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[doc] [java] Improve docs on NonThreadSafeSingleton

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This commit is contained in:
Juan Martín Sotuyo Dodero
2017-01-30 16:18:57 -03:00
committed by Andreas Dangel
parent e45c10431f
commit 03306df325
1 changed files with 5 additions and 1 deletions
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6
pmd-java/src/main/resources/rulesets/java/design.xml
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@ -1289,7 +1289,11 @@ Non-thread safe singletons can result in bad state changes. Eliminate
static singletons if possible by instantiating the object directly. Static
singletons are usually not needed as only a single instance exists anyway.
Other possible fixes are to synchronize the entire method or to use an
initialize-on-demand holder class (do not use the double-check idiom).
[initialize-on-demand holder class](https://en.wikipedia.org/wiki/Initialization-on-demand_holder_idiom).
Refrain from using the double-checked locking pattern. The Java Memory Model doesn't
guarantee it to work unless the variable is declared as `volatile`, adding an uneeded
performance penalty. [Reference](http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html)
See Effective Java, item 48.
</description>