Add support for ConcurrentMap.putIfAbsent()
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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
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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