FlowableCombineLatest.java

/**
 * Copyright 2016 Netflix, Inc.
 * 
 * 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.atomic.*;

import org.reactivestreams.*;

import io.reactivex.Flowable;
import io.reactivex.exceptions.Exceptions;
import io.reactivex.functions.Function;
import io.reactivex.internal.functions.Objects;
import io.reactivex.internal.queue.SpscLinkedArrayQueue;
import io.reactivex.internal.subscriptions.*;
import io.reactivex.internal.util.*;
import io.reactivex.plugins.RxJavaPlugins;

/**
 * Combines the latest values from multiple sources through a function.
 *
 * @param <T> the value type of the sources
 * @param <R> the result type
 */
public final class FlowableCombineLatest<T, R> 
extends Flowable<R> {

    final Publisher<? extends T>[] array;

    final Iterable<? extends Publisher<? extends T>> iterable;

    final Function<Object[], ? extends R> combiner;
    
    final int bufferSize;
    
    final boolean delayErrors;

    public FlowableCombineLatest(Publisher<? extends T>[] array,
            Function<Object[], ? extends R> combiner,
                    int bufferSize, boolean delayErrors) {
        if (bufferSize <= 0) {
            throw new IllegalArgumentException("BUFFER_SIZE > 0 required but it was " + bufferSize);
        }

        this.array = Objects.requireNonNull(array, "array");
        this.iterable = null;
        this.combiner = Objects.requireNonNull(combiner, "combiner");
        this.bufferSize = bufferSize;
        this.delayErrors = delayErrors;
    }
    
    public FlowableCombineLatest(Iterable<? extends Publisher<? extends T>> iterable,
            Function<Object[], ? extends R> combiner,
                    int bufferSize, boolean delayErrors) {
        if (bufferSize <= 0) {
            throw new IllegalArgumentException("BUFFER_SIZE > 0 required but it was " + bufferSize);
        }
        
        this.array = null;
        this.iterable = Objects.requireNonNull(iterable, "iterable");
        this.combiner = Objects.requireNonNull(combiner, "combiner");
        this.bufferSize = bufferSize;
        this.delayErrors = delayErrors;
    }

    @SuppressWarnings("unchecked")
    @Override
    public void subscribeActual(Subscriber<? super R> s) {
        Publisher<? extends T>[] a = array;
        int n;
        if (a == null) {
            n = 0;
            a = new Publisher[8];

            Iterator<? extends Publisher<? extends T>> it;

            try {
                it = iterable.iterator();
            } catch (Throwable e) {
                EmptySubscription.error(e, s);
                return;
            }

            if (it == null) {
                EmptySubscription.error(new NullPointerException("The iterator returned is null"), s);
                return;
            }

            for (;;) {

                boolean b;

                try {
                    b = it.hasNext();
                } catch (Throwable e) {
                    EmptySubscription.error(e, s);
                    return;
                }

                if (!b) {
                    break;
                }

                Publisher<? extends T> p;

                try {
                    p = it.next();
                } catch (Throwable e) {
                    EmptySubscription.error(e, s);
                    return;
                }

                if (p == null) {
                    EmptySubscription.error(new NullPointerException("The Publisher returned by the iterator is " +
                      "null"), s);
                    return;
                }

                if (n == a.length) {
                    Publisher<? extends T>[] c = new Publisher[n + (n >> 2)];
                    System.arraycopy(a, 0, c, 0, n);
                    a = c;
                }
                a[n++] = p;
            }

        } else {
            n = a.length;
        }

        if (n == 0) {
            EmptySubscription.complete(s);
            return;
        }
        if (n == 1) {
            new FlowableMap<T, R>((Publisher<T>)a[0], new Function<T, R>() {
                @Override
                public R apply(T t) throws Exception {
                    return combiner.apply(new Object[] { t });
                }
            }).subscribe(s);
            return;
        }
        
        
        CombineLatestCoordinator<T, R> coordinator = 
                new CombineLatestCoordinator<T, R>(s, combiner, n, bufferSize, delayErrors);
        
        s.onSubscribe(coordinator);
        
        coordinator.subscribe(a, n);
    }
    
    static final class CombineLatestCoordinator<T, R>
    extends BasicIntQueueSubscription<R> {

        /** */
        private static final long serialVersionUID = -5082275438355852221L;

        final Subscriber<? super R> actual;
        
        final Function<Object[], ? extends R> combiner;
        
        final CombineLatestInnerSubscriber<T>[] subscribers;
        
        final SpscLinkedArrayQueue<Object> queue;
        
        final Object[] latest;
        
        final boolean delayErrors;
        
        boolean outputFused;

        int nonEmptySources;
        
        int completedSources;
        
        volatile boolean cancelled;
        
        final AtomicLong requested;
        
        volatile boolean done;

        final AtomicReference<Throwable> error;
        
        public CombineLatestCoordinator(Subscriber<? super R> actual, 
                Function<Object[], ? extends R> combiner, int n,
                int bufferSize, boolean delayErrors) {
            this.actual = actual;
            this.combiner = combiner;
            @SuppressWarnings("unchecked")
            CombineLatestInnerSubscriber<T>[] a = new CombineLatestInnerSubscriber[n];
            for (int i = 0; i < n; i++) {
                a[i] = new CombineLatestInnerSubscriber<T>(this, i, bufferSize);
            }
            this.subscribers = a;
            this.latest = new Object[n];
            this.queue = new SpscLinkedArrayQueue<Object>(bufferSize);
            this.requested = new AtomicLong();
            this.error = new  AtomicReference<Throwable>();
            this.delayErrors = delayErrors;
        }

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

        @Override
        public void cancel() {
            cancelled = true;
            cancelAll();
        }

        void subscribe(Publisher<? extends T>[] sources, int n) {
            CombineLatestInnerSubscriber<T>[] a = subscribers;
            
            for (int i = 0; i < n; i++) {
                if (done || cancelled) {
                    return;
                }
                sources[i].subscribe(a[i]);
            }
        }
        
        void innerValue(int index, T value) {
            
            boolean replenishInsteadOfDrain;
            
            synchronized (this) {
                Object[] os = latest;

                int localNonEmptySources = nonEmptySources;
                
                if (os[index] == null) {
                    localNonEmptySources++;
                    nonEmptySources = localNonEmptySources;
                }
                
                os[index] = value;

                if (os.length == localNonEmptySources) {
                    
                    queue.offer(subscribers[index], os.clone());
                    
                    replenishInsteadOfDrain = false;
                } else {
                    replenishInsteadOfDrain = true;
                }
            }
            
            if (replenishInsteadOfDrain) {
                subscribers[index].requestOne();
            } else {
                drain();
            }
        }
        
        void innerComplete(int index) {
            synchronized (this) {
                Object[] os = latest;
                
                if (os[index] != null) {
                    int localCompletedSources = completedSources + 1;
                    
                    if (localCompletedSources == os.length) {
                        done = true;
                    } else {
                        completedSources = localCompletedSources;
                        return;
                    }
                } else {
                    done = true;
                }
            }
            drain();
        }
        
        void innerError(int index, Throwable e) {
            
            if (ExceptionHelper.addThrowable(error, e)) {
                if (!delayErrors) {
                    cancelAll();
                    done = true;
                    drain();
                } else {
                    innerComplete(index);
                }
            } else {
                RxJavaPlugins.onError(e);
            }
        }
        
        void drainOutput() {
            final Subscriber<? super R> a = actual;
            final SpscLinkedArrayQueue<Object> q = queue;
            
            int missed = 1;
            
            for (;;) {
                
                if (cancelled) {
                    q.clear();
                    return;
                }
                
                Throwable ex = error.get();
                if (ex != null) {
                    q.clear();
                    
                    a.onError(ex);
                    return;
                }
                
                boolean d = done;
                
                boolean empty = q.isEmpty();
                
                if (!empty) {
                    a.onNext(null);
                }
                
                if (d && empty) {
                    a.onComplete();
                    return;
                }
                
                missed = addAndGet(-missed);
                if (missed == 0) {
                    break;
                }
            }
        }
        
        @SuppressWarnings("unchecked")
        void drainAsync() {
            final Subscriber<? super R> a = actual;
            final SpscLinkedArrayQueue<Object> q = queue;
            
            int missed = 1;
            
            for (;;) {
                
                long r = requested.get();
                long e = 0L;
                
                while (e != r) {
                    boolean d = done;
                    
                    Object v = q.poll();
                    
                    boolean empty = v == null;
                    
                    if (checkTerminated(d, empty, a, q)) {
                        return;
                    }
                    
                    if (empty) {
                        break;
                    }
                    
                    T[] va = (T[])q.poll();
                    
                    R w;
                    
                    try {
                        w = Objects.requireNonNull(combiner.apply(va), "The combiner returned a null value");
                    } catch (Throwable ex) {
                        Exceptions.throwIfFatal(ex);
                        
                        cancelAll();
                        ExceptionHelper.addThrowable(error, ex);
                        ex = ExceptionHelper.terminate(error);

                        a.onError(ex);
                        return;
                    }
                    
                    a.onNext(w);
                    
                    ((CombineLatestInnerSubscriber<T>)v).requestOne();
                    
                    e++;
                }
                
                if (e == r) {
                    if (checkTerminated(done, q.isEmpty(), a, q)) {
                        return;
                    }
                }
                
                if (e != 0L && r != Long.MAX_VALUE) {
                    requested.addAndGet(-e);
                }
                
                missed = addAndGet(-missed);
                if (missed == 0) {
                    break;
                }
            }
        }
        
        void drain() {
            if (getAndIncrement() != 0) {
                return;
            }
            
            if (outputFused) {
                drainOutput();
            } else {
                drainAsync();
            }
        }
        
        boolean checkTerminated(boolean d, boolean empty, Subscriber<?> a, SpscLinkedArrayQueue<?> q) {
            if (cancelled) {
                cancelAll();
                q.clear();
                return true;
            }
            
            if (d) {
                if (delayErrors) {
                    if (empty) {
                        Throwable e = ExceptionHelper.terminate(error);
                        
                        if (e != null && e != ExceptionHelper.TERMINATED) {
                            a.onError(e);
                        } else {
                            a.onComplete();
                        }
                        return true;
                    }
                } else {
                    Throwable e = ExceptionHelper.terminate(error);
                    
                    if (e != null && e != ExceptionHelper.TERMINATED) {
                        cancelAll();
                        q.clear();
                        a.onError(e);
                        return true;
                    } else
                    if (empty) {
                        cancelAll();
    
                        a.onComplete();
                        return true;
                    }
                }
            }
            return false;
        }
        
        void cancelAll() {
            for (CombineLatestInnerSubscriber<T> inner : subscribers) {
                inner.cancel();
            }
        }
        
        @Override
        public int requestFusion(int requestedMode) {
            if ((requestedMode & BOUNDARY) != 0) {
                return NONE;
            }
            int m = requestedMode & ASYNC;
            outputFused = m != 0;
            return m;
        }
        
        @SuppressWarnings("unchecked")
        @Override
        public R poll() throws Exception {
            Object e = queue.poll();
            if (e == null) {
                return null;
            }
            T[] a = (T[])queue.poll();
            R r = combiner.apply(a);
            ((CombineLatestInnerSubscriber<T>)e).requestOne();
            return r;
        }
        
        @Override
        public void clear() {
            queue.clear();
        }
        
        @Override
        public boolean isEmpty() {
            return queue.isEmpty();
        }
    }
    
    static final class CombineLatestInnerSubscriber<T>
    extends AtomicReference<Subscription>
            implements Subscriber<T> {

        /** */
        private static final long serialVersionUID = -8730235182291002949L;

        final CombineLatestCoordinator<T, ?> parent;

        final int index;

        final int prefetch;
        
        final int limit;
        
        int produced;
        
        public CombineLatestInnerSubscriber(CombineLatestCoordinator<T, ?> parent, int index, int prefetch) {
            this.parent = parent;
            this.index = index;
            this.prefetch = prefetch;
            this.limit = prefetch - (prefetch >> 2);
        }

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

        @Override
        public void onNext(T t) {
            parent.innerValue(index, t);
        }

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

        @Override
        public void onComplete() {
            parent.innerComplete(index);
        }
        
        public void cancel() {
            SubscriptionHelper.dispose(this);
        }
        
        public void requestOne() {
            
            int p = produced + 1;
            if (p == limit) {
                produced = 0;
                get().request(p);
            } else {
                produced = p;
            }
            
        }
    }
}