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.single;
  
  import java.util.concurrent.atomic.*;
  
  import io.reactivex.rxjava3.core.*;
  import io.reactivex.rxjava3.disposables.Disposable;
  
  public final class SingleCache<T> extends Single<T> implements SingleObserver<T> {
  
      @SuppressWarnings("rawtypes")
      static final CacheDisposable[] EMPTY = new CacheDisposable[0];
      @SuppressWarnings("rawtypes")
      static final CacheDisposable[] TERMINATED = new CacheDisposable[0];
  
      final SingleSource<? extends T> source;
  
      final AtomicInteger wip;
  
      final AtomicReference<CacheDisposable<T>[]> observers;
  
      T value;
  
      Throwable error;
  
      @SuppressWarnings("unchecked")
      public SingleCache(SingleSource<? extends T> source) {
          this.source = source;
          this.wip = new AtomicInteger();
          this.observers = new AtomicReference<>(EMPTY);
      }
  
      @Override
      protected void subscribeActual(final SingleObserver<? super T> observer) {
          CacheDisposable<T> d = new CacheDisposable<>(observer, this);
          observer.onSubscribe(d);
  
          if (add(d)) {
              if (d.isDisposed()) {
                  remove(d);
              }
          } else {
              Throwable ex = error;
              if (ex != null) {
                  observer.onError(ex);
              } else {
                  observer.onSuccess(value);
              }
              return;
          }
  
          if (wip.getAndIncrement() == 0) {
              source.subscribe(this);
          }
      }
  
      boolean add(CacheDisposable<T> observer) {
          for (;;) {
              CacheDisposable<T>[] a = observers.get();
              if (a == TERMINATED) {
                  return false;
              }
              int n = a.length;
              @SuppressWarnings("unchecked")
              CacheDisposable<T>[] b = new CacheDisposable[n + 1];
              System.arraycopy(a, 0, b, 0, n);
              b[n] = observer;
              if (observers.compareAndSet(a, b)) {
                  return true;
              }
          }
      }
  
      @SuppressWarnings("unchecked")
      void remove(CacheDisposable<T> observer) {
          for (;;) {
              CacheDisposable<T>[] a = observers.get();
              int n = a.length;
              if (n == 0) {
                  return;
              }
  
              int j = -1;
              for (int i = 0; i < n; i++) {
                  if (a[i] == observer) {
                      j = i;
                      break;
                  }
              }
  
              if (j < 0) {
                  return;
              }
  
              CacheDisposable<T>[] b;
  
              if (n == 1) {
                  b = EMPTY;
              } else {
                  b = new CacheDisposable[n - 1];
                  System.arraycopy(a, 0, b, 0, j);
                  System.arraycopy(a, j + 1, b, j, n - j - 1);
              }
              if (observers.compareAndSet(a, b)) {
                  return;
              }
          }
      }
  
      @Override
      public void onSubscribe(Disposable d) {
          // not supported by this operator
      }
  
      @SuppressWarnings("unchecked")
      @Override
      public void onSuccess(T value) {
          this.value = value;
  
          for (CacheDisposable<T> d : observers.getAndSet(TERMINATED)) {
              if (!d.isDisposed()) {
                  d.downstream.onSuccess(value);
              }
          }
      }
  
      @SuppressWarnings("unchecked")
      @Override
      public void onError(Throwable e) {
          this.error = e;
  
          for (CacheDisposable<T> d : observers.getAndSet(TERMINATED)) {
              if (!d.isDisposed()) {
                  d.downstream.onError(e);
              }
          }
      }
  
      static final class CacheDisposable<T>
      extends AtomicBoolean
      implements Disposable {
  
          private static final long serialVersionUID = 7514387411091976596L;
  
          final SingleObserver<? super T> downstream;
  
          final SingleCache<T> parent;
  
          CacheDisposable(SingleObserver<? super T> actual, SingleCache<T> parent) {
              this.downstream = actual;
              this.parent = parent;
          }
  
          @Override
          public boolean isDisposed() {
              return get();
          }
  
          @Override
          public void dispose() {
              if (compareAndSet(false, true)) {
                  parent.remove(this);
              }
          }
      }
  }
  