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https://issues.apache.org/jira/browse/JENA-522?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Andy Seaborne closed JENA-522.
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> DatasetGraphWithLock claims to support multiple readers but appears not to
> --------------------------------------------------------------------------
>
> Key: JENA-522
> URL: https://issues.apache.org/jira/browse/JENA-522
> Project: Apache Jena
> Issue Type: Bug
> Components: ARQ
> Affects Versions: Jena 2.11.0
> Reporter: Rob Vesse
> Assignee: Andy Seaborne
> Labels: concurrency, lock, multi-threading
> Fix For: Jena 2.11.0
>
> Attachments: JENA-522.patch
>
>
> This bug originates out of a StackOverflow question pertaining to jena-text
> http://stackoverflow.com/q/18385738/107591
> However upon investigation the culprit appears to be
> {{DatasetGraphWithLock}}, reproducing my analysis from my SO answer here:
> {quote}
> The issue is that the dataset with inference implicitly uses ARQ's standard
> in-memory Dataset implementation and this does not support transactions.
> However text datasets which correspond to {{DatasetGraphText}} internally
> (and in your stack trace) requires the wrapped dataset to support
> transactions and where they do not wraps them with {{DatasetGraphWithLock}}.
> It is this that appears to be encountering the problem with the lock, the
> documentation states that this should support multiple readers but having
> followed the logic of the code I'm not sure that it actually allows this.
> {quote}
> I put together the following test case which illustrates the issue:
> {noformat}
> @Test
> public synchronized void dsg_with_lock_concurrency_02() throws
> InterruptedException, ExecutionException, TimeoutException {
> ExecutorService executor = Executors.newCachedThreadPool();
> try {
> final DatasetGraphWithLock dsg = new
> DatasetGraphWithLock(DatasetGraphFactory.createMem());
> Callable<Boolean> callable = new Callable<Boolean>() {
> @Override
> public Boolean call() throws Exception {
> // Get a read lock
> dsg.begin(ReadWrite.READ);
> // Hold the lock for a short time
> try {
> Thread.sleep(500);
> } catch (InterruptedException e) {
> // Ignore error
> }
> // Release the lock
> dsg.commit();
> return true;
> }
> };
> // Run the callable a bunch of times
> List<Future<Boolean>> futures = new ArrayList<Future<Boolean>>();
> for (int i = 0; i < 100; i++) {
> futures.add(executor.submit(callable));
> }
> // Check all the futures come back OK
> for (Future<Boolean> f : futures) {
> Assert.assertTrue(f.get(3, TimeUnit.SECONDS));
> }
> } finally {
> executor.shutdownNow();
> }
> }
> {noformat}
> So the problem appears to be that DatasetGraphWithLock claims multi-reader
> support but in reality does not allow this.
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