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.observable;
  
  import java.util.Objects;
  import java.util.concurrent.atomic.AtomicBoolean;
  
  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 ObservableUsing<T, D> extends Observable<T> {
      final Supplier<? extends D> resourceSupplier;
      final Function<? super D, ? extends ObservableSource<? extends T>> sourceSupplier;
      final Consumer<? super D> disposer;
      final boolean eager;
  
      public ObservableUsing(Supplier<? extends D> resourceSupplier,
              Function<? super D, ? extends ObservableSource<? extends T>> sourceSupplier,
              Consumer<? super D> disposer,
              boolean eager) {
          this.resourceSupplier = resourceSupplier;
          this.sourceSupplier = sourceSupplier;
          this.disposer = disposer;
          this.eager = eager;
      }
  
      @Override
      public void subscribeActual(Observer<? super T> observer) {
          D resource;
  
          try {
              resource = resourceSupplier.get();
          } catch (Throwable e) {
              Exceptions.throwIfFatal(e);
              EmptyDisposable.error(e, observer);
              return;
          }
  
          ObservableSource<? extends T> source;
          try {
              source = Objects.requireNonNull(sourceSupplier.apply(resource), "The sourceSupplier returned a null ObservableSource");
          } catch (Throwable e) {
              Exceptions.throwIfFatal(e);
              try {
                  disposer.accept(resource);
              } catch (Throwable ex) {
                  Exceptions.throwIfFatal(ex);
                  EmptyDisposable.error(new CompositeException(e, ex), observer);
                  return;
              }
              EmptyDisposable.error(e, observer);
              return;
          }
  
          UsingObserver<T, D> us = new UsingObserver<>(observer, resource, disposer, eager);
  
          source.subscribe(us);
      }
  
      static final class UsingObserver<T, D> extends AtomicBoolean implements Observer<T>, Disposable {
  
          private static final long serialVersionUID = 5904473792286235046L;
  
          final Observer<? super T> downstream;
          final D resource;
          final Consumer<? super D> disposer;
          final boolean eager;
  
          Disposable upstream;
  
          UsingObserver(Observer<? super T> actual, D resource, Consumer<? super D> disposer, boolean eager) {
              this.downstream = actual;
              this.resource = resource;
              this.disposer = disposer;
              this.eager = eager;
          }
  
          @Override
          public void onSubscribe(Disposable d) {
              if (DisposableHelper.validate(this.upstream, d)) {
                  this.upstream = d;
                  downstream.onSubscribe(this);
              }
          }
  
          @Override
          public void onNext(T t) {
              downstream.onNext(t);
          }
  
          @Override
          public void onError(Throwable t) {
              if (eager) {
                  if (compareAndSet(false, true)) {
                      try {
                          disposer.accept(resource);
                      } catch (Throwable e) {
                          Exceptions.throwIfFatal(e);
                          t = new CompositeException(t, e);
                      }
                  }
  
                  downstream.onError(t);
              } else {
                  downstream.onError(t);
                  disposeResource();
              }
          }
  
          @Override
          public void onComplete() {
              if (eager) {
                  if (compareAndSet(false, true)) {
                      try {
                          disposer.accept(resource);
                      } catch (Throwable e) {
                          Exceptions.throwIfFatal(e);
                          downstream.onError(e);
                          return;
                      }
                  }
  
                  downstream.onComplete();
              } else {
                  downstream.onComplete();
                  disposeResource();
              }
          }
  
          @Override
          public void dispose() {
              if (eager) {
                  disposeResource();
                  upstream.dispose();
                  upstream = DisposableHelper.DISPOSED;
              } else {
                  upstream.dispose();
                  upstream = DisposableHelper.DISPOSED;
                  disposeResource();
              }
          }
  
          @Override
          public boolean isDisposed() {
              return get();
          }
  
          void disposeResource() {
              if (compareAndSet(false, true)) {
                  try {
                      disposer.accept(resource);
                  } catch (Throwable e) {
                      Exceptions.throwIfFatal(e);
                      // can't call actual.onError unless it is serialized, which is expensive
                      RxJavaPlugins.onError(e);
                  }
              }
          }
      }
  }
  