* under the terms of the license (GNU LGPL) which comes with this package. */
#include "src/mc/explo/udpor/Configuration.hpp"
+#include "src/mc/explo/udpor/Comb.hpp"
#include "src/mc/explo/udpor/History.hpp"
+#include "src/mc/explo/udpor/Unfolding.hpp"
#include "src/mc/explo/udpor/UnfoldingEvent.hpp"
+#include "src/mc/explo/udpor/maximal_subsets_iterator.hpp"
+#include "xbt/asserts.h"
#include <algorithm>
-#include <stack>
#include <stdexcept>
namespace simgrid::mc::udpor {
-Configuration::Configuration(std::initializer_list<UnfoldingEvent*> events) : Configuration(EventSet(std::move(events)))
+Configuration::Configuration(std::initializer_list<const UnfoldingEvent*> events)
+ : Configuration(EventSet(std::move(events)))
{
}
-Configuration::Configuration(EventSet events) : events_(events)
+Configuration::Configuration(const UnfoldingEvent* e) : Configuration(e->get_history())
+{
+ // The local configuration should always be a valid configuration. We
+ // check the invariant regardless as a sanity check
+}
+
+Configuration::Configuration(const EventSet& events) : events_(events)
{
if (!events_.is_valid_configuration()) {
throw std::invalid_argument("The events do not form a valid configuration");
}
}
-void Configuration::add_event(UnfoldingEvent* e)
+Configuration::Configuration(const History& history) : Configuration(history.get_all_events()) {}
+
+void Configuration::add_event(const UnfoldingEvent* e)
{
if (e == nullptr) {
throw std::invalid_argument("Expected a nonnull `UnfoldingEvent*` but received NULL instead");
return;
}
+ // Preserves the property that the configuration is conflict-free
+ if (e->conflicts_with(*this)) {
+ throw std::invalid_argument("The newly added event conflicts with the events already "
+ "contained in the configuration. Adding this event violates "
+ "the property that a configuration is conflict-free");
+ }
+
this->events_.insert(e);
this->newest_event = e;
- // Preserves the property that the configuration is valid
- History history(e);
- if (!this->events_.contains(history)) {
+ // Preserves the property that the configuration is causally closed
+ if (auto history = History(e); !this->events_.contains(history)) {
throw std::invalid_argument("The newly added event has dependencies "
"which are missing from this configuration");
}
}
-std::vector<UnfoldingEvent*> Configuration::get_topologically_sorted_events() const
+bool Configuration::is_compatible_with(const UnfoldingEvent* e) const
{
- if (events_.empty()) {
- return std::vector<UnfoldingEvent*>();
- }
+ return not e->conflicts_with(*this);
+}
- std::stack<UnfoldingEvent*> event_stack;
- std::vector<UnfoldingEvent*> topological_ordering;
- EventSet unknown_events = events_, temporarily_marked_events, permanently_marked_events;
-
- while (not unknown_events.empty()) {
- EventSet discovered_events;
- event_stack.push(*unknown_events.begin());
-
- while (not event_stack.empty()) {
- UnfoldingEvent* evt = event_stack.top();
- discovered_events.insert(evt);
-
- if (not temporarily_marked_events.contains(evt)) {
- // If this event hasn't yet been marked, do
- // so now so that if we see it again in a child we can
- // detect a cycle and if we see it again here
- // we can detect that the node is re-processed
- temporarily_marked_events.insert(evt);
-
- EventSet immediate_causes = evt->get_immediate_causes();
- if (!immediate_causes.empty() && immediate_causes.is_subset_of(temporarily_marked_events)) {
- throw std::invalid_argument("Attempted to perform a topological sort on a configuration "
- "whose contents contain a cycle. The configuration (and the graph "
- "connecting all of the events) is an invalid event structure");
- }
- immediate_causes.subtract(discovered_events);
- immediate_causes.subtract(permanently_marked_events);
- const EventSet undiscovered_causes = std::move(immediate_causes);
-
- for (const auto cause : undiscovered_causes) {
- event_stack.push(cause);
- }
- } else {
- // Mark this event as:
- // 1. discovered across all DFSs performed
- // 2. permanently marked
- // 3. part of the topological search
- unknown_events.remove(evt);
- temporarily_marked_events.remove(evt);
- permanently_marked_events.insert(evt);
-
- // In moving this event to the end of the list,
- // we are saying this events "happens before" other
- // events that are added later.
- topological_ordering.push_back(evt);
-
- // Only now do we remove the event, i.e. once
- // we've processed the same event again
- event_stack.pop();
- }
+bool Configuration::is_compatible_with(const History& history) const
+{
+ return std::none_of(history.begin(), history.end(),
+ [&](const UnfoldingEvent* e) { return e->conflicts_with(*this); });
+}
+
+std::vector<const UnfoldingEvent*> Configuration::get_topologically_sorted_events() const
+{
+ return this->events_.get_topological_ordering();
+}
+
+std::vector<const UnfoldingEvent*> Configuration::get_topologically_sorted_events_of_reverse_graph() const
+{
+ return this->events_.get_topological_ordering_of_reverse_graph();
+}
+
+EventSet Configuration::get_minimally_reproducible_events() const
+{
+ // The implementation exploits the following observations:
+ //
+ // To select the smallest reproducible set of events, we want
+ // to pick events that "knock out" a lot of others. Furthermore,
+ // we need to ensure that the events furthest down in the
+ // causality graph are also selected. If you combine these ideas,
+ // you're basically left with traversing the set of maximal
+ // subsets of C! And we have an iterator for that already!
+ //
+ // The next observation is that the moment we don't increase in size
+ // the current maximal set (or decrease the number of events),
+ // we know that the prior set `S` covered the entire history of C and
+ // was maximal. Subsequent sets will miss events earlier in the
+ // topological ordering that appear in `S`
+ EventSet minimally_reproducible_events = EventSet();
+
+ for (const auto& maximal_set : maximal_subsets_iterator_wrapper<Configuration>(*this)) {
+ if (maximal_set.size() > minimally_reproducible_events.size()) {
+ minimally_reproducible_events = maximal_set;
+ } else {
+ // The moment we see the iterator generate a set of size
+ // that is not monotonically increasing, we can stop:
+ // the set prior was the minimally-reproducible one
+ return minimally_reproducible_events;
}
}
- return topological_ordering;
+ return minimally_reproducible_events;
+}
+
+std::optional<Configuration> Configuration::compute_alternative_to(const EventSet& D, const Unfolding& U) const
+{
+ // A full alternative can be computed by checking against everything in D
+ return compute_k_partial_alternative_to(D, U, D.size());
}
-std::vector<UnfoldingEvent*> Configuration::get_topologically_sorted_events_of_reverse_graph() const
+std::optional<Configuration> Configuration::compute_k_partial_alternative_to(const EventSet& D, const Unfolding& U,
+ size_t k) const
{
- // The method exploits the property that
- // a topological sorting S^R of the reverse graph G^R
- // of some graph G is simply the reverse of any
- // topological sorting S of G.
- auto topological_events = get_topologically_sorted_events();
- std::reverse(topological_events.begin(), topological_events.end());
- return topological_events;
+ // 1. Select k (of |D|, whichever is smaller) arbitrary events e_1, ..., e_k from D
+ const auto D_hat = [&]() {
+ const size_t size = std::min(k, D.size());
+ std::vector<const UnfoldingEvent*> D_hat(size);
+ // TODO: Since any subset suffices for computing `k`-partial alternatives,
+ // potentially select intelligently here (e.g. perhaps pick events
+ // with transitions that we know are totally independent). This may be
+ // especially important if the enumeration is the slowest part of
+ // UDPOR
+ //
+ // For now, simply pick the first `k` events
+ std::copy_n(D.begin(), size, D_hat.begin());
+ return D_hat;
+ }();
+
+ // 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 which associated additonal data structures with each unfolding event.
+ // Since that is a rather complicated addition, we defer it to a later time...
+ Comb comb(k);
+
+ for (const auto* e : U) {
+ for (unsigned i = 0; i < k; i++) {
+ const UnfoldingEvent* e_i = D_hat[i];
+ if (const auto e_local_config = History(e);
+ e_i->conflicts_with(e) and (not D.intersects(e_local_config)) and is_compatible_with(e_local_config)) {
+ comb[i].push_back(e);
+ }
+ }
+ }
+
+ // 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
+ // the number of events)
+ 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;
+ }
+
+ // 5. J := [e_1] + [e_2] + ... + [e_k] is a k-partial alternative
+ return Configuration(History(map_events(*alternative)));
}
} // namespace simgrid::mc::udpor
