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https://issues.apache.org/jira/browse/DERBY-2861?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12604222#action_12604222
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Bryan Pendleton commented on DERBY-2861:
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I ran the test program a number of times with the current trunk.
Sometimes the program ran successfully, sometimes I got
lock timeout errors, sometimes I got "table/view already exists" errors.
I never saw the NPE observed by the original poster.
This was on Ubuntu 8 with Sun JDK 1.5 on a fairly slow old machine.
> Thread safety issue in TableDescriptor
> --------------------------------------
>
> Key: DERBY-2861
> URL: https://issues.apache.org/jira/browse/DERBY-2861
> Project: Derby
> Issue Type: Bug
> Components: SQL
> Environment: Tested on a dual-core 3GHz Pentium machine running
> Windows Vista Business, using JDK 1.4.2_13 and Derby trunk revision 548822.
> Reporter: Jeff Clary
> Attachments: TestEmbeddedMultiThreading.java
>
>
> A NullPointerException occurs in
> org.apache.derby.iapi.sql.dictionary.TableDescriptor.getObjectName when
> accessing the same object on many threads (each with its own connection).
> The attached test program starts N threads each creating and then dropping a
> separate view against the same source view, repeated M times. I can
> reproduce the problem with N=100 and M=100 on my machine, but not every run.
> An instance member named referencedColumnMap is checked for null at the top
> of the getObjectName method, but later when it is dereferenced it is null,
> because it was set to null by another thread. I am not sure what
> getObjectName is used for other than error reporting. I have considered a
> fix of just saving the non-null reference as a method variable, to avoid the
> later NullPointerException. But I don't know what unintended consequences
> this may have.
> When the test program does show the exception, the stack trace looks like
> this:
> java.lang.NullPointerException
> at
> org.apache.derby.iapi.sql.dictionary.TableDescriptor.getObjectName(TableDescriptor.java:758)
> at
> org.apache.derby.impl.sql.depend.BasicDependencyManager.getPersistentProviderInfos(BasicDependencyManager.java:677)
> at
> org.apache.derby.impl.sql.compile.CreateViewNode.bindViewDefinition(CreateViewNode.java:287)
> at
> org.apache.derby.impl.sql.compile.CreateViewNode.bind(CreateViewNode.java:183)
> at
> org.apache.derby.impl.sql.GenericStatement.prepMinion(GenericStatement.java:345)
> at
> org.apache.derby.impl.sql.GenericStatement.prepare(GenericStatement.java:119)
> at
> org.apache.derby.impl.sql.conn.GenericLanguageConnectionContext.prepareInternalStatement(GenericLanguageConnectionContext.java:745)
> at
> org.apache.derby.impl.jdbc.EmbedStatement.execute(EmbedStatement.java:568)
> at
> org.apache.derby.impl.jdbc.EmbedStatement.execute(EmbedStatement.java:517)
> at
> TestEmbeddedMultiThreading.executeStatement(TestEmbeddedMultiThreading.java:109)
> at
> TestEmbeddedMultiThreading.access$100(TestEmbeddedMultiThreading.java:10)
> at
> TestEmbeddedMultiThreading$ViewCreatorDropper.run(TestEmbeddedMultiThreading.java:173)
> at java.lang.Thread.run(Thread.java:534)
>
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