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https://issues.apache.org/jira/browse/LANG-678?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Oliver Heger resolved LANG-678.
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Resolution: Fixed
Fix Version/s: 3.0
Patch applied in revision 1071402.
> Add support for ConcurrentMap.putIfAbsent()
> -------------------------------------------
>
> Key: LANG-678
> URL: https://issues.apache.org/jira/browse/LANG-678
> Project: Commons Lang
> Issue Type: New Feature
> Components: lang.concurrent.*
> Reporter: Oliver Heger
> Priority: Minor
> Fix For: 3.0
>
> Attachments: putIfAbsent.patch
>
>
> The ConcurrentMap interface provides the {{putIfAbsent()}} method for adding
> keys which are not yet present in the map in an atomic operation. However,
> using this method is not always convenient because in many cases the return
> value is not what you want: If the value is newly added, *null* is returned.
> Typically the calling code is rather interested in the value which is now
> stored in the map. This is a proposal to add a new {{putIfAbsent()}} method
> to {{ConcurrentUtils}} which returns this value.
> Also, when working with a concurrent map, a typical pattern is to check
> whether the map contains a key. If not, a value is created and put into the
> map - unless another thread was faster. An example of such a use case is a
> map acting as a cache. {{ConcurrentUtils}} can provide support for such use
> cases by combining the {{putIfAbsent()}} operation with a
> {{ConcurrentInitializer}}: If the key is not found in the map, the
> initializer is called to create the corresponding value. Finally,
> {{putIfAbsent()}} is called to add the value to the map.
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