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Reactive Extensions for Java
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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.internal.operators.single;

import java.util.concurrent.Callable;
import java.util.concurrent.atomic.AtomicReference;

import io.reactivex.*;
import io.reactivex.disposables.Disposable;
import io.reactivex.exceptions.*;
import io.reactivex.functions.*;
import io.reactivex.internal.disposables.*;
import io.reactivex.internal.functions.ObjectHelper;
import io.reactivex.plugins.RxJavaPlugins;

public final class SingleUsing extends Single {

    final Callable resourceSupplier;
    final Function> singleFunction;
    final Consumer disposer;
    final boolean eager;

    public SingleUsing(Callable resourceSupplier,
                       Function> singleFunction,
                       Consumer disposer,
                       boolean eager) {
        this.resourceSupplier = resourceSupplier;
        this.singleFunction = singleFunction;
        this.disposer = disposer;
        this.eager = eager;
    }

    @Override
    protected void subscribeActual(final SingleObserver observer) {

        final U resource; // NOPMD

        try {
            resource = resourceSupplier.call();
        } catch (Throwable ex) {
            Exceptions.throwIfFatal(ex);
            EmptyDisposable.error(ex, observer);
            return;
        }

        SingleSource source;

        try {
            source = ObjectHelper.requireNonNull(singleFunction.apply(resource), "The singleFunction returned a null SingleSource");
        } catch (Throwable ex) {
            Exceptions.throwIfFatal(ex);

            if (eager) {
                try {
                    disposer.accept(resource);
                } catch (Throwable exc) {
                    Exceptions.throwIfFatal(exc);
                    ex = new CompositeException(ex, exc);
                }
            }
            EmptyDisposable.error(ex, observer);
            if (!eager) {
                try {
                    disposer.accept(resource);
                } catch (Throwable exc) {
                    Exceptions.throwIfFatal(exc);
                    RxJavaPlugins.onError(exc);
                }
            }
            return;
        }

        source.subscribe(new UsingSingleObserver(observer, resource, eager, disposer));
    }

    static final class UsingSingleObserver extends
    AtomicReference