Begin tracking latest events for each actor

[simgrid.git] / src / mc / explo / UdporChecker.cpp

/* 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/History.hpp"
#include "src/mc/explo/udpor/maximal_subsets_iterator.hpp"

#include <xbt/asserts.h>
#include <xbt/log.h>

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, true) {}

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());

  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)
{
  auto exC       = compute_exC(C, *stateC, prev_exC);
  const auto enC = compute_enC(C, exC);

  // 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)) {
    if (not C.get_events().empty()) {
      // Report information...
    }

    // 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()) {
      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);
  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();

  // Ce := C + {e}
  Configuration Ce = C;
  Ce.add_event(e);

  A.remove(e);
  exC.remove(e);

  // Explore(C + {e}, D, A \ {e})
  explore(Ce, D, std::move(A), std::move(stateCe), std::move(exC));

  // D <-- D + {e}
  D.insert(e);

  constexpr unsigned K = 10;
  if (auto J = C.compute_k_partial_alternative_to(D, this->unfolding, K); 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);

    // Explore(C, D + {e}, J \ C)
    auto J_minus_C = J.value().get_events().subtracting(C.get_events());
    explore(C, D, std::move(J_minus_C), std::move(stateC), std::move(prev_exC));
  }

  // 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{<a, K> : 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);

  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));
      }
    }
  }
  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 event        = std::make_unique<UnfoldingEvent>(maximal_subset, action);
      const auto handle = unfolding.insert(std::move(event));
      incremental_exC.insert(handle);
    }
  }
  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)) {
      enC.insert(e);
    }
  }
  return enC;
}

void UdporChecker::move_to_stateCe(State& state, const 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");
  state.execute_next(next_actor, get_remote_app());
}

void UdporChecker::restore_program_state_to(const State& stateC)
{
  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
}

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->consider_all();

  return next_state;
}

const UnfoldingEvent* UdporChecker::select_next_unfolding_event(const EventSet& A, const EventSet& enC)
{
  if (!enC.empty()) {
    return *(enC.begin());
  }

  for (const auto& event : A) {
    if (enC.contains(event)) {
      return event;
    }
  }
  return nullptr;
}

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());

  // Move {e} \ Q_CDU from U to G
  if (Q_CDU.contains(e)) {
    this->unfolding.remove(e);
  }

  // foreach ê in #ⁱ_U(e)
  for (const auto* e_hat : es_immediate_conflicts) {
    // Move [ê] \ Q_CDU from U to G
    const EventSet to_remove = e_hat->get_history().subtracting(Q_CDU);
    this->unfolding.remove(to_remove);
  }
}

RecordTrace UdporChecker::get_record_trace()
{
  RecordTrace res;
  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 {

Exploration* create_udpor_checker(const std::vector<char*>& args)
{
  return new simgrid::mc::udpor::UdporChecker(args);
}

} // namespace simgrid::mc