1 /* Copyright (c) 2008-2023. 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 #include "src/mc/explo/odpor/Execution.hpp"
7 #include "src/mc/api/State.hpp"
8 #include "xbt/asserts.h"
13 namespace simgrid::mc::odpor {
15 void Execution::push_transition(std::shared_ptr<Transition> t)
18 throw std::invalid_argument("Unexpectedly received `nullptr`");
20 ClockVector max_clock_vector;
21 for (const Event& e : this->contents_) {
22 if (e.get_transition()->depends(t.get())) {
23 max_clock_vector = ClockVector::max(max_clock_vector, e.get_clock_vector());
26 max_clock_vector[t->aid_] = this->size();
27 contents_.push_back(Event({std::move(t), max_clock_vector}));
30 std::unordered_set<Execution::EventHandle> Execution::get_racing_events_of(Execution::EventHandle target) const
32 std::unordered_set<Execution::EventHandle> racing_events;
33 std::unordered_set<Execution::EventHandle> disqualified_events;
35 // For each event of the execution
36 for (auto e_i = target; e_i != std::numeric_limits<Execution::EventHandle>::max(); e_i--) {
37 // We need `e_i -->_E target` as a necessary condition
38 if (not happens_before(e_i, target)) {
42 // Further, `proc(e_i) != proc(target)`
43 if (get_actor_with_handle(e_i) == get_actor_with_handle(target)) {
44 disqualified_events.insert(e_i);
48 // There could an event that "happens-between" the two events which would discount `e_i` as a race
49 for (auto e_j = e_i; e_j < target; e_j++) {
51 // 1. e_i --->_E e_j; and
52 // 2. disqualified_events.count(e_j) > 0
53 // then e_i --->_E target indirectly (either through
54 // e_j directly, or transitively through e_j)
55 if (happens_before(e_i, e_j) and disqualified_events.count(e_j) > 0) {
56 disqualified_events.insert(e_i);
61 // If `e_i` wasn't disqualified in the last round,
62 // it's in a race with `target`. After marking it
63 // as such, we ensure no other event `e` can happen-before
64 // it (since this would transitively make it the event
65 // which "happens-between" `target` and `e`)
66 if (disqualified_events.count(e_i) == 0) {
67 racing_events.insert(e_i);
68 disqualified_events.insert(e_i);
75 Execution Execution::get_prefix_before(Execution::EventHandle handle) const
77 return Execution(std::vector<Event>{contents_.begin(), contents_.begin() + handle});
80 std::optional<aid_t> Execution::get_first_sdpor_initial_from(EventHandle e,
81 std::unordered_set<aid_t> disqualified_actors) const
83 // If this execution is empty, there are no initials
84 // relative to the last transition added to the execution
85 // since such a transition does not exist
90 // To actually compute `I_[E'](v) ∩ backtrack(E')`, we must
91 // first compute `E'` and "move" in the direction of `v`.
92 // We perform a scan over `E` (this execution) and make
93 // note of any events which occur after `e` but don't
94 // "happen-after" `e` by pushing them onto `E'`. Note that
95 // correctness is still preserved in computing `v` "on-the-fly"
96 // to determine if an actor `q` is an initial for `E'` after `v`:
97 // only those events that "occur-before" `v`
98 // could happen-before `v` for any valid happens-before relation.
100 // First, grab `E' := pre(e, E)` and determine what actor `p` is
101 const auto next_E_p = get_latest_event_handle().value();
102 Execution E_prime_v = get_prefix_before(e);
103 std::vector<sdpor::Execution::EventHandle> v;
105 // Note `e + 1` here: `notdep(e, E)` is defined as the
106 // set of events that *occur-after* but don't *happen-after* `e`
107 for (auto e_prime = e + 1; e_prime <= next_E_p; ++e_prime) {
108 // Any event `e*` which occurs after `e` but which does not
109 // happen after `e` is a member of `v`. In addition to marking
110 // the event in `v`, we also "simulate" running the action `v`
112 if (not happens_before(e, e_prime) or e_prime == next_E_p) {
113 // First, push the transition onto the hypothetical execution
114 E_prime_v.push_transition(get_event_with_handle(e_prime).get_transition());
115 const EventHandle e_prime_in_E_prime_v = E_prime_v.get_latest_event_handle().value();
117 // When checking whether any event in `dom_[E'](v)` happens before
118 // `next_[E'](q)` below for thread `q`, we must consider that the
119 // events relative to `E` (this execution) are different than those
120 // relative to `E'.v`. Thus e.g. event `7` in `E` may be event `4`
121 // in `E'.v`. Since we are asking about "happens-before"
122 // `-->_[E'.v]` about `E'.v`, we must build `v` relative to `E'`
123 v.push_back(e_prime_in_E_prime_v);
125 // Note that we add `q` to v regardless of whether `q` itself has been
126 // disqualified since `q` may itself disqualify other actors
127 // (i.e. even if `q` is disqualified from being an initial, it
128 // is still contained in the sequence `v`)
129 const aid_t q = E_prime_v.get_actor_with_handle(e_prime_in_E_prime_v);
130 if (disqualified_actors.count(q) > 0) {
133 const bool is_initial = std::none_of(v.begin(), v.end(), [&](const auto& e_star) {
134 return E_prime_v.happens_before(e_star, e_prime_in_E_prime_v);
139 // If `q` is disqualified as a candidate, clearly
140 // no event occurring after `e_prime` in `E` executed
141 // by actor `q` will qualify since any (valid) happens-before
142 // relation orders actions taken by each actor
143 disqualified_actors.insert(q);
150 std::optional<PartialExecution> Execution::get_odpor_extension_from(EventHandle e, EventHandle e_prime,
151 const State& state_at_e) const
153 // `e` is assumed to be in a reversible race with `e_prime`.
154 // If `e > e_prime`, then `e` occurs-after `e_prime` which means
155 // `e` could not race with if
157 throw std::invalid_argument("ODPOR extensions can only be computed for "
158 "events in a reversible race, which is claimed, "
159 "yet the racing event 'occurs-after' the target");
167 Execution E_prime_v = get_prefix_before(e);
168 std::unordered_set<aid_t> disqualified_actors = state_at_e.get_sleeping_actors();
169 std::vector<sdpor::Execution::EventHandle> v_handles;
170 bool located_actor_in_initial = false;
172 // Note `e + 1` here: `notdep(e, E)` is defined as the
173 // set of events that *occur-after* but don't *happen-after* `e`
175 // SUBTLE NOTE: ODPOR requires us to compute `notdep(e, E)` EVEN THOUGH
176 // the race is between `e` and `e'`; that is, events occurring in `E`
177 // that "occur-after" `e'` may end up in the partial execution `v`.
179 // Observe that `notdep(e, E).proc(e')` will contain all transitions
180 // that don't happen-after `e` in the order they appear FOLLOWED BY
181 // THE **TRANSITION** ASSOCIATED WITH **`e'`**!!
183 // SUBTLE NOTE: Observe that any event that "happens-after" `e'`
184 // must necessarily "happen-after" `e` as well, since `e` and
185 // `e'` are presumed to be in a reversible race. Hence, we know that
186 // all events `e_star` that `e` "happens-before" cannot affect
187 // the enabledness of `e'`; furthermore, `e'` cannot affect the enabledness
188 // of any event independent with `e` that "occurs-after" `e'`
189 for (auto e_star = e + 1; e_star <= get_latest_event_handle().value(); ++e_star) {
190 // Any event `e*` which occurs after `e` but which does not
191 // happen after `e` is a member of `v`. In addition to marking
192 // the event in `v`, we also "simulate" running the action `v` from E'
193 // to be able to compute `--->[E'.v]`
194 if (not happens_before(e, e_star)) {
195 xbt_assert(e_star != e_prime,
196 "Invariant Violation: We claimed events %u and %u were in a reversible race, yet we also "
197 "claim that they do not happen-before one another. This is impossible: "
198 "are you sure that the two events are in a reversible race?",
200 E_prime_v.push_transition(get_event_with_handle(e_star).get_transition());
201 v.push_back(get_event_with_handle(e_star).get_transition());
203 const EventHandle e_star_in_E_prime_v = E_prime_v.get_latest_event_handle().value();
205 // When checking whether any event in `dom_[E'](v)` happens before
206 // `next_[E'](q)` below for thread `q`, we must consider that the
207 // events relative to `E` (this execution) are different than those
208 // relative to `E'.v`. Thus e.g. event `7` in `E` may be event `4`
209 // in `E'.v`. Since we are asking about "happens-before"
210 // `-->_[E'.v]` about `E'.v`, we must build `v` relative to `E'`
211 v_handles.push_back(e_star_in_E_prime_v);
213 if (located_actor_in_initial) {
214 // It suffices that we find one initial. If we've already found
215 // one, we simply need to finish building `v`
219 // Note that we add `q` to v regardless of whether `q` itself has been
220 // disqualified since `q` may itself disqualify other actors
221 // (i.e. even if `q` is disqualified from being an initial, it
222 // is still contained in the sequence `v`)
223 const aid_t q = E_prime_v.get_actor_with_handle(e_star_in_E_prime_v);
224 if (disqualified_actors.count(q) > 0) {
227 const bool is_initial = std::none_of(v_handles.begin(), v_handles.end(), [&](const auto& e_loc) {
228 return E_prime_v.happens_before(e_loc, e_star_in_E_prime_v);
231 located_actor_in_initial = true;
233 // If `q` is disqualified as a candidate, clearly
234 // no event occurring after `e_prime` in `E` executed
235 // by actor `q` will qualify since any (valid) happens-before
236 // relation orders actions taken by each actor
237 disqualified_actors.insert(q);
242 // Now we add `e_prime := <q, i>` to `E'.v` and repeat the same work
244 v.push_back(get_event_with_handle(e_prime).get_transition());
246 if (not located_actor_in_initial) {
247 // It's possible `proc(e_prime)` is an initial
248 E_prime_v.push_transition(get_event_with_handle(e_prime).get_transition());
249 const EventHandle e_prime_in_E_prime_v = E_prime_v.get_latest_event_handle().value();
250 v_handles.push_back(e_prime_in_E_prime_v);
252 const aid_t q = E_prime_v.get_actor_with_handle(e_prime_in_E_prime_v);
253 located_actor_in_initial = disqualified_actors.count(q) == 0 and
254 std::none_of(v_handles.begin(), v_handles.end(), [&](const auto& e_loc) {
255 return E_prime_v.happens_before(e_loc, e_prime_in_E_prime_v);
260 /** Some actor `p` in `v` is an initial for `E' := pre(e, E)`*/
261 if (located_actor_in_initial) {
265 const Execution pre_E_e = get_prefix_before(e);
266 const auto sleeping_actors = state_at_e.get_sleeping_actors();
268 // Otherwise, for each enabled actor also not in the sleep set, check if
269 // any of them are independent with this execution after `v`. This
270 // completes the check for weak initials
271 for (const auto& [aid, astate] : state_at_e.get_actors_list()) {
272 // TODO: We have to be able to react appropriately here when adding new
273 // types of transitions (multiple choices can be made :( )
274 if (sleeping_actors.count(aid) == 0 and pre_E_e.is_independent_with_execution_of(v, astate.get_transition(0))) {
282 bool Execution::is_initial_after_execution_of(const PartialExecution& w, aid_t p) const
285 std::vector<EventHandle> w_handles;
286 for (const auto& w_i : w) {
287 // Take one step in the direction of `w`
288 E_w.push_transition(w_i);
290 // If that step happened to be executed by `p`,
291 // great: we know that `p` is contained in `w`.
292 // We now need to verify that it doens't "happen-after"
293 // any events which occur before it
294 if (w_i->aid_ == p) {
295 const auto p_handle = E_w.get_latest_event_handle().value();
296 return std::none_of(w_handles.begin(), w_handles.end(),
297 [&](const auto handle) { return E_w.happens_before(handle, p_handle); });
299 w_handles.push_back(E_w.get_latest_event_handle().value());
305 bool Execution::is_independent_with_execution_of(const PartialExecution& w, std::shared_ptr<Transition> next_E_p) const
307 // INVARIANT: Here, we assume that for any process `p_i` of `w`,
308 // the events of this execution followed by the execution of all
309 // actors occurring before `p_i` in `v` (`p_j`, `0 <= j < i`)
310 // are sufficient to enable `p_i`. This is fortunately the case
311 // with what ODPOR requires of us, viz. to ask the question about
312 // `v := notdep(e, E)` for some execution `E` and event `e` of
315 E_p_w.push_transition(std::move(next_E_p));
316 const auto p_handle = E_p_w.get_latest_event_handle().value();
318 // As we add events to `w`, verify that none
319 // of them "happen-after" the event associated with
320 // the step `next_E_p` (viz. p_handle)
321 for (const auto& w_i : w) {
322 E_p_w.push_transition(w_i);
323 const auto w_i_handle = E_p_w.get_latest_event_handle().value();
324 if (E_p_w.happens_before(p_handle, w_i_handle)) {
331 std::optional<PartialExecution> Execution::get_shortest_odpor_sq_subset_insertion(const PartialExecution& v,
332 const PartialExecution& w) const
334 // See section 4 of Abdulla. et al.'s 2017 ODPOR paper for details (specifically
335 // where the [iterative] computation of `v ~_[E] w` is described)
339 for (const auto& next_E_p : v) {
340 const aid_t p = next_E_p->aid_;
342 // Is `p in `I_[E](w)`?
343 if (E_v.is_initial_after_execution_of(w_now, p)) {
344 // Remove `p` from w and continue
346 // TODO: If `p` occurs in `w`, it had better refer to the same
347 // transition referenced by `v`. Unfortunately, we have two
348 // sources of truth here which can be manipulated at the same
349 // time as arguments to the function. If ODPOR works correctly,
350 // they should always refer to the same value; but as a sanity check,
351 // we have an assert that tests that at least the types are the same.
352 const auto action_by_p_in_w =
353 std::find_if(w_now.begin(), w_now.end(), [=](const auto& action) { return action->aid_ == p; });
354 xbt_assert(action_by_p_in_w != w_now.end(), "Invariant violated: actor `p` "
355 "is claimed to be an initial after `w` but is "
356 "not actually contained in `w`. This indicates that there "
357 "is a bug computing initials");
358 const auto& w_action = *action_by_p_in_w;
359 xbt_assert(w_action->type_ == next_E_p->type_,
360 "Invariant violated: `v` claims that actor `%ld` executes '%s' while "
361 "`w` claims that it executes '%s'. These two partial executions both "
362 "refer to `next_[E](p)`, which should be the same",
363 p, next_E_p->to_string(false).c_str(), w_action->to_string(false).c_str());
364 w_now.erase(action_by_p_in_w);
367 else if (E_v.is_independent_with_execution_of(w, next_E_p)) {
368 // INVARIANT: Note that it is impossible for `p` to be
369 // excluded from the set `I_[E](w)` BUT ALSO be contained in
370 // `w` itself if `E ⊢ p ◇ w` (intuitively, the fact that `E ⊢ p ◇ w`
371 // means that are able to move `p` anywhere in `w` IF it occurred, so
372 // if it really does occur we know it must then be an initial).
373 // We assert this is the case here
374 const auto action_by_p_in_w =
375 std::find_if(w_now.begin(), w_now.end(), [=](const auto& action) { return action->aid_ == p; });
376 xbt_assert(action_by_p_in_w == w_now.end(),
377 "Invariant violated: We claimed that actor `%ld` is not an initial "
378 "after `w`, yet it's independent with all actions of `w` AND occurs in `w`."
379 "This indicates that there is a bug computing initials",
382 // Neither of the two above conditions hold, so the relation fails
386 // Move one step forward in the direction of `v` and repeat
387 E_v.push_transition(next_E_p);
389 return std::optional<PartialExecution>{std::move(w_now)};
392 bool Execution::happens_before(Execution::EventHandle e1_handle, Execution::EventHandle e2_handle) const
394 // 1. "happens-before" (-->_E) is a subset of "occurs before" (<_E)
395 // and is an irreflexive relation
396 if (e1_handle >= e2_handle) {
400 // Each execution maintains a stack of clock vectors which are updated
401 // according to the procedure outlined in section 4 of the original DPOR paper
402 const Event& e2 = get_event_with_handle(e2_handle);
403 const aid_t proc_e1 = get_actor_with_handle(e1_handle);
405 if (const auto e1_in_e2_clock = e2.get_clock_vector().get(proc_e1); e1_in_e2_clock.has_value()) {
406 return e1_handle <= e1_in_e2_clock.value();
408 // If `e1` does not appear in e2's clock vector, this implies
409 // not only that the transitions associated with `e1` and `e2
410 // are independent, but further that there are no transitive
411 // dependencies between e1 and e2
415 } // namespace simgrid::mc::odpor