[jira] [Created] (JENA-2310) NPE with geospatial property function due to query rewrite index issue

["Lorenz Bühmann (Jira)" <ji...@apache.org>]

Lorenz Bühmann created JENA-2310:
------------------------------------

             Summary: NPE with geospatial property function due to query rewrite index issue
                 Key: JENA-2310
                 URL: https://issues.apache.org/jira/browse/JENA-2310
             Project: Apache Jena
          Issue Type: Bug
          Components: GeoSPARQL
    Affects Versions: Jena 4.4.0
         Environment: {code:java}
// code placeholder
{code}
{code:java}
// Some comments here
public String getFoo()
{
    return foo;
}
{code}
            Reporter: Lorenz Bühmann


Using a GeoSPARQL query with a geospatial property function, e.g.
{code:java}
SELECT * {
:x geo:hasGeometry ?geo1 .
?s2 geo:hasGeometry ?geo2 .
?geo1 geo:sfContains ?geo2
}{code}
leads to an nondeterministic NPE when we're doing this query a a larger dataset.

The reason is explained here:
 - evaluation of the property function leads to {{GenericPropertyFunction}} class with

{code:java}
 private QueryIterator bothBound(Binding binding, Node subject, Node predicate, Node object, ExecutionContext execCxt) {

        Graph graph = execCxt.getActiveGraph();
        QueryRewriteIndex queryRewriteIndex = QueryRewriteIndex.retrieve(execCxt);

        Boolean isPositiveResult = queryRewrite(graph, subject, predicate, object, queryRewriteIndex);
        if (isPositiveResult) {
{code}
 
which leads to the query rewrite part and in {{QueryRewriteIndex}} class we have
{code:java}
 if (index.containsKey(key)) {
         result = index.get(key);
 } else {
         result = propertyFunction.testFilterFunction(subjectGeometryLiteral, objectGeometryLiteral);
         index.put(key, result);
}
{code}
{{index}} is an {{ExpiringMap}} which extends {{ConcurrentHashMap}} with an additional {{TimerTask}} clearing the map periodically - and this is why we get an NPE sometimes. Have a look at the lines above, in particular
{code:java}
if (index.containsKey(key)){
   result = index.get(key); 
}
{code}
 that part isn't atomic, thus, while {{containsKey}} could be true, the {{TimerTask}} might clear the map before we go to get - this will lead to a {{null}} value returned which will lead to an NPE in the check

Since Java 8 the atomic way is to use {{computeIfAbsent}}, i.e. we can do
{code:java}
Boolean result = index.computeIfAbsent(key, k -> propertyFunction.testFilterFunction(subjectGeometryLiteral, objectGeometryLiteral));{code}

 



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