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https://issues.apache.org/jira/browse/GEODE-4957?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16436113#comment-16436113
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ASF subversion and git services commented on GEODE-4957:
--------------------------------------------------------

Commit 65b52f28f4e11b9f5ec82b0e457fc0292132e5da in geode's branch 
refs/heads/develop from [~dschneider]
[ https://gitbox.apache.org/repos/asf?p=geode.git;h=65b52f2 ]

GEODE-4957: fix race in concurrent create on region (#1750)

Refactored basicPut so that a RegionEntry with REMOVE_PHASE1
is added to the map, it will already be synchronized.
This prevents a second concurrent threads from "stealing" it and
creating a region entry with a key that is the same but has a different
identity.


> The key used in a putIfAbsent call that returns null may not be the one in 
> the RegionEntry
> ------------------------------------------------------------------------------------------
>
>                 Key: GEODE-4957
>                 URL: https://issues.apache.org/jira/browse/GEODE-4957
>             Project: Geode
>          Issue Type: Bug
>          Components: regions
>            Reporter: Barry Oglesby
>            Priority: Major
>              Labels: pull-request-available
>          Time Spent: 20m
>  Remaining Estimate: 0h
>
> With simultaneous putIfAbsent calls, sometimes the thread that returns null 
> is not the thread that actually creates the RegionEntry.
> Below is some logging that shows this behavior.
> Thread-77 returns null from the putIfAbsent call (which means there was no 
> previous value). 1 ms before Thread-77's putEntryIfAbsent call, Thread-9 
> creates the RegionEntry. You can see that because not only is oldRe=null for 
> Thread-9, but also the event's key (eventKey) and entry's key (reKey) are 
> identical. But Thread-9 returns a non-null old value.
> {noformat}
> Thread-77 at 1522187267493: AbstractRegionMap.putEntryIfAbsent 
> regionEntry=VersionedStatsDiskLRURegionEntryHeapObjectKey@6a8119a0 
> (key=ComplexKey[identity=1682369152; key=key]; rawValue=REMOVED_PHASE1; 
> version=\{v0; rv0; ds=0; time=0};member=null); 
> oldRe=VersionedStatsDiskLRURegionEntryHeapObjectKey@1aac7604 
> (key=ComplexKey[identity=342592289; key=key]; rawValue=REMOVED_PHASE1; 
> version=\{v0; rv0; ds=0; time=0};member=null)
> Thread-77 at 1522187267493: AbstractRegionMap.basicPut 
> eventKey=ComplexKey[identity=1682369152; key=key]; 
> reKey=ComplexKey[identity=342592289; key=key]
> Thread-77 at 1522187267500: LocalRegion.putIfAbsent returning null
> {noformat}
> {noformat}
> Thread-9 at 1522187267492: AbstractRegionMap.putEntryIfAbsent 
> regionEntry=VersionedStatsDiskLRURegionEntryHeapObjectKey@1aac7604 
> (key=ComplexKey[identity=342592289; key=key]; rawValue=REMOVED_PHASE1; 
> version=\{v0; rv0; ds=0; time=0};member=null); oldRe=null
> Thread-9 at 1522187267495: AbstractRegionMap.basicPut 
> eventKey=ComplexKey[identity=342592289; key=key]; 
> reKey=ComplexKey[identity=342592289; key=key]
> Thread-9 at 1522187267504: LocalRegion.putIfAbsent returning v1
> {noformat}



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