PreparedLineString: Use thread-safe lazy init

Author: dbaston

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;

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();
 }