https://github.com/ReactiveX/RxJava: Reactive Extensions for Java
  • David Karnok 
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.

/**
 * 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.flowable;

import java.util.Iterator;
import java.util.concurrent.Callable;
import java.util.concurrent.atomic.*;

import org.reactivestreams.*;

import io.reactivex.*;
import io.reactivex.annotations.Nullable;
import io.reactivex.exceptions.*;
import io.reactivex.functions.Function;
import io.reactivex.internal.functions.ObjectHelper;
import io.reactivex.internal.fuseable.*;
import io.reactivex.internal.queue.SpscArrayQueue;
import io.reactivex.internal.subscriptions.*;
import io.reactivex.internal.util.*;
import io.reactivex.plugins.RxJavaPlugins;

public final class FlowableFlattenIterable<T, R> extends AbstractFlowableWithUpstream<T, R> {

    final Function<? super T, ? extends Iterable<? extends R>> mapper;

    final int prefetch;

    public FlowableFlattenIterable(Flowable<T> source,
            Function<? super T, ? extends Iterable<? extends R>> mapper, int prefetch) {
        super(source);
        this.mapper = mapper;
        this.prefetch = prefetch;
    }

    @SuppressWarnings("unchecked")
    @Override
    public void subscribeActual(Subscriber<? super R> s) {
        if (source instanceof Callable) {
            T v;

            try {
                v = ((Callable<T>)source).call();
            } catch (Throwable ex) {
                Exceptions.throwIfFatal(ex);
                EmptySubscription.error(ex, s);
                return;
            }

            if (v == null) {
                EmptySubscription.complete(s);
                return;
            }

            Iterator<? extends R> it;

            try {
                Iterable<? extends R> iterable = mapper.apply(v);

                it = iterable.iterator();
            } catch (Throwable ex) {
                Exceptions.throwIfFatal(ex);
                EmptySubscription.error(ex, s);
                return;
            }

            FlowableFromIterable.subscribe(s, it);

            return;
        }
        source.subscribe(new FlattenIterableSubscriber<T, R>(s, mapper, prefetch));
    }

    static final class FlattenIterableSubscriber<T, R>
    extends BasicIntQueueSubscription<R>
    implements FlowableSubscriber<T> {

        private static final long serialVersionUID = -3096000382929934955L;

        final Subscriber<? super R> downstream;

        final Function<? super T, ? extends Iterable<? extends R>> mapper;

        final int prefetch;

        final int limit;

        final AtomicLong requested;

        Subscription upstream;

        SimpleQueue<T> queue;

        volatile boolean done;

        volatile boolean cancelled;

        final AtomicReference<Throwable> error;

        Iterator<? extends R> current;

        int consumed;

        int fusionMode;

        FlattenIterableSubscriber(Subscriber<? super R> actual,
                Function<? super T, ? extends Iterable<? extends R>> mapper, int prefetch) {
            this.downstream = actual;
            this.mapper = mapper;
            this.prefetch = prefetch;
            this.limit = prefetch - (prefetch >> 2);
            this.error = new AtomicReference<Throwable>();
            this.requested = new AtomicLong();
        }

        @Override
        public void onSubscribe(Subscription s) {
            if (SubscriptionHelper.validate(this.upstream, s)) {
                this.upstream = s;

                if (s instanceof QueueSubscription) {
                    @SuppressWarnings("unchecked")
                    QueueSubscription<T> qs = (QueueSubscription<T>) s;

                    int m = qs.requestFusion(ANY);

                    if (m == SYNC) {
                        fusionMode = m;
                        this.queue = qs;
                        done = true;

                        downstream.onSubscribe(this);

                        return;
                    }
                    if (m == ASYNC) {
                        fusionMode = m;
                        this.queue = qs;

                        downstream.onSubscribe(this);

                        s.request(prefetch);
                        return;
                    }
                }

                queue = new SpscArrayQueue<T>(prefetch);

                downstream.onSubscribe(this);

                s.request(prefetch);
            }
        }

        @Override
        public void onNext(T t) {
            if (done) {
                return;
            }
            if (fusionMode == NONE && !queue.offer(t)) {
                onError(new MissingBackpressureException("Queue is full?!"));
                return;
            }
            drain();
        }

        @Override
        public void onError(Throwable t) {
            if (!done && ExceptionHelper.addThrowable(error, t)) {
                done = true;
                drain();
            } else {
                RxJavaPlugins.onError(t);
            }
        }

        @Override
        public void onComplete() {
            if (done) {
                return;
            }
            done = true;
            drain();
        }

        @Override
        public void request(long n) {
            if (SubscriptionHelper.validate(n)) {
                BackpressureHelper.add(requested, n);
                drain();
            }
        }

        @Override
        public void cancel() {
            if (!cancelled) {
                cancelled = true;

                upstream.cancel();

                if (getAndIncrement() == 0) {
                    queue.clear();
                }
            }
        }

        void drain() {
            if (getAndIncrement() != 0) {
                return;
            }

            final Subscriber<? super R> a = downstream;
            final SimpleQueue<T> q = queue;
            final boolean replenish = fusionMode != SYNC;

            int missed = 1;

            Iterator<? extends R> it = current;

            for (;;) {

                if (it == null) {

                    boolean d = done;

                    T t;

                    try {
                        t = q.poll();
                    } catch (Throwable ex) {
                        Exceptions.throwIfFatal(ex);
                        upstream.cancel();
                        ExceptionHelper.addThrowable(error, ex);
                        ex = ExceptionHelper.terminate(error);

                        current = null;
                        q.clear();

                        a.onError(ex);
                        return;
                    }

                    boolean empty = t == null;

                    if (checkTerminated(d, empty, a, q)) {
                        return;
                    }

                    if (t != null) {
                        Iterable<? extends R> iterable;

                        boolean b;

                        try {
                            iterable = mapper.apply(t);

                            it = iterable.iterator();

                            b = it.hasNext();
                        } catch (Throwable ex) {
                            Exceptions.throwIfFatal(ex);
                            upstream.cancel();
                            ExceptionHelper.addThrowable(error, ex);
                            ex = ExceptionHelper.terminate(error);
                            a.onError(ex);
                            return;
                        }

                        if (!b) {
                            it = null;
                            consumedOne(replenish);
                            continue;
                        }

                        current = it;
                    }
                }

                if (it != null) {
                    long r = requested.get();
                    long e = 0L;

                    while (e != r) {
                        if (checkTerminated(done, false, a, q)) {
                            return;
                        }

                        R v;

                        try {
                            v = ObjectHelper.requireNonNull(it.next(), "The iterator returned a null value");
                        } catch (Throwable ex) {
                            Exceptions.throwIfFatal(ex);
                            current = null;
                            upstream.cancel();
                            ExceptionHelper.addThrowable(error, ex);
                            ex = ExceptionHelper.terminate(error);
                            a.onError(ex);
                            return;
                        }

                        a.onNext(v);

                        if (checkTerminated(done, false, a, q)) {
                            return;
                        }

                        e++;

                        boolean b;

                        try {
                            b = it.hasNext();
                        } catch (Throwable ex) {
                            Exceptions.throwIfFatal(ex);
                            current = null;
                            upstream.cancel();
                            ExceptionHelper.addThrowable(error, ex);
                            ex = ExceptionHelper.terminate(error);
                            a.onError(ex);
                            return;
                        }

                        if (!b) {
                            consumedOne(replenish);
                            it = null;
                            current = null;
                            break;
                        }
                    }

                    if (e == r) {
                        boolean d = done;
                        boolean empty = q.isEmpty() && it == null;

                        if (checkTerminated(d, empty, a, q)) {
                            return;
                        }
                    }

                    if (e != 0L) {
                        if (r != Long.MAX_VALUE) {
                            requested.addAndGet(-e);
                        }
                    }

                    if (it == null) {
                        continue;
                    }
                }

                missed = addAndGet(-missed);
                if (missed == 0) {
                    break;
                }
            }
        }

        void consumedOne(boolean enabled) {
            if (enabled) {
                int c = consumed + 1;
                if (c == limit) {
                    consumed = 0;
                    upstream.request(c);
                } else {
                    consumed = c;
                }
            }
        }

        boolean checkTerminated(boolean d, boolean empty, Subscriber<?> a, SimpleQueue<?> q) {
            if (cancelled) {
                current = null;
                q.clear();
                return true;
            }
            if (d) {
                Throwable ex = error.get();
                if (ex != null) {
                    ex = ExceptionHelper.terminate(error);

                    current = null;
                    q.clear();

                    a.onError(ex);
                    return true;
                } else if (empty) {
                    a.onComplete();
                    return true;
                }
            }
            return false;
        }

        @Override
        public void clear() {
            current = null;
            queue.clear();
        }

        @Override
        public boolean isEmpty() {
            return current == null && queue.isEmpty();
        }

        @Nullable
        @Override
        public R poll() throws Exception {
            Iterator<? extends R> it = current;
            for (;;) {
                if (it == null) {
                    T v = queue.poll();
                    if (v == null) {
                        return null;
                    }

                    it = mapper.apply(v).iterator();

                    if (!it.hasNext()) {
                        it = null;
                        continue;
                    }
                    current = it;
                }

                R r = ObjectHelper.requireNonNull(it.next(), "The iterator returned a null value");

                if (!it.hasNext()) {
                    current = null;
                }

                return r;
            }
        }

        @Override
        public int requestFusion(int requestedMode) {
            if ((requestedMode & SYNC) != 0 && fusionMode == SYNC) {
                return SYNC;
            }
            return NONE;
        }
    }
}