record.hpp"
13 #include "src/mc/transition/Transition.hpp"
17 #include <unordered_set>
20 namespace simgrid::mc::odpor {
22 std::vector<std::string> get_textual_trace(const PartialExecution& w);
25 * @brief The occurrence of a transition in an execution
27 * An execution is set of *events*, where each element represents
28 * the occurrence or execution of the `i`th step of a particular
32 std::pair<std::shared_ptr<Transition>, ClockVector> contents_;
36 Event(Event&&) = default;
37 Event(const Event&) = default;
38 Event& operator=(const Event&) = default;
39 explicit Event(std::pair<std::shared_ptr<Transition>, ClockVector> pair) : contents_(std::move(pair)) {}
41 std::shared_ptr<Transition> get_transition() const { return std::get<0>(contents_); }
42 const ClockVector& get_clock_vector() const { return std::get<1>(contents_); }
46 * @brief An ordered sequence of transitions which describe
47 * the evolution of a process undergoing model checking
49 * An execution conceptually is just a string of actors
50 * ids (e.g. "1.2.3.1.2.2.1.1"), where the `i`th occurrence
51 * of actor id `j` corresponds to the `i`th action executed
52 * by the actor with id `j` (viz. the `i`th step of actor `j`).
53 * Executions can stand alone on their own or can extend
54 * the execution of other sequences
56 * Executions are conceived based on the following papers:
57 * 1. "Source Sets: A Foundation for Optimal Dynamic Partial Order Reduction"
60 * In addition to representing an actual steps taken,
61 * an execution keeps track of the "happens-before"
62 * relation among the transitions in the execution
63 * by following the procedure outlined in section 4 of the
64 * original DPOR paper with clock vectors.
65 * As new transitions are added to the execution, clock vectors are
66 * computed as appropriate and associated with the corresponding position
67 * in the execution. This allows us to determine “happens-before” in
68 * constant-time between points in the execution (called events
69 * [which is unfortunately the same name used in UDPOR for a slightly
70 * different concept]), albeit for an up-front cost of traversing the
71 * execution stack. The happens-before relation is important in many
72 * places in SDPOR and ODPOR.
74 * @note: For more nuanced happens-before relations, clock
75 * vectors may not always suffice. Clock vectors work
76 * well with transition-based dependencies like that used in
77 * SimGrid; but to have a more refined independence relation,
78 * an event-based dependency approach is needed. See the section 2
79 * in the ODPOR paper [1] concerning event-based dependencies and
80 * how the happens-before relation can be refined in a
81 * computation model much like that of SimGrid. In fact, the same issue
82 * arrises with UDPOR with context-sensitive dependencies:
83 * the two concepts are analogous if not identical
87 std::vector<Event> contents_;
88 Execution(std::vector<Event>&& contents) : contents_(std::move(contents)) {}
91 using EventHandle = uint32_t;
93 Execution() = default;
94 Execution(const Execution&) = default;
95 Execution& operator=(Execution const&) = default;
96 Execution(Execution&&) = default;
98 std::vector<std::string> get_textual_trace() const;
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;
148 * @brief Computes the analogous lines from the SDPOR algorithm
149 * in the ODPOR algorithm, viz. the intersection of the slee set
150 * and the set of weak initials with respect to the given pair
153 * This method computes lines 4-6 of the ODPOR pseudocode, viz.:
155 * 4 | let E' := pre(E, e)
156 * 5 | let v := notdep(e, E).e'^
157 * 6 | if sleep(E') ∩ WI_[E'](v) = empty then ...
159 * The sequence `v` is computed and returned as needed, based on whether
160 * the check on line 6 passes.
162 * @invariant: This method assumes that events `e` and
163 * `e_prime` are in a *reversible* race as is the case
166 std::optional<PartialExecution> get_odpor_extension_from(EventHandle e, EventHandle e_prime,
167 const State& state_at_e) const;
170 * @brief For a given sequence of actors `v` and a sequence of transitions `w`,
171 * computes the sequence, if any, that should be inserted as a child in wakeup tree for
174 * Recall that the procedure for implementing the insertion
175 * is outlined in section 6.2 of Abdulla et al. 2017 as follows:
177 * | Let `v` be the smallest (w.r.t to "<") sequence in [the tree] B
178 * | such that `v ~_[E] w`. If `v` is a leaf node, the tree can be left
181 * | Otherwise let `w'` be the shortest sequence such that `w [=_[E] v.w'`
182 * | and add `v.w'` as a new leaf, ordered after all already existing nodes
183 * | of the form `v.w''`
185 * This method computes the result `v.w'` as needed (viz. only if `v ~_[E] w`
186 * with respect to this execution `E`)
188 * The procedure for determining `v ~_[E] w` is given as Lemma 4.6 of
189 * Abdulla et al. 2017:
191 * | The relation `v ~_[E] w` holds if either
193 * | (2) v := p.v' and either
194 * | (a) p in I_[E](w) and `v' ~_[E.p] (w \ p)`
195 * | (b) E ⊢ p ◊ w and `v' ~_[E.p] w`
197 * @invariant: This method assumes that `E.v` is a valid execution, viz.
198 * that the events of `E` are sufficient to enabled `v_0` and that
199 * `v_0, ..., v_{i - 1}` are sufficient to enable `v_i`. This is the
200 * case when e.g. `v := notdep(e, E).p` for example in ODPOR
202 * @returns a partial execution `w'` that should be inserted
203 * as a child of a wakeup tree node with the associated sequence `v`.
205 std::optional<PartialExecution> get_shortest_odpor_sq_subset_insertion(const PartialExecution& v,
206 const PartialExecution& w) const;
209 * @brief For a given sequence `w`, determines whether p in I_[E](w)
211 * @note: You may notice that some of the other methods compute this
212 * value as well. What we notice, though, in those cases is that
213 * we are repeatedly asking about initials with respect to an execution.
214 * It is better, then, to bunch the work together in those cases to
215 * get asymptotically better results (e.g. instead of calling with all
216 * `N` actors, we can process them "in-parallel" as is done with the
217 * computation of SDPOR initials)
219 bool is_initial_after_execution_of(const PartialExecution& w, aid_t p) const;
222 * @brief Determines whether `E ⊢ p ◊ w` given the next action taken by `p`
224 bool is_independent_with_execution_of(const PartialExecution& w, std::shared_ptr<Transition> next_E_p) const;
227 * @brief Determines the event associated with
228 * the given handle `handle`
230 const Event& get_event_with_handle(EventHandle handle) const { return contents_[handle]; }
233 * @brief Determines the actor associated with
234 * the given event handle `handle`
236 aid_t get_actor_with_handle(EventHandle handle) const { return get_event_with_handle(handle).get_transition()->aid_; }
239 * @brief Determines the transition associated with the given handle `handle`
241 const Transition* get_transition_for_handle(EventHandle handle) const
243 return get_event_with_handle(handle).get_transition().get();
247 * @brief Returns a handle to the newest event of the execution,
248 * if such an event exists
250 std::optional<EventHandle> get_latest_event_handle() const
252 return contents_.empty() ? std::nullopt : std::optional<EventHandle>{static_cast<EventHandle>(size() - 1)};
256 * @brief Returns a set of events which are in
257 * "immediate conflict" (according to the definition given
258 * in the ODPOR paper) with the given event
260 * Two events `e` and `e'` in an execution `E` are said to
263 * 1. `proc(e) != proc(e')`; that is, the events correspond to
264 * the execution of different actors
265 * 2. `e -->_E e'` and there is no `e''` in `E` such that
266 * `e -->_E e''` and `e'' -->_E e'`; that is, the two events
267 * "happen-before" one another in `E` and no other event in
268 * `E` "happens-between" `e` and `e'`
270 * @param handle the event with respect to which races are
272 * @returns a set of event handles from which race with `handle`
274 std::unordered_set<EventHandle> get_racing_events_of(EventHandle handle) const;
277 * @brief Returns a set of events which are in a reversible
278 * race with the given event handle `handle`
280 * Two events `e` and `e'` in an execution `E` are said to
281 * be in a reversible race iff
283 * 1. `e` and `e'` race
284 * 2. In any equivalent execution sequence `E'` to `E`
285 * where `e` occurs immediately before `e'`, the actor
286 * running `e'` was enabled in the state prior to `e`
288 * @param handle the event with respect to which
289 * reversible races are computed
290 * @returns a set of event handles from which are in a reversible
293 std::unordered_set<EventHandle> get_reversible_races_of(EventHandle handle) const;
296 * @brief Computes `pre(e, E)` as described in ODPOR [1]
298 * The execution `pre(e, E)` for an event `e` in an
299 * execution `E` is the contiguous prefix of events
300 * `E' <= E` up to by excluding the event `e` itself.
301 * The prefix intuitively represents the "history" of
302 * causes that permitted event `e` to exist (roughly
305 Execution get_prefix_before(EventHandle) const;
308 * @brief Whether the event represented by `e1`
309 * "happens-before" the event represented by
310 * `e2` in the context of this execution
312 * In the terminology of the ODPOR paper,
313 * this function computes
317 * where `E` is this execution
319 * @note: The happens-before relation computed by this
320 * execution is "coarse" in the sense that context-sensitive
321 * independence is not exploited. To include such context-sensitive
322 * dependencies requires a new method of keeping track of
323 * the happens-before procedure, which is nontrivial...
325 bool happens_before(EventHandle e1, EventHandle e2) const;
328 * @brief Extends the execution by one more step
330 * Intutively, pushing a transition `t` onto execution `E`
331 * is equivalent to making the execution become (using the
332 * notation of [1]) `E.proc(t)` where `proc(t)` is the
333 * actor which executed transition `t`.
335 void push_transition(std::shared_ptr<Transition>);
338 } // namespace simgrid::mc::odpor