Re: [JBoss-dev] JBoss 3.2 problem with trackConnectionByTx and jdbc xa datasources

[Igor F. <ife...@th...>]

Ok, here is the same example with some more details/comments. There was 
a mistake in my original explanation and I apoligize for confusion.

BeanA allocates a connection
   - TxConnectionManager.getManagedConnection allocates
     new managed connection mc1 of type
     org.jboss.resource.adapter.jdbc.xa.XAManagedConnection which
     is a wrapper for (oracle) xa connection xaconn1.
   - TxConnectionManager.registerConnectionEventListener(mc1)
     creates new TxConnectionEventListener and calls
     mc1.addConnectionEventListener
   - mc1 gets enlisted into the transaction,
     TxConnectionEventListener.enlist is called and mc1 is added
     into txToManagedConnectionMap
   - mc1.getConnection() is called to get sql connection, it
     gets conn1 through xaconn1.getConnection()
BeanA calls BeanB
   - nothing special here
BeanB allocates a connection and gets instance conn2 from the same xaconn1
   - TxConnectionManager.getManagedConnection gets mc1 from
     txToManagedConnectionMap
   - mc1.getConnection() is called to get sql connection, it
     gets conn2 through xaconn1.getConnection() and implicitly
     invalidates conn1 held by BeanA (see quote below)
BeanB closes the connection and returns
   - nothing special
BeanA tries to use the connection
   - SQLException("Logical handle no longer valid").

A quote from JDBC 2.0 stdext, section  6.2.3 "Retrieving a Connection":

<quote>
An individual PooledConnection object will usually be asked to produce a 
series of Connection objects during its lifetime. Only one of these 
Connection objects may be open at a particular point in time. The 
connection pooling implementation must call 
PooledConnection.getConnection() each time a new reference to a 
pooledConnection is handed out to the JDBC application layer. Each call 
to PooledConnection.getConnection() must return a newly constructed 
Connection object that exhibits the default Connection behavior. Only 
the most recent Connection object produced from a particular 
PooledConnection is open. An existing Connection object is automatically 
closed, if the getConnection() method of its associated Pooled-
Connection is called again, before it has been explicitly closed by the 
application. This gives the application server a way to ‘take away’ a 
Connection from the application if it wishes, and give it out to someone 
else. This capability will not likely be used frequently in practice.
</quote>

Attached is a proposed fix. Hope this makes the problem clearer.

David Jencks wrote:
> I don't understand.  Can you repeat your explanation of the problem clearly
> indicating what is a ManagedConnection and what is a Connection?  From your
> description it looks like perhaps the problem is that we are reusing the
> java.sql.Connection obtained from a XAConnection?  This would not be a
> problem with the trackConnectionByTx logic but with the xa wrapper.
> 
> thanks
> david jencks
> 
> 
> On 2002.11.01 08:12:05 -0500 Igor Fedorenko wrote:
> 
>>Hi,
>>
>>There is a problem with trackConnectionByTx in the current CVS version
>>of JBoss 3.2 which occurs when two beans access the same datasource
>>from the same transaction. I am not 100% sure about original 
>>implementation intends and would like to give others an opportunity to 
>>complain before I check in updated trackConnectionByTx logic.
>>Consider the following example
>>
>>- BeanA allocates a connection and gets an instance conn1
>>- BeanA calls BeanB
>>- BeanB allocates a connection and gets the same instance conn1
>>- BeanB closes the connection and returns
>>- BeanA tries to use the connection and gets SQLException("Logical
>>handle is closed").
>>
>>Updated trackConnectionByTx logic will return the
>>same connection only if the connection has not been allocated yet
>>(condition
>>"BaseConnectionManager2.ConnectionListener.isManagedConnectionFree()");
>>otherwise allocate and return new connection.
>>
>>Any objections?

-- 
Igor Fedorenko
Think smart. Think automated. Think Dynamics.
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