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https://issues.apache.org/jira/browse/LANG-429?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12592062#action_12592062
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Julien Aymé commented on LANG-429:
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IMHO, this is rather an example of a data-race issue due to the cInstanceCache
field not being final and not being synchronized in <clinit> in FastDateFormat
in Lang 2.2.
I suppose that the following scenario could explain your problem:
- at least two Threads concurrently access to FastDateFormat.getInstance()
method, while FastDateFormat is not being loaded by the current classloader:
- Thread A loads FastDateFormat.class, and creates cInstanceCache.
- Thread B enters the FastDateFormat.getInstance() method, BUT
FastDateFormat.class is in a incoherent state (cInstanceCache is null) because
of memory synchronization and/or compiler optimizations
=> this causes the NullPointerException in Thread B
- Thread A enters in FastDateFormat.getInstance() method and everything is
correct.
I suggest you to upgrade to Lang 2.4 in which the cInstanceCache field has been
made final, and see if this problem still occurs.
Furthermore, the semantic of final keyword has been strengthen due to JSR-133 ,
which is part of Java 5.
I encourage you to read the following section:
http://www.cs.umd.edu/~pugh/java/memoryModel/jsr-133-faq.html#finalWrong
and the Final Fields paragraph in JSR-133:
http://www.cs.umd.edu/~pugh/java/memoryModel/jsr133.pdf
> NullPointerException (NPE) in
> FastDateFormat.getInstance(FastDateFormat.java:211)
> ---------------------------------------------------------------------------------
>
> Key: LANG-429
> URL: https://issues.apache.org/jira/browse/LANG-429
> Project: Commons Lang
> Issue Type: Bug
> Affects Versions: 2.2
> Environment: MS Windows XP (SP 2), Java 1.5.0 Update 11
> Reporter: Kai Burjack
>
> Sometimes (sadly this is not reproducible) the following method call results
> in a NullPointerException (NPE):
> Stacktrace:
> java.lang.NullPointerException
> at
> org.apache.commons.lang.time.FastDateFormat.getInstance(FastDateFormat.java:211)
> at
> org.apache.commons.lang.time.DateFormatUtils.format(DateFormatUtils.java:258)
> at
> org.apache.commons.lang.time.DateFormatUtils.format(DateFormatUtils.java:232)
> I don't know how this is actually possible, since the exception is being
> raised when accessing a static field 'cInstanceCache' that will be implicitly
> initialized...
> Could this have something to do with class gc?
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