creating pngs in background mode leaks (much less) memory

[danlipsa]

This is a continuation of
#1397
While our VTK fix improved the leak considerably (from 500 MB to 6MB for 500 iterations) there is still a memory increase. It is possible that certain resources are still leaked.
More investigation is required to create a test that pinpoints the problem.

Here is the test program I used on linux:
png-memory.zip

[danlipsa]

@aashish24 @doutriaux1 I created this follow-up issue if we want to dig more into this.

[durack1]

@danlipsa I think this should be reviewed alongside #1424 as the problems may be linked. I'm just running my #1424 test script against 2.6.0 and it seems there are still quite a number of problems remaining.. @chaosphere2112 pinging you here

[chaosphere2112]

#1424 will remain unresolved for now, I wasn't able to get a pull request in before the release. I'll try and get something together shortly so it can go into nightly builds. For the present, I'd recommend just using the "donotstoredisplay" argument.

[chengzhuzhang]

Hi Charles @charlesdoutriaux ,

Here is our repo for acme_diags:
https://github.com/zshaheen/acme_diags
Here is the documentation to run the package on aims4:

https://github.com/zshaheen/acme_diags/blob/master/docs/quick-guide-aims4.ipynb
make sure in myparams.py, set backend = 'vcs'

If you do below (which create a lot of pngs)
set5_driver.py -p myparams.py

Process gets slower and slower. No problem for cartopy backend...

Also we have this libGL error when testing on aims4.
@zshaheen

[durack1]

@chengzhuzhang does your behavior look similar to #1424 (comment)? So you get a progressive slow down after each loop step?

Oh and @doutriaux1 is the best github handle for Chucky (@charlesdoutriaux is his personal/non-work handle)

[zshaheen]

@chengzhuzhang I'm fairly sure we're getting the libGL error b/c we aren't using vcs-nox. I'll try with that and we'll see what's good. It gets slow b/c of the libGL error, vcs in and of itself isn't causing that.

@doutriaux1 No need to run it. If we're still getting errors, we'll let you know.

[chengzhuzhang]

@durack1 Thank you for the hint in poking Chucky :)
We will update here if vcs-nox can fix the libGL and the slowness.