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To: ojb-dev@db.apache.org
From: Martin Davidsson <martin.davidsson@gmail.com>
Subject: Write lock where Read expected
Date: Tue, 17 May 2005 11:50:10 -0400

Hello,

I upgraded to OJB version 1.0.3 and started seeing some new  
exceptions during run-time. OJB said it was unable to perform a WRITE  
lock on some of my objects. I didn't expect a WRITE lock to be  
necessary at all in this particular situation since I was pulling up  
a page on my site that doesn't perform any modifications to the  
database. I traced the source and got to the org/apache/ojb/odmg/oql/ 
OQLQueryImpl.java file. On line 329 we have the statement  
"tx.lockAndRegister(rt, Transaction.WRITE, true);" despite multiple  
comments above it pointing to the fact that a READ lock should occur.  
I tried changing Transaction.WRITE to Transaction.READ and my  
problems went away, but perhaps this statement should in fact be the  
way it's pasted below and it's just that the comments are throwing me  
off. I was wondering if anybody on the list could set me straight.

Also, were there ever any plans to create a DSetImpl_2... similar to  
the old DListImpl_2? Thank you!

Here is the relevant function in context:

protected void performLockingIfRequired(
             TransactionImpl tx,
             PersistenceBroker broker,
             ManageableCollection result)
     {
         // if tx is available and implicit locking is required,
         // we do READ-lock all found objects
         if ((tx != null) && tx.isImplicitLocking() && tx.isOpen())
         {
             // read-lock all resulting objects to the current  
transaction
             Iterator iter = result.ojbIterator();
             Object toBeLocked = null;
             try
             {
                 while (iter.hasNext())
                 {
                     toBeLocked = iter.next();
                     RuntimeObject rt = new RuntimeObject(toBeLocked,  
tx, false);
                     tx.lockAndRegister(rt, Transaction.WRITE, true);
                 }
             }
             finally
             {
                 tx.lockAndRegisterCleanup();
             }
         }
}

-- Martin Davidsson

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