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https://issues.apache.org/jira/browse/CLEREZZA-431?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Reto Bachmann-Gmür closed CLEREZZA-431.
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Resolution: Fixed
> RDFList should not write in its constructor
> -------------------------------------------
>
> Key: CLEREZZA-431
> URL: https://issues.apache.org/jira/browse/CLEREZZA-431
> Project: Clerezza
> Issue Type: Improvement
> Reporter: Daniel Spicar
> Assignee: Reto Bachmann-Gmür
> Labels: list, rdfList
> Attachments: clerezza-431-patch.diff
>
>
> The implementation of RdfList in the rdf.utils project performs a write when
> creating an empty RdfList.
> This is dangerous because when the underlying graph is a
> LockableMGraphWrapper it tries to get a write lock on the graph before
> adding. If the creation of the list happens inside a read lock on the same
> graph this will create a deadlock. It requires a lot of knowledge of the
> implementation to be aware of these side-effects.
> It may be better for users of RdflList if no such unexpected locks are set.
> The write access happens, because for an empty list, the triple "listResource
> owl:sameAs rdf:Nil" is added to the underlying graph. This is correct but not
> necessary. The suggestion is that the presence of an rdf:first property is
> used to determine whether the list is empty or not. We can provide a static
> method for the user to create an empty list with the owl:sameAs rdf:Nil
> triple if a user desires to do so and is aware of the side effects. In the
> add and remove methods the owl:sameAs rdf:Nil triple can still be
> removed/added as these operations clearly require write access.
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