Refactor MPSolver interface registration to include runtime readiness checks. (#4973)

This PR is removing the need for `linear_solver` to depend on `GurobiIsCorrectlyInstalled` and `XpressIsCorrectlyInstalled`.

ortools/linear_solver/gurobi_interface.cc

@@ -1417,7 +1417,8 @@ namespace {
 const void* const kRegisterGurobiLp ABSL_ATTRIBUTE_UNUSED = [] {
   MPSolverInterfaceFactoryRepository::GetInstance()->Register(
       [](MPSolver* solver) { return new GurobiInterface(solver, false); },
-      MPSolver::GUROBI_LINEAR_PROGRAMMING);
+      MPSolver::GUROBI_LINEAR_PROGRAMMING,
+      []() { return GurobiIsCorrectlyInstalled(); });
   return nullptr;
 }();
 
@@ -1425,7 +1426,8 @@ const void* const kRegisterGurobiLp ABSL_ATTRIBUTE_UNUSED = [] {
 const void* const kRegisterGurobiMip ABSL_ATTRIBUTE_UNUSED = [] {
   MPSolverInterfaceFactoryRepository::GetInstance()->Register(
       [](MPSolver* solver) { return new GurobiInterface(solver, true); },
-      MPSolver::GUROBI_MIXED_INTEGER_PROGRAMMING);
+      MPSolver::GUROBI_MIXED_INTEGER_PROGRAMMING,
+      []() { return GurobiIsCorrectlyInstalled(); });
   return nullptr;
 }();
 

ortools/linear_solver/linear_solver.cc

@@ -412,26 +412,10 @@ MPSolver::MPSolver(const std::string& name,
 
 MPSolver::~MPSolver() { Clear(); }
 
-extern bool GurobiIsCorrectlyInstalled();
-extern bool XpressIsCorrectlyInstalled();
-
 // static
 bool MPSolver::SupportsProblemType(OptimizationProblemType problem_type) {
-  if (!MPSolverInterfaceFactoryRepository::GetInstance()->Supports(
-          problem_type)) {
-    return false;
-  }
-  switch (problem_type) {
-    case GUROBI_LINEAR_PROGRAMMING:
-    case GUROBI_MIXED_INTEGER_PROGRAMMING:
-      return GurobiIsCorrectlyInstalled();
-    case XPRESS_LINEAR_PROGRAMMING:
-    case XPRESS_MIXED_INTEGER_PROGRAMMING:
-      return XpressIsCorrectlyInstalled();
-    default:
-      break;
-  }
-  return true;
+  return MPSolverInterfaceFactoryRepository::GetInstance()->Supports(
+      problem_type);
 }
 
 // TODO(user): post c++ 14, instead use
@@ -2238,9 +2222,14 @@ MPSolverInterfaceFactoryRepository::~MPSolverInterfaceFactoryRepository() {
 
 void MPSolverInterfaceFactoryRepository::Register(
     MPSolverInterfaceFactory factory,
-    MPSolver::OptimizationProblemType problem_type) {
+    MPSolver::OptimizationProblemType problem_type,
+    std::function<bool()> is_runtime_ready) {
   absl::MutexLock lock(mutex_);
-  map_[problem_type] = std::move(factory);
+  if (!is_runtime_ready) is_runtime_ready = []() { return true; };
+  map_[problem_type] = Entry{
+      .factory = std::move(factory),
+      .is_runtime_ready = std::move(is_runtime_ready),
+  };
 }
 
 bool MPSolverInterfaceFactoryRepository::Unregister(
@@ -2252,17 +2241,20 @@ bool MPSolverInterfaceFactoryRepository::Unregister(
 MPSolverInterface* MPSolverInterfaceFactoryRepository::Create(
     MPSolver* solver) const {
   absl::MutexLock lock(mutex_);
-  const MPSolverInterfaceFactory factory =
-      gtl::FindWithDefault(map_, solver->ProblemType(), nullptr);
-  if (!factory) {
-    return nullptr;
-  }
-  return factory(solver);
+  const Entry* entry = gtl::FindOrNull(map_, solver->ProblemType());
+  CHECK(entry != nullptr) << "No factory registered for problem type "
+                          << ToString(solver->ProblemType());
+  CHECK(entry->is_runtime_ready())
+      << "Solver for problem type " << ToString(solver->ProblemType())
+      << " is not ready.";
+  return entry->factory(solver);
 }
 
 bool MPSolverInterfaceFactoryRepository::Supports(
     MPSolver::OptimizationProblemType problem_type) const {
-  return map_.count(problem_type) > 0;
+  const Entry* entry = gtl::FindOrNull(map_, problem_type);
+  if (entry == nullptr) return false;
+  return entry->is_runtime_ready();
 }
 
 std::vector<MPSolver::OptimizationProblemType>

ortools/linear_solver/linear_solver.h

@@ -152,6 +152,7 @@
 #include "absl/container/flat_hash_map.h"
 #include "absl/flags/declare.h"
 #include "absl/log/check.h"
+#include "absl/log/log.h"
 #include "absl/status/status.h"
 #include "absl/strings/str_format.h"
 #include "absl/strings/string_view.h"
@@ -1959,17 +1960,20 @@ class MPSolverInterfaceFactoryRepository {
  public:
   static MPSolverInterfaceFactoryRepository* GetInstance();
 
-  // Maps the given factory to the given problem type. If a factory was already
-  // assigned to this problem type, it will be replaced.
+  // Maps the given factory to the given problem type. For solver needing
+  // runtime checks an additional `is_runtime_ready` argument can be set. If
+  // a factory was already assigned to this problem type, it will be replaced.
   void Register(MPSolverInterfaceFactory factory,
-                MPSolver::OptimizationProblemType problem_type);
+                MPSolver::OptimizationProblemType problem_type,
+                std::function<bool()> is_runtime_ready = {});
 
-  // Invokes the factory associated to the given solver's problem type,
-  // or return NULL if no factory was found for it.
+  // Invokes the factory associated to the given solver's problem type and fails
+  // if no factory is registered or its runtime is not ready.
+  // Use `Supports` below to check if `Create` succeeds.
   MPSolverInterface* Create(MPSolver* solver) const;
 
   // Whether the implementation associated to the given problem type is
-  // available.
+  // available and ready to use.
   bool Supports(MPSolver::OptimizationProblemType problem_type) const;
 
   // List all the problem types.
@@ -1991,7 +1995,11 @@ class MPSolverInterfaceFactoryRepository {
   ~MPSolverInterfaceFactoryRepository();
 
   mutable absl::Mutex mutex_;
-  std::map<MPSolver::OptimizationProblemType, MPSolverInterfaceFactory> map_;
+  struct Entry {
+    MPSolverInterfaceFactory factory;
+    std::function<bool()> is_runtime_ready;
+  };
+  std::map<MPSolver::OptimizationProblemType, Entry> map_;
 };
 
 }  // namespace operations_research

ortools/linear_solver/xpress_interface.cc

@@ -2289,7 +2289,8 @@ namespace {
 const void* const kRegisterXpress ABSL_ATTRIBUTE_UNUSED = [] {
   MPSolverInterfaceFactoryRepository::GetInstance()->Register(
       [](MPSolver* const solver) { return new XpressInterface(solver, false); },
-      MPSolver::XPRESS_LINEAR_PROGRAMMING);
+      MPSolver::XPRESS_LINEAR_PROGRAMMING,
+      []() { return XpressIsCorrectlyInstalled(); });
   return nullptr;
 }();
 
@@ -2297,7 +2298,8 @@ const void* const kRegisterXpress ABSL_ATTRIBUTE_UNUSED = [] {
 const void* const kRegisterXpressMip ABSL_ATTRIBUTE_UNUSED = [] {
   MPSolverInterfaceFactoryRepository::GetInstance()->Register(
       [](MPSolver* const solver) { return new XpressInterface(solver, true); },
-      MPSolver::XPRESS_MIXED_INTEGER_PROGRAMMING);
+      MPSolver::XPRESS_MIXED_INTEGER_PROGRAMMING,
+      []() { return XpressIsCorrectlyInstalled(); });
   return nullptr;
 }();