1 /* Copyright (c) 2016-2023. The SimGrid Team. All rights reserved. */
3 /* This program is free software; you can redistribute it and/or modify it
4 * under the terms of the license (GNU LGPL) which comes with this package. */
6 #include "src/mc/explo/DFSExplorer.hpp"
7 #include "src/mc/mc_config.hpp"
8 #include "src/mc/mc_exit.hpp"
9 #include "src/mc/mc_private.hpp"
10 #include "src/mc/mc_record.hpp"
11 #include "src/mc/transition/Transition.hpp"
13 #if SIMGRID_HAVE_STATEFUL_MC
14 #include "src/mc/VisitedState.hpp"
17 #include "src/xbt/mmalloc/mmprivate.h"
19 #include "xbt/string.hpp"
20 #include "xbt/sysdep.h"
29 XBT_LOG_NEW_DEFAULT_SUBCATEGORY(mc_dfs, mc, "DFS exploration algorithm of the model-checker");
31 namespace simgrid::mc {
33 xbt::signal<void(RemoteApp&)> DFSExplorer::on_exploration_start_signal;
34 xbt::signal<void(RemoteApp&)> DFSExplorer::on_backtracking_signal;
36 xbt::signal<void(State*, RemoteApp&)> DFSExplorer::on_state_creation_signal;
38 xbt::signal<void(State*, RemoteApp&)> DFSExplorer::on_restore_system_state_signal;
39 xbt::signal<void(RemoteApp&)> DFSExplorer::on_restore_initial_state_signal;
40 xbt::signal<void(Transition*, RemoteApp&)> DFSExplorer::on_transition_replay_signal;
41 xbt::signal<void(Transition*, RemoteApp&)> DFSExplorer::on_transition_execute_signal;
43 xbt::signal<void(RemoteApp&)> DFSExplorer::on_log_state_signal;
45 void DFSExplorer::check_non_termination(const State* current_state)
47 #if SIMGRID_HAVE_STATEFUL_MC
48 for (auto const& state : stack_) {
49 if (state->get_system_state()->equals_to(*current_state->get_system_state(),
50 *get_remote_app().get_remote_process_memory())) {
51 XBT_INFO("Non-progressive cycle: state %ld -> state %ld", state->get_num(), current_state->get_num());
52 XBT_INFO("******************************************");
53 XBT_INFO("*** NON-PROGRESSIVE CYCLE DETECTED ***");
54 XBT_INFO("******************************************");
55 XBT_INFO("Counter-example execution trace:");
56 for (auto const& s : get_textual_trace())
57 XBT_INFO(" %s", s.c_str());
58 XBT_INFO("You can debug the problem (and see the whole details) by rerunning out of simgrid-mc with "
59 "--cfg=model-check/replay:'%s'",
60 get_record_trace().to_string().c_str());
63 throw McError(ExitStatus::NON_TERMINATION);
69 RecordTrace DFSExplorer::get_record_trace() // override
73 if (const auto trans = stack_.back()->get_transition_out(); trans != nullptr)
74 res.push_back(trans.get());
75 for (const auto* state = stack_.back().get(); state != nullptr; state = state->get_parent_state().get())
76 if (state->get_transition_in() != nullptr)
77 res.push_front(state->get_transition_in().get());
82 void DFSExplorer::restore_stack(std::shared_ptr<State> state)
85 auto current_state = state;
86 stack_.emplace_front(current_state);
87 // condition corresponds to reaching initial state
88 while (current_state->get_parent_state() != nullptr) {
89 current_state = current_state->get_parent_state();
90 stack_.emplace_front(current_state);
92 XBT_DEBUG("Replaced stack by %s", get_record_trace().to_string().c_str());
95 void DFSExplorer::log_state() // override
97 on_log_state_signal(get_remote_app());
98 XBT_INFO("DFS exploration ended. %ld unique states visited; %lu backtracks (%lu transition replays, %lu states "
100 State::get_expanded_states(), backtrack_count_, visited_states_count_,
101 Transition::get_replayed_transitions());
102 Exploration::log_state();
105 void DFSExplorer::run()
107 on_exploration_start_signal(get_remote_app());
108 /* This function runs the DFS algorithm the state space.
109 * We do so iteratively instead of recursively, dealing with the call stack manually.
110 * This allows one to explore the call stack at will. */
112 while (not stack_.empty()) {
113 /* Get current state */
114 auto state = stack_.back();
116 XBT_DEBUG("**************************************************");
117 XBT_DEBUG("Exploration depth=%zu (state:#%ld; %zu interleaves todo)", stack_.size(), state->get_num(),
118 state->count_todo());
120 visited_states_count_++;
122 // Backtrack if we reached the maximum depth
123 if (stack_.size() > (std::size_t)_sg_mc_max_depth) {
124 if (reduction_mode_ == ReductionMode::dpor) {
125 XBT_ERROR("/!\\ Max depth of %d reached! THIS WILL PROBABLY BREAK the dpor reduction /!\\",
126 _sg_mc_max_depth.get());
127 XBT_ERROR("/!\\ If bad things happen, disable dpor with --cfg=model-check/reduction:none /!\\");
129 XBT_WARN("/!\\ Max depth reached ! /!\\ ");
134 #if SIMGRID_HAVE_STATEFUL_MC
135 // Backtrack if we are revisiting a state we saw previously while applying state-equality reduction
136 if (visited_state_ != nullptr) {
137 XBT_DEBUG("State already visited (equal to state %ld), exploration stopped on this path.",
138 visited_state_->original_num_ == -1 ? visited_state_->num_ : visited_state_->original_num_);
140 visited_state_ = nullptr;
146 // Search for the next transition
147 // next_transition returns a pair<aid_t, int> in case we want to consider multiple state (eg. during backtrack)
148 auto [next, _] = state->next_transition_guided();
150 if (next < 0) { // If there is no more transition in the current state, backtrack.
151 XBT_VERB("%lu actors remain, but none of them need to be interleaved (depth %zu).", state->get_actor_count(),
154 if (state->get_actor_count() == 0) {
155 get_remote_app().finalize_app();
156 XBT_VERB("Execution came to an end at %s (state: %ld, depth: %zu)", get_record_trace().to_string().c_str(),
157 state->get_num(), stack_.size());
164 if (_sg_mc_sleep_set && XBT_LOG_ISENABLED(mc_dfs, xbt_log_priority_verbose)) {
165 XBT_VERB("Sleep set actually containing:");
166 for (auto& [aid, transition] : state->get_sleep_set())
167 XBT_VERB(" <%ld,%s>", aid, transition.to_string().c_str());
170 /* Actually answer the request: let's execute the selected request (MCed does one step) */
171 state->execute_next(next, get_remote_app());
172 on_transition_execute_signal(state->get_transition_out().get(), get_remote_app());
174 // If there are processes to interleave and the maximum depth has not been
175 // reached then perform one step of the exploration algorithm.
176 XBT_VERB("Execute %ld: %.60s (stack depth: %zu, state: %ld, %zu interleaves)", state->get_transition_out()->aid_,
177 state->get_transition_out()->to_string().c_str(), stack_.size(), state->get_num(), state->count_todo());
179 /* Create the new expanded state (copy the state of MCed into our MCer data) */
180 auto next_state = std::make_shared<State>(get_remote_app(), state);
181 on_state_creation_signal(next_state.get(), get_remote_app());
183 /* Sleep set procedure:
184 * adding the taken transition to the sleep set of the original state.
185 * <!> Since the parent sleep set is used to compute the child sleep set, this need to be
186 * done after next_state creation */
187 XBT_DEBUG("Marking Transition >>%s<< of process %ld done and adding it to the sleep set",
188 state->get_transition_out()->to_string().c_str(), state->get_transition_out()->aid_);
189 state->add_sleep_set(state->get_transition_out()); // Actors are marked done when they are considerd in ActorState
191 /* DPOR persistent set procedure:
192 * for each new transition considered, check if it depends on any other previous transition executed before it
193 * on another process. If there exists one, find the more recent, and add its process to the interleave set.
194 * If the process is not enabled at this point, then add every enabled process to the interleave */
195 if (reduction_mode_ == ReductionMode::dpor) {
196 aid_t issuer_id = state->get_transition_out()->aid_;
197 stack_t tmp_stack = stack_;
198 while (not tmp_stack.empty()) {
199 if (const State* prev_state = tmp_stack.back().get();
200 state->get_transition_out()->aid_ == prev_state->get_transition_out()->aid_) {
201 XBT_DEBUG("Simcall >>%s<< and >>%s<< with same issuer %ld", state->get_transition_out()->to_string().c_str(),
202 prev_state->get_transition_out()->to_string().c_str(), issuer_id);
203 tmp_stack.pop_back();
205 } else if (prev_state->get_transition_out()->depends(state->get_transition_out().get())) {
206 XBT_VERB("Dependent Transitions:");
207 XBT_VERB(" %s (state=%ld)", prev_state->get_transition_out()->to_string().c_str(), prev_state->get_num());
208 XBT_VERB(" %s (state=%ld)", state->get_transition_out()->to_string().c_str(), state->get_num());
210 if (prev_state->is_actor_enabled(issuer_id)) {
211 if (not prev_state->is_actor_done(issuer_id)) {
212 prev_state->consider_one(issuer_id);
213 opened_states_.emplace_back(tmp_stack.back());
215 XBT_DEBUG("Actor %ld is already in done set: no need to explore it again", issuer_id);
217 XBT_DEBUG("Actor %ld is not enabled: DPOR may be failing. To stay sound, we are marking every enabled "
218 "transition as todo",
220 // If we ended up marking at least a transition, explore it at some point
221 if (prev_state->consider_all() > 0)
222 opened_states_.emplace_back(tmp_stack.back());
226 XBT_VERB("INDEPENDENT Transitions:");
227 XBT_VERB(" %s (state=%ld)", prev_state->get_transition_out()->to_string().c_str(), prev_state->get_num());
228 XBT_VERB(" %s (state=%ld)", state->get_transition_out()->to_string().c_str(), state->get_num());
230 tmp_stack.pop_back();
234 // Before leaving that state, if the transition we just took can be taken multiple times, we
235 // need to give it to the opened states
236 if (stack_.back()->count_todo_multiples() > 0)
237 opened_states_.emplace_back(stack_.back());
239 if (_sg_mc_termination)
240 this->check_non_termination(next_state.get());
242 #if SIMGRID_HAVE_STATEFUL_MC
243 /* Check whether we already explored next_state in the past (but only if interested in state-equality reduction) */
244 if (_sg_mc_max_visited_states > 0)
245 visited_state_ = visited_states_.addVisitedState(next_state->get_num(), next_state.get(), get_remote_app());
248 stack_.emplace_back(std::move(next_state));
250 /* If this is a new state (or if we don't care about state-equality reduction) */
251 if (visited_state_ == nullptr) {
252 /* Get an enabled process and insert it in the interleave set of the next state */
253 if (reduction_mode_ == ReductionMode::dpor)
254 stack_.back()->consider_best(); // Take only one transition if DPOR: others may be considered later if required
256 stack_.back()->consider_all();
259 dot_output("\"%ld\" -> \"%ld\" [%s];\n", state->get_num(), stack_.back()->get_num(),
260 state->get_transition_out()->dot_string().c_str());
261 #if SIMGRID_HAVE_STATEFUL_MC
263 dot_output("\"%ld\" -> \"%ld\" [%s];\n", state->get_num(),
264 visited_state_->original_num_ == -1 ? visited_state_->num_ : visited_state_->original_num_,
265 state->get_transition_out()->dot_string().c_str());
272 std::shared_ptr<State> DFSExplorer::best_opened_state()
274 int best_prio = 0; // cache the value for the best priority found so far (initialized to silence gcc)
275 auto best = end(opened_states_); // iterator to the state to explore having the best priority
276 auto valid = begin(opened_states_); // iterator marking the limit between states still to explore, and already
279 // Keep only still non-explored states (aid != -1), and record the one with the best (greater) priority.
280 for (auto current = begin(opened_states_); current != end(opened_states_); ++current) {
281 auto [aid, prio] = (*current)->next_transition_guided();
284 if (valid != current)
285 *valid = std::move(*current);
286 if (best == end(opened_states_) || prio < best_prio) {
293 std::shared_ptr<State> best_state;
295 // There are non-explored states, and one of them has the best priority. Remove it from opened_states_ before
297 best_state = std::move(*best);
300 *best = std::move(*valid);
302 opened_states_.erase(valid, end(opened_states_));
307 void DFSExplorer::backtrack()
309 XBT_VERB("Backtracking from %s", get_record_trace().to_string().c_str());
310 XBT_DEBUG("%lu alternatives are yet to be explored:", opened_states_.size());
312 on_backtracking_signal(get_remote_app());
313 get_remote_app().check_deadlock();
315 // Take the point with smallest distance
316 auto backtracking_point = best_opened_state();
318 // if no backtracking point, then set the stack_ to empty so we can end the exploration
319 if (not backtracking_point) {
320 XBT_DEBUG("No more opened point of exploration, the search will end");
325 // We found a backtracking point, let's go to it
327 XBT_DEBUG("Backtracking to state#%ld", backtracking_point->get_num());
329 #if SIMGRID_HAVE_STATEFUL_MC
330 /* If asked to rollback on a state that has a snapshot, restore it */
331 if (const auto* system_state = backtracking_point->get_system_state()) {
332 system_state->restore(*get_remote_app().get_remote_process_memory());
333 on_restore_system_state_signal(backtracking_point.get(), get_remote_app());
334 this->restore_stack(backtracking_point);
339 // Search how to restore the backtracking point
340 State* init_state = nullptr;
341 std::deque<Transition*> replay_recipe;
342 for (auto* s = backtracking_point.get(); s != nullptr; s = s->get_parent_state().get()) {
343 #if SIMGRID_HAVE_STATEFUL_MC
344 if (s->get_system_state() != nullptr) { // Found a state that I can restore
349 if (s->get_transition_in() != nullptr) // The root has no transition_in
350 replay_recipe.push_front(s->get_transition_in().get());
353 // Restore the init_state, if any
354 if (init_state != nullptr) {
355 #if SIMGRID_HAVE_STATEFUL_MC
356 const auto* system_state = init_state->get_system_state();
357 system_state->restore(*get_remote_app().get_remote_process_memory());
358 on_restore_system_state_signal(init_state, get_remote_app());
360 } else { // Restore the initial state if no intermediate state was found
361 get_remote_app().restore_initial_state();
362 on_restore_initial_state_signal(get_remote_app());
365 /* if no snapshot, we need to restore the initial state and replay the transitions */
366 /* Traverse the stack from the state at position start and re-execute the transitions */
367 for (auto& transition : replay_recipe) {
368 transition->replay(get_remote_app());
369 on_transition_replay_signal(transition, get_remote_app());
370 visited_states_count_++;
372 this->restore_stack(backtracking_point);
375 DFSExplorer::DFSExplorer(const std::vector<char*>& args, bool with_dpor, bool need_memory_info)
376 : Exploration(args, need_memory_info || _sg_mc_termination
377 #if SIMGRID_HAVE_STATEFUL_MC
378 || _sg_mc_checkpoint > 0
383 reduction_mode_ = ReductionMode::dpor;
385 reduction_mode_ = ReductionMode::none;
387 if (_sg_mc_termination) {
389 XBT_INFO("Check non progressive cycles (turning DPOR off)");
390 reduction_mode_ = ReductionMode::none;
392 XBT_INFO("Check non progressive cycles");
395 XBT_INFO("Start a DFS exploration. Reduction is: %s.", to_c_str(reduction_mode_));
397 auto initial_state = std::make_shared<State>(get_remote_app());
399 XBT_DEBUG("**************************************************");
401 stack_.emplace_back(std::move(initial_state));
403 /* Get an enabled actor and insert it in the interleave set of the initial state */
404 XBT_DEBUG("Initial state. %lu actors to consider", stack_.back()->get_actor_count());
405 if (reduction_mode_ == ReductionMode::dpor)
406 stack_.back()->consider_best();
408 stack_.back()->consider_all();
410 if (stack_.back()->count_todo_multiples() > 1)
411 opened_states_.emplace_back(stack_.back());
414 Exploration* create_dfs_exploration(const std::vector<char*>& args, bool with_dpor)
416 return new DFSExplorer(args, with_dpor);
419 } // namespace simgrid::mc