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Posted to derby-dev@db.apache.org by "Rick Hillegas (JIRA)" <ji...@apache.org> on 2006/12/12 23:14:23 UTC
[jira] Updated: (DERBY-2142) NullPointerException while using
XAConnection/PooledConnection in a heavily contended multithreaded scenario
[ http://issues.apache.org/jira/browse/DERBY-2142?page=all ]
Rick Hillegas updated DERBY-2142:
---------------------------------
Urgency: Normal (was: Urgent)
Priority: Major (was: Critical)
Adjusting urgency and priority to the standard levels.
> NullPointerException while using XAConnection/PooledConnection in a heavily contended multithreaded scenario
> ------------------------------------------------------------------------------------------------------------
>
> Key: DERBY-2142
> URL: http://issues.apache.org/jira/browse/DERBY-2142
> Project: Derby
> Issue Type: Bug
> Components: JDBC
> Affects Versions: 10.0.2.0, 10.0.2.1, 10.1.1.0, 10.2.1.6, 10.1.2.1, 10.1.3.1
> Environment: The issue can appear in any environment as the bug is in the source code . The bug has been verified in Suse Linux env.
> Reporter: Asif H. Shahid
>
> We are using the Derby's Transactional DataSource class ( org.apache.derby.jdbc.EmbeddedXADataSource ) to create a pool of XAConnections in our application.
> Whenever a thread in a JTA transaction requests for a SQLConnection , we retrieve an XAConnection from the pool. From the XAConnection , we register the XAResource with the TransactionManager & return a java.sql.Connection to the application.
> A class implementing the ConnectionEventListener is registered with the XAConnection to get callback connectionClosed ( ) when the thead closes the java.sql.Connection. In this callback, we invoke XAResource.end & return the XAConnection to our pool so that other threads can use it.
> We have encountered NullPointerException , when performing operation on java.sql.Connection.
> The stacktrace is as follows
> at
> org.apache.derby.jdbc.XAStatementControl.<init>(XAStatementControl.java:71)
> at
> org.apache.derby.jdbc.EmbedXAConnection.wrapStatement(EmbedXAConnection.java:162)
> at
> org.apache.derby.iapi.jdbc.BrokeredConnection.createStatement(Unknown
> Source)
> at
> com.gemstone.gemfire.internal.datasource.ConnectionPoolingTest$1.run(ConnectionPoolingTest.java:174)
> at java.lang.Thread.run(Thread.java:595)
> I have done some debugging on source code of db-derby-10.2.1.6-src & have following explanation of the bug & a suggested fix. However, I want to confirm that it is genuinely a bug & not a problem in our understanding of the Datasource spec behaviour.
> Reason for the bug:-
> The class EmbedPooledConnection.java stores in the field currentConnectionHandle ( of class BrokeredConnection) a reference of the java.sql.Connection object , being returned to the application,
> Now ,whenever the client closes the java.sql.Connection , the code flow is
> EmbedPooledConnection.close() --> EmbedPooledConnection.notifyClose().
> In the function EmbedPooledConnection.notifyClose(), it notifies my listener ( javax.sql.ConnectionEventListener) ) where I return the XAConnection to the pool ( after deregistering the XAResource).
> The last line of EmbedPooledConnection.close() makes the currentConnectionHandle field as null.
> The issue here is that javax.sql.ConnectionEventListener.connectionClosed is invoked before making the currentConenctionHandle field as null. Thus XAConnection is returned to the pool , ready for pickup by a new thread. This new thread obtains a java.sql.Connection whose reference gets assigned to the currentConnectionHandle field, meanwhile the previous thread completes the EmbedPooledConnection.close making the newly assigned currentConnectionHandle as null.
> Thus a previous thread's close makes a field null of an XAConnection, which has been assigned to a new thread.
> The bug is easily reproducible in a multi threaded scenario ( 20 threads or so) with a pool size of around 4 XAConnections so that there is heavy contention on XAConnection.
> The fix is to rearrange the code of EmbedPooledConenction.java 's closingConnection () as
> bug :
> public boolean closingConnection() {
> notifyClose();
> currentConnectionHandle = null;
> return false;
> }
> bug fix :
> public boolean closingConnection() {
> currentConnectionHandle = null;
> notifyClose();
> return false;
> }
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