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[mc] Get rid of MC_state_set_executed_request() in order to simplify the Checkers
[simgrid.git] / src / mc / LivenessChecker.cpp
index cc3ae5d..be0149b 100644 (file)
@@ -40,7 +40,8 @@ namespace mc {
 
 VisitedPair::VisitedPair(
   int pair_num, xbt_automaton_state_t automaton_state,
-  std::vector<int> const& atomic_propositions, std::shared_ptr<simgrid::mc::State> graph_state)
+  std::shared_ptr<const std::vector<int>> atomic_propositions,
+  std::shared_ptr<simgrid::mc::State> graph_state)
 {
   simgrid::mc::Process* process = &(mc_model_checker->process());
 
@@ -51,57 +52,43 @@ VisitedPair::VisitedPair(
     process->get_heap()->heaplimit,
     process->get_malloc_info());
 
-  this->nb_processes =
-    mc_model_checker->process().simix_processes().size();
+  this->nb_processes = mc_model_checker->process().simix_processes().size();
 
   this->automaton_state = automaton_state;
   this->num = pair_num;
   this->other_num = -1;
-  this->atomic_propositions = atomic_propositions;
+  this->atomic_propositions = std::move(atomic_propositions);
 }
 
 VisitedPair::~VisitedPair()
 {
 }
 
-static int MC_automaton_evaluate_label(
-  xbt_automaton_exp_label_t l,
-  std::vector<int> const& atomic_propositions_values)
+static bool evaluate_label(
+  xbt_automaton_exp_label_t l, std::vector<int> const& values)
 {
-
   switch (l->type) {
-  case xbt_automaton_exp_label::AUT_OR:{
-      int left_res = MC_automaton_evaluate_label(
-        l->u.or_and.left_exp, atomic_propositions_values);
-      int right_res = MC_automaton_evaluate_label(
-        l->u.or_and.right_exp, atomic_propositions_values);
-      return (left_res || right_res);
-    }
-  case xbt_automaton_exp_label::AUT_AND:{
-      int left_res = MC_automaton_evaluate_label(
-        l->u.or_and.left_exp, atomic_propositions_values);
-      int right_res = MC_automaton_evaluate_label(
-        l->u.or_and.right_exp, atomic_propositions_values);
-      return (left_res && right_res);
-    }
-  case xbt_automaton_exp_label::AUT_NOT:{
-      int res = MC_automaton_evaluate_label(
-        l->u.exp_not, atomic_propositions_values);
-      return (!res);
-    }
+  case xbt_automaton_exp_label::AUT_OR:
+    return evaluate_label(l->u.or_and.left_exp, values)
+      || evaluate_label(l->u.or_and.right_exp, values);
+  case xbt_automaton_exp_label::AUT_AND:
+    return evaluate_label(l->u.or_and.left_exp, values)
+      && evaluate_label(l->u.or_and.right_exp, values);
+  case xbt_automaton_exp_label::AUT_NOT:
+    return !evaluate_label(l->u.exp_not, values);
   case xbt_automaton_exp_label::AUT_PREDICAT:{
       unsigned int cursor = 0;
       xbt_automaton_propositional_symbol_t p = nullptr;
       xbt_dynar_foreach(simgrid::mc::property_automaton->propositional_symbols, cursor, p) {
         if (std::strcmp(xbt_automaton_propositional_symbol_get_name(p), l->u.predicat) == 0)
-          return atomic_propositions_values[cursor];
+          return values[cursor] != 0;
       }
-      return -1;
+      xbt_die("Missing predicate");
     }
   case xbt_automaton_exp_label::AUT_ONE:
-    return 2;
+    return true;
   default:
-    return -1;
+    xbt_die("Unexpected vaue for automaton");
   }
 }
 
@@ -110,14 +97,14 @@ Pair::Pair() : num(++mc_stats->expanded_pairs)
 
 Pair::~Pair() {}
 
-std::vector<int> LivenessChecker::getPropositionValues()
+std::shared_ptr<const std::vector<int>> LivenessChecker::getPropositionValues()
 {
   std::vector<int> values;
   unsigned int cursor = 0;
   xbt_automaton_propositional_symbol_t ps = nullptr;
   xbt_dynar_foreach(simgrid::mc::property_automaton->propositional_symbols, cursor, ps)
     values.push_back(xbt_automaton_propositional_symbol_evaluate(ps));
-  return values;
+  return std::make_shared<const std::vector<int>>(std::move(values));
 }
 
 int LivenessChecker::compare(simgrid::mc::VisitedPair* state1, simgrid::mc::VisitedPair* state2)
@@ -138,21 +125,22 @@ std::shared_ptr<VisitedPair> LivenessChecker::insertAcceptancePair(simgrid::mc::
   auto res = std::equal_range(acceptancePairs_.begin(), acceptancePairs_.end(),
     new_pair.get(), simgrid::mc::DerefAndCompareByNbProcessesAndUsedHeap());
 
-  if (pair->search_cycle)
-    for (auto i = res.first; i != res.second; ++i) {
-      std::shared_ptr<simgrid::mc::VisitedPair> const& pair_test = *i;
-      if (xbt_automaton_state_compare(pair_test->automaton_state, new_pair->automaton_state) == 0) {
-        if (pair_test->atomic_propositions == new_pair->atomic_propositions) {
-          if (this->compare(pair_test.get(), new_pair.get()) == 0) {
-            XBT_INFO("Pair %d already reached (equal to pair %d) !", new_pair->num, pair_test->num);
-            livenessStack_.pop_back();
-            if (dot_output != nullptr)
-              fprintf(dot_output, "\"%d\" -> \"%d\" [%s];\n", initial_global_state->prev_pair, pair_test->num, initial_global_state->prev_req);
-            return nullptr;
-          }
-        }
-      }
-    }
+  if (pair->search_cycle) for (auto i = res.first; i != res.second; ++i) {
+    std::shared_ptr<simgrid::mc::VisitedPair> const& pair_test = *i;
+    if (xbt_automaton_state_compare(
+          pair_test->automaton_state, new_pair->automaton_state) != 0
+        || *(pair_test->atomic_propositions) != *(new_pair->atomic_propositions)
+        || this->compare(pair_test.get(), new_pair.get()) != 0)
+      continue;
+    XBT_INFO("Pair %d already reached (equal to pair %d) !",
+      new_pair->num, pair_test->num);
+    explorationStack_.pop_back();
+    if (dot_output != nullptr)
+      fprintf(dot_output, "\"%d\" -> \"%d\" [%s];\n",
+        initial_global_state->prev_pair, pair_test->num,
+        initial_global_state->prev_req.c_str());
+    return nullptr;
+  }
 
   acceptancePairs_.insert(res.first, new_pair);
   return new_pair;
@@ -169,49 +157,29 @@ void LivenessChecker::removeAcceptancePair(int pair_num)
 
 void LivenessChecker::prepare(void)
 {
-  simgrid::mc::Pair* initial_pair = nullptr;
   mc_model_checker->wait_for_requests();
-
   initial_global_state->snapshot = simgrid::mc::take_snapshot(0);
   initial_global_state->prev_pair = 0;
 
+  std::shared_ptr<const std::vector<int>> propos = this->getPropositionValues();
+
+  // For each initial state of the property automaton, push a
+  // (application_state, automaton_state) pair to the exploration stack:
   unsigned int cursor = 0;
   xbt_automaton_state_t automaton_state;
-
-  xbt_dynar_foreach(simgrid::mc::property_automaton->states, cursor, automaton_state) {
-    if (automaton_state->type == -1) {  /* Initial automaton state */
-
-      initial_pair = new Pair();
-      initial_pair->automaton_state = automaton_state;
-      initial_pair->graph_state = std::shared_ptr<simgrid::mc::State>(MC_state_new());
-      initial_pair->atomic_propositions = this->getPropositionValues();
-      initial_pair->depth = 1;
-
-      /* Get enabled processes and insert them in the interleave set of the graph_state */
-      for (auto& p : mc_model_checker->process().simix_processes())
-        if (simgrid::mc::process_is_enabled(&p.copy))
-          MC_state_interleave_process(initial_pair->graph_state.get(), &p.copy);
-
-      initial_pair->requests = MC_state_interleave_size(initial_pair->graph_state.get());
-      initial_pair->search_cycle = false;
-
-      livenessStack_.push_back(initial_pair);
-    }
-  }
+  xbt_dynar_foreach(simgrid::mc::property_automaton->states, cursor, automaton_state)
+    if (automaton_state->type == -1)
+      explorationStack_.push_back(this->newPair(nullptr, automaton_state, propos));
 }
 
 
 void LivenessChecker::replay()
 {
-  smx_simcall_t req = nullptr, saved_req = NULL;
-  int value, depth = 1;
-  char *req_str;
-
   XBT_DEBUG("**** Begin Replay ****");
 
   /* Intermediate backtracking */
   if(_sg_mc_checkpoint > 0) {
-    simgrid::mc::Pair* pair = livenessStack_.back();
+    simgrid::mc::Pair* pair = explorationStack_.back().get();
     if(pair->graph_state->system_state){
       simgrid::mc::restore_snapshot(pair->graph_state->system_state);
       return;
@@ -222,40 +190,43 @@ void LivenessChecker::replay()
   simgrid::mc::restore_snapshot(initial_global_state->snapshot);
 
   /* Traverse the stack from the initial state and re-execute the transitions */
-  for (simgrid::mc::Pair* pair : livenessStack_) {
-    if (pair == livenessStack_.back())
+  int depth = 1;
+  for (std::shared_ptr<Pair> const& pair : explorationStack_) {
+    if (pair == explorationStack_.back())
       break;
 
-      std::shared_ptr<State> state = pair->graph_state;
-
-      if (pair->exploration_started) {
+    std::shared_ptr<State> state = pair->graph_state;
 
-        saved_req = MC_state_get_executed_request(state.get(), &value);
+    if (pair->exploration_started) {
 
-        if (saved_req != nullptr) {
-          /* because we got a copy of the executed request, we have to fetch the
-             real one, pointed by the request field of the issuer process */
-          const smx_process_t issuer = MC_smx_simcall_get_issuer(saved_req);
-          req = &issuer->simcall;
+      int value;
+      smx_simcall_t saved_req = MC_state_get_executed_request(state.get(), &value);
 
-          /* Debug information */
-          if (XBT_LOG_ISENABLED(mc_liveness, xbt_log_priority_debug)) {
-            req_str = simgrid::mc::request_to_string(req, value, simgrid::mc::RequestType::simix);
-            XBT_DEBUG("Replay (depth = %d) : %s (%p)", depth, req_str, state.get());
-            xbt_free(req_str);
-          }
+      smx_simcall_t req = nullptr;
 
-        }
-
-        simgrid::mc::handle_simcall(req, value);
-        mc_model_checker->wait_for_requests();
+      if (saved_req != nullptr) {
+        /* because we got a copy of the executed request, we have to fetch the
+             real one, pointed by the request field of the issuer process */
+        const smx_process_t issuer = MC_smx_simcall_get_issuer(saved_req);
+        req = &issuer->simcall;
+
+        /* Debug information */
+        XBT_DEBUG("Replay (depth = %d) : %s (%p)",
+          depth,
+          simgrid::mc::request_to_string(
+            req, value, simgrid::mc::RequestType::simix).c_str(),
+          state.get());
       }
 
-      /* Update statistics */
-      mc_stats->visited_pairs++;
-      mc_stats->executed_transitions++;
+      simgrid::mc::handle_simcall(req, value);
+      mc_model_checker->wait_for_requests();
+    }
 
-      depth++;
+    /* Update statistics */
+    mc_stats->visited_pairs++;
+    mc_stats->executed_transitions++;
+
+    depth++;
 
   }
 
@@ -280,43 +251,38 @@ int LivenessChecker::insertVisitedPair(std::shared_ptr<VisitedPair> visited_pair
 
   for (auto i = range.first; i != range.second; ++i) {
     VisitedPair* pair_test = i->get();
-    if (xbt_automaton_state_compare(pair_test->automaton_state, visited_pair->automaton_state) == 0) {
-      if (pair_test->atomic_propositions == visited_pair->atomic_propositions) {
-        if (this->compare(pair_test, visited_pair.get()) == 0) {
-          if (pair_test->other_num == -1)
-            visited_pair->other_num = pair_test->num;
-          else
-            visited_pair->other_num = pair_test->other_num;
-          if (dot_output == nullptr)
-            XBT_DEBUG("Pair %d already visited ! (equal to pair %d)",
-            visited_pair->num, pair_test->num);
-          else
-            XBT_DEBUG("Pair %d already visited ! (equal to pair %d (pair %d in dot_output))",
-              visited_pair->num, pair_test->num, visited_pair->other_num);
-          (*i) = std::move(visited_pair);
-          return (*i)->other_num;
-        }
-      }
-    }
+    if (xbt_automaton_state_compare(
+          pair_test->automaton_state, visited_pair->automaton_state) != 0
+        || *(pair_test->atomic_propositions) != *(visited_pair->atomic_propositions)
+        || this->compare(pair_test, visited_pair.get()) != 0)
+        continue;
+    if (pair_test->other_num == -1)
+      visited_pair->other_num = pair_test->num;
+    else
+      visited_pair->other_num = pair_test->other_num;
+    if (dot_output == nullptr)
+      XBT_DEBUG("Pair %d already visited ! (equal to pair %d)", visited_pair->num, pair_test->num);
+    else
+      XBT_DEBUG("Pair %d already visited ! (equal to pair %d (pair %d in dot_output))",
+        visited_pair->num, pair_test->num, visited_pair->other_num);
+    (*i) = std::move(visited_pair);
+    return (*i)->other_num;
   }
 
   visitedPairs_.insert(range.first, std::move(visited_pair));
+  this->purgeVisitedPairs();
+  return -1;
+}
 
-  if (visitedPairs_.size() > (std::size_t) _sg_mc_visited) {
-    int min2 = mc_stats->expanded_pairs;
-
-    std::list<std::shared_ptr<VisitedPair>>::iterator index2;
-    for (auto i = visitedPairs_.begin(); i != visitedPairs_.end(); ++i) {
-      if ((*i)->num < min2) {
-        index2 = i;
-        min2 = (*i)->num;
-      }
-    }
-
-    visitedPairs_.erase(index2);
+void LivenessChecker::purgeVisitedPairs()
+{
+  if (_sg_mc_visited != 0 && visitedPairs_.size() > (std::size_t) _sg_mc_visited) {
+    // Remove the oldest entry with a linear search:
+    visitedPairs_.erase(std::min_element(
+      visitedPairs_.begin(), visitedPairs_.end(),
+      [](std::shared_ptr<VisitedPair> const a, std::shared_ptr<VisitedPair> const& b) {
+        return a->num < b->num; } ));
   }
-
-  return -1;
 }
 
 LivenessChecker::LivenessChecker(Session& session) : Checker(session)
@@ -330,14 +296,12 @@ LivenessChecker::~LivenessChecker()
 RecordTrace LivenessChecker::getRecordTrace() // override
 {
   RecordTrace res;
-  for (simgrid::mc::Pair* pair : livenessStack_) {
+  for (std::shared_ptr<Pair> const& pair : explorationStack_) {
     int value;
     smx_simcall_t req = MC_state_get_executed_request(pair->graph_state.get(), &value);
     if (req && req->call != SIMCALL_NONE) {
       smx_process_t issuer = MC_smx_simcall_get_issuer(req);
       const int pid = issuer->pid;
-
-      // Serialization the (pid, value) pair:
       res.push_back(RecordTraceElement(pid, value));
     }
   }
@@ -360,163 +324,107 @@ void LivenessChecker::showAcceptanceCycle(std::size_t depth)
 std::vector<std::string> LivenessChecker::getTextualTrace() // override
 {
   std::vector<std::string> trace;
-  for (simgrid::mc::Pair* pair : livenessStack_) {
+  for (std::shared_ptr<Pair> const& pair : explorationStack_) {
     int value;
     smx_simcall_t req = MC_state_get_executed_request(pair->graph_state.get(), &value);
-    if (req && req->call != SIMCALL_NONE) {
-      char* req_str = simgrid::mc::request_to_string(req, value, simgrid::mc::RequestType::executed);
-      trace.push_back(std::string(req_str));
-      xbt_free(req_str);
-    }
+    if (req && req->call != SIMCALL_NONE)
+      trace.push_back(simgrid::mc::request_to_string(
+        req, value, simgrid::mc::RequestType::executed));
   }
   return trace;
 }
 
 int LivenessChecker::main(void)
 {
-  simgrid::mc::Pair* current_pair = nullptr;
-  int value, res, visited_num = -1;
-  smx_simcall_t req = nullptr;
-  xbt_automaton_transition_t transition_succ = nullptr;
-  int cursor = 0;
-  std::shared_ptr<VisitedPair> reached_pair = nullptr;
-
-  while (!livenessStack_.empty()){
-
-    /* Get current pair */
-    current_pair = livenessStack_.back();
+  while (!explorationStack_.empty()){
+    std::shared_ptr<Pair> current_pair = explorationStack_.back();
 
     /* Update current state in buchi automaton */
     simgrid::mc::property_automaton->current_state = current_pair->automaton_state;
 
-    XBT_DEBUG("********************* ( Depth = %d, search_cycle = %d, interleave size = %d, pair_num = %d, requests = %d)",
+    XBT_DEBUG("********************* ( Depth = %d, search_cycle = %d, interleave size = %zd, pair_num = %d, requests = %d)",
        current_pair->depth, current_pair->search_cycle,
-       MC_state_interleave_size(current_pair->graph_state.get()), current_pair->num,
+       current_pair->graph_state->interleaveSize(),
+       current_pair->num,
        current_pair->requests);
 
-    if (current_pair->requests > 0) {
+    if (current_pair->requests == 0) {
+      this->backtrack();
+      continue;
+    }
 
-      if (current_pair->automaton_state->type == 1 && !current_pair->exploration_started) {
-        /* If new acceptance pair, return new pair */
-        if ((reached_pair = this->insertAcceptancePair(current_pair)) == nullptr) {
-          this->showAcceptanceCycle(current_pair->depth);
-          return SIMGRID_MC_EXIT_LIVENESS;
-        }
+    std::shared_ptr<VisitedPair> reached_pair;
+    if (current_pair->automaton_state->type == 1 && !current_pair->exploration_started
+        && (reached_pair = this->insertAcceptancePair(current_pair.get())) == nullptr) {
+      this->showAcceptanceCycle(current_pair->depth);
+      return SIMGRID_MC_EXIT_LIVENESS;
+    }
+
+    /* Pair already visited ? stop the exploration on the current path */
+    int visited_num = -1;
+    if ((!current_pair->exploration_started)
+      && (visited_num = this->insertVisitedPair(
+        reached_pair, current_pair.get())) != -1) {
+      if (dot_output != nullptr){
+        fprintf(dot_output, "\"%d\" -> \"%d\" [%s];\n",
+          initial_global_state->prev_pair, visited_num,
+          initial_global_state->prev_req.c_str());
+        fflush(dot_output);
       }
+      XBT_DEBUG("Pair already visited (equal to pair %d), exploration on the current path stopped.", visited_num);
+      current_pair->requests = 0;
+      this->backtrack();
+      continue;
+    }
 
-      /* Pair already visited ? stop the exploration on the current path */
-      if ((!current_pair->exploration_started)
-        && (visited_num = this->insertVisitedPair(
-          reached_pair, current_pair)) != -1) {
-
-        if (dot_output != nullptr){
-          fprintf(dot_output, "\"%d\" -> \"%d\" [%s];\n", initial_global_state->prev_pair, visited_num, initial_global_state->prev_req);
-          fflush(dot_output);
-        }
-
-        XBT_DEBUG("Pair already visited (equal to pair %d), exploration on the current path stopped.", visited_num);
-        current_pair->requests = 0;
-        goto backtracking;
-
-      }else{
-
-        req = MC_state_get_request(current_pair->graph_state.get(), &value);
-
-         if (dot_output != nullptr) {
-           if (initial_global_state->prev_pair != 0 && initial_global_state->prev_pair != current_pair->num) {
-             fprintf(dot_output, "\"%d\" -> \"%d\" [%s];\n", initial_global_state->prev_pair, current_pair->num, initial_global_state->prev_req);
-             xbt_free(initial_global_state->prev_req);
-           }
-           initial_global_state->prev_pair = current_pair->num;
-           initial_global_state->prev_req = simgrid::mc::request_get_dot_output(req, value);
-           if (current_pair->search_cycle)
-             fprintf(dot_output, "%d [shape=doublecircle];\n", current_pair->num);
-           fflush(dot_output);
-         }
-
-         char* req_str = simgrid::mc::request_to_string(req, value, simgrid::mc::RequestType::simix);
-         XBT_DEBUG("Execute: %s", req_str);
-         xbt_free(req_str);
-
-         /* Set request as executed */
-         MC_state_set_executed_request(current_pair->graph_state.get(), req, value);
-
-         /* Update mc_stats */
-         mc_stats->executed_transitions++;
-         if (!current_pair->exploration_started)
-           mc_stats->visited_pairs++;
-
-         /* Answer the request */
-         simgrid::mc::handle_simcall(req, value);
-
-         /* Wait for requests (schedules processes) */
-         mc_model_checker->wait_for_requests();
-
-         current_pair->requests--;
-         current_pair->exploration_started = true;
-
-         /* Get values of atomic propositions (variables used in the property formula) */
-         std::vector<int> prop_values = this->getPropositionValues();
-
-         /* Evaluate enabled/true transitions in automaton according to atomic propositions values and create new pairs */
-         cursor = xbt_dynar_length(current_pair->automaton_state->out) - 1;
-         while (cursor >= 0) {
-           transition_succ = (xbt_automaton_transition_t)xbt_dynar_get_as(current_pair->automaton_state->out, cursor, xbt_automaton_transition_t);
-           res = MC_automaton_evaluate_label(transition_succ->label, prop_values);
-           if (res == 1 || res == 2) { /* 1 = True transition (always enabled), 2 = enabled transition according to atomic prop values */
-              Pair* next_pair = new Pair();
-              next_pair->graph_state = std::shared_ptr<simgrid::mc::State>(MC_state_new());
-              next_pair->automaton_state = transition_succ->dst;
-              next_pair->atomic_propositions = this->getPropositionValues();
-              next_pair->depth = current_pair->depth + 1;
-              /* Get enabled processes and insert them in the interleave set of the next graph_state */
-              for (auto& p : mc_model_checker->process().simix_processes())
-                if (simgrid::mc::process_is_enabled(&p.copy))
-                  MC_state_interleave_process(next_pair->graph_state.get(), &p.copy);
-
-              next_pair->requests = MC_state_interleave_size(next_pair->graph_state.get());
-
-              /* FIXME : get search_cycle value for each acceptant state */
-              if (next_pair->automaton_state->type == 1 || current_pair->search_cycle)
-                next_pair->search_cycle = true;
-
-              /* Add new pair to the exploration stack */
-              livenessStack_.push_back(next_pair);
-
-           }
-           cursor--;
-         }
-
-      } /* End of visited_pair test */
+    int value;
+    smx_simcall_t req = MC_state_get_request(current_pair->graph_state.get(), &value);
+
+    if (dot_output != nullptr) {
+      if (initial_global_state->prev_pair != 0 && initial_global_state->prev_pair != current_pair->num) {
+        fprintf(dot_output, "\"%d\" -> \"%d\" [%s];\n",
+          initial_global_state->prev_pair, current_pair->num,
+          initial_global_state->prev_req.c_str());
+        initial_global_state->prev_req.clear();
+      }
+      initial_global_state->prev_pair = current_pair->num;
+      initial_global_state->prev_req = simgrid::mc::request_get_dot_output(req, value);
+      if (current_pair->search_cycle)
+        fprintf(dot_output, "%d [shape=doublecircle];\n", current_pair->num);
+      fflush(dot_output);
+    }
 
-    } else {
+    XBT_DEBUG("Execute: %s",
+      simgrid::mc::request_to_string(
+        req, value, simgrid::mc::RequestType::simix).c_str());
 
-    backtracking:
-      if(visited_num == -1)
-        XBT_DEBUG("No more request to execute. Looking for backtracking point.");
-
-      /* Traverse the stack backwards until a pair with a non empty interleave
-         set is found, deleting all the pairs that have it empty in the way. */
-      while (!livenessStack_.empty()) {
-        current_pair = livenessStack_.back();
-        livenessStack_.pop_back();
-        if (current_pair->requests > 0) {
-          /* We found a backtracking point */
-          XBT_DEBUG("Backtracking to depth %d", current_pair->depth);
-          livenessStack_.push_back(current_pair);
-          this->replay();
-          XBT_DEBUG("Backtracking done");
-          break;
-        }else{
-          /* Delete pair */
-          XBT_DEBUG("Delete pair %d at depth %d", current_pair->num, current_pair->depth);
-          if (current_pair->automaton_state->type == 1)
-            this->removeAcceptancePair(current_pair->num);
-          delete current_pair;
-        }
-      }
+    /* Update mc_stats */
+    mc_stats->executed_transitions++;
+    if (!current_pair->exploration_started)
+      mc_stats->visited_pairs++;
+
+    /* Answer the request */
+    simgrid::mc::handle_simcall(req, value);
+
+    /* Wait for requests (schedules processes) */
+    mc_model_checker->wait_for_requests();
+
+    current_pair->requests--;
+    current_pair->exploration_started = true;
 
-    } /* End of if (current_pair->requests > 0) else ... */
+    /* Get values of atomic propositions (variables used in the property formula) */
+    std::shared_ptr<const std::vector<int>> prop_values = this->getPropositionValues();
+
+    // For each enabled transition in the property automaton, push a
+    // (application_state, automaton_state) pair to the exploration stack:
+    int cursor = xbt_dynar_length(current_pair->automaton_state->out) - 1;
+    while (cursor >= 0) {
+      xbt_automaton_transition_t transition_succ = (xbt_automaton_transition_t)xbt_dynar_get_as(current_pair->automaton_state->out, cursor, xbt_automaton_transition_t);
+      if (evaluate_label(transition_succ->label, *prop_values))
+          explorationStack_.push_back(this->newPair(
+            current_pair.get(), transition_succ->dst, prop_values));
+       cursor--;
+     }
 
   }
 
@@ -525,6 +433,52 @@ int LivenessChecker::main(void)
   return SIMGRID_MC_EXIT_SUCCESS;
 }
 
+std::shared_ptr<Pair> LivenessChecker::newPair(Pair* current_pair, xbt_automaton_state_t state, std::shared_ptr<const std::vector<int>> propositions)
+{
+  std::shared_ptr<Pair> next_pair = std::make_shared<Pair>();
+  next_pair->automaton_state = state;
+  next_pair->graph_state = std::shared_ptr<simgrid::mc::State>(MC_state_new());
+  next_pair->atomic_propositions = std::move(propositions);
+  if (current_pair)
+    next_pair->depth = current_pair->depth + 1;
+  else
+    next_pair->depth = 1;
+  /* Get enabled processes and insert them in the interleave set of the next graph_state */
+  for (auto& p : mc_model_checker->process().simix_processes())
+    if (simgrid::mc::process_is_enabled(&p.copy))
+      MC_state_interleave_process(next_pair->graph_state.get(), &p.copy);
+  next_pair->requests = next_pair->graph_state->interleaveSize();
+  /* FIXME : get search_cycle value for each acceptant state */
+  if (next_pair->automaton_state->type == 1 ||
+      (current_pair && current_pair->search_cycle))
+    next_pair->search_cycle = true;
+  else
+    next_pair->search_cycle = false;
+  return std::move(next_pair);
+}
+
+void LivenessChecker::backtrack()
+{
+  /* Traverse the stack backwards until a pair with a non empty interleave
+     set is found, deleting all the pairs that have it empty in the way. */
+  while (!explorationStack_.empty()) {
+    std::shared_ptr<simgrid::mc::Pair> current_pair = explorationStack_.back();
+    explorationStack_.pop_back();
+    if (current_pair->requests > 0) {
+      /* We found a backtracking point */
+      XBT_DEBUG("Backtracking to depth %d", current_pair->depth);
+      explorationStack_.push_back(std::move(current_pair));
+      this->replay();
+      XBT_DEBUG("Backtracking done");
+      break;
+    } else {
+      XBT_DEBUG("Delete pair %d at depth %d", current_pair->num, current_pair->depth);
+      if (current_pair->automaton_state->type == 1)
+        this->removeAcceptancePair(current_pair->num);
+    }
+  }
+}
+
 int LivenessChecker::run()
 {
   XBT_INFO("Check the liveness property %s", _sg_mc_property_file);