Example usage for java.util.concurrent CompletionService poll

Introduction

In this page you can find the example usage for java.util.concurrent CompletionService poll.

Prototype

Future<V> poll();

Source Link

Document

Retrieves and removes the Future representing the next completed task, or null if none are present.

Usage

From source file:io.prestosql.plugin.accumulo.index.ColumnCardinalityCache.java

/**
 * 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// w w  w.java  2 s  . c  om
 * @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);
}

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From source file:com.facebook.presto.accumulo.index.ColumnCardinalityCache.java

/**
 * 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//from   www. j ava  2  s .  co m
 * @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) throws ExecutionException, TableNotFoundException {
    // 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);
}

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From source file:org.codice.ddf.admin.common.PrioritizedBatchExecutor.java

private Optional<R> pollRemainingBatches(long totalWaitTime, TimeUnit timeUnit,
        CompletionService<T> completionService, int currentBatchSize, int index) {
    Future<T> taskFuture;//from   w ww  .  java 2s .c o  m
    String timeUnitString = timeUnit.toString();
    LOGGER.debug("\tExceeded max wait time of {} {}. Polling remaining batches.", totalWaitTime,
            timeUnitString);

    while ((taskFuture = completionService.poll()) != null) {
        Optional<R> result = handleTaskResult(taskFuture);
        if (result.isPresent()) {
            LOGGER.debug("\tReturning valid task result {} of {} tasks.", index + 1, currentBatchSize);

            return result;
        }
    }
    return Optional.empty();
}

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