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
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.
--
This message is automatically generated by JIRA.
-
For more information on JIRA, see: http://www.atlassian.com/software/jira
