[hibernate-issues] [Hibernate-JIRA] Issue Comment Edited: (HHH-6689) DefaultMergeEventListener changes CheckNullability flag - not thread save

[Piotr Findeisen (JIRA)]

    [ http://opensource.atlassian.com/projects/hibernate/browse/HHH-6689?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=44192#comment-44192 ] 

Piotr Findeisen edited comment on HHH-6689 at 10/28/11 4:07 AM:
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Btw. it seems very probable that the sequence the following operations done in {{saveTransientEntity}} ([see source on github|https://github.com/hibernate/hibernate-core/blob/3.6/hibernate-core/src/main/java/org/hibernate/event/def/DefaultMergeEventListener.java#L407])
 * read global checkNullability flag
 * change global checkNullability flag to true
 * restore global checkNullability flag to read value

when executed by 2 threads at the same time can *change checkNullability flag to {{true}} for ever*. For this to happen it's enough that
 * first thread reads the flag and sets it temporarily to {{true}}
 * second thread reads {{true}} (the temporary value)
 * first thread completes {{merge}} and restores flag to the original value
 * second threads completes {{merge}} and restores flag to the temporary value of {{true}}

      was (Author: piofinsy):
    Btw. it seems very probable that the sequence the following operations done in {{saveTransientEntity}} ([see source on github|https://github.com/hibernate/hibernate-core/blob/3.6/hibernate-core/src/main/java/org/hibernate/event/def/DefaultMergeEventListener.java#L409])
 * read global checkNullability flag
 * change global checkNullability flag to true
 * restore global checkNullability flag to read value

when executed by 2 threads at the same time can *change checkNullability flag to {{true}} for ever*. For this to happen it's enough that
 * first thread reads the flag and sets it temporarily to {{true}}
 * second thread reads {{true}} (the temporary value)
 * first thread completes {{merge}} and restores flag to the original value
 * second threads completes {{merge}} and restores flag to the temporary value of {{true}}
  
> DefaultMergeEventListener changes CheckNullability flag - not thread save
> -------------------------------------------------------------------------
>
>                 Key: HHH-6689
>                 URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-6689
>             Project: Hibernate Core
>          Issue Type: Bug
>          Components: core
>    Affects Versions: 3.6.5
>         Environment: Websphere Application Server 7.0,  DB2,  Windows Server, Hibernate 3.6.5
>            Reporter: John SMith
>              Labels: hibernate
>
> saveTransientEntity() method saves the CheckNullability setting,  changes it using the getFactory().getSettings().setCheckNullability  method, and does save processing.   After save processing, the saved value is restored.
> During load testing, we have had situations where the CheckNullability becomes set to TRUE and causes failures because of null checks.
> It has been difficult to debug, but it appears that this is not thread safe - multiple threads accessing this method can change the value of this setting.
> It can also be that a database error can cause an exception that will cause the checkNullability flan not to be reset.

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