constraint_solver.cc

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// Copyright 2010-2021 Google LLC
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//
// This file implements the core objects of the constraint solver:
// Solver, Search, Queue, ... along with the main resolution loop.

#include "ortools/constraint_solver/constraint_solver.h"

#include <csetjmp>
#include <cstdint>
#include <deque>
#include <iosfwd>
#include <limits>
#include <memory>
#include <string>
#include <utility>

#include "absl/memory/memory.h"
#include "absl/time/clock.h"
#include "absl/time/time.h"
#include "ortools/base/commandlineflags.h"
#include "ortools/base/file.h"
#include "ortools/base/integral_types.h"
#include "ortools/base/logging.h"
#include "ortools/base/macros.h"
#include "ortools/base/map_util.h"
#include "ortools/base/recordio.h"
#include "ortools/base/stl_util.h"
#include "ortools/base/sysinfo.h"
#include "ortools/constraint_solver/constraint_solveri.h"
#include "ortools/util/tuple_set.h"
#include "zlib.h"

// These flags are used to set the fields in the DefaultSolverParameters proto.
ABSL_FLAG(bool, cp_trace_propagation, false,
          "Trace propagation events (constraint and demon executions,"
          " variable modifications).");
ABSL_FLAG(bool, cp_trace_search, false, "Trace search events");
ABSL_FLAG(bool, cp_print_added_constraints, false,
          "show all constraints added to the solver.");
ABSL_FLAG(bool, cp_print_model, false,
          "use PrintModelVisitor on model before solving.");
ABSL_FLAG(bool, cp_model_stats, false,
          "use StatisticsModelVisitor on model before solving.");
ABSL_FLAG(bool, cp_disable_solve, false,
          "Force failure at the beginning of a search.");
ABSL_FLAG(std::string, cp_profile_file, "",
          "Export profiling overview to file.");
ABSL_FLAG(bool, cp_print_local_search_profile, false,
          "Print local search profiling data after solving.");
ABSL_FLAG(bool, cp_name_variables, false, "Force all variables to have names.");
ABSL_FLAG(bool, cp_name_cast_variables, false,
          "Name variables casted from expressions");
ABSL_FLAG(bool, cp_use_small_table, true,
          "Use small compact table constraint when possible.");
ABSL_FLAG(bool, cp_use_cumulative_edge_finder, true,
          "Use the O(n log n) cumulative edge finding algorithm described "
          "in 'Edge Finding Filtering Algorithm for Discrete  Cumulative "
          "Resources in O(kn log n)' by Petr Vilim, CP 2009.");
ABSL_FLAG(bool, cp_use_cumulative_time_table, true,
          "Use a O(n^2) cumulative time table propagation algorithm.");
ABSL_FLAG(bool, cp_use_cumulative_time_table_sync, false,
          "Use a synchronized O(n^2 log n) cumulative time table propagation "
          "algorithm.");
ABSL_FLAG(bool, cp_use_sequence_high_demand_tasks, true,
          "Use a sequence constraints for cumulative tasks that have a "
          "demand greater than half of the capacity of the resource.");
ABSL_FLAG(bool, cp_use_all_possible_disjunctions, true,
          "Post temporal disjunctions for all pairs of tasks sharing a "
          "cumulative resource and that cannot overlap because the sum of "
          "their demand exceeds the capacity.");
ABSL_FLAG(int, cp_max_edge_finder_size, 50,
          "Do not post the edge finder in the cumulative constraints if "
          "it contains more than this number of tasks");
ABSL_FLAG(bool, cp_diffn_use_cumulative, true,
          "Diffn constraint adds redundant cumulative constraint");
ABSL_FLAG(bool, cp_use_element_rmq, true,
          "If true, rmq's will be used in element expressions.");
ABSL_FLAG(int, cp_check_solution_period, 1,
          "Number of solutions explored between two solution checks during "
          "local search.");
ABSL_FLAG(int64_t, cp_random_seed, 12345,
          "Random seed used in several (but not all) random number "
          "generators used by the CP solver. Use -1 to auto-generate an"
          "undeterministic random seed.");

void ConstraintSolverFailsHere() { VLOG(3) << "Fail"; }

#if defined(_MSC_VER)  // WINDOWS
#pragma warning(disable : 4351 4355)
#endif

namespace operations_research {

namespace {
// Calls the given method with the provided arguments on all objects in the
// collection.
template <typename T, typename MethodPointer, typename... Args>
void ForAll(const std::vector<T*>& objects, MethodPointer method,
            const Args&... args) {
  for (T* const object : objects) {
    DCHECK(object != nullptr);
    (object->*method)(args...);
  }
}
}  // namespace

// ----- ConstraintSolverParameters -----

ConstraintSolverParameters Solver::DefaultSolverParameters() {
  ConstraintSolverParameters params;
  params.set_compress_trail(ConstraintSolverParameters::NO_COMPRESSION);
  params.set_trail_block_size(8000);
  params.set_array_split_size(16);
  params.set_store_names(true);
  params.set_profile_propagation(!absl::GetFlag(FLAGS_cp_profile_file).empty());
  params.set_trace_propagation(absl::GetFlag(FLAGS_cp_trace_propagation));
  params.set_trace_search(absl::GetFlag(FLAGS_cp_trace_search));
  params.set_name_all_variables(absl::GetFlag(FLAGS_cp_name_variables));
  params.set_profile_file(absl::GetFlag(FLAGS_cp_profile_file));
  params.set_profile_local_search(
      absl::GetFlag(FLAGS_cp_print_local_search_profile));
  params.set_print_local_search_profile(
      absl::GetFlag(FLAGS_cp_print_local_search_profile));
  params.set_print_model(absl::GetFlag(FLAGS_cp_print_model));
  params.set_print_model_stats(absl::GetFlag(FLAGS_cp_model_stats));
  params.set_disable_solve(absl::GetFlag(FLAGS_cp_disable_solve));
  params.set_name_cast_variables(absl::GetFlag(FLAGS_cp_name_cast_variables));
  params.set_print_added_constraints(
      absl::GetFlag(FLAGS_cp_print_added_constraints));
  params.set_use_small_table(absl::GetFlag(FLAGS_cp_use_small_table));
  params.set_use_cumulative_edge_finder(
      absl::GetFlag(FLAGS_cp_use_cumulative_edge_finder));
  params.set_use_cumulative_time_table(
      absl::GetFlag(FLAGS_cp_use_cumulative_time_table));
  params.set_use_cumulative_time_table_sync(
      absl::GetFlag(FLAGS_cp_use_cumulative_time_table_sync));
  params.set_use_sequence_high_demand_tasks(
      absl::GetFlag(FLAGS_cp_use_sequence_high_demand_tasks));
  params.set_use_all_possible_disjunctions(
      absl::GetFlag(FLAGS_cp_use_all_possible_disjunctions));
  params.set_max_edge_finder_size(absl::GetFlag(FLAGS_cp_max_edge_finder_size));
  params.set_diffn_use_cumulative(absl::GetFlag(FLAGS_cp_diffn_use_cumulative));
  params.set_use_element_rmq(absl::GetFlag(FLAGS_cp_use_element_rmq));
  params.set_check_solution_period(
      absl::GetFlag(FLAGS_cp_check_solution_period));
  return params;
}

// ----- Forward Declarations and Profiling Support -----
extern DemonProfiler* BuildDemonProfiler(Solver* const solver);
extern void DeleteDemonProfiler(DemonProfiler* const monitor);
extern void InstallDemonProfiler(DemonProfiler* const monitor);
extern LocalSearchProfiler* BuildLocalSearchProfiler(Solver* solver);
extern void DeleteLocalSearchProfiler(LocalSearchProfiler* monitor);
extern void InstallLocalSearchProfiler(LocalSearchProfiler* monitor);

// TODO(user): remove this complex logic.
// We need the double test because parameters are set too late when using
// python in the open source. This is the cheapest work-around.
bool Solver::InstrumentsDemons() const {
  return IsProfilingEnabled() || InstrumentsVariables();
}

bool Solver::IsProfilingEnabled() const {
  return parameters_.profile_propagation() ||
         !parameters_.profile_file().empty();
}

bool Solver::IsLocalSearchProfilingEnabled() const {
  return parameters_.profile_local_search() ||
         parameters_.print_local_search_profile();
}

bool Solver::InstrumentsVariables() const {
  return parameters_.trace_propagation();
}

bool Solver::NameAllVariables() const {
  return parameters_.name_all_variables();
}

// ------------------ Demon class ----------------

Solver::DemonPriority Demon::priority() const {
  return Solver::NORMAL_PRIORITY;
}

std::string Demon::DebugString() const { return "Demon"; }

void Demon::inhibit(Solver* const s) {
  if (stamp_ < std::numeric_limits<uint64_t>::max()) {
    s->SaveAndSetValue(&stamp_, std::numeric_limits<uint64_t>::max());
  }
}

void Demon::desinhibit(Solver* const s) {
  if (stamp_ == std::numeric_limits<uint64_t>::max()) {
    s->SaveAndSetValue(&stamp_, s->stamp() - 1);
  }
}

// ------------------ Queue class ------------------

extern void CleanVariableOnFail(IntVar* const var);

class Queue {
 public:
  static constexpr int64_t kTestPeriod = 10000;

  explicit Queue(Solver* const s)
      : solver_(s),
        stamp_(1),
        freeze_level_(0),
        in_process_(false),
        clean_action_(nullptr),
        clean_variable_(nullptr),
        in_add_(false),
        instruments_demons_(s->InstrumentsDemons()) {}

  ~Queue() {}

  void Freeze() {
    freeze_level_++;
    stamp_++;
  }

  void Unfreeze() {
    if (--freeze_level_ == 0) {
      Process();
    }
  }

  void ProcessOneDemon(Demon* const demon) {
    demon->set_stamp(stamp_ - 1);
    if (!instruments_demons_) {
      if (++solver_->demon_runs_[demon->priority()] % kTestPeriod == 0) {
        solver_->TopPeriodicCheck();
      }
      demon->Run(solver_);
      solver_->CheckFail();
    } else {
      solver_->GetPropagationMonitor()->BeginDemonRun(demon);
      if (++solver_->demon_runs_[demon->priority()] % kTestPeriod == 0) {
        solver_->TopPeriodicCheck();
      }
      demon->Run(solver_);
      solver_->CheckFail();
      solver_->GetPropagationMonitor()->EndDemonRun(demon);
    }
  }

  void Process() {
    if (!in_process_) {
      in_process_ = true;
      while (!var_queue_.empty() || !delayed_queue_.empty()) {
        if (!var_queue_.empty()) {
          Demon* const demon = var_queue_.front();
          var_queue_.pop_front();
          ProcessOneDemon(demon);
        } else {
          DCHECK(!delayed_queue_.empty());
          Demon* const demon = delayed_queue_.front();
          delayed_queue_.pop_front();
          ProcessOneDemon(demon);
        }
      }
      in_process_ = false;
    }
  }

  void ExecuteAll(const SimpleRevFIFO<Demon*>& demons) {
    if (!instruments_demons_) {
      for (SimpleRevFIFO<Demon*>::Iterator it(&demons); it.ok(); ++it) {
        Demon* const demon = *it;
        if (demon->stamp() < stamp_) {
          DCHECK_EQ(demon->priority(), Solver::NORMAL_PRIORITY);
          if (++solver_->demon_runs_[Solver::NORMAL_PRIORITY] % kTestPeriod ==
              0) {
            solver_->TopPeriodicCheck();
          }
          demon->Run(solver_);
          solver_->CheckFail();
        }
      }
    } else {
      for (SimpleRevFIFO<Demon*>::Iterator it(&demons); it.ok(); ++it) {
        Demon* const demon = *it;
        if (demon->stamp() < stamp_) {
          DCHECK_EQ(demon->priority(), Solver::NORMAL_PRIORITY);
          solver_->GetPropagationMonitor()->BeginDemonRun(demon);
          if (++solver_->demon_runs_[Solver::NORMAL_PRIORITY] % kTestPeriod ==
              0) {
            solver_->TopPeriodicCheck();
          }
          demon->Run(solver_);
          solver_->CheckFail();
          solver_->GetPropagationMonitor()->EndDemonRun(demon);
        }
      }
    }
  }

  void EnqueueAll(const SimpleRevFIFO<Demon*>& demons) {
    for (SimpleRevFIFO<Demon*>::Iterator it(&demons); it.ok(); ++it) {
      EnqueueDelayedDemon(*it);
    }
  }

  void EnqueueVar(Demon* const demon) {
    DCHECK(demon->priority() == Solver::VAR_PRIORITY);
    if (demon->stamp() < stamp_) {
      demon->set_stamp(stamp_);
      var_queue_.push_back(demon);
      if (freeze_level_ == 0) {
        Process();
      }
    }
  }

  void EnqueueDelayedDemon(Demon* const demon) {
    DCHECK(demon->priority() == Solver::DELAYED_PRIORITY);
    if (demon->stamp() < stamp_) {
      demon->set_stamp(stamp_);
      delayed_queue_.push_back(demon);
    }
  }

  void AfterFailure() {
    // Clean queue.
    var_queue_.clear();
    delayed_queue_.clear();

    // Call cleaning actions on variables.
    if (clean_action_ != nullptr) {
      clean_action_(solver_);
      clean_action_ = nullptr;
    } else if (clean_variable_ != nullptr) {
      CleanVariableOnFail(clean_variable_);
      clean_variable_ = nullptr;
    }

    freeze_level_ = 0;
    in_process_ = false;
    in_add_ = false;
    to_add_.clear();
  }

  void increase_stamp() { stamp_++; }

  uint64_t stamp() const { return stamp_; }

  void set_action_on_fail(Solver::Action a) {
    DCHECK(clean_variable_ == nullptr);
    clean_action_ = std::move(a);
  }

  void set_variable_to_clean_on_fail(IntVar* var) {
    DCHECK(clean_action_ == nullptr);
    clean_variable_ = var;
  }

  void reset_action_on_fail() {
    DCHECK(clean_variable_ == nullptr);
    clean_action_ = nullptr;
  }

  void AddConstraint(Constraint* const c) {
    to_add_.push_back(c);
    ProcessConstraints();
  }

  void ProcessConstraints() {
    if (!in_add_) {
      in_add_ = true;
      // We cannot store to_add_.size() as constraints can add other
      // constraints. For the same reason a range-based for loop cannot be used.
      // TODO(user): Make to_add_ a queue to make the behavior more obvious.
      for (int counter = 0; counter < to_add_.size(); ++counter) {
        Constraint* const constraint = to_add_[counter];
        // TODO(user): Add profiling to initial propagation
        constraint->PostAndPropagate();
      }
      in_add_ = false;
      to_add_.clear();
    }
  }

 private:
  Solver* const solver_;
  std::deque<Demon*> var_queue_;
  std::deque<Demon*> delayed_queue_;
  uint64_t stamp_;
  // The number of nested freeze levels. The queue is frozen if and only if
  // freeze_level_ > 0.
  uint32_t freeze_level_;
  bool in_process_;
  Solver::Action clean_action_;
  IntVar* clean_variable_;
  std::vector<Constraint*> to_add_;
  bool in_add_;
  const bool instruments_demons_;
};

// ------------------ StateMarker / StateInfo struct -----------

struct StateInfo {  // This is an internal structure to store
                    // additional information on the choice point.
 public:
  StateInfo()
      : ptr_info(nullptr),
        int_info(0),
        depth(0),
        left_depth(0),
        reversible_action(nullptr) {}
  StateInfo(void* pinfo, int iinfo)
      : ptr_info(pinfo),
        int_info(iinfo),
        depth(0),
        left_depth(0),
        reversible_action(nullptr) {}
  StateInfo(void* pinfo, int iinfo, int d, int ld)
      : ptr_info(pinfo),
        int_info(iinfo),
        depth(d),
        left_depth(ld),
        reversible_action(nullptr) {}
  StateInfo(Solver::Action a, bool fast)
      : ptr_info(nullptr),
        int_info(static_cast<int>(fast)),
        depth(0),
        left_depth(0),
        reversible_action(std::move(a)) {}

  void* ptr_info;
  int int_info;
  int depth;
  int left_depth;
  Solver::Action reversible_action;
};

struct StateMarker {
 public:
  StateMarker(Solver::MarkerType t, const StateInfo& info);
  friend class Solver;
  friend struct Trail;

 private:
  Solver::MarkerType type_;
  int rev_int_index_;
  int rev_int64_index_;
  int rev_uint64_index_;
  int rev_double_index_;
  int rev_ptr_index_;
  int rev_boolvar_list_index_;
  int rev_bools_index_;
  int rev_int_memory_index_;
  int rev_int64_memory_index_;
  int rev_double_memory_index_;
  int rev_object_memory_index_;
  int rev_object_array_memory_index_;
  int rev_memory_index_;
  int rev_memory_array_index_;
  StateInfo info_;
};

StateMarker::StateMarker(Solver::MarkerType t, const StateInfo& info)
    : type_(t),
      rev_int_index_(0),
      rev_int64_index_(0),
      rev_uint64_index_(0),
      rev_double_index_(0),
      rev_ptr_index_(0),
      rev_boolvar_list_index_(0),
      rev_bools_index_(0),
      rev_int_memory_index_(0),
      rev_int64_memory_index_(0),
      rev_double_memory_index_(0),
      rev_object_memory_index_(0),
      rev_object_array_memory_index_(0),
      info_(info) {}

// ---------- Trail and Reversibility ----------

namespace {
// ----- addrval struct -----

// This template class is used internally to implement reversibility.
// It stores an address and the value that was at the address.
template <class T>
struct addrval {
 public:
  addrval() : address_(nullptr) {}
  explicit addrval(T* adr) : address_(adr), old_value_(*adr) {}
  void restore() const { (*address_) = old_value_; }

 private:
  T* address_;
  T old_value_;
};

// ----- Compressed trail -----

// ---------- Trail Packer ---------
// Abstract class to pack trail blocks.

template <class T>
class TrailPacker {
 public:
  explicit TrailPacker(int block_size) : block_size_(block_size) {}
  virtual ~TrailPacker() {}
  int input_size() const { return block_size_ * sizeof(addrval<T>); }
  virtual void Pack(const addrval<T>* block, std::string* packed_block) = 0;
  virtual void Unpack(const std::string& packed_block, addrval<T>* block) = 0;

 private:
  const int block_size_;
  DISALLOW_COPY_AND_ASSIGN(TrailPacker);
};

template <class T>
class NoCompressionTrailPacker : public TrailPacker<T> {
 public:
  explicit NoCompressionTrailPacker(int block_size)
      : TrailPacker<T>(block_size) {}
  ~NoCompressionTrailPacker() override {}
  void Pack(const addrval<T>* block, std::string* packed_block) override {
    DCHECK(block != nullptr);
    DCHECK(packed_block != nullptr);
    absl::string_view block_str(reinterpret_cast<const char*>(block),
                                this->input_size());
    packed_block->assign(block_str.data(), block_str.size());
  }
  void Unpack(const std::string& packed_block, addrval<T>* block) override {
    DCHECK(block != nullptr);
    memcpy(block, packed_block.c_str(), packed_block.size());
  }

 private:
  DISALLOW_COPY_AND_ASSIGN(NoCompressionTrailPacker<T>);
};

template <class T>
class ZlibTrailPacker : public TrailPacker<T> {
 public:
  explicit ZlibTrailPacker(int block_size)
      : TrailPacker<T>(block_size),
        tmp_size_(compressBound(this->input_size())),
        tmp_block_(new char[tmp_size_]) {}

  ~ZlibTrailPacker() override {}

  void Pack(const addrval<T>* block, std::string* packed_block) override {
    DCHECK(block != nullptr);
    DCHECK(packed_block != nullptr);
    uLongf size = tmp_size_;
    const int result =
        compress(reinterpret_cast<Bytef*>(tmp_block_.get()), &size,
                 reinterpret_cast<const Bytef*>(block), this->input_size());
    CHECK_EQ(Z_OK, result);
    absl::string_view block_str;
    block_str = absl::string_view(tmp_block_.get(), size);
    packed_block->assign(block_str.data(), block_str.size());
  }

  void Unpack(const std::string& packed_block, addrval<T>* block) override {
    DCHECK(block != nullptr);
    uLongf size = this->input_size();
    const int result =
        uncompress(reinterpret_cast<Bytef*>(block), &size,
                   reinterpret_cast<const Bytef*>(packed_block.c_str()),
                   packed_block.size());
    CHECK_EQ(Z_OK, result);
  }

 private:
  const uint64_t tmp_size_;
  std::unique_ptr<char[]> tmp_block_;
  DISALLOW_COPY_AND_ASSIGN(ZlibTrailPacker<T>);
};

template <class T>
class CompressedTrail {
 public:
  CompressedTrail(
      int block_size,
      ConstraintSolverParameters::TrailCompression compression_level)
      : block_size_(block_size),
        blocks_(nullptr),
        free_blocks_(nullptr),
        data_(new addrval<T>[block_size]),
        buffer_(new addrval<T>[block_size]),
        buffer_used_(false),
        current_(0),
        size_(0) {
    switch (compression_level) {
      case ConstraintSolverParameters::NO_COMPRESSION: {
        packer_.reset(new NoCompressionTrailPacker<T>(block_size));
        break;
      }
      case ConstraintSolverParameters::COMPRESS_WITH_ZLIB: {
        packer_.reset(new ZlibTrailPacker<T>(block_size));
        break;
      }
      default: {
        LOG(ERROR) << "Should not be here";
      }
    }

    // We zero all memory used by addrval arrays.
    // Because of padding, all bytes may not be initialized, while compression
    // will read them all, even if the uninitialized bytes are never used.
    // This makes valgrind happy.

    memset(data_.get(), 0, sizeof(*data_.get()) * block_size);
    memset(buffer_.get(), 0, sizeof(*buffer_.get()) * block_size);
  }
  ~CompressedTrail() {
    FreeBlocks(blocks_);
    FreeBlocks(free_blocks_);
  }
  const addrval<T>& Back() const {
    // Back of empty trail.
    DCHECK_GT(current_, 0);
    return data_[current_ - 1];
  }
  void PopBack() {
    if (size_ > 0) {
      --current_;
      if (current_ <= 0) {
        if (buffer_used_) {
          data_.swap(buffer_);
          current_ = block_size_;
          buffer_used_ = false;
        } else if (blocks_ != nullptr) {
          packer_->Unpack(blocks_->compressed, data_.get());
          FreeTopBlock();
          current_ = block_size_;
        }
      }
      --size_;
    }
  }
  void PushBack(const addrval<T>& addr_val) {
    if (current_ >= block_size_) {
      if (buffer_used_) {  // Buffer is used.
        NewTopBlock();
        packer_->Pack(buffer_.get(), &blocks_->compressed);
        // O(1) operation.
        data_.swap(buffer_);
      } else {
        data_.swap(buffer_);
        buffer_used_ = true;
      }
      current_ = 0;
    }
    data_[current_] = addr_val;
    ++current_;
    ++size_;
  }
  int64_t size() const { return size_; }

 private:
  struct Block {
    std::string compressed;
    Block* next;
  };

  void FreeTopBlock() {
    Block* block = blocks_;
    blocks_ = block->next;
    block->compressed.clear();
    block->next = free_blocks_;
    free_blocks_ = block;
  }
  void NewTopBlock() {
    Block* block = nullptr;
    if (free_blocks_ != nullptr) {
      block = free_blocks_;
      free_blocks_ = block->next;
    } else {
      block = new Block;
    }
    block->next = blocks_;
    blocks_ = block;
  }
  void FreeBlocks(Block* blocks) {
    while (nullptr != blocks) {
      Block* next = blocks->next;
      delete blocks;
      blocks = next;
    }
  }

  std::unique_ptr<TrailPacker<T> > packer_;
  const int block_size_;
  Block* blocks_;
  Block* free_blocks_;
  std::unique_ptr<addrval<T>[]> data_;
  std::unique_ptr<addrval<T>[]> buffer_;
  bool buffer_used_;
  int current_;
  int size_;
};
}  // namespace

// ----- Trail -----

// Object are explicitly copied using the copy ctor instead of
// passing and storing a pointer. As objects are small, copying is
// much faster than allocating (around 35% on a complete solve).

extern void RestoreBoolValue(IntVar* const var);

struct Trail {
  CompressedTrail<int> rev_ints_;
  CompressedTrail<int64_t> rev_int64s_;
  CompressedTrail<uint64_t> rev_uint64s_;
  CompressedTrail<double> rev_doubles_;
  CompressedTrail<void*> rev_ptrs_;
  std::vector<IntVar*> rev_boolvar_list_;
  std::vector<bool*> rev_bools_;
  std::vector<bool> rev_bool_value_;
  std::vector<int*> rev_int_memory_;
  std::vector<int64_t*> rev_int64_memory_;
  std::vector<double*> rev_double_memory_;
  std::vector<BaseObject*> rev_object_memory_;
  std::vector<BaseObject**> rev_object_array_memory_;
  std::vector<void*> rev_memory_;
  std::vector<void**> rev_memory_array_;

  Trail(int block_size,
        ConstraintSolverParameters::TrailCompression compression_level)
      : rev_ints_(block_size, compression_level),
        rev_int64s_(block_size, compression_level),
        rev_uint64s_(block_size, compression_level),
        rev_doubles_(block_size, compression_level),
        rev_ptrs_(block_size, compression_level) {}

  void BacktrackTo(StateMarker* m) {
    int target = m->rev_int_index_;
    for (int curr = rev_ints_.size(); curr > target; --curr) {
      const addrval<int>& cell = rev_ints_.Back();
      cell.restore();
      rev_ints_.PopBack();
    }
    DCHECK_EQ(rev_ints_.size(), target);
    // Incorrect trail size after backtrack.
    target = m->rev_int64_index_;
    for (int curr = rev_int64s_.size(); curr > target; --curr) {
      const addrval<int64_t>& cell = rev_int64s_.Back();
      cell.restore();
      rev_int64s_.PopBack();
    }
    DCHECK_EQ(rev_int64s_.size(), target);
    // Incorrect trail size after backtrack.
    target = m->rev_uint64_index_;
    for (int curr = rev_uint64s_.size(); curr > target; --curr) {
      const addrval<uint64_t>& cell = rev_uint64s_.Back();
      cell.restore();
      rev_uint64s_.PopBack();
    }
    DCHECK_EQ(rev_uint64s_.size(), target);
    // Incorrect trail size after backtrack.
    target = m->rev_double_index_;
    for (int curr = rev_doubles_.size(); curr > target; --curr) {
      const addrval<double>& cell = rev_doubles_.Back();
      cell.restore();
      rev_doubles_.PopBack();
    }
    DCHECK_EQ(rev_doubles_.size(), target);
    // Incorrect trail size after backtrack.
    target = m->rev_ptr_index_;
    for (int curr = rev_ptrs_.size(); curr > target; --curr) {
      const addrval<void*>& cell = rev_ptrs_.Back();
      cell.restore();
      rev_ptrs_.PopBack();
    }
    DCHECK_EQ(rev_ptrs_.size(), target);
    // Incorrect trail size after backtrack.
    target = m->rev_boolvar_list_index_;
    for (int curr = rev_boolvar_list_.size() - 1; curr >= target; --curr) {
      IntVar* const var = rev_boolvar_list_[curr];
      RestoreBoolValue(var);
    }
    rev_boolvar_list_.resize(target);

    DCHECK_EQ(rev_bools_.size(), rev_bool_value_.size());
    target = m->rev_bools_index_;
    for (int curr = rev_bools_.size() - 1; curr >= target; --curr) {
      *(rev_bools_[curr]) = rev_bool_value_[curr];
    }
    rev_bools_.resize(target);
    rev_bool_value_.resize(target);

    target = m->rev_int_memory_index_;
    for (int curr = rev_int_memory_.size() - 1; curr >= target; --curr) {
      delete[] rev_int_memory_[curr];
    }
    rev_int_memory_.resize(target);

    target = m->rev_int64_memory_index_;
    for (int curr = rev_int64_memory_.size() - 1; curr >= target; --curr) {
      delete[] rev_int64_memory_[curr];
    }
    rev_int64_memory_.resize(target);

    target = m->rev_double_memory_index_;
    for (int curr = rev_double_memory_.size() - 1; curr >= target; --curr) {
      delete[] rev_double_memory_[curr];
    }
    rev_double_memory_.resize(target);

    target = m->rev_object_memory_index_;
    for (int curr = rev_object_memory_.size() - 1; curr >= target; --curr) {
      delete rev_object_memory_[curr];
    }
    rev_object_memory_.resize(target);

    target = m->rev_object_array_memory_index_;
    for (int curr = rev_object_array_memory_.size() - 1; curr >= target;
         --curr) {
      delete[] rev_object_array_memory_[curr];
    }
    rev_object_array_memory_.resize(target);

    target = m->rev_memory_index_;
    for (int curr = rev_memory_.size() - 1; curr >= target; --curr) {
      // Explicitly call unsized delete
      ::operator delete(reinterpret_cast<char*>(rev_memory_[curr]));
      // The previous cast is necessary to deallocate generic memory
      // described by a void* when passed to the RevAlloc procedure
      // We cannot do a delete[] there
      // This is useful for cells of RevFIFO and should not be used outside
      // of the product
    }
    rev_memory_.resize(target);

    target = m->rev_memory_array_index_;
    for (int curr = rev_memory_array_.size() - 1; curr >= target; --curr) {
      delete[] rev_memory_array_[curr];
      // delete [] version of the previous unsafe case.
    }
    rev_memory_array_.resize(target);
  }
};

void Solver::InternalSaveValue(int* valptr) {
  trail_->rev_ints_.PushBack(addrval<int>(valptr));
}

void Solver::InternalSaveValue(int64_t* valptr) {
  trail_->rev_int64s_.PushBack(addrval<int64_t>(valptr));
}

void Solver::InternalSaveValue(uint64_t* valptr) {
  trail_->rev_uint64s_.PushBack(addrval<uint64_t>(valptr));
}

void Solver::InternalSaveValue(double* valptr) {
  trail_->rev_doubles_.PushBack(addrval<double>(valptr));
}

void Solver::InternalSaveValue(void** valptr) {
  trail_->rev_ptrs_.PushBack(addrval<void*>(valptr));
}

// TODO(user) : this code is unsafe if you save the same alternating
// bool multiple times.
// The correct code should use a bitset and a single list.
void Solver::InternalSaveValue(bool* valptr) {
  trail_->rev_bools_.push_back(valptr);
  trail_->rev_bool_value_.push_back(*valptr);
}

BaseObject* Solver::SafeRevAlloc(BaseObject* ptr) {
  check_alloc_state();
  trail_->rev_object_memory_.push_back(ptr);
  return ptr;
}

int* Solver::SafeRevAllocArray(int* ptr) {
  check_alloc_state();
  trail_->rev_int_memory_.push_back(ptr);
  return ptr;
}

int64_t* Solver::SafeRevAllocArray(int64_t* ptr) {
  check_alloc_state();
  trail_->rev_int64_memory_.push_back(ptr);
  return ptr;
}

double* Solver::SafeRevAllocArray(double* ptr) {
  check_alloc_state();
  trail_->rev_double_memory_.push_back(ptr);
  return ptr;
}

uint64_t* Solver::SafeRevAllocArray(uint64_t* ptr) {
  check_alloc_state();
  trail_->rev_int64_memory_.push_back(reinterpret_cast<int64_t*>(ptr));
  return ptr;
}

BaseObject** Solver::SafeRevAllocArray(BaseObject** ptr) {
  check_alloc_state();
  trail_->rev_object_array_memory_.push_back(ptr);
  return ptr;
}

IntVar** Solver::SafeRevAllocArray(IntVar** ptr) {
  BaseObject** in = SafeRevAllocArray(reinterpret_cast<BaseObject**>(ptr));
  return reinterpret_cast<IntVar**>(in);
}

IntExpr** Solver::SafeRevAllocArray(IntExpr** ptr) {
  BaseObject** in = SafeRevAllocArray(reinterpret_cast<BaseObject**>(ptr));
  return reinterpret_cast<IntExpr**>(in);
}

Constraint** Solver::SafeRevAllocArray(Constraint** ptr) {
  BaseObject** in = SafeRevAllocArray(reinterpret_cast<BaseObject**>(ptr));
  return reinterpret_cast<Constraint**>(in);
}

void* Solver::UnsafeRevAllocAux(void* ptr) {
  check_alloc_state();
  trail_->rev_memory_.push_back(ptr);
  return ptr;
}

void** Solver::UnsafeRevAllocArrayAux(void** ptr) {
  check_alloc_state();
  trail_->rev_memory_array_.push_back(ptr);
  return ptr;
}

void InternalSaveBooleanVarValue(Solver* const solver, IntVar* const var) {
  solver->trail_->rev_boolvar_list_.push_back(var);
}

// ------------------ Search class -----------------

class Search {
 public:
  explicit Search(Solver* const s)
      : solver_(s),
        marker_stack_(),
        fail_buffer_(),
        solution_counter_(0),
        unchecked_solution_counter_(0),
        decision_builder_(nullptr),
        created_by_solve_(false),
        search_depth_(0),
        left_search_depth_(0),
        should_restart_(false),
        should_finish_(false),
        sentinel_pushed_(0),
        jmpbuf_filled_(false),
        backtrack_at_the_end_of_the_search_(true) {}

  // Constructor for a dummy search. The only difference between a dummy search
  // and a regular one is that the search depth and left search depth is
  // initialized to -1 instead of zero.
  Search(Solver* const s, int /* dummy_argument */)
      : solver_(s),
        marker_stack_(),
        fail_buffer_(),
        solution_counter_(0),
        unchecked_solution_counter_(0),
        decision_builder_(nullptr),
        created_by_solve_(false),
        search_depth_(-1),
        left_search_depth_(-1),
        should_restart_(false),
        should_finish_(false),
        sentinel_pushed_(0),
        jmpbuf_filled_(false),
        backtrack_at_the_end_of_the_search_(true) {}

  ~Search() { gtl::STLDeleteElements(&marker_stack_); }

  void EnterSearch();
  void RestartSearch();
  void ExitSearch();
  void BeginNextDecision(DecisionBuilder* const db);
  void EndNextDecision(DecisionBuilder* const db, Decision* const d);
  void ApplyDecision(Decision* const d);
  void AfterDecision(Decision* const d, bool apply);
  void RefuteDecision(Decision* const d);
  void BeginFail();
  void EndFail();
  void BeginInitialPropagation();
  void EndInitialPropagation();
  bool AtSolution();
  bool AcceptSolution();
  void NoMoreSolutions();
  bool LocalOptimum();
  bool AcceptDelta(Assignment* delta, Assignment* deltadelta);
  void AcceptNeighbor();
  void AcceptUncheckedNeighbor();
  bool IsUncheckedSolutionLimitReached();
  void PeriodicCheck();
  int ProgressPercent();
  void Accept(ModelVisitor* const visitor) const;
  void push_monitor(SearchMonitor* const m);
  void Clear();
  void IncrementSolutionCounter() { ++solution_counter_; }
  int64_t solution_counter() const { return solution_counter_; }
  void IncrementUncheckedSolutionCounter() { ++unchecked_solution_counter_; }
  int64_t unchecked_solution_counter() const {
    return unchecked_solution_counter_;
  }
  void set_decision_builder(DecisionBuilder* const db) {
    decision_builder_ = db;
  }
  DecisionBuilder* decision_builder() const { return decision_builder_; }
  void set_created_by_solve(bool c) { created_by_solve_ = c; }
  bool created_by_solve() const { return created_by_solve_; }
  Solver::DecisionModification ModifyDecision();
  void SetBranchSelector(Solver::BranchSelector bs);
  void LeftMove() {
    search_depth_++;
    left_search_depth_++;
  }
  void RightMove() { search_depth_++; }
  bool backtrack_at_the_end_of_the_search() const {
    return backtrack_at_the_end_of_the_search_;
  }
  void set_backtrack_at_the_end_of_the_search(bool restore) {
    backtrack_at_the_end_of_the_search_ = restore;
  }
  int search_depth() const { return search_depth_; }
  void set_search_depth(int d) { search_depth_ = d; }
  int left_search_depth() const { return left_search_depth_; }
  void set_search_left_depth(int d) { left_search_depth_ = d; }
  void set_should_restart(bool s) { should_restart_ = s; }
  bool should_restart() const { return should_restart_; }
  void set_should_finish(bool s) { should_finish_ = s; }
  bool should_finish() const { return should_finish_; }
  void CheckFail() {
    if (should_finish_ || should_restart_) {
      solver_->Fail();
    }
  }
  void set_search_context(const std::string& search_context) {
    search_context_ = search_context;
  }
  std::string search_context() const { return search_context_; }
  friend class Solver;

 private:
  // Jumps back to the previous choice point, Checks if it was correctly set.
  void JumpBack();
  void ClearBuffer() {
    CHECK(jmpbuf_filled_) << "Internal error in backtracking";
    jmpbuf_filled_ = false;
  }

  Solver* const solver_;
  std::vector<StateMarker*> marker_stack_;
  std::vector<SearchMonitor*> monitors_;
  jmp_buf fail_buffer_;
  int64_t solution_counter_;
  int64_t unchecked_solution_counter_;
  DecisionBuilder* decision_builder_;
  bool created_by_solve_;
  Solver::BranchSelector selector_;
  int search_depth_;
  int left_search_depth_;
  bool should_restart_;
  bool should_finish_;
  int sentinel_pushed_;
  bool jmpbuf_filled_;
  bool backtrack_at_the_end_of_the_search_;
  std::string search_context_;
};

// Backtrack is implemented using 3 primitives:
// CP_TRY to start searching
// CP_DO_FAIL to signal a failure. The program will continue on the CP_ON_FAIL
// primitive.
// Implementation of backtrack using setjmp/longjmp.
// The clean portable way is to use exceptions, unfortunately, it can be much
// slower.  Thus we use ideas from Prolog, CP/CLP implementations,
// continuations in C and implement the default failing and backtracking
// using setjmp/longjmp. You can still use exceptions by defining
// CP_USE_EXCEPTIONS_FOR_BACKTRACK
#ifndef CP_USE_EXCEPTIONS_FOR_BACKTRACK
// We cannot use a method/function for this as we would lose the
// context in the setjmp implementation.
#define CP_TRY(search)                                              \
  CHECK(!search->jmpbuf_filled_) << "Fail() called outside search"; \
  search->jmpbuf_filled_ = true;                                    \
  if (setjmp(search->fail_buffer_) == 0)
#define CP_ON_FAIL else
#define CP_DO_FAIL(search) longjmp(search->fail_buffer_, 1)
#else  // CP_USE_EXCEPTIONS_FOR_BACKTRACK
class FailException {};
#define CP_TRY(search)                                              \
  CHECK(!search->jmpbuf_filled_) << "Fail() called outside search"; \
  search->jmpbuf_filled_ = true;                                    \
  try
#define CP_ON_FAIL catch (FailException&)
#define CP_DO_FAIL(search) throw FailException()
#endif  // CP_USE_EXCEPTIONS_FOR_BACKTRACK

void Search::JumpBack() {
  if (jmpbuf_filled_) {
    jmpbuf_filled_ = false;
    CP_DO_FAIL(this);
  } else {
    std::string explanation = "Failure outside of search";
    solver_->AddConstraint(solver_->MakeFalseConstraint(explanation));
  }
}

Search* Solver::ActiveSearch() const { return searches_.back(); }

namespace {
class ApplyBranchSelector : public DecisionBuilder {
 public:
  explicit ApplyBranchSelector(Solver::BranchSelector bs)
      : selector_(std::move(bs)) {}
  ~ApplyBranchSelector() override {}

  Decision* Next(Solver* const s) override {
    s->SetBranchSelector(selector_);
    return nullptr;
  }

  std::string DebugString() const override { return "Apply(BranchSelector)"; }

 private:
  Solver::BranchSelector const selector_;
};
}  // namespace

void Search::SetBranchSelector(Solver::BranchSelector bs) {
  selector_ = std::move(bs);
}

void Solver::SetBranchSelector(BranchSelector bs) {
  // We cannot use the trail as the search can be nested and thus
  // deleted upon backtrack. Thus we guard the undo action by a
  // check on the number of nesting of solve().
  const int solve_depth = SolveDepth();
  AddBacktrackAction(
      [solve_depth](Solver* s) {
        if (s->SolveDepth() == solve_depth) {
          s->ActiveSearch()->SetBranchSelector(nullptr);
        }
      },
      false);
  searches_.back()->SetBranchSelector(std::move(bs));
}

DecisionBuilder* Solver::MakeApplyBranchSelector(BranchSelector bs) {
  return RevAlloc(new ApplyBranchSelector(std::move(bs)));
}

int Solver::SolveDepth() const {
  return state_ == OUTSIDE_SEARCH ? 0 : searches_.size() - 1;
}

int Solver::SearchDepth() const { return searches_.back()->search_depth(); }

int Solver::SearchLeftDepth() const {
  return searches_.back()->left_search_depth();
}

Solver::DecisionModification Search::ModifyDecision() {
  if (selector_ != nullptr) {
    return selector_();
  }
  return Solver::NO_CHANGE;
}

void Search::push_monitor(SearchMonitor* const m) {
  if (m) {
    monitors_.push_back(m);
  }
}

void Search::Clear() {
  monitors_.clear();
  search_depth_ = 0;
  left_search_depth_ = 0;
  selector_ = nullptr;
  backtrack_at_the_end_of_the_search_ = true;
}

void Search::EnterSearch() {
  // The solution counter is reset when entering search and not when
  // leaving search. This enables the information to persist outside of
  // top-level search.
  solution_counter_ = 0;
  unchecked_solution_counter_ = 0;

  ForAll(monitors_, &SearchMonitor::EnterSearch);
}

void Search::ExitSearch() {
  // Backtrack to the correct state.
  ForAll(monitors_, &SearchMonitor::ExitSearch);
}

void Search::RestartSearch() {
  ForAll(monitors_, &SearchMonitor::RestartSearch);
}

void Search::BeginNextDecision(DecisionBuilder* const db) {
  ForAll(monitors_, &SearchMonitor::BeginNextDecision, db);
  CheckFail();
}

void Search::EndNextDecision(DecisionBuilder* const db, Decision* const d) {
  ForAll(monitors_, &SearchMonitor::EndNextDecision, db, d);
  CheckFail();
}

void Search::ApplyDecision(Decision* const d) {
  ForAll(monitors_, &SearchMonitor::ApplyDecision, d);
  CheckFail();
}

void Search::AfterDecision(Decision* const d, bool apply) {
  ForAll(monitors_, &SearchMonitor::AfterDecision, d, apply);
  CheckFail();
}

void Search::RefuteDecision(Decision* const d) {
  ForAll(monitors_, &SearchMonitor::RefuteDecision, d);
  CheckFail();
}

void Search::BeginFail() { ForAll(monitors_, &SearchMonitor::BeginFail); }

void Search::EndFail() { ForAll(monitors_, &SearchMonitor::EndFail); }

void Search::BeginInitialPropagation() {
  ForAll(monitors_, &SearchMonitor::BeginInitialPropagation);
}

void Search::EndInitialPropagation() {
  ForAll(monitors_, &SearchMonitor::EndInitialPropagation);
}

bool Search::AcceptSolution() {
  bool valid = true;
  for (SearchMonitor* const monitor : monitors_) {
    if (!monitor->AcceptSolution()) {
      // Even though we know the return value, we cannot return yet: this would
      // break the contract we have with solution monitors. They all deserve
      // a chance to look at the solution.
      valid = false;
    }
  }
  return valid;
}

bool Search::AtSolution() {
  bool should_continue = false;
  for (SearchMonitor* const monitor : monitors_) {
    if (monitor->AtSolution()) {
      // Even though we know the return value, we cannot return yet: this would
      // break the contract we have with solution monitors. They all deserve
      // a chance to look at the solution.
      should_continue = true;
    }
  }
  return should_continue;
}

void Search::NoMoreSolutions() {
  ForAll(monitors_, &SearchMonitor::NoMoreSolutions);
}

bool Search::LocalOptimum() {
  bool res = false;
  for (SearchMonitor* const monitor : monitors_) {
    if (monitor->LocalOptimum()) {
      res = true;
    }
  }
  return res;
}

bool Search::AcceptDelta(Assignment* delta, Assignment* deltadelta) {
  bool accept = true;
  for (SearchMonitor* const monitor : monitors_) {
    if (!monitor->AcceptDelta(delta, deltadelta)) {
      accept = false;
    }
  }
  return accept;
}

void Search::AcceptNeighbor() {
  ForAll(monitors_, &SearchMonitor::AcceptNeighbor);
}

void Search::AcceptUncheckedNeighbor() {
  ForAll(monitors_, &SearchMonitor::AcceptUncheckedNeighbor);
}

bool Search::IsUncheckedSolutionLimitReached() {
  for (SearchMonitor* const monitor : monitors_) {
    if (monitor->IsUncheckedSolutionLimitReached()) {
      return true;
    }
  }
  return false;
}

void Search::PeriodicCheck() {
  ForAll(monitors_, &SearchMonitor::PeriodicCheck);
}

int Search::ProgressPercent() {
  int progress = SearchMonitor::kNoProgress;
  for (SearchMonitor* const monitor : monitors_) {
    progress = std::max(progress, monitor->ProgressPercent());
  }
  return progress;
}

void Search::Accept(ModelVisitor* const visitor) const {
  ForAll(monitors_, &SearchMonitor::Accept, visitor);
  if (decision_builder_ != nullptr) {
    decision_builder_->Accept(visitor);
  }
}

bool LocalOptimumReached(Search* const search) {
  return search->LocalOptimum();
}

bool AcceptDelta(Search* const search, Assignment* delta,
                 Assignment* deltadelta) {
  return search->AcceptDelta(delta, deltadelta);
}

void AcceptNeighbor(Search* const search) { search->AcceptNeighbor(); }

void AcceptUncheckedNeighbor(Search* const search) {
  search->AcceptUncheckedNeighbor();
}

namespace {

// ---------- Fail Decision ----------

class FailDecision : public Decision {
 public:
  void Apply(Solver* const s) override { s->Fail(); }
  void Refute(Solver* const s) override { s->Fail(); }
};

// Balancing decision

class BalancingDecision : public Decision {
 public:
  ~BalancingDecision() override {}
  void Apply(Solver* const s) override {}
  void Refute(Solver* const s) override {}
};
}  // namespace

Decision* Solver::MakeFailDecision() { return fail_decision_.get(); }

// ------------------ Solver class -----------------

// These magic numbers are there to make sure we pop the correct
// sentinels throughout the search.
namespace {
enum SentinelMarker {
  INITIAL_SEARCH_SENTINEL = 10000000,
  ROOT_NODE_SENTINEL = 20000000,
  SOLVER_CTOR_SENTINEL = 40000000
};
}  // namespace

extern PropagationMonitor* BuildTrace(Solver* const s);
extern LocalSearchMonitor* BuildLocalSearchMonitorMaster(Solver* const s);
extern ModelCache* BuildModelCache(Solver* const solver);

std::string Solver::model_name() const { return name_; }

namespace {
void CheckSolverParameters(const ConstraintSolverParameters& parameters) {
  CHECK_GT(parameters.array_split_size(), 0)
      << "Were parameters built using Solver::DefaultSolverParameters() ?";
}
}  // namespace

Solver::Solver(const std::string& name,
               const ConstraintSolverParameters& parameters)
    : name_(name),
      parameters_(parameters),
      random_(CpRandomSeed()),
      demon_profiler_(BuildDemonProfiler(this)),
      use_fast_local_search_(true),
      local_search_profiler_(BuildLocalSearchProfiler(this)) {
  Init();
}

Solver::Solver(const std::string& name)
    : name_(name),
      parameters_(DefaultSolverParameters()),
      random_(CpRandomSeed()),
      demon_profiler_(BuildDemonProfiler(this)),
      use_fast_local_search_(true),
      local_search_profiler_(BuildLocalSearchProfiler(this)) {
  Init();
}

void Solver::Init() {
  CheckSolverParameters(parameters_);
  queue_ = absl::make_unique<Queue>(this);
  trail_ = absl::make_unique<Trail>(parameters_.trail_block_size(),
                                    parameters_.compress_trail());
  state_ = OUTSIDE_SEARCH;
  branches_ = 0;
  fails_ = 0;
  decisions_ = 0;
  neighbors_ = 0;
  filtered_neighbors_ = 0;
  accepted_neighbors_ = 0;
  optimization_direction_ = NOT_SET;
  timer_ = absl::make_unique<ClockTimer>();
  searches_.assign(1, new Search(this, 0));
  fail_stamp_ = uint64_t{1};
  balancing_decision_ = absl::make_unique<BalancingDecision>();
  fail_intercept_ = nullptr;
  true_constraint_ = nullptr;
  false_constraint_ = nullptr;
  fail_decision_ = absl::make_unique<FailDecision>();
  constraint_index_ = 0;
  additional_constraint_index_ = 0;
  num_int_vars_ = 0;
  propagation_monitor_.reset(BuildTrace(this));
  local_search_monitor_.reset(BuildLocalSearchMonitorMaster(this));
  print_trace_ = nullptr;
  anonymous_variable_index_ = 0;
  should_fail_ = false;

  for (int i = 0; i < kNumPriorities; ++i) {
    demon_runs_[i] = 0;
  }
  searches_.push_back(new Search(this));
  PushSentinel(SOLVER_CTOR_SENTINEL);
  InitCachedIntConstants();  // to be called after the SENTINEL is set.
  InitCachedConstraint();    // Cache the true constraint.
  timer_->Restart();
  model_cache_.reset(BuildModelCache(this));
  AddPropagationMonitor(reinterpret_cast<PropagationMonitor*>(demon_profiler_));
  AddLocalSearchMonitor(
      reinterpret_cast<LocalSearchMonitor*>(local_search_profiler_));
}

Solver::~Solver() {
  // solver destructor called with searches open.
  CHECK_EQ(2, searches_.size());
  BacktrackToSentinel(INITIAL_SEARCH_SENTINEL);

  StateInfo info;
  Solver::MarkerType finalType = PopState(&info);
  // Not popping a SENTINEL in Solver destructor.
  DCHECK_EQ(finalType, SENTINEL);
  // Not popping initial SENTINEL in Solver destructor.
  DCHECK_EQ(info.int_info, SOLVER_CTOR_SENTINEL);
  gtl::STLDeleteElements(&searches_);
  DeleteDemonProfiler(demon_profiler_);
  DeleteLocalSearchProfiler(local_search_profiler_);
}

std::string Solver::DebugString() const {
  std::string out = "Solver(name = \"" + name_ + "\", state = ";
  switch (state_) {
    case OUTSIDE_SEARCH:
      out += "OUTSIDE_SEARCH";
      break;
    case IN_ROOT_NODE:
      out += "IN_ROOT_NODE";
      break;
    case IN_SEARCH:
      out += "IN_SEARCH";
      break;
    case AT_SOLUTION:
      out += "AT_SOLUTION";
      break;
    case NO_MORE_SOLUTIONS:
      out += "NO_MORE_SOLUTIONS";
      break;
    case PROBLEM_INFEASIBLE:
      out += "PROBLEM_INFEASIBLE";
      break;
  }
  absl::StrAppendFormat(
      &out,
      ", branches = %d, fails = %d, decisions = %d, delayed demon runs = %d, "
      "var demon runs = %d, normal demon runs = %d, Run time = %d ms)",
      branches_, fails_, decisions_, demon_runs_[DELAYED_PRIORITY],
      demon_runs_[VAR_PRIORITY], demon_runs_[NORMAL_PRIORITY], wall_time());
  return out;
}

int64_t Solver::MemoryUsage() { return GetProcessMemoryUsage(); }

int64_t Solver::wall_time() const {
  return absl::ToInt64Milliseconds(timer_->GetDuration());
}

absl::Time Solver::Now() const {
  return absl::FromUnixSeconds(0) + timer_->GetDuration();
}

int64_t Solver::solutions() const {
  return TopLevelSearch()->solution_counter();
}

int64_t Solver::unchecked_solutions() const {
  return TopLevelSearch()->unchecked_solution_counter();
}

void Solver::IncrementUncheckedSolutionCounter() {
  TopLevelSearch()->IncrementUncheckedSolutionCounter();
}

bool Solver::IsUncheckedSolutionLimitReached() {
  return TopLevelSearch()->IsUncheckedSolutionLimitReached();
}

void Solver::TopPeriodicCheck() { TopLevelSearch()->PeriodicCheck(); }

int Solver::TopProgressPercent() { return TopLevelSearch()->ProgressPercent(); }

ConstraintSolverStatistics Solver::GetConstraintSolverStatistics() const {
  ConstraintSolverStatistics stats;
  stats.set_num_branches(branches());
  stats.set_num_failures(failures());
  stats.set_num_solutions(solutions());
  stats.set_bytes_used(MemoryUsage());
  stats.set_duration_seconds(absl::ToDoubleSeconds(timer_->GetDuration()));
  return stats;
}

void Solver::PushState() {
  StateInfo info;
  PushState(SIMPLE_MARKER, info);
}

void Solver::PopState() {
  StateInfo info;
  Solver::MarkerType t = PopState(&info);
  CHECK_EQ(SIMPLE_MARKER, t);
}

void Solver::PushState(Solver::MarkerType t, const StateInfo& info) {
  StateMarker* m = new StateMarker(t, info);
  if (t != REVERSIBLE_ACTION || info.int_info == 0) {
    m->rev_int_index_ = trail_->rev_ints_.size();
    m->rev_int64_index_ = trail_->rev_int64s_.size();
    m->rev_uint64_index_ = trail_->rev_uint64s_.size();
    m->rev_double_index_ = trail_->rev_doubles_.size();
    m->rev_ptr_index_ = trail_->rev_ptrs_.size();
    m->rev_boolvar_list_index_ = trail_->rev_boolvar_list_.size();
    m->rev_bools_index_ = trail_->rev_bools_.size();
    m->rev_int_memory_index_ = trail_->rev_int_memory_.size();
    m->rev_int64_memory_index_ = trail_->rev_int64_memory_.size();
    m->rev_double_memory_index_ = trail_->rev_double_memory_.size();
    m->rev_object_memory_index_ = trail_->rev_object_memory_.size();
    m->rev_object_array_memory_index_ = trail_->rev_object_array_memory_.size();
    m->rev_memory_index_ = trail_->rev_memory_.size();
    m->rev_memory_array_index_ = trail_->rev_memory_array_.size();
  }
  searches_.back()->marker_stack_.push_back(m);
  queue_->increase_stamp();
}

void Solver::AddBacktrackAction(Action a, bool fast) {
  StateInfo info(std::move(a), fast);
  PushState(REVERSIBLE_ACTION, info);
}

Solver::MarkerType Solver::PopState(StateInfo* info) {
  CHECK(!searches_.back()->marker_stack_.empty())
      << "PopState() on an empty stack";
  CHECK(info != nullptr);
  StateMarker* const m = searches_.back()->marker_stack_.back();
  if (m->type_ != REVERSIBLE_ACTION || m->info_.int_info == 0) {
    trail_->BacktrackTo(m);
  }
  Solver::MarkerType t = m->type_;
  (*info) = m->info_;
  searches_.back()->marker_stack_.pop_back();
  delete m;
  queue_->increase_stamp();
  return t;
}

void Solver::check_alloc_state() {
  switch (state_) {
    case OUTSIDE_SEARCH:
    case IN_ROOT_NODE:
    case IN_SEARCH:
    case NO_MORE_SOLUTIONS:
    case PROBLEM_INFEASIBLE:
      break;
    case AT_SOLUTION:
      LOG(FATAL) << "allocating at a leaf node";
    default:
      LOG(FATAL) << "This switch was supposed to be exhaustive, but it is not!";
  }
}

void Solver::FreezeQueue() { queue_->Freeze(); }

void Solver::UnfreezeQueue() { queue_->Unfreeze(); }

void Solver::EnqueueVar(Demon* const d) { queue_->EnqueueVar(d); }

void Solver::EnqueueDelayedDemon(Demon* const d) {
  queue_->EnqueueDelayedDemon(d);
}

void Solver::ExecuteAll(const SimpleRevFIFO<Demon*>& demons) {
  queue_->ExecuteAll(demons);
}

void Solver::EnqueueAll(const SimpleRevFIFO<Demon*>& demons) {
  queue_->EnqueueAll(demons);
}

uint64_t Solver::stamp() const { return queue_->stamp(); }

uint64_t Solver::fail_stamp() const { return fail_stamp_; }

void Solver::set_action_on_fail(Action a) {
  queue_->set_action_on_fail(std::move(a));
}

void Solver::set_variable_to_clean_on_fail(IntVar* v) {
  queue_->set_variable_to_clean_on_fail(v);
}

void Solver::reset_action_on_fail() { queue_->reset_action_on_fail(); }

void Solver::AddConstraint(Constraint* const c) {
  DCHECK(c != nullptr);
  if (c == true_constraint_) {
    return;
  }
  if (state_ == IN_SEARCH) {
    queue_->AddConstraint(c);
  } else if (state_ == IN_ROOT_NODE) {
    DCHECK_GE(constraint_index_, 0);
    DCHECK_LE(constraint_index_, constraints_list_.size());
    const int constraint_parent =
        constraint_index_ == constraints_list_.size()
            ? additional_constraints_parent_list_[additional_constraint_index_]
            : constraint_index_;
    additional_constraints_list_.push_back(c);
    additional_constraints_parent_list_.push_back(constraint_parent);
  } else {
    if (parameters_.print_added_constraints()) {
      LOG(INFO) << c->DebugString();
    }
    constraints_list_.push_back(c);
  }
}

void Solver::AddCastConstraint(CastConstraint* const constraint,
                               IntVar* const target_var, IntExpr* const expr) {
  if (constraint != nullptr) {
    if (state_ != IN_SEARCH) {
      cast_constraints_.insert(constraint);
      cast_information_[target_var] =
          Solver::IntegerCastInfo(target_var, expr, constraint);
    }
    AddConstraint(constraint);
  }
}

void Solver::Accept(ModelVisitor* const visitor) const {
  visitor->BeginVisitModel(name_);
  ForAll(constraints_list_, &Constraint::Accept, visitor);
  visitor->EndVisitModel(name_);
}

void Solver::ProcessConstraints() {
  // Both constraints_list_ and additional_constraints_list_ are used in
  // a FIFO way.
  if (parameters_.print_model()) {
    ModelVisitor* const visitor = MakePrintModelVisitor();
    Accept(visitor);
  }
  if (parameters_.print_model_stats()) {
    ModelVisitor* const visitor = MakeStatisticsModelVisitor();
    Accept(visitor);
  }

  if (parameters_.disable_solve()) {
    LOG(INFO) << "Forcing early failure";
    Fail();
  }

  // Clear state before processing constraints.
  const int constraints_size = constraints_list_.size();
  additional_constraints_list_.clear();
  additional_constraints_parent_list_.clear();

  for (constraint_index_ = 0; constraint_index_ < constraints_size;
       ++constraint_index_) {
    Constraint* const constraint = constraints_list_[constraint_index_];
    propagation_monitor_->BeginConstraintInitialPropagation(constraint);
    constraint->PostAndPropagate();
    propagation_monitor_->EndConstraintInitialPropagation(constraint);
  }
  CHECK_EQ(constraints_list_.size(), constraints_size);

  // Process nested constraints added during the previous step.
  for (int additional_constraint_index_ = 0;
       additional_constraint_index_ < additional_constraints_list_.size();
       ++additional_constraint_index_) {
    Constraint* const nested =
        additional_constraints_list_[additional_constraint_index_];
    const int parent_index =
        additional_constraints_parent_list_[additional_constraint_index_];
    Constraint* const parent = constraints_list_[parent_index];
    propagation_monitor_->BeginNestedConstraintInitialPropagation(parent,
                                                                  nested);
    nested->PostAndPropagate();
    propagation_monitor_->EndNestedConstraintInitialPropagation(parent, nested);
  }
}

bool Solver::CurrentlyInSolve() const {
  DCHECK_GT(SolveDepth(), 0);
  DCHECK(searches_.back() != nullptr);
  return searches_.back()->created_by_solve();
}

bool Solver::Solve(DecisionBuilder* const db, SearchMonitor* const m1) {
  std::vector<SearchMonitor*> monitors;
  monitors.push_back(m1);
  return Solve(db, monitors);
}

bool Solver::Solve(DecisionBuilder* const db) {
  std::vector<SearchMonitor*> monitors;
  return Solve(db, monitors);
}

bool Solver::Solve(DecisionBuilder* const db, SearchMonitor* const m1,
                   SearchMonitor* const m2) {
  std::vector<SearchMonitor*> monitors;
  monitors.push_back(m1);
  monitors.push_back(m2);
  return Solve(db, monitors);
}

bool Solver::Solve(DecisionBuilder* const db, SearchMonitor* const m1,
                   SearchMonitor* const m2, SearchMonitor* const m3) {
  std::vector<SearchMonitor*> monitors;
  monitors.push_back(m1);
  monitors.push_back(m2);
  monitors.push_back(m3);
  return Solve(db, monitors);
}

bool Solver::Solve(DecisionBuilder* const db, SearchMonitor* const m1,
                   SearchMonitor* const m2, SearchMonitor* const m3,
                   SearchMonitor* const m4) {
  std::vector<SearchMonitor*> monitors;
  monitors.push_back(m1);
  monitors.push_back(m2);
  monitors.push_back(m3);
  monitors.push_back(m4);
  return Solve(db, monitors);
}

bool Solver::Solve(DecisionBuilder* const db,
                   const std::vector<SearchMonitor*>& monitors) {
  NewSearch(db, monitors);
  searches_.back()->set_created_by_solve(true);  // Overwrites default.
  NextSolution();
  const bool solution_found = searches_.back()->solution_counter() > 0;
  EndSearch();
  return solution_found;
}

void Solver::NewSearch(DecisionBuilder* const db, SearchMonitor* const m1) {
  std::vector<SearchMonitor*> monitors;
  monitors.push_back(m1);
  return NewSearch(db, monitors);
}

void Solver::NewSearch(DecisionBuilder* const db) {
  std::vector<SearchMonitor*> monitors;
  return NewSearch(db, monitors);
}

void Solver::NewSearch(DecisionBuilder* const db, SearchMonitor* const m1,
                       SearchMonitor* const m2) {
  std::vector<SearchMonitor*> monitors;
  monitors.push_back(m1);
  monitors.push_back(m2);
  return NewSearch(db, monitors);
}

void Solver::NewSearch(DecisionBuilder* const db, SearchMonitor* const m1,
                       SearchMonitor* const m2, SearchMonitor* const m3) {
  std::vector<SearchMonitor*> monitors;
  monitors.push_back(m1);
  monitors.push_back(m2);
  monitors.push_back(m3);
  return NewSearch(db, monitors);
}

void Solver::NewSearch(DecisionBuilder* const db, SearchMonitor* const m1,
                       SearchMonitor* const m2, SearchMonitor* const m3,
                       SearchMonitor* const m4) {
  std::vector<SearchMonitor*> monitors;
  monitors.push_back(m1);
  monitors.push_back(m2);
  monitors.push_back(m3);
  monitors.push_back(m4);
  return NewSearch(db, monitors);
}

extern PropagationMonitor* BuildPrintTrace(Solver* const s);

// Opens a new top level search.
void Solver::NewSearch(DecisionBuilder* const db,
                       const std::vector<SearchMonitor*>& monitors) {
  // TODO(user) : reset statistics

  CHECK(db != nullptr);
  const bool nested = state_ == IN_SEARCH;

  if (state_ == IN_ROOT_NODE) {
    LOG(FATAL) << "Cannot start new searches here.";
  }

  Search* const search = nested ? new Search(this) : searches_.back();
  search->set_created_by_solve(false);  // default behavior.

  // ----- jumps to correct state -----

  if (nested) {
    // Nested searches are created on demand, and deleted afterwards.
    DCHECK_GE(searches_.size(), 2);
    searches_.push_back(search);
  } else {
    // Top level search is persistent.
    // TODO(user): delete top level search after EndSearch().
    DCHECK_EQ(2, searches_.size());
    // TODO(user): Check if these two lines are still necessary.
    BacktrackToSentinel(INITIAL_SEARCH_SENTINEL);
    state_ = OUTSIDE_SEARCH;
  }

  // ----- manages all monitors -----

  // Always install the main propagation and local search monitors.
  propagation_monitor_->Install();
  if (demon_profiler_ != nullptr) {
    InstallDemonProfiler(demon_profiler_);
  }
  local_search_monitor_->Install();
  if (local_search_profiler_ != nullptr) {
    InstallLocalSearchProfiler(local_search_profiler_);
  }

  // Push monitors and enter search.
  for (SearchMonitor* const monitor : monitors) {
    if (monitor != nullptr) {
      monitor->Install();
    }
  }
  std::vector<SearchMonitor*> extras;
  db->AppendMonitors(this, &extras);
  for (SearchMonitor* const monitor : extras) {
    if (monitor != nullptr) {
      monitor->Install();
    }
  }
  // Install the print trace if needed.
  // The print_trace needs to be last to detect propagation from the objective.
  if (nested) {
    if (print_trace_ != nullptr) {  // Was installed at the top level?
      print_trace_->Install();      // Propagates to nested search.
    }
  } else {                   // Top level search
    print_trace_ = nullptr;  // Clears it first.
    if (parameters_.trace_propagation()) {
      print_trace_ = BuildPrintTrace(this);
      print_trace_->Install();
    } else if (parameters_.trace_search()) {
      // This is useful to trace the exact behavior of the search.
      // The '######## ' prefix is the same as the progagation trace.
      // Search trace is subsumed by propagation trace, thus only one
      // is necessary.
      SearchMonitor* const trace = MakeSearchTrace("######## ");
      trace->Install();
    }
  }

  // ----- enters search -----

  search->EnterSearch();

  // Push sentinel and set decision builder.
  PushSentinel(INITIAL_SEARCH_SENTINEL);
  search->set_decision_builder(db);
}

// Backtrack to the last open right branch in the search tree.
// It returns true in case the search tree has been completely explored.
bool Solver::BacktrackOneLevel(Decision** const fail_decision) {
  bool no_more_solutions = false;
  bool end_loop = false;
  while (!end_loop) {
    StateInfo info;
    Solver::MarkerType t = PopState(&info);
    switch (t) {
      case SENTINEL:
        CHECK_EQ(info.ptr_info, this) << "Wrong sentinel found";
        CHECK((info.int_info == ROOT_NODE_SENTINEL && SolveDepth() == 1) ||
              (info.int_info == INITIAL_SEARCH_SENTINEL && SolveDepth() > 1));
        searches_.back()->sentinel_pushed_--;
        no_more_solutions = true;
        end_loop = true;
        break;
      case SIMPLE_MARKER:
        LOG(ERROR) << "Simple markers should not be encountered during search";
        break;
      case CHOICE_POINT:
        if (info.int_info == 0) {  // was left branch
          (*fail_decision) = reinterpret_cast<Decision*>(info.ptr_info);
          end_loop = true;
          searches_.back()->set_search_depth(info.depth);
          searches_.back()->set_search_left_depth(info.left_depth);
        }
        break;
      case REVERSIBLE_ACTION: {
        if (info.reversible_action != nullptr) {
          info.reversible_action(this);
        }
        break;
      }
    }
  }
  Search* const search = searches_.back();
  search->EndFail();
  fail_stamp_++;
  if (no_more_solutions) {
    search->NoMoreSolutions();
  }
  return no_more_solutions;
}

void Solver::PushSentinel(int magic_code) {
  StateInfo info(this, magic_code);
  PushState(SENTINEL, info);
  // We do not count the sentinel pushed in the ctor.
  if (magic_code != SOLVER_CTOR_SENTINEL) {
    searches_.back()->sentinel_pushed_++;
  }
  const int pushed = searches_.back()->sentinel_pushed_;
  DCHECK((magic_code == SOLVER_CTOR_SENTINEL) ||
         (magic_code == INITIAL_SEARCH_SENTINEL && pushed == 1) ||
         (magic_code == ROOT_NODE_SENTINEL && pushed == 2));
}

void Solver::RestartSearch() {
  Search* const search = searches_.back();
  CHECK_NE(0, search->sentinel_pushed_);
  if (SolveDepth() == 1) {  // top level.
    if (search->sentinel_pushed_ > 1) {
      BacktrackToSentinel(ROOT_NODE_SENTINEL);
    }
    CHECK_EQ(1, search->sentinel_pushed_);
    PushSentinel(ROOT_NODE_SENTINEL);
    state_ = IN_SEARCH;
  } else {
    CHECK_EQ(IN_SEARCH, state_);
    if (search->sentinel_pushed_ > 0) {
      BacktrackToSentinel(INITIAL_SEARCH_SENTINEL);
    }
    CHECK_EQ(0, search->sentinel_pushed_);
    PushSentinel(INITIAL_SEARCH_SENTINEL);
  }

  search->RestartSearch();
}

// Backtrack to the initial search sentinel.
// Does not change the state, this should be done by the caller.
void Solver::BacktrackToSentinel(int magic_code) {
  Search* const search = searches_.back();
  bool end_loop = search->sentinel_pushed_ == 0;
  while (!end_loop) {
    StateInfo info;
    Solver::MarkerType t = PopState(&info);
    switch (t) {
      case SENTINEL: {
        CHECK_EQ(info.ptr_info, this) << "Wrong sentinel found";
        CHECK_GE(--search->sentinel_pushed_, 0);
        search->set_search_depth(0);
        search->set_search_left_depth(0);

        if (info.int_info == magic_code) {
          end_loop = true;
        }
        break;
      }
      case SIMPLE_MARKER:
        break;
      case CHOICE_POINT:
        break;
      case REVERSIBLE_ACTION: {
        info.reversible_action(this);
        break;
      }
    }
  }
  fail_stamp_++;
}

// Closes the current search without backtrack.
void Solver::JumpToSentinelWhenNested() {
  CHECK_GT(SolveDepth(), 1) << "calling JumpToSentinel from top level";
  Search* c = searches_.back();
  Search* p = ParentSearch();
  bool found = false;
  while (!c->marker_stack_.empty()) {
    StateMarker* const m = c->marker_stack_.back();
    if (m->type_ == REVERSIBLE_ACTION) {
      p->marker_stack_.push_back(m);
    } else {
      if (m->type_ == SENTINEL) {
        CHECK_EQ(c->marker_stack_.size(), 1) << "Sentinel found too early";
        found = true;
      }
      delete m;
    }
    c->marker_stack_.pop_back();
  }
  c->set_search_depth(0);
  c->set_search_left_depth(0);
  CHECK_EQ(found, true) << "Sentinel not found";
}

namespace {
class ReverseDecision : public Decision {
 public:
  explicit ReverseDecision(Decision* const d) : decision_(d) {
    CHECK(d != nullptr);
  }
  ~ReverseDecision() override {}

  void Apply(Solver* const s) override { decision_->Refute(s); }

  void Refute(Solver* const s) override { decision_->Apply(s); }

  void Accept(DecisionVisitor* const visitor) const override {
    decision_->Accept(visitor);
  }

  std::string DebugString() const override {
    std::string str = "Reverse(";
    str += decision_->DebugString();
    str += ")";
    return str;
  }

 private:
  Decision* const decision_;
};
}  // namespace

// Search for the next solution in the search tree.
bool Solver::NextSolution() {
  Search* const search = searches_.back();
  Decision* fd = nullptr;
  const int solve_depth = SolveDepth();
  const bool top_level = solve_depth <= 1;

  if (solve_depth == 0 && !search->decision_builder()) {
    LOG(WARNING) << "NextSolution() called without a NewSearch before";
    return false;
  }

  if (top_level) {  // Manage top level state.
    switch (state_) {
      case PROBLEM_INFEASIBLE:
        return false;
      case NO_MORE_SOLUTIONS:
        return false;
      case AT_SOLUTION: {
        if (BacktrackOneLevel(&fd)) {  // No more solutions.
          state_ = NO_MORE_SOLUTIONS;
          return false;
        }
        state_ = IN_SEARCH;
        break;
      }
      case OUTSIDE_SEARCH: {
        state_ = IN_ROOT_NODE;
        search->BeginInitialPropagation();
        CP_TRY(search) {
          ProcessConstraints();
          search->EndInitialPropagation();
          PushSentinel(ROOT_NODE_SENTINEL);
          state_ = IN_SEARCH;
          search->ClearBuffer();
        }
        CP_ON_FAIL {
          queue_->AfterFailure();
          BacktrackToSentinel(INITIAL_SEARCH_SENTINEL);
          state_ = PROBLEM_INFEASIBLE;
          return false;
        }
        break;
      }
      case IN_SEARCH:  // Usually after a RestartSearch
        break;
      case IN_ROOT_NODE:
        LOG(FATAL) << "Should not happen";
        break;
    }
  }

  volatile bool finish = false;
  volatile bool result = false;
  DecisionBuilder* const db = search->decision_builder();

  while (!finish) {
    CP_TRY(search) {
      if (fd != nullptr) {
        StateInfo i1(fd, 1, search->search_depth(),
                     search->left_search_depth());  // 1 for right branch
        PushState(CHOICE_POINT, i1);
        search->RefuteDecision(fd);
        branches_++;
        fd->Refute(this);
        // Check the fail state that could have been set in the python/java/C#
        // layer.
        CheckFail();
        search->AfterDecision(fd, false);
        search->RightMove();
        fd = nullptr;
      }
      Decision* d = nullptr;
      for (;;) {
        search->BeginNextDecision(db);
        d = db->Next(this);
        search->EndNextDecision(db, d);
        if (d == fail_decision_.get()) {
          Fail();  // fail now instead of after 2 branches.
        }
        if (d != nullptr) {
          DecisionModification modification = search->ModifyDecision();
          switch (modification) {
            case SWITCH_BRANCHES: {
              d = RevAlloc(new ReverseDecision(d));
              // We reverse the decision and fall through the normal code.
              ABSL_FALLTHROUGH_INTENDED;
            }
            case NO_CHANGE: {
              decisions_++;
              StateInfo i2(d, 0, search->search_depth(),
                           search->left_search_depth());  // 0 for left branch
              PushState(CHOICE_POINT, i2);
              search->ApplyDecision(d);
              branches_++;
              d->Apply(this);
              CheckFail();
              search->AfterDecision(d, true);
              search->LeftMove();
              break;
            }
            case KEEP_LEFT: {
              search->ApplyDecision(d);
              d->Apply(this);
              CheckFail();
              search->AfterDecision(d, true);
              break;
            }
            case KEEP_RIGHT: {
              search->RefuteDecision(d);
              d->Refute(this);
              CheckFail();
              search->AfterDecision(d, false);
              break;
            }
            case KILL_BOTH: {
              Fail();
            }
          }
        } else {
          break;
        }
      }
      if (search->AcceptSolution()) {
        search->IncrementSolutionCounter();
        if (!search->AtSolution() || !CurrentlyInSolve()) {
          result = true;
          finish = true;
        } else {
          Fail();
        }
      } else {
        Fail();
      }
    }
    CP_ON_FAIL {
      queue_->AfterFailure();
      if (search->should_finish()) {
        fd = nullptr;
        BacktrackToSentinel(top_level ? ROOT_NODE_SENTINEL
                                      : INITIAL_SEARCH_SENTINEL);
        result = false;
        finish = true;
        search->set_should_finish(false);
        search->set_should_restart(false);
        // We do not need to push back the sentinel as we are exiting anyway.
      } else if (search->should_restart()) {
        fd = nullptr;
        BacktrackToSentinel(top_level ? ROOT_NODE_SENTINEL
                                      : INITIAL_SEARCH_SENTINEL);
        search->set_should_finish(false);
        search->set_should_restart(false);
        PushSentinel(top_level ? ROOT_NODE_SENTINEL : INITIAL_SEARCH_SENTINEL);
        search->RestartSearch();
      } else {
        if (BacktrackOneLevel(&fd)) {  // no more solutions.
          result = false;
          finish = true;
        }
      }
    }
  }
  if (result) {
    search->ClearBuffer();
  }
  if (top_level) {  // Manage state after NextSolution().
    state_ = (result ? AT_SOLUTION : NO_MORE_SOLUTIONS);
  }
  return result;
}

void Solver::EndSearch() {
  Search* const search = searches_.back();
  if (search->backtrack_at_the_end_of_the_search()) {
    BacktrackToSentinel(INITIAL_SEARCH_SENTINEL);
  } else {
    CHECK_GT(searches_.size(), 2);
    if (search->sentinel_pushed_ > 0) {
      JumpToSentinelWhenNested();
    }
  }
  search->ExitSearch();
  search->Clear();
  if (2 == searches_.size()) {  // Ending top level search.
    // Restores the state.
    state_ = OUTSIDE_SEARCH;
    // Checks if we want to export the profile info.
    if (!parameters_.profile_file().empty()) {
      const std::string& file_name = parameters_.profile_file();
      LOG(INFO) << "Exporting profile to " << file_name;
      ExportProfilingOverview(file_name);
    }
    if (parameters_.print_local_search_profile()) {
      LOG(INFO) << LocalSearchProfile();
    }
  } else {  // We clean the nested Search.
    delete search;
    searches_.pop_back();
  }
}

bool Solver::CheckAssignment(Assignment* const solution) {
  CHECK(solution);
  if (state_ == IN_SEARCH || state_ == IN_ROOT_NODE) {
    LOG(FATAL) << "CheckAssignment is only available at the top level.";
  }
  // Check state and go to OUTSIDE_SEARCH.
  Search* const search = searches_.back();
  search->set_created_by_solve(false);  // default behavior.

  BacktrackToSentinel(INITIAL_SEARCH_SENTINEL);
  state_ = OUTSIDE_SEARCH;

  // Push monitors and enter search.
  search->EnterSearch();

  // Push sentinel and set decision builder.
  DCHECK_EQ(0, SolveDepth());
  DCHECK_EQ(2, searches_.size());
  PushSentinel(INITIAL_SEARCH_SENTINEL);
  search->BeginInitialPropagation();
  CP_TRY(search) {
    state_ = IN_ROOT_NODE;
    DecisionBuilder* const restore = MakeRestoreAssignment(solution);
    restore->Next(this);
    ProcessConstraints();
    search->EndInitialPropagation();
    BacktrackToSentinel(INITIAL_SEARCH_SENTINEL);
    search->ClearBuffer();
    state_ = OUTSIDE_SEARCH;
    return true;
  }
  CP_ON_FAIL {
    const int index =
        constraint_index_ < constraints_list_.size()
            ? constraint_index_
            : additional_constraints_parent_list_[additional_constraint_index_];
    Constraint* const ct = constraints_list_[index];
    if (ct->name().empty()) {
      LOG(INFO) << "Failing constraint = " << ct->DebugString();
    } else {
      LOG(INFO) << "Failing constraint = " << ct->name() << ":"
                << ct->DebugString();
    }
    queue_->AfterFailure();
    BacktrackToSentinel(INITIAL_SEARCH_SENTINEL);
    state_ = PROBLEM_INFEASIBLE;
    return false;
  }
}

namespace {
class AddConstraintDecisionBuilder : public DecisionBuilder {
 public:
  explicit AddConstraintDecisionBuilder(Constraint* const ct)
      : constraint_(ct) {
    CHECK(ct != nullptr);
  }

  ~AddConstraintDecisionBuilder() override {}

  Decision* Next(Solver* const solver) override {
    solver->AddConstraint(constraint_);
    return nullptr;
  }

  std::string DebugString() const override {
    return absl::StrFormat("AddConstraintDecisionBuilder(%s)",
                           constraint_->DebugString());
  }

 private:
  Constraint* const constraint_;
};
}  // namespace

DecisionBuilder* Solver::MakeConstraintAdder(Constraint* const ct) {
  return RevAlloc(new AddConstraintDecisionBuilder(ct));
}

bool Solver::CheckConstraint(Constraint* const ct) {
  return Solve(MakeConstraintAdder(ct));
}

bool Solver::SolveAndCommit(DecisionBuilder* const db,
                            SearchMonitor* const m1) {
  std::vector<SearchMonitor*> monitors;
  monitors.push_back(m1);
  return SolveAndCommit(db, monitors);
}

bool Solver::SolveAndCommit(DecisionBuilder* const db) {
  std::vector<SearchMonitor*> monitors;
  return SolveAndCommit(db, monitors);
}

bool Solver::SolveAndCommit(DecisionBuilder* const db, SearchMonitor* const m1,
                            SearchMonitor* const m2) {
  std::vector<SearchMonitor*> monitors;
  monitors.push_back(m1);
  monitors.push_back(m2);
  return SolveAndCommit(db, monitors);
}

bool Solver::SolveAndCommit(DecisionBuilder* const db, SearchMonitor* const m1,
                            SearchMonitor* const m2, SearchMonitor* const m3) {
  std::vector<SearchMonitor*> monitors;
  monitors.push_back(m1);
  monitors.push_back(m2);
  monitors.push_back(m3);
  return SolveAndCommit(db, monitors);
}

bool Solver::SolveAndCommit(DecisionBuilder* const db,
                            const std::vector<SearchMonitor*>& monitors) {
  NewSearch(db, monitors);
  searches_.back()->set_created_by_solve(true);  // Overwrites default.
  searches_.back()->set_backtrack_at_the_end_of_the_search(false);
  NextSolution();
  const bool solution_found = searches_.back()->solution_counter() > 0;
  EndSearch();
  return solution_found;
}

void Solver::Fail() {
  if (fail_intercept_) {
    fail_intercept_();
    return;
  }
  ConstraintSolverFailsHere();
  fails_++;
  searches_.back()->BeginFail();
  searches_.back()->JumpBack();
}

void Solver::FinishCurrentSearch() {
  searches_.back()->set_should_finish(true);
}

void Solver::RestartCurrentSearch() {
  searches_.back()->set_should_restart(true);
}

// ----- Cast Expression -----

IntExpr* Solver::CastExpression(const IntVar* const var) const {
  const IntegerCastInfo* const cast_info =
      gtl::FindOrNull(cast_information_, var);
  if (cast_info != nullptr) {
    return cast_info->expression;
  }
  return nullptr;
}

// --- Propagation object names ---

std::string Solver::GetName(const PropagationBaseObject* object) {
  const std::string* name = gtl::FindOrNull(propagation_object_names_, object);
  if (name != nullptr) {
    return *name;
  }
  const IntegerCastInfo* const cast_info =
      gtl::FindOrNull(cast_information_, object);
  if (cast_info != nullptr && cast_info->expression != nullptr) {
    if (cast_info->expression->HasName()) {
      return absl::StrFormat("Var<%s>", cast_info->expression->name());
    } else if (parameters_.name_cast_variables()) {
      return absl::StrFormat("Var<%s>", cast_info->expression->DebugString());
    } else {
      const std::string new_name =
          absl::StrFormat("CastVar<%d>", anonymous_variable_index_++);
      propagation_object_names_[object] = new_name;
      return new_name;
    }
  }
  const std::string base_name = object->BaseName();
  if (parameters_.name_all_variables() && !base_name.empty()) {
    const std::string new_name =
        absl::StrFormat("%s_%d", base_name, anonymous_variable_index_++);
    propagation_object_names_[object] = new_name;
    return new_name;
  }
  return empty_name_;
}

void Solver::SetName(const PropagationBaseObject* object,
                     const std::string& name) {
  if (parameters_.store_names() &&
      GetName(object) != name) {  // in particular if name.empty()
    propagation_object_names_[object] = name;
  }
}

bool Solver::HasName(const PropagationBaseObject* const object) const {
  return gtl::ContainsKey(propagation_object_names_,
                          const_cast<PropagationBaseObject*>(object)) ||
         (!object->BaseName().empty() && parameters_.name_all_variables());
}

// ------------------ Useful Operators ------------------

std::ostream& operator<<(std::ostream& out, const Solver* const s) {
  out << s->DebugString();
  return out;
}

std::ostream& operator<<(std::ostream& out, const BaseObject* const o) {
  out << o->DebugString();
  return out;
}

// ---------- PropagationBaseObject ---------

std::string PropagationBaseObject::name() const {
  return solver_->GetName(this);
}

void PropagationBaseObject::set_name(const std::string& name) {
  solver_->SetName(this, name);
}

bool PropagationBaseObject::HasName() const { return solver_->HasName(this); }

std::string PropagationBaseObject::BaseName() const { return ""; }

void PropagationBaseObject::ExecuteAll(const SimpleRevFIFO<Demon*>& demons) {
  solver_->ExecuteAll(demons);
}

void PropagationBaseObject::EnqueueAll(const SimpleRevFIFO<Demon*>& demons) {
  solver_->EnqueueAll(demons);
}

// ---------- Decision Builder ----------

std::string DecisionBuilder::DebugString() const { return "DecisionBuilder"; }

void DecisionBuilder::AppendMonitors(
    Solver* const solver, std::vector<SearchMonitor*>* const extras) {}

void DecisionBuilder::Accept(ModelVisitor* const visitor) const {}

// ---------- Decision and DecisionVisitor ----------

void Decision::Accept(DecisionVisitor* const visitor) const {
  visitor->VisitUnknownDecision();
}

void DecisionVisitor::VisitSetVariableValue(IntVar* const var, int64_t value) {}
void DecisionVisitor::VisitSplitVariableDomain(IntVar* const var, int64_t value,
                                               bool lower) {}
void DecisionVisitor::VisitUnknownDecision() {}
void DecisionVisitor::VisitScheduleOrPostpone(IntervalVar* const var,
                                              int64_t est) {}
void DecisionVisitor::VisitScheduleOrExpedite(IntervalVar* const var,
                                              int64_t est) {}
void DecisionVisitor::VisitRankFirstInterval(SequenceVar* const sequence,
                                             int index) {}

void DecisionVisitor::VisitRankLastInterval(SequenceVar* const sequence,
                                            int index) {}

// ---------- ModelVisitor ----------

// Tags for constraints, arguments, extensions.

const char ModelVisitor::kAbs[] = "Abs";
const char ModelVisitor::kAbsEqual[] = "AbsEqual";
const char ModelVisitor::kAllDifferent[] = "AllDifferent";
const char ModelVisitor::kAllowedAssignments[] = "AllowedAssignments";
const char ModelVisitor::kAtMost[] = "AtMost";
const char ModelVisitor::kBetween[] = "Between";
const char ModelVisitor::kConditionalExpr[] = "ConditionalExpr";
const char ModelVisitor::kCircuit[] = "Circuit";
const char ModelVisitor::kConvexPiecewise[] = "ConvexPiecewise";
const char ModelVisitor::kCountEqual[] = "CountEqual";
const char ModelVisitor::kCover[] = "Cover";
const char ModelVisitor::kCumulative[] = "Cumulative";
const char ModelVisitor::kDeviation[] = "Deviation";
const char ModelVisitor::kDifference[] = "Difference";
const char ModelVisitor::kDisjunctive[] = "Disjunctive";
const char ModelVisitor::kDistribute[] = "Distribute";
const char ModelVisitor::kDivide[] = "Divide";
const char ModelVisitor::kDurationExpr[] = "DurationExpression";
const char ModelVisitor::kElement[] = "Element";
const char ModelVisitor::kElementEqual[] = "ElementEqual";
const char ModelVisitor::kEndExpr[] = "EndExpression";
const char ModelVisitor::kEquality[] = "Equal";
const char ModelVisitor::kFalseConstraint[] = "FalseConstraint";
const char ModelVisitor::kGlobalCardinality[] = "GlobalCardinality";
const char ModelVisitor::kGreater[] = "Greater";
const char ModelVisitor::kGreaterOrEqual[] = "GreaterOrEqual";
const char ModelVisitor::kIndexOf[] = "IndexOf";
const char ModelVisitor::kIntegerVariable[] = "IntegerVariable";
const char ModelVisitor::kIntervalBinaryRelation[] = "IntervalBinaryRelation";
const char ModelVisitor::kIntervalDisjunction[] = "IntervalDisjunction";
const char ModelVisitor::kIntervalUnaryRelation[] = "IntervalUnaryRelation";
const char ModelVisitor::kIntervalVariable[] = "IntervalVariable";
const char ModelVisitor::kInversePermutation[] = "InversePermutation";
const char ModelVisitor::kIsBetween[] = "IsBetween;";
const char ModelVisitor::kIsDifferent[] = "IsDifferent";
const char ModelVisitor::kIsEqual[] = "IsEqual";
const char ModelVisitor::kIsGreater[] = "IsGreater";
const char ModelVisitor::kIsGreaterOrEqual[] = "IsGreaterOrEqual";
const char ModelVisitor::kIsLess[] = "IsLess";
const char ModelVisitor::kIsLessOrEqual[] = "IsLessOrEqual";
const char ModelVisitor::kIsMember[] = "IsMember;";
const char ModelVisitor::kLess[] = "Less";
const char ModelVisitor::kLessOrEqual[] = "LessOrEqual";
const char ModelVisitor::kLexLess[] = "LexLess";
const char ModelVisitor::kLinkExprVar[] = "CastExpressionIntoVariable";
const char ModelVisitor::kMapDomain[] = "MapDomain";
const char ModelVisitor::kMax[] = "Max";
const char ModelVisitor::kMaxEqual[] = "MaxEqual";
const char ModelVisitor::kMember[] = "Member";
const char ModelVisitor::kMin[] = "Min";
const char ModelVisitor::kMinEqual[] = "MinEqual";
const char ModelVisitor::kModulo[] = "Modulo";
const char ModelVisitor::kNoCycle[] = "NoCycle";
const char ModelVisitor::kNonEqual[] = "NonEqual";
const char ModelVisitor::kNotBetween[] = "NotBetween";
const char ModelVisitor::kNotMember[] = "NotMember";
const char ModelVisitor::kNullIntersect[] = "NullIntersect";
const char ModelVisitor::kOpposite[] = "Opposite";
const char ModelVisitor::kPack[] = "Pack";
const char ModelVisitor::kPathCumul[] = "PathCumul";
const char ModelVisitor::kDelayedPathCumul[] = "DelayedPathCumul";
const char ModelVisitor::kPerformedExpr[] = "PerformedExpression";
const char ModelVisitor::kPower[] = "Power";
const char ModelVisitor::kProduct[] = "Product";
const char ModelVisitor::kScalProd[] = "ScalarProduct";
const char ModelVisitor::kScalProdEqual[] = "ScalarProductEqual";
const char ModelVisitor::kScalProdGreaterOrEqual[] =
    "ScalarProductGreaterOrEqual";
const char ModelVisitor::kScalProdLessOrEqual[] = "ScalarProductLessOrEqual";
const char ModelVisitor::kSemiContinuous[] = "SemiContinuous";
const char ModelVisitor::kSequenceVariable[] = "SequenceVariable";
const char ModelVisitor::kSortingConstraint[] = "SortingConstraint";
const char ModelVisitor::kSquare[] = "Square";
const char ModelVisitor::kStartExpr[] = "StartExpression";
const char ModelVisitor::kSum[] = "Sum";
const char ModelVisitor::kSumEqual[] = "SumEqual";
const char ModelVisitor::kSumGreaterOrEqual[] = "SumGreaterOrEqual";
const char ModelVisitor::kSumLessOrEqual[] = "SumLessOrEqual";
const char ModelVisitor::kTransition[] = "Transition";
const char ModelVisitor::kTrace[] = "Trace";
const char ModelVisitor::kTrueConstraint[] = "TrueConstraint";
const char ModelVisitor::kVarBoundWatcher[] = "VarBoundWatcher";
const char ModelVisitor::kVarValueWatcher[] = "VarValueWatcher";

const char ModelVisitor::kCountAssignedItemsExtension[] = "CountAssignedItems";
const char ModelVisitor::kCountUsedBinsExtension[] = "CountUsedBins";
const char ModelVisitor::kInt64ToBoolExtension[] = "Int64ToBoolFunction";
const char ModelVisitor::kInt64ToInt64Extension[] = "Int64ToInt64Function";
const char ModelVisitor::kObjectiveExtension[] = "Objective";
const char ModelVisitor::kSearchLimitExtension[] = "SearchLimit";
const char ModelVisitor::kUsageEqualVariableExtension[] = "UsageEqualVariable";

const char ModelVisitor::kUsageLessConstantExtension[] = "UsageLessConstant";
const char ModelVisitor::kVariableGroupExtension[] = "VariableGroup";
const char ModelVisitor::kVariableUsageLessConstantExtension[] =
    "VariableUsageLessConstant";
const char ModelVisitor::kWeightedSumOfAssignedEqualVariableExtension[] =
    "WeightedSumOfAssignedEqualVariable";

const char ModelVisitor::kActiveArgument[] = "active";
const char ModelVisitor::kAssumePathsArgument[] = "assume_paths";
const char ModelVisitor::kBranchesLimitArgument[] = "branches_limit";
const char ModelVisitor::kCapacityArgument[] = "capacity";
const char ModelVisitor::kCardsArgument[] = "cardinalities";
const char ModelVisitor::kCoefficientsArgument[] = "coefficients";
const char ModelVisitor::kCountArgument[] = "count";
const char ModelVisitor::kCumulativeArgument[] = "cumulative";
const char ModelVisitor::kCumulsArgument[] = "cumuls";
const char ModelVisitor::kDemandsArgument[] = "demands";
const char ModelVisitor::kDurationMinArgument[] = "duration_min";
const char ModelVisitor::kDurationMaxArgument[] = "duration_max";
const char ModelVisitor::kEarlyCostArgument[] = "early_cost";
const char ModelVisitor::kEarlyDateArgument[] = "early_date";
const char ModelVisitor::kEndMinArgument[] = "end_min";
const char ModelVisitor::kEndMaxArgument[] = "end_max";
const char ModelVisitor::kEndsArgument[] = "ends";
const char ModelVisitor::kExpressionArgument[] = "expression";
const char ModelVisitor::kFailuresLimitArgument[] = "failures_limit";
const char ModelVisitor::kFinalStatesArgument[] = "final_states";
const char ModelVisitor::kFixedChargeArgument[] = "fixed_charge";
const char ModelVisitor::kIndex2Argument[] = "index2";
const char ModelVisitor::kIndexArgument[] = "index";
const char ModelVisitor::kInitialState[] = "initial_state";
const char ModelVisitor::kIntervalArgument[] = "interval";
const char ModelVisitor::kIntervalsArgument[] = "intervals";
const char ModelVisitor::kLateCostArgument[] = "late_cost";
const char ModelVisitor::kLateDateArgument[] = "late_date";
const char ModelVisitor::kLeftArgument[] = "left";
const char ModelVisitor::kMaxArgument[] = "max_value";
const char ModelVisitor::kMaximizeArgument[] = "maximize";
const char ModelVisitor::kMinArgument[] = "min_value";
const char ModelVisitor::kModuloArgument[] = "modulo";
const char ModelVisitor::kNextsArgument[] = "nexts";
const char ModelVisitor::kOptionalArgument[] = "optional";
const char ModelVisitor::kPartialArgument[] = "partial";
const char ModelVisitor::kPositionXArgument[] = "position_x";
const char ModelVisitor::kPositionYArgument[] = "position_y";
const char ModelVisitor::kRangeArgument[] = "range";
const char ModelVisitor::kRelationArgument[] = "relation";
const char ModelVisitor::kRightArgument[] = "right";
const char ModelVisitor::kSequenceArgument[] = "sequence";
const char ModelVisitor::kSequencesArgument[] = "sequences";
const char ModelVisitor::kSmartTimeCheckArgument[] = "smart_time_check";
const char ModelVisitor::kSizeArgument[] = "size";
const char ModelVisitor::kSizeXArgument[] = "size_x";
const char ModelVisitor::kSizeYArgument[] = "size_y";
const char ModelVisitor::kSolutionLimitArgument[] = "solutions_limit";
const char ModelVisitor::kStartMinArgument[] = "start_min";
const char ModelVisitor::kStartMaxArgument[] = "start_max";
const char ModelVisitor::kStartsArgument[] = "starts";
const char ModelVisitor::kStepArgument[] = "step";
const char ModelVisitor::kTargetArgument[] = "target_variable";
const char ModelVisitor::kTimeLimitArgument[] = "time_limit";
const char ModelVisitor::kTransitsArgument[] = "transits";
const char ModelVisitor::kTuplesArgument[] = "tuples";
const char ModelVisitor::kValueArgument[] = "value";
const char ModelVisitor::kValuesArgument[] = "values";
const char ModelVisitor::kVarsArgument[] = "variables";
const char ModelVisitor::kEvaluatorArgument[] = "evaluator";

const char ModelVisitor::kVariableArgument[] = "variable";

const char ModelVisitor::kMirrorOperation[] = "mirror";
const char ModelVisitor::kRelaxedMaxOperation[] = "relaxed_max";
const char ModelVisitor::kRelaxedMinOperation[] = "relaxed_min";
const char ModelVisitor::kSumOperation[] = "sum";
const char ModelVisitor::kDifferenceOperation[] = "difference";
const char ModelVisitor::kProductOperation[] = "product";
const char ModelVisitor::kStartSyncOnStartOperation[] = "start_synced_on_start";
const char ModelVisitor::kStartSyncOnEndOperation[] = "start_synced_on_end";
const char ModelVisitor::kTraceOperation[] = "trace";

// Methods

ModelVisitor::~ModelVisitor() {}

void ModelVisitor::BeginVisitModel(const std::string& type_name) {}
void ModelVisitor::EndVisitModel(const std::string& type_name) {}

void ModelVisitor::BeginVisitConstraint(const std::string& type_name,
                                        const Constraint* const constraint) {}
void ModelVisitor::EndVisitConstraint(const std::string& type_name,
                                      const Constraint* const constraint) {}

void ModelVisitor::BeginVisitExtension(const std::string& type) {}
void ModelVisitor::EndVisitExtension(const std::string& type) {}

void ModelVisitor::BeginVisitIntegerExpression(const std::string& type_name,
                                               const IntExpr* const expr) {}
void ModelVisitor::EndVisitIntegerExpression(const std::string& type_name,
                                             const IntExpr* const expr) {}

void ModelVisitor::VisitIntegerVariable(const IntVar* const variable,
                                        IntExpr* const delegate) {
  if (delegate != nullptr) {
    delegate->Accept(this);
  }
}

void ModelVisitor::VisitIntegerVariable(const IntVar* const variable,
                                        const std::string& operation,
                                        int64_t value, IntVar* const delegate) {
  if (delegate != nullptr) {
    delegate->Accept(this);
  }
}

void ModelVisitor::VisitIntervalVariable(const IntervalVar* const variable,
                                         const std::string& operation,
                                         int64_t value,
                                         IntervalVar* const delegate) {
  if (delegate != nullptr) {
    delegate->Accept(this);
  }
}

void ModelVisitor::VisitSequenceVariable(const SequenceVar* const variable) {
  for (int i = 0; i < variable->size(); ++i) {
    variable->Interval(i)->Accept(this);
  }
}

void ModelVisitor::VisitIntegerArgument(const std::string& arg_name,
                                        int64_t value) {}

void ModelVisitor::VisitIntegerArrayArgument(
    const std::string& arg_name, const std::vector<int64_t>& values) {}

void ModelVisitor::VisitIntegerMatrixArgument(const std::string& arg_name,
                                              const IntTupleSet& tuples) {}

void ModelVisitor::VisitIntegerExpressionArgument(const std::string& arg_name,
                                                  IntExpr* const argument) {
  argument->Accept(this);
}

void ModelVisitor::VisitIntegerVariableEvaluatorArgument(
    const std::string& arg_name, const Solver::Int64ToIntVar& arguments) {}

void ModelVisitor::VisitIntegerVariableArrayArgument(
    const std::string& arg_name, const std::vector<IntVar*>& arguments) {
  ForAll(arguments, &IntVar::Accept, this);
}

void ModelVisitor::VisitIntervalArgument(const std::string& arg_name,
                                         IntervalVar* const argument) {
  argument->Accept(this);
}

void ModelVisitor::VisitIntervalArrayArgument(
    const std::string& arg_name, const std::vector<IntervalVar*>& arguments) {
  ForAll(arguments, &IntervalVar::Accept, this);
}

void ModelVisitor::VisitSequenceArgument(const std::string& arg_name,
                                         SequenceVar* const argument) {
  argument->Accept(this);
}

void ModelVisitor::VisitSequenceArrayArgument(
    const std::string& arg_name, const std::vector<SequenceVar*>& arguments) {
  ForAll(arguments, &SequenceVar::Accept, this);
}

// ----- Helpers -----

void ModelVisitor::VisitInt64ToBoolExtension(Solver::IndexFilter1 filter,
                                             int64_t index_min,
                                             int64_t index_max) {
  if (filter != nullptr) {
    std::vector<int64_t> cached_results;
    for (int i = index_min; i <= index_max; ++i) {
      cached_results.push_back(filter(i));
    }
    BeginVisitExtension(kInt64ToBoolExtension);
    VisitIntegerArgument(kMinArgument, index_min);
    VisitIntegerArgument(kMaxArgument, index_max);
    VisitIntegerArrayArgument(kValuesArgument, cached_results);
    EndVisitExtension(kInt64ToBoolExtension);
  }
}

void ModelVisitor::VisitInt64ToInt64Extension(
    const Solver::IndexEvaluator1& eval, int64_t index_min, int64_t index_max) {
  CHECK(eval != nullptr);
  std::vector<int64_t> cached_results;
  for (int i = index_min; i <= index_max; ++i) {
    cached_results.push_back(eval(i));
  }
  BeginVisitExtension(kInt64ToInt64Extension);
  VisitIntegerArgument(kMinArgument, index_min);
  VisitIntegerArgument(kMaxArgument, index_max);
  VisitIntegerArrayArgument(kValuesArgument, cached_results);
  EndVisitExtension(kInt64ToInt64Extension);
}

void ModelVisitor::VisitInt64ToInt64AsArray(const Solver::IndexEvaluator1& eval,
                                            const std::string& arg_name,
                                            int64_t index_max) {
  CHECK(eval != nullptr);
  std::vector<int64_t> cached_results;
  for (int i = 0; i <= index_max; ++i) {
    cached_results.push_back(eval(i));
  }
  VisitIntegerArrayArgument(arg_name, cached_results);
}

// ---------- Search Monitor ----------

void SearchMonitor::EnterSearch() {}
void SearchMonitor::RestartSearch() {}
void SearchMonitor::ExitSearch() {}
void SearchMonitor::BeginNextDecision(DecisionBuilder* const b) {}
void SearchMonitor::EndNextDecision(DecisionBuilder* const b,
                                    Decision* const d) {}
void SearchMonitor::ApplyDecision(Decision* const d) {}
void SearchMonitor::RefuteDecision(Decision* const d) {}
void SearchMonitor::AfterDecision(Decision* const d, bool apply) {}
void SearchMonitor::BeginFail() {}
void SearchMonitor::EndFail() {}
void SearchMonitor::BeginInitialPropagation() {}
void SearchMonitor::EndInitialPropagation() {}
bool SearchMonitor::AcceptSolution() { return true; }
bool SearchMonitor::AtSolution() { return false; }
void SearchMonitor::NoMoreSolutions() {}
bool SearchMonitor::LocalOptimum() { return false; }
bool SearchMonitor::AcceptDelta(Assignment* delta, Assignment* deltadelta) {
  return true;
}
void SearchMonitor::AcceptNeighbor() {}
void SearchMonitor::AcceptUncheckedNeighbor() {}
void SearchMonitor::PeriodicCheck() {}
void SearchMonitor::Accept(ModelVisitor* const visitor) const {}
// A search monitors adds itself on the active search.
void SearchMonitor::Install() {
  solver()->searches_.back()->push_monitor(this);
}

// ---------- Propagation Monitor -----------
PropagationMonitor::PropagationMonitor(Solver* const solver)
    : SearchMonitor(solver) {}

PropagationMonitor::~PropagationMonitor() {}

// A propagation monitor listens to search events as well as propagation events.
void PropagationMonitor::Install() {
  SearchMonitor::Install();
  solver()->AddPropagationMonitor(this);
}

// ---------- Local Search Monitor -----------
LocalSearchMonitor::LocalSearchMonitor(Solver* const solver)
    : SearchMonitor(solver) {}

LocalSearchMonitor::~LocalSearchMonitor() {}

// A local search monitor listens to search events as well as local search
// events.
void LocalSearchMonitor::Install() {
  SearchMonitor::Install();
  solver()->AddLocalSearchMonitor(this);
}

// ---------- Trace ----------

class Trace : public PropagationMonitor {
 public:
  explicit Trace(Solver* const s) : PropagationMonitor(s) {}

  ~Trace() override {}

  void BeginConstraintInitialPropagation(
      Constraint* const constraint) override {
    ForAll(monitors_, &PropagationMonitor::BeginConstraintInitialPropagation,
           constraint);
  }

  void EndConstraintInitialPropagation(Constraint* const constraint) override {
    ForAll(monitors_, &PropagationMonitor::EndConstraintInitialPropagation,
           constraint);
  }

  void BeginNestedConstraintInitialPropagation(
      Constraint* const parent, Constraint* const nested) override {
    ForAll(monitors_,
           &PropagationMonitor::BeginNestedConstraintInitialPropagation, parent,
           nested);
  }

  void EndNestedConstraintInitialPropagation(
      Constraint* const parent, Constraint* const nested) override {
    ForAll(monitors_,
           &PropagationMonitor::EndNestedConstraintInitialPropagation, parent,
           nested);
  }

  void RegisterDemon(Demon* const demon) override {
    ForAll(monitors_, &PropagationMonitor::RegisterDemon, demon);
  }

  void BeginDemonRun(Demon* const demon) override {
    ForAll(monitors_, &PropagationMonitor::BeginDemonRun, demon);
  }

  void EndDemonRun(Demon* const demon) override {
    ForAll(monitors_, &PropagationMonitor::EndDemonRun, demon);
  }

  void StartProcessingIntegerVariable(IntVar* const var) override {
    ForAll(monitors_, &PropagationMonitor::StartProcessingIntegerVariable, var);
  }

  void EndProcessingIntegerVariable(IntVar* const var) override {
    ForAll(monitors_, &PropagationMonitor::EndProcessingIntegerVariable, var);
  }

  void PushContext(const std::string& context) override {
    ForAll(monitors_, &PropagationMonitor::PushContext, context);
  }

  void PopContext() override {
    ForAll(monitors_, &PropagationMonitor::PopContext);
  }

  // IntExpr modifiers.
  void SetMin(IntExpr* const expr, int64_t new_min) override {
    for (PropagationMonitor* const monitor : monitors_) {
      monitor->SetMin(expr, new_min);
    }
  }

  void SetMax(IntExpr* const expr, int64_t new_max) override {
    for (PropagationMonitor* const monitor : monitors_) {
      monitor->SetMax(expr, new_max);
    }
  }

  void SetRange(IntExpr* const expr, int64_t new_min,
                int64_t new_max) override {
    for (PropagationMonitor* const monitor : monitors_) {
      monitor->SetRange(expr, new_min, new_max);
    }
  }

  // IntVar modifiers.
  void SetMin(IntVar* const var, int64_t new_min) override {
    for (PropagationMonitor* const monitor : monitors_) {
      monitor->SetMin(var, new_min);
    }
  }

  void SetMax(IntVar* const var, int64_t new_max) override {
    for (PropagationMonitor* const monitor : monitors_) {
      monitor->SetMax(var, new_max);
    }
  }

  void SetRange(IntVar* const var, int64_t new_min, int64_t new_max) override {
    for (PropagationMonitor* const monitor : monitors_) {
      monitor->SetRange(var, new_min, new_max);
    }
  }

  void RemoveValue(IntVar* const var, int64_t value) override {
    ForAll(monitors_, &PropagationMonitor::RemoveValue, var, value);
  }

  void SetValue(IntVar* const var, int64_t value) override {
    ForAll(monitors_, &PropagationMonitor::SetValue, var, value);
  }

  void RemoveInterval(IntVar* const var, int64_t imin, int64_t imax) override {
    ForAll(monitors_, &PropagationMonitor::RemoveInterval, var, imin, imax);
  }

  void SetValues(IntVar* const var,
                 const std::vector<int64_t>& values) override {
    ForAll(monitors_, &PropagationMonitor::SetValues, var, values);
  }

  void RemoveValues(IntVar* const var,
                    const std::vector<int64_t>& values) override {
    ForAll(monitors_, &PropagationMonitor::RemoveValues, var, values);
  }

  // IntervalVar modifiers.
  void SetStartMin(IntervalVar* const var, int64_t new_min) override {
    ForAll(monitors_, &PropagationMonitor::SetStartMin, var, new_min);
  }

  void SetStartMax(IntervalVar* const var, int64_t new_max) override {
    ForAll(monitors_, &PropagationMonitor::SetStartMax, var, new_max);
  }

  void SetStartRange(IntervalVar* const var, int64_t new_min,
                     int64_t new_max) override {
    ForAll(monitors_, &PropagationMonitor::SetStartRange, var, new_min,
           new_max);
  }

  void SetEndMin(IntervalVar* const var, int64_t new_min) override {
    ForAll(monitors_, &PropagationMonitor::SetEndMin, var, new_min);
  }

  void SetEndMax(IntervalVar* const var, int64_t new_max) override {
    ForAll(monitors_, &PropagationMonitor::SetEndMax, var, new_max);
  }

  void SetEndRange(IntervalVar* const var, int64_t new_min,
                   int64_t new_max) override {
    ForAll(monitors_, &PropagationMonitor::SetEndRange, var, new_min, new_max);
  }

  void SetDurationMin(IntervalVar* const var, int64_t new_min) override {
    ForAll(monitors_, &PropagationMonitor::SetDurationMin, var, new_min);
  }

  void SetDurationMax(IntervalVar* const var, int64_t new_max) override {
    ForAll(monitors_, &PropagationMonitor::SetDurationMax, var, new_max);
  }

  void SetDurationRange(IntervalVar* const var, int64_t new_min,
                        int64_t new_max) override {
    ForAll(monitors_, &PropagationMonitor::SetDurationRange, var, new_min,
           new_max);
  }

  void SetPerformed(IntervalVar* const var, bool value) override {
    ForAll(monitors_, &PropagationMonitor::SetPerformed, var, value);
  }

  void RankFirst(SequenceVar* const var, int index) override {
    ForAll(monitors_, &PropagationMonitor::RankFirst, var, index);
  }

  void RankNotFirst(SequenceVar* const var, int index) override {
    ForAll(monitors_, &PropagationMonitor::RankNotFirst, var, index);
  }

  void RankLast(SequenceVar* const var, int index) override {
    ForAll(monitors_, &PropagationMonitor::RankLast, var, index);
  }

  void RankNotLast(SequenceVar* const var, int index) override {
    ForAll(monitors_, &PropagationMonitor::RankNotLast, var, index);
  }

  void RankSequence(SequenceVar* const var, const std::vector<int>& rank_first,
                    const std::vector<int>& rank_last,
                    const std::vector<int>& unperformed) override {
    ForAll(monitors_, &PropagationMonitor::RankSequence, var, rank_first,
           rank_last, unperformed);
  }

  // Does not take ownership of monitor.
  void Add(PropagationMonitor* const monitor) {
    if (monitor != nullptr) {
      monitors_.push_back(monitor);
    }
  }

  // The trace will dispatch propagation events. It needs to listen to search
  // events.
  void Install() override { SearchMonitor::Install(); }

  std::string DebugString() const override { return "Trace"; }

 private:
  std::vector<PropagationMonitor*> monitors_;
};

PropagationMonitor* BuildTrace(Solver* const s) { return new Trace(s); }

void Solver::AddPropagationMonitor(PropagationMonitor* const monitor) {
  // TODO(user): Check solver state?
  reinterpret_cast<class Trace*>(propagation_monitor_.get())->Add(monitor);
}

PropagationMonitor* Solver::GetPropagationMonitor() const {
  return propagation_monitor_.get();
}

// ---------- Local Search Monitor Master ----------

class LocalSearchMonitorMaster : public LocalSearchMonitor {
 public:
  explicit LocalSearchMonitorMaster(Solver* solver)
      : LocalSearchMonitor(solver) {}

  void BeginOperatorStart() override {
    ForAll(monitors_, &LocalSearchMonitor::BeginOperatorStart);
  }
  void EndOperatorStart() override {
    ForAll(monitors_, &LocalSearchMonitor::EndOperatorStart);
  }
  void BeginMakeNextNeighbor(const LocalSearchOperator* op) override {
    ForAll(monitors_, &LocalSearchMonitor::BeginMakeNextNeighbor, op);
  }
  void EndMakeNextNeighbor(const LocalSearchOperator* op, bool neighbor_found,
                           const Assignment* delta,
                           const Assignment* deltadelta) override {
    ForAll(monitors_, &LocalSearchMonitor::EndMakeNextNeighbor, op,
           neighbor_found, delta, deltadelta);
  }
  void BeginFilterNeighbor(const LocalSearchOperator* op) override {
    ForAll(monitors_, &LocalSearchMonitor::BeginFilterNeighbor, op);
  }
  void EndFilterNeighbor(const LocalSearchOperator* op,
                         bool neighbor_found) override {
    ForAll(monitors_, &LocalSearchMonitor::EndFilterNeighbor, op,
           neighbor_found);
  }
  void BeginAcceptNeighbor(const LocalSearchOperator* op) override {
    ForAll(monitors_, &LocalSearchMonitor::BeginAcceptNeighbor, op);
  }
  void EndAcceptNeighbor(const LocalSearchOperator* op,
                         bool neighbor_found) override {
    ForAll(monitors_, &LocalSearchMonitor::EndAcceptNeighbor, op,
           neighbor_found);
  }
  void BeginFiltering(const LocalSearchFilter* filter) override {
    ForAll(monitors_, &LocalSearchMonitor::BeginFiltering, filter);
  }
  void EndFiltering(const LocalSearchFilter* filter, bool reject) override {
    ForAll(monitors_, &LocalSearchMonitor::EndFiltering, filter, reject);
  }

  // Does not take ownership of monitor.
  void Add(LocalSearchMonitor* monitor) {
    if (monitor != nullptr) {
      monitors_.push_back(monitor);
    }
  }

  // The trace will dispatch propagation events. It needs to listen to search
  // events.
  void Install() override { SearchMonitor::Install(); }

  std::string DebugString() const override {
    return "LocalSearchMonitorMaster";
  }

 private:
  std::vector<LocalSearchMonitor*> monitors_;
};

LocalSearchMonitor* BuildLocalSearchMonitorMaster(Solver* const s) {
  return new LocalSearchMonitorMaster(s);
}

void Solver::AddLocalSearchMonitor(LocalSearchMonitor* const monitor) {
  reinterpret_cast<class LocalSearchMonitorMaster*>(local_search_monitor_.get())
      ->Add(monitor);
}

LocalSearchMonitor* Solver::GetLocalSearchMonitor() const {
  return local_search_monitor_.get();
}

void Solver::SetSearchContext(Search* search,
                              const std::string& search_context) {
  search->set_search_context(search_context);
}

std::string Solver::SearchContext() const {
  return ActiveSearch()->search_context();
}

std::string Solver::SearchContext(const Search* search) const {
  return search->search_context();
}

Assignment* Solver::GetOrCreateLocalSearchState() {
  if (local_search_state_ == nullptr) {
    local_search_state_ = absl::make_unique<Assignment>(this);
  }
  return local_search_state_.get();
}

// ----------------- Constraint class -------------------

std::string Constraint::DebugString() const { return "Constraint"; }

void Constraint::PostAndPropagate() {
  FreezeQueue();
  Post();
  InitialPropagate();
  solver()->CheckFail();
  UnfreezeQueue();
}

void Constraint::Accept(ModelVisitor* const visitor) const {
  visitor->BeginVisitConstraint("unknown", this);
  VLOG(3) << "Unknown constraint " << DebugString();
  visitor->EndVisitConstraint("unknown", this);
}

bool Constraint::IsCastConstraint() const {
  return gtl::ContainsKey(solver()->cast_constraints_, this);
}

IntVar* Constraint::Var() { return nullptr; }

// ----- Class IntExpr -----

void IntExpr::Accept(ModelVisitor* const visitor) const {
  visitor->BeginVisitIntegerExpression("unknown", this);
  VLOG(3) << "Unknown expression " << DebugString();
  visitor->EndVisitIntegerExpression("unknown", this);
}

#undef CP_TRY  // We no longer need those.
#undef CP_ON_FAIL
#undef CP_DO_FAIL

}  // namespace operations_research