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From "roger.keays" <roger.ke...@ninthavenue.com.au>
Subject concurrent access to LRS
Date Wed, 13 Dec 2006 02:26:53 GMT

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.createDataModel(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.HtmlTableRendererBase.encodeInnerHtml(HtmlTableRendererBase.java:226)

org.apache.myfaces.shared_tomahawk.renderkit.html.HtmlTableRendererBase.encodeChildren(HtmlTableRendererBase.java:134)

org.apache.myfaces.renderkit.html.ext.HtmlTableRenderer.encodeChildren(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.HtmlTableRendererBase.encodeInnerHtml(HtmlTableRendererBase.java:257)

org.apache.myfaces.shared_tomahawk.renderkit.html.HtmlTableRendererBase.encodeChildren(HtmlTableRendererBase.java:134)

org.apache.myfaces.renderkit.html.ext.HtmlTableRenderer.encodeChildren(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
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