Rob Vesse created JENA-522:
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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.
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