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Reactive Extensions for Java
There is a newer version: 3.1.9
/*
 * 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.rxjava3.internal.operators.single;

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

import io.reactivex.rxjava3.core.*;
import io.reactivex.rxjava3.disposables.Disposable;
import io.reactivex.rxjava3.exceptions.Exceptions;
import io.reactivex.rxjava3.functions.Function;
import io.reactivex.rxjava3.internal.disposables.DisposableHelper;
import io.reactivex.rxjava3.plugins.RxJavaPlugins;

public final class SingleZipArray extends Single {

    final SingleSource[] sources;

    final Function zipper;

    public SingleZipArray(SingleSource[] sources, Function zipper) {
        this.sources = sources;
        this.zipper = zipper;
    }

    @Override
    protected void subscribeActual(SingleObserver observer) {
        SingleSource[] sources = this.sources;
        int n = sources.length;

        if (n == 1) {
            sources[0].subscribe(new SingleMap.MapSingleObserver<>(observer, new SingletonArrayFunc()));
            return;
        }

        ZipCoordinator parent = new ZipCoordinator<>(observer, n, zipper);

        observer.onSubscribe(parent);

        for (int i = 0; i < n; i++) {
            if (parent.isDisposed()) {
                return;
            }

            SingleSource source = sources[i];

            if (source == null) {
                parent.innerError(new NullPointerException("One of the sources is null"), i);
                return;
            }

            source.subscribe(parent.observers[i]);
        }
    }

    static final class ZipCoordinator extends AtomicInteger implements Disposable {

        private static final long serialVersionUID = -5556924161382950569L;

        final SingleObserver downstream;

        final Function zipper;

        final ZipSingleObserver[] observers;

        Object[] values;

        @SuppressWarnings("unchecked")
        ZipCoordinator(SingleObserver observer, int n, Function zipper) {
            super(n);
            this.downstream = observer;
            this.zipper = zipper;
            ZipSingleObserver[] o = new ZipSingleObserver[n];
            for (int i = 0; i < n; i++) {
                o[i] = new ZipSingleObserver<>(this, i);
            }
            this.observers = o;
            this.values = new Object[n];
        }

        @Override
        public boolean isDisposed() {
            return get() <= 0;
        }

        @Override
        public void dispose() {
            if (getAndSet(0) > 0) {
                for (ZipSingleObserver d : observers) {
                    d.dispose();
                }

                values = null;
            }
        }

        void innerSuccess(T value, int index) {
            Object[] values = this.values;
            if (values != null) {
                values[index] = value;
            }
            if (decrementAndGet() == 0) {
                R v;

                try {
                    v = Objects.requireNonNull(zipper.apply(values), "The zipper returned a null value");
                } catch (Throwable ex) {
                    Exceptions.throwIfFatal(ex);
                    this.values = null;
                    downstream.onError(ex);
                    return;
                }

                this.values = null;
                downstream.onSuccess(v);
            }
        }

        void disposeExcept(int index) {
            ZipSingleObserver[] observers = this.observers;
            int n = observers.length;
            for (int i = 0; i < index; i++) {
                observers[i].dispose();
            }
            for (int i = index + 1; i < n; i++) {
                observers[i].dispose();
            }
        }

        void innerError(Throwable ex, int index) {
            if (getAndSet(0) > 0) {
                disposeExcept(index);
                values = null;
                downstream.onError(ex);
            } else {
                RxJavaPlugins.onError(ex);
            }
        }
    }

    static final class ZipSingleObserver
    extends AtomicReference
    implements SingleObserver {

        private static final long serialVersionUID = 3323743579927613702L;

        final ZipCoordinator parent;

        final int index;

        ZipSingleObserver(ZipCoordinator parent, int index) {
            this.parent = parent;
            this.index = index;
        }

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

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

        @Override
        public void onSuccess(T value) {
            parent.innerSuccess(value, index);
        }

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

    final class SingletonArrayFunc implements Function {
        @Override
        public R apply(T t) throws Throwable {
            return Objects.requireNonNull(zipper.apply(new Object[] { t }), "The zipper returned a null value");
        }
    }
}