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/*
 * Copyright (c) 2008-2021, Hazelcast, Inc. All Rights Reserved.
 *
 * Licensed 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 com.hazelcast.map.impl;

import com.hazelcast.cluster.Address;
import com.hazelcast.cluster.Member;
import com.hazelcast.config.MaxSizePolicy;
import com.hazelcast.internal.cluster.ClusterService;
import com.hazelcast.internal.partition.IPartition;
import com.hazelcast.internal.partition.IPartitionService;
import com.hazelcast.internal.serialization.Data;
import com.hazelcast.internal.util.FutureUtil;
import com.hazelcast.internal.util.StateMachine;
import com.hazelcast.internal.util.concurrent.BackoffIdleStrategy;
import com.hazelcast.internal.util.concurrent.IdleStrategy;
import com.hazelcast.internal.util.scheduler.CoalescingDelayedTrigger;
import com.hazelcast.logging.ILogger;
import com.hazelcast.map.MapLoader;
import com.hazelcast.map.impl.mapstore.MapStoreContext;
import com.hazelcast.map.impl.operation.KeyLoadStatusOperation;
import com.hazelcast.map.impl.operation.KeyLoadStatusOperationFactory;
import com.hazelcast.map.impl.operation.MapOperation;
import com.hazelcast.map.impl.operation.MapOperationProvider;
import com.hazelcast.map.impl.operation.TriggerLoadIfNeededOperation;
import com.hazelcast.spi.impl.InternalCompletableFuture;
import com.hazelcast.spi.impl.executionservice.ExecutionService;
import com.hazelcast.spi.impl.operationservice.Operation;
import com.hazelcast.spi.impl.operationservice.OperationService;
import com.hazelcast.spi.properties.ClusterProperty;
import com.hazelcast.spi.properties.HazelcastProperty;

import java.io.Closeable;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
import java.util.concurrent.Future;
import java.util.concurrent.Semaphore;
import java.util.concurrent.TimeUnit;
import java.util.function.BiConsumer;
import java.util.function.Function;

import static com.hazelcast.internal.nio.IOUtil.closeResource;
import static com.hazelcast.internal.util.IterableUtil.limit;
import static com.hazelcast.internal.util.IterableUtil.map;
import static com.hazelcast.logging.Logger.getLogger;
import static com.hazelcast.map.impl.MapKeyLoaderUtil.assignRole;
import static com.hazelcast.map.impl.MapKeyLoaderUtil.toBatches;
import static com.hazelcast.map.impl.MapKeyLoaderUtil.toPartition;
import static com.hazelcast.map.impl.MapService.SERVICE_NAME;
import static com.hazelcast.spi.impl.executionservice.ExecutionService.MAP_LOAD_ALL_KEYS_EXECUTOR;
import static java.util.concurrent.TimeUnit.MILLISECONDS;
import static java.util.concurrent.TimeUnit.SECONDS;

/**
 * One instance of this class is created per {@link
 * com.hazelcast.map.impl.recordstore.RecordStore}.
 *
 * It loads keys via {@link MapLoader#loadAllKeys} and sends
 * them to all map partitions. Matching values of these keys are
 * loaded in partition owner nodes via {@link MapLoader#loadAll}.
 */
public class MapKeyLoader {

    /**
     * Puts node-wide loaded key limit for all {@link
     * MapLoader#loadAllKeys()} calls being done at the same time.
     */
    public static final int DEFAULT_LOADED_KEY_LIMIT_PER_NODE = 50000;
    public static final String PROP_LOADED_KEY_LIMITER_PER_NODE = "hazelcast.map.loaded.key.limit.per.node";
    public static final HazelcastProperty LOADED_KEY_LIMITER_PER_NODE
            = new HazelcastProperty(PROP_LOADED_KEY_LIMITER_PER_NODE, DEFAULT_LOADED_KEY_LIMIT_PER_NODE);

    private static final long LOADING_TRIGGER_DELAY = SECONDS.toMillis(5);
    private static final IdleStrategy IDLE_STRATEGY = new BackoffIdleStrategy(
            0, 0, MILLISECONDS.toNanos(1), MILLISECONDS.toNanos(500));

    private ILogger logger;
    private String mapName;
    private OperationService opService;
    private IPartitionService partitionService;
    private Function toData;
    private ExecutionService execService;
    private CoalescingDelayedTrigger delayedTrigger;
    /**
     * The configured maximum entry count per node or
     * {@code -1} if the default is used or the max size
     * policy is not {@link MaxSizePolicy#PER_NODE}
     */
    private int maxSizePerNode;
    /**
     * The maximum size of a batch of loaded keys
     * sent to a single partition for value loading
     *
     * @see ClusterProperty#MAP_LOAD_CHUNK_SIZE
     */
    private int maxBatch;
    private int mapNamePartition;
    private int partitionId;
    private boolean hasBackup;
    /**
     * The future representing pending completion of the key loading
     * task on the {@link Role#SENDER} partition. The result of this
     * future represents the result of process of key loading and
     * dispatching to the partition owners for value loading but
     * not the result of the value loading itself or the overall
     * result of populating the record stores with map loader
     * data. This future may also denote that this is the map key
     * loader with the {@link Role#RECEIVER} role and that it has
     * triggered key loading on the {@link Role#SENDER} partition.
     *
     * @see #sendKeys(MapStoreContext, boolean) @see
     * #triggerLoading() @see #trackLoading(boolean,
     * Throwable) @see MapLoader#loadAllKeys()
     */
    private LoadFinishedFuture keyLoadFinished = new LoadFinishedFuture(true);
    private MapOperationProvider operationProvider;

    /**
     * Role of this {@link MapKeyLoader}
     */
    enum Role {
        NONE,
        /**
         * Loads keys from the map loader and dispatches them to the
         * partition owners. The sender map key loader is equal to the
         * partition owner for the partition containing the map name.
         *
         * @see MapLoader#loadAllKeys() @see
         * com.hazelcast.map.impl.operation.LoadMapOperation
         */
        SENDER,
        /**
         * Receives keys from sender. The receiver map key loader
         * is the partition owner for keys received by the sender.
         */
        RECEIVER,
        /**
         * Restarts sending if SENDER fails. The sender
         * backup map key loader is equal to the first
         * replica of the partition containing the map name.
         */
        SENDER_BACKUP
    }

    enum State {
        NOT_LOADED,
        LOADING,
        LOADED
    }

    private final StateMachine role = StateMachine.of(Role.NONE)
            .withTransition(Role.NONE, Role.SENDER, Role.RECEIVER, Role.SENDER_BACKUP)
            .withTransition(Role.SENDER_BACKUP, Role.SENDER);

    private final StateMachine state = StateMachine.of(State.NOT_LOADED)
            .withTransition(State.NOT_LOADED, State.LOADING)
            .withTransition(State.LOADING, State.LOADED, State.NOT_LOADED)
            .withTransition(State.LOADED, State.LOADING);

    /**
     * Controls the loaded number of keys during
     * {@link MapLoader#loadAllKeys()} call to
     * use heap effectively and to prevent OOME.
     */
    private final Semaphore nodeWideLoadedKeyLimiter;
    private final ClusterService clusterService;

    public MapKeyLoader(String mapName, OperationService opService, IPartitionService ps,
                        ClusterService clusterService, ExecutionService execService,
                        Function serialize, Semaphore nodeWideLoadedKeyLimiter) {
        this.mapName = mapName;
        this.opService = opService;
        this.partitionService = ps;
        this.clusterService = clusterService;
        this.toData = serialize;
        this.execService = execService;
        this.logger = getLogger(MapKeyLoader.class);
        this.nodeWideLoadedKeyLimiter = nodeWideLoadedKeyLimiter;
    }

    /**
     * Triggers key loading on the map key loader with the {@link Role#SENDER}
     * role.
     *
     * @param mapStoreContext the map store context for this map
     * @param partitionId     the partition ID of this map key loader
     * @return a future representing pending completion of the key loading task
     */
    public Future startInitialLoad(MapStoreContext mapStoreContext, int partitionId) {
        this.partitionId = partitionId;
        this.mapNamePartition = partitionService.getPartitionId(toData.apply(mapName));
        Role newRole = calculateRole();

        role.nextOrStay(newRole);
        state.next(State.LOADING);

        if (logger.isFinestEnabled()) {
            logger.finest("startInitialLoad invoked " + getStateMessage());
        }

        switch (newRole) {
            case SENDER:
                return sendKeys(mapStoreContext, false);
            case SENDER_BACKUP:
            case RECEIVER:
                return triggerLoading();
            default:
                return keyLoadFinished;
        }
    }

    /**
     * Calculates and returns the role for the map key loader on this partition
     */
    private Role calculateRole() {
        boolean isPartitionOwner = partitionService.isPartitionOwner(partitionId);
        boolean isMapNamePartition = partitionId == mapNamePartition;
        boolean isMapNamePartitionFirstReplica = false;
        if (hasBackup && isMapNamePartition) {
            IPartition partition = partitionService.getPartition(partitionId);
            Address firstReplicaAddress = partition.getReplicaAddress(1);
            Member member = clusterService.getMember(firstReplicaAddress);
            if (member != null) {
                isMapNamePartitionFirstReplica = member.localMember();
            }
        }
        return assignRole(isPartitionOwner, isMapNamePartition, isMapNamePartitionFirstReplica);
    }

    /**
     * Triggers key loading if there is no ongoing key loading task, otherwise
     * does nothing. The actual loading is done on the
     * {@link ExecutionService#MAP_LOAD_ALL_KEYS_EXECUTOR} executor.
     * The loaded keys will be dispatched to partition owners for value loading.
     *
     * @param mapStoreContext       the map store context for this map
     * @param replaceExistingValues if the existing entries for the loaded keys should be replaced
     * @return a future representing pending completion of the key loading task
     * @see MapLoader#loadAllKeys()
     * @see #sendKeysInBatches(MapStoreContext, boolean)
     */
    private Future sendKeys(final MapStoreContext mapStoreContext, final boolean replaceExistingValues) {
        if (keyLoadFinished.isDone()) {
            keyLoadFinished = new LoadFinishedFuture();

            Future sent = execService.submit(MAP_LOAD_ALL_KEYS_EXECUTOR, () -> {
                sendKeysInBatches(mapStoreContext, replaceExistingValues);
                return false;
            });

            execService.asCompletableFuture(sent).whenCompleteAsync(keyLoadFinished);
        }

        return keyLoadFinished;
    }

    /**
     * Triggers key loading if needed on the map key loader with the
     * {@link Role#SENDER} or {@link Role#SENDER_BACKUP} role if this
     * partition does not have any ongoing key loading task.
     *
     * @return a future representing pending completion of the key loading task
     */
    private Future triggerLoading() {
        if (keyLoadFinished.isDone()) {
            keyLoadFinished = new LoadFinishedFuture();

            // side effect -> just trigger load on SENDER_BACKUP ID SENDER died
            execService.execute(MAP_LOAD_ALL_KEYS_EXECUTOR, () -> {
                // checks if loading has finished and triggers loading in case SENDER died and SENDER_BACKUP took over.
                Operation op = new TriggerLoadIfNeededOperation(mapName);
                opService.invokeOnPartition(SERVICE_NAME, op, mapNamePartition)
                        // required since loading may be triggered after migration
                        // and in this case the callback is the only way to get to know if the key load finished or not.
                        .whenCompleteAsync(loadingFinishedCallback());
            });
        }
        return keyLoadFinished;
    }


    /**
     * Returns an execution callback to notify the record store for this map
     * key loader that the key loading has finished.
     */
    private BiConsumer loadingFinishedCallback() {
        return (loadingFinished, throwable) -> {
            if (throwable == null) {
                if (loadingFinished) {
                    updateLocalKeyLoadStatus(null);
                }
            } else {
                updateLocalKeyLoadStatus(throwable);
            }
        };
    }

    /**
     * Notifies the record store of this map key loader that key loading has
     * completed.
     *
     * @param t an exception that occurred during key loading or {@code null}
     *          if there was no exception
     */
    private void updateLocalKeyLoadStatus(Throwable t) {
        Operation op = new KeyLoadStatusOperation(mapName, t);
        // This updates the local record store on the partition thread.
        // If invoked by the SENDER_BACKUP however it's the replica index has to be set to 1, otherwise
        // it will be a remote call to the SENDER who is the owner of the given partitionId.
        if (hasBackup && role.is(Role.SENDER_BACKUP)) {
            opService.createInvocationBuilder(SERVICE_NAME, op, partitionId).setReplicaIndex(1).invoke();
        } else {
            opService.createInvocationBuilder(SERVICE_NAME, op, partitionId).invoke();
        }
    }

    /**
     * Triggers key and value loading if there is no ongoing or completed
     * key loading task, otherwise does nothing.
     * The actual loading is done on a separate thread.
     *
     * @param mapStoreContext       the map store context for this map
     * @param replaceExistingValues if the existing entries for the loaded keys should be replaced
     * @return a future representing pending completion of the key loading task
     */
    public Future startLoading(MapStoreContext mapStoreContext, boolean replaceExistingValues) {
        role.nextOrStay(Role.SENDER);

        if (state.is(State.LOADING)) {
            return keyLoadFinished;
        }
        state.next(State.LOADING);

        return sendKeys(mapStoreContext, replaceExistingValues);
    }

    /**
     * Advances the state of this map key loader and sets the {@link #keyLoadFinished}
     * result if the {@code lastBatch} is {@code true}.
     * 

     * If there was an exception during key loading, you may pass it as the
     * {@code exception} paramter and it will be set as the result of the future.
     *
     * @param lastBatch if the last key batch was sent
     * @param exception an exception that occurred during key loading
     */
    public void trackLoading(boolean lastBatch, Throwable exception) {
        if (lastBatch) {
            state.nextOrStay(State.LOADED);
            if (exception != null) {
                keyLoadFinished.completeExceptionally(exception);
            } else {
                keyLoadFinished.complete(true);
            }
        } else if (state.is(State.LOADED)) {
            state.next(State.LOADING);
        }
    }

    /**
     * Triggers key loading on SENDER if it hadn't started. Delays triggering if invoked multiple times.
     */
    public void triggerLoadingWithDelay() {
        if (delayedTrigger == null) {
            Runnable runnable = () -> {
                Operation op = new TriggerLoadIfNeededOperation(mapName);
                opService.invokeOnPartition(SERVICE_NAME, op, mapNamePartition);
            };
            delayedTrigger = new CoalescingDelayedTrigger(execService, LOADING_TRIGGER_DELAY, LOADING_TRIGGER_DELAY, runnable);
        }

        delayedTrigger.executeWithDelay();
    }

    /**
     * Returns {@code true} if the keys are not loaded yet, promoting this key
     * loader and resetting the loading state if necessary in the process.
     * If this gets invoked on SENDER BACKUP it means the SENDER died and
     * SENDER BACKUP takes over.
     */
    public boolean shouldDoInitialLoad() {
        if (role.is(Role.SENDER_BACKUP)) {
            // was backup. become primary sender
            role.next(Role.SENDER);

            if (state.is(State.LOADING)) {
                // previous loading was in progress. cancel and start from scratch
                state.next(State.NOT_LOADED);
                keyLoadFinished.complete(false);
            }
        }

        return state.is(State.NOT_LOADED);
    }

    /**
     * Loads keys from the map loader and sends them to the partition owners in batches
     * for value loading. This method will return after all keys have been dispatched
     * to the partition owners for value loading and all partitions have been notified
     * that the key loading has completed.
     * The values will still be loaded asynchronously and can be put into the record
     * stores after this method has returned.
     * If there is a configured max size policy per node, the keys will be loaded until this
     * many keys have been loaded from the map loader. If the keys returned from the
     * map loader are not equally distributed over all partitions, this may cause some nodes
     * to load more entries than others and exceed the configured policy.
     *
     * @param mapStoreContext       the map store context for this map
     * @param replaceExistingValues if the existing entries for the loaded keys should be replaced
     * @throws Exception if there was an exception when notifying the record stores that the key
     *                   loading has finished
     * @see MapLoader#loadAllKeys()
     */
    private void sendKeysInBatches(MapStoreContext mapStoreContext, boolean replaceExistingValues) throws Exception {
        if (logger.isFinestEnabled()) {
            logger.finest("sendKeysInBatches invoked " + getStateMessage());
        }

        int clusterSize = partitionService.getMemberPartitionsMap().size();
        Iterator keys = null;
        Throwable loadError = null;

        try {
            Iterable allKeys = mapStoreContext.loadAllKeys();
            keys = allKeys.iterator();
            Iterator dataKeys = map(keys, toData);
            int mapMaxSize = clusterSize * maxSizePerNode;

            if (mapMaxSize > 0) {
                dataKeys = limit(dataKeys, mapMaxSize);
            }

            Iterator> partitionsAndKeys = map(dataKeys, toPartition(partitionService));
            Iterator>> batches = toBatches(partitionsAndKeys, maxBatch, nodeWideLoadedKeyLimiter);

            int callCount = 0;
            List futures = new ArrayList<>();
            while (batches.hasNext()) {
                Map> batch = batches.next();
                if (batch.isEmpty()) {
                    IDLE_STRATEGY.idle(++callCount);
                } else {
                    callCount = 0;
                    futures.addAll(sendBatch(batch, replaceExistingValues, nodeWideLoadedKeyLimiter));
                }
            }

            // This acts as a barrier to prevent re-ordering of key distribution operations (LoadAllOperation)
            // and LoadStatusOperation(s) which indicates all keys were already loaded.
            // Re-ordering of in-flight operations can happen during a partition migration. We are waiting here
            // for all LoadAllOperation(s) to be ACKed by receivers and only then we send them the LoadStatusOperation
            // See https://github.com/hazelcast/hazelcast/issues/4024 for additional details
            FutureUtil.waitForever(futures);

        } catch (Exception caught) {
            loadError = caught;
        } finally {
            sendKeyLoadCompleted(clusterSize, loadError);

            if (keys instanceof Closeable) {
                closeResource((Closeable) keys);
            }
        }
    }

    /**
     * Sends the key batches to the partition owners for value
     * loading. The returned futures represent pending offloading
     * of the value loading on the partition owner. This means
     * that once the partition owner receives the keys, it will
     * offload the value loading task and return immediately,
     * thus completing the future. The future does not mean
     * the value loading tasks have been completed or that the
     * entries have been loaded and put into the record store.
     *
     * @param batch                    a map from partition ID
     *                                 to a batch of keys for that partition
     * @param replaceExistingValues    if the existing
     *                                 entries for the loaded keys should be replaced
     * @param nodeWideLoadedKeyLimiter controls number of loaded keys
     * @return a list of futures representing pending
     * completion of the value offloading task
     */
    private List sendBatch(Map> batch, boolean replaceExistingValues,
                                   Semaphore nodeWideLoadedKeyLimiter) {
        Set>> entries = batch.entrySet();

        List futures = new ArrayList<>(entries.size());

        Iterator>> iterator = entries.iterator();
        while (iterator.hasNext()) {
            Entry> e = iterator.next();
            int partitionId = e.getKey();
            List keys = e.getValue();
            int numberOfLoadedKeys = keys.size();

            try {
                MapOperation op = operationProvider.createLoadAllOperation(mapName, keys, replaceExistingValues);
                InternalCompletableFuture future = opService.invokeOnPartition(SERVICE_NAME, op, partitionId);
                futures.add(future);
            } finally {
                nodeWideLoadedKeyLimiter.release(numberOfLoadedKeys);
            }

            iterator.remove();
        }

        return futures;
    }

    /**
     * Notifies the record stores of the {@link MapKeyLoader.Role#SENDER},
     * {@link MapKeyLoader.Role#SENDER_BACKUP} and all other partition record
     * stores that the key loading has finished and the keys have been dispatched
     * to the partition owners for value loading.
     *
     * @param clusterSize the size of the cluster
     * @param exception   the exception that occurred during key loading or
     *                    {@code null} if there was no exception
     * @throws Exception if there was an exception when notifying the record stores that the key
     *                   loading has finished
     * @see com.hazelcast.map.impl.recordstore.RecordStore#updateLoadStatus(boolean, Throwable)
     */
    private void sendKeyLoadCompleted(int clusterSize, Throwable exception) throws Exception {
        // Notify SENDER first - reason why this is so important:
        // Someone may do map.get(other_nodes_key) and when it finishes do map.loadAll
        // The problem is that map.get may finish earlier than then overall loading on the SENDER due to the fact
        // that the LoadStatusOperation may first reach the node that did map.get and not the SENDER.
        // The SENDER will be then in the LOADING status, thus the loadAll call will be ignored.
        // it happens only if all LoadAllOperation finish before the sendKeyLoadCompleted is started (test case, little data)
        // Fixes https://github.com/hazelcast/hazelcast/issues/5453
        List futures = new ArrayList<>();
        Operation senderStatus = new KeyLoadStatusOperation(mapName, exception);
        Future senderFuture = opService.createInvocationBuilder(SERVICE_NAME, senderStatus, mapNamePartition)
                .setReplicaIndex(0).invoke();
        futures.add(senderFuture);

        // notify SENDER_BACKUP
        if (hasBackup && clusterSize > 1) {
            Operation senderBackupStatus = new KeyLoadStatusOperation(mapName, exception);
            Future senderBackupFuture = opService.createInvocationBuilder(SERVICE_NAME, senderBackupStatus, mapNamePartition)
                    .setReplicaIndex(1).invoke();
            futures.add(senderBackupFuture);
        }

        // Blocks until finished on SENDER & SENDER_BACKUP PARTITIONS
        // We need to wait for these operation to finished before the map-key-loader returns from the call
        // otherwise the loading won't be finished on SENDER and SENDER_BACKUP but the user may be able to call loadAll which
        // will be ignored since the SENDER and SENDER_BACKUP are still loading.
        FutureUtil.waitForever(futures);

        // INVOKES AND BLOCKS UNTIL FINISHED on ALL PARTITIONS (SENDER AND SENDER BACKUP WILL BE REPEATED)
        // notify all partitions about loading status: finished or exception encountered
        opService.invokeOnAllPartitions(SERVICE_NAME, new KeyLoadStatusOperationFactory(mapName, exception));
    }

    /**
     * Sets the maximum size of a batch of loaded keys sent
     * to the partition owner for value loading.
     *
     * @param maxBatch the maximum size for a key batch
     */
    public void setMaxBatch(int maxBatch) {
        this.maxBatch = maxBatch;
    }

    /**
     * Sets the configured maximum entry count per node.
     *
     * @param maxSize the maximum entry count per node
     * @see com.hazelcast.config.EvictionConfig
     */
    public void setMaxSize(int maxSize) {
        this.maxSizePerNode = maxSize;
    }

    /**
     * Sets if this map is configured with at least one backup.
     *
     * @param hasBackup if this map is configured with at least one backup
     */
    public void setHasBackup(boolean hasBackup) {
        this.hasBackup = hasBackup;
    }

    public void setMapOperationProvider(MapOperationProvider operationProvider) {
        this.operationProvider = operationProvider;
    }

    /**
     * Returns {@code true} if there is no ongoing key loading and dispatching
     * task on this map key loader.
     */
    public boolean isKeyLoadFinished() {
        return keyLoadFinished.isDone();
    }

    /**
     * Advances the state of the map key loader to {@link State#LOADED}
     */
    public void promoteToLoadedOnMigration() {
        // The state machine cannot skip states so we need to promote to loaded step by step
        state.next(State.LOADING);
        state.next(State.LOADED);
    }

    private String getStateMessage() {
        return "on partitionId=" + partitionId + " on " + clusterService.getThisAddress() + " role=" + role
                + " state=" + state;
    }

    /**
     * A future that can be used as a callback for a pending task.
     *
     * @see #sendKeys(MapStoreContext, boolean)
     * @see #triggerLoading()
     * @see MapLoader#loadAllKeys()
     */
    private static final class LoadFinishedFuture extends InternalCompletableFuture
            implements BiConsumer {

        private LoadFinishedFuture(Boolean result) {
            this.complete(result);
        }

        private LoadFinishedFuture() {
        }

        @Override
        public Boolean get(long timeout, TimeUnit timeUnit) {
            if (isDone()) {
                return joinInternal();
            }
            throw new UnsupportedOperationException("Future is not done yet");
        }

        @Override
        public boolean cancel(boolean mayInterruptIfRunning) {
            return false;
        }

        @Override
        public void accept(Boolean loaded, Throwable throwable) {
            if (throwable == null) {
                if (loaded) {
                    complete(true);
                }
            } else {
                completeExceptionally(throwable);
            }
        }

        @Override
        public String toString() {
            return getClass().getSimpleName() + "{done=" + isDone() + "}";
        }
    }

}
 















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