QGIS3 implementation thread assertion failure

[ccrook]

QGIS3 implementation under development. Currently failing with
" ASSERT failure in QgsFeatureRenderer::renderFeature: "renderFeature called in a different thread - use a cloned renderer instead"

Looking at QgsFeatureRenderer code it appears this is caused by a two calls to QgsFeatureRenderer::startRender from different threads, or from a call to renderFeature without a corresponding call to startRender.

https://qgis.org/api/classQgsFeatureRenderer.html#af01839c584bf5fc58e259adaa318c0bd

Python plugin code for startRender is at:

https://github.com/ccrook/QGIS-VectorFieldRenderer-Plugin/blob/qgis3_wip/VectorFieldRenderer/VectorFieldRenderer.py#L412

The plugin does not override renderFeature, but does override startRender, stopRender, and symbolsForFeature.

Sample project attached below. Steps to reproduce are select test.csv layer, open properties/symbology
select VectorField renderer, set X attribute to dx and Y attribute to dy, then Ok.

Running gdb qgis.bin gives following abbreviated stack trace:

Fatal: ASSERT failure in QgsFeatureRenderer::renderFeature: "renderFeature called in a different thread - use a
 cloned renderer instead", file ../../src/core/symbology/qgsrenderer.cpp, line 121
QGIS died on signal -1Warning: QPainter::end: Painter not active, aborted
Stacktrace (piped through c++filt):
/usr/bin/qgis.bin(+0xca4d)[0x555555560a4d]
/usr/bin/qgis.bin(+0xcf5a)[0x555555560f5a]
/usr/lib/x86_64-linux-gnu/libQt5Core.so.5(+0x914c6)[0x7ffff4ae64c6]
/usr/lib/x86_64-linux-gnu/libQt5Core.so.5(QMessageLogger::warning(char const*, ...) const+0xac)[0x7ffff4ae728c]
/usr/lib/x86_64-linux-gnu/libQt5Gui.so.5(QPainter::end()+0x35e)[0x7ffff52635ee]
/usr/lib/libqgis_core.so.2.99.0(QgsSymbolLayerUtils::symbolPreviewPixmap(QgsSymbol*, QSize, int, QgsRenderConte
xt*)+0x167)[0x7ffff5f18955]
/usr/lib/libqgis_core.so.2.99.0(QgsSymbolLegendNode::minimumIconSize(QgsRenderContext*) const+0xd3)[0x7ffff5f92
f13]
/usr/lib/libqgis_core.so.2.99.0(QgsLayerTreeModel::invalidateLegendMapBasedData()+0x1b3)[0x7ffff5f87879]
/usr/lib/libqgis_core.so.2.99.0(+0x49044b)[0x7ffff5f9044b]
/usr/lib/libqgis_core.so.2.99.0(+0x48f747)[0x7ffff5f8f747]
/usr/lib/libqgis_core.so.2.99.0(+0x48df9f)[0x7ffff5f8df9f]
/usr/lib/x86_64-linux-gnu/libQt5Core.so.5(QMetaObject::activate(QObject*, int, int, void**)+0x66f)[0x7ffff4d09b
af]
/usr/lib/x86_64-linux-gnu/libQt5Core.so.5(QTimer::timerEvent(QTimerEvent*)+0x28)[0x7ffff4d165c8]
/usr/lib/x86_64-linux-gnu/libQt5Core.so.5(QObject::event(QEvent*)+0xa3)[0x7ffff4d0abb3]
/usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5(QApplicationPrivate::notify_helper(QObject*, QEvent*)+0x8c)[0x7fff
f55ce05c]
/usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5(QApplication::notify(QObject*, QEvent*)+0x256)[0x7ffff55d3516]
/usr/lib/libqgis_core.so.2.99.0(QgsApplication::notify(QObject*, QEvent*)+0x9b)[0x7ffff611b319]
/usr/lib/x86_64-linux-gnu/libQt5Core.so.5(QCoreApplication::notifyInternal(QObject*, QEvent*)+0xdb)[0x7ffff4cdb
38b]
/usr/lib/x86_64-linux-gnu/libQt5Core.so.5(QTimerInfoList::activateTimers()+0x52d)[0x7ffff4d305ed]
/usr/lib/x86_64-linux-gnu/libQt5Core.so.5(+0x2dbaf1)[0x7ffff4d30af1]
../../src/core/qgsmessagelog.cpp: 27: (logMessage) [695ms] 2018-02-11T23:26:03 Qt[1] QPainter::end: Painter not
 active, aborted
Warning: QPainter::end: Painter not active, aborted
Stacktrace (piped through c++filt):
/usr/bin/qgis.bin(+0xca4d)[0x555555560a4d]
/usr/bin/qgis.bin(+0xcf5a)[0x555555560f5a]
/usr/lib/x86_64-linux-gnu/libQt5Core.so.5(+0x914c6)[0x7ffff4ae64c6]
/usr/lib/x86_64-linux-gnu/libQt5Core.so.5(QMessageLogger::warning(char const*, ...) const+0xac)[0x7ffff4ae728c]
/usr/lib/x86_64-linux-gnu/libQt5Gui.so.5(QPainter::end()+0x35e)[0x7ffff52635ee]
/usr/lib/libqgis_core.so.2.99.0(QgsSymbolLayerUtils::symbolPreviewPixmap(QgsSymbol*, QSize, int, QgsRenderConte
xt*)+0x167)[0x7ffff5f18955]
/usr/lib/libqgis_core.so.2.99.0(QgsSymbolLegendNode::minimumIconSize(QgsRenderContext*) const+0xd3)[0x7ffff5f92
f13]
/usr/lib/libqgis_core.so.2.99.0(QgsLayerTreeModel::invalidateLegendMapBasedData()+0x1b3)[0x7ffff5f87879]
/usr/lib/libqgis_core.so.2.99.0(+0x49044b)[0x7ffff5f9044b]
/usr/lib/libqgis_core.so.2.99.0(+0x48f747)[0x7ffff5f8f747]
/usr/lib/libqgis_core.so.2.99.0(+0x48df9f)[0x7ffff5f8df9f]
/usr/lib/x86_64-linux-gnu/libQt5Core.so.5(QMetaObject::activate(QObject*, int, int, void**)+0x66f)[0x7ffff4d09b
af]
/usr/lib/x86_64-linux-gnu/libQt5Core.so.5(QTimer::timerEvent(QTimerEvent*)+0x28)[0x7ffff4d165c8]
/usr/lib/x86_64-linux-gnu/libQt5Core.so.5(QObject::event(QEvent*)+0xa3)[0x7ffff4d0abb3]
/usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5(QApplicationPrivate::notify_helper(QObject*, QEvent*)+0x8c)[0x7fff
f55ce05c]
/usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5(QApplication::notify(QObject*, QEvent*)+0x256)[0x7ffff55d3516]
/usr/lib/libqgis_core.so.2.99.0(QgsApplication::notify(QObject*, QEvent*)+0x9b)[0x7ffff611b319]
/usr/lib/x86_64-linux-gnu/libQt5Core.so.5(QCoreApplication::notifyInternal(QObject*, QEvent*)+0xdb)[0x7ffff4cdb
38b]
/usr/lib/x86_64-linux-gnu/libQt5Core.so.5(QTimerInfoList::activateTimers()+0x52d)[0x7ffff4d305ed]
/usr/lib/x86_64-linux-gnu/libQt5Core.so.5(+0x2dbaf1)[0x7ffff4d30af1]

Using ubuntu 16.04 nightly-ubuntugis .. details from About are

QGIS version	2.99.0-Master	QGIS code revision	779fe1a
Compiled against Qt	5.5.1	Running against Qt	5.5.1
Compiled against GDAL/OGR	2.2.2	Running against GDAL/OGR	2.2.2
Compiled against GEOS	3.5.1-CAPI-1.9.1	Running against GEOS	3.5.1-CAPI-1.9.1 r4246
PostgreSQL Client Version	9.5.2	SpatiaLite Version	4.3.0a
QWT Version	6.1.2	PROJ.4 Version	492
QScintilla2 Version	2.9.1	This copy of QGIS writes debugging output.

vectest.zip

[ccrook]

Resolved. Simple code bug of not including self in call to base class function :-(