Add a small cache for geometries built from WKT strings

This can be very expensive, so by caching them we can save a lot of time A quick benchtest using a delimited text layer with WKT strings for geometries: Before: average redraw time: 3338 ms After: average redraw time: 670 ms (Of course, this benefit assumes that all the layer's geometries can fit in the cache. But even when the cache is exhausted there's no noticable drop in performance)
qgis · Nov 15, 2021 · 87452aa · 87452aa
1 parent e0447a1
commit 87452aa
Showing 1 changed file with 14 additions and 6 deletions.
diff --git a/src/core/geometry/qgsgeometry.cpp b/src/core/geometry/qgsgeometry.cpp
@@ -18,6 +18,7 @@ email                : morb at ozemail dot com dot au
 #include <cstdio>
 #include <cmath>
 #include <nlohmann/json.hpp>
+#include <QCache>
 
 #include "qgis.h"
 #include "qgsgeometry.h"
@@ -53,6 +54,7 @@ email                : morb at ozemail dot com dot au
 #include "qgslinestring.h"
 #include "qgscircle.h"
 #include "qgscurve.h"
+#include "qgsreadwritelocker.h"
 
 struct QgsGeometryPrivate
 {
@@ -159,12 +161,18 @@ bool QgsGeometry::isNull() const
 
 QgsGeometry QgsGeometry::fromWkt( const QString &wkt )
 {
-  std::unique_ptr< QgsAbstractGeometry > geom = QgsGeometryFactory::geomFromWkt( wkt );
-  if ( !geom )
-  {
-    return QgsGeometry();
-  }
-  return QgsGeometry( std::move( geom ) );
+  static QCache< QString, QgsGeometry > sWktCache( 2000 ); // store up to 2000 geometries
+  static QReadWriteLock sCacheLock;
+
+  QgsReadWriteLocker lock( sCacheLock, QgsReadWriteLocker::Read );
+  if ( const QgsGeometry *cached = sWktCache.object( wkt ) )
+    return *cached;
+  lock.unlock();
+
+  const QgsGeometry result( QgsGeometryFactory::geomFromWkt( wkt ) );
+  lock.changeMode( QgsReadWriteLocker::Write );
+  sWktCache.insert( wkt, new QgsGeometry( result ), 1 );
+  return result;
 }
 
 QgsGeometry QgsGeometry::fromPointXY( const QgsPointXY &point )