From: Wolfgang Bangerth <bangerth@colostate.edu>
Date: Tue, 31 Aug 2021 17:21:52 +0000 (-0600)
Subject: Make some static local variables mutable members.
X-Git-Tag: v9.4.0-rc1~1013^2
X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=c0998ed3890b9d5cd0397d0986581d4d8e54c228;p=dealii.git

Make some static local variables mutable members.
---

diff --git a/include/deal.II/base/polynomials_raviart_thomas.h b/include/deal.II/base/polynomials_raviart_thomas.h
index a5b6c8fe30..6553972587 100644
--- a/include/deal.II/base/polynomials_raviart_thomas.h
+++ b/include/deal.II/base/polynomials_raviart_thomas.h
@@ -27,8 +27,10 @@
 #include <deal.II/base/tensor_polynomials_base.h>
 #include <deal.II/base/tensor_product_polynomials.h>
 
+#include <mutex>
 #include <vector>
 
+
 DEAL_II_NAMESPACE_OPEN
 
 /**
@@ -58,6 +60,11 @@ public:
    */
   PolynomialsRaviartThomas(const unsigned int k);
 
+  /**
+   * Copy constructor.
+   */
+  PolynomialsRaviartThomas(const PolynomialsRaviartThomas &other);
+
   /**
    * Compute the value and the first and second derivatives of each Raviart-
    * Thomas polynomial at @p unit_point.
@@ -111,9 +118,28 @@ private:
    */
   static std::vector<std::vector<Polynomials::Polynomial<double>>>
   create_polynomials(const unsigned int k);
+
+  /**
+   * A mutex with which to guard access to the following `mutable`
+   * variables.
+   */
+  mutable std::mutex scratch_arrays_mutex;
+
+  /**
+   * The following arrays are used as scratch data in the evaluate() function.
+   * Since that function is `const`, they have to be marked as `mutable`, and
+   * since we want that function to be thread-safe, access to these scratch
+   * arrays is guarded by the mutex above.
+   */
+  mutable std::vector<double>         scratch_values;
+  mutable std::vector<Tensor<1, dim>> scratch_grads;
+  mutable std::vector<Tensor<2, dim>> scratch_grad_grads;
+  mutable std::vector<Tensor<3, dim>> scratch_third_derivatives;
+  mutable std::vector<Tensor<4, dim>> scratch_fourth_derivatives;
 };
 
 
+
 template <int dim>
 inline std::string
 PolynomialsRaviartThomas<dim>::name() const
diff --git a/source/base/polynomials_raviart_thomas.cc b/source/base/polynomials_raviart_thomas.cc
index ddf589a918..48db5aac6d 100644
--- a/source/base/polynomials_raviart_thomas.cc
+++ b/source/base/polynomials_raviart_thomas.cc
@@ -42,6 +42,16 @@ PolynomialsRaviartThomas<dim>::PolynomialsRaviartThomas(const unsigned int k)
 
 
 
+template <int dim>
+PolynomialsRaviartThomas<dim>::PolynomialsRaviartThomas(
+  const PolynomialsRaviartThomas &other)
+  : TensorPolynomialsBase<dim>(other)
+  , polynomial_space(other.polynomial_space)
+// no need to copy the scratch data, or the mutex
+{}
+
+
+
 template <int dim>
 std::vector<std::vector<Polynomials::Polynomial<double>>>
 PolynomialsRaviartThomas<dim>::create_polynomials(const unsigned int k)
@@ -80,6 +90,7 @@ PolynomialsRaviartThomas<dim>::create_polynomials(const unsigned int k)
 }
 
 
+
 template <int dim>
 void
 PolynomialsRaviartThomas<dim>::evaluate(
@@ -102,34 +113,19 @@ PolynomialsRaviartThomas<dim>::evaluate(
            fourth_derivatives.size() == 0,
          ExcDimensionMismatch(fourth_derivatives.size(), this->n()));
 
-  // have a few scratch
-  // arrays. because we don't want to
-  // re-allocate them every time this
-  // function is called, we make them
-  // static. however, in return we
-  // have to ensure that the calls to
-  // the use of these variables is
-  // locked with a mutex. if the
-  // mutex is removed, several tests
-  // (notably
-  // deal.II/create_mass_matrix_05)
-  // will start to produce random
-  // results in multithread mode
-  static std::mutex           mutex;
-  std::lock_guard<std::mutex> lock(mutex);
-
-  static std::vector<double>         p_values;
-  static std::vector<Tensor<1, dim>> p_grads;
-  static std::vector<Tensor<2, dim>> p_grad_grads;
-  static std::vector<Tensor<3, dim>> p_third_derivatives;
-  static std::vector<Tensor<4, dim>> p_fourth_derivatives;
+  // In the following, we will access the scratch arrays declared as 'mutable'
+  // in the class. In order to do so from this function, we have to make sure
+  // that we guard this access by a mutex so that the invokation of this 'const'
+  // function is thread-safe.
+  std::lock_guard<std::mutex> lock(scratch_arrays_mutex);
 
   const unsigned int n_sub = polynomial_space.n();
-  p_values.resize((values.size() == 0) ? 0 : n_sub);
-  p_grads.resize((grads.size() == 0) ? 0 : n_sub);
-  p_grad_grads.resize((grad_grads.size() == 0) ? 0 : n_sub);
-  p_third_derivatives.resize((third_derivatives.size() == 0) ? 0 : n_sub);
-  p_fourth_derivatives.resize((fourth_derivatives.size() == 0) ? 0 : n_sub);
+  scratch_values.resize((values.size() == 0) ? 0 : n_sub);
+  scratch_grads.resize((grads.size() == 0) ? 0 : n_sub);
+  scratch_grad_grads.resize((grad_grads.size() == 0) ? 0 : n_sub);
+  scratch_third_derivatives.resize((third_derivatives.size() == 0) ? 0 : n_sub);
+  scratch_fourth_derivatives.resize((fourth_derivatives.size() == 0) ? 0 :
+                                                                       n_sub);
 
   for (unsigned int d = 0; d < dim; ++d)
     {
@@ -149,34 +145,34 @@ PolynomialsRaviartThomas<dim>::evaluate(
         p(c) = unit_point((c + d) % dim);
 
       polynomial_space.evaluate(p,
-                                p_values,
-                                p_grads,
-                                p_grad_grads,
-                                p_third_derivatives,
-                                p_fourth_derivatives);
+                                scratch_values,
+                                scratch_grads,
+                                scratch_grad_grads,
+                                scratch_third_derivatives,
+                                scratch_fourth_derivatives);
 
-      for (unsigned int i = 0; i < p_values.size(); ++i)
-        values[i + d * n_sub][d] = p_values[i];
+      for (unsigned int i = 0; i < scratch_values.size(); ++i)
+        values[i + d * n_sub][d] = scratch_values[i];
 
-      for (unsigned int i = 0; i < p_grads.size(); ++i)
+      for (unsigned int i = 0; i < scratch_grads.size(); ++i)
         for (unsigned int d1 = 0; d1 < dim; ++d1)
-          grads[i + d * n_sub][d][(d1 + d) % dim] = p_grads[i][d1];
+          grads[i + d * n_sub][d][(d1 + d) % dim] = scratch_grads[i][d1];
 
-      for (unsigned int i = 0; i < p_grad_grads.size(); ++i)
+      for (unsigned int i = 0; i < scratch_grad_grads.size(); ++i)
         for (unsigned int d1 = 0; d1 < dim; ++d1)
           for (unsigned int d2 = 0; d2 < dim; ++d2)
             grad_grads[i + d * n_sub][d][(d1 + d) % dim][(d2 + d) % dim] =
-              p_grad_grads[i][d1][d2];
+              scratch_grad_grads[i][d1][d2];
 
-      for (unsigned int i = 0; i < p_third_derivatives.size(); ++i)
+      for (unsigned int i = 0; i < scratch_third_derivatives.size(); ++i)
         for (unsigned int d1 = 0; d1 < dim; ++d1)
           for (unsigned int d2 = 0; d2 < dim; ++d2)
             for (unsigned int d3 = 0; d3 < dim; ++d3)
               third_derivatives[i + d * n_sub][d][(d1 + d) % dim]
                                [(d2 + d) % dim][(d3 + d) % dim] =
-                                 p_third_derivatives[i][d1][d2][d3];
+                                 scratch_third_derivatives[i][d1][d2][d3];
 
-      for (unsigned int i = 0; i < p_fourth_derivatives.size(); ++i)
+      for (unsigned int i = 0; i < scratch_fourth_derivatives.size(); ++i)
         for (unsigned int d1 = 0; d1 < dim; ++d1)
           for (unsigned int d2 = 0; d2 < dim; ++d2)
             for (unsigned int d3 = 0; d3 < dim; ++d3)
@@ -184,7 +180,8 @@ PolynomialsRaviartThomas<dim>::evaluate(
                 fourth_derivatives[i + d * n_sub][d][(d1 + d) % dim]
                                   [(d2 + d) % dim][(d3 + d) % dim]
                                   [(d4 + d) % dim] =
-                                    p_fourth_derivatives[i][d1][d2][d3][d4];
+                                    scratch_fourth_derivatives[i][d1][d2][d3]
+                                                              [d4];
     }
 }