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.maybe;
  
  import java.util.concurrent.atomic.AtomicReference;
  
  import io.reactivex.rxjava3.core.*;
  import io.reactivex.rxjava3.disposables.Disposable;
  import io.reactivex.rxjava3.exceptions.Exceptions;
  import io.reactivex.rxjava3.functions.Cancellable;
  import io.reactivex.rxjava3.internal.disposables.*;
  import io.reactivex.rxjava3.internal.util.ExceptionHelper;
  import io.reactivex.rxjava3.plugins.RxJavaPlugins;
  
  /**
   * Provides an API over MaybeObserver that serializes calls to onXXX and manages cancellation
   * in a safe manner.
   *
   * @param <T> the value type emitted
   */
  public final class MaybeCreate<T> extends Maybe<T> {
  
      final MaybeOnSubscribe<T> source;
  
      public MaybeCreate(MaybeOnSubscribe<T> source) {
          this.source = source;
      }
  
      @Override
      protected void subscribeActual(MaybeObserver<? super T> observer) {
          Emitter<T> parent = new Emitter<>(observer);
          observer.onSubscribe(parent);
  
          try {
              source.subscribe(parent);
          } catch (Throwable ex) {
              Exceptions.throwIfFatal(ex);
              parent.onError(ex);
          }
      }
  
      static final class Emitter<T>
      extends AtomicReference<Disposable>
      implements MaybeEmitter<T>, Disposable {
  
          final MaybeObserver<? super T> downstream;
  
          Emitter(MaybeObserver<? super T> downstream) {
              this.downstream = downstream;
          }
  
          private static final long serialVersionUID = -2467358622224974244L;
  
          @Override
          public void onSuccess(T value) {
              if (get() != DisposableHelper.DISPOSED) {
                  Disposable d = getAndSet(DisposableHelper.DISPOSED);
                  if (d != DisposableHelper.DISPOSED) {
                      try {
                          if (value == null) {
                              downstream.onError(ExceptionHelper.createNullPointerException("onSuccess called with a null value."));
                          } else {
                              downstream.onSuccess(value);
                          }
                      } finally {
                          if (d != null) {
                              d.dispose();
                          }
                      }
                  }
              }
          }
  
          @Override
          public void onError(Throwable t) {
              if (!tryOnError(t)) {
                  RxJavaPlugins.onError(t);
              }
          }
  
          @Override
          public boolean tryOnError(Throwable t) {
              if (t == null) {
                  t = ExceptionHelper.createNullPointerException("onError called with a null Throwable.");
              }
              if (get() != DisposableHelper.DISPOSED) {
                  Disposable d = getAndSet(DisposableHelper.DISPOSED);
                  if (d != DisposableHelper.DISPOSED) {
                      try {
                          downstream.onError(t);
                      } finally {
                          if (d != null) {
                              d.dispose();
                          }
                      }
                      return true;
                  }
              }
              return false;
          }
  
          @Override
          public void onComplete() {
              if (get() != DisposableHelper.DISPOSED) {
                  Disposable d = getAndSet(DisposableHelper.DISPOSED);
                  if (d != DisposableHelper.DISPOSED) {
                      try {
                          downstream.onComplete();
                      } finally {
                          if (d != null) {
                              d.dispose();
                          }
                      }
                  }
              }
          }
  
          @Override
          public void setDisposable(Disposable d) {
              DisposableHelper.set(this, d);
          }
  
          @Override
          public void setCancellable(Cancellable c) {
              setDisposable(new CancellableDisposable(c));
          }
  
          @Override
          public void dispose() {
              DisposableHelper.dispose(this);
          }
  
          @Override
          public boolean isDisposed() {
              return DisposableHelper.isDisposed(get());
          }
  
          @Override
          public String toString() {
              return String.format("%s{%s}", getClass().getSimpleName(), super.toString());
          }
      }
  }
  