[hibernate-issues] [Hibernate-JIRA] Commented: (HHH-3628) Hilo optimizer problem in case of multiple threads accessing the sequence table

[Hassan Hammoud (JIRA)]

    [ http://opensource.atlassian.com/projects/hibernate/browse/HHH-3628?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=31881#action_31881 ] 

Hassan Hammoud commented on HHH-3628:
-------------------------------------

Hello Cyril :), I still think that in the ticket they didn't describe the case correctly. I don't think they meant in one call of generate() but instead two or more threads are calling the generate().

In brief, 
            1- Thread one called "value = callback.getNextValue()" inside the "else if ( value >= hiValue )";
            2- Thread two called  "value = callback.getNextValue()" inside the "if ( hiValue < 0 )" hence resetting the value variable;
            3- Thread one called "hiValue = callback.getNextValue();" inside the "else if ( value >= hiValue )";

check the attached PooledOptimizerTest.java in  HHH-3608 and run it you will understand what they mean.

Although the generate() is a synchronized function it is still not static -> so only synchronized inside the same PooledOptimizer Object. If another PooledOptimizer  in another thread calls the generate(), it will execute. It's only that the value variable is common to the two objects through the DB or the callback.getNextValue();

> Hilo optimizer problem in case of multiple threads accessing the sequence table
> -------------------------------------------------------------------------------
>
>                 Key: HHH-3628
>                 URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-3628
>             Project: Hibernate Core
>          Issue Type: Bug
>    Affects Versions: 3.2.6
>         Environment: Sybase
>            Reporter: Montagnon Cyril
>
> If 2 (or more) threads access the table storing the ids, this optimizer won't work and will try to insert entities with twice the same idea.
> The problem is the way the HiLoOptimizer class generates the id : 
>             public synchronized Serializable generate(AccessCallback callback) {
> 			if ( lastSourceValue < 0 ) {
> 				lastSourceValue = callback.getNextValue();
> 				while ( lastSourceValue <= 0 ) {
> 					lastSourceValue = callback.getNextValue();
> 				}
> 				hiValue = ( lastSourceValue * incrementSize ) + 1;
> 				value = hiValue - incrementSize;
> 			}
> 			else if ( value >= hiValue ) {
> 				lastSourceValue = callback.getNextValue();
> 				hiValue = ( lastSourceValue * incrementSize ) + 1;
> 			}
> 			return make( value++ );
> 		}
> In the 'else if' part, the 'value' variable isn't reaffected, which means the current thread will try to insert entities with an id that has already been used by another thread. The value should be reset with hiValue - incrementSize.

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