#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 <numeric>
#include <xbt/asserts.h>
#include <xbt/log.h>
+#include <xbt/string.hpp>
XBT_LOG_NEW_DEFAULT_SUBCATEGORY(mc_udpor, mc, "Logging specific to verification using UDPOR");
namespace simgrid::mc::udpor {
-UdporChecker::UdporChecker(const std::vector<char*>& args) : Exploration(args)
-{
- // Initialize the map
-}
+UdporChecker::UdporChecker(const std::vector<char*>& args) : Exploration(args) {}
void UdporChecker::run()
{
XBT_INFO("Starting a UDPOR exploration");
- // NOTE: `A`, `D`, and `C` are derived from the
- // original UDPOR paper [1], while `prev_exC` arises
- // from the incremental computation of ex(C) from [3]
- Configuration C_root;
-
- // TODO: Move computing the root configuration into a method on the Unfolding
- auto initial_state = get_current_state();
- auto root_event = std::make_unique<UnfoldingEvent>(EventSet(), std::make_shared<Transition>());
- auto* root_event_handle = root_event.get();
- unfolding.insert(std::move(root_event));
- C_root.add_event(root_event_handle);
-
- explore(C_root, EventSet(), EventSet(), std::move(initial_state), EventSet());
-
+ 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, std::unique_ptr<State> stateC,
- EventSet prev_exC)
+void UdporChecker::explore(const Configuration& C, EventSet D, EventSet A, EventSet prev_exC)
{
- auto exC = compute_exC(C, *stateC, 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
// exploration would lead to a so-called
// "sleep-set blocked" trace.
if (enC.is_subset_of(D)) {
-
- if (not C.get_events().empty()) {
- // Report information...
- }
+ 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
// 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;
}
-
- // TODO: Add verbose logging about which event is being explored
-
- const UnfoldingEvent* e = select_next_unfolding_event(A, enC);
+ 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");
-
- // Move the application into stateCe and make note of that state
- move_to_stateCe(*stateC, *e);
- auto stateCe = record_current_state();
+ 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;
exC.remove(e);
// Explore(C + {e}, D, A \ {e})
- explore(Ce, D, std::move(A), std::move(stateCe), std::move(exC));
+
+ // 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));
+
+ // 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();
// D <-- D + {e}
D.insert(e);
- constexpr unsigned K = 10;
- if (auto J_minus_C = compute_k_partial_alternative(D, C, K); J_minus_C.has_value()) {
+ 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 `stateC` (the recursive
- // search moved the program into `stateCe`)
- restore_program_state_to(*stateC);
+ // 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)
- explore(C, D, std::move(J_minus_C.value()), std::move(stateC), std::move(prev_exC));
+ 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}
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<Key>` (see the return type of `State::get_actors_list()`)
for (const auto& [aid, actor_state] : stateC.get_actors_list()) {
- for (const auto& transition : actor_state.get_enabled_transitions()) {
- // First check for a specialized function that can compute the extension
- // set "quickly" based on its type. Otherwise, fall back to computing
- // the set "by hand"
- const auto specialized_extension_function = incremental_extension_functions.find(transition->type_);
- if (specialized_extension_function != incremental_extension_functions.end()) {
- exC.form_union((specialized_extension_function->second)(C, transition));
- } else {
- exC.form_union(this->compute_exC_by_enumeration(C, transition));
+ 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_exC_by_enumeration(const Configuration& C, const std::shared_ptr<Transition> action)
-{
- // Here we're computing the following:
- //
- // U{<a, K> : K is maximal, `a` depends on all of K, `a` enabled at config(K) }
- //
- // where `a` is the `action` given to us. Note that `a` is presumed to be enabled
- EventSet incremental_exC;
-
- for (auto begin =
- maximal_subsets_iterator(C, {[&](const UnfoldingEvent* e) { return e->is_dependent_with(action.get()); }});
- begin != maximal_subsets_iterator(); ++begin) {
- const EventSet& maximal_subset = *begin;
-
- // Determining if `a` is enabled here might not be possible while looking at `a` opaquely
- // We leave the implementation as-is to ensure that any addition would be simple
- // if it were ever added
- const bool enabled_at_config_k = false;
-
- if (enabled_at_config_k) {
- auto candidate_handle = std::make_unique<UnfoldingEvent>(maximal_subset, action);
- if (auto candidate_event = candidate_handle.get(); not unfolding.contains_event_equivalent_to(candidate_event)) {
- // This is a new event (i.e. one we haven't yet seen)
- unfolding.insert(std::move(candidate_handle));
- incremental_exC.insert(candidate_event);
- }
- }
- }
- return incremental_exC;
-}
-
EventSet UdporChecker::compute_enC(const Configuration& C, const EventSet& exC) const
{
EventSet enC;
- for (const auto e : exC) {
- if (not e->conflicts_with(C)) {
+ for (const auto* e : exC) {
+ if (C.is_compatible_with(e)) {
enC.insert(e);
}
}
return enC;
}
-void UdporChecker::move_to_stateCe(State& state, const UnfoldingEvent& e)
+void UdporChecker::move_to_stateCe(State* state, UnfoldingEvent* e)
{
- const aid_t next_actor = e.get_transition()->aid_;
+ 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"
"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");
- state.execute_next(next_actor);
+ 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_to(const State& stateC)
+void UdporChecker::restore_program_state_with_current_stack()
{
+ XBT_DEBUG("Restoring state using the current stack");
get_remote_app().restore_initial_state();
- // TODO: We need to have the stack of past states available at this
- // point. Since the method is recursive, we'll need to keep track of
- // this as we progress
+
+ /* Traverse the stack from the state at position start and re-execute the transitions */
+ for (const std::unique_ptr<State>& 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<State> 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->mark_all_enabled_todo();
+ next_state->consider_all();
return next_state;
}
-const UnfoldingEvent* UdporChecker::select_next_unfolding_event(const EventSet& A, const EventSet& enC)
+UnfoldingEvent* UdporChecker::select_next_unfolding_event(const EventSet& A, const EventSet& enC)
{
- if (!enC.empty()) {
- return *(enC.begin());
+ 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?");
}
- for (const auto& event : A) {
- if (enC.contains(event)) {
- return event;
- }
+ // 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<UnfoldingEvent*>(*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<UnfoldingEvent*>(*min_event);
}
- return nullptr;
}
-std::vector<const UnfoldingEvent*> UdporChecker::pick_k_partial_alternative_events(const EventSet& D,
- const unsigned k) const
+void UdporChecker::clean_up_explore(const UnfoldingEvent* e, const Configuration& C, const EventSet& D)
{
- const unsigned size = std::min(k, static_cast<unsigned>(D.size()));
- std::vector<const UnfoldingEvent*> D_hat(size);
-
- // Potentially select intelligently here (e.g. perhaps pick events
- // with transitions that we know are totally independent)...
+ // 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.
//
- // For now, simply pick the first `k` events (any subset suffices)
- std::copy_n(D.begin(), size, D_hat.begin());
- return D_hat;
-}
+ // 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;
-std::optional<EventSet> UdporChecker::compute_k_partial_alternative(const EventSet& D, const Configuration& C,
- const unsigned k) const
-{
- // 1. Select k (of |D|, whichever is smaller) arbitrary events e_1, ..., e_k from D
- const auto D_hat = pick_k_partial_alternative_events(D, k);
+ // Q_(C, D, U) = C u D u U (complicated expression)
+ // See page 9 of "Unfolding-based Partial Order Reduction"
- // 2. Build a U-comb <s_1, ..., s_k> of size k, where spike `s_i` contains
- // all events in conflict with `e_i`
- //
- // 3. EXCEPT those events e' for which [e'] + C is not a configuration or
- // [e'] intersects D
- //
- // NOTE: This is an expensive operation as we must traverse the entire unfolding
- // and compute `C.is_compatible_with(History)` for every event in the structure :/.
- // A later performance improvement would be to incorporate the work of Nguyen et al.
- // into SimGrid. Since that is a rather complicated addition, we defer to the addition
- // for a later time...
- Comb comb(k);
-
- for (const auto* e : this->unfolding) {
- for (unsigned i = 0; i < k; i++) {
- const auto& e_i = D_hat[i];
- if (const auto e_local_config = History(e);
- e_i->conflicts_with(e) and (not D.contains(e_local_config)) and C.is_compatible_with(e_local_config)) {
- comb[i].push_back(e);
- }
- }
- }
+ // "C u D" portion
+ const EventSet C_union_D = C.get_events().make_union(D);
- // 4. Find any such combination <e_1', ..., e_k'> in comb satisfying
- // ~(e_i' # e_j') for i != j
- //
- // NOTE: This is a VERY expensive operation: it enumerates all possible
- // ways to select an element from each spike. Unfortunately there's no
- // way around the enumeration, as computing a full alternative in general is
- // NP-complete (although computing the k-partial alternative is polynomial in n)
- const auto map_events = [](const std::vector<Spike::const_iterator>& spikes) {
- std::vector<const UnfoldingEvent*> events;
- for (const auto& event_in_spike : spikes) {
- events.push_back(*event_in_spike);
- }
- return EventSet(std::move(events));
- };
- const auto alternative =
- std::find_if(comb.combinations_begin(), comb.combinations_end(),
- [&map_events](const auto& vector) { return map_events(vector).is_conflict_free(); });
-
- // No such alternative exists
- if (alternative == comb.combinations_end()) {
- return std::nullopt;
- }
+ // "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));
+ });
- // 5. J := [e_1] + [e_2] + ... + [e_k] is a k-partial alternative
- // NOTE: This function computes J / C, which is what is actually used in UDPOR
- return History(map_events(*alternative)).get_event_diff_with(C);
-}
+ const EventSet Q_CDU = C_union_D.make_union(conflict_union.get_local_config());
-void UdporChecker::clean_up_explore(const UnfoldingEvent* e, const Configuration& C, const EventSet& D)
-{
- const EventSet C_union_D = C.get_events().make_union(D);
- const EventSet es_immediate_conflicts = this->unfolding.get_immediate_conflicts_of(e);
- const EventSet Q_CDU = C_union_D.make_union(es_immediate_conflicts.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 (Q_CDU.contains(e)) {
- this->unfolding.remove(e);
+ 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 : es_immediate_conflicts) {
+ 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_history().subtracting(Q_CDU);
- this->unfolding.remove(to_remove);
+ 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<std::string> UdporChecker::get_textual_trace()
-{
- // TODO: Topologically sort the events of the latest configuration
- // and iterate through that topological sorting
- std::vector<std::string> trace;
- return trace;
-}
-
} // namespace simgrid::mc::udpor
namespace simgrid::mc {
