From 3cfed69f99cbb0c9a542cd0d68c745ced4f06a9e Mon Sep 17 00:00:00 2001
From: Daniel Baston <dbaston@gmail.com>
Date: Wed, 15 Feb 2023 21:12:56 -0500
Subject: [PATCH] PreparedLineString: Use thread-safe lazy init

---
 include/geos/geom/prep/PreparedLineString.h |  7 +++++--
 src/geom/prep/PreparedLineString.cpp        | 20 +++++++++++---------
 2 files changed, 16 insertions(+), 11 deletions(-)

diff --git a/include/geos/geom/prep/PreparedLineString.h b/include/geos/geom/prep/PreparedLineString.h
index 017e06e72f..3a9d2c4279 100644
--- a/include/geos/geom/prep/PreparedLineString.h
+++ b/include/geos/geom/prep/PreparedLineString.h
@@ -40,10 +40,13 @@ namespace prep { // geos::geom::prep
  */
 class PreparedLineString : public BasicPreparedGeometry {
 private:
-    std::unique_ptr<noding::FastSegmentSetIntersectionFinder> segIntFinder;
+    mutable std::unique_ptr<noding::FastSegmentSetIntersectionFinder> segIntFinder;
     mutable noding::SegmentString::ConstVect segStrings;
     mutable std::unique_ptr<operation::distance::IndexedFacetDistance> indexedDistance;
 
+    mutable std::once_flag segIntFinderFlag;
+    mutable std::once_flag indexedDistanceFlag;
+
 protected:
 public:
     PreparedLineString(const Geometry* geom)
@@ -54,7 +57,7 @@ class PreparedLineString : public BasicPreparedGeometry {
 
     ~PreparedLineString() override;
 
-    noding::FastSegmentSetIntersectionFinder* getIntersectionFinder();
+    noding::FastSegmentSetIntersectionFinder* getIntersectionFinder() const;
 
     bool intersects(const geom::Geometry* g) const override;
     std::unique_ptr<geom::CoordinateSequence> nearestPoints(const geom::Geometry* g) const override;
diff --git a/src/geom/prep/PreparedLineString.cpp b/src/geom/prep/PreparedLineString.cpp
index 819a42d6cb..2da0586137 100644
--- a/src/geom/prep/PreparedLineString.cpp
+++ b/src/geom/prep/PreparedLineString.cpp
@@ -27,6 +27,8 @@
 #include <geos/noding/FastSegmentSetIntersectionFinder.h>
 #include <geos/operation/distance/IndexedFacetDistance.h>
 
+#include <mutex>
+
 namespace geos {
 namespace geom { // geos.geom
 namespace prep { // geos.geom.prep
@@ -44,12 +46,12 @@ PreparedLineString::~PreparedLineString()
 }
 
 noding::FastSegmentSetIntersectionFinder*
-PreparedLineString::getIntersectionFinder()
+PreparedLineString::getIntersectionFinder() const
 {
-    if(! segIntFinder) {
+    std::call_once(segIntFinderFlag, [this]() {
         noding::SegmentStringUtil::extractSegmentStrings(&getGeometry(), segStrings);
-        segIntFinder.reset(new noding::FastSegmentSetIntersectionFinder(&segStrings));
-    }
+        segIntFinder = detail::make_unique<noding::FastSegmentSetIntersectionFinder>(&segStrings);
+    });
 
     return segIntFinder.get();
 }
@@ -68,12 +70,12 @@ PreparedLineString::intersects(const geom::Geometry* g) const
 
 /* public */
 operation::distance::IndexedFacetDistance*
-PreparedLineString::
-getIndexedFacetDistance() const
+PreparedLineString::getIndexedFacetDistance() const
 {
-    if(! indexedDistance ) {
-        indexedDistance.reset(new operation::distance::IndexedFacetDistance(&getGeometry()));
-    }
+    std::call_once(indexedDistanceFlag, [this]() {
+        indexedDistance = detail::make_unique<operation::distance::IndexedFacetDistance>(&getGeometry());
+    });
+
     return indexedDistance.get();
 }