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.completable;
  
  import java.util.concurrent.atomic.*;
  
  import io.reactivex.rxjava3.core.*;
  import io.reactivex.rxjava3.disposables.Disposable;
  
  /**
   * Consume the upstream source exactly once and cache its terminal event.
   * <p>History: 2.0.4 - experimental
   * @since 2.1
   */
  public final class CompletableCache extends Completable implements CompletableObserver {
  
      static final InnerCompletableCache[] EMPTY = new InnerCompletableCache[0];
  
      static final InnerCompletableCache[] TERMINATED = new InnerCompletableCache[0];
  
      final CompletableSource source;
  
      final AtomicReference<InnerCompletableCache[]> observers;
  
      final AtomicBoolean once;
  
      Throwable error;
  
      public CompletableCache(CompletableSource source) {
          this.source = source;
          this.observers = new AtomicReference<>(EMPTY);
          this.once = new AtomicBoolean();
      }
  
      @Override
      protected void subscribeActual(CompletableObserver observer) {
          InnerCompletableCache inner = new InnerCompletableCache(observer);
          observer.onSubscribe(inner);
  
          if (add(inner)) {
              if (inner.isDisposed()) {
                  remove(inner);
              }
  
              if (once.compareAndSet(false, true)) {
                  source.subscribe(this);
              }
          } else {
              Throwable ex = error;
              if (ex != null) {
                  observer.onError(ex);
              } else {
                  observer.onComplete();
              }
          }
      }
  
      @Override
      public void onSubscribe(Disposable d) {
          // not used
      }
  
      @Override
      public void onError(Throwable e) {
          error = e;
          for (InnerCompletableCache inner : observers.getAndSet(TERMINATED)) {
              if (!inner.get()) {
                  inner.downstream.onError(e);
              }
          }
      }
  
      @Override
      public void onComplete() {
          for (InnerCompletableCache inner : observers.getAndSet(TERMINATED)) {
              if (!inner.get()) {
                  inner.downstream.onComplete();
              }
          }
      }
  
      boolean add(InnerCompletableCache inner) {
          for (;;) {
              InnerCompletableCache[] a = observers.get();
              if (a == TERMINATED) {
                  return false;
              }
              int n = a.length;
              InnerCompletableCache[] b = new InnerCompletableCache[n + 1];
              System.arraycopy(a, 0, b, 0, n);
              b[n] = inner;
              if (observers.compareAndSet(a, b)) {
                  return true;
              }
          }
      }
  
      void remove(InnerCompletableCache inner) {
          for (;;) {
              InnerCompletableCache[] a = observers.get();
              int n = a.length;
              if (n == 0) {
                  return;
              }
  
              int j = -1;
  
              for (int i = 0; i < n; i++) {
                  if (a[i] == inner) {
                      j = i;
                      break;
                  }
              }
  
              if (j < 0) {
                  return;
              }
  
              InnerCompletableCache[] b;
  
              if (n == 1) {
                  b = EMPTY;
              } else {
                  b = new InnerCompletableCache[n - 1];
                  System.arraycopy(a, 0, b, 0, j);
                  System.arraycopy(a, j + 1, b, j, n - j - 1);
              }
  
              if (observers.compareAndSet(a, b)) {
                  break;
              }
          }
      }
  
      final class InnerCompletableCache
      extends AtomicBoolean
      implements Disposable {
  
          private static final long serialVersionUID = 8943152917179642732L;
  
          final CompletableObserver downstream;
  
          InnerCompletableCache(CompletableObserver downstream) {
              this.downstream = downstream;
          }
  
          @Override
          public boolean isDisposed() {
              return get();
          }
  
          @Override
          public void dispose() {
              if (compareAndSet(false, true)) {
                  remove(this);
              }
          }
      }
  }
  