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rxjava3-observable developed by David Karnok
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/**
 * 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.observable.internal.operators;

import java.util.concurrent.atomic.*;

import io.reactivex.common.*;
import io.reactivex.common.exceptions.Exceptions;
import io.reactivex.common.functions.Cancellable;
import io.reactivex.common.internal.disposables.*;
import io.reactivex.common.internal.utils.AtomicThrowable;
import io.reactivex.observable.*;
import io.reactivex.observable.extensions.SimpleQueue;
import io.reactivex.observable.internal.queues.SpscLinkedArrayQueue;

public final class ObservableCreate extends Observable {
    final ObservableOnSubscribe source;

    public ObservableCreate(ObservableOnSubscribe source) {
        this.source = source;
    }

    @Override
    protected void subscribeActual(Observer observer) {
        CreateEmitter parent = new CreateEmitter(observer);
        observer.onSubscribe(parent);

        try {
            source.subscribe(parent);
        } catch (Throwable ex) {
            Exceptions.throwIfFatal(ex);
            parent.onError(ex);
        }
    }

    static final class CreateEmitter
    extends AtomicReference
    implements ObservableEmitter, Disposable {


        private static final long serialVersionUID = -3434801548987643227L;

        final Observer observer;

        CreateEmitter(Observer observer) {
            this.observer = observer;
        }

        @Override
        public void onNext(T t) {
            if (t == null) {
                onError(new NullPointerException("onNext called with null. Null values are generally not allowed in 2.x operators and sources."));
                return;
            }
            if (!isDisposed()) {
                observer.onNext(t);
            }
        }

        @Override
        public void onError(Throwable t) {
            if (t == null) {
                t = new NullPointerException("onError called with null. Null values are generally not allowed in 2.x operators and sources.");
            }
            if (!isDisposed()) {
                try {
                    observer.onError(t);
                } finally {
                    dispose();
                }
            } else {
                RxJavaCommonPlugins.onError(t);
            }
        }

        @Override
        public void onComplete() {
            if (!isDisposed()) {
                try {
                    observer.onComplete();
                } finally {
                    dispose();
                }
            }
        }

        @Override
        public void setDisposable(Disposable d) {
            DisposableHelper.set(this, d);
        }

        @Override
        public void setCancellable(Cancellable c) {
            setDisposable(new CancellableDisposable(c));
        }

        @Override
        public ObservableEmitter serialize() {
            return new SerializedEmitter(this);
        }

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

        @Override
        public boolean isDisposed() {
            return DisposableHelper.isDisposed(get());
        }
    }

    /**
     * Serializes calls to onNext, onError and onComplete.
     *
     * @param  the value type
     */
    static final class SerializedEmitter
    extends AtomicInteger
    implements ObservableEmitter {

        private static final long serialVersionUID = 4883307006032401862L;

        final ObservableEmitter emitter;

        final AtomicThrowable error;

        final SpscLinkedArrayQueue queue;

        volatile boolean done;

        SerializedEmitter(ObservableEmitter emitter) {
            this.emitter = emitter;
            this.error = new AtomicThrowable();
            this.queue = new SpscLinkedArrayQueue(16);
        }

        @Override
        public void onNext(T t) {
            if (emitter.isDisposed() || done) {
                return;
            }
            if (t == null) {
                onError(new NullPointerException("onNext called with null. Null values are generally not allowed in 2.x operators and sources."));
                return;
            }
            if (get() == 0 && compareAndSet(0, 1)) {
                emitter.onNext(t);
                if (decrementAndGet() == 0) {
                    return;
                }
            } else {
                SimpleQueue q = queue;
                synchronized (q) {
                    q.offer(t);
                }
                if (getAndIncrement() != 0) {
                    return;
                }
            }
            drainLoop();
        }

        @Override
        public void onError(Throwable t) {
            if (emitter.isDisposed() || done) {
                RxJavaCommonPlugins.onError(t);
                return;
            }
            if (t == null) {
                t = new NullPointerException("onError called with null. Null values are generally not allowed in 2.x operators and sources.");
            }
            if (error.addThrowable(t)) {
                done = true;
                drain();
            } else {
                RxJavaCommonPlugins.onError(t);
            }
        }

        @Override
        public void onComplete() {
            if (emitter.isDisposed() || done) {
                return;
            }
            done = true;
            drain();
        }

        void drain() {
            if (getAndIncrement() == 0) {
                drainLoop();
            }
        }

        void drainLoop() {
            ObservableEmitter e = emitter;
            SpscLinkedArrayQueue q = queue;
            AtomicThrowable error = this.error;
            int missed = 1;
            for (;;) {

                for (;;) {
                    if (e.isDisposed()) {
                        q.clear();
                        return;
                    }

                    if (error.get() != null) {
                        q.clear();
                        e.onError(error.terminate());
                        return;
                    }

                    boolean d = done;
                    T v = q.poll();

                    boolean empty = v == null;

                    if (d && empty) {
                        e.onComplete();
                        return;
                    }

                    if (empty) {
                        break;
                    }

                    e.onNext(v);
                }

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

        @Override
        public void setDisposable(Disposable s) {
            emitter.setDisposable(s);
        }

        @Override
        public void setCancellable(Cancellable c) {
            emitter.setCancellable(c);
        }

        @Override
        public boolean isDisposed() {
            return emitter.isDisposed();
        }

        @Override
        public ObservableEmitter serialize() {
            return this;
        }
    }

}