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.ArrayDeque;
import java.util.concurrent.atomic.*;

import org.reactivestreams.*;

import io.reactivex.*;
import io.reactivex.internal.queue.SpscLinkedArrayQueue;
import io.reactivex.internal.subscriptions.SubscriptionHelper;
import io.reactivex.internal.util.BackpressureHelper;
import io.reactivex.plugins.RxJavaPlugins;
import io.reactivex.processors.UnicastProcessor;

public final class FlowableWindow<T> extends AbstractFlowableWithUpstream<T, Flowable<T>> {
    final long size;

    final long skip;

    final int bufferSize;

    public FlowableWindow(Flowable<T> source, long size, long skip,  int bufferSize) {
        super(source);
        this.size = size;
        this.skip = skip;
        this.bufferSize = bufferSize;
    }

    @Override
    public void subscribeActual(Subscriber<? super Flowable<T>> s) {
        if (skip == size) {
            source.subscribe(new WindowExactSubscriber<T>(s, size, bufferSize));
        } else
        if (skip > size) {
            source.subscribe(new WindowSkipSubscriber<T>(s, size, skip, bufferSize));
        } else {
            source.subscribe(new WindowOverlapSubscriber<T>(s, size, skip, bufferSize));
        }
    }

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

        private static final long serialVersionUID = -2365647875069161133L;

        final Subscriber<? super Flowable<T>> downstream;

        final long size;

        final AtomicBoolean once;

        final int bufferSize;

        long index;

        Subscription upstream;

        UnicastProcessor<T> window;

        WindowExactSubscriber(Subscriber<? super Flowable<T>> actual, long size, int bufferSize) {
            super(1);
            this.downstream = actual;
            this.size = size;
            this.once = new AtomicBoolean();
            this.bufferSize = bufferSize;
        }

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

        @Override
        public void onNext(T t) {
            long i = index;

            UnicastProcessor<T> w = window;
            if (i == 0) {
                getAndIncrement();

                w = UnicastProcessor.<T>create(bufferSize, this);
                window = w;

                downstream.onNext(w);
            }

            i++;

            w.onNext(t);

            if (i == size) {
                index = 0;
                window = null;
                w.onComplete();
            } else {
                index = i;
            }
        }

        @Override
        public void onError(Throwable t) {
            Processor<T, T> w = window;
            if (w != null) {
                window = null;
                w.onError(t);
            }

            downstream.onError(t);
        }

        @Override
        public void onComplete() {
            Processor<T, T> w = window;
            if (w != null) {
                window = null;
                w.onComplete();
            }

            downstream.onComplete();
        }

        @Override
        public void request(long n) {
            if (SubscriptionHelper.validate(n)) {
                long u = BackpressureHelper.multiplyCap(size, n);
                upstream.request(u);
            }
        }

        @Override
        public void cancel() {
            if (once.compareAndSet(false, true)) {
                run();
            }
        }

        @Override
        public void run() {
            if (decrementAndGet() == 0) {
                upstream.cancel();
            }
        }
    }

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

        private static final long serialVersionUID = -8792836352386833856L;

        final Subscriber<? super Flowable<T>> downstream;

        final long size;

        final long skip;

        final AtomicBoolean once;

        final AtomicBoolean firstRequest;

        final int bufferSize;

        long index;

        Subscription upstream;

        UnicastProcessor<T> window;

        WindowSkipSubscriber(Subscriber<? super Flowable<T>> actual, long size, long skip, int bufferSize) {
            super(1);
            this.downstream = actual;
            this.size = size;
            this.skip = skip;
            this.once = new AtomicBoolean();
            this.firstRequest = new AtomicBoolean();
            this.bufferSize = bufferSize;
        }

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

        @Override
        public void onNext(T t) {
            long i = index;

            UnicastProcessor<T> w = window;
            if (i == 0) {
                getAndIncrement();

                w = UnicastProcessor.<T>create(bufferSize, this);
                window = w;

                downstream.onNext(w);
            }

            i++;

            if (w != null) {
                w.onNext(t);
            }

            if (i == size) {
                window = null;
                w.onComplete();
            }

            if (i == skip) {
                index = 0;
            } else {
                index = i;
            }
        }

        @Override
        public void onError(Throwable t) {
            Processor<T, T> w = window;
            if (w != null) {
                window = null;
                w.onError(t);
            }

            downstream.onError(t);
        }

        @Override
        public void onComplete() {
            Processor<T, T> w = window;
            if (w != null) {
                window = null;
                w.onComplete();
            }

            downstream.onComplete();
        }

        @Override
        public void request(long n) {
            if (SubscriptionHelper.validate(n)) {
                if (!firstRequest.get() && firstRequest.compareAndSet(false, true)) {
                    long u = BackpressureHelper.multiplyCap(size, n);
                    long v = BackpressureHelper.multiplyCap(skip - size, n - 1);
                    long w = BackpressureHelper.addCap(u, v);
                    upstream.request(w);
                } else {
                    long u = BackpressureHelper.multiplyCap(skip, n);
                    upstream.request(u);
                }
            }
        }

        @Override
        public void cancel() {
            if (once.compareAndSet(false, true)) {
                run();
            }
        }

        @Override
        public void run() {
            if (decrementAndGet() == 0) {
                upstream.cancel();
            }
        }
    }

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

        private static final long serialVersionUID = 2428527070996323976L;

        final Subscriber<? super Flowable<T>> downstream;

        final SpscLinkedArrayQueue<UnicastProcessor<T>> queue;

        final long size;

        final long skip;

        final ArrayDeque<UnicastProcessor<T>> windows;

        final AtomicBoolean once;

        final AtomicBoolean firstRequest;

        final AtomicLong requested;

        final AtomicInteger wip;

        final int bufferSize;

        long index;

        long produced;

        Subscription upstream;

        volatile boolean done;
        Throwable error;

        volatile boolean cancelled;

        WindowOverlapSubscriber(Subscriber<? super Flowable<T>> actual, long size, long skip, int bufferSize) {
            super(1);
            this.downstream = actual;
            this.size = size;
            this.skip = skip;
            this.queue = new SpscLinkedArrayQueue<UnicastProcessor<T>>(bufferSize);
            this.windows = new ArrayDeque<UnicastProcessor<T>>();
            this.once = new AtomicBoolean();
            this.firstRequest = new AtomicBoolean();
            this.requested = new AtomicLong();
            this.wip = new AtomicInteger();
            this.bufferSize = bufferSize;
        }

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

        @Override
        public void onNext(T t) {
            if (done) {
                return;
            }

            long i = index;

            if (i == 0) {
                if (!cancelled) {
                    getAndIncrement();

                    UnicastProcessor<T> w = UnicastProcessor.<T>create(bufferSize, this);

                    windows.offer(w);

                    queue.offer(w);
                    drain();
                }
            }

            i++;

            for (Processor<T, T> w : windows) {
                w.onNext(t);
            }

            long p = produced + 1;
            if (p == size) {
                produced = p - skip;

                Processor<T, T> w = windows.poll();
                if (w != null) {
                    w.onComplete();
                }
            } else {
                produced = p;
            }

            if (i == skip) {
                index = 0;
            } else {
                index = i;
            }
        }

        @Override
        public void onError(Throwable t) {
            if (done) {
                RxJavaPlugins.onError(t);
                return;
            }

            for (Processor<T, T> w : windows) {
                w.onError(t);
            }
            windows.clear();

            error = t;
            done = true;
            drain();
        }

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

            for (Processor<T, T> w : windows) {
                w.onComplete();
            }
            windows.clear();

            done = true;
            drain();
        }

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

            final Subscriber<? super Flowable<T>> a = downstream;
            final SpscLinkedArrayQueue<UnicastProcessor<T>> q = queue;
            int missed = 1;

            for (;;) {

                long r = requested.get();
                long e = 0;

                while (e != r) {
                    boolean d = done;

                    UnicastProcessor<T> t = q.poll();

                    boolean empty = t == null;

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

                    if (empty) {
                        break;
                    }

                    a.onNext(t);

                    e++;
                }

                if (e == r) {
                    if (checkTerminated(done, q.isEmpty(), a, q)) {
                        return;
                    }
                }

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

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

        boolean checkTerminated(boolean d, boolean empty, Subscriber<?> a, SpscLinkedArrayQueue<?> q) {
            if (cancelled) {
                q.clear();
                return true;
            }

            if (d) {
                Throwable e = error;

                if (e != null) {
                    q.clear();
                    a.onError(e);
                    return true;
                } else
                if (empty) {
                    a.onComplete();
                    return true;
                }
            }

            return false;
        }

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

                if (!firstRequest.get() && firstRequest.compareAndSet(false, true)) {
                    long u = BackpressureHelper.multiplyCap(skip, n - 1);
                    long v = BackpressureHelper.addCap(size, u);
                    upstream.request(v);
                } else {
                    long u = BackpressureHelper.multiplyCap(skip, n);
                    upstream.request(u);
                }

                drain();
            }
        }

        @Override
        public void cancel() {
            cancelled = true;
            if (once.compareAndSet(false, true)) {
                run();
            }
        }

        @Override
        public void run() {
            if (decrementAndGet() == 0) {
                upstream.cancel();
            }
        }
    }
}