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.mixed;

import java.util.concurrent.atomic.*;

import io.reactivex.*;
import io.reactivex.disposables.Disposable;
import io.reactivex.exceptions.Exceptions;
import io.reactivex.functions.Function;
import io.reactivex.internal.disposables.DisposableHelper;
import io.reactivex.internal.functions.ObjectHelper;
import io.reactivex.internal.fuseable.SimplePlainQueue;
import io.reactivex.internal.queue.SpscLinkedArrayQueue;
import io.reactivex.internal.util.*;
import io.reactivex.plugins.RxJavaPlugins;


Maps each upstream item into a SingleSource, subscribes to them one after the other terminates and relays their success values, optionally delaying any errors till the main and inner sources terminate. 
History: 2.1.11 - experimental

Type parameters:
  • <T> – the upstream element type
  • <R> – the output element type
Since:2.2
/**
 * Maps each upstream item into a {@link SingleSource}, subscribes to them one after the other terminates
 * and relays their success values, optionally delaying any errors till the main and inner sources
 * terminate.
 * <p>History: 2.1.11 - experimental
 * @param <T> the upstream element type
 * @param <R> the output element type
 * @since 2.2
 */
public final class ObservableConcatMapSingle<T, R> extends Observable<R> {

    final Observable<T> source;

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

    final ErrorMode errorMode;

    final int prefetch;

    public ObservableConcatMapSingle(Observable<T> source,
            Function<? super T, ? extends SingleSource<? extends R>> mapper,
                    ErrorMode errorMode, int prefetch) {
        this.source = source;
        this.mapper = mapper;
        this.errorMode = errorMode;
        this.prefetch = prefetch;
    }

    @Override
    protected void subscribeActual(Observer<? super R> observer) {
        if (!ScalarXMapZHelper.tryAsSingle(source, mapper, observer)) {
            source.subscribe(new ConcatMapSingleMainObserver<T, R>(observer, mapper, prefetch, errorMode));
        }
    }

    static final class ConcatMapSingleMainObserver<T, R>
    extends AtomicInteger
    implements Observer<T>, Disposable {

        private static final long serialVersionUID = -9140123220065488293L;

        final Observer<? super R> downstream;

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

        final AtomicThrowable errors;

        final ConcatMapSingleObserver<R> inner;

        final SimplePlainQueue<T> queue;

        final ErrorMode errorMode;

        Disposable upstream;

        volatile boolean done;

        volatile boolean cancelled;

        R item;

        volatile int state;

        
No inner SingleSource is running. 
/** No inner SingleSource is running. */
        static final int STATE_INACTIVE = 0;
        
An inner SingleSource is running but there are no results yet. 
/** An inner SingleSource is running but there are no results yet. */
        static final int STATE_ACTIVE = 1;
        
The inner SingleSource succeeded with a value in ConcatMapSingleMainObserver<T,R>.item. 
/** The inner SingleSource succeeded with a value in {@link #item}. */
        static final int STATE_RESULT_VALUE = 2;

        ConcatMapSingleMainObserver(Observer<? super R> downstream,
                Function<? super T, ? extends SingleSource<? extends R>> mapper,
                        int prefetch, ErrorMode errorMode) {
            this.downstream = downstream;
            this.mapper = mapper;
            this.errorMode = errorMode;
            this.errors = new AtomicThrowable();
            this.inner = new ConcatMapSingleObserver<R>(this);
            this.queue = new SpscLinkedArrayQueue<T>(prefetch);
        }

        @Override
        public void onSubscribe(Disposable d) {
            if (DisposableHelper.validate(upstream, d)) {
                upstream = d;
                downstream.onSubscribe(this);
            }
        }

        @Override
        public void onNext(T t) {
            queue.offer(t);
            drain();
        }

        @Override
        public void onError(Throwable t) {
            if (errors.addThrowable(t)) {
                if (errorMode == ErrorMode.IMMEDIATE) {
                    inner.dispose();
                }
                done = true;
                drain();
            } else {
                RxJavaPlugins.onError(t);
            }
        }

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

        @Override
        public void dispose() {
            cancelled = true;
            upstream.dispose();
            inner.dispose();
            if (getAndIncrement() == 0) {
                queue.clear();
                item = null;
            }
        }

        @Override
        public boolean isDisposed() {
            return cancelled;
        }

        void innerSuccess(R item) {
            this.item = item;
            this.state = STATE_RESULT_VALUE;
            drain();
        }

        void innerError(Throwable ex) {
            if (errors.addThrowable(ex)) {
                if (errorMode != ErrorMode.END) {
                    upstream.dispose();
                }
                this.state = STATE_INACTIVE;
                drain();
            } else {
                RxJavaPlugins.onError(ex);
            }
        }

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

            int missed = 1;
            Observer<? super R> downstream = this.downstream;
            ErrorMode errorMode = this.errorMode;
            SimplePlainQueue<T> queue = this.queue;
            AtomicThrowable errors = this.errors;

            for (;;) {

                for (;;) {
                    if (cancelled) {
                        queue.clear();
                        item = null;
                        break;
                    }

                    int s = state;

                    if (errors.get() != null) {
                        if (errorMode == ErrorMode.IMMEDIATE
                                || (errorMode == ErrorMode.BOUNDARY && s == STATE_INACTIVE)) {
                            queue.clear();
                            item = null;
                            Throwable ex = errors.terminate();
                            downstream.onError(ex);
                            return;
                        }
                    }

                    if (s == STATE_INACTIVE) {
                        boolean d = done;
                        T v = queue.poll();
                        boolean empty = v == null;

                        if (d && empty) {
                            Throwable ex = errors.terminate();
                            if (ex == null) {
                                downstream.onComplete();
                            } else {
                                downstream.onError(ex);
                            }
                            return;
                        }

                        if (empty) {
                            break;
                        }

                        SingleSource<? extends R> ss;

                        try {
                            ss = ObjectHelper.requireNonNull(mapper.apply(v), "The mapper returned a null SingleSource");
                        } catch (Throwable ex) {
                            Exceptions.throwIfFatal(ex);
                            upstream.dispose();
                            queue.clear();
                            errors.addThrowable(ex);
                            ex = errors.terminate();
                            downstream.onError(ex);
                            return;
                        }

                        state = STATE_ACTIVE;
                        ss.subscribe(inner);
                        break;
                    } else if (s == STATE_RESULT_VALUE) {
                        R w = item;
                        item = null;
                        downstream.onNext(w);

                        state = STATE_INACTIVE;
                    } else {
                        break;
                    }
                }

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

        static final class ConcatMapSingleObserver<R>
        extends AtomicReference<Disposable>
        implements SingleObserver<R> {

            private static final long serialVersionUID = -3051469169682093892L;

            final ConcatMapSingleMainObserver<?, R> parent;

            ConcatMapSingleObserver(ConcatMapSingleMainObserver<?, R> parent) {
                this.parent = parent;
            }

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

            @Override
            public void onSuccess(R t) {
                parent.innerSuccess(t);
            }

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

            void dispose() {
                DisposableHelper.dispose(this);
            }
        }
    }
}