Mailing-List: contact derby-dev-help@db.apache.org; run by ezmlm
Precedence: bulk
Reply-To: <derby-dev@db.apache.org>
Message-ID: <312458305.1213192125241.JavaMail.jira@brutus>
Date: Wed, 11 Jun 2008 06:48:45 -0700 (PDT)
From: "Bryan Pendleton (JIRA)" <jira@apache.org>
To: derby-dev@db.apache.org
Subject: [jira] Commented: (DERBY-2861) Thread safety issue in
 TableDescriptor
In-Reply-To: <6034208.1182524427532.JavaMail.jira@brutus>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 7bit


    [ https://issues.apache.org/jira/browse/DERBY-2861?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12604222#action_12604222 ] 

Bryan Pendleton commented on DERBY-2861:
----------------------------------------

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)
>  

-- 
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.