[bugfix][LimitPass] Store models and numflux as objects.

dune/fem-dg/operator/fv/fvoperator.hh

@@ -193,8 +193,9 @@ namespace detail
                        std::integral_constant<bool, value> higherOrder ) const;
 
     const DiscreteFunctionSpaceType& space_;
-    const ModelType    &model_;
-    const NumFluxType  &numFlux_;
+    // copy model and numFlux for thread safety
+    ModelType    model_;
+    NumFluxType  numFlux_;
     double time_;
     mutable double dtEst_;
 

dune/fem-dg/operator/limiter/limitpass.hh

@@ -366,7 +366,7 @@ namespace Fem
      *  \param  vQ         order of volume quadrature
      *  \param  fQ         order of face quadrature
      */
-    LimitDGPass(DiscreteModelType& problem,
+    LimitDGPass(const DiscreteModelType& problem,
                 PreviousPassType& pass,
                 const DiscreteFunctionSpaceType& spc,
                 const int vQ = -1,
@@ -386,7 +386,7 @@ namespace Fem
      *  \param  fQ         order of face quadrature
      */
 
-    LimitDGPass(DiscreteModelType& problem,
+    LimitDGPass(const DiscreteModelType& problem,
                 PreviousPassType& pass,
                 const DiscreteFunctionSpaceType& spc,
                 const Dune::Fem::ParameterReader &parameter = Dune::Fem::Parameter::container(),
@@ -1825,7 +1825,7 @@ namespace Fem
 
   private:
     mutable std::unique_ptr< DiscreteModelCallerType > caller_;
-    DiscreteModelType& discreteModel_;
+    mutable DiscreteModelType discreteModel_;
     mutable double currentTime_;
 
     mutable ArgumentType* arg_;