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Reactive Extensions for Java
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/*
 * Copyright (c) 2016-present, RxJava Contributors.
 *
 * 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 io.reactivex.rxjava3.internal.operators.flowable;

import java.util.*;
import java.util.concurrent.atomic.AtomicReference;
import java.util.concurrent.locks.*;

import org.reactivestreams.Subscription;

import io.reactivex.rxjava3.core.*;
import io.reactivex.rxjava3.disposables.Disposable;
import io.reactivex.rxjava3.exceptions.*;
import io.reactivex.rxjava3.internal.subscriptions.SubscriptionHelper;
import io.reactivex.rxjava3.internal.util.*;
import io.reactivex.rxjava3.operators.SpscArrayQueue;

public final class BlockingFlowableIterable implements Iterable {
    final Flowable source;

    final int bufferSize;

    public BlockingFlowableIterable(Flowable source, int bufferSize) {
        this.source = source;
        this.bufferSize = bufferSize;
    }

    @Override
    public Iterator iterator() {
        BlockingFlowableIterator it = new BlockingFlowableIterator<>(bufferSize);
        source.subscribe(it);
        return it;
    }

    static final class BlockingFlowableIterator
    extends AtomicReference
    implements FlowableSubscriber, Iterator, Runnable, Disposable {

        private static final long serialVersionUID = 6695226475494099826L;

        final SpscArrayQueue queue;

        final long batchSize;

        final long limit;

        final Lock lock;

        final Condition condition;

        long produced;

        volatile boolean done;
        volatile Throwable error;

        BlockingFlowableIterator(int batchSize) {
            this.queue = new SpscArrayQueue<>(batchSize);
            this.batchSize = batchSize;
            this.limit = batchSize - (batchSize >> 2);
            this.lock = new ReentrantLock();
            this.condition = lock.newCondition();
        }

        @Override
        public boolean hasNext() {
            for (;;) {
                if (isDisposed()) {
                    Throwable e = error;
                    if (e != null) {
                        throw ExceptionHelper.wrapOrThrow(e);
                    }
                    return false;
                }
                boolean d = done;
                boolean empty = queue.isEmpty();
                if (d) {
                    Throwable e = error;
                    if (e != null) {
                        throw ExceptionHelper.wrapOrThrow(e);
                    } else
                    if (empty) {
                        return false;
                    }
                }
                if (empty) {
                    BlockingHelper.verifyNonBlocking();
                    lock.lock();
                    try {
                        while (!done && queue.isEmpty() && !isDisposed()) {
                            condition.await();
                        }
                    } catch (InterruptedException ex) {
                        run();
                        throw ExceptionHelper.wrapOrThrow(ex);
                    } finally {
                        lock.unlock();
                    }
                } else {
                    return true;
                }
            }
        }

        @Override
        public T next() {
            if (hasNext()) {
                T v = queue.poll();

                long p = produced + 1;
                if (p == limit) {
                    produced = 0;
                    get().request(p);
                } else {
                    produced = p;
                }

                return v;
            }
            throw new NoSuchElementException();
        }

        @Override
        public void onSubscribe(Subscription s) {
            SubscriptionHelper.setOnce(this, s, batchSize);
        }

        @Override
        public void onNext(T t) {
            if (!queue.offer(t)) {
                SubscriptionHelper.cancel(this);

                onError(new MissingBackpressureException("Queue full?!"));
            } else {
                signalConsumer();
            }
        }

        @Override
        public void onError(Throwable t) {
            error = t;
            done = true;
            signalConsumer();
        }

        @Override
        public void onComplete() {
            done = true;
            signalConsumer();
        }

        void signalConsumer() {
            lock.lock();
            try {
                condition.signalAll();
            } finally {
                lock.unlock();
            }
        }

        @Override
        public void run() {
            SubscriptionHelper.cancel(this);
            signalConsumer();
        }

        @Override // otherwise default method which isn't available in Java 7
        public void remove() {
            throw new UnsupportedOperationException("remove");
        }

        @Override
        public void dispose() {
            SubscriptionHelper.cancel(this);
            signalConsumer(); // Just in case it is currently blocking in hasNext.
        }

        @Override
        public boolean isDisposed() {
            return get() == SubscriptionHelper.CANCELLED;
        }
    }
}