From c6b7908499ae33adca68b25d8b11b59ba581379c Mon Sep 17 00:00:00 2001
From: Matthias Koefferlein <matthias@klayout.de>
Date: Sat, 19 Aug 2023 01:55:04 +0200
Subject: [PATCH] Triangles: Memory optimization

---
 src/db/db/dbTriangle.h   |  3 ++-
 src/db/db/dbTriangles.cc | 29 +++++++++++++++++++++--------
 src/db/db/dbTriangles.h  |  5 +++--
 3 files changed, 26 insertions(+), 11 deletions(-)

diff --git a/src/db/db/dbTriangle.h b/src/db/db/dbTriangle.h
index d2966509d..20afe1097 100644
--- a/src/db/db/dbTriangle.h
+++ b/src/db/db/dbTriangle.h
@@ -30,6 +30,7 @@
 #include "dbEdge.h"
 
 #include "tlObjectCollection.h"
+#include "tlList.h"
 
 namespace db
 {
@@ -428,7 +429,7 @@ struct TriangleEdgeLessFunc
  *  @brief A class representing a triangle
  */
 class DB_PUBLIC Triangle
-  : public tl::Object
+  : public tl::list_node<Triangle>, public tl::Object
 {
 public:
   Triangle ();
diff --git a/src/db/db/dbTriangles.cc b/src/db/db/dbTriangles.cc
index 11f713abf..0e717923e 100644
--- a/src/db/db/dbTriangles.cc
+++ b/src/db/db/dbTriangles.cc
@@ -42,7 +42,7 @@ Triangles::Triangles ()
 Triangles::~Triangles ()
 {
   while (! mp_triangles.empty ()) {
-    remove (mp_triangles.front ());
+    remove (mp_triangles.begin ().operator-> ());
   }
 }
 
@@ -63,10 +63,20 @@ Triangles::create_vertex (const db::DPoint &pt)
 db::TriangleEdge *
 Triangles::create_edge (db::Vertex *v1, db::Vertex *v2)
 {
-  m_edges_heap.push_back (db::TriangleEdge (v1, v2));
-  m_edges_heap.back ().link ();
-  m_edges_heap.back ().set_id (++m_id);
-  return &m_edges_heap.back ();
+  db::TriangleEdge *edge = 0;
+
+  if (! m_returned_edges.empty ()) {
+    edge = m_returned_edges.back ();
+    m_returned_edges.pop_back ();
+    *edge = db::TriangleEdge (v1, v2);
+  } else {
+    m_edges_heap.push_back (db::TriangleEdge (v1, v2));
+    edge = &m_edges_heap.back ();
+  }
+
+  edge->link ();
+  edge->set_id (++m_id);
+  return edge;
 }
 
 db::Triangle *
@@ -90,8 +100,10 @@ Triangles::remove (db::Triangle *tri)
 
   //  clean up edges we do no longer need
   for (int i = 0; i < 3; ++i) {
-    if (edges [i] && edges [i]->left () == 0 && edges [i]->right () == 0) {
-      edges [i]->unlink ();
+    db::TriangleEdge *e = edges [i];
+    if (e && e->left () == 0 && e->right () == 0 && e->v1 ()) {
+      e->unlink ();
+      m_returned_edges.push_back (e);
     }
   }
 }
@@ -392,7 +404,7 @@ Triangles::find_closest_edge (const db::DPoint &p, db::Vertex *vstart, bool insi
       //  A sample heuristics that takes a sqrt(N) sample from the
       //  vertexes to find a good starting point
 
-      vstart = mp_triangles.front ()->vertex (0);
+      vstart = mp_triangles.begin ()->vertex (0);
       double dmin = vstart->distance (p);
 
       while (ls * ls < m) {
@@ -1381,6 +1393,7 @@ Triangles::clear ()
   m_edges_heap.clear ();
   mp_triangles.clear ();
   m_vertex_heap.clear ();
+  m_returned_edges.clear ();
   m_is_constrained = false;
   m_level = 0;
   m_id = 0;
diff --git a/src/db/db/dbTriangles.h b/src/db/db/dbTriangles.h
index bb085fbd8..c0271b635 100644
--- a/src/db/db/dbTriangles.h
+++ b/src/db/db/dbTriangles.h
@@ -77,7 +77,7 @@ public:
     int base_verbosity;
   };
 
-  typedef tl::shared_collection<db::Triangle> triangles_type;
+  typedef tl::list<db::Triangle> triangles_type;
   typedef triangles_type::const_iterator triangle_iterator;
 
   Triangles ();
@@ -252,8 +252,9 @@ public:
   std::vector<db::Vertex *> find_inside_circle (const db::DPoint &center, double radius) const;
 
 private:
-  tl::shared_collection<db::Triangle> mp_triangles;
+  tl::list<db::Triangle> mp_triangles;
   tl::stable_vector<db::TriangleEdge> m_edges_heap;
+  std::vector<db::TriangleEdge *> m_returned_edges;
   tl::stable_vector<db::Vertex> m_vertex_heap;
   bool m_is_constrained;
   size_t m_level;