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 {
20 using ProcessSequence = std::list<aid_t>;
21 using ExecutionSequence = std::list<const State*>;
22 using Hypothetical = ExecutionSequence;
25 * @brief The occurrence of a transition in an execution
28 std::pair<const Transition*, ClockVector> contents_;
32 Event(Event&&) = default;
33 Event(const Event&) = default;
34 Event& operator=(const Event&) = default;
36 explicit Event(std::pair<const Transition*, ClockVector> pair) : contents_(std::move(pair)) {}
38 const Transition* get_transition() const { return std::get<0>(contents_); }
39 const ClockVector& get_clock_vector() const { return std::get<1>(contents_); }
43 * @brief An ordered sequence of transitions which describe
44 * the evolution of a process undergoing model checking
46 * An execution conceptually is just a string of actors
47 * ids (e.g. "1.2.3.1.2.2.1.1"), where the `i`th occurrence
48 * of actor id `j` corresponds to the `i`th action executed
49 * by the actor with id `j` (viz. the `i`th step of actor `j`).
50 * Executions can stand alone on their own or can extend
51 * the execution of other sequences
53 * Executions are conceived based on the following papers:
54 * 1. "Source Sets: A Foundation for Optimal Dynamic Partial Order Reduction"
57 * In addition to representing an actual steps taken,
58 * an execution keeps track of the "happens-before"
59 * relation among the transitions in the execution
60 * by following the procedure outlined in the
61 * original DPOR paper with clock vectors
63 * @note: For more nuanced happens-before relations, clock
64 * vectors may not always suffice. Clock vectors work
65 * well with transition-based dependencies like that used in
66 * SimGrid; but to have a more refined independence relation,
67 * an event-based dependency approach is needed. See the section 2
68 * in the ODPOR paper [1] concerning event-based dependencies and
69 * how the happens-before relation can be refined in a
70 * computation model much like that of SimGrid. In fact, the same issue
71 * arrises with UDPOR with context-sensitive dependencies:
72 * the two concepts are analogous if not identical
77 * @brief The actual steps that are taken by the process
78 * during exploration, relative to the
80 std::vector<Event> contents_;
82 Execution(std::vector<Event>&& contents) : contents_(std::move(contents)) {}
85 using Handle = decltype(contents_)::const_iterator;
86 using EventHandle = uint32_t;
88 Execution() = default;
89 Execution(const Execution&) = default;
90 Execution& operator=(Execution const&) = default;
91 Execution(Execution&&) = default;
92 Execution(ExecutionSequence&& seq);
93 Execution(const ExecutionSequence& seq);
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 end
105 * See the SDPOR algorithm pseudocode in [1] for more
106 * details for the context of the function.
108 * @invariant: This method assumes that events `e` and
109 * `e' := get_latest_event_handle()` are in a *reversible* race
110 * as is the case in SDPOR
112 * @returns an actor not contained in `disqualified` which
113 * can serve as an initial to reverse the race between `e`
116 std::optional<aid_t> get_first_sdpor_initial_from(EventHandle e, std::unordered_set<aid_t> disqualified) const;
119 * @brief Determines the event associated with
120 * the given handle `handle`
122 const Event& get_event_with_handle(EventHandle handle) const { return contents_[handle]; }
125 * @brief Determines the actor associated with
126 * the given event handle `handle`
128 aid_t get_actor_with_handle(EventHandle handle) const { return get_event_with_handle(handle).get_transition()->aid_; }
131 * @brief Returns a set of events which are in
132 * "immediate conflict" (according to the definition given
133 * in the ODPOR paper) with the given event
135 * Two events `e` and `e'` in an execution `E` are said to
138 * 1. `proc(e) != proc(e')`; that is, the events correspond to
139 * the execution of different actors
140 * 2. `e -->_E e'` and there is no `e''` in `E` such that
141 * `e -->_E e''` and `e'' -->_E e'`; that is, the two events
142 * "happen-before" one another in `E` and no other event in
143 * `E` "happens-between" `e` and `e'`
145 * @param handle the event with respect to which races are
147 * @returns a set of event handles from which race with `handle`
149 std::unordered_set<EventHandle> get_racing_events_of(EventHandle handle) const;
152 * @brief Returns a handle to the newest event of the execution,
153 * if such an event exists
155 std::optional<EventHandle> get_latest_event_handle() const
157 return contents_.empty() ? std::nullopt : std::optional<EventHandle>{static_cast<EventHandle>(size() - 1)};
161 * @brief Computes `pre(e, E)` as described in ODPOR [1]
163 * The execution `pre(e, E)` for an event `e` in an
164 * execution `E` is the contiguous prefix of events
165 * `E' <= E` up to by excluding the event `e` itself.
166 * The prefix intuitively represents the "history" of
167 * causes that permitted event `e` to exist (roughly
170 Execution get_prefix_up_to(EventHandle) const;
173 * @brief Whether the event represented by `e1`
174 * "happens-before" the event represented by
175 * `e2` in the context of this execution
177 * In the terminology of the ODPOR paper,
178 * this function computes
182 * where `E` is this execution
184 * @note: The happens-before relation computed by this
185 * execution is "coarse" in the sense that context-sensitive
186 * independence is not exploited. To include such context-sensitive
187 * dependencies requires a new method of keeping track of
188 * the happens-before procedure, which is nontrivial...
190 bool happens_before(EventHandle e1, EventHandle e2) const;
193 * @brief Removes the last event of the execution,
194 * if such an event exists
196 * @note: When you remove events from an execution, any views
197 * of the execution referring to those removed events
203 * @brief Extends the execution by one more step
205 * Intutively, pushing a transition `t` onto execution `E`
206 * is equivalent to making the execution become (using the
207 * notation of [1]) `E.proc(t)` where `proc(t)` is the
208 * actor which executed transition `t`.
210 void push_transition(const Transition*);
213 } // namespace simgrid::mc::odpor