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.disposables;
  
  import java.util.concurrent.atomic.AtomicReference;
  
  import io.reactivex.rxjava3.disposables.Disposable;
  
  /**
   * A Disposable container that allows updating/replacing a Disposable
   * atomically and with respect of disposing the container itself.
   * <p>
   * The class extends AtomicReference directly so watch out for the API leak!
   * @since 2.0
   */
  public final class SequentialDisposable
  extends AtomicReference<Disposable>
  implements Disposable {
  
      private static final long serialVersionUID = -754898800686245608L;
  
      /**
       * Constructs an empty SequentialDisposable.
       */
      public SequentialDisposable() {
          // nothing to do
      }
  
      /**
       * Construct a SequentialDisposable with the initial Disposable provided.
       * @param initial the initial disposable, null allowed
       */
      public SequentialDisposable(Disposable initial) {
          lazySet(initial);
      }
  
      /**
       * Atomically: set the next disposable on this container and dispose the previous
       * one (if any) or dispose next if the container has been disposed.
       * @param next the Disposable to set, may be null
       * @return true if the operation succeeded, false if the container has been disposed
       * @see #replace(Disposable)
       */
      public boolean update(Disposable next) {
          return DisposableHelper.set(this, next);
      }
  
      /**
       * Atomically: set the next disposable on this container but don't dispose the previous
       * one (if any) or dispose next if the container has been disposed.
       * @param next the Disposable to set, may be null
       * @return true if the operation succeeded, false if the container has been disposed
       * @see #update(Disposable)
       */
      public boolean replace(Disposable next) {
          return DisposableHelper.replace(this, next);
      }
  
      @Override
      public void dispose() {
          DisposableHelper.dispose(this);
      }
  
      @Override
      public boolean isDisposed() {
          return DisposableHelper.isDisposed(get());
      }
  }
  