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.AtomicReferenceArray;
  
  import org.reactivestreams.Subscription;
  
  import io.reactivex.rxjava3.disposables.Disposable;
  
  /**
   * A composite disposable with a fixed number of slots.
   *
   * <p>Note that since the implementation leaks the methods of AtomicReferenceArray, one must be
   * careful to only call setResource, replaceResource and dispose on it. All other methods may lead to undefined behavior
   * and should be used by internal means only.
   */
  public final class ArrayCompositeSubscription extends AtomicReferenceArray<Subscription> implements Disposable {
  
      private static final long serialVersionUID = 2746389416410565408L;
  
      public ArrayCompositeSubscription(int capacity) {
          super(capacity);
      }
  
      /**
       * Sets the resource at the specified index and disposes the old resource.
       * @param index the index of the resource to set
       * @param resource the new resource
       * @return true if the resource has ben set, false if the composite has been disposed
       */
      public boolean setResource(int index, Subscription resource) {
          for (;;) {
              Subscription o = get(index);
              if (o == SubscriptionHelper.CANCELLED) {
                  if (resource != null) {
                      resource.cancel();
                  }
                  return false;
              }
              if (compareAndSet(index, o, resource)) {
                  if (o != null) {
                      o.cancel();
                  }
                  return true;
              }
          }
      }
  
      /**
       * Replaces the resource at the specified index and returns the old resource.
       * @param index the index of the resource to replace
       * @param resource the new resource
       * @return the old resource, can be null
       */
      public Subscription replaceResource(int index, Subscription resource) {
          for (;;) {
              Subscription o = get(index);
              if (o == SubscriptionHelper.CANCELLED) {
                  if (resource != null) {
                      resource.cancel();
                  }
                  return null;
              }
              if (compareAndSet(index, o, resource)) {
                  return o;
              }
          }
      }
  
      @Override
      public void dispose() {
          if (get(0) != SubscriptionHelper.CANCELLED) {
              int s = length();
              for (int i = 0; i < s; i++) {
                  Subscription o = get(i);
                  if (o != SubscriptionHelper.CANCELLED) {
                      o = getAndSet(i, SubscriptionHelper.CANCELLED);
                      if (o != SubscriptionHelper.CANCELLED && o != null) {
                          o.cancel();
                      }
                  }
              }
          }
      }
  
      @Override
      public boolean isDisposed() {
          return get(0) == SubscriptionHelper.CANCELLED;
      }
  }
  