Make sure random behavior is deterministic

Ensure random generator is seeded with same seed when inserting vertices to ensure deterministic behavior
artem-ogre · Nov 26, 2021 · cbd5cf3 · cbd5cf3
1 parent 1d12539
commit cbd5cf3
Show file tree

Hide file tree

Showing 2 changed files with 15 additions and 7 deletions.
diff --git a/CDT/include/CDT.h b/CDT/include/CDT.h
@@ -517,25 +517,33 @@ struct hash<CDT::V2d<T> >
 namespace CDT
 {
 
+namespace detail
+{
+
 #ifdef CDT_CXX11_IS_SUPPORTED
+
+static mt19937 randGenerator(9001);
 inline void shuffle_indices(std::vector<VertInd>& indices)
 {
-    static mt19937 g(9001);
-    std::shuffle(indices.begin(), indices.end(), g);
+    std::shuffle(indices.begin(), indices.end(), randGenerator);
 }
+
 #else
+
 inline size_t randomCDT(const size_t i)
 {
-    static mt19937 g(9001);
-    return g() % i;
+    return randGenerator() % i;
 }
 
 inline void shuffle_indices(std::vector<VertInd>& indices)
 {
     std::random_shuffle(indices.begin(), indices.end(), randomCDT);
 }
+
 #endif
 
+} // namespace detail
+
 //-----------------------
 // Triangulation methods
 //-----------------------
@@ -550,6 +558,7 @@ void Triangulation<T, TNearPointLocator>::insertVertices(
     TGetVertexCoordX getX,
     TGetVertexCoordY getY)
 {
+    detail::randGenerator.seed(9001); // ensure deterministic behavior
     if(vertices.empty())
     {
         addSuperTriangle(envelopBox<T>(first, last, getX, getY));
@@ -573,7 +582,7 @@ void Triangulation<T, TNearPointLocator>::insertVertices(
         VertInd value = nExistingVerts;
         for(Iter it = ii.begin(); it != ii.end(); ++it, ++value)
             *it = value;
-        shuffle_indices(ii);
+        detail::shuffle_indices(ii);
         for(Iter it = ii.begin(); it != ii.end(); ++it)
             insertVertex(*it);
         break;

diff --git a/CDT/include/CDT.hpp b/CDT/include/CDT.hpp
@@ -21,7 +21,6 @@ typedef std::deque<TriInd> TriDeque;
 
 namespace detail
 {
-static mt19937 randGen(9001);
 
 /// Needed for c++03 compatibility (no uniform initialization available)
 template <typename T>
@@ -659,7 +658,7 @@ TriInd Triangulation<T, TNearPointLocator>::walkTriangles(
         const Triangle& t = triangles[currTri];
         found = true;
         // stochastic offset to randomize which edge we check first
-        const Index offset(detail::randGen() % 3);
+        const Index offset(detail::randGenerator() % 3);
         for(Index i_(0); i_ < Index(3); ++i_)
         {
             const Index i((i_ + offset) % 3);