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https://issues.apache.org/jira/browse/LUCENE-7080?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15186829#comment-15186829
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Simon Willnauer edited comment on LUCENE-7080 at 3/9/16 9:26 AM:
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[~mariusneo], the lucene test framework uses randomized runner which takes care 
of the reproducibility of our PRNG. The framework / test uses a random seed to 
initialize the PRNG and that allows use to draw random number like this in a 
reproducible fashion. The problem here is that different JDKs can have 
different hashing schemes for the hash set and that causes different iteration 
order which in-turn breaks the reproducibility.


was (Author: simonw):
[~mariusneo] the lucene test framework uses randomized runner which takes care 
of the reproducibility of our PRNG. The framework / test uses a random seed to 
initialize the PRNG and that allows use to draw random number like this in a 
reproducible fashion. The problem here is that different JDKs can have 
different hashing schemes for the hash set and that causes different iteration 
order which in-turn breaks the reproducibility.

> MockDirectoryWrapper relies on HashSet iteration order
> ------------------------------------------------------
>
>                 Key: LUCENE-7080
>                 URL: https://issues.apache.org/jira/browse/LUCENE-7080
>             Project: Lucene - Core
>          Issue Type: Bug
>          Components: general/test
>    Affects Versions: 5.5, 6.0
>            Reporter: Simon Willnauer
>            Assignee: Simon Willnauer
>
> MDW relies on HashSet iteration order in 
> {code}
>   public synchronized void corruptFiles(Collection<String> files) throws 
> IOException {
>     // Must make a copy because we change the incoming unsyncedFiles
>     // when we create temp files, delete, etc., below:
>     for(String name : new ArrayList<>(files)) { // <<<<< this should be sorted
>       int damage = randomState.nextInt(6);
> {code}
> this causes reproducibility issues when files get corrupted.



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