[publican-list] QPaintDevice: Cannot destroy paint device that is being painted

[Jeff Fearn]

Hi, this warning just started appearing for some larger books. It's due 
to the number of file handles open hitting the default limit.

The number of files goes something like:

coverpage file + toc file + main file + ((footer file + header file) * 
pages main file is paginated too))

On Linux you can run `ulimit -n` to get the current limit.

So 1024 - 3 / 2 = 510.5

So assuming you have some file handles open for other things, at around 
500 pages this will start happening with the default file handle limit.

On some Linuxes you can run `ulimit -n 8192` to change the limit for the 
current shell. Handy for testing.

To make this permanent:

sudo vim /etc/security/limits.conf

Then add these two lines:

*                 soft    nofile          8192
*                 hard    nofile          8192

Save, and re-login for it to take effect.

FYI for packagers, the Brew/Koji limits are set to 8192 so this will not 
affect packages building.

Cheers, Jeff.

-- 
Jeff Fearn <jfearn at redhat.com>
Senior Software Engineer
Infrastructure Engineering & Development (AEU)
Red Hat Asia Pacific Pty Ltd
GPG: 0x0357E8F0