solver.h

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// Copyright 2010-2022 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.
 
#ifndef OR_TOOLS_MATH_OPT_CORE_SOLVER_H_
#define OR_TOOLS_MATH_OPT_CORE_SOLVER_H_
 
#include <functional>
#include <memory>
 
#include "absl/status/status.h"
#include "absl/status/statusor.h"
#include "absl/synchronization/mutex.h"
#include "ortools/math_opt/callback.pb.h"
#include "ortools/math_opt/core/concurrent_calls_guard.h"
#include "ortools/math_opt/core/model_summary.h"
#include "ortools/math_opt/core/solve_interrupter.h"
#include "ortools/math_opt/core/solver_interface.h"
#include "ortools/math_opt/model.pb.h"
#include "ortools/math_opt/model_parameters.pb.h"
#include "ortools/math_opt/model_update.pb.h"
#include "ortools/math_opt/parameters.pb.h"
#include "ortools/math_opt/result.pb.h"
 
namespace operations_research {
namespace math_opt {
 
// A solver for a given model and solver implementation.
//
// Use the New() function to build a new solver instance; then call Solve() to
// solve the model. You can then update the model using Update() and resolve.
//
// Thread-safety: methods Solve() and Update() must not be called concurrently;
// they will immediately return with an error status if this happens. Some
// solvers may add more restriction regarding threading. Please see
// SOLVER_TYPE_XXX documentation for details.
//
// Usage:
//   const ModelProto model = ...;
//   const auto solver = Solver::New(SOLVER_TYPE_GSCIP,
//                                   model,
//                                   /*arguments=*/{});
//   CHECK_OK(solver.status());
//   Solver::SolveArgs solve_arguments;
//   ...
//
//   // First solve of the initial Model.
//   const auto first_solution = (*solver)->Solve(solve_arguments);
//   CHECK_OK(first_solution.status());
//   // Use the first_solution here.
//
//   // Update the Model with a ModelUpdate.
//   const ModelUpdate update = ...;
//   CHECK_OK((*solver)->Update(update));
//   const auto second_solution = (*solver)->Solve(solve_arguments);
//   CHECK_OK(second_solution.status());
//   // Use the second_solution of the updated problem here.
//
class Solver {
 public:
  using InitArgs = SolverInterface::InitArgs;
 
  // Callback function for messages callback sent by the solver.
  //
  // Each message represents a single output line from the solver, and each
  // message does not contain any '\n' character in it.
  //
  // Thread-safety: a callback may be called concurrently from multiple
  // threads. The users is expected to use proper synchronization primitives to
  // deal with that.
  using MessageCallback = SolverInterface::MessageCallback;
 
  // Callback function type for MIP/LP callbacks.
  using Callback = std::function<CallbackResultProto(const CallbackDataProto&)>;
 
  // Arguments used when calling Solve() to solve the problem.
  struct SolveArgs {
    SolveParametersProto parameters;
    ModelSolveParametersProto model_parameters;
 
    // An optional callback for messages emitted by the solver.
    //
    // When set it enables the solver messages and ignores the `enable_output`
    // in solve parameters; messages are redirected to the callback and not
    // printed on stdout/stderr/logs anymore.
    MessageCallback message_callback = nullptr;
 
    CallbackRegistrationProto callback_registration;
    Callback user_cb = nullptr;
 
    // An optional interrupter that the solver can use to interrupt the solve
    // early.
    SolveInterrupter* interrupter = nullptr;
  };
 
  // A shortcut for calling Solver::New() and then Solver::Solve().
  static absl::StatusOr<SolveResultProto> NonIncrementalSolve(
      const ModelProto& model, SolverTypeProto solver_type,
      const InitArgs& init_args, const SolveArgs& solve_args);
 
  // Builds a solver of the given type with the provided model and
  // initialization parameters.
  static absl::StatusOr<std::unique_ptr<Solver>> New(
      SolverTypeProto solver_type, const ModelProto& model,
      const InitArgs& arguments);
 
  Solver(const Solver&) = delete;
  Solver& operator=(const Solver&) = delete;
 
  ~Solver();
 
  // Solves the current model (included all updates).
  absl::StatusOr<SolveResultProto> Solve(const SolveArgs& arguments);
 
  // Updates the model to solve and returns true, or returns false if this
  // update is not supported by the underlying solver.
  //
  // A status error will be returned if the model_update is invalid or the
  // underlying solver has an internal error.
  //
  // When this function returns false, the Solver object is in a failed
  // state. In that case the underlying SolverInterface implementation has been
  // destroyed (this enables the caller to instantiate a new Solver without
  // destroying the previous one first even if they use Gurobi with a single-use
  // license).
  absl::StatusOr<bool> Update(const ModelUpdateProto& model_update);
 
 private:
  Solver(std::unique_ptr<SolverInterface> underlying_solver,
         ModelSummary model_summary);
 
  // Tracker used to ensure that Solve() and Update() are not called
  // concurrently.
  ConcurrentCallsGuard::Tracker concurrent_calls_tracker_;
 
  // Can be nullptr only if fatal_failure_occurred_ is true (but the contrary is
  // not true). This happens when Update() returns false.
  std::unique_ptr<SolverInterface> underlying_solver_;
 
  ModelSummary model_summary_;
 
  // Set to true if a previous call to Solve() or Update() returned a failing
  // status (or if Update() returned false).
  //
  // This is guarded by concurrent_calls_tracker_.
  bool fatal_failure_occurred_ = false;
};
 
namespace internal {
 
// Validates that the input streamable and non_streamable init arguments are
// either not set or are the one of solver_type.
absl::Status ValidateInitArgs(const Solver::InitArgs& init_args,
                              SolverTypeProto solver_type);
 
}  // namespace internal
}  // namespace math_opt
}  // namespace operations_research
 
#endif  // OR_TOOLS_MATH_OPT_CORE_SOLVER_H_