Add threadsafe method to get featuresource from layer

Author: m-kuhn

src/core/qgsvectorlayerutils.cpp

@@ -498,6 +498,34 @@ QgsFeature QgsVectorLayerUtils::duplicateFeature( QgsVectorLayer *layer, const Q
   return newFeature;
 }
 
+std::unique_ptr<QgsVectorLayerFeatureSource> QgsVectorLayerUtils::getFeatureSource( QWeakPointer<QgsVectorLayer> layer )
+{
+  std::unique_ptr<QgsVectorLayerFeatureSource> featureSource;
+
+  auto getFeatureSource = [ layer, &featureSource ]
+  {
+    QgsVectorLayer *lyr = layer.data();
+
+    if ( lyr )
+    {
+      featureSource.reset( new QgsVectorLayerFeatureSource( lyr ) );
+    }
+  };
+
+#if QT_VERSION >= QT_VERSION_CHECK( 5, 10, 0 )
+  // Make sure we only deal with the vector layer on the main thread where it lives.
+  // Anything else risks a crash.
+  if ( QThread::currentThread() == qApp->thread() )
+    getFeatureSource();
+  else
+    QMetaObject::invokeMethod( qApp, getFeatureSource, Qt::BlockingQueuedConnection );
+#else
+  getFeatureSource();
+#endif
+
+  return featureSource;
+}
+
 QList<QgsVectorLayer *> QgsVectorLayerUtils::QgsDuplicateFeatureContext::layers() const
 {
   QList<QgsVectorLayer *> layers;

src/core/qgsvectorlayerutils.h

@@ -19,6 +19,7 @@
 #include "qgis_core.h"
 #include "qgsvectorlayer.h"
 #include "qgsgeometry.h"
+#include "qgsvectorlayerfeatureiterator.h"
 
 /**
  * \ingroup core
@@ -155,6 +156,17 @@ class CORE_EXPORT QgsVectorLayerUtils
      */
     static QgsFeature duplicateFeature( QgsVectorLayer *layer, const QgsFeature &feature, QgsProject *project, int depth, QgsDuplicateFeatureContext &duplicateFeatureContext SIP_OUT );
 
+    /**
+     * Gets the feature source from a weak QgsVectorLayer pointer.
+     * This method is thread-safe but will block the main thread for execution. Executing it from the main
+     * thread is safe too.
+     * This should be used in scenarios, where a ``QWeakPointer<QgsVectorLayer>`` is kept in a thread
+     * and features should be fetched from this layer. Using the layer directly is not safe to do.
+     *
+     * \note Requires Qt >= 5.10 to make use of the thread-safe implementation
+     * \since QGIS 3.4
+     */
+    static std::unique_ptr<QgsVectorLayerFeatureSource> getFeatureSource( QWeakPointer<QgsVectorLayer> layer ) SIP_SKIP;
 };