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.concurrent.atomic.*;

import org.reactivestreams.*;

import io.reactivex.*;
import io.reactivex.disposables.Disposable;
import io.reactivex.internal.disposables.DisposableHelper;
import io.reactivex.internal.fuseable.SimplePlainQueue;
import io.reactivex.internal.queue.SpscArrayQueue;
import io.reactivex.internal.subscriptions.SubscriptionHelper;
import io.reactivex.internal.util.*;
import io.reactivex.plugins.RxJavaPlugins;


Merges an Observable and a Maybe by emitting the items of the Observable and the success
value of the Maybe and waiting until both the Observable and Maybe terminate normally.

History: 2.1.10 - experimental

Type parameters:
  • <T> – the element type of the Observable
Since:2.2
/**
 * Merges an Observable and a Maybe by emitting the items of the Observable and the success
 * value of the Maybe and waiting until both the Observable and Maybe terminate normally.
 * <p>History: 2.1.10 - experimental
 * @param <T> the element type of the Observable
 * @since 2.2
 */
public final class FlowableMergeWithSingle<T> extends AbstractFlowableWithUpstream<T, T> {

    final SingleSource<? extends T> other;

    public FlowableMergeWithSingle(Flowable<T> source, SingleSource<? extends T> other) {
        super(source);
        this.other = other;
    }

    @Override
    protected void subscribeActual(Subscriber<? super T> subscriber) {
        MergeWithObserver<T> parent = new MergeWithObserver<T>(subscriber);
        subscriber.onSubscribe(parent);
        source.subscribe(parent);
        other.subscribe(parent.otherObserver);
    }

    static final class MergeWithObserver<T> extends AtomicInteger
    implements FlowableSubscriber<T>, Subscription {

        private static final long serialVersionUID = -4592979584110982903L;

        final Subscriber<? super T> downstream;

        final AtomicReference<Subscription> mainSubscription;

        final OtherObserver<T> otherObserver;

        final AtomicThrowable error;

        final AtomicLong requested;

        final int prefetch;

        final int limit;

        volatile SimplePlainQueue<T> queue;

        T singleItem;

        volatile boolean cancelled;

        volatile boolean mainDone;

        volatile int otherState;

        long emitted;

        int consumed;

        static final int OTHER_STATE_HAS_VALUE = 1;

        static final int OTHER_STATE_CONSUMED_OR_EMPTY = 2;

        MergeWithObserver(Subscriber<? super T> downstream) {
            this.downstream = downstream;
            this.mainSubscription = new AtomicReference<Subscription>();
            this.otherObserver = new OtherObserver<T>(this);
            this.error = new AtomicThrowable();
            this.requested = new AtomicLong();
            this.prefetch = bufferSize();
            this.limit = prefetch - (prefetch >> 2);
        }

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

        @Override
        public void onNext(T t) {
            if (compareAndSet(0, 1)) {
                long e = emitted;
                if (requested.get() != e) {
                    SimplePlainQueue<T> q = queue;
                    if (q == null || q.isEmpty()) {

                        emitted = e + 1;
                        downstream.onNext(t);

                        int c = consumed + 1;
                        if (c == limit) {
                            consumed = 0;
                            mainSubscription.get().request(c);
                        } else {
                            consumed = c;
                        }
                    } else {
                        q.offer(t);
                    }
                } else {
                    SimplePlainQueue<T> q = getOrCreateQueue();
                    q.offer(t);
                }
                if (decrementAndGet() == 0) {
                    return;
                }
            } else {
                SimplePlainQueue<T> q = getOrCreateQueue();
                q.offer(t);
                if (getAndIncrement() != 0) {
                    return;
                }
            }
            drainLoop();
        }

        @Override
        public void onError(Throwable ex) {
            if (error.addThrowable(ex)) {
                DisposableHelper.dispose(otherObserver);
                drain();
            } else {
                RxJavaPlugins.onError(ex);
            }
        }

        @Override
        public void onComplete() {
            mainDone = true;
            drain();
        }

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

        @Override
        public void cancel() {
            cancelled = true;
            SubscriptionHelper.cancel(mainSubscription);
            DisposableHelper.dispose(otherObserver);
            if (getAndIncrement() == 0) {
                queue = null;
                singleItem = null;
            }
        }

        void otherSuccess(T value) {
            if (compareAndSet(0, 1)) {
                long e = emitted;
                if (requested.get() != e) {

                    emitted = e + 1;
                    downstream.onNext(value);
                    otherState = OTHER_STATE_CONSUMED_OR_EMPTY;
                } else {
                    singleItem = value;
                    otherState = OTHER_STATE_HAS_VALUE;
                    if (decrementAndGet() == 0) {
                        return;
                    }
                }
            } else {
                singleItem = value;
                otherState = OTHER_STATE_HAS_VALUE;
                if (getAndIncrement() != 0) {
                    return;
                }
            }
            drainLoop();
        }

        void otherError(Throwable ex) {
            if (error.addThrowable(ex)) {
                SubscriptionHelper.cancel(mainSubscription);
                drain();
            } else {
                RxJavaPlugins.onError(ex);
            }
        }

        SimplePlainQueue<T> getOrCreateQueue() {
            SimplePlainQueue<T> q = queue;
            if (q == null) {
                q = new SpscArrayQueue<T>(bufferSize());
                queue = q;
            }
            return q;
        }

        void drain() {
            if (getAndIncrement() == 0) {
                drainLoop();
            }
        }

        void drainLoop() {
            Subscriber<? super T> actual = this.downstream;
            int missed = 1;
            long e = emitted;
            int c = consumed;
            int lim = limit;
            for (;;) {

                long r = requested.get();

                while (e != r) {
                    if (cancelled) {
                        singleItem = null;
                        queue = null;
                        return;
                    }

                    if (error.get() != null) {
                        singleItem = null;
                        queue = null;
                        actual.onError(error.terminate());
                        return;
                    }

                    int os = otherState;
                    if (os == OTHER_STATE_HAS_VALUE) {
                        T v = singleItem;
                        singleItem = null;
                        otherState = OTHER_STATE_CONSUMED_OR_EMPTY;
                        os = OTHER_STATE_CONSUMED_OR_EMPTY;
                        actual.onNext(v);

                        e++;
                        continue;
                    }

                    boolean d = mainDone;
                    SimplePlainQueue<T> q = queue;
                    T v = q != null ? q.poll() : null;
                    boolean empty = v == null;

                    if (d && empty && os == OTHER_STATE_CONSUMED_OR_EMPTY) {
                        queue = null;
                        actual.onComplete();
                        return;
                    }

                    if (empty) {
                        break;
                    }

                    actual.onNext(v);

                    e++;

                    if (++c == lim) {
                        c = 0;
                        mainSubscription.get().request(lim);
                    }
                }

                if (e == r) {
                    if (cancelled) {
                        singleItem = null;
                        queue = null;
                        return;
                    }

                    if (error.get() != null) {
                        singleItem = null;
                        queue = null;
                        actual.onError(error.terminate());
                        return;
                    }

                    boolean d = mainDone;
                    SimplePlainQueue<T> q = queue;
                    boolean empty = q == null || q.isEmpty();

                    if (d && empty && otherState == 2) {
                        queue = null;
                        actual.onComplete();
                        return;
                    }
                }

                emitted = e;
                consumed = c;
                missed = addAndGet(-missed);
                if (missed == 0) {
                    break;
                }
            }
        }

        static final class OtherObserver<T> extends AtomicReference<Disposable>
        implements SingleObserver<T> {

            private static final long serialVersionUID = -2935427570954647017L;

            final MergeWithObserver<T> parent;

            OtherObserver(MergeWithObserver<T> parent) {
                this.parent = parent;
            }

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

            @Override
            public void onSuccess(T t) {
                parent.otherSuccess(t);
            }

            @Override
            public void onError(Throwable e) {
                parent.otherError(e);
            }
        }
    }
}