[Octave-bug-tracker] [bug #45458] Plot does not work and freeze

[Philipp Mengs]

Follow-up Comment #36, bug #45458 (project octave):

*Possible Fix*: modify fc_update bat to delete the cache folder, then call
fc-cache.
Implementation: add "@del /Q /S %LOCALAPPDATA%\fontconfig\cache\" after "@echo
off"

Explanation: fc_update.bat calls fc-cache.exe. fc-cache creates and deletes
several temporary files, like "$long_hex_string.cache-7.LCK" or
"$long_hex_string.cache-7.NEW". If fc-cache is killed before it can delete
these temporary files then these files will persist and fc-cache fails the
next time it is executed and tries to create these files.

How to test:
0 Modify a font file, e.g. by renaming it, to force fc-cache to rescan the
directories.
0 run fc_update.bat -> it should now take some time to complete.
0 cancel the operation as soon as a .NEW file is created in
%LOCALAPPDATA%\fontconfig\cache\. There should now be a .NEW file in the
directory.
0 rerun fc_update.bat -> it will now take some time before it fails. The .NEW
file remains in the directory.
0 manually delete all files inside the %LOCALAPPDATA%\fontconfig\cache
directory and rerun fc_update.bat -> it should now take some time to complete
successfully. There should now be a .cache-7 file inside the directory (and a
CACHEFILE.TAG).

Octave must be closed before running fc_update, otherwise the font cache
cannot be updated (error: permission denied).

For additional debug info from fc-cache.exe: setting the environment variable
FC_DEBUG to 16 prints info about the cache files written (see
https://www.freedesktop.org/software/fontconfig/fontconfig-user.html)

This is basically a fontconfig bug and not an octave bug, but the above
workaround should fix it. The fix breaks if the fontconfig cache directory
changes.
I assume that this bug resurfaces when a font gets added to the system (when
other software gets installed) and fc-update is killed at an unfortunate time.

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