+/* Copyright (c) 2008-2023. 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/odpor/Execution.hpp"
+#include <exception>
+#include <limits>
+
+namespace simgrid::mc::odpor {
+
+void Execution::push_transition(const Transition* t)
+{
+ if (t == nullptr) {
+ throw std::invalid_argument("Unexpectedly received `nullptr`");
+ }
+ ClockVector max_clock_vector;
+ for (const Event& e : this->contents_) {
+ if (e.get_transition()->depends(t)) {
+ max_clock_vector = ClockVector::max(max_clock_vector, e.get_clock_vector());
+ }
+ }
+ max_clock_vector[t->aid_] = this->size();
+ contents_.push_back(Event({t, max_clock_vector}));
+}
+
+std::unordered_set<Execution::EventHandle> Execution::get_racing_events_of(Execution::EventHandle target) const
+{
+ std::unordered_set<Execution::EventHandle> racing_events;
+ std::unordered_set<Execution::EventHandle> disqualified_events;
+
+ // For each event of the execution
+ for (auto e_i = target; e_i != std::numeric_limits<Execution::EventHandle>::max(); e_i--) {
+ // We need `e_i -->_E target` as a necessary condition
+ if (not happens_before(e_i, target)) {
+ continue;
+ }
+
+ // Further, `proc(e_i) != proc(target)`
+ if (get_actor_with_handle(e_i) == get_actor_with_handle(target)) {
+ disqualified_events.insert(e_i);
+ continue;
+ }
+
+ // There could an event that "happens-between" the two events which would discount `e_i` as a race
+ for (auto e_j = e_i; e_j < target; e_j++) {
+ // If both:
+ // 1. e_i --->_E e_j; and
+ // 2. disqualified_events.count(e_j) > 0
+ // then e_i --->_E target indirectly (either through
+ // e_j directly, or transitively through e_j)
+ if (happens_before(e_i, e_j) and disqualified_events.count(e_j) > 0) {
+ disqualified_events.insert(e_i);
+ break;
+ }
+ }
+
+ // If `e_i` wasn't disqualified in the last round,
+ // it's in a race with `target`. After marking it
+ // as such, we ensure no other event `e` can happen-before
+ // it (since this would transitively make it the event
+ // which "happens-between" `target` and `e`)
+ if (disqualified_events.count(e_i) == 0) {
+ racing_events.insert(e_i);
+ disqualified_events.insert(e_i);
+ }
+ }
+
+ return racing_events;
+}
+
+Execution Execution::get_prefix_up_to(Execution::EventHandle handle) const
+{
+ return Execution(std::vector<Event>{contents_.begin(), contents_.begin() + handle});
+}
+
+std::optional<aid_t> Execution::get_first_sdpor_initial_from(EventHandle e,
+ std::unordered_set<aid_t> disqualified_actors) const
+{
+ // If this execution is empty, there are no initials
+ // relative to the last transition added to the execution
+ // since such a transition does not exist
+ if (empty()) {
+ return std::nullopt;
+ }
+
+ // To actually compute `I_[E'](v) ∩ backtrack(E')`, we must
+ // first compute `E'` and "move" in the direction of `v`.
+ // We perform a scan over `E` (this execution) and make
+ // note of any events which occur after `e` but don't
+ // "happen-after" `e` by pushing them onto `E'`. Note that
+ // correctness is still preserved in computing `v` "on-the-fly"
+ // to determine if an actor `q` is an initial for `E'` after `v`:
+ // only those events that "occur-before" `v`
+ // could happen-before `v` for any valid happens-before relation.
+
+ // First, grab `E' := pre(e, E)` and determine what actor `p` is
+ // TODO: Instead of copying around these big structs, it
+ // would behoove us to incorporate some way to reference
+ // portions of an execution. For simplicity and for a
+ // "proof of concept" version, we opt to simply copy
+ // the contents instead of making a view into the execution
+ const auto next_E_p = get_latest_event_handle().value();
+ Execution E_prime_v = get_prefix_up_to(e);
+ std::vector<sdpor::Execution::EventHandle> v;
+
+ // Note `e + 1` here: `notdep(e, E)` is defined as the
+ // set of events that *occur-after* but don't *happen-after* `e`
+ for (auto e_prime = e + 1; e_prime <= next_E_p; ++e_prime) {
+ // Any event `e*` which occurs after `e` but which does not
+ // happen after `e` is a member of `v`. In addition to marking
+ // the event in `v`, we also "simulate" running the action `v`
+ // from E'
+ if (not happens_before(e, e_prime) or e_prime == next_E_p) {
+ // First, push the transition onto the hypothetical execution
+ E_prime_v.push_transition(get_event_with_handle(e_prime).get_transition());
+ const EventHandle e_prime_in_E_prime_v = E_prime_v.get_latest_event_handle().value();
+
+ // When checking whether any event in `dom_[E'](v)` happens before
+ // `next_[E'](q)` below for thread `q`, we must consider that the
+ // events relative to `E` (this execution) are different than those
+ // relative to `E'.v`. Thus e.g. event `7` in `E` may be event `4`
+ // in `E'.v`. Since we are asking about "happens-before"
+ // `-->_[E'.v]` about `E'.v`, we must build `v` relative to `E'`
+ v.push_back(e_prime_in_E_prime_v);
+
+ // Note that we add `q` to v regardless of whether `q` itself has been
+ // disqualified since `q` may itself disqualify other actors
+ // (i.e. even if `q` is disqualified from being an initial, it
+ // is still contained in the sequence `v`)
+ const aid_t q = E_prime_v.get_actor_with_handle(e_prime_in_E_prime_v);
+ if (disqualified_actors.count(q) > 0) {
+ continue;
+ }
+ const bool is_initial = std::none_of(v.begin(), v.end(), [&](const auto& e_star) {
+ return E_prime_v.happens_before(e_star, e_prime_in_E_prime_v);
+ });
+ if (is_initial) {
+ return q;
+ } else {
+ // If `q` is disqualified as a candidate, clearly
+ // no event occurring after `e_prime` in `E` executed
+ // by actor `q` will qualify since any (valid) happens-before
+ // relation orders actions taken by each actor
+ disqualified_actors.insert(q);
+ }
+ }
+ }
+ return std::nullopt;
+}
+
+bool Execution::happens_before(Execution::EventHandle e1_handle, Execution::EventHandle e2_handle) const
+{
+ // 1. "happens-before" (-->_E) is a subset of "occurs before" (<_E)
+ // and is an irreflexive relation
+ if (e1_handle >= e2_handle) {
+ return false;
+ }
+
+ // Each execution maintains a stack of clock vectors which are updated
+ // according to the procedure outlined in section 4 of the original DPOR paper
+ const Event& e2 = get_event_with_handle(e2_handle);
+ const aid_t proc_e1 = get_actor_with_handle(e1_handle);
+
+ if (const auto e1_in_e2_clock = e2.get_clock_vector().get(proc_e1); e1_in_e2_clock.has_value()) {
+ return e1_handle <= e1_in_e2_clock.value();
+ }
+ // If `e1` does not appear in e2's clock vector, this implies
+ // not only that the transitions associated with `e1` and `e2
+ // are independent, but further that there are no transitive
+ // dependencies between e1 and e2
+ return false;
+}
+
+} // namespace simgrid::mc::odpor
\ No newline at end of file
