Java Code Examples for java.util.concurrent.CompletionService#poll()

/**
 * Test that LoggingRegistry is concurrent-sage initialized over multiple calls. Creating more than 1000 threads can
 * cause significant performance impact.
 *
 * @throws InterruptedException
 * @throws ExecutionException
 */
@Test( timeout = 30000 )
public void testLoggingRegistryConcurrentInitialization() throws InterruptedException, ExecutionException {
  CountDownLatch start = new CountDownLatch( 1 );

  int count = 10;
  CompletionService<LoggingRegistry> drover = registerHounds( count, start );
  // fire!
  start.countDown();

  Set<LoggingRegistry> distinct = new HashSet<LoggingRegistry>();

  int i = 0;
  while ( i < count ) {
    Future<LoggingRegistry> complete = drover.poll( 15, TimeUnit.SECONDS );
    LoggingRegistry instance = complete.get();
    distinct.add( instance );
    i++;
  }
  Assert.assertEquals( "Only one singlton instance ;)", 1, distinct.size() );
}
 

/**
 * poll returns non-null when the returned task is completed
 */
public void testPoll1()
    throws InterruptedException, ExecutionException {
    CompletionService cs = new ExecutorCompletionService(cachedThreadPool);
    assertNull(cs.poll());
    cs.submit(new StringTask());

    long startTime = System.nanoTime();
    Future f;
    while ((f = cs.poll()) == null) {
        if (millisElapsedSince(startTime) > LONG_DELAY_MS)
            fail("timed out");
        Thread.yield();
    }
    assertTrue(f.isDone());
    assertSame(TEST_STRING, f.get());
}
 

/**
 * timed poll returns non-null when the returned task is completed
 */
public void testPoll2()
    throws InterruptedException, ExecutionException {
    CompletionService cs = new ExecutorCompletionService(cachedThreadPool);
    assertNull(cs.poll());
    cs.submit(new StringTask());

    long startTime = System.nanoTime();
    Future f;
    while ((f = cs.poll(SHORT_DELAY_MS, MILLISECONDS)) == null) {
        if (millisElapsedSince(startTime) > LONG_DELAY_MS)
            fail("timed out");
        Thread.yield();
    }
    assertTrue(f.isDone());
    assertSame(TEST_STRING, f.get());
}
 

/**
 * Test that LoggingRegistry is concurrent-sage initialized over multiple calls. Creating more than 1000 threads can
 * cause significant performance impact.
 * 
 * @throws InterruptedException
 * @throws ExecutionException
 * 
 */
@Test( timeout = 30000 )
public void testLoggingRegistryConcurrentInitialization() throws InterruptedException, ExecutionException {
  CountDownLatch start = new CountDownLatch( 1 );

  int count = 10;
  CompletionService<LoggingRegistry> drover = registerHounds( count, start );
  // fire!
  start.countDown();

  Set<LoggingRegistry> distinct = new HashSet<LoggingRegistry>();

  int i = 0;
  while ( i < count ) {
    Future<LoggingRegistry> complete = drover.poll( 15, TimeUnit.SECONDS );
    LoggingRegistry instance = complete.get();
    distinct.add( instance );
    i++;
  }
  Assert.assertEquals( "Only one singlton instance ;)", 1, distinct.size() );
}
 

/**
 * Gets the cardinality for each {@link AccumuloColumnConstraint}.
 * Given constraints are expected to be indexed! Who knows what would happen if they weren't!
 *
 * @param schema Schema name
 * @param table Table name
 * @param auths Scan authorizations
 * @param idxConstraintRangePairs Mapping of all ranges for a given constraint
 * @param earlyReturnThreshold Smallest acceptable cardinality to return early while other tasks complete
 * @param pollingDuration Duration for polling the cardinality completion service
 * @return An immutable multimap of cardinality to column constraint, sorted by cardinality from smallest to largest
 * @throws TableNotFoundException If the metrics table does not exist
 * @throws ExecutionException If another error occurs; I really don't even know anymore.
 */
public Multimap<Long, AccumuloColumnConstraint> getCardinalities(String schema, String table, Authorizations auths, Multimap<AccumuloColumnConstraint, Range> idxConstraintRangePairs, long earlyReturnThreshold, Duration pollingDuration)
{
    // Submit tasks to the executor to fetch column cardinality, adding it to the Guava cache if necessary
    CompletionService<Pair<Long, AccumuloColumnConstraint>> executor = new ExecutorCompletionService<>(executorService);
    idxConstraintRangePairs.asMap().forEach((key, value) -> executor.submit(() -> {
        long cardinality = getColumnCardinality(schema, table, auths, key.getFamily(), key.getQualifier(), value);
        LOG.debug("Cardinality for column %s is %s", key.getName(), cardinality);
        return Pair.of(cardinality, key);
    }));

    // Create a multi map sorted by cardinality
    ListMultimap<Long, AccumuloColumnConstraint> cardinalityToConstraints = MultimapBuilder.treeKeys().arrayListValues().build();
    try {
        boolean earlyReturn = false;
        int numTasks = idxConstraintRangePairs.asMap().entrySet().size();
        do {
            // Sleep for the polling duration to allow concurrent tasks to run for this time
            Thread.sleep(pollingDuration.toMillis());

            // Poll each task, retrieving the result if it is done
            for (int i = 0; i < numTasks; ++i) {
                Future<Pair<Long, AccumuloColumnConstraint>> futureCardinality = executor.poll();
                if (futureCardinality != null && futureCardinality.isDone()) {
                    Pair<Long, AccumuloColumnConstraint> columnCardinality = futureCardinality.get();
                    cardinalityToConstraints.put(columnCardinality.getLeft(), columnCardinality.getRight());
                }
            }

            // If the smallest cardinality is present and below the threshold, set the earlyReturn flag
            Optional<Entry<Long, AccumuloColumnConstraint>> smallestCardinality = cardinalityToConstraints.entries().stream().findFirst();
            if (smallestCardinality.isPresent()) {
                if (smallestCardinality.get().getKey() <= earlyReturnThreshold) {
                    LOG.info("Cardinality %s, is below threshold. Returning early while other tasks finish", smallestCardinality);
                    earlyReturn = true;
                }
            }
        }
        while (!earlyReturn && cardinalityToConstraints.entries().size() < numTasks);
    }
    catch (ExecutionException | InterruptedException e) {
        if (e instanceof InterruptedException) {
            Thread.currentThread().interrupt();
        }
        throw new PrestoException(UNEXPECTED_ACCUMULO_ERROR, "Exception when getting cardinality", e);
    }

    // Create a copy of the cardinalities
    return ImmutableMultimap.copyOf(cardinalityToConstraints);
}