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/*
 * Copyright (C) 2016, 2017, 2018, 2019 HaiYang Li
 *
 * 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.landawn.abacus.util.stream;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Comparator;
import java.util.Deque;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.atomic.AtomicLong;

import com.landawn.abacus.util.AsyncExecutor;
import com.landawn.abacus.util.ByteIterator;
import com.landawn.abacus.util.CharIterator;
import com.landawn.abacus.util.ContinuableFuture;
import com.landawn.abacus.util.DoubleIterator;
import com.landawn.abacus.util.FloatIterator;
import com.landawn.abacus.util.Fn.Suppliers;
import com.landawn.abacus.util.IntIterator;
import com.landawn.abacus.util.LongIterator;
import com.landawn.abacus.util.Multimap;
import com.landawn.abacus.util.Multiset;
import com.landawn.abacus.util.MutableBoolean;
import com.landawn.abacus.util.MutableLong;
import com.landawn.abacus.util.N;
import com.landawn.abacus.util.Nth;
import com.landawn.abacus.util.ObjIterator;
import com.landawn.abacus.util.Pair;
import com.landawn.abacus.util.ShortIterator;
import com.landawn.abacus.util.Try;
import com.landawn.abacus.util.u.Holder;
import com.landawn.abacus.util.u.Optional;
import com.landawn.abacus.util.function.BiConsumer;
import com.landawn.abacus.util.function.BiFunction;
import com.landawn.abacus.util.function.BinaryOperator;
import com.landawn.abacus.util.function.Consumer;
import com.landawn.abacus.util.function.Function;
import com.landawn.abacus.util.function.Predicate;
import com.landawn.abacus.util.function.Supplier;
import com.landawn.abacus.util.function.ToByteFunction;
import com.landawn.abacus.util.function.ToCharFunction;
import com.landawn.abacus.util.function.ToDoubleFunction;
import com.landawn.abacus.util.function.ToFloatFunction;
import com.landawn.abacus.util.function.ToIntFunction;
import com.landawn.abacus.util.function.ToLongFunction;
import com.landawn.abacus.util.function.ToShortFunction;
import com.landawn.abacus.util.function.TriFunction;

/**
 * 
 */
final class ParallelIteratorStream extends IteratorStream {
    private final int maxThreadNum;
    private final Splitor splitor;
    private final AsyncExecutor asyncExecutor;
    private volatile IteratorStream sequential;

    ParallelIteratorStream(final Iterator values, final boolean sorted, final Comparator comparator, final int maxThreadNum,
            final Splitor splitor, final AsyncExecutor asyncExector, final Collection closeHandlers) {
        super(values, sorted, comparator, closeHandlers);

        this.maxThreadNum = checkMaxThreadNum(maxThreadNum);
        this.splitor = splitor == null ? DEFAULT_SPLITOR : splitor;
        this.asyncExecutor = asyncExector == null ? DEFAULT_ASYNC_EXECUTOR : asyncExector;
    }

    ParallelIteratorStream(final Stream stream, final boolean sorted, final Comparator comparator, final int maxThreadNum, final Splitor splitor,
            final AsyncExecutor asyncExector, final Deque closeHandlers) {
        this(stream.iterator(), sorted, comparator, maxThreadNum, splitor, asyncExector, mergeCloseHandlers(stream, closeHandlers));
    }

    @Override
    public Stream filter(final Predicate predicate) {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            return super.filter(predicate);
        }

        final List> iters = new ArrayList<>(maxThreadNum);

        for (int i = 0; i < maxThreadNum; i++) {
            iters.add(new ObjIteratorEx() {
                private T next = null;
                private boolean hasNext = false;

                @Override
                public boolean hasNext() {
                    if (hasNext == false) {
                        while (true) {
                            synchronized (elements) {
                                if (elements.hasNext()) {
                                    next = elements.next();
                                } else {
                                    break;
                                }
                            }

                            if (predicate.test(next)) {
                                hasNext = true;
                                break;
                            }
                        }
                    }

                    return hasNext;
                }

                @Override
                public T next() {
                    if (hasNext == false && hasNext() == false) {
                        throw new NoSuchElementException();
                    }

                    hasNext = false;
                    return next;
                }
            });
        }

        return new ParallelIteratorStream<>(Stream.parallelConcatt(iters, iters.size()), false, null, maxThreadNum, splitor, asyncExecutor, closeHandlers);
    }

    @Override
    public Stream takeWhile(final Predicate predicate) {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            return super.takeWhile(predicate);
        }

        final List> iters = new ArrayList<>(maxThreadNum);
        final MutableBoolean hasMore = MutableBoolean.of(true);

        for (int i = 0; i < maxThreadNum; i++) {
            iters.add(new ObjIteratorEx() {
                private T next = null;
                private boolean hasNext = false;

                @Override
                public boolean hasNext() {
                    if (hasNext == false && hasMore.isTrue()) {
                        synchronized (elements) {
                            if (elements.hasNext()) {
                                next = elements.next();
                                hasNext = true;
                            } else {
                                hasMore.setFalse();
                            }
                        }

                        if (hasNext && predicate.test(next) == false) {
                            hasNext = false;
                            hasMore.setFalse();
                        }
                    }

                    return hasNext;
                }

                @Override
                public T next() {
                    if (hasNext == false && hasNext() == false) {
                        throw new NoSuchElementException();
                    }

                    hasNext = false;
                    return next;
                }
            });
        }

        return new ParallelIteratorStream<>(Stream.parallelConcatt(iters, iters.size()), false, null, maxThreadNum, splitor, asyncExecutor, closeHandlers);
    }

    @Override
    public Stream dropWhile(final Predicate predicate) {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            return super.dropWhile(predicate);
        }

        final List> iters = new ArrayList<>(maxThreadNum);
        final MutableBoolean dropped = MutableBoolean.of(false);

        for (int i = 0; i < maxThreadNum; i++) {
            iters.add(new ObjIteratorEx() {
                private T next = null;
                private boolean hasNext = false;

                @Override
                public boolean hasNext() {
                    if (hasNext == false) {
                        // Only one thread is kept for running after it's dropped.
                        if (dropped.isTrue()) {
                            synchronized (elements) {
                                if (elements.hasNext()) {
                                    next = elements.next();
                                    hasNext = true;
                                }
                            }
                        } else {
                            while (dropped.isFalse()) {
                                synchronized (elements) {
                                    if (elements.hasNext()) {
                                        next = elements.next();
                                    } else {
                                        break;
                                    }
                                }

                                if (predicate.test(next) == false) {
                                    hasNext = true;
                                    dropped.setTrue();
                                    break;
                                }
                            }

                            if (hasNext == false && dropped.isTrue()) {
                                synchronized (elements) {
                                    if (elements.hasNext()) {
                                        next = elements.next();
                                        hasNext = true;
                                    }
                                }
                            }
                        }
                    }

                    return hasNext;
                }

                @Override
                public T next() {
                    if (hasNext == false && hasNext() == false) {
                        throw new NoSuchElementException();
                    }

                    hasNext = false;
                    return next;
                }
            });
        }

        return new ParallelIteratorStream<>(Stream.parallelConcatt(iters, iters.size()), false, null, maxThreadNum, splitor, asyncExecutor, closeHandlers);
    }

    @Override
    public  Stream map(final Function mapper) {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            return super.map(mapper);
        }

        final List> iters = new ArrayList<>(maxThreadNum);

        for (int i = 0; i < maxThreadNum; i++) {
            iters.add(new ObjIteratorEx() {
                private Object next = NONE;

                @Override
                public boolean hasNext() {
                    if (next == NONE) {
                        synchronized (elements) {
                            if (elements.hasNext()) {
                                next = elements.next();
                            }
                        }
                    }

                    return next != NONE;
                }

                @Override
                public R next() {
                    if (next == NONE && hasNext() == false) {
                        throw new NoSuchElementException();
                    }

                    R result = mapper.apply((T) next);
                    next = NONE;
                    return result;
                }
            });
        }

        return new ParallelIteratorStream<>(Stream.parallelConcatt(iters, iters.size()), false, null, maxThreadNum, splitor, asyncExecutor, closeHandlers);
    }

    //    @Override
    //    public  Stream biMap(final BiFunction mapper, final boolean ignoreNotPaired) {
    //        if (maxThreadNum <= 1) {
    //            return new ParallelIteratorStream<>(sequential().biMap(mapper, ignoreNotPaired).iterator(), false, null, maxThreadNum, splitor, asyncExecutor, closeHandlers);
    //        }
    //
    //        final List> iters = new ArrayList<>(maxThreadNum);
    //
    //        for (int i = 0; i < maxThreadNum; i++) {
    //            iters.add(new ObjIteratorEx() {
    //                private Object pre = NONE;
    //                private Object next = NONE;
    //
    //                @Override
    //                public boolean hasNext() {
    //                    if (pre == NONE) {
    //                        synchronized (elements) {
    //                            if (elements.hasNext()) {
    //                                pre = elements.next();
    //
    //                                if (elements.hasNext()) {
    //                                    next = elements.next();
    //                                }
    //                            }
    //                        }
    //                    }
    //
    //                    return ignoreNotPaired ? next != NONE : pre != NONE;
    //                }
    //
    //                @Override
    //                public R next() {
    //                    if (next == NONE && hasNext() == false) {
    //                        throw new NoSuchElementException();
    //                    }
    //
    //                    final R result = mapper.apply((T) pre, next == NONE ? null : (T) next);
    //                    pre = NONE;
    //                    next = NONE;
    //                    return result;
    //                }
    //            });
    //        }
    //
    //        return new ParallelIteratorStream<>(Stream.parallelConcatt(iters, iters.size()), false, null, maxThreadNum, splitor, asyncExecutor, closeHandlers);
    //    }
    //
    //    @Override
    //    public  Stream triMap(final TriFunction mapper, final boolean ignoreNotPaired) {
    //        if (maxThreadNum <= 1) {
    //            return new ParallelIteratorStream<>(sequential().triMap(mapper, ignoreNotPaired).iterator(), false, null, maxThreadNum, splitor, asyncExecutor, closeHandlers);
    //        }
    //
    //        final List> iters = new ArrayList<>(maxThreadNum);
    //
    //        for (int i = 0; i < maxThreadNum; i++) {
    //            iters.add(new ObjIteratorEx() {
    //                private Object prepre = NONE;
    //                private Object pre = NONE;
    //                private Object next = NONE;
    //
    //                @Override
    //                public boolean hasNext() {
    //                    if (prepre == NONE) {
    //                        synchronized (elements) {
    //                            if (elements.hasNext()) {
    //                                prepre = elements.next();
    //
    //                                if (elements.hasNext()) {
    //                                    pre = elements.next();
    //
    //                                    if (elements.hasNext()) {
    //                                        next = elements.next();
    //                                    }
    //                                }
    //                            }
    //                        }
    //                    }
    //
    //                    return ignoreNotPaired ? next != NONE : prepre != NONE;
    //                }
    //
    //                @Override
    //                public R next() {
    //                    if (next == NONE && hasNext() == false) {
    //                        throw new NoSuchElementException();
    //                    }
    //
    //                    final R result = mapper.apply((T) prepre, pre == NONE ? null : (T) pre, next == NONE ? null : (T) next);
    //                    prepre = NONE;
    //                    pre = NONE;
    //                    next = NONE;
    //                    return result;
    //                }
    //            });
    //        }
    //
    //        return new ParallelIteratorStream<>(Stream.parallelConcatt(iters, iters.size()), false, null, maxThreadNum, splitor, asyncExecutor, closeHandlers);
    //    }

    @Override
    public  Stream slidingMap(final BiFunction mapper, final int increment, final boolean ignoreNotPaired) {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            return new ParallelIteratorStream<>(sequential().slidingMap(mapper, increment).iterator(), false, null, maxThreadNum, splitor, asyncExecutor,
                    closeHandlers);
        }

        final int windowSize = 2;

        checkArgPositive(increment, "increment");

        final List> iters = new ArrayList<>(maxThreadNum);
        final MutableBoolean isFirst = MutableBoolean.of(true);
        final Holder prev = new Holder<>();

        for (int i = 0; i < maxThreadNum; i++) {
            iters.add(new ObjIteratorEx() {
                @SuppressWarnings("unchecked")
                private final T NONE = (T) StreamBase.NONE;

                private T first = NONE;
                private T second = NONE;

                @Override
                public boolean hasNext() {
                    if (first == NONE) {
                        synchronized (elements) {
                            if (elements.hasNext()) {
                                if (increment > windowSize && isFirst.isFalse()) {
                                    int skipNum = increment - windowSize;

                                    while (skipNum-- > 0 && elements.hasNext()) {
                                        elements.next();
                                    }
                                }

                                if (elements.hasNext()) {
                                    if (increment == 1) {
                                        first = isFirst.isTrue() ? elements.next() : prev.value();
                                        second = elements.hasNext() ? elements.next() : NONE;

                                        prev.setValue(second);

                                    } else {
                                        first = elements.next();
                                        second = elements.hasNext() ? elements.next() : NONE;
                                    }
                                }

                                isFirst.setFalse();
                            }
                        }
                    }

                    return ignoreNotPaired ? second != NONE : first != NONE;
                }

                @Override
                public R next() {
                    if ((ignoreNotPaired ? second == NONE : first == NONE) && hasNext() == false) {
                        throw new NoSuchElementException();
                    }

                    final R result = mapper.apply(first, second == NONE ? null : second);
                    first = NONE;
                    second = NONE;
                    return result;
                }
            });
        }

        return new ParallelIteratorStream<>(Stream.parallelConcatt(iters, iters.size()), false, null, maxThreadNum, splitor, asyncExecutor, closeHandlers);
    }

    @Override
    public  Stream slidingMap(final TriFunction mapper, final int increment, final boolean ignoreNotPaired) {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            return new ParallelIteratorStream<>(sequential().slidingMap(mapper, increment).iterator(), false, null, maxThreadNum, splitor, asyncExecutor,
                    closeHandlers);
        }

        final int windowSize = 3;

        checkArgPositive(increment, "increment");

        final List> iters = new ArrayList<>(maxThreadNum);
        final MutableBoolean isFirst = MutableBoolean.of(true);
        final Holder prev = new Holder<>();
        final Holder prev2 = new Holder<>();

        for (int i = 0; i < maxThreadNum; i++) {
            iters.add(new ObjIteratorEx() {
                @SuppressWarnings("unchecked")
                private final T NONE = (T) StreamBase.NONE;

                private T first = NONE;
                private T second = NONE;
                private T third = NONE;

                @Override
                public boolean hasNext() {
                    if (first == NONE) {
                        synchronized (elements) {
                            if (elements.hasNext()) {
                                if (increment > windowSize && isFirst.isFalse()) {
                                    int skipNum = increment - windowSize;

                                    while (skipNum-- > 0 && elements.hasNext()) {
                                        elements.next();
                                    }
                                }

                                if (elements.hasNext()) {
                                    if (increment == 1) {
                                        first = isFirst.isTrue() ? elements.next() : prev2.value();
                                        second = isFirst.isTrue() ? (elements.hasNext() ? elements.next() : NONE) : prev.value();
                                        third = elements.hasNext() ? elements.next() : NONE;

                                        prev2.setValue(second);
                                        prev.setValue(third);
                                    } else if (increment == 2) {
                                        first = isFirst.isTrue() ? elements.next() : prev.value();
                                        second = elements.hasNext() ? elements.next() : NONE;
                                        third = elements.hasNext() ? elements.next() : NONE;

                                        prev.setValue(third);
                                    } else {
                                        first = elements.next();
                                        second = elements.hasNext() ? elements.next() : NONE;
                                        third = elements.hasNext() ? elements.next() : NONE;
                                    }
                                }

                                isFirst.setFalse();
                            }
                        }
                    }

                    return ignoreNotPaired ? third != NONE : first != NONE;
                }

                @Override
                public R next() {
                    if ((ignoreNotPaired ? third == NONE : first == NONE) && hasNext() == false) {
                        throw new NoSuchElementException();
                    }

                    final R result = mapper.apply(first, second == NONE ? null : second, third == NONE ? null : third);
                    first = NONE;
                    second = NONE;
                    third = NONE;
                    return result;
                }
            });
        }

        return new ParallelIteratorStream<>(Stream.parallelConcatt(iters, iters.size()), false, null, maxThreadNum, splitor, asyncExecutor, closeHandlers);
    }

    @Override
    public  Stream mapFirstOrElse(final Function mapperForFirst, final Function mapperForElse) {
        checkArgNotNull(mapperForFirst);
        checkArgNotNull(mapperForElse);

        if (maxThreadNum <= 1) {
            return super.mapFirstOrElse(mapperForFirst, mapperForElse);
        }

        if (elements.hasNext()) {
            final Function mapperForFirst2 = (Function) mapperForFirst;
            final Function mapperForElse2 = (Function) mapperForElse;
            final T first = elements.next();

            return map(mapperForElse2).prepend(Stream.of(first).map(mapperForFirst2));
        } else {
            return (Stream) this;
        }
    }

    @Override
    public  Stream mapLastOrElse(final Function mapperForLast, final Function mapperForElse) {
        checkArgNotNull(mapperForLast);
        checkArgNotNull(mapperForElse);

        if (maxThreadNum <= 1) {
            return super.mapLastOrElse(mapperForLast, mapperForElse);
        }

        final List> iters = new ArrayList<>(maxThreadNum);

        for (int i = 0; i < maxThreadNum; i++) {
            iters.add(new ObjIteratorEx() {
                private Object next = NONE;
                private boolean isLast = false;

                @Override
                public boolean hasNext() {
                    if (next == NONE) {
                        synchronized (elements) {
                            if (elements.hasNext()) {
                                next = elements.next();

                                if (elements.hasNext() == false) {
                                    isLast = true;
                                }
                            }
                        }
                    }

                    return next != NONE;
                }

                @Override
                public R next() {
                    if (next == NONE && hasNext() == false) {
                        throw new NoSuchElementException();
                    }

                    final R result = isLast ? mapperForLast.apply((T) next) : mapperForElse.apply((T) next);
                    next = NONE;
                    return result;
                }
            });
        }

        return new ParallelIteratorStream<>(Stream.parallelConcatt(iters, iters.size()), false, null, maxThreadNum, splitor, asyncExecutor, closeHandlers);
    }

    @Override
    public CharStream mapToChar(final ToCharFunction mapper) {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            return super.mapToChar(mapper);
        }

        final List> iters = new ArrayList<>(maxThreadNum);

        for (int i = 0; i < maxThreadNum; i++) {
            iters.add(new ObjIteratorEx() {
                private Object next = NONE;

                @Override
                public boolean hasNext() {
                    if (next == NONE) {
                        synchronized (elements) {
                            if (elements.hasNext()) {
                                next = elements.next();
                            }
                        }
                    }

                    return next != NONE;
                }

                @Override
                public Character next() {
                    if (next == NONE && hasNext() == false) {
                        throw new NoSuchElementException();
                    }

                    Character result = mapper.applyAsChar((T) next);
                    next = NONE;
                    return result;
                }
            });
        }

        return new ParallelIteratorCharStream(Stream.parallelConcatt(iters, iters.size()), false, maxThreadNum, splitor, asyncExecutor, closeHandlers);
    }

    @Override
    public ByteStream mapToByte(final ToByteFunction mapper) {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            return super.mapToByte(mapper);
        }

        final List> iters = new ArrayList<>(maxThreadNum);

        for (int i = 0; i < maxThreadNum; i++) {
            iters.add(new ObjIteratorEx() {
                private Object next = NONE;

                @Override
                public boolean hasNext() {
                    if (next == NONE) {
                        synchronized (elements) {
                            if (elements.hasNext()) {
                                next = elements.next();
                            }
                        }
                    }

                    return next != NONE;
                }

                @Override
                public Byte next() {
                    if (next == NONE && hasNext() == false) {
                        throw new NoSuchElementException();
                    }

                    Byte result = mapper.applyAsByte((T) next);
                    next = NONE;
                    return result;
                }
            });
        }

        return new ParallelIteratorByteStream(Stream.parallelConcatt(iters, iters.size()), false, maxThreadNum, splitor, asyncExecutor, closeHandlers);
    }

    @Override
    public ShortStream mapToShort(final ToShortFunction mapper) {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            return super.mapToShort(mapper);
        }

        final List> iters = new ArrayList<>(maxThreadNum);

        for (int i = 0; i < maxThreadNum; i++) {
            iters.add(new ObjIteratorEx() {
                private Object next = NONE;

                @Override
                public boolean hasNext() {
                    if (next == NONE) {
                        synchronized (elements) {
                            if (elements.hasNext()) {
                                next = elements.next();
                            }
                        }
                    }

                    return next != NONE;
                }

                @Override
                public Short next() {
                    if (next == NONE && hasNext() == false) {
                        throw new NoSuchElementException();
                    }

                    Short result = mapper.applyAsShort((T) next);
                    next = NONE;
                    return result;
                }
            });
        }

        return new ParallelIteratorShortStream(Stream.parallelConcatt(iters, iters.size()), false, maxThreadNum, splitor, asyncExecutor, closeHandlers);
    }

    @Override
    public IntStream mapToInt(final ToIntFunction mapper) {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            return super.mapToInt(mapper);
        }

        final List> iters = new ArrayList<>(maxThreadNum);

        for (int i = 0; i < maxThreadNum; i++) {
            iters.add(new ObjIteratorEx() {
                private Object next = NONE;

                @Override
                public boolean hasNext() {
                    if (next == NONE) {
                        synchronized (elements) {
                            if (elements.hasNext()) {
                                next = elements.next();
                            }
                        }
                    }

                    return next != NONE;
                }

                @Override
                public Integer next() {
                    if (next == NONE && hasNext() == false) {
                        throw new NoSuchElementException();
                    }

                    Integer result = mapper.applyAsInt((T) next);
                    next = NONE;
                    return result;
                }
            });
        }

        return new ParallelIteratorIntStream(Stream.parallelConcatt(iters, iters.size()), false, maxThreadNum, splitor, asyncExecutor, closeHandlers);
    }

    @Override
    public LongStream mapToLong(final ToLongFunction mapper) {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            return super.mapToLong(mapper);
        }

        final List> iters = new ArrayList<>(maxThreadNum);

        for (int i = 0; i < maxThreadNum; i++) {
            iters.add(new ObjIteratorEx() {
                private Object next = NONE;

                @Override
                public boolean hasNext() {
                    if (next == NONE) {
                        synchronized (elements) {
                            if (elements.hasNext()) {
                                next = elements.next();
                            }
                        }
                    }

                    return next != NONE;
                }

                @Override
                public Long next() {
                    if (next == NONE && hasNext() == false) {
                        throw new NoSuchElementException();
                    }

                    Long result = mapper.applyAsLong((T) next);
                    next = NONE;
                    return result;
                }
            });
        }

        return new ParallelIteratorLongStream(Stream.parallelConcatt(iters, iters.size()), false, maxThreadNum, splitor, asyncExecutor, closeHandlers);
    }

    @Override
    public FloatStream mapToFloat(final ToFloatFunction mapper) {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            return super.mapToFloat(mapper);
        }

        final List> iters = new ArrayList<>(maxThreadNum);

        for (int i = 0; i < maxThreadNum; i++) {
            iters.add(new ObjIteratorEx() {
                private Object next = NONE;

                @Override
                public boolean hasNext() {
                    if (next == NONE) {
                        synchronized (elements) {
                            if (elements.hasNext()) {
                                next = elements.next();
                            }
                        }
                    }

                    return next != NONE;
                }

                @Override
                public Float next() {
                    if (next == NONE && hasNext() == false) {
                        throw new NoSuchElementException();
                    }

                    Float result = mapper.applyAsFloat((T) next);
                    next = NONE;
                    return result;
                }
            });
        }

        return new ParallelIteratorFloatStream(Stream.parallelConcatt(iters, iters.size()), false, maxThreadNum, splitor, asyncExecutor, closeHandlers);
    }

    @Override
    public DoubleStream mapToDouble(final ToDoubleFunction mapper) {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            return super.mapToDouble(mapper);
        }

        final List> iters = new ArrayList<>(maxThreadNum);

        for (int i = 0; i < maxThreadNum; i++) {
            iters.add(new ObjIteratorEx() {
                private Object next = NONE;

                @Override
                public boolean hasNext() {
                    if (next == NONE) {
                        synchronized (elements) {
                            if (elements.hasNext()) {
                                next = elements.next();
                            }
                        }
                    }

                    return next != NONE;
                }

                @Override
                public Double next() {
                    if (next == NONE && hasNext() == false) {
                        throw new NoSuchElementException();
                    }

                    Double result = mapper.applyAsDouble((T) next);
                    next = NONE;
                    return result;
                }
            });
        }

        return new ParallelIteratorDoubleStream(Stream.parallelConcatt(iters, iters.size()), false, maxThreadNum, splitor, asyncExecutor, closeHandlers);
    }

    @Override
    public  Stream flatMap(final Function> mapper) {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            return new ParallelIteratorStream<>(sequential().flatMap(mapper), false, null, maxThreadNum, splitor, asyncExecutor, null);
        }

        final List> iters = new ArrayList<>(maxThreadNum);

        for (int i = 0; i < maxThreadNum; i++) {
            iters.add(new ObjIteratorEx() {
                private T next = null;
                private Iterator cur = null;
                private Stream s = null;
                private Runnable closeHandle = null;

                @Override
                public boolean hasNext() {
                    while ((cur == null || cur.hasNext() == false) && next != NONE) {
                        synchronized (elements) {
                            if (elements.hasNext()) {
                                next = elements.next();
                            } else {
                                next = (T) NONE;
                                break;
                            }
                        }

                        if (closeHandle != null) {
                            final Runnable tmp = closeHandle;
                            closeHandle = null;
                            tmp.run();
                        }

                        s = mapper.apply(next);

                        if (N.notNullOrEmpty(s.closeHandlers)) {
                            final Deque tmp = s.closeHandlers;

                            closeHandle = new Runnable() {
                                @Override
                                public void run() {
                                    Stream.close(tmp);
                                }
                            };
                        }

                        cur = s.iterator();
                    }

                    return cur != null && cur.hasNext();
                }

                @Override
                public R next() {
                    if ((cur == null || cur.hasNext() == false) && hasNext() == false) {
                        throw new NoSuchElementException();
                    }

                    return cur.next();
                }

                @Override
                public void close() {
                    if (closeHandle != null) {
                        final Runnable tmp = closeHandle;
                        closeHandle = null;
                        tmp.run();
                    }
                }
            });
        }

        final Deque newCloseHandlers = N.isNullOrEmpty(closeHandlers) ? new LocalArrayDeque(1)
                : new LocalArrayDeque(closeHandlers);

        newCloseHandlers.add(new Runnable() {

            @Override
            public void run() {
                Stream.close(iters);
            }

        });

        return new ParallelIteratorStream<>(Stream.parallelConcatt(iters, iters.size()), false, null, maxThreadNum, splitor, asyncExecutor, newCloseHandlers);
    }

    @Override
    public CharStream flatMapToChar(final Function mapper) {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            return new ParallelIteratorCharStream(sequential().flatMapToChar(mapper), false, maxThreadNum, splitor, asyncExecutor, null);
        }

        final List> iters = new ArrayList<>(maxThreadNum);

        for (int i = 0; i < maxThreadNum; i++) {
            iters.add(new ObjIteratorEx() {
                private T next = null;
                private CharIterator cur = null;
                private CharStream s = null;
                private Runnable closeHandle = null;

                @Override
                public boolean hasNext() {
                    while ((cur == null || cur.hasNext() == false) && next != NONE) {
                        synchronized (elements) {
                            if (elements.hasNext()) {
                                next = elements.next();
                            } else {
                                next = (T) NONE;
                                break;
                            }
                        }

                        if (closeHandle != null) {
                            final Runnable tmp = closeHandle;
                            closeHandle = null;
                            tmp.run();
                        }

                        s = mapper.apply(next);

                        if (N.notNullOrEmpty(s.closeHandlers)) {
                            final Deque tmp = s.closeHandlers;

                            closeHandle = new Runnable() {
                                @Override
                                public void run() {
                                    Stream.close(tmp);
                                }
                            };
                        }

                        cur = s.iterator();
                    }

                    return cur != null && cur.hasNext();
                }

                @Override
                public Character next() {
                    if ((cur == null || cur.hasNext() == false) && hasNext() == false) {
                        throw new NoSuchElementException();
                    }

                    return cur.nextChar();
                }

                @Override
                public void close() {
                    if (closeHandle != null) {
                        final Runnable tmp = closeHandle;
                        closeHandle = null;
                        tmp.run();
                    }
                }
            });
        }

        final Deque newCloseHandlers = N.isNullOrEmpty(closeHandlers) ? new LocalArrayDeque(1)
                : new LocalArrayDeque(closeHandlers);

        newCloseHandlers.add(new Runnable() {

            @Override
            public void run() {
                Stream.close(iters);
            }

        });

        return new ParallelIteratorCharStream(Stream.parallelConcatt(iters, iters.size()), false, maxThreadNum, splitor, asyncExecutor, newCloseHandlers);
    }

    @Override
    public ByteStream flatMapToByte(final Function mapper) {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            return new ParallelIteratorByteStream(sequential().flatMapToByte(mapper), false, maxThreadNum, splitor, asyncExecutor, null);
        }

        final List> iters = new ArrayList<>(maxThreadNum);

        for (int i = 0; i < maxThreadNum; i++) {
            iters.add(new ObjIteratorEx() {
                private T next = null;
                private ByteIterator cur = null;
                private ByteStream s = null;
                private Runnable closeHandle = null;

                @Override
                public boolean hasNext() {
                    while ((cur == null || cur.hasNext() == false) && next != NONE) {
                        synchronized (elements) {
                            if (elements.hasNext()) {
                                next = elements.next();
                            } else {
                                next = (T) NONE;
                                break;
                            }
                        }

                        if (closeHandle != null) {
                            final Runnable tmp = closeHandle;
                            closeHandle = null;
                            tmp.run();
                        }

                        s = mapper.apply(next);

                        if (N.notNullOrEmpty(s.closeHandlers)) {
                            final Deque tmp = s.closeHandlers;

                            closeHandle = new Runnable() {
                                @Override
                                public void run() {
                                    Stream.close(tmp);
                                }
                            };
                        }

                        cur = s.iterator();
                    }

                    return cur != null && cur.hasNext();
                }

                @Override
                public Byte next() {
                    if ((cur == null || cur.hasNext() == false) && hasNext() == false) {
                        throw new NoSuchElementException();
                    }

                    return cur.nextByte();
                }

                @Override
                public void close() {
                    if (closeHandle != null) {
                        final Runnable tmp = closeHandle;
                        closeHandle = null;
                        tmp.run();
                    }
                }
            });
        }

        final Deque newCloseHandlers = N.isNullOrEmpty(closeHandlers) ? new LocalArrayDeque(1)
                : new LocalArrayDeque(closeHandlers);

        newCloseHandlers.add(new Runnable() {

            @Override
            public void run() {
                Stream.close(iters);
            }

        });

        return new ParallelIteratorByteStream(Stream.parallelConcatt(iters, iters.size()), false, maxThreadNum, splitor, asyncExecutor, newCloseHandlers);
    }

    @Override
    public ShortStream flatMapToShort(final Function mapper) {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            return new ParallelIteratorShortStream(sequential().flatMapToShort(mapper), false, maxThreadNum, splitor, asyncExecutor, null);
        }

        final List> iters = new ArrayList<>(maxThreadNum);

        for (int i = 0; i < maxThreadNum; i++) {
            iters.add(new ObjIteratorEx() {
                private T next = null;
                private ShortIterator cur = null;
                private ShortStream s = null;
                private Runnable closeHandle = null;

                @Override
                public boolean hasNext() {
                    while ((cur == null || cur.hasNext() == false) && next != NONE) {
                        synchronized (elements) {
                            if (elements.hasNext()) {
                                next = elements.next();
                            } else {
                                next = (T) NONE;
                                break;
                            }
                        }

                        if (closeHandle != null) {
                            final Runnable tmp = closeHandle;
                            closeHandle = null;
                            tmp.run();
                        }

                        s = mapper.apply(next);

                        if (N.notNullOrEmpty(s.closeHandlers)) {
                            final Deque tmp = s.closeHandlers;

                            closeHandle = new Runnable() {
                                @Override
                                public void run() {
                                    Stream.close(tmp);
                                }
                            };
                        }

                        cur = s.iterator();
                    }

                    return cur != null && cur.hasNext();
                }

                @Override
                public Short next() {
                    if ((cur == null || cur.hasNext() == false) && hasNext() == false) {
                        throw new NoSuchElementException();
                    }

                    return cur.nextShort();
                }

                @Override
                public void close() {
                    if (closeHandle != null) {
                        final Runnable tmp = closeHandle;
                        closeHandle = null;
                        tmp.run();
                    }
                }
            });
        }

        final Deque newCloseHandlers = N.isNullOrEmpty(closeHandlers) ? new LocalArrayDeque(1)
                : new LocalArrayDeque(closeHandlers);

        newCloseHandlers.add(new Runnable() {

            @Override
            public void run() {
                Stream.close(iters);
            }

        });

        return new ParallelIteratorShortStream(Stream.parallelConcatt(iters, iters.size()), false, maxThreadNum, splitor, asyncExecutor, newCloseHandlers);
    }

    @Override
    public IntStream flatMapToInt(final Function mapper) {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            return new ParallelIteratorIntStream(sequential().flatMapToInt(mapper), false, maxThreadNum, splitor, asyncExecutor, null);
        }

        final List> iters = new ArrayList<>(maxThreadNum);

        for (int i = 0; i < maxThreadNum; i++) {
            iters.add(new ObjIteratorEx() {
                private T next = null;
                private IntIterator cur = null;
                private IntStream s = null;
                private Runnable closeHandle = null;

                @Override
                public boolean hasNext() {
                    while ((cur == null || cur.hasNext() == false) && next != NONE) {
                        synchronized (elements) {
                            if (elements.hasNext()) {
                                next = elements.next();
                            } else {
                                next = (T) NONE;
                                break;
                            }
                        }

                        if (closeHandle != null) {
                            final Runnable tmp = closeHandle;
                            closeHandle = null;
                            tmp.run();
                        }

                        s = mapper.apply(next);

                        if (N.notNullOrEmpty(s.closeHandlers)) {
                            final Deque tmp = s.closeHandlers;

                            closeHandle = new Runnable() {
                                @Override
                                public void run() {
                                    Stream.close(tmp);
                                }
                            };
                        }

                        cur = s.iterator();
                    }

                    return cur != null && cur.hasNext();
                }

                @Override
                public Integer next() {
                    if ((cur == null || cur.hasNext() == false) && hasNext() == false) {
                        throw new NoSuchElementException();
                    }

                    return cur.nextInt();
                }

                @Override
                public void close() {
                    if (closeHandle != null) {
                        final Runnable tmp = closeHandle;
                        closeHandle = null;
                        tmp.run();
                    }
                }
            });
        }

        final Deque newCloseHandlers = N.isNullOrEmpty(closeHandlers) ? new LocalArrayDeque(1)
                : new LocalArrayDeque(closeHandlers);

        newCloseHandlers.add(new Runnable() {

            @Override
            public void run() {
                Stream.close(iters);
            }

        });

        return new ParallelIteratorIntStream(Stream.parallelConcatt(iters, iters.size()), false, maxThreadNum, splitor, asyncExecutor, newCloseHandlers);
    }

    @Override
    public LongStream flatMapToLong(final Function mapper) {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            return new ParallelIteratorLongStream(sequential().flatMapToLong(mapper), false, maxThreadNum, splitor, asyncExecutor, null);
        }

        final List> iters = new ArrayList<>(maxThreadNum);

        for (int i = 0; i < maxThreadNum; i++) {
            iters.add(new ObjIteratorEx() {
                private T next = null;
                private LongIterator cur = null;
                private LongStream s = null;
                private Runnable closeHandle = null;

                @Override
                public boolean hasNext() {
                    while ((cur == null || cur.hasNext() == false) && next != NONE) {
                        synchronized (elements) {
                            if (elements.hasNext()) {
                                next = elements.next();
                            } else {
                                next = (T) NONE;
                                break;
                            }
                        }

                        if (closeHandle != null) {
                            final Runnable tmp = closeHandle;
                            closeHandle = null;
                            tmp.run();
                        }

                        s = mapper.apply(next);

                        if (N.notNullOrEmpty(s.closeHandlers)) {
                            final Deque tmp = s.closeHandlers;

                            closeHandle = new Runnable() {
                                @Override
                                public void run() {
                                    Stream.close(tmp);
                                }
                            };
                        }

                        cur = s.iterator();
                    }

                    return cur != null && cur.hasNext();
                }

                @Override
                public Long next() {
                    if ((cur == null || cur.hasNext() == false) && hasNext() == false) {
                        throw new NoSuchElementException();
                    }

                    return cur.nextLong();
                }

                @Override
                public void close() {
                    if (closeHandle != null) {
                        final Runnable tmp = closeHandle;
                        closeHandle = null;
                        tmp.run();
                    }
                }
            });
        }

        final Deque newCloseHandlers = N.isNullOrEmpty(closeHandlers) ? new LocalArrayDeque(1)
                : new LocalArrayDeque(closeHandlers);

        newCloseHandlers.add(new Runnable() {

            @Override
            public void run() {
                Stream.close(iters);
            }

        });

        return new ParallelIteratorLongStream(Stream.parallelConcatt(iters, iters.size()), false, maxThreadNum, splitor, asyncExecutor, newCloseHandlers);
    }

    @Override
    public FloatStream flatMapToFloat(final Function mapper) {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            return new ParallelIteratorFloatStream(sequential().flatMapToFloat(mapper), false, maxThreadNum, splitor, asyncExecutor, null);
        }

        final List> iters = new ArrayList<>(maxThreadNum);

        for (int i = 0; i < maxThreadNum; i++) {
            iters.add(new ObjIteratorEx() {
                private T next = null;
                private FloatIterator cur = null;
                private FloatStream s = null;
                private Runnable closeHandle = null;

                @Override
                public boolean hasNext() {
                    while ((cur == null || cur.hasNext() == false) && next != NONE) {
                        synchronized (elements) {
                            if (elements.hasNext()) {
                                next = elements.next();
                            } else {
                                next = (T) NONE;
                                break;
                            }
                        }

                        if (closeHandle != null) {
                            final Runnable tmp = closeHandle;
                            closeHandle = null;
                            tmp.run();
                        }

                        s = mapper.apply(next);

                        if (N.notNullOrEmpty(s.closeHandlers)) {
                            final Deque tmp = s.closeHandlers;

                            closeHandle = new Runnable() {
                                @Override
                                public void run() {
                                    Stream.close(tmp);
                                }
                            };
                        }

                        cur = s.iterator();
                    }

                    return cur != null && cur.hasNext();
                }

                @Override
                public Float next() {
                    if ((cur == null || cur.hasNext() == false) && hasNext() == false) {
                        throw new NoSuchElementException();
                    }

                    return cur.nextFloat();
                }

                @Override
                public void close() {
                    if (closeHandle != null) {
                        final Runnable tmp = closeHandle;
                        closeHandle = null;
                        tmp.run();
                    }
                }
            });
        }

        final Deque newCloseHandlers = N.isNullOrEmpty(closeHandlers) ? new LocalArrayDeque(1)
                : new LocalArrayDeque(closeHandlers);

        newCloseHandlers.add(new Runnable() {

            @Override
            public void run() {
                Stream.close(iters);
            }

        });

        return new ParallelIteratorFloatStream(Stream.parallelConcatt(iters, iters.size()), false, maxThreadNum, splitor, asyncExecutor, newCloseHandlers);
    }

    @Override
    public DoubleStream flatMapToDouble(final Function mapper) {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            return new ParallelIteratorDoubleStream(sequential().flatMapToDouble(mapper), false, maxThreadNum, splitor, asyncExecutor, null);
        }

        final List> iters = new ArrayList<>(maxThreadNum);

        for (int i = 0; i < maxThreadNum; i++) {
            iters.add(new ObjIteratorEx() {
                private T next = null;
                private DoubleIterator cur = null;
                private DoubleStream s = null;
                private Runnable closeHandle = null;

                @Override
                public boolean hasNext() {
                    while ((cur == null || cur.hasNext() == false) && next != NONE) {
                        synchronized (elements) {
                            if (elements.hasNext()) {
                                next = elements.next();
                            } else {
                                next = (T) NONE;
                                break;
                            }
                        }

                        if (closeHandle != null) {
                            final Runnable tmp = closeHandle;
                            closeHandle = null;
                            tmp.run();
                        }

                        s = mapper.apply(next);

                        if (N.notNullOrEmpty(s.closeHandlers)) {
                            final Deque tmp = s.closeHandlers;

                            closeHandle = new Runnable() {
                                @Override
                                public void run() {
                                    Stream.close(tmp);
                                }
                            };
                        }

                        cur = s.iterator();
                    }

                    return cur != null && cur.hasNext();
                }

                @Override
                public Double next() {
                    if ((cur == null || cur.hasNext() == false) && hasNext() == false) {
                        throw new NoSuchElementException();
                    }

                    return cur.nextDouble();
                }

                @Override
                public void close() {
                    if (closeHandle != null) {
                        final Runnable tmp = closeHandle;
                        closeHandle = null;
                        tmp.run();
                    }
                }
            });
        }

        final Deque newCloseHandlers = N.isNullOrEmpty(closeHandlers) ? new LocalArrayDeque(1)
                : new LocalArrayDeque(closeHandlers);

        newCloseHandlers.add(new Runnable() {

            @Override
            public void run() {
                Stream.close(iters);
            }

        });

        return new ParallelIteratorDoubleStream(Stream.parallelConcatt(iters, iters.size()), false, maxThreadNum, splitor, asyncExecutor, newCloseHandlers);
    }

    @Override
    public Stream peek(final Consumer action) {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            return super.peek(action);
        }

        final List> iters = new ArrayList<>(maxThreadNum);

        for (int i = 0; i < maxThreadNum; i++) {
            iters.add(new ObjIteratorEx() {
                private Object next = NONE;

                @Override
                public boolean hasNext() {
                    if (next == NONE) {
                        synchronized (elements) {
                            if (elements.hasNext()) {
                                next = elements.next();
                            }
                        }
                    }

                    return next != NONE;
                }

                @Override
                public T next() {
                    if (next == NONE && hasNext() == false) {
                        throw new NoSuchElementException();
                    }

                    final T result = (T) next;
                    action.accept(result);
                    next = NONE;
                    return result;
                }
            });
        }

        return new ParallelIteratorStream<>(Stream.parallelConcatt(iters, iters.size()), false, null, maxThreadNum, splitor, asyncExecutor, closeHandlers);
    }

    @Override
    public  void forEach(final Try.Consumer action, final Try.Runnable onComplete) throws E, E2 {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            super.forEach(action, onComplete);
            return;
        }

        final List> futureList = new ArrayList<>(maxThreadNum);
        final Holder eHolder = new Holder<>();

        for (int i = 0; i < maxThreadNum; i++) {
            futureList.add(asyncExecutor.execute(new Try.Runnable() {
                @Override
                public void run() {
                    T next = null;

                    try {
                        while (eHolder.value() == null) {
                            synchronized (elements) {
                                if (elements.hasNext()) {
                                    next = elements.next();
                                } else {
                                    break;
                                }
                            }

                            action.accept(next);
                        }
                    } catch (Exception e) {
                        setError(eHolder, e);
                    }
                }
            }));
        }

        try {
            complette(futureList, eHolder, (E) null);

            onComplete.run();
        } finally {
            close();
        }
    }

    @Override
    public  void forEach(final Try.Function, E> flatMapper,
            final Try.BiConsumer action) throws E, E2 {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            super.forEach(flatMapper, action);
            return;
        }

        final List> futureList = new ArrayList<>(maxThreadNum);
        final Holder eHolder = new Holder<>();

        for (int i = 0; i < maxThreadNum; i++) {
            futureList.add(asyncExecutor.execute(new Try.Runnable() {
                @Override
                public void run() {
                    Collection c = null;
                    T next = null;

                    try {
                        while (eHolder.value() == null) {
                            synchronized (elements) {
                                if (elements.hasNext()) {
                                    next = elements.next();
                                } else {
                                    break;
                                }
                            }

                            c = flatMapper.apply(next);

                            if (N.notNullOrEmpty(c)) {
                                for (U u : c) {
                                    action.accept(next, u);
                                }
                            }
                        }
                    } catch (Exception e) {
                        setError(eHolder, e);
                    }
                }
            }));
        }

        try {
            complette(futureList, eHolder, (E) null);
        } finally {
            close();
        }
    }

    @Override
    public  void forEach(
            final Try.Function, E> flatMapper, final Try.Function, E2> flatMapper2,
            final Try.TriConsumer action) throws E, E2, E3 {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            super.forEach(flatMapper, flatMapper2, action);
            return;
        }

        final List> futureList = new ArrayList<>(maxThreadNum);
        final Holder eHolder = new Holder<>();

        for (int i = 0; i < maxThreadNum; i++) {
            futureList.add(asyncExecutor.execute(new Try.Runnable() {
                @Override
                public void run() {
                    Collection c2 = null;
                    Collection c3 = null;
                    T next = null;

                    try {
                        while (eHolder.value() == null) {
                            synchronized (elements) {
                                if (elements.hasNext()) {
                                    next = elements.next();
                                } else {
                                    break;
                                }
                            }

                            c2 = flatMapper.apply(next);

                            if (N.notNullOrEmpty(c2)) {
                                for (T2 t2 : c2) {
                                    c3 = flatMapper2.apply(t2);

                                    if (N.notNullOrEmpty(c3)) {
                                        for (T3 t3 : c3) {
                                            action.accept(next, t2, t3);
                                        }
                                    }
                                }
                            }
                        }
                    } catch (Exception e) {
                        setError(eHolder, e);
                    }
                }
            }));
        }

        try {
            complette(futureList, eHolder, (E) null);
        } finally {
            close();
        }
    }

    @Override
    public  void forEachPair(final Try.BiConsumer action, final int increment) throws E {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            super.forEachPair(action, increment);
            return;
        }

        final int windowSize = 2;

        checkArgPositive(increment, "increment");

        final List> futureList = new ArrayList<>(maxThreadNum);
        final Holder eHolder = new Holder<>();
        final Holder prev = new Holder<>();
        final MutableBoolean isFirst = MutableBoolean.of(true);

        for (int i = 0; i < maxThreadNum; i++) {
            futureList.add(asyncExecutor.execute(new Try.Runnable() {
                private T first = null;
                private T second = null;

                @Override
                public void run() {
                    try {
                        while (eHolder.value() == null) {
                            synchronized (elements) {
                                if (elements.hasNext()) {
                                    if (increment > windowSize && isFirst.isFalse()) {
                                        int skipNum = increment - windowSize;

                                        while (skipNum-- > 0 && elements.hasNext()) {
                                            elements.next();
                                        }

                                        if (elements.hasNext() == false) {
                                            break;
                                        }
                                    }

                                    if (increment == 1) {
                                        first = isFirst.isTrue() ? elements.next() : prev.value();
                                        second = elements.hasNext() ? elements.next() : null;

                                        prev.setValue(second);
                                    } else {
                                        first = elements.next();
                                        second = elements.hasNext() ? elements.next() : null;
                                    }

                                    isFirst.setFalse();
                                } else {
                                    break;
                                }
                            }

                            action.accept(first, second);
                        }
                    } catch (Exception e) {
                        setError(eHolder, e);
                    }
                }
            }));
        }

        try {
            complette(futureList, eHolder, (E) null);
        } finally {
            close();
        }
    }

    @Override
    public  void forEachTriple(final Try.TriConsumer action, final int increment) throws E {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            super.forEachTriple(action, increment);
            return;
        }

        final int windowSize = 3;

        checkArgPositive(increment, "increment");

        final List> futureList = new ArrayList<>(maxThreadNum);
        final Holder eHolder = new Holder<>();
        final Holder prev = new Holder<>();
        final Holder prev2 = new Holder<>();
        final MutableBoolean isFirst = MutableBoolean.of(true);

        for (int i = 0; i < maxThreadNum; i++) {
            futureList.add(asyncExecutor.execute(new Try.Runnable() {
                private T first = null;
                private T second = null;
                private T third = null;

                @Override
                public void run() {
                    try {
                        while (eHolder.value() == null) {
                            synchronized (elements) {
                                if (elements.hasNext()) {
                                    if (increment > windowSize && isFirst.isFalse()) {
                                        int skipNum = increment - windowSize;

                                        while (skipNum-- > 0 && elements.hasNext()) {
                                            elements.next();
                                        }

                                        if (elements.hasNext() == false) {
                                            break;
                                        }
                                    }

                                    if (increment == 1) {
                                        first = isFirst.isTrue() ? elements.next() : prev2.value();
                                        second = isFirst.isTrue() ? (elements.hasNext() ? elements.next() : null) : prev.value();
                                        third = elements.hasNext() ? elements.next() : null;

                                        prev2.setValue(second);
                                        prev.setValue(third);
                                    } else if (increment == 2) {
                                        first = isFirst.isTrue() ? elements.next() : prev.value();
                                        second = elements.hasNext() ? elements.next() : null;
                                        third = elements.hasNext() ? elements.next() : null;

                                        prev.setValue(third);
                                    } else {
                                        first = elements.next();
                                        second = elements.hasNext() ? elements.next() : null;
                                        third = elements.hasNext() ? elements.next() : null;
                                    }

                                    isFirst.setFalse();
                                } else {
                                    break;
                                }
                            }

                            action.accept(first, second, third);
                        }
                    } catch (Exception e) {
                        setError(eHolder, e);
                    }
                }
            }));
        }

        try {
            complette(futureList, eHolder, (E) null);
        } finally {
            close();
        }
    }

    @Override
     A[] toArray(A[] a) {
        assertNotClosed();

        try {
            return elements.toArray(a);
        } finally {
            close();
        }
    }

    @Override
    public > M toMap(final Function keyMapper, final Function valueMapper,
            final BinaryOperator mergeFunction, final Supplier mapFactory) {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            return super.toMap(keyMapper, valueMapper, mergeFunction, mapFactory);
        }

        // return collect(Collectors.toMap(keyMapper, valueMapper, mapFactory));

        //    final M res = mapFactory.get();
        //    res.putAll(collect(Collectors.toConcurrentMap(keyMapper, valueMapper, mergeFunction)));
        //    return res;

        final List> futureList = new ArrayList<>(maxThreadNum);
        final Holder eHolder = new Holder<>();

        for (int i = 0; i < maxThreadNum; i++) {
            futureList.add(asyncExecutor.execute(new Callable() {

                @Override
                public M call() {
                    M map = mapFactory.get();
                    T next = null;

                    try {
                        while (eHolder.value() == null) {
                            synchronized (elements) {
                                if (elements.hasNext()) {
                                    next = elements.next();
                                } else {
                                    break;
                                }
                            }

                            Collectors.merge(map, keyMapper.apply(next), valueMapper.apply(next), mergeFunction);
                        }
                    } catch (Exception e) {
                        setError(eHolder, e);
                    }

                    return map;
                }
            }));
        }

        if (eHolder.value() != null) {
            close();
            throw N.toRuntimeException(eHolder.value());
        }

        M res = null;

        try {
            for (ContinuableFuture future : futureList) {
                if (res == null) {
                    res = future.get();
                } else {
                    final M m = future.get();

                    for (Map.Entry entry : m.entrySet()) {
                        Collectors.merge(res, entry.getKey(), entry.getValue(), mergeFunction);
                    }
                }
            }
        } catch (InterruptedException | ExecutionException e) {
            throw N.toRuntimeException(e);
        } finally {
            close();
        }

        return res;
    }

    @Override
    public > M toMap(final Function keyMapper, final Function valueMapper,
            final Collector downstream, final Supplier mapFactory) {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            return super.toMap(keyMapper, valueMapper, downstream, mapFactory);
        }

        // return collect(Collectors.groupingBy(keyMapper, downstream, mapFactory));

        //    final M res = mapFactory.get();
        //    res.putAll(collect(Collectors.groupingByConcurrent(keyMapper, downstream)));
        //    return res;

        final Supplier downstreamSupplier = downstream.supplier();
        final BiConsumer downstreamAccumulator = downstream.accumulator();
        final BinaryOperator downstreamCombiner = downstream.combiner();
        final Function downstreamFinisher = downstream.finisher();

        final List>> futureList = new ArrayList<>(maxThreadNum);
        final Holder eHolder = new Holder<>();

        for (int i = 0; i < maxThreadNum; i++) {
            futureList.add(asyncExecutor.execute(new Callable>() {

                @Override
                public Map call() {
                    @SuppressWarnings("rawtypes")
                    Map map = (Map) mapFactory.get();
                    K key = null;
                    A value = null;
                    T next = null;

                    try {
                        while (eHolder.value() == null) {
                            synchronized (elements) {
                                if (elements.hasNext()) {
                                    next = elements.next();
                                } else {
                                    break;
                                }
                            }

                            key = checkArgNotNull(keyMapper.apply(next), "element cannot be mapped to a null key");
                            value = map.get(key);

                            if (value == null) {
                                value = downstreamSupplier.get();
                                map.put(key, value);
                            }

                            downstreamAccumulator.accept(value, valueMapper.apply(next));
                        }
                    } catch (Exception e) {
                        setError(eHolder, e);
                    }

                    return map;
                }
            }));
        }

        if (eHolder.value() != null) {
            close();
            throw N.toRuntimeException(eHolder.value());
        }

        Map intermediate = null;

        try {
            for (ContinuableFuture> future : futureList) {
                if (intermediate == null) {
                    intermediate = future.get();
                } else {
                    final Map m = future.get();
                    K key = null;

                    for (Map.Entry entry : m.entrySet()) {
                        key = entry.getKey();

                        if (intermediate.containsKey(key)) {
                            intermediate.put(key, downstreamCombiner.apply(intermediate.get(key), m.get(key)));
                        } else {
                            intermediate.put(key, m.get(key));
                        }
                    }
                }
            }
        } catch (InterruptedException | ExecutionException e) {
            throw N.toRuntimeException(e);
        } finally {
            close();
        }

        final BiFunction function = new BiFunction() {

            @Override
            public A apply(K k, A v) {
                return (A) downstreamFinisher.apply(v);
            }

        };

        Collectors.replaceAll(intermediate, function);

        return (M) intermediate;
    }

    //    @Override
    //    public > M flatToMap(final Function> flatKeyMapper,
    //            final BiFunction valueMapper, final BinaryOperator mergeFunction, final Supplier mapFactory) {
    //        assertNotClosed();
    //
    //        if (maxThreadNum <= 1) {
    //            return super.flatToMap(flatKeyMapper, valueMapper, mergeFunction, mapFactory);
    //        }
    //
    //        // return collect(Collectors.toMap(keyMapper, valueMapper, mapFactory));
    //
    //        //    final M res = mapFactory.get();
    //        //    res.putAll(collect(Collectors.toConcurrentMap(keyMapper, valueMapper, mergeFunction)));
    //        //    return res;
    //
    //        final List> futureList = new ArrayList<>(maxThreadNum);
    //        final Holder eHolder = new Holder<>();
    //
    //        for (int i = 0; i < maxThreadNum; i++) {
    //            futureList.add(asyncExecutor.execute(new Callable() {
    //
    //                @Override
    //                public M call() {
    //                    M map = mapFactory.get();
    //                    ObjIterator keyIter = null;
    //                    T next = null;
    //                    K key = null;
    //
    //                    try {
    //                        while (eHolder.value() == null) {
    //                            synchronized (elements) {
    //                                if (elements.hasNext()) {
    //                                    next = elements.next();
    //                                } else {
    //                                    break;
    //                                }
    //                            }
    //
    //                            try (Stream ks = flatKeyMapper.apply(next)) {
    //                                keyIter = ks.iterator();
    //
    //                                while (keyIter.hasNext()) {
    //                                    key = keyIter.next();
    //                                    Collectors.merge(map, key, valueMapper.apply(key, next), mergeFunction);
    //                                }
    //                            }
    //
    //                        }
    //                    } catch (Exception e) {
    //                        setError(eHolder, e);
    //                    }
    //
    //                    return map;
    //                }
    //            }));
    //        }
    //
    //        if (eHolder.value() != null) {
    //            close();
    //            throw N.toRuntimeException(eHolder.value());
    //        }
    //
    //        M res = null;
    //
    //        try {
    //            for (ContinuableFuture future : futureList) {
    //                if (res == null) {
    //                    res = future.get();
    //                } else {
    //                    final M m = future.get();
    //
    //                    for (Map.Entry entry : m.entrySet()) {
    //                        Collectors.merge(res, entry.getKey(), entry.getValue(), mergeFunction);
    //                    }
    //                }
    //            }
    //        } catch (InterruptedException | ExecutionException e) {
    //            throw N.toRuntimeException(e);
    //        } finally {
    //            close();
    //        }
    //
    //        return res;
    //    }
    //
    //    @Override
    //    public > M flatToMap(final Function> flatKeyMapper,
    //            final BiFunction valueMapper, final Collector downstream,
    //            final Supplier mapFactory) {
    //        assertNotClosed();
    //
    //        if (maxThreadNum <= 1) {
    //            return super.flatToMap(flatKeyMapper, valueMapper, downstream, mapFactory);
    //        }
    //
    //        // return collect(Collectors.groupingBy(keyMapper, downstream, mapFactory));
    //
    //        //    final M res = mapFactory.get();
    //        //    res.putAll(collect(Collectors.groupingByConcurrent(keyMapper, downstream)));
    //        //    return res;
    //
    //        final Supplier downstreamSupplier = downstream.supplier();
    //        final BiConsumer downstreamAccumulator = downstream.accumulator();
    //        final BinaryOperator downstreamCombiner = downstream.combiner();
    //        final Function downstreamFinisher = downstream.finisher();
    //
    //        final List>> futureList = new ArrayList<>(maxThreadNum);
    //        final Holder eHolder = new Holder<>();
    //
    //        for (int i = 0; i < maxThreadNum; i++) {
    //            futureList.add(asyncExecutor.execute(new Callable>() {
    //
    //                @Override
    //                public Map call() {
    //                    @SuppressWarnings("rawtypes")
    //                    Map map = (Map) mapFactory.get();
    //                    ObjIterator keyIter = null;
    //                    K key = null;
    //                    A value = null;
    //                    T next = null;
    //
    //                    try {
    //                        while (eHolder.value() == null) {
    //                            synchronized (elements) {
    //                                if (elements.hasNext()) {
    //                                    next = elements.next();
    //                                } else {
    //                                    break;
    //                                }
    //                            }
    //
    //                            try (Stream ks = flatKeyMapper.apply(next)) {
    //                                keyIter = ks.iterator();
    //
    //                                while (keyIter.hasNext()) {
    //                                    key = checkArgNotNull(keyIter.next(), "element cannot be mapped to a null key");
    //                                    value = map.get(key);
    //
    //                                    if (value == null) {
    //                                        value = downstreamSupplier.get();
    //                                        map.put(key, value);
    //                                    }
    //
    //                                    downstreamAccumulator.accept(value, valueMapper.apply(key, next));
    //                                }
    //                            }
    //                        }
    //                    } catch (Exception e) {
    //                        setError(eHolder, e);
    //                    }
    //
    //                    return map;
    //                }
    //            }));
    //        }
    //
    //        if (eHolder.value() != null) {
    //            close();
    //            throw N.toRuntimeException(eHolder.value());
    //        }
    //
    //        Map intermediate = null;
    //
    //        try {
    //            for (ContinuableFuture> future : futureList) {
    //                if (intermediate == null) {
    //                    intermediate = future.get();
    //                } else {
    //                    final Map m = future.get();
    //                    K key = null;
    //
    //                    for (Map.Entry entry : m.entrySet()) {
    //                        key = entry.getKey();
    //
    //                        if (intermediate.containsKey(key)) {
    //                            intermediate.put(key, downstreamCombiner.apply(intermediate.get(key), m.get(key)));
    //                        } else {
    //                            intermediate.put(key, m.get(key));
    //                        }
    //                    }
    //                }
    //            }
    //        } catch (InterruptedException | ExecutionException e) {
    //            throw N.toRuntimeException(e);
    //        } finally {
    //            close();
    //        }
    //
    //        final BiFunction function = new BiFunction() {
    //
    //            @Override
    //            public A apply(K k, A v) {
    //                return (A) downstreamFinisher.apply(v);
    //            }
    //
    //        };
    //
    //        Collectors.replaceAll(intermediate, function);
    //
    //        return (M) intermediate;
    //    }
    //
    //    @Override
    //    public > M flattToMap(final Function> flatKeyMapper,
    //            final BiFunction valueMapper, final BinaryOperator mergeFunction, final Supplier mapFactory) {
    //        return flatToMap(new Function>() {
    //            @Override
    //            public Stream apply(T t) {
    //                return Stream.of(flatKeyMapper.apply(t));
    //            }
    //        }, valueMapper, mergeFunction, mapFactory);
    //    }
    //
    //    @Override
    //    public > M flattToMap(final Function> flatKeyMapper,
    //            final BiFunction valueMapper, final Collector downstream,
    //            final Supplier mapFactory) {
    //        return flatToMap(new Function>() {
    //            @Override
    //            public Stream apply(T t) {
    //                return Stream.of(flatKeyMapper.apply(t));
    //            }
    //        }, valueMapper, downstream, mapFactory);
    //    }

    @Override
    public , M extends Multimap> M toMultimap(final Function keyMapper,
            final Function valueMapper, final Supplier mapFactory) {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            return super.toMultimap(keyMapper, valueMapper, mapFactory);
        }

        // return collect(Collectors.toMultimap(keyMapper, valueMapper, mapFactory));

        //    final M res = mapFactory.get();
        //    final ConcurrentMap> tmp = collect(Collectors.groupingByConcurrent(keyMapper, Collectors.mapping(valueMapper, Collectors. toList())));
        //
        //    for (Map.Entry> entry : tmp.entrySet()) {
        //        res.putAll(entry.getKey(), entry.getValue());
        //    }
        //
        //    return res;

        final List> futureList = new ArrayList<>(maxThreadNum);
        final Holder eHolder = new Holder<>();

        for (int i = 0; i < maxThreadNum; i++) {
            futureList.add(asyncExecutor.execute(new Callable() {

                @Override
                public M call() {
                    M map = mapFactory.get();
                    T next = null;

                    try {
                        while (eHolder.value() == null) {
                            synchronized (elements) {
                                if (elements.hasNext()) {
                                    next = elements.next();
                                } else {
                                    break;
                                }
                            }

                            map.put(keyMapper.apply(next), valueMapper.apply(next));
                        }
                    } catch (Exception e) {
                        setError(eHolder, e);
                    }

                    return map;
                }
            }));
        }

        if (eHolder.value() != null) {
            close();
            throw N.toRuntimeException(eHolder.value());
        }

        M res = null;

        try {
            for (ContinuableFuture future : futureList) {
                if (res == null) {
                    res = future.get();
                } else {
                    final M m = future.get();

                    for (Map.Entry entry : m.entrySet()) {
                        res.putAll(entry.getKey(), entry.getValue());
                    }
                }
            }
        } catch (InterruptedException | ExecutionException e) {
            throw N.toRuntimeException(e);
        } finally {
            close();
        }

        return res;
    }

    @Override
    public , M extends Multimap> M flatToMultimap(final Function> flatKeyMapper,
            final BiFunction valueMapper, final Supplier mapFactory) {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            return super.flatToMultimap(flatKeyMapper, valueMapper, mapFactory);
        }

        final List> futureList = new ArrayList<>(maxThreadNum);
        final Holder eHolder = new Holder<>();

        for (int i = 0; i < maxThreadNum; i++) {
            futureList.add(asyncExecutor.execute(new Callable() {

                @Override
                public M call() {
                    M map = mapFactory.get();
                    ObjIterator keyIter = null;
                    K k = null;
                    T next = null;

                    try {
                        while (eHolder.value() == null) {
                            synchronized (elements) {
                                if (elements.hasNext()) {
                                    next = elements.next();
                                } else {
                                    break;
                                }
                            }

                            try (Stream ks = flatKeyMapper.apply(next)) {
                                keyIter = ks.iterator();

                                while (keyIter.hasNext()) {
                                    k = keyIter.next();
                                    map.put(k, valueMapper.apply(k, next));
                                }
                            }
                        }
                    } catch (Exception e) {
                        setError(eHolder, e);
                    }

                    return map;
                }
            }));
        }

        if (eHolder.value() != null) {
            close();
            throw N.toRuntimeException(eHolder.value());
        }

        M res = null;

        try {
            for (ContinuableFuture future : futureList) {
                if (res == null) {
                    res = future.get();
                } else {
                    final M m = future.get();

                    for (Map.Entry entry : m.entrySet()) {
                        res.putAll(entry.getKey(), entry.getValue());
                    }
                }
            }
        } catch (InterruptedException | ExecutionException e) {
            throw N.toRuntimeException(e);
        } finally {
            close();
        }

        return res;
    }

    @Override
    public , M extends Multimap> M flattToMultimap(
            final Function> flatKeyMapper, final BiFunction valueMapper,
            final Supplier mapFactory) {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            return super.flattToMultimap(flatKeyMapper, valueMapper, mapFactory);
        }

        final List> futureList = new ArrayList<>(maxThreadNum);
        final Holder eHolder = new Holder<>();

        for (int i = 0; i < maxThreadNum; i++) {
            futureList.add(asyncExecutor.execute(new Callable() {

                @Override
                public M call() {
                    M map = mapFactory.get();
                    Collection ks = null;
                    T next = null;

                    try {
                        while (eHolder.value() == null) {
                            synchronized (elements) {
                                if (elements.hasNext()) {
                                    next = elements.next();
                                } else {
                                    break;
                                }
                            }

                            ks = flatKeyMapper.apply(next);

                            if (N.notNullOrEmpty(ks)) {
                                for (K k : ks) {
                                    map.put(k, valueMapper.apply(k, next));
                                }
                            }
                        }
                    } catch (Exception e) {
                        setError(eHolder, e);
                    }

                    return map;
                }
            }));
        }

        if (eHolder.value() != null) {
            close();
            throw N.toRuntimeException(eHolder.value());
        }

        M res = null;

        try {
            for (ContinuableFuture future : futureList) {
                if (res == null) {
                    res = future.get();
                } else {
                    final M m = future.get();

                    for (Map.Entry entry : m.entrySet()) {
                        res.putAll(entry.getKey(), entry.getValue());
                    }
                }
            }
        } catch (InterruptedException | ExecutionException e) {
            throw N.toRuntimeException(e);
        } finally {
            close();
        }

        return res;
    }

    @Override
    public  Map partitionTo(final Predicate predicate, Collector downstream) {
        final Function keyMapper = new Function() {
            @Override
            public Boolean apply(T t) {
                return predicate.test(t);
            }
        };

        final Supplier> mapFactory = Suppliers.ofMap();
        final Map map = toMap(keyMapper, downstream, mapFactory);

        if (map.containsKey(Boolean.TRUE) == false) {
            map.put(Boolean.TRUE, downstream.finisher().apply(downstream.supplier().get()));
        } else if (map.containsKey(Boolean.FALSE) == false) {
            map.put(Boolean.FALSE, downstream.finisher().apply(downstream.supplier().get()));
        }

        return map;
    }

    @Override
    public T reduce(final T identity, final BinaryOperator accumulator) {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            return super.reduce(identity, accumulator);
        }

        final List> futureList = new ArrayList<>(maxThreadNum);
        final Holder eHolder = new Holder<>();

        for (int i = 0; i < maxThreadNum; i++) {
            futureList.add(asyncExecutor.execute(new Callable() {
                @Override
                public T call() {
                    T result = identity;
                    T next = null;

                    try {
                        while (eHolder.value() == null) {
                            synchronized (elements) {
                                if (elements.hasNext()) {
                                    next = elements.next();
                                } else {
                                    break;
                                }
                            }

                            result = accumulator.apply(result, next);
                        }
                    } catch (Exception e) {
                        setError(eHolder, e);
                    }

                    return result;
                }
            }));
        }

        if (eHolder.value() != null) {
            close();
            throw N.toRuntimeException(eHolder.value());
        }

        T result = (T) NONE;

        try {
            for (ContinuableFuture future : futureList) {
                if (result == NONE) {
                    result = future.get();
                } else {
                    result = accumulator.apply(result, future.get());
                }
            }
        } catch (InterruptedException | ExecutionException e) {
            throw N.toRuntimeException(e);
        } finally {
            close();
        }

        return result == NONE ? identity : result;
    }

    @Override
    public Optional reduce(final BinaryOperator accumulator) {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            return super.reduce(accumulator);
        }

        final List> futureList = new ArrayList<>(maxThreadNum);
        final Holder eHolder = new Holder<>();

        for (int i = 0; i < maxThreadNum; i++) {
            futureList.add(asyncExecutor.execute(new Callable() {
                @Override
                public T call() {
                    T result = (T) NONE;
                    T next = null;

                    try {
                        while (eHolder.value() == null) {
                            synchronized (elements) {
                                if (elements.hasNext()) {
                                    next = elements.next();
                                } else {
                                    break;
                                }
                            }

                            result = result == NONE ? next : accumulator.apply(result, next);
                        }
                    } catch (Exception e) {
                        setError(eHolder, e);
                    }

                    return result;
                }
            }));
        }

        if (eHolder.value() != null) {
            close();
            throw N.toRuntimeException(eHolder.value());
        }

        T result = (T) NONE;

        try {
            for (ContinuableFuture future : futureList) {
                final T tmp = future.get();

                if (tmp == NONE) {
                    continue;
                } else if (result == NONE) {
                    result = tmp;
                } else {
                    result = accumulator.apply(result, tmp);
                }
            }
        } catch (InterruptedException | ExecutionException e) {
            throw N.toRuntimeException(e);
        } finally {
            close();
        }

        return result == NONE ? (Optional) Optional.empty() : Optional.of(result);
    }

    @Override
    public  U reduce(final U identity, final BiFunction accumulator, final BinaryOperator combiner) {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            return super.reduce(identity, accumulator, combiner);
        }

        final List> futureList = new ArrayList<>(maxThreadNum);
        final Holder eHolder = new Holder<>();

        for (int i = 0; i < maxThreadNum; i++) {
            futureList.add(asyncExecutor.execute(new Callable() {
                @Override
                public U call() {
                    U result = identity;
                    T next = null;

                    try {
                        while (eHolder.value() == null) {
                            synchronized (elements) {
                                if (elements.hasNext()) {
                                    next = elements.next();
                                } else {
                                    break;
                                }
                            }

                            result = accumulator.apply(result, next);
                        }
                    } catch (Exception e) {
                        setError(eHolder, e);
                    }

                    return result;
                }
            }));
        }

        if (eHolder.value() != null) {
            close();
            throw N.toRuntimeException(eHolder.value());
        }

        U result = (U) NONE;

        try {
            for (ContinuableFuture future : futureList) {
                if (result == NONE) {
                    result = future.get();
                } else {
                    result = combiner.apply(result, future.get());
                }
            }
        } catch (InterruptedException | ExecutionException e) {
            throw N.toRuntimeException(e);
        } finally {
            close();
        }

        return result == NONE ? identity : result;
    }

    @Override
    public  R collect(final Supplier supplier, final BiConsumer accumulator, final BiConsumer combiner) {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            return super.collect(supplier, accumulator, combiner);
        }

        final List> futureList = new ArrayList<>(maxThreadNum);
        final Holder eHolder = new Holder<>();

        for (int i = 0; i < maxThreadNum; i++) {
            futureList.add(asyncExecutor.execute(new Callable() {
                @Override
                public R call() {
                    final R container = supplier.get();
                    T next = null;

                    try {
                        while (eHolder.value() == null) {
                            synchronized (elements) {
                                if (elements.hasNext()) {
                                    next = elements.next();
                                } else {
                                    break;
                                }
                            }

                            accumulator.accept(container, next);
                        }
                    } catch (Exception e) {
                        setError(eHolder, e);
                    }

                    return container;
                }
            }));
        }

        if (eHolder.value() != null) {
            close();
            throw N.toRuntimeException(eHolder.value());
        }

        R container = (R) NONE;

        try {
            for (ContinuableFuture future : futureList) {
                if (container == NONE) {
                    container = future.get();
                } else {
                    combiner.accept(container, future.get());
                }
            }
        } catch (InterruptedException | ExecutionException e) {
            throw N.toRuntimeException(e);
        } finally {
            close();
        }

        return container == NONE ? supplier.get() : container;
    }

    @Override
    public  R collect(final Collector collector) {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            return sequential().collect(collector);
        }

        //    if (/*collector.characteristics().contains(Collector.Characteristics.CONCURRENT) == false
        //               || */ collector.characteristics().contains(Collector.Characteristics.UNORDERED) == false) {
        //        return sequential().collect(collector);
        //    }

        final boolean isConcurrentCollector = N.notNullOrEmpty(collector.characteristics())
                && collector.characteristics().contains(Collector.Characteristics.CONCURRENT);

        final Supplier supplier = collector.supplier();
        final BiConsumer accumulator = collector.accumulator();
        final BinaryOperator combiner = collector.combiner();
        final Function finisher = collector.finisher();

        final List> futureList = new ArrayList<>(maxThreadNum);
        final Holder eHolder = new Holder<>();
        final A singleContainer = isConcurrentCollector ? supplier.get() : null;

        for (int i = 0; i < maxThreadNum; i++) {
            futureList.add(asyncExecutor.execute(new Callable() {
                @Override
                public A call() {
                    A container = isConcurrentCollector ? singleContainer : supplier.get();
                    T next = null;

                    try {
                        while (eHolder.value() == null) {
                            synchronized (elements) {
                                if (elements.hasNext()) {
                                    next = elements.next();
                                } else {
                                    break;
                                }
                            }

                            accumulator.accept(container, next);
                        }
                    } catch (Exception e) {
                        setError(eHolder, e);
                    }

                    return container;
                }
            }));
        }

        if (eHolder.value() != null) {
            close();
            throw N.toRuntimeException(eHolder.value());
        }

        A container = isConcurrentCollector ? singleContainer : (A) NONE;

        try {
            for (ContinuableFuture future : futureList) {
                if (isConcurrentCollector) {
                    future.get();
                } else {
                    if (container == NONE) {
                        container = future.get();
                    } else {
                        container = combiner.apply(container, future.get());
                    }
                }
            }

            return finisher.apply(container == NONE ? supplier.get() : container);
        } catch (InterruptedException | ExecutionException e) {
            throw N.toRuntimeException(e);
        } finally {
            close();
        }
    }

    @Override
    public Optional min(Comparator comparator) {
        boolean isDone = true;

        try {
            if (elements.hasNext() == false) {
                return Optional.empty();
            } else if (sorted && isSameComparator(comparator, cmp)) {
                return Optional.of(elements.next());
            } else {
                isDone = false;
            }
        } finally {
            if (isDone) {
                close();
            }
        }

        comparator = comparator == null ? NATURAL_COMPARATOR : comparator;

        return collect(Collectors.minBy(comparator));
    }

    @Override
    public Optional max(Comparator comparator) {
        boolean isDone = true;

        try {
            if (elements.hasNext() == false) {
                return Optional.empty();
            } else if (sorted && isSameComparator(comparator, cmp)) {
                T next = null;

                while (elements.hasNext()) {
                    next = elements.next();
                }

                return Optional.of(next);
            } else {
                isDone = false;
            }
        } finally {
            if (isDone) {
                close();
            }
        }

        comparator = comparator == null ? NATURAL_COMPARATOR : comparator;

        return collect(Collectors.maxBy(comparator));
    }

    @Override
    public  boolean anyMatch(final Try.Predicate predicate) throws E {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            return super.anyMatch(predicate);
        }

        final List> futureList = new ArrayList<>(maxThreadNum);
        final Holder eHolder = new Holder<>();
        final MutableBoolean result = MutableBoolean.of(false);

        for (int i = 0; i < maxThreadNum; i++) {
            futureList.add(asyncExecutor.execute(new Try.Runnable() {
                @Override
                public void run() {
                    T next = null;

                    try {
                        while (result.isFalse() && eHolder.value() == null) {
                            synchronized (elements) {
                                if (elements.hasNext()) {
                                    next = elements.next();
                                } else {
                                    break;
                                }
                            }

                            if (predicate.test(next)) {
                                result.setTrue();
                                break;
                            }
                        }
                    } catch (Exception e) {
                        setError(eHolder, e);
                    }
                }
            }));
        }

        try {
            complette(futureList, eHolder, (E) null);
        } finally {
            close();
        }

        return result.value();
    }

    @Override
    public  boolean allMatch(final Try.Predicate predicate) throws E {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            return super.allMatch(predicate);
        }

        final List> futureList = new ArrayList<>(maxThreadNum);
        final Holder eHolder = new Holder<>();
        final MutableBoolean result = MutableBoolean.of(true);

        for (int i = 0; i < maxThreadNum; i++) {
            futureList.add(asyncExecutor.execute(new Try.Runnable() {
                @Override
                public void run() {
                    T next = null;

                    try {
                        while (result.isTrue() && eHolder.value() == null) {
                            synchronized (elements) {
                                if (elements.hasNext()) {
                                    next = elements.next();
                                } else {
                                    break;
                                }
                            }

                            if (predicate.test(next) == false) {
                                result.setFalse();
                                break;
                            }
                        }
                    } catch (Exception e) {
                        setError(eHolder, e);
                    }
                }
            }));
        }

        try {
            complette(futureList, eHolder, (E) null);
        } finally {
            close();
        }

        return result.value();
    }

    @Override
    public  boolean noneMatch(final Try.Predicate predicate) throws E {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            return super.noneMatch(predicate);
        }

        final List> futureList = new ArrayList<>(maxThreadNum);
        final Holder eHolder = new Holder<>();
        final MutableBoolean result = MutableBoolean.of(true);

        for (int i = 0; i < maxThreadNum; i++) {
            futureList.add(asyncExecutor.execute(new Try.Runnable() {
                @Override
                public void run() {
                    T next = null;

                    try {
                        while (result.isTrue() && eHolder.value() == null) {
                            synchronized (elements) {
                                if (elements.hasNext()) {
                                    next = elements.next();
                                } else {
                                    break;
                                }
                            }

                            if (predicate.test(next)) {
                                result.setFalse();
                                break;
                            }
                        }
                    } catch (Exception e) {
                        setError(eHolder, e);
                    }
                }
            }));
        }

        try {
            complette(futureList, eHolder, (E) null);
        } finally {
            close();
        }

        return result.value();
    }

    @Override
    public  boolean nMatch(final long atLeast, final long atMost, final Try.Predicate predicate) throws E {
        checkArgNotNegative(atLeast, "atLeast");
        checkArgNotNegative(atMost, "atMost");
        checkArgument(atLeast <= atMost, "'atLeast' must be <= 'atMost'");

        assertNotClosed();

        if (maxThreadNum <= 1) {
            return super.nMatch(atLeast, atMost, predicate);
        }

        final List> futureList = new ArrayList<>(maxThreadNum);
        final Holder eHolder = new Holder<>();
        final AtomicLong cnt = new AtomicLong(0);

        for (int i = 0; i < maxThreadNum; i++) {
            futureList.add(asyncExecutor.execute(new Try.Runnable() {
                @Override
                public void run() {
                    T next = null;

                    try {
                        while (cnt.get() <= atMost && eHolder.value() == null) {
                            synchronized (elements) {
                                if (elements.hasNext()) {
                                    next = elements.next();
                                } else {
                                    break;
                                }
                            }

                            if (predicate.test(next)) {
                                if (cnt.incrementAndGet() > atMost) {
                                    break;
                                }
                            }
                        }
                    } catch (Exception e) {
                        setError(eHolder, e);
                    }
                }
            }));
        }

        try {
            complette(futureList, eHolder, (E) null);
        } finally {
            close();
        }

        return cnt.get() >= atLeast && cnt.get() <= atMost;
    }

    @Override
    public  Optional findFirst(final Try.Predicate predicate) throws E {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            return super.findFirst(predicate);
        }

        final List> futureList = new ArrayList<>(maxThreadNum);
        final Holder eHolder = new Holder<>();
        final Holder> resultHolder = new Holder<>();
        final MutableLong index = MutableLong.of(0);

        for (int i = 0; i < maxThreadNum; i++) {
            futureList.add(asyncExecutor.execute(new Try.Runnable() {
                @Override
                public void run() {
                    final Pair pair = new Pair<>();

                    try {
                        while (resultHolder.value() == null && eHolder.value() == null) {
                            synchronized (elements) {
                                if (elements.hasNext()) {
                                    pair.left = index.getAndIncrement();
                                    pair.right = elements.next();
                                } else {
                                    break;
                                }
                            }

                            if (predicate.test(pair.right)) {
                                synchronized (resultHolder) {
                                    if (resultHolder.value() == null || pair.left < resultHolder.value().left) {
                                        resultHolder.setValue(pair.copy());
                                    }
                                }

                                break;
                            }
                        }
                    } catch (Exception e) {
                        setError(eHolder, e);
                    }
                }
            }));
        }

        try {
            complette(futureList, eHolder, (E) null);
        } finally {
            close();
        }

        return resultHolder.value() == null ? (Optional) Optional.empty() : Optional.of(resultHolder.value().right);
    }

    @Override
    public  Optional findLast(final Try.Predicate predicate) throws E {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            return super.findLast(predicate);
        }

        final List> futureList = new ArrayList<>(maxThreadNum);
        final Holder eHolder = new Holder<>();
        final Holder> resultHolder = new Holder<>();
        final MutableLong index = MutableLong.of(0);

        for (int i = 0; i < maxThreadNum; i++) {
            futureList.add(asyncExecutor.execute(new Try.Runnable() {
                @Override
                public void run() {
                    final Pair pair = new Pair<>();

                    try {
                        while (eHolder.value() == null) {
                            synchronized (elements) {
                                if (elements.hasNext()) {
                                    pair.left = index.getAndIncrement();
                                    pair.right = elements.next();
                                } else {
                                    break;
                                }
                            }

                            if (predicate.test(pair.right)) {
                                synchronized (resultHolder) {
                                    if (resultHolder.value() == null || pair.left > resultHolder.value().left) {
                                        resultHolder.setValue(pair.copy());
                                    }
                                }
                            }
                        }
                    } catch (Exception e) {
                        setError(eHolder, e);
                    }
                }
            }));
        }

        try {
            complette(futureList, eHolder, (E) null);
        } finally {
            close();
        }

        return resultHolder.value() == null ? (Optional) Optional.empty() : Optional.of(resultHolder.value().right);
    }

    @Override
    public  Optional findAny(final Try.Predicate predicate) throws E {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            return super.findAny(predicate);
        }

        final List> futureList = new ArrayList<>(maxThreadNum);
        final Holder eHolder = new Holder<>();
        final Holder resultHolder = Holder.of((T) NONE);

        for (int i = 0; i < maxThreadNum; i++) {
            futureList.add(asyncExecutor.execute(new Try.Runnable() {
                @Override
                public void run() {
                    T next = null;

                    try {
                        while (resultHolder.value() == NONE && eHolder.value() == null) {
                            synchronized (elements) {
                                if (elements.hasNext()) {
                                    next = elements.next();
                                } else {
                                    break;
                                }
                            }

                            if (predicate.test(next)) {
                                synchronized (resultHolder) {
                                    if (resultHolder.value() == NONE) {
                                        resultHolder.setValue(next);
                                    }
                                }

                                break;
                            }
                        }
                    } catch (Exception e) {
                        setError(eHolder, e);
                    }
                }
            }));
        }

        try {
            complette(futureList, eHolder, (E) null);
        } finally {
            close();
        }

        return resultHolder.value() == NONE ? (Optional) Optional.empty() : Optional.of(resultHolder.value());
    }

    @Override
    public Stream intersection(final Function mapper, final Collection c) {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            super.intersection(mapper, c);
        }

        final Multiset multiset = Multiset.from(c);

        return filter(new Predicate() {
            @Override
            public boolean test(T value) {
                final Object key = mapper.apply(value);

                synchronized (multiset) {
                    return multiset.getAndRemove(key) > 0;
                }
            }
        });
    }

    @Override
    public Stream difference(final Function mapper, final Collection c) {
        assertNotClosed();

        if (maxThreadNum <= 1) {
            return super.intersection(mapper, c);
        }

        final Multiset multiset = Multiset.from(c);

        return filter(new Predicate() {
            @Override
            public boolean test(T value) {
                final Object key = mapper.apply(value);

                synchronized (multiset) {
                    return multiset.getAndRemove(key) < 1;
                }
            }
        });
    }

    @Override
    public Stream append(Stream stream) {
        return new ParallelIteratorStream<>(Stream.concat(this, stream), false, null, maxThreadNum, splitor, asyncExecutor, closeHandlers);
    }

    @Override
    public Stream prepend(Stream stream) {
        return new ParallelIteratorStream<>(Stream.concat(stream, this), false, null, maxThreadNum, splitor, asyncExecutor, closeHandlers);
    }

    @Override
    public Stream merge(final Stream b, final BiFunction nextSelector) {
        return new ParallelIteratorStream<>(Stream.merge(this, b, nextSelector), false, null, maxThreadNum, splitor, asyncExecutor, closeHandlers);
    }

    @Override
    public  Stream zipWith(Stream b, BiFunction zipFunction) {
        return new ParallelIteratorStream<>(Stream.parallelZip(this, b, zipFunction), false, null, maxThreadNum, splitor, asyncExecutor, closeHandlers);
    }

    @Override
    public  Stream zipWith(Stream b, Stream c, TriFunction zipFunction) {
        return new ParallelIteratorStream<>(Stream.parallelZip(this, b, c, zipFunction), false, null, maxThreadNum, splitor, asyncExecutor, closeHandlers);
    }

    @Override
    public  Stream zipWith(Stream b, T valueForNoneA, T2 valueForNoneB, BiFunction zipFunction) {
        return new ParallelIteratorStream<>(Stream.parallelZip(this, b, valueForNoneA, valueForNoneB, zipFunction), false, null, maxThreadNum, splitor,
                asyncExecutor, closeHandlers);
    }

    @Override
    public  Stream zipWith(Stream b, Stream c, T valueForNoneA, T2 valueForNoneB, T3 valueForNoneC,
            TriFunction zipFunction) {
        return new ParallelIteratorStream<>(Stream.parallelZip(this, b, c, valueForNoneA, valueForNoneB, valueForNoneC, zipFunction), false, null, maxThreadNum,
                splitor, asyncExecutor, closeHandlers);
    }

    //    @Override
    //    public long persist(final PreparedStatement stmt, final int batchSize, final int batchInterval,
    //            final JdbcUtil.BiParametersSetter stmtSetter) {
    //        checkArgument(batchSize > 0 && batchInterval >= 0, "'batchSize'=%s must be greater than 0 and 'batchInterval'=%s can't be negative", batchSize,
    //                batchInterval);
    //
    //        if (maxThreadNum <= 1) {
    //            return sequential().persist(stmt, batchSize, batchInterval, stmtSetter);
    //        }
    //
    //        final List> futureList = new ArrayList<>(maxThreadNum);
    //        final Holder eHolder = new Holder<>();
    //        final AtomicLong result = new AtomicLong();
    //
    //        for (int i = 0; i < maxThreadNum; i++) {
    //            futureList.add(asyncExecutor.execute(new Try.Runnable() {
    //                @Override
    //                public void run() {
    //                    long cnt = 0;
    //                    T next = null;
    //
    //                    try {
    //                        while (eHolder.value() == null) {
    //                            synchronized (elements) {
    //                                if (elements.hasNext()) {
    //                                    next = elements.next();
    //                                } else {
    //                                    break;
    //                                }
    //                            }
    //
    //                            stmtSetter.accept(stmt, next);
    //                            stmt.addBatch();
    //
    //                            if ((++cnt % batchSize) == 0) {
    //                                stmt.executeBatch();
    //                                stmt.clearBatch();
    //
    //                                if (batchInterval > 0) {
    //                                    N.sleep(batchInterval);
    //                                }
    //                            }
    //                        }
    //
    //                        if ((cnt % batchSize) > 0) {
    //                            stmt.executeBatch();
    //                            stmt.clearBatch();
    //                        }
    //
    //                        result.addAndGet(cnt);
    //                    } catch (Exception e) {
    //                        setError(eHolder, e);
    //                    }
    //                }
    //            }));
    //        }
    //
    //        complete(futureList, eHolder);
    //
    //        return result.longValue();
    //    }

    @Override
    public boolean isParallel() {
        return true;
    }

    @Override
    public Stream sequential() {
        IteratorStream tmp = sequential;

        if (tmp == null) {
            tmp = new IteratorStream<>(elements, sorted, cmp, closeHandlers);
            sequential = tmp;
        }

        return tmp;
    }

    @Override
    public Stream parallel(int maxThreadNum, Splitor splitor) {
        checkMaxThreadNum(maxThreadNum);
        checkSplitor(splitor);

        return new ParallelIteratorStream<>(elements, sorted, cmp, maxThreadNum, splitor, asyncExecutor, closeHandlers);
    }

    @Override
    protected int maxThreadNum() {
        return maxThreadNum;
    }

    @Override
    protected BaseStream.Splitor splitor() {
        return splitor;
    }

    @Override
    protected AsyncExecutor asyncExecutor() {
        return asyncExecutor;
    }

    @Override
    public Stream onClose(Runnable closeHandler) {
        final Deque newCloseHandlers = new LocalArrayDeque<>(N.isNullOrEmpty(this.closeHandlers) ? 1 : this.closeHandlers.size() + 1);

        newCloseHandlers.add(wrapCloseHandlers(closeHandler));

        if (N.notNullOrEmpty(this.closeHandlers)) {
            newCloseHandlers.addAll(this.closeHandlers);
        }

        return new ParallelIteratorStream<>(elements, sorted, cmp, maxThreadNum, splitor, asyncExecutor, newCloseHandlers);
    }
}