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.observable;

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.*;
import io.reactivex.internal.queue.SpscLinkedArrayQueue;
import io.reactivex.internal.util.AtomicThrowable;
import io.reactivex.plugins.RxJavaPlugins;

public final class ObservableSwitchMap<T, R> extends AbstractObservableWithUpstream<T, R> {
    final Function<? super T, ? extends ObservableSource<? extends R>> mapper;
    final int bufferSize;

    final boolean delayErrors;

    public ObservableSwitchMap(ObservableSource<T> source,
                               Function<? super T, ? extends ObservableSource<? extends R>> mapper, int bufferSize,
                                       boolean delayErrors) {
        super(source);
        this.mapper = mapper;
        this.bufferSize = bufferSize;
        this.delayErrors = delayErrors;
    }

    @Override
    public void subscribeActual(Observer<? super R> t) {

        if (ObservableScalarXMap.tryScalarXMapSubscribe(source, t, mapper)) {
            return;
        }

        source.subscribe(new SwitchMapObserver<T, R>(t, mapper, bufferSize, delayErrors));
    }

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

        private static final long serialVersionUID = -3491074160481096299L;
        final Observer<? super R> downstream;
        final Function<? super T, ? extends ObservableSource<? extends R>> mapper;
        final int bufferSize;

        final boolean delayErrors;

        final AtomicThrowable errors;

        volatile boolean done;

        volatile boolean cancelled;

        Disposable upstream;

        final AtomicReference<SwitchMapInnerObserver<T, R>> active = new AtomicReference<SwitchMapInnerObserver<T, R>>();

        static final SwitchMapInnerObserver<Object, Object> CANCELLED;
        static {
            CANCELLED = new SwitchMapInnerObserver<Object, Object>(null, -1L, 1);
            CANCELLED.cancel();
        }

        volatile long unique;

        SwitchMapObserver(Observer<? super R> actual,
                Function<? super T, ? extends ObservableSource<? extends R>> mapper, int bufferSize,
                        boolean delayErrors) {
            this.downstream = actual;
            this.mapper = mapper;
            this.bufferSize = bufferSize;
            this.delayErrors = delayErrors;
            this.errors = new AtomicThrowable();
        }

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

        @Override
        public void onNext(T t) {
            long c = unique + 1;
            unique = c;

            SwitchMapInnerObserver<T, R> inner = active.get();
            if (inner != null) {
                inner.cancel();
            }

            ObservableSource<? extends R> p;
            try {
                p = ObjectHelper.requireNonNull(mapper.apply(t), "The ObservableSource returned is null");
            } catch (Throwable e) {
                Exceptions.throwIfFatal(e);
                upstream.dispose();
                onError(e);
                return;
            }

            SwitchMapInnerObserver<T, R> nextInner = new SwitchMapInnerObserver<T, R>(this, c, bufferSize);

            for (;;) {
                inner = active.get();
                if (inner == CANCELLED) {
                    break;
                }
                if (active.compareAndSet(inner, nextInner)) {
                    p.subscribe(nextInner);
                    break;
                }
            }
        }

        @Override
        public void onError(Throwable t) {
            if (!done && errors.addThrowable(t)) {
                if (!delayErrors) {
                    disposeInner();
                }
                done = true;
                drain();
            } else {
                RxJavaPlugins.onError(t);
            }
        }

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

        @Override
        public void dispose() {
            if (!cancelled) {
                cancelled = true;
                upstream.dispose();
                disposeInner();
            }
        }

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

        @SuppressWarnings("unchecked")
        void disposeInner() {
            SwitchMapInnerObserver<T, R> a = active.get();
            if (a != CANCELLED) {
                a = active.getAndSet((SwitchMapInnerObserver<T, R>)CANCELLED);
                if (a != CANCELLED && a != null) {
                    a.cancel();
                }
            }
        }

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

            final Observer<? super R> a = downstream;
            final AtomicReference<SwitchMapInnerObserver<T, R>> active = this.active;
            final boolean delayErrors = this.delayErrors;

            int missing = 1;

            for (;;) {

                if (cancelled) {
                    return;
                }

                if (done) {
                    boolean empty = active.get() == null;
                    if (delayErrors) {
                        if (empty) {
                            Throwable ex = errors.get();
                            if (ex != null) {
                                a.onError(ex);
                            } else {
                                a.onComplete();
                            }
                            return;
                        }
                    } else {
                        Throwable ex = errors.get();
                        if (ex != null) {
                            a.onError(errors.terminate());
                            return;
                        }
                        if (empty) {
                            a.onComplete();
                            return;
                        }
                    }
                }

                SwitchMapInnerObserver<T, R> inner = active.get();

                if (inner != null) {
                    SimpleQueue<R> q = inner.queue;

                    if (q != null) {
                        if (inner.done) {
                            boolean empty = q.isEmpty();
                            if (delayErrors) {
                                if (empty) {
                                    active.compareAndSet(inner, null);
                                    continue;
                                }
                            } else {
                                Throwable ex = errors.get();
                                if (ex != null) {
                                    a.onError(errors.terminate());
                                    return;
                                }
                                if (empty) {
                                    active.compareAndSet(inner, null);
                                    continue;
                                }
                            }
                        }

                        boolean retry = false;

                        for (;;) {
                            if (cancelled) {
                                return;
                            }
                            if (inner != active.get()) {
                                retry = true;
                                break;
                            }

                            if (!delayErrors) {
                                Throwable ex = errors.get();
                                if (ex != null) {
                                    a.onError(errors.terminate());
                                    return;
                                }
                            }

                            boolean d = inner.done;
                            R v;

                            try {
                                v = q.poll();
                            } catch (Throwable ex) {
                                Exceptions.throwIfFatal(ex);
                                errors.addThrowable(ex);
                                active.compareAndSet(inner, null);
                                if (!delayErrors) {
                                    disposeInner();
                                    upstream.dispose();
                                    done = true;
                                } else {
                                    inner.cancel();
                                }
                                v = null;
                                retry = true;
                            }
                            boolean empty = v == null;

                            if (d && empty) {
                                active.compareAndSet(inner, null);
                                retry = true;
                                break;
                            }

                            if (empty) {
                                break;
                            }

                            a.onNext(v);
                        }

                        if (retry) {
                            continue;
                        }
                    }
                }

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

        void innerError(SwitchMapInnerObserver<T, R> inner, Throwable ex) {
            if (inner.index == unique && errors.addThrowable(ex)) {
                if (!delayErrors) {
                    upstream.dispose();
                }
                inner.done = true;
                drain();
            } else {
                RxJavaPlugins.onError(ex);
            }
        }
    }

    static final class SwitchMapInnerObserver<T, R> extends AtomicReference<Disposable> implements Observer<R> {

        private static final long serialVersionUID = 3837284832786408377L;
        final SwitchMapObserver<T, R> parent;
        final long index;

        final int bufferSize;

        volatile SimpleQueue<R> queue;

        volatile boolean done;

        SwitchMapInnerObserver(SwitchMapObserver<T, R> parent, long index, int bufferSize) {
            this.parent = parent;
            this.index = index;
            this.bufferSize = bufferSize;
        }

        @Override
        public void onSubscribe(Disposable d) {
            if (DisposableHelper.setOnce(this, d)) {
                if (d instanceof QueueDisposable) {
                    @SuppressWarnings("unchecked")
                    QueueDisposable<R> qd = (QueueDisposable<R>) d;

                    int m = qd.requestFusion(QueueDisposable.ANY | QueueDisposable.BOUNDARY);
                    if (m == QueueDisposable.SYNC) {
                        queue = qd;
                        done = true;
                        parent.drain();
                        return;
                    }
                    if (m == QueueDisposable.ASYNC) {
                        queue = qd;
                        return;
                    }
                }

                queue = new SpscLinkedArrayQueue<R>(bufferSize);
            }
        }

        @Override
        public void onNext(R t) {
            if (index == parent.unique) {
                if (t != null) {
                    queue.offer(t);
                }
                parent.drain();
            }
        }

        @Override
        public void onError(Throwable t) {
            parent.innerError(this, t);
        }

        @Override
        public void onComplete() {
            if (index == parent.unique) {
                done = true;
                parent.drain();
            }
        }

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