com.google.common.util.concurrent.ForwardingListeningExecutorService

1. CachingClusteredClientTest#testOutOfOrderBackgroundCachePopulation()

@Test
public void testOutOfOrderBackgroundCachePopulation() throws Exception {
    // to trigger the actual execution when we are ready to shuffle the order.
    abstract class DrainTask implements Runnable {
    }
    final ForwardingListeningExecutorService randomizingExecutorService = new ForwardingListeningExecutorService() {

        final ConcurrentLinkedDeque<Pair<SettableFuture, Object>> taskQueue = new ConcurrentLinkedDeque<>();

        final ListeningExecutorService delegate = MoreExecutors.listeningDecorator(// are complete before moving on to the next query run.
        MoreExecutors.sameThreadExecutor());

        @Override
        protected ListeningExecutorService delegate() {
            return delegate;
        }

        private <T> ListenableFuture<T> maybeSubmitTask(Object task, boolean wait) {
            if (wait) {
                SettableFuture<T> future = SettableFuture.create();
                taskQueue.addFirst(Pair.<SettableFuture, Object>of(future, task));
                return future;
            } else {
                List<Pair<SettableFuture, Object>> tasks = Lists.newArrayList(taskQueue.iterator());
                Collections.shuffle(tasks, new Random(0));
                for (final Pair<SettableFuture, Object> pair : tasks) {
                    ListenableFuture future = pair.rhs instanceof Callable ? delegate.submit((Callable) pair.rhs) : delegate.submit((Runnable) pair.rhs);
                    Futures.addCallback(future, new FutureCallback() {

                        @Override
                        public void onSuccess(@Nullable Object result) {
                            pair.lhs.set(result);
                        }

                        @Override
                        public void onFailure(Throwable t) {
                            pair.lhs.setException(t);
                        }
                    });
                }
            }
            return task instanceof Callable ? delegate.submit((Callable) task) : delegate.submit((Runnable) task);
        }

        @Override
        public <T> ListenableFuture<T> submit(Callable<T> task) {
            return maybeSubmitTask(task, true);
        }

        @Override
        public ListenableFuture<?> submit(Runnable task) {
            if (task instanceof DrainTask) {
                return maybeSubmitTask(task, false);
            } else {
                return maybeSubmitTask(task, true);
            }
        }
    };
    client = makeClient(randomizingExecutorService);
    // callback to be run every time a query run is complete, to ensure all background
    // caching tasks are executed, and cache is populated before we move onto the next query
    queryCompletedCallback = new Runnable() {

        @Override
        public void run() {
            try {
                randomizingExecutorService.submit(new DrainTask() {

                    @Override
                    public void run() {
                    // no-op
                    }
                }).get();
            } catch (Exception e) {
                Throwables.propagate(e);
            }
        }
    };
    final Druids.TimeseriesQueryBuilder builder = Druids.newTimeseriesQueryBuilder().dataSource(DATA_SOURCE).intervals(SEG_SPEC).filters(DIM_FILTER).granularity(GRANULARITY).aggregators(AGGS).postAggregators(POST_AGGS).context(CONTEXT);
    QueryRunner runner = new FinalizeResultsQueryRunner(client, new TimeseriesQueryQueryToolChest(QueryRunnerTestHelper.NoopIntervalChunkingQueryRunnerDecorator()));
    testQueryCaching(runner, builder.build(), new Interval("2011-01-05/2011-01-10"), makeTimeResults(new DateTime("2011-01-05"), 85, 102, new DateTime("2011-01-06"), 412, 521, new DateTime("2011-01-07"), 122, 21894, new DateTime("2011-01-08"), 5, 20, new DateTime("2011-01-09"), 18, 521), new Interval("2011-01-10/2011-01-13"), makeTimeResults(new DateTime("2011-01-10"), 85, 102, new DateTime("2011-01-11"), 412, 521, new DateTime("2011-01-12"), 122, 21894));
}