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Reactive Extensions for Java
There is a newer version: 2.2.21
/**
 * 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.concurrent.atomic.AtomicLong;

import org.reactivestreams.*;

import io.reactivex.*;
import io.reactivex.exceptions.MissingBackpressureException;
import io.reactivex.internal.subscriptions.SubscriptionHelper;
import io.reactivex.internal.util.BackpressureHelper;
import io.reactivex.plugins.RxJavaPlugins;

public final class FlowableOnBackpressureError extends AbstractFlowableWithUpstream {

    public FlowableOnBackpressureError(Flowable source) {
        super(source);
    }

    @Override
    protected void subscribeActual(Subscriber s) {
        this.source.subscribe(new BackpressureErrorSubscriber(s));
    }

    static final class BackpressureErrorSubscriber
            extends AtomicLong implements FlowableSubscriber, Subscription {
        private static final long serialVersionUID = -3176480756392482682L;

        final Subscriber downstream;
        Subscription upstream;
        boolean done;

        BackpressureErrorSubscriber(Subscriber downstream) {
            this.downstream = downstream;
        }

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

        @Override
        public void onNext(T t) {
            if (done) {
                return;
            }
            long r = get();
            if (r != 0L) {
                downstream.onNext(t);
                BackpressureHelper.produced(this, 1);
            } else {
                onError(new MissingBackpressureException("could not emit value due to lack of requests"));
            }
        }

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

        @Override
        public void onComplete() {
            if (done) {
                return;
            }
            done = true;
            downstream.onComplete();
        }

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

        @Override
        public void cancel() {
            upstream.cancel();
        }
    }
}