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<std::shared_ptr<Transition>, ClockVector> contents_;
32 Event(Event&&) = default;
33 Event(const Event&) = default;
34 Event& operator=(const Event&) = default;
35 explicit Event(std::pair<std::shared_ptr<Transition>, ClockVector> pair) : contents_(std::move(pair)) {}
37 std::shared_ptr<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
83 std::vector<Event> contents_;
84 Execution(std::vector<Event>&& contents) : contents_(std::move(contents)) {}
87 using Handle = decltype(contents_)::const_iterator;
88 using EventHandle = uint32_t;
90 Execution() = default;
91 Execution(const Execution&) = default;
92 Execution& operator=(Execution const&) = default;
93 Execution(Execution&&) = default;
95 size_t size() const { return this->contents_.size(); }
96 bool empty() const { return this->contents_.empty(); }
97 auto begin() const { return this->contents_.begin(); }
98 auto end() const { return this->contents_.end(); }
101 * @brief Computes the "core" portion the SDPOR algorithm,
102 * viz. the intersection of the backtracking set and the
103 * set of initials with respect to the *last* event added
106 * The "core" portion of the SDPOR algorithm is found on
107 * lines 6-9 of the pseudocode:
109 * 6 | let E' := pre(E, e)
110 * 7 | let v := notdep(e, E).p
111 * 8 | if I_[E'](v) ∩ backtrack(E') = empty then
112 * 9 | --> add some q in I_[E'](v) to backtrack(E')
114 * This method computes all of the lines simultaneously,
115 * returning some actor `q` if it passes line 8 and exists.
116 * The event `e` and the set `backtrack(E')` are the provided
117 * arguments to the method.
119 * @param e the event with respect to which to determine
120 * whether a backtrack point needs to be added for the
121 * prefix corresponding to the execution prior to `e`
123 * @param backtrack_set The set of actors which should
124 * not be considered for selection as an SDPOR initial.
125 * While this set need not necessarily correspond to the
126 * backtrack set `backtrack(E')`, doing so provides what
127 * is expected for SDPOR
129 * See the SDPOR algorithm pseudocode in [1] for more
130 * details for the context of the function.
132 * @invariant: This method assumes that events `e` and
133 * `e' := get_latest_event_handle()` are in a *reversible* race
134 * as is explicitly the case in SDPOR
136 * @returns an actor not contained in `disqualified` which
137 * can serve as an initial to reverse the race between `e`
140 std::optional<aid_t> get_first_sdpor_initial_from(EventHandle e, std::unordered_set<aid_t> backtrack_set) const;
143 * @brief For a given sequence of actors `v` and a sequence of transitions `w`,
144 * computes the sequence, if any, that should be inserted as a child a WakeupTree for
147 std::optional<PartialExecution> get_shortest_odpor_sq_subset_insertion(const PartialExecution& v,
148 const PartialExecution& w) const;
151 * @brief For a given reversible race
153 std::optional<PartialExecution> get_odpor_extension_from(EventHandle, EventHandle,
154 std::unordered_set<aid_t> sleep_set,
155 std::unordered_set<aid_t> enabled_actors) const;
157 bool is_initial_after_execution(const PartialExecution& w, aid_t p) const;
158 bool is_independent_with_execution(const PartialExecution& w, std::shared_ptr<Transition> next_E_p) const;
161 * @brief Determines the event associated with
162 * the given handle `handle`
164 const Event& get_event_with_handle(EventHandle handle) const { return contents_[handle]; }
167 * @brief Determines the actor associated with
168 * the given event handle `handle`
170 aid_t get_actor_with_handle(EventHandle handle) const { return get_event_with_handle(handle).get_transition()->aid_; }
173 * @brief Returns a handle to the newest event of the execution,
174 * if such an event exists
176 std::optional<EventHandle> get_latest_event_handle() const
178 return contents_.empty() ? std::nullopt : std::optional<EventHandle>{static_cast<EventHandle>(size() - 1)};
182 * @brief Returns a set of events which are in
183 * "immediate conflict" (according to the definition given
184 * in the ODPOR paper) with the given event
186 * Two events `e` and `e'` in an execution `E` are said to
189 * 1. `proc(e) != proc(e')`; that is, the events correspond to
190 * the execution of different actors
191 * 2. `e -->_E e'` and there is no `e''` in `E` such that
192 * `e -->_E e''` and `e'' -->_E e'`; that is, the two events
193 * "happen-before" one another in `E` and no other event in
194 * `E` "happens-between" `e` and `e'`
196 * @param handle the event with respect to which races are
198 * @returns a set of event handles from which race with `handle`
200 std::unordered_set<EventHandle> get_racing_events_of(EventHandle handle) const;
203 * @brief Computes `pre(e, E)` as described in ODPOR [1]
205 * The execution `pre(e, E)` for an event `e` in an
206 * execution `E` is the contiguous prefix of events
207 * `E' <= E` up to by excluding the event `e` itself.
208 * The prefix intuitively represents the "history" of
209 * causes that permitted event `e` to exist (roughly
212 Execution get_prefix_before(EventHandle) const;
215 * @brief Whether the event represented by `e1`
216 * "happens-before" the event represented by
217 * `e2` in the context of this execution
219 * In the terminology of the ODPOR paper,
220 * this function computes
224 * where `E` is this execution
226 * @note: The happens-before relation computed by this
227 * execution is "coarse" in the sense that context-sensitive
228 * independence is not exploited. To include such context-sensitive
229 * dependencies requires a new method of keeping track of
230 * the happens-before procedure, which is nontrivial...
232 bool happens_before(EventHandle e1, EventHandle e2) const;
235 * @brief Extends the execution by one more step
237 * Intutively, pushing a transition `t` onto execution `E`
238 * is equivalent to making the execution become (using the
239 * notation of [1]) `E.proc(t)` where `proc(t)` is the
240 * actor which executed transition `t`.
242 void push_transition(std::shared_ptr<Transition>);
245 } // namespace simgrid::mc::odpor