[Qgis-developer] Multithread rendering with GRASS vectors crash

[Radim Blazek]

Multithread rendering crashes if multiple GRASS vector layers from the
same map are rendered simultaneously. It is mentioned in #9980.

That happens because to save resources, the GRASS vector provider
keeps only single instance of each opened vector map in static
QgsGrassProvider::mMaps. I am not sure if the crash comes from GRASS
lib or from the provider. Parallel rendering of layers from different
maps works OK. It means that only one layer from a map may be rendered
at time but parallel rendering of multiple layers from different maps
is desired.

What can be done Martin? Some conditional mutex? Can you fix that?

Radim