[Qgis-developer] Multithread rendering with GRASS vectors crash

[Radim Blazek]

On Sun, Apr 27, 2014 at 1:14 PM, Martin Dobias <wonder.sk at gmail.com> wrote:
> On Wed, Apr 23, 2014 at 3:41 PM, Radim Blazek <radim.blazek at gmail.com> wrote:
>> 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.
>
> Actually it was a broader problem with any GRASS maps, I have found
> out that GRASS library is not reentrant and simply cannot be used from
> multiple threads.
>
>
>> What can be done Martin? Some conditional mutex? Can you fix that?
>
> Yes, a mutex should work - should be fixed in 40b20f. As a result, all
> access to GRASS from iterators is serialized.

Great, thank you.

Radim

> Cheers
> Martin