Sascha Vogt created FELIX-6515:
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Summary: File install race condition leads to empty config files
Key: FELIX-6515
URL: https://issues.apache.org/jira/browse/FELIX-6515
Project: Felix
Issue Type: Bug
Components: File Install
Affects Versions: fileinstall-3.7.4
Reporter: Sascha Vogt
We discovered an ugly race condition within Felix Fileinstall together with the
Config Admin.
ConfigInstaller opens the existing config file in a new writer, basically
emptying out the file on disk
(https://github.com/apache/felix-dev/blob/master/fileinstall/src/main/java/org/apache/felix/fileinstall/internal/ConfigInstaller.java#L285)
- If at the same time file install reads the file during it's regular poll
interval, it will read an empty file. That leads to a new config admin "update"
event where the config is empty. Now the first update finishes writing the
config to disk and then the second event gets processed in the ConfigInstaller,
which then detects all keys need to be removed.
This then leads to configs which are empty besides the first comment header in
the existing file (because only keys afterwards are emptied).
We have a patch ready which we are currently testing internally which writes to
a temp file and do a rename afterwards + skipping to write fully empty configs
(that part might not make sense in the official version, but for us, we're
never going to "empty" out config files through code, instead we would delete
the whole file...). That seems to solve the issue for us, yet still a bit hacky.
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