[Fontconfig-bugs] [Bug 69845] New: race condition issue?

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=69845

          Priority: medium
            Bug ID: 69845
          Assignee: fontconfig-bugs at lists.freedesktop.org
           Summary: race condition issue?
        QA Contact: freedesktop at behdad.org
          Severity: normal
    Classification: Unclassified
                OS: All
          Reporter: akira at tagoh.org
          Hardware: Other
            Status: NEW
           Version: unspecified
         Component: fc-cache
           Product: fontconfig

There seems the kind of the race condition issue when updating the fontconfig
cache for directory. it is, somehow the directory cache is missing a directory
'a'  when creating a directory, installing a font and generating a cache.
That seems most likely to happen when installing OS newly.

I'm not quite sure the details and root-cause but the scenario what I can
imagine is:

1. installing 'a' font package
2. generating a cache for 'a'
3. installing 'b' font package at the same time
4. generating a cache for 'b'
5. somehow updating the parent directory cache from 'b' first
6. updating the parent directory cache from 'a'

If there are no 'b' directory when processing 'a', this might happens.

possible some idea to address this situation:
a) remember the time when starting to generate the cache and write it into the
cache. so if it's newer than one has, they can just stop to proceed.

b) when failed to lock the cache, restart the process from reading the
directory

any other idea?

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