[Qgis-user] excessive threads?

[Greg Troxel]

"Johannes Kröger (WhereGroup) via Qgis-user" <qgis-user at lists.osgeo.org>
writes:

> Am 31.07.22 um 18:11 schrieb Mike Stanton via Qgis-user:
>>
>> It all depends on the module you are running and whether it
>> effectively uses the “-multi” option with “all_available_cores” and
>> of course how many cores are available on your system.
>>
> I think there is some confusion here. Greg, can you confirm that you
> are talking about QGIS' thread usage "at rest", so when a project is
> open and browsed but not while you are running an analysis or data
> processing tool? That is how I understand your question.

Yes, at rest.  I have a project with a lot of layers.  Many of them are
just gpx files - basically raw data from surveying.  I have a bunch of
geopackage layers where I store processed observations and my current
map data, and then various basemap stuff.

I don't do a lot of heavy analysis/processing.  It's mostly
editing/curating this data and occasional pdf map production.

I had this project open on a different desktop after having looked at
something (might have opened to ask what is the distance from point x to
point y) and just didn't close it.  Just idling in display mode.  I
hadn't touched it in hours.

Then I had some other program hit the (wrongly too low, not the point)
limit, and on investigation found far more threads than I expected.

If I only had N threads, for N = 4 * hw.ncpu, I would not have even
thought about writing.  But I had 157 on a 4-core machine.

> I could imagine that QGIS uses at least one thread per data source.

Maybe, but it seems like if it reads a gpx and doesn't intend to reread
it that thread should be joined.

I opened a very small project, with just an OSM basemap (TMS) and a tiff
(from the georeferencer in an earlier session), and had only 16.  I
added a few geopackage layers and the count bounced around a little and
settled at 9.  I added a few jp2 tiles and also that settled down.

But when I zoomed to a tile, it changed to 16.

So it seems .jp2 tiles, when displayed (when in viewport?) provoke
thread usage -- but I really mean 'seems' so far.

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