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.subscriptions;
  
  import java.util.concurrent.atomic.*;
  
  import org.reactivestreams.Subscription;
  
  import io.reactivex.rxjava3.disposables.Disposable;
  import io.reactivex.rxjava3.internal.disposables.DisposableHelper;
  
  /**
   * A subscription implementation that arbitrates exactly one other Subscription and can
   * hold a single disposable resource.
   *
   * <p>All methods are thread-safe.
   */
  public final class AsyncSubscription extends AtomicLong implements Subscription, Disposable {
  
      private static final long serialVersionUID = 7028635084060361255L;
  
      final AtomicReference<Subscription> actual;
  
      final AtomicReference<Disposable> resource;
  
      public AsyncSubscription() {
          resource = new AtomicReference<>();
          actual = new AtomicReference<>();
      }
  
      public AsyncSubscription(Disposable resource) {
          this();
          this.resource.lazySet(resource);
      }
  
      @Override
      public void request(long n) {
          SubscriptionHelper.deferredRequest(actual, this, n);
      }
  
      @Override
      public void cancel() {
          dispose();
      }
  
      @Override
      public void dispose() {
          SubscriptionHelper.cancel(actual);
          DisposableHelper.dispose(resource);
      }
  
      @Override
      public boolean isDisposed() {
          return actual.get() == SubscriptionHelper.CANCELLED;
      }
  
      /**
       * Sets a new resource and disposes the currently held resource.
       * @param r the new resource to set
       * @return false if this AsyncSubscription has been cancelled/disposed
       * @see #replaceResource(Disposable)
       */
      public boolean setResource(Disposable r) {
          return DisposableHelper.set(resource, r);
      }
  
      /**
       * Replaces the currently held resource with the given new one without disposing the old.
       * @param r the new resource to set
       * @return false if this AsyncSubscription has been cancelled/disposed
       */
      public boolean replaceResource(Disposable r) {
          return DisposableHelper.replace(resource, r);
      }
  
      /**
       * Sets the given subscription if there isn't any subscription held.
       * @param s the first and only subscription to set
       */
      public void setSubscription(Subscription s) {
          SubscriptionHelper.deferredSetOnce(actual, this, s);
      }
  }
  