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 {
23 * @brief The occurrence of a transition in an execution
25 * An execution is set of *events*, where each element represents
26 * the occurrence or execution of the `i`th step of a particular
30 std::pair<std::shared_ptr<Transition>, ClockVector> contents_;
34 Event(Event&&) = default;
35 Event(const Event&) = default;
36 Event& operator=(const Event&) = default;
37 explicit Event(std::pair<std::shared_ptr<Transition>, ClockVector> pair) : contents_(std::move(pair)) {}
39 std::shared_ptr<Transition> get_transition() const { return std::get<0>(contents_); }
40 const ClockVector& get_clock_vector() const { return std::get<1>(contents_); }
44 * @brief An ordered sequence of transitions which describe
45 * the evolution of a process undergoing model checking
47 * An execution conceptually is just a string of actors
48 * ids (e.g. "1.2.3.1.2.2.1.1"), where the `i`th occurrence
49 * of actor id `j` corresponds to the `i`th action executed
50 * by the actor with id `j` (viz. the `i`th step of actor `j`).
51 * Executions can stand alone on their own or can extend
52 * the execution of other sequences
54 * Executions are conceived based on the following papers:
55 * 1. "Source Sets: A Foundation for Optimal Dynamic Partial Order Reduction"
58 * In addition to representing an actual steps taken,
59 * an execution keeps track of the "happens-before"
60 * relation among the transitions in the execution
61 * by following the procedure outlined in section 4 of the
62 * original DPOR paper with clock vectors.
63 * As new transitions are added to the execution, clock vectors are
64 * computed as appropriate and associated with the corresponding position
65 * in the execution. This allows us to determine “happens-before” in
66 * constant-time between points in the execution (called events
67 * [which is unfortunately the same name used in UDPOR for a slightly
68 * different concept]), albeit for an up-front cost of traversing the
69 * execution stack. The happens-before relation is important in many
70 * places in SDPOR and ODPOR.
72 * @note: For more nuanced happens-before relations, clock
73 * vectors may not always suffice. Clock vectors work
74 * well with transition-based dependencies like that used in
75 * SimGrid; but to have a more refined independence relation,
76 * an event-based dependency approach is needed. See the section 2
77 * in the ODPOR paper [1] concerning event-based dependencies and
78 * how the happens-before relation can be refined in a
79 * computation model much like that of SimGrid. In fact, the same issue
80 * arrises with UDPOR with context-sensitive dependencies:
81 * the two concepts are analogous if not identical
85 std::vector<Event> contents_;
86 Execution(std::vector<Event>&& contents) : contents_(std::move(contents)) {}
89 using Handle = decltype(contents_)::const_iterator;
90 using EventHandle = uint32_t;
92 Execution() = default;
93 Execution(const Execution&) = default;
94 Execution& operator=(Execution const&) = default;
95 Execution(Execution&&) = default;
97 size_t size() const { return this->contents_.size(); }
98 bool empty() const { return this->contents_.empty(); }
99 auto begin() const { return this->contents_.begin(); }
100 auto end() const { return this->contents_.end(); }
103 * @brief Computes the "core" portion the SDPOR algorithm,
104 * viz. the intersection of the backtracking set and the
105 * set of initials with respect to the *last* event added
108 * The "core" portion of the SDPOR algorithm is found on
109 * lines 6-9 of the pseudocode:
111 * 6 | let E' := pre(E, e)
112 * 7 | let v := notdep(e, E).p
113 * 8 | if I_[E'](v) ∩ backtrack(E') = empty then
114 * 9 | --> add some q in I_[E'](v) to backtrack(E')
116 * This method computes all of the lines simultaneously,
117 * returning some actor `q` if it passes line 8 and exists.
118 * The event `e` and the set `backtrack(E')` are the provided
119 * arguments to the method.
121 * @param e the event with respect to which to determine
122 * whether a backtrack point needs to be added for the
123 * prefix corresponding to the execution prior to `e`
125 * @param backtrack_set The set of actors which should
126 * not be considered for selection as an SDPOR initial.
127 * While this set need not necessarily correspond to the
128 * backtrack set `backtrack(E')`, doing so provides what
129 * is expected for SDPOR
131 * See the SDPOR algorithm pseudocode in [1] for more
132 * details for the context of the function.
134 * @invariant: This method assumes that events `e` and
135 * `e' := get_latest_event_handle()` are in a *reversible* race
136 * as is explicitly the case in SDPOR
138 * @returns an actor not contained in `disqualified` which
139 * can serve as an initial to reverse the race between `e`
142 std::optional<aid_t> get_first_sdpor_initial_from(EventHandle e, std::unordered_set<aid_t> backtrack_set) const;
145 * @brief Computes the analogous lines from the SDPOR algorithm
146 * in the ODPOR algorithm, viz. the intersection of the slee set
147 * and the set of weak initials with respect to the given pair
150 * This method computes lines 4-6 of the ODPOR pseudocode, viz.:
152 * 4 | let E' := pre(E, e)
153 * 5 | let v := notdep(e, E).e'^
154 * 6 | if sleep(E') ∩ WI_[E'](v) = empty then ...
156 * The sequence `v` is computed and returned as needed, based on whether
157 * the check on line 6 passes.
159 * @invariant: This method assumes that events `e` and
160 * `e_prime` are in a *reversible* race as is the case
163 std::optional<PartialExecution> get_odpor_extension_from(EventHandle e, EventHandle e_prime,
164 const State& state_at_e) const;
167 * @brief For a given sequence of actors `v` and a sequence of transitions `w`,
168 * computes the sequence, if any, that should be inserted as a child in wakeup tree for
171 * Recall that the procedure for implementing the insertion
172 * is outlined in section 6.2 of Abdulla et al. 2017 as follows:
174 * | Let `v` be the smallest (w.r.t to "<") sequence in [the tree] B
175 * | such that `v ~_[E] w`. If `v` is a leaf node, the tree can be left
178 * | Otherwise let `w'` be the shortest sequence such that `w [=_[E] v.w'`
179 * | and add `v.w'` as a new leaf, ordered after all already existing nodes
180 * | of the form `v.w''`
182 * This method computes the result `v.w'` as needed (viz. only if `v ~_[E] w`
183 * with respect to this execution `E`)
185 * The procedure for determining `v ~_[E] w` is given as Lemma 4.6 of
186 * Abdulla et al. 2017:
188 * | The relation `v ~_[E] w` holds if either
190 * | (2) v := p.v' and either
191 * | (a) p in I_[E](w) and `v' ~_[E.p] (w \ p)`
192 * | (b) E ⊢ p ◊ w and `v' ~_[E.p] w`
194 * @invariant: This method assumes that `E.v` is a valid execution, viz.
195 * that the events of `E` are sufficient to enabled `v_0` and that
196 * `v_0, ..., v_{i - 1}` are sufficient to enable `v_i`. This is the
197 * case when e.g. `v := notdep(e, E).p` for example in ODPOR
199 * @returns a partial execution `w'` that should be inserted
200 * as a child of a wakeup tree node with the associated sequence `v`.
202 std::optional<PartialExecution> get_shortest_odpor_sq_subset_insertion(const PartialExecution& v,
203 const PartialExecution& w) const;
206 * @brief For a given sequence `w`, determines whether p in I_[E](w)
208 * @note: You may notice that some of the other methods compute this
209 * value as well. What we notice, though, in those cases is that
210 * we are repeatedly asking about initials with respect to an execution.
211 * It is better, then, to bunch the work together in those cases to
212 * get asymptotically better results (e.g. instead of calling with all
213 * `N` actors, we can process them "in-parallel" as is done with the
214 * computation of SDPOR initials)
216 bool is_initial_after_execution_of(const PartialExecution& w, aid_t p) const;
219 * @brief Determines whether `E ⊢ p ◊ w` given the next action taken by `p`
221 bool is_independent_with_execution_of(const PartialExecution& w, std::shared_ptr<Transition> next_E_p) const;
224 * @brief Determines the event associated with
225 * the given handle `handle`
227 const Event& get_event_with_handle(EventHandle handle) const { return contents_[handle]; }
230 * @brief Determines the actor associated with
231 * the given event handle `handle`
233 aid_t get_actor_with_handle(EventHandle handle) const { return get_event_with_handle(handle).get_transition()->aid_; }
236 * @brief Returns a handle to the newest event of the execution,
237 * if such an event exists
239 std::optional<EventHandle> get_latest_event_handle() const
241 return contents_.empty() ? std::nullopt : std::optional<EventHandle>{static_cast<EventHandle>(size() - 1)};
245 * @brief Returns a set of events which are in
246 * "immediate conflict" (according to the definition given
247 * in the ODPOR paper) with the given event
249 * Two events `e` and `e'` in an execution `E` are said to
252 * 1. `proc(e) != proc(e')`; that is, the events correspond to
253 * the execution of different actors
254 * 2. `e -->_E e'` and there is no `e''` in `E` such that
255 * `e -->_E e''` and `e'' -->_E e'`; that is, the two events
256 * "happen-before" one another in `E` and no other event in
257 * `E` "happens-between" `e` and `e'`
259 * @param handle the event with respect to which races are
261 * @returns a set of event handles from which race with `handle`
263 std::unordered_set<EventHandle> get_racing_events_of(EventHandle handle) const;
266 * @brief Computes `pre(e, E)` as described in ODPOR [1]
268 * The execution `pre(e, E)` for an event `e` in an
269 * execution `E` is the contiguous prefix of events
270 * `E' <= E` up to by excluding the event `e` itself.
271 * The prefix intuitively represents the "history" of
272 * causes that permitted event `e` to exist (roughly
275 Execution get_prefix_before(EventHandle) const;
278 * @brief Whether the event represented by `e1`
279 * "happens-before" the event represented by
280 * `e2` in the context of this execution
282 * In the terminology of the ODPOR paper,
283 * this function computes
287 * where `E` is this execution
289 * @note: The happens-before relation computed by this
290 * execution is "coarse" in the sense that context-sensitive
291 * independence is not exploited. To include such context-sensitive
292 * dependencies requires a new method of keeping track of
293 * the happens-before procedure, which is nontrivial...
295 bool happens_before(EventHandle e1, EventHandle e2) const;
298 * @brief Extends the execution by one more step
300 * Intutively, pushing a transition `t` onto execution `E`
301 * is equivalent to making the execution become (using the
302 * notation of [1]) `E.proc(t)` where `proc(t)` is the
303 * actor which executed transition `t`.
305 void push_transition(std::shared_ptr<Transition>);
308 } // namespace simgrid::mc::odpor