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Don't compute the dependencies locally in the checker, but through the observers...
[simgrid.git] / src / mc / api.cpp
index ecab76b..f3e5b16 100644 (file)
@@ -1,15 +1,22 @@
+/* Copyright (c) 2020-2022. 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 "api.hpp"
 
 #include "src/kernel/activity/MailboxImpl.hpp"
 #include "src/kernel/activity/MutexImpl.hpp"
+#include "src/kernel/actor/SimcallObserver.hpp"
 #include "src/mc/Session.hpp"
 #include "src/mc/checker/Checker.hpp"
-#include "src/mc/checker/SimcallObserver.hpp"
+#include "src/mc/mc_base.hpp"
 #include "src/mc/mc_comm_pattern.hpp"
 #include "src/mc/mc_exit.hpp"
 #include "src/mc/mc_pattern.hpp"
 #include "src/mc/mc_private.hpp"
 #include "src/mc/remote/RemoteProcess.hpp"
+#include "src/surf/HostImpl.hpp"
 
 #include <xbt/asserts.h>
 #include <xbt/log.h>
@@ -20,6 +27,7 @@
 #endif
 
 XBT_LOG_NEW_DEFAULT_SUBCATEGORY(Api, mc, "Logging specific to MC Facade APIs ");
+XBT_LOG_EXTERNAL_CATEGORY(mc_global);
 
 using Simcall = simgrid::simix::Simcall;
 
@@ -44,9 +52,6 @@ static std::string buff_size_to_string(size_t buff_size)
   return XBT_LOG_ISENABLED(Api, xbt_log_priority_verbose) ? std::to_string(buff_size) : "(verbose only)";
 }
 
-static void simcall_translate(smx_simcall_t req,
-                              simgrid::mc::Remote<simgrid::kernel::activity::CommImpl>& buffered_comm);
-
 /* Search an enabled transition for the given process.
  *
  * This can be seen as an iterator returning the next transition of the process.
@@ -59,11 +64,12 @@ static void simcall_translate(smx_simcall_t req,
  * Things can get muddled with the WAITANY and TESTANY simcalls, that are rewritten on the fly to a bunch of WAIT
  * (resp TEST) transitions using the transition.argument field to remember what was the last returned sub-transition.
  */
-static inline smx_simcall_t MC_state_choose_request_for_process(simgrid::mc::State* state, smx_actor_t actor)
+static inline smx_simcall_t MC_state_choose_request_for_process(const RemoteProcess& process, simgrid::mc::State* state,
+                                                                smx_actor_t actor)
 {
   /* reset the outgoing transition */
   simgrid::mc::ActorState* procstate = &state->actor_states_[actor->get_pid()];
-  state->transition_.pid_            = -1;
+  state->transition_.aid_              = -1;
   state->transition_.times_considered_ = -1;
   state->transition_.textual[0]        = '\0';
   state->executed_req_.call_         = Simcall::NONE;
@@ -73,137 +79,34 @@ static inline smx_simcall_t MC_state_choose_request_for_process(simgrid::mc::Sta
 
   smx_simcall_t req = nullptr;
   if (actor->simcall_.observer_ != nullptr) {
-    state->transition_.times_considered_ = procstate->times_considered;
-    procstate->times_considered++;
-    if (actor->simcall_.mc_max_consider_ <= procstate->times_considered)
+    state->transition_.times_considered_ = procstate->get_times_considered_and_inc();
+    if (actor->simcall_.mc_max_consider_ <= procstate->get_times_considered())
       procstate->set_done();
     req = &actor->simcall_;
-  } else
-    switch (actor->simcall_.call_) {
-      case Simcall::COMM_WAITANY:
-        state->transition_.times_considered_ = -1;
-        while (procstate->times_considered < simcall_comm_waitany__get__count(&actor->simcall_)) {
-          if (simgrid::mc::request_is_enabled_by_idx(&actor->simcall_, procstate->times_considered)) {
-            state->transition_.times_considered_ = procstate->times_considered;
-            ++procstate->times_considered;
-            break;
-          }
-          ++procstate->times_considered;
-        }
-
-        if (procstate->times_considered >= simcall_comm_waitany__get__count(&actor->simcall_))
-          procstate->set_done();
-        if (state->transition_.times_considered_ != -1)
-          req = &actor->simcall_;
-        break;
-
-      case Simcall::COMM_TESTANY:
-        state->transition_.times_considered_ = -1;
-        while (procstate->times_considered < simcall_comm_testany__get__count(&actor->simcall_)) {
-          if (simgrid::mc::request_is_enabled_by_idx(&actor->simcall_, procstate->times_considered)) {
-            state->transition_.times_considered_ = procstate->times_considered;
-            ++procstate->times_considered;
-            break;
-          }
-          ++procstate->times_considered;
-        }
-
-        if (procstate->times_considered >= simcall_comm_testany__get__count(&actor->simcall_))
-          procstate->set_done();
-        if (state->transition_.times_considered_ != -1)
-          req = &actor->simcall_;
-        break;
-
-      case Simcall::COMM_WAIT: {
-        simgrid::mc::RemotePtr<simgrid::kernel::activity::CommImpl> remote_act =
-            remote(simcall_comm_wait__get__comm(&actor->simcall_));
-        simgrid::mc::Remote<simgrid::kernel::activity::CommImpl> temp_act;
-        mc_model_checker->get_remote_process().read(temp_act, remote_act);
-        const simgrid::kernel::activity::CommImpl* act = temp_act.get_buffer();
-        if (act->src_actor_.get() && act->dst_actor_.get())
-          state->transition_.times_considered_ = 0; // OK
-        else if (act->src_actor_.get() == nullptr && act->state_ == simgrid::kernel::activity::State::READY &&
-                 act->detached())
-          state->transition_.times_considered_ = 0; // OK
-        else
-          state->transition_.times_considered_ = -1; // timeout
-        procstate->set_done();
-        req = &actor->simcall_;
-        break;
-      }
-
-      default:
-        procstate->set_done();
-        state->transition_.times_considered_ = 0;
-        req                                  = &actor->simcall_;
-        break;
-    }
+  } else {
+    procstate->set_done();
+    state->transition_.times_considered_ = 0;
+    req                                  = &actor->simcall_;
+  }
   if (not req)
     return nullptr;
 
-  state->transition_.pid_ = actor->get_pid();
+  state->transition_.aid_ = actor->get_pid();
   state->executed_req_    = *req;
 
   // Fetch the data of the request and translate it:
   state->internal_req_ = *req;
   state->internal_req_.mc_value_ = state->transition_.times_considered_;
-  simcall_translate(&state->internal_req_, state->internal_comm_);
 
   return req;
 }
 
-static void simcall_translate(smx_simcall_t req,
-                              simgrid::mc::Remote<simgrid::kernel::activity::CommImpl>& buffered_comm)
-{
-  simgrid::kernel::activity::CommImpl* chosen_comm;
-
-  /* The waitany and testany request are transformed into a wait or test request over the corresponding communication
-   * action so it can be treated later by the dependence function. */
-  switch (req->call_) {
-    case Simcall::COMM_WAITANY:
-      req->call_  = Simcall::COMM_WAIT;
-      chosen_comm =
-          mc_model_checker->get_remote_process().read(remote(simcall_comm_waitany__get__comms(req) + req->mc_value_));
-
-      mc_model_checker->get_remote_process().read(buffered_comm, remote(chosen_comm));
-      simcall_comm_wait__set__comm(req, buffered_comm.get_buffer());
-      simcall_comm_wait__set__timeout(req, 0);
-      break;
-
-    case Simcall::COMM_TESTANY:
-      req->call_  = Simcall::COMM_TEST;
-      chosen_comm =
-          mc_model_checker->get_remote_process().read(remote(simcall_comm_testany__get__comms(req) + req->mc_value_));
-
-      mc_model_checker->get_remote_process().read(buffered_comm, remote(chosen_comm));
-      simcall_comm_test__set__comm(req, buffered_comm.get_buffer());
-      simcall_comm_test__set__result(req, req->mc_value_);
-      break;
-
-    case Simcall::COMM_WAIT:
-      chosen_comm = simcall_comm_wait__get__comm(req);
-      mc_model_checker->get_remote_process().read(buffered_comm, remote(chosen_comm));
-      simcall_comm_wait__set__comm(req, buffered_comm.get_buffer());
-      break;
-
-    case Simcall::COMM_TEST:
-      chosen_comm = simcall_comm_test__get__comm(req);
-      mc_model_checker->get_remote_process().read(buffered_comm, remote(chosen_comm));
-      simcall_comm_test__set__comm(req, buffered_comm.get_buffer());
-      break;
-
-    default:
-      /* No translation needed */
-      break;
-  }
-}
-
-simgrid::kernel::activity::CommImpl* Api::get_comm_or_nullptr(smx_simcall_t const r) const
+kernel::activity::CommImpl* Api::get_comm_or_nullptr(smx_simcall_t const r) const
 {
-  if (r->call_ == Simcall::COMM_WAIT)
-    return simcall_comm_wait__get__comm(r);
-  if (r->call_ == Simcall::COMM_TEST)
-    return simcall_comm_test__get__comm(r);
+  if (auto wait = dynamic_cast<kernel::actor::ActivityWaitSimcall*>(r->observer_))
+    return static_cast<kernel::activity::CommImpl*>(wait->get_activity());
+  if (auto test = dynamic_cast<kernel::actor::ActivityTestSimcall*>(r->observer_))
+    return static_cast<kernel::activity::CommImpl*>(test->get_activity());
   return nullptr;
 }
 
@@ -222,110 +125,12 @@ simgrid::mc::ActorInformation* Api::actor_info_cast(smx_actor_t actor) const
   return process_info;
 }
 
-bool Api::simcall_check_dependency(smx_simcall_t req1, smx_simcall_t req2) const
+bool Api::requests_are_dependent(RemotePtr<kernel::actor::SimcallObserver> obs1,
+                                 RemotePtr<kernel::actor::SimcallObserver> obs2) const
 {
-  const auto IRECV = Simcall::COMM_IRECV;
-  const auto ISEND = Simcall::COMM_ISEND;
-  const auto TEST  = Simcall::COMM_TEST;
-  const auto WAIT  = Simcall::COMM_WAIT;
-
-  if (req1->issuer_ == req2->issuer_)
-    return false;
-
-  /* The independence theorem only consider 4 simcalls. All others are dependent with anything. */
-  if (req1->call_ != ISEND && req1->call_ != IRECV && req1->call_ != TEST && req1->call_ != WAIT)
-    return true;
-  if (req2->call_ != ISEND && req2->call_ != IRECV && req2->call_ != TEST && req2->call_ != WAIT)
-    return true;
-
-  /* Timeouts in wait transitions are not considered by the independence theorem, thus assumed dependent */
-  if ((req1->call_ == WAIT && simcall_comm_wait__get__timeout(req1) > 0) ||
-      (req2->call_ == WAIT && simcall_comm_wait__get__timeout(req2) > 0))
-    return true;
-
-  /* Make sure that req1 and req2 are in alphabetic order */
-  if (req1->call_ > req2->call_) {
-    auto temp = req1;
-    req1      = req2;
-    req2      = temp;
-  }
-
-  auto comm1 = get_comm_or_nullptr(req1);
-  auto comm2 = get_comm_or_nullptr(req2);
-
-  /* First case: that's not the same kind of request (we also know that req1 < req2 alphabetically) */
-  if (req1->call_ != req2->call_) {
-    if (req1->call_ == IRECV && req2->call_ == ISEND)
-      return false;
-
-    if ((req1->call_ == IRECV || req1->call_ == ISEND) && req2->call_ == WAIT) {
-      auto mbox1 = get_mbox_remote_addr(req1);
-      auto mbox2 = remote(comm2->mbox_cpy);
-
-      if (mbox1 != mbox2 && simcall_comm_wait__get__timeout(req2) <= 0)
-        return false;
-
-      if ((req1->issuer_ != comm2->src_actor_.get()) && (req1->issuer_ != comm2->dst_actor_.get()) &&
-          simcall_comm_wait__get__timeout(req2) <= 0)
-        return false;
-
-      if ((req1->call_ == ISEND) && (comm2->type_ == kernel::activity::CommImpl::Type::SEND) &&
-          (comm2->src_buff_ != simcall_comm_isend__get__src_buff(req1)) && simcall_comm_wait__get__timeout(req2) <= 0)
-        return false;
-
-      if ((req1->call_ == IRECV) && (comm2->type_ == kernel::activity::CommImpl::Type::RECEIVE) &&
-          (comm2->dst_buff_ != simcall_comm_irecv__get__dst_buff(req1)) && simcall_comm_wait__get__timeout(req2) <= 0)
-        return false;
-    }
-
-    /* FIXME: the following rule assumes that the result of the isend/irecv call is not stored in a buffer used in the
-     * test call. */
-#if 0
-  if((req1->call == ISEND || req1->call == IRECV)
-      &&  req2->call == TEST)
-    return false;
-#endif
-
-    if (req1->call_ == TEST && req2->call_ == WAIT &&
-        (comm1->src_actor_.get() == nullptr || comm1->dst_actor_.get() == nullptr))
-      return false;
-
-    if (req1->call_ == TEST &&
-        (simcall_comm_test__get__comm(req1) == nullptr || comm1->src_buff_ == nullptr || comm1->dst_buff_ == nullptr))
-      return false;
-    if (req2->call_ == TEST &&
-        (simcall_comm_test__get__comm(req2) == nullptr || comm2->src_buff_ == nullptr || comm2->dst_buff_ == nullptr))
-      return false;
-
-    if (req1->call_ == TEST && req2->call_ == WAIT && comm1->src_buff_ == comm2->src_buff_ &&
-        comm1->dst_buff_ == comm2->dst_buff_)
-      return false;
-
-    if (req1->call_ == TEST && req2->call_ == WAIT && comm1->src_buff_ != nullptr && comm1->dst_buff_ != nullptr &&
-        comm2->src_buff_ != nullptr && comm2->dst_buff_ != nullptr && comm1->dst_buff_ != comm2->src_buff_ &&
-        comm1->dst_buff_ != comm2->dst_buff_ && comm2->dst_buff_ != comm1->src_buff_)
-      return false;
-
-    return true;
-  }
+  xbt_assert(mc_model_checker != nullptr, "Must be called from MCer");
 
-  /* Second case: req1 and req2 are of the same call type */
-  switch (req1->call_) {
-    case ISEND:
-      return simcall_comm_isend__get__mbox(req1) == simcall_comm_isend__get__mbox(req2);
-    case IRECV:
-      return simcall_comm_irecv__get__mbox(req1) == simcall_comm_irecv__get__mbox(req2);
-    case WAIT:
-      if (comm1->src_buff_ == comm2->src_buff_ && comm1->dst_buff_ == comm2->dst_buff_)
-        return false;
-      if (comm1->src_buff_ != nullptr && comm1->dst_buff_ != nullptr && comm2->src_buff_ != nullptr &&
-          comm2->dst_buff_ != nullptr && comm1->dst_buff_ != comm2->src_buff_ && comm1->dst_buff_ != comm2->dst_buff_ &&
-          comm2->dst_buff_ != comm1->src_buff_)
-        return false;
-      return true;
-    default:
-      return true;
-  }
+  return mc_model_checker->requests_are_dependent(obs1, obs2);
 }
 
 xbt::string const& Api::get_actor_host_name(smx_actor_t actor) const
@@ -337,20 +142,23 @@ xbt::string const& Api::get_actor_host_name(smx_actor_t actor) const
 
   // Read the simgrid::xbt::string in the MCed process:
   simgrid::mc::ActorInformation* info = actor_info_cast(actor);
-  auto remote_string_address =
-      remote(reinterpret_cast<const simgrid::xbt::string_data*>(&actor->get_host()->get_name()));
-  simgrid::xbt::string_data remote_string = process->read(remote_string_address);
-  std::vector<char> hostname(remote_string.len + 1);
-  // no need to read the terminating null byte, and thus hostname[remote_string.len] is guaranteed to be '\0'
-  process->read_bytes(hostname.data(), remote_string.len, remote(remote_string.data));
-  info->hostname = &mc_model_checker->get_host_name(hostname.data());
+
+  if (not info->hostname) {
+    Remote<s4u::Host> temp_host = process->read(remote(actor->get_host()));
+    auto remote_string_address  = remote(&xbt::string::to_string_data(temp_host.get_buffer()->get_impl()->get_name()));
+    simgrid::xbt::string_data remote_string = process->read(remote_string_address);
+    std::vector<char> hostname(remote_string.len + 1);
+    // no need to read the terminating null byte, and thus hostname[remote_string.len] is guaranteed to be '\0'
+    process->read_bytes(hostname.data(), remote_string.len, remote(remote_string.data));
+    info->hostname = &mc_model_checker->get_host_name(hostname.data());
+  }
   return *info->hostname;
 }
 
-std::string Api::get_actor_name(smx_actor_t actor) const
+xbt::string const& Api::get_actor_name(smx_actor_t actor) const
 {
   if (mc_model_checker == nullptr)
-    return actor->get_cname();
+    return actor->get_name();
 
   simgrid::mc::ActorInformation* info = actor_info_cast(actor);
   if (info->name.empty()) {
@@ -368,7 +176,7 @@ std::string Api::get_actor_string(smx_actor_t actor) const
   if (actor) {
     res = "(" + std::to_string(actor->get_pid()) + ")";
     if (actor->get_host())
-      res += std::string(get_actor_host_name(actor)) + " (" + get_actor_name(actor) + ")";
+      res += std::string(get_actor_host_name(actor)) + " (" + std::string(get_actor_name(actor)) + ")";
     else
       res += get_actor_name(actor);
   } else
@@ -386,38 +194,40 @@ std::string Api::get_actor_dot_label(smx_actor_t actor) const
 
 simgrid::mc::Checker* Api::initialize(char** argv, simgrid::mc::CheckerAlgorithm algo) const
 {
-  simgrid::mc::session = new simgrid::mc::Session([argv] {
+  auto session = new simgrid::mc::Session([argv] {
     int i = 1;
     while (argv[i] != nullptr && argv[i][0] == '-')
       i++;
     xbt_assert(argv[i] != nullptr,
                "Unable to find a binary to exec on the command line. Did you only pass config flags?");
     execvp(argv[i], argv + i);
-    xbt_die("The model-checked process failed to exec(): %s", strerror(errno));
+    xbt_die("The model-checked process failed to exec(%s): %s", argv[i], strerror(errno));
   });
 
   simgrid::mc::Checker* checker;
   switch (algo) {
     case CheckerAlgorithm::CommDeterminism:
-      checker = simgrid::mc::createCommunicationDeterminismChecker();
+      checker = simgrid::mc::create_communication_determinism_checker(session);
       break;
 
     case CheckerAlgorithm::UDPOR:
-      checker = simgrid::mc::createUdporChecker();
+      checker = simgrid::mc::create_udpor_checker(session);
       break;
 
     case CheckerAlgorithm::Safety:
-      checker = simgrid::mc::createSafetyChecker();
+      checker = simgrid::mc::create_safety_checker(session);
       break;
 
     case CheckerAlgorithm::Liveness:
-      checker = simgrid::mc::createLivenessChecker();
+      checker = simgrid::mc::create_liveness_checker(session);
       break;
 
     default:
       THROW_IMPOSSIBLE;
   }
 
+  // FIXME: session and checker are never deleted
+  simgrid::mc::session_singleton = session;
   mc_model_checker->setChecker(checker);
   return checker;
 }
@@ -427,22 +237,9 @@ std::vector<simgrid::mc::ActorInformation>& Api::get_actors() const
   return mc_model_checker->get_remote_process().actors();
 }
 
-bool Api::actor_is_enabled(aid_t pid) const
-{
-  return session->actor_is_enabled(pid);
-}
-
 unsigned long Api::get_maxpid() const
 {
-  static const char* name = nullptr;
-  if (not name) {
-    name = "simgrid::kernel::actor::maxpid";
-    if (mc_model_checker->get_remote_process().find_variable(name) == nullptr)
-      name = "maxpid"; // We seem to miss the namespaces when compiling with GCC
-  }
-  unsigned long maxpid;
-  mc_model_checker->get_remote_process().read_variable(name, &maxpid, sizeof(maxpid));
-  return maxpid;
+  return mc_model_checker->get_remote_process().get_maxpid();
 }
 
 int Api::get_actors_size() const
@@ -511,10 +308,10 @@ std::vector<char> Api::get_pattern_comm_data(RemotePtr<kernel::activity::CommImp
 #if HAVE_SMPI
 bool Api::check_send_request_detached(smx_simcall_t const& simcall) const
 {
-  simgrid::smpi::Request mpi_request;
+  Remote<simgrid::smpi::Request> mpi_request;
   mc_model_checker->get_remote_process().read(
-      &mpi_request, remote(static_cast<smpi::Request*>(simcall_comm_isend__get__data(simcall))));
-  return mpi_request.detached();
+      mpi_request, remote(static_cast<smpi::Request*>(simcall_comm_isend__get__data(simcall))));
+  return mpi_request.get_buffer()->detached();
 }
 #endif
 
@@ -545,11 +342,6 @@ std::size_t Api::get_remote_heap_bytes() const
   return heap_bytes_used;
 }
 
-void Api::session_initialize() const
-{
-  session->initialize();
-}
-
 void Api::mc_inc_visited_states() const
 {
   mc_model_checker->visited_states++;
@@ -573,7 +365,14 @@ unsigned long Api::mc_get_executed_trans() const
 void Api::mc_check_deadlock() const
 {
   if (mc_model_checker->checkDeadlock()) {
-    MC_show_deadlock();
+    XBT_CINFO(mc_global, "**************************");
+    XBT_CINFO(mc_global, "*** DEADLOCK DETECTED ***");
+    XBT_CINFO(mc_global, "**************************");
+    XBT_CINFO(mc_global, "Counter-example execution trace:");
+    for (auto const& s : mc_model_checker->getChecker()->get_textual_trace())
+      XBT_CINFO(mc_global, "  %s", s.c_str());
+    simgrid::mc::dumpRecordPath();
+    simgrid::mc::session_singleton->log_state();
     throw DeadlockError();
   }
 }
@@ -605,11 +404,6 @@ smx_actor_t Api::simcall_get_issuer(s_smx_simcall const* req) const
   xbt_die("Issuer not found");
 }
 
-long Api::simcall_get_actor_id(s_smx_simcall const* req) const
-{
-  return simcall_get_issuer(req)->get_pid();
-}
-
 RemotePtr<kernel::activity::MailboxImpl> Api::get_mbox_remote_addr(smx_simcall_t const req) const
 {
   if (req->call_ == Simcall::COMM_ISEND)
@@ -628,17 +422,6 @@ RemotePtr<kernel::activity::ActivityImpl> Api::get_comm_remote_addr(smx_simcall_
   THROW_IMPOSSIBLE;
 }
 
-bool Api::mc_is_null() const
-{
-  auto is_null = (mc_model_checker == nullptr) ? true : false;
-  return is_null;
-}
-
-Checker* Api::mc_get_checker() const
-{
-  return mc_model_checker->getChecker();
-}
-
 void Api::handle_simcall(Transition const& transition) const
 {
   mc_model_checker->handle_simcall(transition);
@@ -661,14 +444,19 @@ void Api::dump_record_path() const
 
 smx_simcall_t Api::mc_state_choose_request(simgrid::mc::State* state) const
 {
-  for (auto& actor : mc_model_checker->get_remote_process().actors()) {
+  RemoteProcess& process = mc_model_checker->get_remote_process();
+  XBT_DEBUG("Search for an actor to run. %zu actors to consider", process.actors().size());
+  for (auto& actor : process.actors()) {
     /* Only consider the actors that were marked as interleaving by the checker algorithm */
     if (not state->actor_states_[actor.copy.get_buffer()->get_pid()].is_todo())
       continue;
 
-    smx_simcall_t res = MC_state_choose_request_for_process(state, actor.copy.get_buffer());
-    if (res)
+    smx_simcall_t res = MC_state_choose_request_for_process(process, state, actor.copy.get_buffer());
+    if (res) {
+      XBT_DEBUG("Let's run actor %ld, going for transition %s", actor.copy.get_buffer()->get_pid(),
+                SIMIX_simcall_name(*res));
       return res;
+    }
   }
   return nullptr;
 }
@@ -712,198 +500,36 @@ std::string Api::request_to_string(smx_simcall_t req, int value) const
 {
   xbt_assert(mc_model_checker != nullptr, "Must be called from MCer");
 
-  std::string type;
-  std::string args;
-
   smx_actor_t issuer = simcall_get_issuer(req);
 
   if (issuer->simcall_.observer_ != nullptr)
     return mc_model_checker->simcall_to_string(issuer->get_pid(), value);
-
-  switch (req->call_) {
-    case Simcall::COMM_ISEND:
-      type = "iSend";
-      args = "src=" + get_actor_string(issuer);
-      args += ", buff=" + pointer_to_string(simcall_comm_isend__get__src_buff(req));
-      args += ", size=" + buff_size_to_string(simcall_comm_isend__get__src_buff_size(req));
-      break;
-
-    case Simcall::COMM_IRECV: {
-      size_t* remote_size = simcall_comm_irecv__get__dst_buff_size(req);
-      size_t size         = 0;
-      if (remote_size)
-        mc_model_checker->get_remote_process().read_bytes(&size, sizeof(size), remote(remote_size));
-
-      type = "iRecv";
-      args = "dst=" + get_actor_string(issuer);
-      args += ", buff=" + pointer_to_string(simcall_comm_irecv__get__dst_buff(req));
-      args += ", size=" + buff_size_to_string(size);
-      break;
-    }
-
-    case Simcall::COMM_WAIT: {
-      simgrid::kernel::activity::CommImpl* remote_act = simcall_comm_wait__get__comm(req);
-      if (value == -1) {
-        type = "WaitTimeout";
-        args = "comm=" + pointer_to_string(remote_act);
-      } else {
-        type = "Wait";
-
-        simgrid::mc::Remote<simgrid::kernel::activity::CommImpl> temp_activity;
-        const simgrid::kernel::activity::CommImpl* act;
-        mc_model_checker->get_remote_process().read(temp_activity, remote(remote_act));
-        act = temp_activity.get_buffer();
-
-        smx_actor_t src_proc =
-            mc_model_checker->get_remote_process().resolve_actor(simgrid::mc::remote(act->src_actor_.get()));
-        smx_actor_t dst_proc =
-            mc_model_checker->get_remote_process().resolve_actor(simgrid::mc::remote(act->dst_actor_.get()));
-        args = "comm=" + pointer_to_string(remote_act);
-        args += " [" + get_actor_string(src_proc) + "-> " + get_actor_string(dst_proc) + "]";
-      }
-      break;
-    }
-
-    case Simcall::COMM_TEST: {
-      simgrid::kernel::activity::CommImpl* remote_act = simcall_comm_test__get__comm(req);
-      simgrid::mc::Remote<simgrid::kernel::activity::CommImpl> temp_activity;
-      const simgrid::kernel::activity::CommImpl* act;
-      mc_model_checker->get_remote_process().read(temp_activity, remote(remote_act));
-      act = temp_activity.get_buffer();
-
-      if (act->src_actor_.get() == nullptr || act->dst_actor_.get() == nullptr) {
-        type = "Test FALSE";
-        args = "comm=" + pointer_to_string(remote_act);
-      } else {
-        type = "Test TRUE";
-
-        smx_actor_t src_proc =
-            mc_model_checker->get_remote_process().resolve_actor(simgrid::mc::remote(act->src_actor_.get()));
-        smx_actor_t dst_proc =
-            mc_model_checker->get_remote_process().resolve_actor(simgrid::mc::remote(act->dst_actor_.get()));
-        args = "comm=" + pointer_to_string(remote_act);
-        args += " [" + get_actor_string(src_proc) + " -> " + get_actor_string(dst_proc) + "]";
-      }
-      break;
-    }
-
-    case Simcall::COMM_WAITANY: {
-      type         = "WaitAny";
-      size_t count = simcall_comm_waitany__get__count(req);
-      if (count > 0) {
-        simgrid::kernel::activity::CommImpl* remote_sync;
-        remote_sync =
-            mc_model_checker->get_remote_process().read(remote(simcall_comm_waitany__get__comms(req) + value));
-        args = "comm=" + pointer_to_string(remote_sync) + xbt::string_printf("(%d of %zu)", value + 1, count);
-      } else
-        args = "comm at idx " + std::to_string(value);
-      break;
-    }
-
-    case Simcall::COMM_TESTANY:
-      if (value == -1) {
-        type = "TestAny FALSE";
-        args = "-";
-      } else {
-        type = "TestAny";
-        args = xbt::string_printf("(%d of %zu)", value + 1, simcall_comm_testany__get__count(req));
-      }
-      break;
-
-    default:
-      type = SIMIX_simcall_name(req->call_);
-      args = "??";
-      break;
-  }
-
-  return "[" + get_actor_string(issuer) + "] " + type + "(" + args + ")";
+  else
+    return "[" + get_actor_string(issuer) + "] " + SIMIX_simcall_name(*req) + "(unknown?)";
 }
 
 std::string Api::request_get_dot_output(smx_simcall_t req, int value) const
 {
-  const smx_actor_t issuer = simcall_get_issuer(req);
-  const char* color        = get_color(issuer->get_pid() - 1);
-
-  std::string label;
-
   if (req->observer_ != nullptr) {
-    label = mc_model_checker->simcall_dot_label(issuer->get_pid(), value);
+    const smx_actor_t issuer = simcall_get_issuer(req);
+    const char* color        = get_color(issuer->get_pid() - 1);
+    return "label = \"" + mc_model_checker->simcall_dot_label(issuer->get_pid(), value) + "\", color = " + color +
+           ", fontcolor = " + color;
   } else
-    switch (req->call_) {
-      case Simcall::COMM_ISEND:
-        label = "[" + get_actor_dot_label(issuer) + "] iSend";
-        break;
-
-      case Simcall::COMM_IRECV:
-        label = "[" + get_actor_dot_label(issuer) + "] iRecv";
-        break;
-
-      case Simcall::COMM_WAIT:
-        if (value == -1) {
-          label = "[" + get_actor_dot_label(issuer) + "] WaitTimeout";
-        } else {
-          kernel::activity::ActivityImpl* remote_act = simcall_comm_wait__get__comm(req);
-          Remote<kernel::activity::CommImpl> temp_comm;
-          mc_model_checker->get_remote_process().read(temp_comm,
-                                                      remote(static_cast<kernel::activity::CommImpl*>(remote_act)));
-          const kernel::activity::CommImpl* comm = temp_comm.get_buffer();
-
-          const kernel::actor::ActorImpl* src_proc =
-              mc_model_checker->get_remote_process().resolve_actor(mc::remote(comm->src_actor_.get()));
-          const kernel::actor::ActorImpl* dst_proc =
-              mc_model_checker->get_remote_process().resolve_actor(mc::remote(comm->dst_actor_.get()));
-          label = "[" + get_actor_dot_label(issuer) + "] Wait";
-          label += " [(" + std::to_string(src_proc ? src_proc->get_pid() : 0) + ")";
-          label += "->(" + std::to_string(dst_proc ? dst_proc->get_pid() : 0) + ")]";
-        }
-        break;
-
-      case Simcall::COMM_TEST: {
-        kernel::activity::ActivityImpl* remote_act = simcall_comm_test__get__comm(req);
-        Remote<simgrid::kernel::activity::CommImpl> temp_comm;
-        mc_model_checker->get_remote_process().read(temp_comm,
-                                                    remote(static_cast<kernel::activity::CommImpl*>(remote_act)));
-        const kernel::activity::CommImpl* comm = temp_comm.get_buffer();
-        if (comm->src_actor_.get() == nullptr || comm->dst_actor_.get() == nullptr) {
-          label = "[" + get_actor_dot_label(issuer) + "] Test FALSE";
-        } else {
-          label = "[" + get_actor_dot_label(issuer) + "] Test TRUE";
-        }
-        break;
-      }
-
-      case Simcall::COMM_WAITANY:
-        label = "[" + get_actor_dot_label(issuer) + "] WaitAny";
-        label += xbt::string_printf(" [%d of %zu]", value + 1, simcall_comm_waitany__get__count(req));
-        break;
-
-      case Simcall::COMM_TESTANY:
-        if (value == -1) {
-          label = "[" + get_actor_dot_label(issuer) + "] TestAny FALSE";
-        } else {
-          label = "[" + get_actor_dot_label(issuer) + "] TestAny TRUE";
-          label += xbt::string_printf(" [%d of %zu]", value + 1, simcall_comm_testany__get__count(req));
-        }
-        break;
-
-      default:
-        THROW_UNIMPLEMENTED;
-    }
-
-  return "label = \"" + label + "\", color = " + color + ", fontcolor = " + color;
+    return "UNIMPLEMENTED";
 }
 
 #if HAVE_SMPI
 int Api::get_smpi_request_tag(smx_simcall_t const& simcall, simgrid::simix::Simcall type) const
 {
-  simgrid::smpi::Request mpi_request;
   void* simcall_data = nullptr;
   if (type == Simcall::COMM_ISEND)
     simcall_data = simcall_comm_isend__get__data(simcall);
   else if (type == Simcall::COMM_IRECV)
     simcall_data = simcall_comm_irecv__get__data(simcall);
-  mc_model_checker->get_remote_process().read(&mpi_request, remote(static_cast<smpi::Request*>(simcall_data)));
-  return mpi_request.tag();
+  Remote<simgrid::smpi::Request> mpi_request;
+  mc_model_checker->get_remote_process().read(mpi_request, remote(static_cast<smpi::Request*>(simcall_data)));
+  return mpi_request.get_buffer()->tag();
 }
 #endif
 
@@ -914,7 +540,7 @@ void Api::restore_state(std::shared_ptr<simgrid::mc::Snapshot> system_state) con
 
 void Api::log_state() const
 {
-  session->log_state();
+  session_singleton->log_state();
 }
 
 bool Api::snapshot_equal(const Snapshot* s1, const Snapshot* s2) const
@@ -930,27 +556,20 @@ simgrid::mc::Snapshot* Api::take_snapshot(int num_state) const
 
 void Api::s_close() const
 {
-  session->close();
+  session_singleton->close();
 }
 
-void Api::restore_initial_state() const
-{
-  session->restore_initial_state();
-}
-
-void Api::execute(Transition& transition, smx_simcall_t simcall) const
+RemotePtr<simgrid::kernel::actor::SimcallObserver> Api::execute(Transition& transition, smx_simcall_t simcall) const
 {
   /* FIXME: once all simcalls have observers, kill the simcall parameter and use mc_model_checker->simcall_to_string() */
   transition.textual = request_to_string(simcall, transition.times_considered_);
-  session->execute(transition);
+  return session_singleton->execute(transition);
 }
 
-#if SIMGRID_HAVE_MC
 void Api::automaton_load(const char* file) const
 {
   MC_automaton_load(file);
 }
-#endif
 
 std::vector<int> Api::automaton_propositional_symbol_evaluate() const
 {