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From "Jeff Clary (JIRA)" <j...@apache.org>
Subject [jira] Created: (DERBY-2861) Thread safety issue in TableDescriptor
Date Fri, 22 Jun 2007 15:00:27 GMT
Thread safety issue in TableDescriptor

                 Key: DERBY-2861
                 URL: https://issues.apache.org/jira/browse/DERBY-2861
             Project: Derby
          Issue Type: Bug
         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:

   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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