code: /*
   * 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.AtomicReference;
  
  import io.reactivex.rxjava3.core.*;
  import io.reactivex.rxjava3.disposables.Disposable;
  import io.reactivex.rxjava3.exceptions.*;
  import io.reactivex.rxjava3.functions.*;
  import io.reactivex.rxjava3.internal.disposables.*;
  import io.reactivex.rxjava3.plugins.RxJavaPlugins;
  
  public final class SingleUsing<T, U> extends Single<T> {
  
      final Supplier<U> resourceSupplier;
      final Function<? super U, ? extends SingleSource<? extends T>> singleFunction;
      final Consumer<? super U> disposer;
      final boolean eager;
  
      public SingleUsing(Supplier<U> resourceSupplier,
                         Function<? super U, ? extends SingleSource<? extends T>> singleFunction,
                         Consumer<? super U> disposer,
                         boolean eager) {
          this.resourceSupplier = resourceSupplier;
          this.singleFunction = singleFunction;
          this.disposer = disposer;
          this.eager = eager;
      }
  
      @Override
      protected void subscribeActual(final SingleObserver<? super T> observer) {
  
          final U resource; // NOPMD
  
          try {
              resource = resourceSupplier.get();
          } catch (Throwable ex) {
              Exceptions.throwIfFatal(ex);
              EmptyDisposable.error(ex, observer);
              return;
          }
  
          SingleSource<? extends T> source;
  
          try {
              source = Objects.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<T, U>(observer, resource, eager, disposer));
      }
  
      static final class UsingSingleObserver<T, U> extends
      AtomicReference<Object> implements SingleObserver<T>, Disposable {
  
          private static final long serialVersionUID = -5331524057054083935L;
  
          final SingleObserver<? super T> downstream;
  
          final Consumer<? super U> disposer;
  
          final boolean eager;
  
          Disposable upstream;
  
          UsingSingleObserver(SingleObserver<? super T> actual, U resource, boolean eager,
                  Consumer<? super U> disposer) {
              super(resource);
              this.downstream = actual;
              this.eager = eager;
              this.disposer = disposer;
          }
  
          @Override
          public void dispose() {
              if (eager) {
                  disposeResource();
                  upstream.dispose();
                  upstream = DisposableHelper.DISPOSED;
              } else {
                  upstream.dispose();
                  upstream = DisposableHelper.DISPOSED;
                  disposeResource();
              }
          }
  
          @Override
          public boolean isDisposed() {
              return upstream.isDisposed();
          }
  
          @Override
          public void onSubscribe(Disposable d) {
              if (DisposableHelper.validate(this.upstream, d)) {
                  this.upstream = d;
  
                  downstream.onSubscribe(this);
              }
          }
  
          @SuppressWarnings("unchecked")
          @Override
          public void onSuccess(T value) {
              upstream = DisposableHelper.DISPOSED;
  
              if (eager) {
                  Object u = getAndSet(this);
                  if (u != this) {
                      try {
                          disposer.accept((U)u);
                      } catch (Throwable ex) {
                          Exceptions.throwIfFatal(ex);
                          downstream.onError(ex);
                          return;
                      }
                  } else {
                      return;
                  }
              }
  
              downstream.onSuccess(value);
  
              if (!eager) {
                  disposeResource();
              }
          }
  
          @SuppressWarnings("unchecked")
          @Override
          public void onError(Throwable e) {
              upstream = DisposableHelper.DISPOSED;
  
              if (eager) {
                  Object u = getAndSet(this);
                  if (u != this) {
                      try {
                          disposer.accept((U)u);
                      } catch (Throwable ex) {
                          Exceptions.throwIfFatal(ex);
                          e = new CompositeException(e, ex);
                      }
                  } else {
                      return;
                  }
              }
  
              downstream.onError(e);
  
              if (!eager) {
                  disposeResource();
              }
          }
  
          @SuppressWarnings("unchecked")
          void disposeResource() {
              Object u = getAndSet(this);
              if (u != this) {
                  try {
                      disposer.accept((U)u);
                  } catch (Throwable ex) {
                      Exceptions.throwIfFatal(ex);
                      RxJavaPlugins.onError(ex);
                  }
              }
          }
      }
  }
  