X-Git-Url: http://info.iut-bm.univ-fcomte.fr/pub/gitweb/simgrid.git/blobdiff_plain/ce2e676ad127f782b9c959499ab1c042195e411a..0433449947b08247ca57c84e32f547c35e351145:/src/mc/LivenessChecker.cpp

diff --git a/src/mc/LivenessChecker.cpp b/src/mc/LivenessChecker.cpp
index e98267245e..537dd9bf74 100644
--- a/src/mc/LivenessChecker.cpp
+++ b/src/mc/LivenessChecker.cpp
@@ -8,6 +8,7 @@
 
 #include <algorithm>
 #include <memory>
+#include <list>
 
 #include <unistd.h>
 #include <sys/wait.h>
@@ -15,7 +16,6 @@
 #include <xbt/automaton.h>
 #include <xbt/dynar.h>
 #include <xbt/dynar.hpp>
-#include <xbt/fifo.h>
 #include <xbt/log.h>
 #include <xbt/sysdep.h>
 
@@ -29,123 +29,84 @@
 #include "src/mc/mc_replay.h"
 #include "src/mc/mc_safety.h"
 #include "src/mc/mc_exit.h"
+#include "src/mc/Transition.hpp"
+#include "src/mc/Session.hpp"
 
 XBT_LOG_NEW_DEFAULT_SUBCATEGORY(mc_liveness, mc,
                                 "Logging specific to algorithms for liveness properties verification");
 
-/********* Global variables *********/
-
-xbt_dynar_t acceptance_pairs;
-static xbt_fifo_t liveness_stack;
-
 /********* Static functions *********/
 
 namespace simgrid {
 namespace mc {
 
-VisitedPair::VisitedPair(int pair_num, xbt_automaton_state_t automaton_state, xbt_dynar_t atomic_propositions, simgrid::mc::State* graph_state)
+VisitedPair::VisitedPair(
+  int pair_num, xbt_automaton_state_t automaton_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());
 
-  this->graph_state = graph_state;
+  this->graph_state = std::move(graph_state);
   if(this->graph_state->system_state == nullptr)
     this->graph_state->system_state = simgrid::mc::take_snapshot(pair_num);
   this->heap_bytes_used = mmalloc_get_bytes_used_remote(
     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->acceptance_removed = 0;
-  this->visited_removed = 0;
-  this->acceptance_pair = 0;
-  this->atomic_propositions = simgrid::xbt::unique_ptr<s_xbt_dynar_t>(
-    xbt_dynar_new(sizeof(int), nullptr));
-
-  unsigned int cursor = 0;
-  int value;
-  xbt_dynar_foreach(atomic_propositions, cursor, value)
-      xbt_dynar_push_as(this->atomic_propositions.get(), int, value);
-}
-
-static int is_exploration_stack_pair(simgrid::mc::VisitedPair* pair){
-  xbt_fifo_item_t item = xbt_fifo_get_first_item(liveness_stack);
-  while (item) {
-    if (((simgrid::mc::Pair*)xbt_fifo_get_item_content(item))->num == pair->num){
-      ((simgrid::mc::Pair*)xbt_fifo_get_item_content(item))->visited_pair_removed = 1;
-      return 1;
-    }
-    item = xbt_fifo_get_next_item(item);
-  }
-  return 0;
+  this->atomic_propositions = std::move(atomic_propositions);
 }
 
 VisitedPair::~VisitedPair()
 {
-  if( !is_exploration_stack_pair(this))
-    MC_state_delete(this->graph_state, 1);
 }
 
-static int MC_automaton_evaluate_label(xbt_automaton_exp_label_t l,
-                                       xbt_dynar_t atomic_propositions_values)
+static bool evaluate_label(
+  xbt_automaton_exp_label_t l, std::vector<int> const& values)
 {
-
   switch (l->type) {
-  case 0:{
-      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 1:{
-      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 2:{
-      int res = MC_automaton_evaluate_label(l->u.exp_not, atomic_propositions_values);
-      return (!res);
-    }
-  case 3:{
+  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 (int) xbt_dynar_get_as(atomic_propositions_values, cursor, int);
+          return values[cursor] != 0;
       }
-      return -1;
+      xbt_die("Missing predicate");
     }
-  case 4:
-    return 2;
+  case xbt_automaton_exp_label::AUT_ONE:
+    return true;
   default:
-    return -1;
+    xbt_die("Unexpected vaue for automaton");
   }
 }
 
-static xbt_dynar_t visited_pairs;
-
-Pair::Pair() : num(++mc_stats->expanded_pairs),
-  visited_pair_removed(_sg_mc_visited > 0 ? 0 : 1)
+Pair::Pair() : num(++mc_stats->expanded_pairs)
 {}
 
-Pair::~Pair() {
-  if (this->visited_pair_removed)
-    MC_state_delete(this->graph_state, 1);
-}
+Pair::~Pair() {}
 
-simgrid::xbt::unique_ptr<s_xbt_dynar_t> 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;
-  simgrid::xbt::unique_ptr<s_xbt_dynar_t> values = simgrid::xbt::unique_ptr<s_xbt_dynar_t>(xbt_dynar_new(sizeof(int), nullptr));
-  xbt_dynar_foreach(simgrid::mc::property_automaton->propositional_symbols, cursor, ps) {
-    int res = xbt_automaton_propositional_symbol_evaluate(ps);
-    xbt_dynar_push_as(values.get(), int, res);
-  }
-  return std::move(values);
+  xbt_dynar_foreach(simgrid::mc::property_automaton->propositional_symbols, cursor, ps)
+    values.push_back(xbt_automaton_propositional_symbol_evaluate(ps));
+  return std::make_shared<const std::vector<int>>(std::move(values));
 }
 
 int LivenessChecker::compare(simgrid::mc::VisitedPair* state1, simgrid::mc::VisitedPair* state2)
@@ -157,117 +118,69 @@ int LivenessChecker::compare(simgrid::mc::VisitedPair* state1, simgrid::mc::Visi
   return simgrid::mc::snapshot_compare(num1, s1, num2, s2);
 }
 
-simgrid::mc::VisitedPair* LivenessChecker::insertAcceptancePair(simgrid::mc::Pair* pair)
+std::shared_ptr<VisitedPair> LivenessChecker::insertAcceptancePair(simgrid::mc::Pair* pair)
 {
-  auto acceptance_pairs = simgrid::xbt::range<simgrid::mc::VisitedPair*>(::acceptance_pairs);
-  auto new_pair =
-    std::unique_ptr<simgrid::mc::VisitedPair>(new VisitedPair(
-      pair->num, pair->automaton_state, pair->atomic_propositions.get(),
-      pair->graph_state));
-  new_pair->acceptance_pair = 1;
-
-  auto res = std::equal_range(acceptance_pairs.begin(), acceptance_pairs.end(),
-    new_pair, simgrid::mc::DerefAndCompareByNbProcessesAndUsedHeap());
-
-  if (pair->search_cycle == 1)
-    for (auto i = res.first; i != res.second; ++i) {
-      simgrid::mc::VisitedPair* pair_test = *i;
-      if (xbt_automaton_state_compare(pair_test->automaton_state, new_pair->automaton_state) == 0) {
-        if (xbt_automaton_propositional_symbols_compare_value(
-            pair_test->atomic_propositions.get(),
-            new_pair->atomic_propositions.get()) == 0) {
-          if (this->compare(pair_test, new_pair.get()) == 0) {
-            XBT_INFO("Pair %d already reached (equal to pair %d) !", new_pair->num, pair_test->num);
-            xbt_fifo_shift(liveness_stack);
-            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;
-          }
-        }
-      }
-    }
+  std::shared_ptr<VisitedPair> new_pair = std::make_shared<VisitedPair>(
+    pair->num, pair->automaton_state, pair->atomic_propositions,
+    pair->graph_state);
+
+  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
+        || *(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;
+  }
 
-  auto new_raw_pair = new_pair.release();
-  xbt_dynar_insert_at(
-    ::acceptance_pairs, res.first - acceptance_pairs.begin(), &new_raw_pair);
-  return new_raw_pair;
+  acceptancePairs_.insert(res.first, new_pair);
+  return new_pair;
 }
 
 void LivenessChecker::removeAcceptancePair(int pair_num)
 {
-  unsigned int cursor = 0;
-  simgrid::mc::VisitedPair* pair_test = nullptr;
-  int pair_found = 0;
-
-  xbt_dynar_foreach(acceptance_pairs, cursor, pair_test)
-    if (pair_test->num == pair_num) {
-       pair_found = 1;
+  for (auto i = acceptancePairs_.begin(); i != acceptancePairs_.end(); ++i)
+    if ((*i)->num == pair_num) {
+      acceptancePairs_.erase(i);
       break;
     }
-
-  if(pair_found == 1) {
-    xbt_dynar_remove_at(acceptance_pairs, cursor, &pair_test);
-
-    pair_test->acceptance_removed = 1;
-
-    if (_sg_mc_visited == 0 || pair_test->visited_removed == 1) 
-      delete pair_test;
-
-  }
 }
 
 void LivenessChecker::prepare(void)
 {
-  simgrid::mc::Pair* initial_pair = nullptr;
-  mc_model_checker->wait_for_requests();
-  acceptance_pairs = xbt_dynar_new(sizeof(simgrid::mc::VisitedPair*), nullptr);
-  if(_sg_mc_visited > 0)
-    simgrid::mc::visited_pairs = xbt_dynar_new(sizeof(simgrid::mc::VisitedPair*), nullptr);
-
   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 = 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, &p.copy);
-
-      initial_pair->requests = MC_state_interleave_size(initial_pair->graph_state);
-      initial_pair->search_cycle = 0;
-
-      xbt_fifo_unshift(liveness_stack, 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(xbt_fifo_t stack)
+void LivenessChecker::replay()
 {
-  xbt_fifo_item_t item;
-  simgrid::mc::Pair* pair = nullptr;
-  simgrid::mc::State* state = nullptr;
-  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) {
-    item = xbt_fifo_get_first_item(stack);
-    pair = (simgrid::mc::Pair*) xbt_fifo_get_item_content(item);
+    simgrid::mc::Pair* pair = explorationStack_.back().get();
     if(pair->graph_state->system_state){
       simgrid::mc::restore_snapshot(pair->graph_state->system_state);
       return;
@@ -277,45 +190,45 @@ void LivenessChecker::replay(xbt_fifo_t stack)
   /* Restore the initial state */
   simgrid::mc::restore_snapshot(initial_global_state->snapshot);
 
-    /* Traverse the stack from the initial state and re-execute the transitions */
-    for (item = xbt_fifo_get_last_item(stack);
-         item != xbt_fifo_get_first_item(stack);
-         item = xbt_fifo_get_prev_item(item)) {
+  /* Traverse the stack from the initial state and re-execute the transitions */
+  int depth = 1;
+  for (std::shared_ptr<Pair> const& pair : explorationStack_) {
+    if (pair == explorationStack_.back())
+      break;
 
-      pair = (simgrid::mc::Pair*) xbt_fifo_get_item_content(item);
+    std::shared_ptr<State> state = pair->graph_state;
 
-      state = (simgrid::mc::State*) pair->graph_state;
+    if (pair->exploration_started) {
 
-      if (pair->exploration_started) {
+      int req_num = state->transition.argument;
+      smx_simcall_t saved_req = &state->executed_req;
 
-        saved_req = MC_state_get_executed_request(state, &value);
+      smx_simcall_t req = nullptr;
 
-        if (saved_req != nullptr) {
-          /* because we got a copy of the executed request, we have to fetch the
+      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 */
-          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);
-            xbt_free(req_str);
-          }
-
-        }
-
-        simgrid::mc::handle_simcall(req, value);
-        mc_model_checker->wait_for_requests();
+        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, req_num, simgrid::mc::RequestType::simix).c_str(),
+          state.get());
       }
 
-      /* Update statistics */
-      mc_stats->visited_pairs++;
-      mc_stats->executed_transitions++;
+      this->getSession().execute(state->transition);
+    }
 
-      depth++;
+    /* Update statistics */
+    mc_stats->visited_pairs++;
+    mc_stats->executed_transitions++;
 
-    }
+    depth++;
+
+  }
 
   XBT_DEBUG("**** End Replay ****");
 }
@@ -323,75 +236,55 @@ void LivenessChecker::replay(xbt_fifo_t stack)
 /**
  * \brief Checks whether a given pair has already been visited by the algorithm.
  */
-int LivenessChecker::insertVisitedPair(simgrid::mc::VisitedPair* visited_pair, simgrid::mc::Pair* pair)
+int LivenessChecker::insertVisitedPair(std::shared_ptr<VisitedPair> visited_pair, simgrid::mc::Pair* pair)
 {
   if (_sg_mc_visited == 0)
     return -1;
 
-  simgrid::mc::VisitedPair* new_visited_pair = nullptr;
   if (visited_pair == nullptr)
-    new_visited_pair = new simgrid::mc::VisitedPair(
-      pair->num, pair->automaton_state, pair->atomic_propositions.get(),
+    visited_pair = std::make_shared<VisitedPair>(
+      pair->num, pair->automaton_state, pair->atomic_propositions,
       pair->graph_state);
-  else
-    new_visited_pair = visited_pair;
 
-  auto visited_pairs = simgrid::xbt::range<simgrid::mc::VisitedPair*>(simgrid::mc::visited_pairs);
-
-  auto range = std::equal_range(visited_pairs.begin(), visited_pairs.end(),
-    new_visited_pair, simgrid::mc::DerefAndCompareByNbProcessesAndUsedHeap());
+  auto range = std::equal_range(visitedPairs_.begin(), visitedPairs_.end(),
+    visited_pair.get(), simgrid::mc::DerefAndCompareByNbProcessesAndUsedHeap());
 
   for (auto i = range.first; i != range.second; ++i) {
-    simgrid::mc::VisitedPair* pair_test = *i;
-    std::size_t cursor = i - visited_pairs.begin();
-    if (xbt_automaton_state_compare(pair_test->automaton_state, new_visited_pair->automaton_state) == 0) {
-      if (xbt_automaton_propositional_symbols_compare_value(
-          pair_test->atomic_propositions.get(),
-          new_visited_pair->atomic_propositions.get()) == 0) {
-        if (this->compare(pair_test, new_visited_pair) == 0) {
-          if (pair_test->other_num == -1)
-            new_visited_pair->other_num = pair_test->num;
-          else
-            new_visited_pair->other_num = pair_test->other_num;
-          if (dot_output == nullptr)
-            XBT_DEBUG("Pair %d already visited ! (equal to pair %d)", new_visited_pair->num, pair_test->num);
-          else
-            XBT_DEBUG("Pair %d already visited ! (equal to pair %d (pair %d in dot_output))", new_visited_pair->num, pair_test->num, new_visited_pair->other_num);
-          xbt_dynar_remove_at(simgrid::mc::visited_pairs, cursor, &pair_test);
-          xbt_dynar_insert_at(simgrid::mc::visited_pairs, cursor, &new_visited_pair);
-          pair_test->visited_removed = 1;
-          if (!pair_test->acceptance_pair
-              || pair_test->acceptance_removed == 1)
-            delete pair_test;
-          return new_visited_pair->other_num;
-        }
-      }
-    }
-  }
-
-  xbt_dynar_insert_at(simgrid::mc::visited_pairs, range.first - visited_pairs.begin(), &new_visited_pair);
-
-  if ((ssize_t) visited_pairs.size() > _sg_mc_visited) {
-    int min2 = mc_stats->expanded_pairs;
-    unsigned int index2 = 0;
-    for (std::size_t i = 0; i != (std::size_t) visited_pairs.size(); ++i) {
-      simgrid::mc::VisitedPair* pair_test = visited_pairs[i];
-      if (!mc_model_checker->is_important_snapshot(*pair_test->graph_state->system_state)
-          && pair_test->num < min2) {
-        index2 = i;
-        min2 = pair_test->num;
-      }
-    }
-    simgrid::mc::VisitedPair* pair_test = nullptr;
-    xbt_dynar_remove_at(simgrid::mc::visited_pairs, index2, &pair_test);
-    pair_test->visited_removed = 1;
-    if (!pair_test->acceptance_pair || pair_test->acceptance_removed)
-      delete pair_test;
+    VisitedPair* pair_test = i->get();
+    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;
 }
 
+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; } ));
+  }
+}
+
 LivenessChecker::LivenessChecker(Session& session) : Checker(session)
 {
 }
@@ -403,22 +296,9 @@ LivenessChecker::~LivenessChecker()
 RecordTrace LivenessChecker::getRecordTrace() // override
 {
   RecordTrace res;
-
-  xbt_fifo_item_t start = xbt_fifo_get_last_item(liveness_stack);
-  for (xbt_fifo_item_t item = start; item; item = xbt_fifo_get_prev_item(item)) {
-    simgrid::mc::Pair* pair = (simgrid::mc::Pair*) xbt_fifo_get_item_content(item);
-    int value;
-    smx_simcall_t req = MC_state_get_executed_request(pair->graph_state, &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));
-    }
-  }
-
-  return std::move(res);
+  for (std::shared_ptr<Pair> const& pair : explorationStack_)
+    res.push_back(pair->graph_state->getTransition());
+  return res;
 }
 
 void LivenessChecker::showAcceptanceCycle(std::size_t depth)
@@ -437,175 +317,161 @@ void LivenessChecker::showAcceptanceCycle(std::size_t depth)
 std::vector<std::string> LivenessChecker::getTextualTrace() // override
 {
   std::vector<std::string> trace;
-  for (xbt_fifo_item_t item = xbt_fifo_get_last_item(liveness_stack);
-       item; item = xbt_fifo_get_prev_item(item)) {
-    simgrid::mc::Pair* pair = (simgrid::mc::Pair*) xbt_fifo_get_item_content(item);
-    int value;
-    smx_simcall_t req = MC_state_get_executed_request(pair->graph_state, &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);
-    }
+  for (std::shared_ptr<Pair> const& pair : explorationStack_) {
+    int req_num = pair->graph_state->transition.argument;
+    smx_simcall_t req = &pair->graph_state->executed_req;
+    if (req && req->call != SIMCALL_NONE)
+      trace.push_back(simgrid::mc::request_to_string(
+        req, req_num, simgrid::mc::RequestType::executed));
   }
-  return std::move(trace);
+  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;
-  simgrid::mc::Pair* next_pair = nullptr;
-  simgrid::xbt::unique_ptr<s_xbt_dynar_t> prop_values;
-  simgrid::mc::VisitedPair* reached_pair = nullptr;
-
-  while(xbt_fifo_size(liveness_stack) > 0){
-
-    /* Get current pair */
-    current_pair = (simgrid::mc::Pair*) xbt_fifo_get_item_content(xbt_fifo_get_first_item(liveness_stack));
+  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), 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 == 0) {
-        /* 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 */
-      if ((current_pair->exploration_started == 0)
-        && (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, &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, req, value);
-
-         /* Update mc_stats */
-         mc_stats->executed_transitions++;
-         if(current_pair->exploration_started == 0)
-           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 = 1;
-
-         /* Get values of atomic propositions (variables used in the property formula) */
-         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.get());
-           if (res == 1 || res == 2) { /* 1 = True transition (always enabled), 2 = enabled transition according to atomic prop values */
-              next_pair = new Pair();
-              next_pair->graph_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, &p.copy);
-
-              next_pair->requests = MC_state_interleave_size(next_pair->graph_state);
-
-              /* FIXME : get search_cycle value for each acceptant state */
-              if (next_pair->automaton_state->type == 1 || current_pair->search_cycle)
-                next_pair->search_cycle = 1;
-
-              /* Add new pair to the exploration stack */
-              xbt_fifo_unshift(liveness_stack, next_pair);
-
-           }
-           cursor--;
-         }
-
-      } /* End of visited_pair test */
+    /* 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;
+    }
 
-    } else {
+    smx_simcall_t req = MC_state_get_request(current_pair->graph_state.get());
+    int req_num = current_pair->graph_state->transition.argument;
 
-    backtracking:
-      if(visited_num == -1)
-        XBT_DEBUG("No more request to execute. Looking for backtracking point.");
-
-      prop_values.reset();
-
-      /* 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 ((current_pair = (simgrid::mc::Pair*) xbt_fifo_shift(liveness_stack)) != nullptr) {
-        if (current_pair->requests > 0) {
-          /* We found a backtracking point */
-          XBT_DEBUG("Backtracking to depth %d", current_pair->depth);
-          xbt_fifo_unshift(liveness_stack, current_pair);
-          this->replay(liveness_stack);
-          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;
-        }
+    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, req_num);
+      if (current_pair->search_cycle)
+        fprintf(dot_output, "%d [shape=doublecircle];\n", current_pair->num);
+      fflush(dot_output);
+    }
+
+    XBT_DEBUG("Execute: %s",
+      simgrid::mc::request_to_string(
+        req, req_num, simgrid::mc::RequestType::simix).c_str());
 
-    } /* End of if (current_pair->requests > 0) else ... */
+    /* Update mc_stats */
+    mc_stats->executed_transitions++;
+    if (!current_pair->exploration_started)
+      mc_stats->visited_pairs++;
+
+    /* Answer the request */
+    mc_model_checker->handle_simcall(current_pair->graph_state->transition);
+
+    /* Wait for requests (schedules processes) */
+    mc_model_checker->wait_for_requests();
+
+    current_pair->requests--;
+    current_pair->exploration_started = true;
 
-  } /* End of while(xbt_fifo_size(liveness_stack) > 0) */
+    /* 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--;
+     }
+
+  }
 
   XBT_INFO("No property violation found.");
   MC_print_statistics(mc_stats);
   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))
+      next_pair->graph_state->interleave(&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);
@@ -613,10 +479,6 @@ int LivenessChecker::run()
   mc_model_checker->wait_for_requests();
 
   XBT_DEBUG("Starting the liveness algorithm");
-  _sg_mc_liveness = 1;
-
-  /* Create exploration stack */
-  liveness_stack = xbt_fifo_new();
 
   /* Create the initial state */
   simgrid::mc::initial_global_state = std::unique_ptr<s_mc_global_t>(new s_mc_global_t());
@@ -624,8 +486,14 @@ int LivenessChecker::run()
   this->prepare();
   int res = this->main();
   simgrid::mc::initial_global_state = nullptr;
+
   return res;
 }
 
+Checker* createLivenessChecker(Session& session)
+{
+  return new LivenessChecker(session);
+}
+
 }
 }