Question

I adopted a the concurrency strategy from this post. However mine looks like this:

ExecutorService executorService = Executors.newFixedThreadPool(NUMBER_OF_CREATE_KNOWLEDGE_THREADS);
List<Callable<Collection<Triple>>> todo = new ArrayList<Callable<Collection<Triple>>>(this.patternMappingList.size());
for (PatternMapping mapping : this.patternMappingList ) {
    todo.add(new CreateKnowledgeCallable(mapping, i++));
}
try {

    List<Future<Collection<Triple>>> answers = executorService.invokeAll(todo);
    for (Future<Collection<Triple>> future : answers) {

        Collection<Triple> triples = future.get();
        this.writeNTriplesFile(triples);
    }    
}
catch (InterruptedException e) { ... }
catch (ExecutionException e) { ... }

executorService.shutdown();
executorService.shutdownNow();

But the ExecutorService never shuts down. I tried to debug how many of the CreateKnowledgeCallable are finished, but this number seems to vary (after no new threads/callables are executed but the service keeps running). I am sure a logged and printed every possible exception but I can’t see one happening. It also seems that after a while nothing happens anymore except that NUMBER_OF_CREATE_KNOWLEDGE_THREADS cpus are spinning at 100% forever. What am I doing wrong?
If you need to more specific infos I would be happy to provide them for you!

Kind regards,
Daniel

Answer 1

Everyone with this sort of problems should try to implement the same algorithm without concurrency. With the help of this method, I found that a component has thrown a runtime exception which was swallowed.