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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.internal.operators.observable;

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

import io.reactivex.ObservableSource;
import io.reactivex.disposables.Disposable;
import io.reactivex.internal.disposables.DisposableHelper;
import io.reactivex.internal.queue.SpscLinkedArrayQueue;
import io.reactivex.internal.util.*;

public final class BlockingObservableIterable implements Iterable {
    final ObservableSource source;

    final int bufferSize;

    public BlockingObservableIterable(ObservableSource source, int bufferSize) {
        this.source = source;
        this.bufferSize = bufferSize;
    }

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

    static final class BlockingObservableIterator
    extends AtomicReference
    implements io.reactivex.Observer, Iterator, Disposable {

        private static final long serialVersionUID = 6695226475494099826L;

        final SpscLinkedArrayQueue queue;

        final Lock lock;

        final Condition condition;

        volatile boolean done;
        volatile Throwable error;

        BlockingObservableIterator(int batchSize) {
            this.queue = new SpscLinkedArrayQueue(batchSize);
            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) {
                    try {
                        BlockingHelper.verifyNonBlocking();
                        lock.lock();
                        try {
                            while (!done && queue.isEmpty() && !isDisposed()) {
                                condition.await();
                            }
                        } finally {
                            lock.unlock();
                        }
                    } catch (InterruptedException ex) {
                        DisposableHelper.dispose(this);
                        signalConsumer();
                        throw ExceptionHelper.wrapOrThrow(ex);
                    }
                } else {
                    return true;
                }
            }
        }

        @Override
        public T next() {
            if (hasNext()) {
                return queue.poll();
            }
            throw new NoSuchElementException();
        }

        @Override
        public void onSubscribe(Disposable d) {
            DisposableHelper.setOnce(this, d);
        }

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

        @Override
        public void dispose() {
            DisposableHelper.dispose(this);
            signalConsumer();
        }

        @Override
        public boolean isDisposed() {
            return DisposableHelper.isDisposed(get());
        }
    }
}