[Qgis-developer] Status of the multi-threaded rendering project

[Martin Dobias]

Hi everyone

As the feature freeze is approaching, I guess this is the right time
for an update about the progress of multi-threded rendering.

Since the last status update in December I have continued with the
implementation, adding support for more data providers, fixing bugs
and re-enabling features I disabled during the implementation [1]. The
code is in a state where it is quite ready for the merge to master and
I am satisfied with the outcome so far. Still, I believe it will be
better not to rush into the merge now for 2.2 and then run into
problems close to the release (or after!). Don't get me wrong - it
works well for me and for the other few brave souls who helped with
testing - but given the amount of changes it is likely that some
problems will appear sooner or later... git diff statistics say: 315
files changed, 13808 insertions(+), 9321 deletions(-).

So, I suggest that we merge the threading branch as soon as the
feature freeze will be lifted again, so we will have plenty of time
until 2.4 release (4 months) for fixing problems that may appear.

To get an idea of what is still missing, here's is my brief to-do list:
- merge from master and resolve any conflicts (mainly geometry simplification)
- update data providers (so that they work again):
  - mssql (Nathan has kindly volunteered to get it done)
  - sqlanywhere (needs to be done by folks who contributed it)
- (nice to have) - ability to cancel raster block requests. Otherwise,
rendering of raster layers may make the GUI unresponsive until they
finish. GDAL currently does not support that either, so this may need
also contributing to GDAL, otherwise only native raster providers
(wms, wcs, grass) would benefit from that

I would appreciate your observations from the testing!

Regards
Martin

[1] https://github.com/wonder-sk/QGIS/commits/threading-revival