Ok after reading
https://docs.qgis.org/3.28/en/docs/pyqgis_developer_cookbook/tasks.html again,
reading the warning:
"Any background task (regardless of how it is created) must NEVER use any QObject
that lives on the main thread, such as accessing QgsVectorLayer, QgsProject or perform
any GUI based operations like creating new widgets or interacting with existing widgets.
Qt widgets must only be accessed or modified from the main thread. Data that is used in a
task must be copied before the task is started. Attempting to use them from background
threads will result in crashes."
Seems to make it pretty clear :-(
Before rereading that, I even tried to pass a QgsMeshLayer-'reference' to the
QgsTask, but that did not work either.
I think I must conclude that I just have to wait for the load... :-)
Regards,
Richard Duivenvoorde
On 2/8/23 21:40, Richard Duivenvoorde via QGIS-Developer wrote:
Hi,
Having to juggle with rather large/long loading netcdf files, I thought to off
load the loading to a QgsTask, so while the netcdf was loaded user could do
other things...
But I get "...is run from a different thread than the object lives in ..."
warnings.
In short:
def run(self) -> bool:
log.info(f'LOADING... {self.netcdf_file}')
try:
self.layer = QgsMeshLayer(self.netcdf_file,
'PythonLoadedMeshLayer', 'mdal')
....
BUT: while it looks like all is fine, I get a Qt warning in my messages, and on
my terminal I get:
[INFO] (Dummy-1 ) LOADING... /tmp/kees/aoi/aoi1/areaOfInterest1.nc
Warning: fileName (/home/richard/git/qgis/src/core/project/qgsproject.cpp:812)
is run from a different thread than the object lives in [0x5593004f1aa0 vs
0x5592ff7e6440]
Stacktrace (piped through c++filt):
/home/richard/bin/qgis_/master/debug/bin/qgis(+0xe26a)[0x5592fe9ba26a]
/home/richard/bin/qgis_/master/debug/bin/qgis(+0xea29)[0x5592fe9baa29]
/lib/x86_64-linux-gnu/libQt5Core.so.5(+0xc3b50)[0x7fc594ec3b50]
/lib/x86_64-linux-gnu/libQt5Core.so.5(qt_message_output(QtMsgType, QMessageLogContext
const&, QString const&)+0xd)[0x7fc594ec50fd]
/lib/x86_64-linux-gnu/libQt5Core.so.5(QDebug::~QDebug()+0x68)[0x7fc594fc6fa8]
/home/richard/bin/qgis_/master/debug/lib/libqgis_core.so.3.29.0(QgsProject::fileName()
const+0x267)[0x7fc592f1af2f]
/home/richard/bin/qgis_/master/debug/lib/libqgis_core.so.3.29.0(QgsMapLayer::loadNamedProperty(QString
const&, QgsMapLayer::PropertyType, bool&,
QFlags<QgsMapLayer::StyleCategory>)+0x752)[0x7fc592a215c0]
/home/richard/bin/qgis_/master/debug/lib/libqgis_core.so.3.29.0(QgsMapLayer::loadNamedStyle(QString
const&, bool&, QFlags<QgsMapLayer::StyleCategory>)+0x2b1)[0x7fc592a20b8f]
/home/richard/bin/qgis_/master/debug/lib/libqgis_core.so.3.29.0(QgsMapLayer::loadDefaultStyle(bool&)+0x2dc)[0x7fc592a1f6ec]
/home/richard/bin/qgis_/master/debug/lib/libqgis_core.so.3.29.0(QgsMeshLayer::loadDefaultStyle(bool&)+0x685)[0x7fc5930a84bb]
/home/richard/bin/qgis_/master/debug/lib/libqgis_core.so.3.29.0(QgsMeshLayer::QgsMeshLayer(QString
const&, QString const&, QString const&, QgsMeshLayer::LayerOptions
const&)+0x2b9)[0x7fc5930a5ab1]
/home/richard/bin/qgis_/master/debug/share/qgis/python/qgis/_core.so(sipQgsMeshLayer::sipQgsMeshLayer(QString
const&, QString const&, QString const&, QgsMeshLayer::LayerOptions
const&)+0x3b)[0x7fc43040b9c7]
/home/richard/bin/qgis_/master/debug/share/qgis/python/qgis/_core.so(+0x121a0bc)[0x7fc43041a0bc]
/usr/lib/python3/dist-packages/PyQt5/sip.cpython-311-x86_64-linux-gnu.so(+0x19f60)[0x7fc4dc271f60]
/lib/x86_64-linux-gnu/libpython3.11.so.1.0(+0x1e02fe)[0x7fc47a5e02fe]
/lib/x86_64-linux-gnu/libpython3.11.so.1.0(_PyObject_MakeTpCall+0x7d)[0x7fc47a57baed]
/lib/x86_64-linux-gnu/libpython3.11.so.1.0(_PyEval_EvalFrameDefault+0x4a63)[0x7fc47a509c63]
/lib/x86_64-linux-gnu/libpython3.11.so.1.0(+0x26a6da)[0x7fc47a66a6da]
/lib/x86_64-linux-gnu/libpython3.11.so.1.0(+0x17f30c)[0x7fc47a57f30c]
/usr/lib/python3/dist-packages/PyQt5/sip.cpython-311-x86_64-linux-gnu.so(+0x1196c)[0x7fc4dc26996c]
[INFO] (MainThread) finished OK
My Questions:
- should I NOT do this?
- or is the loading/construction of a QgsMeshLayer having pointers to places it
should not?
(mmm loading a QgsVectorLayer (shape via ogr) also results in about the same
warnings...
so next question: is there another way to load these large netcdf's without
blocking QGIS ?)
Thanks for any info.
Regards,
Richard Duivenvoorde
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