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https://issues.apache.org/jira/browse/LUCENE-9001?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16951200#comment-16951200
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ASF subversion and git services commented on LUCENE-9001:
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Commit dad15ba15e00df4fef024dae3b101b7969775ed6 in lucene-solr's branch
refs/heads/branch_8x from Przemko Robakowski
[ https://gitbox.apache.org/repos/asf?p=lucene-solr.git;h=dad15ba ]
LUCENE-9001: Fix race condition in SetOnce (#931)
> Race condition in SetOnce
> -------------------------
>
> Key: LUCENE-9001
> URL: https://issues.apache.org/jira/browse/LUCENE-9001
> Project: Lucene - Core
> Issue Type: Bug
> Reporter: Przemko Robakowski
> Priority: Minor
> Time Spent: 20m
> Remaining Estimate: 0h
>
> There is race condition in SetOnce that can cause code below fail with
> NullPointerException:
> {code:java}
> SetOnce<String> setOnce = new SetOnce<>();
> new Thread(() -> setOnce.set("thread")).start();
> try{
> setOnce.set("main");
> } catch (SetOnce.AlreadySetException e){
> setOnce.get().hashCode(); //possible NPE!
> }
> {code}
> This is caused by 2 separate write operations - 1 for set marker field and 1
> for actual object. So it's possible that marker is already set to true
> (causing AlreadySetException on second write attempt) but object is still not
> set (causing NullPointerException).
> This can be avoided by using single AtomicReference instead to serve both
> purposes.
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