X-Git-Url: http://info.iut-bm.univ-fcomte.fr/pub/gitweb/simgrid.git/blobdiff_plain/96d605fde63f72480bf570f7bc7609e2954cb2d7..HEAD:/src/mc/explo/UdporChecker.cpp?ds=sidebyside diff --git a/src/mc/explo/UdporChecker.cpp b/src/mc/explo/UdporChecker.cpp index b935dcccaa..f5c512f480 100644 --- a/src/mc/explo/UdporChecker.cpp +++ b/src/mc/explo/UdporChecker.cpp @@ -1,36 +1,360 @@ -/* Copyright (c) 2016-2022. The SimGrid Team. All rights reserved. */ +/* Copyright (c) 2016-2023. The SimGrid Team. All rights reserved. */ /* This program is free software; you can redistribute it and/or modify it * under the terms of the license (GNU LGPL) which comes with this package. */ #include "src/mc/explo/UdporChecker.hpp" +#include "src/mc/api/State.hpp" +#include "src/mc/explo/udpor/Comb.hpp" +#include "src/mc/explo/udpor/ExtensionSetCalculator.hpp" +#include "src/mc/explo/udpor/History.hpp" +#include "src/mc/explo/udpor/maximal_subsets_iterator.hpp" + +#include +#include #include +#include -XBT_LOG_NEW_DEFAULT_SUBCATEGORY(mc_udpor, mc, "Logging specific to MC safety verification "); +XBT_LOG_NEW_DEFAULT_SUBCATEGORY(mc_udpor, mc, "Logging specific to verification using UDPOR"); -namespace simgrid::mc { +namespace simgrid::mc::udpor { + +UdporChecker::UdporChecker(const std::vector& args) : Exploration(args) {} + +void UdporChecker::run() +{ + XBT_INFO("Starting a UDPOR exploration"); + state_stack.clear(); + state_stack.push_back(get_current_state()); + explore(Configuration(), EventSet(), EventSet(), EventSet()); + XBT_INFO("UDPOR exploration terminated -- model checking completed"); +} + +void UdporChecker::explore(const Configuration& C, EventSet D, EventSet A, EventSet prev_exC) +{ + auto& stateC = *state_stack.back(); + auto exC = compute_exC(C, stateC, prev_exC); + const auto enC = compute_enC(C, exC); + XBT_DEBUG("explore(C, D, A) with:\n" + "C\t := %s \n" + "D\t := %s \n" + "A\t := %s \n" + "ex(C)\t := %s \n" + "en(C)\t := %s \n", + C.to_string().c_str(), D.to_string().c_str(), A.to_string().c_str(), exC.to_string().c_str(), + enC.to_string().c_str()); + XBT_DEBUG("ex(C) has %zu elements, of which %zu are in en(C)", exC.size(), enC.size()); + + // If enC is a subset of D, intuitively + // there aren't any enabled transitions + // which are "worth" exploring since their + // exploration would lead to a so-called + // "sleep-set blocked" trace. + if (enC.is_subset_of(D)) { + XBT_DEBUG("en(C) is a subset of the sleep set D (size %zu); if we " + "kept exploring, we'd hit a sleep-set blocked trace", + D.size()); + XBT_DEBUG("The current configuration has %zu elements", C.get_events().size()); + + // When `en(C)` is empty, intuitively this means that there + // are no enabled transitions that can be executed from the + // state reached by `C` (denoted `state(C)`), i.e. by some + // execution of the transitions in C obeying the causality + // relation. Here, then, we may be in a deadlock (the other + // possibility is that we've finished running everything, and + // we wouldn't be in deadlock then) + if (enC.empty()) { + XBT_VERB("**************************"); + XBT_VERB("*** TRACE INVESTIGATED ***"); + XBT_VERB("**************************"); + XBT_VERB("Execution sequence:"); + for (auto const& s : get_textual_trace()) + XBT_VERB(" %s", s.c_str()); + get_remote_app().check_deadlock(); + } + + return; + } + UnfoldingEvent* e = select_next_unfolding_event(A, enC); + xbt_assert(e != nullptr, "\n\n****** INVARIANT VIOLATION ******\n" + "UDPOR guarantees that an event will be chosen at each point in\n" + "the search, yet no events were actually chosen\n" + "*********************************\n\n"); + XBT_DEBUG("Selected event `%s` (%zu dependencies) to extend the configuration", e->to_string().c_str(), + e->get_immediate_causes().size()); + + // Ce := C + {e} + Configuration Ce = C; + Ce.add_event(e); + + A.remove(e); + exC.remove(e); + + // Explore(C + {e}, D, A \ {e}) + + // Move the application into stateCe (i.e. `state(C + {e})`) and make note of that state + move_to_stateCe(&stateC, e); + state_stack.push_back(record_current_state()); + + explore(Ce, D, std::move(A), std::move(exC)); -UdporChecker::UdporChecker(RemoteApp* remote_app) : Exploration(remote_app) {} + // Prepare to move the application back one state. + // We need only remove the state from the stack here: if we perform + // another `Explore()` after computing an alternative, at that + // point we'll actually create a fresh RemoteProcess + state_stack.pop_back(); -void UdporChecker::run() {} + // D <-- D + {e} + D.insert(e); + + XBT_DEBUG("Checking for the existence of an alternative..."); + if (auto J = C.compute_alternative_to(D, this->unfolding); J.has_value()) { + // Before searching the "right half", we need to make + // sure the program actually reflects the fact + // that we are searching again from `state(C)`. While the + // stack of states is properly adjusted to represent + // `state(C)` all together, the RemoteApp is currently sitting + // at some *future* state with respect to `state(C)` since the + // recursive calls had moved it there. + restore_program_state_with_current_stack(); + + // Explore(C, D + {e}, J \ C) + auto J_minus_C = J.value().get_events().subtracting(C.get_events()); + + XBT_DEBUG("Alternative detected! The alternative is:\n" + "J\t := %s \n" + "J / C := %s\n" + "UDPOR is going to explore it...", + J.value().to_string().c_str(), J_minus_C.to_string().c_str()); + explore(C, D, std::move(J_minus_C), std::move(prev_exC)); + } else { + XBT_DEBUG("No alternative detected with:\n" + "C\t := %s \n" + "D\t := %s \n" + "A\t := %s \n", + C.to_string().c_str(), D.to_string().c_str(), A.to_string().c_str()); + } + + // D <-- D - {e} + D.remove(e); + + // Remove(e, C, D) + clean_up_explore(e, C, D); +} + +EventSet UdporChecker::compute_exC(const Configuration& C, const State& stateC, const EventSet& prev_exC) +{ + // See eqs. 5.7 of section 5.2 of [3] + // C = C' + {e_cur}, i.e. C' = C - {e_cur} + // + // Then + // + // ex(C) = ex(C' + {e_cur}) = ex(C') / {e_cur} + + // U{ : K is maximal, `a` depends on all of K, `a` enabled at config(K) } + const UnfoldingEvent* e_cur = C.get_latest_event(); + EventSet exC = prev_exC; + exC.remove(e_cur); + + // IMPORTANT NOTE: In order to have deterministic results, we need to process + // the actors in a deterministic manner so that events are discovered by + // UDPOR in a deterministic order. The processing done here always processes + // actors in a consistent order since `std::map` is by-default ordered using + // `std::less` (see the return type of `State::get_actors_list()`) + for (const auto& [aid, actor_state] : stateC.get_actors_list()) { + const auto& enabled_transitions = actor_state.get_enabled_transitions(); + if (enabled_transitions.empty()) { + XBT_DEBUG("\t Actor `%ld` is disabled: no partial extensions need to be considered", aid); + } else { + XBT_DEBUG("\t Actor `%ld` is enabled", aid); + for (const auto& transition : enabled_transitions) { + XBT_DEBUG("\t Considering partial extension for %s", transition->to_string().c_str()); + EventSet extension = ExtensionSetCalculator::partially_extend(C, &unfolding, transition); + exC.form_union(extension); + } + } + } + return exC; +} + +EventSet UdporChecker::compute_enC(const Configuration& C, const EventSet& exC) const +{ + EventSet enC; + for (const auto* e : exC) { + if (C.is_compatible_with(e)) { + enC.insert(e); + } + } + return enC; +} + +void UdporChecker::move_to_stateCe(State* state, UnfoldingEvent* e) +{ + const aid_t next_actor = e->get_transition()->aid_; + + // TODO: Add the trace if possible for reporting a bug + xbt_assert(next_actor >= 0, "\n\n****** INVARIANT VIOLATION ******\n" + "In reaching this execution path, UDPOR ensures that at least one\n" + "one transition of the state of an visited event is enabled, yet no\n" + "state was actually enabled. Please report this as a bug.\n" + "*********************************\n\n"); + auto latest_transition_by_next_actor = state->execute_next(next_actor, get_remote_app()); + + // The transition that is associated with the event was just + // executed, so it's possible that the new version of the transition + // (i.e. the one after execution) has *more* information than + // that which existed *prior* to execution. + // + // + // ------- !!!!! UDPOR INVARIANT !!!!! ------- + // + // At this point, we are leveraging the fact that + // UDPOR will not contain more than one copy of any + // transition executed by any actor for any + // particular step taken by that actor. That is, + // if transition `i` of the `j`th actor is contained in the + // configuration `C` currently under consideration + // by UDPOR, then only one and only one copy exists in `C` + // + // This means that we can referesh the transitions associated + // with each event lazily, i.e. only after we have chosen the + // event to continue our execution. + e->set_transition(std::move(latest_transition_by_next_actor)); +} + +void UdporChecker::restore_program_state_with_current_stack() +{ + XBT_DEBUG("Restoring state using the current stack"); + get_remote_app().restore_initial_state(); + + /* Traverse the stack from the state at position start and re-execute the transitions */ + for (const std::unique_ptr& state : state_stack) { + if (state == state_stack.back()) /* If we are arrived on the target state, don't replay the outgoing transition */ + break; + state->get_transition_out()->replay(get_remote_app()); + } +} + +std::unique_ptr UdporChecker::record_current_state() +{ + auto next_state = this->get_current_state(); + + // In UDPOR, we care about all enabled transitions in a given state + next_state->consider_all(); + + return next_state; +} + +UnfoldingEvent* UdporChecker::select_next_unfolding_event(const EventSet& A, const EventSet& enC) +{ + if (enC.empty()) { + throw std::invalid_argument("There are no unfolding events to select. " + "Are you sure that you checked that en(C) was not " + "empty before attempting to select an event from it?"); + } + + // UDPOR's exploration is non-deterministic (as is DPOR's) + // in the sense that at any given point there may + // be multiple paths that can be followed. The correctness and optimality + // of the algorithm remains unaffected by the route taken by UDPOR when + // given multiple choices; but to ensure that SimGrid itself has deterministic + // behavior on all platforms, we always pick events with lower id's + // to ensure we explore the unfolding deterministically. + if (A.empty()) { + const auto min_event = std::min_element(enC.begin(), enC.end(), + [](const auto e1, const auto e2) { return e1->get_id() < e2->get_id(); }); + return const_cast(*min_event); + } else { + const auto intersection = A.make_intersection(enC); + const auto min_event = std::min_element(intersection.begin(), intersection.end(), + [](const auto e1, const auto e2) { return e1->get_id() < e2->get_id(); }); + return const_cast(*min_event); + } +} + +void UdporChecker::clean_up_explore(const UnfoldingEvent* e, const Configuration& C, const EventSet& D) +{ + // The "clean-up set" conceptually represents + // those events which will no longer be considered + // by UDPOR during its exploration. The concept is + // introduced to avoid modification during iteration + // over the current unfolding to determine who needs to + // be removed. Since sets are unordered, it's quite possible + // that e.g. two events `e` and `e'` such that `e < e'` + // which are determined eligible for removal are removed + // in the order `e` and then `e'`. Determining that `e'` + // needs to be removed requires that its history be in + // tact to e.g. compute the conflicts with the event. + // + // Thus, we compute the set and remove all of the events + // at once in lieu of removing events while iterating over them. + // We can hypothesize that processing the events in reverse + // topological order would prevent any issues concerning + // the order in which are processed + EventSet clean_up_set; + + // Q_(C, D, U) = C u D u U (complicated expression) + // See page 9 of "Unfolding-based Partial Order Reduction" + + // "C u D" portion + const EventSet C_union_D = C.get_events().make_union(D); + + // "U (complicated expression)" portion + const EventSet conflict_union = std::accumulate( + C_union_D.begin(), C_union_D.end(), EventSet(), [&](const EventSet& acc, const UnfoldingEvent* e_prime) { + return acc.make_union(unfolding.get_immediate_conflicts_of(e_prime)); + }); + + const EventSet Q_CDU = C_union_D.make_union(conflict_union.get_local_config()); + + XBT_DEBUG("Computed Q_CDU as '%s'", Q_CDU.to_string().c_str()); + + // Move {e} \ Q_CDU from U to G + if (not Q_CDU.contains(e)) { + XBT_DEBUG("Moving %s from U to G...", e->to_string().c_str()); + clean_up_set.insert(e); + } + + // foreach ê in #ⁱ_U(e) + for (const auto* e_hat : this->unfolding.get_immediate_conflicts_of(e)) { + // Move [ê] \ Q_CDU from U to G + const EventSet to_remove = e_hat->get_local_config().subtracting(Q_CDU); + XBT_DEBUG("Moving {%s} from U to G...", to_remove.to_string().c_str()); + clean_up_set.form_union(to_remove); + } + + // TODO: We still perhaps need to + // figure out how to deal with the fact that the previous + // extension sets computed for past configurations + // contain events that may be removed from `U`. Perhaps + // it would be best to keep them around forever (they + // are moved to `G` after all and can be discarded at will, + // which means they may never have to be removed at all). + // + // Of course, the benefit of moving them into the set `G` + // is that the computation for immediate conflicts becomes + // more efficient (we have to search all of `U` for such conflicts, + // and there would be no reason to search those events + // that UDPOR has marked as no longer being important) + // For now, there appear to be no "obvious" issues (although + // UDPOR's behavior is often far from obvious...) + this->unfolding.mark_finished(clean_up_set); +} RecordTrace UdporChecker::get_record_trace() { RecordTrace res; + for (auto const& state : state_stack) + res.push_back(state->get_transition_out().get()); return res; } -std::vector UdporChecker::get_textual_trace() -{ - std::vector trace; - return trace; -} +} // namespace simgrid::mc::udpor -void UdporChecker::log_state() {} +namespace simgrid::mc { -Exploration* create_udpor_checker(RemoteApp* remote_app) +Exploration* create_udpor_checker(const std::vector& args) { - return new UdporChecker(remote_app); + return new simgrid::mc::udpor::UdporChecker(args); } } // namespace simgrid::mc