On Tue, Dec 3, 2013 at 7:20 PM, Andy Seaborne <[email protected]> wrote:
> On 03/12/13 15:13, Reto Bachmann-Gmür wrote:
>
>> So here's some code to reproduced the ConcurrentModificationException
>> directly with jena (using transactions):
>>
>> String directory = "target/Dataset1";
>> Dataset dataset = TDBFactory.createDataset(directory);
>> {
>> dataset.begin(ReadWrite.WRITE);
>> Model foo1 = ModelFactory.createDefaultModel();
>> foo1.add(RDFS.Class, RDF.type, RDFS.Class);
>> foo1.add(RDFS.Class, RDF.type, RDFS.Resource);
>> dataset.addNamedModel(URNXFOO1, foo1);
>> dataset.commit();
>> dataset.end();
>> }
>> {
>> dataset.begin(ReadWrite.WRITE);
>> Model foo2 = ModelFactory.createDefaultModel();
>> dataset.addNamedModel(URNXFOO2, foo2);
>> dataset.commit();
>> dataset.end();
>> }
>> {
>> dataset.begin(ReadWrite.WRITE);
>> Model foo1 = dataset.getNamedModel(URNXFOO1);
>> Model foo2 = dataset.getNamedModel(URNXFOO2);
>> StmtIterator iter = foo1.listStatements();
>> while (iter.hasNext()) {
>> foo2.add(iter.nextStatement());
>> }
>>
>
> You are modifying the dataset while iterating over it.
>
> Model foo2 is just a view of the dataset, not an isolated copy. 'fraid
> you can't modify the dataset and get a consistent view for the iterator at
> the same time. The code just happens to check otherwise there would be
> non-deterministic behaviour. (The check isn't perfect BTW.)
>
I don't see why Jena can't be a bit more selective, an addition to another
graph cannot possibly affect the current iterator. The above is what
happens when we addAll is invoked on a clerezza graph. Isee that for
simialr methods the jena implementation copy the graph to be added to
memory first, it would be good to have a more efficient solution.
>
> This does it as well - and no transactions.
>
> public static void main1() throws Exception {
> String directory = "target/Dataset1";
> String URNXFOO1 = "urn:x-foo:1" ;
> String URNXFOO2 = "urn:x-foo:2" ;
>
> Dataset dataset = TDBFactory.createDataset();
> dataset.getNamedModel(URNXFOO1).add(RDFS.Class, RDF.type,
> RDFS.Class);
> dataset.getNamedModel(URNXFOO1).add(RDFS.Class, RDF.type,
> RDFS.Resource);
>
>
> Model foo1 = dataset.getNamedModel(URNXFOO1);
> Model foo2 = dataset.getNamedModel(URNXFOO2);
> StmtIterator iter = foo1.listStatements();
> while (iter.hasNext()) {
> foo2.add(iter.nextStatement());
> }
> }
>
That's more elegant ;)
Reto
>
>
>
> Andy
>
>
> dataset.commit();
>> dataset.end();
>> }
>>
>>
>> On Wed, Oct 30, 2013 at 2:42 PM, Reto Bachmann-Gmür <[email protected]
>> >wrote:
>>
>> Hi Minto
>>>
>>> Interesting problem you have there.
>>>
>>>>
>>>>
>>> Thanks ;)
>>>
>>>
>>>> Best is to fix the dreaded ConcurrentModificationException.
>>>> Occasionally
>>>> I run into it it als well. But most probably it is not that trivial to
>>>> solve.
>>>>
>>>>
>>> On hand we had some concurrency issues that caused the exception. I fixed
>>> (some of) them recently, the tests are now passing.
>>>
>>> On the other hand the exception is coming from Jena (as well as as from
>>> java collections) if the dataset (respectively the collection) is
>>> modified
>>> while iterating over it. Inthe case of addAll the modification of the
>>> underlying dataset is necessary, so this is not about some
>>> timing/concurrency.
>>>
>>> Cheers,
>>> Reto
>>>
>>>
>>>
>>>
>>>
>>>> The only work around that I see is copy the MGraph to a different
>>>> provider and do the normal addAll(). This other provider does not
>>>> necessarily need to be in memory. Basically it is 2x addAll(). One to a
>>>> different provider and one back.
>>>>
>>>> My knowledge is too limited to comment on forwarding it to Jena.
>>>>
>>>> Hope this is of some help to you.
>>>>
>>>> Regards,
>>>>
>>>> Minto
>>>>
>>>> Reto Bachmann-Gmür schreef op 30-10-2013 12:46:
>>>>
>>>>> Hi
>>>>>
>>>>> I'm having a problem using addAll two add one Mgraph from
>>>>> SingeTdbDatasetProvider to another such MGraph.
>>>>>
>>>>> The problem is that the iterator over that added graph will return a
>>>>> ConcurrentModificationException as soon as a triple has been added to
>>>>>
>>>> the
>>>>
>>>>> target graph.
>>>>>
>>>>> I don't know how to solve this. Copying the graph to be added to memory
>>>>> doesn't seem to be a compealing solution. Maybe the add-all could be
>>>>> forwarded to Jena but this would solve the problem only in some cases,
>>>>>
>>>> not
>>>>
>>>>> if there is any wrapper on the added graph or if union-graphs are used.
>>>>>
>>>>> Cheers,
>>>>> Reto
>>>>>
>>>>>
>>>>
>>>> --
>>>> ir. ing. Minto van der Sluis
>>>> Software innovator / renovator
>>>> Xup BV
>>>>
>>>> Mobiel: +31 (0) 626 014541
>>>>
>>>>
>>>>
>>>
>>
>
