/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.kafka.streams.processor.internals;

import org.apache.kafka.clients.admin.Admin;
import org.apache.kafka.clients.admin.DeleteRecordsResult;
import org.apache.kafka.clients.admin.RecordsToDelete;
import org.apache.kafka.clients.consumer.CommitFailedException;
import org.apache.kafka.clients.consumer.Consumer;
import org.apache.kafka.clients.consumer.ConsumerRecords;
import org.apache.kafka.clients.consumer.OffsetAndMetadata;
import org.apache.kafka.common.KafkaException;
import org.apache.kafka.common.Metric;
import org.apache.kafka.common.MetricName;
import org.apache.kafka.common.TopicPartition;
import org.apache.kafka.common.errors.TimeoutException;
import org.apache.kafka.common.utils.LogContext;
import org.apache.kafka.common.utils.Time;
import org.apache.kafka.streams.errors.LockException;
import org.apache.kafka.streams.errors.StreamsException;
import org.apache.kafka.streams.errors.TaskCorruptedException;
import org.apache.kafka.streams.errors.TaskIdFormatException;
import org.apache.kafka.streams.errors.TaskMigratedException;
import org.apache.kafka.streams.processor.TaskId;
import org.apache.kafka.streams.processor.internals.Task.State;
import org.apache.kafka.streams.processor.internals.metrics.StreamsMetricsImpl;
import org.apache.kafka.streams.state.internals.OffsetCheckpoint;
import org.slf4j.Logger;

import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
import java.util.TreeSet;
import java.util.UUID;
import java.util.concurrent.atomic.AtomicReference;
import java.util.stream.Collectors;
import java.util.stream.Stream;

import static org.apache.kafka.common.utils.Utils.intersection;
import static org.apache.kafka.common.utils.Utils.union;
import static org.apache.kafka.streams.processor.internals.StreamThread.ProcessingMode.EXACTLY_ONCE_ALPHA;
import static org.apache.kafka.streams.processor.internals.StreamThread.ProcessingMode.EXACTLY_ONCE_BETA;

public class TaskManager {
    // initialize the task list
    // activeTasks needs to be concurrent as it can be accessed
    // by QueryableState
    private final Logger log;
    private final Time time;
    private final ChangelogReader changelogReader;
    private final UUID processId;
    private final String logPrefix;
    private final InternalTopologyBuilder builder;
    private final Admin adminClient;
    private final StateDirectory stateDirectory;
    private final StreamThread.ProcessingMode processingMode;
    private final Tasks tasks;

    private Consumer<byte[], byte[]> mainConsumer;

    private DeleteRecordsResult deleteRecordsResult;

    private boolean rebalanceInProgress = false;  // if we are in the middle of a rebalance, it is not safe to commit

    // includes assigned & initialized tasks and unassigned tasks we locked temporarily during rebalance
    private final Set<TaskId> lockedTaskDirectories = new HashSet<>();

    TaskManager(final Time time,
                final ChangelogReader changelogReader,
                final UUID processId,
                final String logPrefix,
                final StreamsMetricsImpl streamsMetrics,
                final ActiveTaskCreator activeTaskCreator,
                final StandbyTaskCreator standbyTaskCreator,
                final InternalTopologyBuilder builder,
                final Admin adminClient,
                final StateDirectory stateDirectory,
                final StreamThread.ProcessingMode processingMode) {
        this.time = time;
        this.changelogReader = changelogReader;
        this.processId = processId;
        this.logPrefix = logPrefix;
        this.builder = builder;
        this.adminClient = adminClient;
        this.stateDirectory = stateDirectory;
        this.processingMode = processingMode;
        this.tasks = new Tasks(logPrefix, builder,  streamsMetrics, activeTaskCreator, standbyTaskCreator);

        final LogContext logContext = new LogContext(logPrefix);
        log = logContext.logger(getClass());
    }

    void setMainConsumer(final Consumer<byte[], byte[]> mainConsumer) {
        this.mainConsumer = mainConsumer;
        tasks.setMainConsumer(mainConsumer);
    }

    public UUID processId() {
        return processId;
    }

    InternalTopologyBuilder builder() {
        return builder;
    }

    boolean isRebalanceInProgress() {
        return rebalanceInProgress;
    }

    void handleRebalanceStart(final Set<String> subscribedTopics) {
        builder.addSubscribedTopicsFromMetadata(subscribedTopics, logPrefix);

        tryToLockAllNonEmptyTaskDirectories();

        rebalanceInProgress = true;
    }

    void handleRebalanceComplete() {
        // we should pause consumer only within the listener since
        // before then the assignment has not been updated yet.
        mainConsumer.pause(mainConsumer.assignment());

        releaseLockedUnassignedTaskDirectories();

        rebalanceInProgress = false;
    }

    /**
     * @throws TaskMigratedException
     */
    void handleCorruption(final Set<TaskId> corruptedTasks) {
        final Set<Task> corruptedActiveTasks = new HashSet<>();
        final Set<Task> corruptedStandbyTasks = new HashSet<>();

        for (final TaskId taskId : corruptedTasks) {
            final Task task = tasks.task(taskId);
            if (task.isActive()) {
                corruptedActiveTasks.add(task);
            } else {
                corruptedStandbyTasks.add(task);
            }
        }

        // Make sure to clean up any corrupted standby tasks in their entirety before committing
        // since TaskMigrated can be thrown and the resulting handleLostAll will only clean up active tasks
        closeDirtyAndRevive(corruptedStandbyTasks, true);

        // We need to commit before closing the corrupted active tasks since this will force the ongoing txn to abort
        try {
            commitAndFillInConsumedOffsetsAndMetadataPerTaskMap(tasks()
                       .values()
                       .stream()
                       .filter(t -> t.state() == Task.State.RUNNING || t.state() == Task.State.RESTORING)
                       .filter(t -> !corruptedTasks.contains(t.id()))
                       .collect(Collectors.toSet()),
                                new HashMap<>()
            );
        } catch (final TaskCorruptedException e) {
            log.info("Some additional tasks were found corrupted while trying to commit, these will be added to the " +
                         "tasks to clean and revive: {}", e.corruptedTasks());
            corruptedActiveTasks.addAll(tasks.tasks(e.corruptedTasks()));
        } catch (final TimeoutException e) {
            log.info("Hit TimeoutException when committing all non-corrupted tasks, these will be closed and revived");
            final Collection<Task> uncorruptedTasks = new HashSet<>(tasks.activeTasks());
            uncorruptedTasks.removeAll(corruptedActiveTasks);
            // Those tasks which just timed out can just be closed dirty without marking changelogs as corrupted
            closeDirtyAndRevive(uncorruptedTasks, false);
        }

        closeDirtyAndRevive(corruptedActiveTasks, true);
    }

    private void closeDirtyAndRevive(final Collection<Task> taskWithChangelogs, final boolean markAsCorrupted) {
        for (final Task task : taskWithChangelogs) {
            final Collection<TopicPartition> corruptedPartitions = task.changelogPartitions();

            // mark corrupted partitions to not be checkpointed, and then close the task as dirty
            if (markAsCorrupted) {
                task.markChangelogAsCorrupted(corruptedPartitions);
            }

            try {
                // we do not need to take the returned offsets since we are not going to commit anyways;
                // this call is only used for active tasks to flush the cache before suspending and
                // closing the topology
                task.prepareCommit();
            } catch (final RuntimeException swallow) {
                log.error("Error flushing cache for corrupted task {} ", task.id(), swallow);
            }

            try {
                task.suspend();

                // we need to enforce a checkpoint that removes the corrupted partitions
                if (markAsCorrupted) {
                    task.postCommit(true);
                }
            } catch (final RuntimeException swallow) {
                log.error("Error suspending corrupted task {} ", task.id(), swallow);
            }
            task.closeDirty();

            // For active tasks pause their input partitions so we won't poll any more records
            // for this task until it has been re-initialized;
            // Note, closeDirty already clears the partition-group for the task.
            if (task.isActive()) {
                final Set<TopicPartition> currentAssignment = mainConsumer.assignment();
                final Set<TopicPartition> taskInputPartitions = task.inputPartitions();
                final Set<TopicPartition> assignedToPauseAndReset =
                    intersection(HashSet::new, currentAssignment, taskInputPartitions);
                if (!assignedToPauseAndReset.equals(taskInputPartitions)) {
                    log.warn(
                        "Expected the current consumer assignment {} to contain the input partitions {}. " +
                            "Will proceed to recover.",
                        currentAssignment,
                        taskInputPartitions
                    );
                }

                task.addPartitionsForOffsetReset(assignedToPauseAndReset);
            }
            task.revive();
        }
    }

    /**
     * @throws TaskMigratedException if the task producer got fenced (EOS only)
     * @throws StreamsException fatal error while creating / initializing the task
     *
     * public for upgrade testing only
     */
    public void handleAssignment(final Map<TaskId, Set<TopicPartition>> activeTasks,
                                 final Map<TaskId, Set<TopicPartition>> standbyTasks) {
        log.info("Handle new assignment with:\n" +
                     "\tNew active tasks: {}\n" +
                     "\tNew standby tasks: {}\n" +
                     "\tExisting active tasks: {}\n" +
                     "\tExisting standby tasks: {}",
                 activeTasks.keySet(), standbyTasks.keySet(), activeTaskIds(), standbyTaskIds());

        builder.addSubscribedTopicsFromAssignment(
            activeTasks.values().stream().flatMap(Collection::stream).collect(Collectors.toList()),
            logPrefix
        );

        final LinkedHashMap<TaskId, RuntimeException> taskCloseExceptions = new LinkedHashMap<>();
        final Map<TaskId, Set<TopicPartition>> activeTasksToCreate = new HashMap<>(activeTasks);
        final Map<TaskId, Set<TopicPartition>> standbyTasksToCreate = new HashMap<>(standbyTasks);
        final Comparator<Task> byId = Comparator.comparing(Task::id);
        final Set<Task> tasksToRecycle = new TreeSet<>(byId);
        final Set<Task> tasksToCloseClean = new TreeSet<>(byId);
        final Set<Task> tasksToCloseDirty = new TreeSet<>(byId);

        // first rectify all existing tasks
        for (final Task task : tasks.allTasks()) {
            if (activeTasks.containsKey(task.id()) && task.isActive()) {
                tasks.updateInputPartitionsAndResume(task, activeTasks.get(task.id()));
                activeTasksToCreate.remove(task.id());
            } else if (standbyTasks.containsKey(task.id()) && !task.isActive()) {
                tasks.updateInputPartitionsAndResume(task, standbyTasks.get(task.id()));
                standbyTasksToCreate.remove(task.id());
            } else if (activeTasks.containsKey(task.id()) || standbyTasks.containsKey(task.id())) {
                // check for tasks that were owned previously but have changed active/standby status
                tasksToRecycle.add(task);
            } else {
                tasksToCloseClean.add(task);
            }
        }

        // close and recycle those tasks
        handleCloseAndRecycle(
            tasksToRecycle,
            tasksToCloseClean,
            tasksToCloseDirty,
            activeTasksToCreate,
            standbyTasksToCreate,
            taskCloseExceptions
        );

        if (!taskCloseExceptions.isEmpty()) {
            log.error("Hit exceptions while closing / recycling tasks: {}", taskCloseExceptions);

            for (final Map.Entry<TaskId, RuntimeException> entry : taskCloseExceptions.entrySet()) {
                if (!(entry.getValue() instanceof TaskMigratedException)) {
                    if (entry.getValue() instanceof KafkaException) {
                        throw entry.getValue();
                    } else {
                        throw new RuntimeException(
                            "Unexpected failure to close " + taskCloseExceptions.size() +
                                " task(s) [" + taskCloseExceptions.keySet() + "]. " +
                                "First unexpected exception (for task " + entry.getKey() + ") follows.", entry.getValue()
                        );
                    }
                }
            }

            // If all exceptions are task-migrated, we would just throw the first one.
            final Map.Entry<TaskId, RuntimeException> first = taskCloseExceptions.entrySet().iterator().next();
            throw first.getValue();
        }

        tasks.createTasks(activeTasksToCreate, standbyTasksToCreate);
    }

    private void handleCloseAndRecycle(final Set<Task> tasksToRecycle,
                                       final Set<Task> tasksToCloseClean,
                                       final Set<Task> tasksToCloseDirty,
                                       final Map<TaskId, Set<TopicPartition>> activeTasksToCreate,
                                       final Map<TaskId, Set<TopicPartition>> standbyTasksToCreate,
                                       final LinkedHashMap<TaskId, RuntimeException> taskCloseExceptions) {
        if (!tasksToCloseDirty.isEmpty()) {
            throw new IllegalArgumentException("Tasks to close-dirty should be empty");
        }

        // for all tasks to close or recycle, we should first right a checkpoint as in post-commit
        final List<Task> tasksToCheckpoint = new ArrayList<>(tasksToCloseClean);
        tasksToCheckpoint.addAll(tasksToRecycle);
        for (final Task task : tasksToCheckpoint) {
            try {
                // Note that we are not actually committing here but just check if we need to write checkpoint file:
                // 1) for active tasks prepareCommit should return empty if it has committed during suspension successfully,
                //    and their changelog positions should not change at all postCommit would not write the checkpoint again.
                // 2) for standby tasks prepareCommit should always return empty, and then in postCommit we would probably
                //    write the checkpoint file.
                final Map<TopicPartition, OffsetAndMetadata> offsets = task.prepareCommit();
                if (!offsets.isEmpty()) {
                    log.error("Task {} should have been committed when it was suspended, but it reports non-empty " +
                                    "offsets {} to commit; this means it failed during last commit and hence should be closed dirty",
                            task.id(), offsets);

                    tasksToCloseDirty.add(task);
                } else if (!task.isActive()) {
                    // For standby tasks, always try to first suspend before committing (checkpointing) it;
                    // Since standby tasks do not actually need to commit offsets but only need to
                    // flush / checkpoint state stores, so we only need to call postCommit here.
                    task.suspend();

                    task.postCommit(true);
                }
            } catch (final RuntimeException e) {
                final String uncleanMessage = String.format(
                        "Failed to checkpoint task %s. Attempting to close remaining tasks before re-throwing:",
                        task.id());
                log.error(uncleanMessage, e);
                taskCloseExceptions.putIfAbsent(task.id(), e);
                // We've already recorded the exception (which is the point of clean).
                // Now, we should go ahead and complete the close because a half-closed task is no good to anyone.
                tasksToCloseDirty.add(task);
            }
        }

        tasksToCloseClean.removeAll(tasksToCloseDirty);
        for (final Task task : tasksToCloseClean) {
            try {
                completeTaskCloseClean(task);
                if (task.isActive()) {
                    tasks.cleanUpTaskProducerAndRemoveTask(task.id(), taskCloseExceptions);
                }
            } catch (final RuntimeException e) {
                final String uncleanMessage = String.format(
                        "Failed to close task %s cleanly. Attempting to close remaining tasks before re-throwing:",
                        task.id());
                log.error(uncleanMessage, e);
                taskCloseExceptions.putIfAbsent(task.id(), e);
                tasksToCloseDirty.add(task);
            }
        }

        tasksToRecycle.removeAll(tasksToCloseDirty);
        for (final Task oldTask : tasksToRecycle) {
            try {
                if (oldTask.isActive()) {
                    final Set<TopicPartition> partitions = standbyTasksToCreate.remove(oldTask.id());
                    tasks.convertActiveToStandby((StreamTask) oldTask, partitions, taskCloseExceptions);
                } else {
                    final Set<TopicPartition> partitions = activeTasksToCreate.remove(oldTask.id());
                    tasks.convertStandbyToActive((StandbyTask) oldTask, partitions);
                }
            } catch (final RuntimeException e) {
                final String uncleanMessage = String.format("Failed to recycle task %s cleanly. Attempting to close remaining tasks before re-throwing:", oldTask.id());
                log.error(uncleanMessage, e);
                taskCloseExceptions.putIfAbsent(oldTask.id(), e);
                tasksToCloseDirty.add(oldTask);
            }
        }

        // for tasks that cannot be cleanly closed or recycled, close them dirty
        for (final Task task : tasksToCloseDirty) {
            closeTaskDirty(task);
            tasks.cleanUpTaskProducerAndRemoveTask(task.id(), taskCloseExceptions);
        }
    }

    /**
     * Tries to initialize any new or still-uninitialized tasks, then checks if they can/have completed restoration.
     *
     * @throws IllegalStateException If store gets registered after initialized is already finished
     * @throws StreamsException if the store's change log does not contain the partition
     * @return {@code true} if all tasks are fully restored
     */
    boolean tryToCompleteRestoration(final long now, final java.util.function.Consumer<Set<TopicPartition>> offsetResetter) {
        boolean allRunning = true;

        final List<Task> activeTasks = new LinkedList<>();
        for (final Task task : tasks.allTasks()) {
            try {
                task.initializeIfNeeded();
                task.clearTaskTimeout();
            } catch (final LockException retriableException) {
                // it is possible that if there are multiple threads within the instance that one thread
                // trying to grab the task from the other, while the other has not released the lock since
                // it did not participate in the rebalance. In this case we can just retry in the next iteration
                log.debug(
                    String.format("Could not initialize %s due to the following exception; will retry", task.id()),
                    retriableException
                );
                allRunning = false;
            } catch (final TimeoutException timeoutException) {
                task.maybeInitTaskTimeoutOrThrow(now, timeoutException);
                allRunning = false;
            }

            if (task.isActive()) {
                activeTasks.add(task);
            }
        }

        if (allRunning && !activeTasks.isEmpty()) {

            final Set<TopicPartition> restored = changelogReader.completedChangelogs();

            for (final Task task : activeTasks) {
                if (restored.containsAll(task.changelogPartitions())) {
                    try {
                        task.completeRestoration(offsetResetter);
                        task.clearTaskTimeout();
                    } catch (final TimeoutException timeoutException) {
                        task.maybeInitTaskTimeoutOrThrow(now, timeoutException);
                        log.debug(
                            String.format(
                                "Could not complete restoration for %s due to the following exception; will retry",
                                task.id()),
                            timeoutException
                        );

                        allRunning = false;
                    }
                } else {
                    // we found a restoring task that isn't done restoring, which is evidence that
                    // not all tasks are running
                    allRunning = false;
                }
            }
        }

        if (allRunning) {
            // we can call resume multiple times since it is idempotent.
            mainConsumer.resume(mainConsumer.assignment());
        }

        return allRunning;
    }

    /**
     * Handle the revoked partitions and prepare for closing the associated tasks in {@link #handleAssignment(Map, Map)}
     * We should commit the revoking tasks first before suspending them as we will not officially own them anymore when
     * {@link #handleAssignment(Map, Map)} is called. Note that only active task partitions are passed in from the
     * rebalance listener, so we only need to consider/commit active tasks here
     *
     * If eos-beta is used, we must commit ALL tasks. Otherwise, we can just commit those (active) tasks which are revoked
     *
     * @throws TaskMigratedException if the task producer got fenced (EOS only)
     */
    void handleRevocation(final Collection<TopicPartition> revokedPartitions) {
        final Set<TopicPartition> remainingRevokedPartitions = new HashSet<>(revokedPartitions);

        final Set<Task> revokedActiveTasks = new HashSet<>();
        final Set<Task> commitNeededActiveTasks = new HashSet<>();
        final Map<Task, Map<TopicPartition, OffsetAndMetadata>> consumedOffsetsPerTask = new HashMap<>();
        final AtomicReference<RuntimeException> firstException = new AtomicReference<>(null);

        for (final Task task : activeTaskIterable()) {
            if (remainingRevokedPartitions.containsAll(task.inputPartitions())) {
                // when the task input partitions are included in the revoked list,
                // this is an active task and should be revoked
                revokedActiveTasks.add(task);
                remainingRevokedPartitions.removeAll(task.inputPartitions());
            } else if (task.commitNeeded()) {
                commitNeededActiveTasks.add(task);
            }
        }

        if (!remainingRevokedPartitions.isEmpty()) {
            log.warn("The following partitions {} are missing from the task partitions. It could potentially " +
                         "due to race condition of consumer detecting the heartbeat failure, or the tasks " +
                         "have been cleaned up by the handleAssignment callback.", remainingRevokedPartitions);
        }

        prepareCommitAndAddOffsetsToMap(revokedActiveTasks, consumedOffsetsPerTask);

        // if we need to commit any revoking task then we just commit all of those needed committing together
        final boolean shouldCommitAdditionalTasks = !consumedOffsetsPerTask.isEmpty();
        if (shouldCommitAdditionalTasks) {
            prepareCommitAndAddOffsetsToMap(commitNeededActiveTasks, consumedOffsetsPerTask);
        }

        // even if commit failed, we should still continue and complete suspending those tasks, so we would capture
        // any exception and rethrow it at the end. some exceptions may be handled immediately and then swallowed,
        // as such we just need to skip those dirty tasks in the checkpoint
        final Set<Task> dirtyTasks = new HashSet<>();
        try {
            // in handleRevocation we must call commitOffsetsOrTransaction() directly rather than
            // commitAndFillInConsumedOffsetsAndMetadataPerTaskMap() to make sure we don't skip the
            // offset commit because we are in a rebalance
            commitOffsetsOrTransaction(consumedOffsetsPerTask);
        } catch (final TaskCorruptedException e) {
            log.warn("Some tasks were corrupted when trying to commit offsets, these will be cleaned and revived: {}",
                     e.corruptedTasks());

            // If we hit a TaskCorruptedException it must be EOS, just handle the cleanup for those corrupted tasks right here
            dirtyTasks.addAll(tasks.tasks(e.corruptedTasks()));
            closeDirtyAndRevive(dirtyTasks, true);
        } catch (final TimeoutException e) {
            log.warn("Timed out while trying to commit all tasks during revocation, these will be cleaned and revived");

            // If we hit a TimeoutException it must be ALOS, just close dirty and revive without wiping the state
            dirtyTasks.addAll(consumedOffsetsPerTask.keySet());
            closeDirtyAndRevive(dirtyTasks, false);
        } catch (final RuntimeException e) {
            log.error("Exception caught while committing those revoked tasks " + revokedActiveTasks, e);
            firstException.compareAndSet(null, e);
            dirtyTasks.addAll(consumedOffsetsPerTask.keySet());
        }

        // we enforce checkpointing upon suspending a task: if it is resumed later we just proceed normally, if it is
        // going to be closed we would checkpoint by then
        for (final Task task : revokedActiveTasks) {
            if (!dirtyTasks.contains(task)) {
                try {
                    task.postCommit(true);
                } catch (final RuntimeException e) {
                    log.error("Exception caught while post-committing task " + task.id(), e);
                    firstException.compareAndSet(null, e);
                }
            }
        }

        if (shouldCommitAdditionalTasks) {
            for (final Task task : commitNeededActiveTasks) {
                if (!dirtyTasks.contains(task)) {
                    try {
                        // for non-revoking active tasks, we should not enforce checkpoint
                        // since if it is EOS enabled, no checkpoint should be written while
                        // the task is in RUNNING tate
                        task.postCommit(false);
                    } catch (final RuntimeException e) {
                        log.error("Exception caught while post-committing task " + task.id(), e);
                        firstException.compareAndSet(null, e);
                    }
                }
            }
        }

        for (final Task task : revokedActiveTasks) {
            try {
                task.suspend();
            } catch (final RuntimeException e) {
                log.error("Caught the following exception while trying to suspend revoked task " + task.id(), e);
                firstException.compareAndSet(null, new StreamsException("Failed to suspend " + task.id(), e));
            }
        }

        if (firstException.get() != null) {
            throw firstException.get();
        }
    }

    private void prepareCommitAndAddOffsetsToMap(final Set<Task> tasksToPrepare,
                                                 final Map<Task, Map<TopicPartition, OffsetAndMetadata>> consumedOffsetsPerTask) {
        for (final Task task : tasksToPrepare) {
            final Map<TopicPartition, OffsetAndMetadata> committableOffsets = task.prepareCommit();
            if (!committableOffsets.isEmpty()) {
                consumedOffsetsPerTask.put(task, committableOffsets);
            }
        }
    }

    /**
     * Closes active tasks as zombies, as these partitions have been lost and are no longer owned.
     * NOTE this method assumes that when it is called, EVERY task/partition has been lost and must
     * be closed as a zombie.
     *
     * @throws TaskMigratedException if the task producer got fenced (EOS only)
     */
    void handleLostAll() {
        log.debug("Closing lost active tasks as zombies.");

        final Set<Task> allTask = new HashSet<>(tasks.allTasks());
        for (final Task task : allTask) {
            // Even though we've apparently dropped out of the group, we can continue safely to maintain our
            // standby tasks while we rejoin.
            if (task.isActive()) {
                closeTaskDirty(task);

                tasks.cleanUpTaskProducerAndRemoveTask(task.id(), new HashMap<>());
            }
        }

        if (processingMode == EXACTLY_ONCE_BETA) {
            tasks.reInitializeThreadProducer();
        }
    }

    /**
     * Compute the offset total summed across all stores in a task. Includes offset sum for any tasks we own the
     * lock for, which includes assigned and unassigned tasks we locked in {@link #tryToLockAllNonEmptyTaskDirectories()}.
     * Does not include stateless or non-logged tasks.
     */
    public Map<TaskId, Long> getTaskOffsetSums() {
        final Map<TaskId, Long> taskOffsetSums = new HashMap<>();

        // Not all tasks will create directories, and there may be directories for tasks we don't currently own,
        // so we consider all tasks that are either owned or on disk. This includes stateless tasks, which should
        // just have an empty changelogOffsets map.
        for (final TaskId id : union(HashSet::new, lockedTaskDirectories, tasks.tasksPerId().keySet())) {
            final Task task = tasks.owned(id) ? tasks.task(id) : null;
            // Closed and uninitialized tasks don't have any offsets so we should read directly from the checkpoint
            if (task != null && task.state() != State.CREATED && task.state() != State.CLOSED) {
                final Map<TopicPartition, Long> changelogOffsets = task.changelogOffsets();
                if (changelogOffsets.isEmpty()) {
                    log.debug("Skipping to encode apparently stateless (or non-logged) offset sum for task {}", id);
                } else {
                    taskOffsetSums.put(id, sumOfChangelogOffsets(id, changelogOffsets));
                }
            } else {
                final File checkpointFile = stateDirectory.checkpointFileFor(id);
                try {
                    if (checkpointFile.exists()) {
                        taskOffsetSums.put(id, sumOfChangelogOffsets(id, new OffsetCheckpoint(checkpointFile).read()));
                    }
                } catch (final IOException e) {
                    log.warn(String.format("Exception caught while trying to read checkpoint for task %s:", id), e);
                }
            }
        }

        return taskOffsetSums;
    }

    /**
     * Makes a weak attempt to lock all non-empty task directories in the state dir. We are responsible for computing and
     * reporting the offset sum for any unassigned tasks we obtain the lock for in the upcoming rebalance. Tasks
     * that we locked but didn't own will be released at the end of the rebalance (unless of course we were
     * assigned the task as a result of the rebalance). This method should be idempotent.
     */
    private void tryToLockAllNonEmptyTaskDirectories() {
        // Always clear the set at the beginning as we're always dealing with the
        // current set of actually-locked tasks.
        lockedTaskDirectories.clear();

        for (final File dir : stateDirectory.listNonEmptyTaskDirectories()) {
            try {
                final TaskId id = TaskId.parse(dir.getName());
                try {
                    if (stateDirectory.lock(id)) {
                        lockedTaskDirectories.add(id);
                        if (!tasks.owned(id)) {
                            log.debug("Temporarily locked unassigned task {} for the upcoming rebalance", id);
                        }
                    }
                } catch (final IOException e) {
                    // if for any reason we can't lock this task dir, just move on
                    log.warn(String.format("Exception caught while attempting to lock task %s:", id), e);
                }
            } catch (final TaskIdFormatException e) {
                // ignore any unknown files that sit in the same directory
            }
        }
    }

    /**
     * We must release the lock for any unassigned tasks that we temporarily locked in preparation for a
     * rebalance in {@link #tryToLockAllNonEmptyTaskDirectories()}.
     */
    private void releaseLockedUnassignedTaskDirectories() {
        final AtomicReference<RuntimeException> firstException = new AtomicReference<>(null);

        final Iterator<TaskId> taskIdIterator = lockedTaskDirectories.iterator();
        while (taskIdIterator.hasNext()) {
            final TaskId id = taskIdIterator.next();
            if (!tasks.owned(id)) {
                try {
                    stateDirectory.unlock(id);
                    taskIdIterator.remove();
                } catch (final IOException e) {
                    log.error(String.format("Caught the following exception while trying to unlock task %s", id), e);
                    firstException.compareAndSet(null,
                        new StreamsException(String.format("Failed to unlock task directory %s", id), e));
                }
            }
        }

        final RuntimeException fatalException = firstException.get();
        if (fatalException != null) {
            throw fatalException;
        }
    }

    private long sumOfChangelogOffsets(final TaskId id, final Map<TopicPartition, Long> changelogOffsets) {
        long offsetSum = 0L;
        for (final Map.Entry<TopicPartition, Long> changelogEntry : changelogOffsets.entrySet()) {
            final long offset = changelogEntry.getValue();


            if (offset == Task.LATEST_OFFSET) {
                // this condition can only be true for active tasks; never for standby
                // for this case, the offset of all partitions is set to `LATEST_OFFSET`
                // and we "forward" the sentinel value directly
                return Task.LATEST_OFFSET;
            } else if (offset != OffsetCheckpoint.OFFSET_UNKNOWN) {
                if (offset < 0) {
                    throw new IllegalStateException("Expected not to get a sentinel offset, but got: " + changelogEntry);
                }
                offsetSum += offset;
                if (offsetSum < 0) {
                    log.warn("Sum of changelog offsets for task {} overflowed, pinning to Long.MAX_VALUE", id);
                    return Long.MAX_VALUE;
                }
            }
        }

        return offsetSum;
    }

    private void closeTaskDirty(final Task task) {
        try {
            // we call this function only to flush the case if necessary
            // before suspending and closing the topology
            task.prepareCommit();
        } catch (final RuntimeException swallow) {
            log.error("Error flushing caches of dirty task {} ", task.id(), swallow);
        }

        try {
            task.suspend();
        } catch (final RuntimeException swallow) {
            log.error("Error suspending dirty task {} ", task.id(), swallow);
        }
        tasks.removeTaskBeforeClosing(task.id());
        task.closeDirty();
    }

    private void completeTaskCloseClean(final Task task) {
        tasks.removeTaskBeforeClosing(task.id());
        task.closeClean();
    }

    void shutdown(final boolean clean) {
        final AtomicReference<RuntimeException> firstException = new AtomicReference<>(null);

        final Set<Task> tasksToCloseDirty = new HashSet<>();
        // TODO: change type to `StreamTask`
        final Set<Task> activeTasks = new TreeSet<>(Comparator.comparing(Task::id));
        activeTasks.addAll(tasks.activeTasks());
        tasksToCloseDirty.addAll(tryCloseCleanAllActiveTasks(clean, firstException));
        tasksToCloseDirty.addAll(tryCloseCleanAllStandbyTasks(clean, firstException));

        for (final Task task : tasksToCloseDirty) {
            closeTaskDirty(task);
        }

        // TODO: change type to `StreamTask`
        for (final Task activeTask : activeTasks) {
            executeAndMaybeSwallow(
                clean,
                () -> tasks.closeAndRemoveTaskProducerIfNeeded(activeTask),
                e -> firstException.compareAndSet(null, e),
                e -> log.warn("Ignoring an exception while closing task " + activeTask.id() + " producer.", e)
            );
        }

        executeAndMaybeSwallow(
            clean,
            tasks::closeThreadProducerIfNeeded,
            e -> firstException.compareAndSet(null, e),
            e -> log.warn("Ignoring an exception while closing thread producer.", e)
        );

        tasks.clear();


        // this should be called after closing all tasks, to make sure we unlock the task dir for tasks that may
        // have still been in CREATED at the time of shutdown, since Task#close will not do so
        executeAndMaybeSwallow(
            clean,
            this::releaseLockedUnassignedTaskDirectories,
            e -> firstException.compareAndSet(null, e),
            e -> log.warn("Ignoring an exception while unlocking remaining task directories.", e)
        );

        final RuntimeException fatalException = firstException.get();
        if (fatalException != null) {
            throw new RuntimeException("Unexpected exception while closing task", fatalException);
        }
    }

    // Returns the set of active tasks that must be closed dirty
    private Collection<Task> tryCloseCleanAllActiveTasks(final boolean clean,
                                                         final AtomicReference<RuntimeException> firstException) {
        if (!clean) {
            return activeTaskIterable();
        }
        final Comparator<Task> byId = Comparator.comparing(Task::id);
        final Set<Task> tasksToCommit = new TreeSet<>(byId);
        final Set<Task> tasksToCloseDirty = new TreeSet<>(byId);
        final Set<Task> tasksToCloseClean = new TreeSet<>(byId);
        final Map<Task, Map<TopicPartition, OffsetAndMetadata>> consumedOffsetsAndMetadataPerTask = new HashMap<>();

        // first committing all tasks and then suspend and close them clean
        for (final Task task : activeTaskIterable()) {
            try {
                final Map<TopicPartition, OffsetAndMetadata> committableOffsets = task.prepareCommit();
                tasksToCommit.add(task);
                if (!committableOffsets.isEmpty()) {
                    consumedOffsetsAndMetadataPerTask.put(task, committableOffsets);
                }
                tasksToCloseClean.add(task);
            } catch (final TaskMigratedException e) {
                // just ignore the exception as it doesn't matter during shutdown
                tasksToCloseDirty.add(task);
            } catch (final RuntimeException e) {
                firstException.compareAndSet(null, e);
                tasksToCloseDirty.add(task);
            }
        }

        // If any active tasks can't be committed, none of them can be, and all that need a commit must be closed dirty
        if (processingMode == EXACTLY_ONCE_BETA && !tasksToCloseDirty.isEmpty()) {
            tasksToCloseClean.removeAll(tasksToCommit);
            tasksToCloseDirty.addAll(tasksToCommit);
        } else {
            try {
                commitOffsetsOrTransaction(consumedOffsetsAndMetadataPerTask);

                for (final Task task : activeTaskIterable()) {
                    try {
                        task.postCommit(true);
                    } catch (final RuntimeException e) {
                        log.error("Exception caught while post-committing task " + task.id(), e);
                        firstException.compareAndSet(null, e);
                        tasksToCloseDirty.add(task);
                        tasksToCloseClean.remove(task);
                    }
                }
            } catch (final TimeoutException timeoutException) {
                firstException.compareAndSet(null, timeoutException);

                tasksToCloseClean.removeAll(tasksToCommit);
                tasksToCloseDirty.addAll(tasksToCommit);
            } catch (final TaskCorruptedException taskCorruptedException) {
                firstException.compareAndSet(null, taskCorruptedException);

                final Set<TaskId> corruptedTaskIds = taskCorruptedException.corruptedTasks();
                final Set<Task> corruptedTasks = tasksToCommit
                        .stream()
                        .filter(task -> corruptedTaskIds.contains(task.id()))
                        .collect(Collectors.toSet());

                tasksToCloseClean.removeAll(corruptedTasks);
                tasksToCloseDirty.addAll(corruptedTasks);
            } catch (final RuntimeException e) {
                log.error("Exception caught while committing tasks during shutdown", e);
                firstException.compareAndSet(null, e);

                // If the commit fails, everyone who participated in it must be closed dirty
                tasksToCloseClean.removeAll(tasksToCommit);
                tasksToCloseDirty.addAll(tasksToCommit);
            }
        }

        for (final Task task : tasksToCloseClean) {
            try {
                task.suspend();
                completeTaskCloseClean(task);
            } catch (final RuntimeException e) {
                log.error("Exception caught while clean-closing task " + task.id(), e);
                firstException.compareAndSet(null, e);
                tasksToCloseDirty.add(task);
            }
        }

        return tasksToCloseDirty;
    }

    // Returns the set of standby tasks that must be closed dirty
    private Collection<Task> tryCloseCleanAllStandbyTasks(final boolean clean,
                                                          final AtomicReference<RuntimeException> firstException) {
        if (!clean) {
            return standbyTaskIterable();
        }
        final Set<Task> tasksToCloseDirty = new HashSet<>();

        // first committing and then suspend / close clean
        for (final Task task : standbyTaskIterable()) {
            try {
                task.prepareCommit();
                task.postCommit(true);
                task.suspend();
                completeTaskCloseClean(task);
            } catch (final TaskMigratedException e) {
                // just ignore the exception as it doesn't matter during shutdown
                tasksToCloseDirty.add(task);
            } catch (final RuntimeException e) {
                firstException.compareAndSet(null, e);
                tasksToCloseDirty.add(task);
            }
        }
        return tasksToCloseDirty;
    }

    Set<TaskId> activeTaskIds() {
        return activeTaskStream()
            .map(Task::id)
            .collect(Collectors.toSet());
    }

    Set<TaskId> standbyTaskIds() {
        return standbyTaskStream()
            .map(Task::id)
            .collect(Collectors.toSet());
    }

    Map<TaskId, Task> tasks() {
        // not bothering with an unmodifiable map, since the tasks themselves are mutable, but
        // if any outside code modifies the map or the tasks, it would be a severe transgression.
        return tasks.tasksPerId();
    }

    Map<TaskId, Task> activeTaskMap() {
        return activeTaskStream().collect(Collectors.toMap(Task::id, t -> t));
    }

    List<Task> activeTaskIterable() {
        return activeTaskStream().collect(Collectors.toList());
    }

    private Stream<Task> activeTaskStream() {
        return tasks.allTasks().stream().filter(Task::isActive);
    }

    Map<TaskId, Task> standbyTaskMap() {
        return standbyTaskStream().collect(Collectors.toMap(Task::id, t -> t));
    }

    private List<Task> standbyTaskIterable() {
        return standbyTaskStream().collect(Collectors.toList());
    }

    private Stream<Task> standbyTaskStream() {
        return tasks.allTasks().stream().filter(t -> !t.isActive());
    }

    // For testing only.
    int commitAll() {
        return commit(new HashSet<>(tasks.allTasks()));
    }

    /**
     * Take records and add them to each respective task
     *
     * @param records Records, can be null
     */
    void addRecordsToTasks(final ConsumerRecords<byte[], byte[]> records) {
        for (final TopicPartition partition : records.partitions()) {
            final Task activeTask = tasks.activeTasksForInputPartition(partition);

            if (activeTask == null) {
                log.error("Unable to locate active task for received-record partition {}. Current tasks: {}",
                    partition, toString(">"));
                throw new NullPointerException("Task was unexpectedly missing for partition " + partition);
            }

            activeTask.addRecords(partition, records.records(partition));
        }
    }

    /**
     * @throws TaskMigratedException if committing offsets failed (non-EOS)
     *                               or if the task producer got fenced (EOS)
     * @throws TimeoutException if task.timeout.ms has been exceeded (non-EOS)
     * @throws TaskCorruptedException if committing offsets failed due to TimeoutException (EOS)
     * @return number of committed offsets, or -1 if we are in the middle of a rebalance and cannot commit
     */
    int commit(final Collection<Task> tasksToCommit) {
        int committed = 0;

        final Map<Task, Map<TopicPartition, OffsetAndMetadata>> consumedOffsetsAndMetadataPerTask = new HashMap<>();
        try {
            committed = commitAndFillInConsumedOffsetsAndMetadataPerTaskMap(tasksToCommit, consumedOffsetsAndMetadataPerTask);
        } catch (final TimeoutException timeoutException) {
            consumedOffsetsAndMetadataPerTask
                .keySet()
                .forEach(t -> t.maybeInitTaskTimeoutOrThrow(time.milliseconds(), timeoutException));
        }

        return committed;
    }

    /**
     * @throws TaskMigratedException if committing offsets failed (non-EOS)
     *                               or if the task producer got fenced (EOS)
     * @throws TimeoutException if committing offsets failed due to TimeoutException (non-EOS)
     * @throws TaskCorruptedException if committing offsets failed due to TimeoutException (EOS)
     * @param consumedOffsetsAndMetadataPerTask an empty map that will be filled in with the prepared offsets
     * @return number of committed offsets, or -1 if we are in the middle of a rebalance and cannot commit
     */
    private int commitAndFillInConsumedOffsetsAndMetadataPerTaskMap(final Collection<Task> tasksToCommit,
                                                                    final Map<Task, Map<TopicPartition, OffsetAndMetadata>> consumedOffsetsAndMetadataPerTask) {
        if (rebalanceInProgress) {
            return -1;
        }

        int committed = 0;
        for (final Task task : tasksToCommit) {
            if (task.commitNeeded()) {
                final Map<TopicPartition, OffsetAndMetadata> offsetAndMetadata = task.prepareCommit();
                if (task.isActive()) {
                    consumedOffsetsAndMetadataPerTask.put(task, offsetAndMetadata);
                }
            }
        }

        commitOffsetsOrTransaction(consumedOffsetsAndMetadataPerTask);

        for (final Task task : tasksToCommit) {
            if (task.commitNeeded()) {
                task.clearTaskTimeout();
                ++committed;
                task.postCommit(false);
            }
        }
        return committed;
    }

    /**
     * @throws TaskMigratedException if committing offsets failed (non-EOS)
     *                               or if the task producer got fenced (EOS)
     */
    int maybeCommitActiveTasksPerUserRequested() {
        if (rebalanceInProgress) {
            return -1;
        } else {
            for (final Task task : activeTaskIterable()) {
                if (task.commitRequested() && task.commitNeeded()) {
                    return commit(activeTaskIterable());
                }
            }
            return 0;
        }
    }

    /**
     * Caution: do not invoke this directly if it's possible a rebalance is occurring, as the commit will fail. If
     * this is a possibility, prefer the {@link #commitAndFillInConsumedOffsetsAndMetadataPerTaskMap} instead.
     *
     * @throws TaskMigratedException   if committing offsets failed due to CommitFailedException (non-EOS)
     * @throws TimeoutException        if committing offsets failed due to TimeoutException (non-EOS)
     * @throws TaskCorruptedException  if committing offsets failed due to TimeoutException (EOS)
     */
    private void commitOffsetsOrTransaction(final Map<Task, Map<TopicPartition, OffsetAndMetadata>> offsetsPerTask) {
        log.debug("Committing task offsets {}", offsetsPerTask.entrySet().stream().collect(Collectors.toMap(t -> t.getKey().id(), Entry::getValue))); // avoid logging actual Task objects

        final Set<TaskId> corruptedTasks = new HashSet<>();

        if (!offsetsPerTask.isEmpty()) {
            if (processingMode == EXACTLY_ONCE_ALPHA) {
                for (final Map.Entry<Task, Map<TopicPartition, OffsetAndMetadata>> taskToCommit : offsetsPerTask.entrySet()) {
                    final Task task = taskToCommit.getKey();
                    try {
                        tasks.streamsProducerForTask(task.id())
                            .commitTransaction(taskToCommit.getValue(), mainConsumer.groupMetadata());
                    } catch (final TimeoutException timeoutException) {
                        log.error(
                            String.format("Committing task %s failed.", task.id()),
                            timeoutException
                        );
                        corruptedTasks.add(task.id());
                    }
                }
            } else {
                final Map<TopicPartition, OffsetAndMetadata> allOffsets = offsetsPerTask.values().stream()
                    .flatMap(e -> e.entrySet().stream()).collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));

                if (processingMode == EXACTLY_ONCE_BETA) {
                    try {
                        tasks.threadProducer().commitTransaction(allOffsets, mainConsumer.groupMetadata());
                    } catch (final TimeoutException timeoutException) {
                        log.error(
                            String.format("Committing task(s) %s failed.",
                                offsetsPerTask
                                    .keySet()
                                    .stream()
                                    .map(t -> t.id().toString())
                                    .collect(Collectors.joining(", "))),
                            timeoutException
                        );
                        offsetsPerTask
                            .keySet()
                            .forEach(task -> corruptedTasks.add(task.id()));
                    }
                } else {
                    try {
                        mainConsumer.commitSync(allOffsets);
                    } catch (final CommitFailedException error) {
                        throw new TaskMigratedException("Consumer committing offsets failed, " +
                                                            "indicating the corresponding thread is no longer part of the group", error);
                    } catch (final TimeoutException timeoutException) {
                        log.error(
                            String.format("Committing task(s) %s failed.",
                                offsetsPerTask
                                    .keySet()
                                    .stream()
                                    .map(t -> t.id().toString())
                                    .collect(Collectors.joining(", "))),
                            timeoutException
                        );
                        throw timeoutException;
                    } catch (final KafkaException error) {
                        throw new StreamsException("Error encountered committing offsets via consumer", error);
                    }
                }
            }

            if (!corruptedTasks.isEmpty()) {
                throw new TaskCorruptedException(corruptedTasks);
            }
        }
    }

    /**
     * @throws TaskMigratedException if the task producer got fenced (EOS only)
     */
    int process(final int maxNumRecords, final Time time) {
        int totalProcessed = 0;

        long now = time.milliseconds();
        for (final Task task : activeTaskIterable()) {
            int processed = 0;
            final long then = now;
            try {
                while (processed < maxNumRecords && task.process(now)) {
                    task.clearTaskTimeout();
                    processed++;
                }
            } catch (final TimeoutException timeoutException) {
                task.maybeInitTaskTimeoutOrThrow(now, timeoutException);
                log.debug(
                    String.format(
                        "Could not complete processing records for %s due to the following exception; will move to next task and retry later",
                        task.id()),
                    timeoutException
                );
            } catch (final TaskMigratedException e) {
                log.info("Failed to process stream task {} since it got migrated to another thread already. " +
                             "Will trigger a new rebalance and close all tasks as zombies together.", task.id());
                throw e;
            } catch (final RuntimeException e) {
                log.error("Failed to process stream task {} due to the following error:", task.id(), e);
                throw e;
            } finally {
                now = time.milliseconds();
                totalProcessed += processed;
                task.recordProcessBatchTime(now - then);
            }
        }

        return totalProcessed;
    }

    void recordTaskProcessRatio(final long totalProcessLatencyMs, final long now) {
        for (final Task task : activeTaskIterable()) {
            task.recordProcessTimeRatioAndBufferSize(totalProcessLatencyMs, now);
        }
    }

    /**
     * @throws TaskMigratedException if the task producer got fenced (EOS only)
     */
    int punctuate() {
        int punctuated = 0;

        for (final Task task : activeTaskIterable()) {
            try {
                if (task.maybePunctuateStreamTime()) {
                    punctuated++;
                }
                if (task.maybePunctuateSystemTime()) {
                    punctuated++;
                }
            } catch (final TaskMigratedException e) {
                log.info("Failed to punctuate stream task {} since it got migrated to another thread already. " +
                             "Will trigger a new rebalance and close all tasks as zombies together.", task.id());
                throw e;
            } catch (final KafkaException e) {
                log.error("Failed to punctuate stream task {} due to the following error:", task.id(), e);
                throw e;
            }
        }

        return punctuated;
    }

    void maybePurgeCommittedRecords() {
        // we do not check any possible exceptions since none of them are fatal
        // that should cause the application to fail, and we will try delete with
        // newer offsets anyways.
        if (deleteRecordsResult == null || deleteRecordsResult.all().isDone()) {

            if (deleteRecordsResult != null && deleteRecordsResult.all().isCompletedExceptionally()) {
                log.debug("Previous delete-records request has failed: {}. Try sending the new request now",
                          deleteRecordsResult.lowWatermarks());
            }

            final Map<TopicPartition, RecordsToDelete> recordsToDelete = new HashMap<>();
            for (final Task task : activeTaskIterable()) {
                for (final Map.Entry<TopicPartition, Long> entry : task.purgeableOffsets().entrySet()) {
                    recordsToDelete.put(entry.getKey(), RecordsToDelete.beforeOffset(entry.getValue()));
                }
            }
            if (!recordsToDelete.isEmpty()) {
                deleteRecordsResult = adminClient.deleteRecords(recordsToDelete);
                log.trace("Sent delete-records request: {}", recordsToDelete);
            }
        }
    }

    /**
     * Produces a string representation containing useful information about the TaskManager.
     * This is useful in debugging scenarios.
     *
     * @return A string representation of the TaskManager instance.
     */
    @Override
    public String toString() {
        return toString("");
    }

    public String toString(final String indent) {
        final StringBuilder stringBuilder = new StringBuilder();
        stringBuilder.append("TaskManager\n");
        stringBuilder.append(indent).append("\tMetadataState:\n");
        stringBuilder.append(indent).append("\tTasks:\n");
        for (final Task task : tasks.allTasks()) {
            stringBuilder.append(indent)
                         .append("\t\t")
                         .append(task.id())
                         .append(" ")
                         .append(task.state())
                         .append(" ")
                         .append(task.getClass().getSimpleName())
                         .append('(').append(task.isActive() ? "active" : "standby").append(')');
        }
        return stringBuilder.toString();
    }

    Map<MetricName, Metric> producerMetrics() {
        return tasks.producerMetrics();
    }

    Set<String> producerClientIds() {
        return tasks.producerClientIds();
    }

    Set<TaskId> lockedTaskDirectories() {
        return Collections.unmodifiableSet(lockedTaskDirectories);
    }

    public static void executeAndMaybeSwallow(final boolean clean,
                                              final Runnable runnable,
                                              final java.util.function.Consumer<RuntimeException> actionIfClean,
                                              final java.util.function.Consumer<RuntimeException> actionIfNotClean) {
        try {
            runnable.run();
        } catch (final RuntimeException e) {
            if (clean) {
                actionIfClean.accept(e);
            } else {
                actionIfNotClean.accept(e);
            }
        }
    }

    public static void executeAndMaybeSwallow(final boolean clean,
                                              final Runnable runnable,
                                              final String name,
                                              final Logger log) {
        executeAndMaybeSwallow(clean, runnable, e -> {
            throw e; },
            e -> log.debug("Ignoring error in unclean {}", name));
    }

    boolean needsInitializationOrRestoration() {
        return tasks().values().stream().anyMatch(Task::needsInitializationOrRestoration);
    }

    // for testing only
    void addTask(final Task task) {
        tasks.addTask(task);
    }
}
