[jira] [Created] (JENA-522) DatasetGraphWithLock claims to support multiple readers but appears not to

["Rob Vesse (JIRA)" <ji...@apache.org>]

Rob Vesse created JENA-522:
------------------------------

             Summary: 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 2.10.2
            Reporter: Rob Vesse


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:

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.

I put together the following test case which illustrates the issue:

    @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 {
                    dsg.begin(ReadWrite.READ);

                    // Hold the lock for a few seconds
                    try {
                        Thread.sleep(500);
                    } catch (InterruptedException e) {
                        // Ignore error
                    }

                    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();
        }
    }

So the problem appears to be that DatasetGraphWithLock claims multi-reader support but in reality does not allow this.

--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators
For more information on JIRA, see: http://www.atlassian.com/software/jira