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From "roger.keays" <roger.ke...@ninthavenue.com.au>
Subject Re: concurrent access to LRS
Date Wed, 13 Dec 2006 09:25:17 GMT


Marc Prud wrote:
> 
> What happens if you synchronized on the result collection when  
> iterating through them?
> 

Unfortunately I don't have that fine-grained access since the result set is
iterated by a JSF dataTable. I can, however, synchronize access by using a
per-session mutex on the entire JSF Render Response phase. It solves the
problem, but is probably a bit of overkill.

I did try adding the synchronized keyword to all the
org.apache.openjpa.kernel.DelegatingResultList methods, but it didn't work
and I was really just stabbing in the dark.

All this synchronizing makes me hungry.



> On Dec 12, 2006, at 7:44 PM, roger.keays wrote:
> 
>>
>> Hi Marc,
>>
>>
>> Marc Prud wrote:
>>>
>>> Was a transaction committed or rolled back between the two requests?
>>> Many databases and/or JDBC drivers do not allow a result set cursor
>>> to span multiple transactions, which might be the cause of this error
>>> (which, admittedly, we are not handling as gracefully as we could  
>>> be).
>>>
>>
>> No, there is no SQL activity between the requests except for that  
>> produced
>> by the LRS. I suspected it could be a JDBC driver issue which is  
>> why I tried
>> MySQL also. I see pretty well the exact same behaviour on MySQL  
>> though.
>>
>> It seems that the result list is closing because of an exception  
>> caused by
>> two threads both trying to use the database connection at the same  
>> time. The
>> first exception is usually a nonsensical one from the JDBC driver -
>> NullPointerException, stuff about BigDecimals (of which I use  
>> none), SQL
>> errors - "portal c_8 does not exist' (?).
>>
>> The only constant I can find is that it works fine if I load the  
>> frames one
>> by one, so my best guess is it is a concurrency issue.
>>
>> Thanks,
>>
>> Roger
>>
>>
>>> On Dec 12, 2006, at 6:26 PM, roger.keays wrote:
>>>
>>>>
>>>> Now that I have an em which lives for longer than one request (as
>>>> per my
>>>> previous thread) I have noticed some concurrency issues accessing
>>>> the large
>>>> result set. Since my app uses frames, there are occasions when two
>>>> frames
>>>> will be refreshed at the same time. When this occurs, and the both
>>>> try to
>>>> iterate the LRS I will frequently get either a  
>>>> NullPointerException or
>>>> NoSuchElementException (result list is closed). Loading the frames
>>>> one by
>>>> one works fine.
>>>>
>>>> I've tried to the following with no avail:
>>>>     * Adding openjpa.Multithreaded=true
>>>>     * Synchronizing the LRS' getter method
>>>>     * Removing connection pooling (i.e. use openjpa's datasource)
>>>>     * Using mysql instead of postgresql
>>>>     * Disabling the query cache
>>>>     * Disabling the data cache
>>>>
>>>> As you can see, I'm a bit stuck. Any suggestions welcome.
>>>>
>>>> The NullPointerException stacktrace is:
>>>>
>>>> java.lang.NullPointerException
>>>>
>>>> org.apache.openjpa.jdbc.kernel.SelectResultObjectProvider.next
>>>> (SelectResultObjectProvider.java:96)
>>>>
>>>> org.apache.openjpa.lib.rop.WindowResultList.getInternal
>>>> (WindowResultList.java:126)
>>>>
>>>> org.apache.openjpa.lib.rop.AbstractNonSequentialResultList.get
>>>> (AbstractNonSequentialResultList.java:69)
>>>>
>>>> org.apache.openjpa.kernel.DelegatingResultList.get
>>>> (DelegatingResultList.java:241)
>>>>  javax.faces.model.ListDataModel.getRowData(ListDataModel.java:141)
>>>>  javax.faces.model.ListDataModel.setRowIndex(ListDataModel.java:175)
>>>>  javax.faces.model.ListDataModel.setWrappedData(ListDataModel.java:
>>>> 209)
>>>>  javax.faces.model.ListDataModel.<init>(ListDataModel.java:68)
>>>>
>>>> org.apache.myfaces.component.html.ext.HtmlDataTableHack.createDataMo 
>>>> de
>>>> l(HtmlDataTableHack.java:448)
>>>>
>>>> org.apache.myfaces.component.html.ext.HtmlDataTable.createDataModel
>>>> (HtmlDataTable.java:847)
>>>>
>>>> org.apache.myfaces.component.html.ext.HtmlDataTableHack.getDataModel
>>>> (HtmlDataTableHack.java:414)
>>>>
>>>> org.apache.myfaces.component.html.ext.HtmlDataTable.getDataModel
>>>> (HtmlDataTable.java:839)
>>>>
>>>> org.apache.myfaces.component.html.ext.HtmlDataTableHack.getRowCount
>>>> (HtmlDataTableHack.java:87)
>>>>
>>>> org.apache.myfaces.shared_tomahawk.renderkit.html.HtmlTableRendererB 
>>>> as
>>>> e.encodeInnerHtml(HtmlTableRendererBase.java:226)
>>>>
>>>> org.apache.myfaces.shared_tomahawk.renderkit.html.HtmlTableRendererB 
>>>> as
>>>> e.encodeChildren(HtmlTableRendererBase.java:134)
>>>>
>>>> org.apache.myfaces.renderkit.html.ext.HtmlTableRenderer.encodeChildr 
>>>> en
>>>> (HtmlTableRenderer.java:187)
>>>>
>>>> javax.faces.component.UIComponentBase.encodeChildren
>>>> (UIComponentBase.java:828)
>>>>  javax.faces.component.UIComponent.encodeAll(UIComponent.java:883)
>>>>  javax.faces.component.UIComponent.encodeAll(UIComponent.java:889)
>>>>  com.sun.facelets.FaceletViewHandler.renderView
>>>> (FaceletViewHandler.java:578)
>>>>
>>>> and the NoSuchElementException:
>>>>
>>>> java.util.NoSuchElementException: The result list has been closed.
>>>>
>>>> org.apache.openjpa.lib.rop.AbstractResultList.assertOpen
>>>> (AbstractResultList.java:91)
>>>>  org.apache.openjpa.lib.rop.WindowResultList.size
>>>> (WindowResultList.java:81)
>>>>
>>>> org.apache.openjpa.kernel.DelegatingResultList.size
>>>> (DelegatingResultList.java:133)
>>>>  javax.faces.model.ListDataModel.isRowAvailable 
>>>> (ListDataModel.java:99)
>>>>  javax.faces.model.ListDataModel.setRowIndex(ListDataModel.java:174)
>>>>
>>>> org.apache.myfaces.component.html.ext.HtmlDataTableHack.setRowIndex
>>>> (HtmlDataTableHack.java:243)
>>>>
>>>> org.apache.myfaces.component.html.ext.HtmlDataTable.setRowIndex
>>>> (HtmlDataTable.java:263)
>>>>
>>>> org.apache.myfaces.shared_tomahawk.renderkit.html.HtmlTableRendererB 
>>>> as
>>>> e.encodeInnerHtml(HtmlTableRendererBase.java:257)
>>>>
>>>> org.apache.myfaces.shared_tomahawk.renderkit.html.HtmlTableRendererB 
>>>> as
>>>> e.encodeChildren(HtmlTableRendererBase.java:134)
>>>>
>>>> org.apache.myfaces.renderkit.html.ext.HtmlTableRenderer.encodeChildr 
>>>> en
>>>> (HtmlTableRenderer.java:187)
>>>>
>>>> javax.faces.component.UIComponentBase.encodeChildren
>>>> (UIComponentBase.java:828)
>>>>  javax.faces.component.UIComponent.encodeAll(UIComponent.java:883)
>>>>  javax.faces.component.UIComponent.encodeAll(UIComponent.java:889)
>>>>  com.sun.facelets.FaceletViewHandler.renderView
>>>> (FaceletViewHandler.java:578)
>>>>
>>>> Cheers,
>>>>
>>>> Roger
>>>> -- 
>>>> View this message in context: http://www.nabble.com/concurrent-
>>>> access-to-LRS-tf2811717.html#a7846241
>>>> Sent from the open-jpa-dev mailing list archive at Nabble.com.
>>>>
>>>
>>>
>>>
>>
>> -- 
>> View this message in context: http://www.nabble.com/concurrent- 
>> access-to-LRS-tf2811717.html#a7846763
>> Sent from the open-jpa-dev mailing list archive at Nabble.com.
>>
> 
> 
> 

-- 
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