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.maybe;
  
  import java.util.concurrent.atomic.AtomicReference;
  
  import io.reactivex.rxjava3.core.*;
  import io.reactivex.rxjava3.disposables.Disposable;
  
  /**
   * Consumes the source once and replays its signal to any current or future MaybeObservers.
   *
   * @param <T> the value type
   */
  public final class MaybeCache<T> extends Maybe<T> implements MaybeObserver<T> {
  
      @SuppressWarnings("rawtypes")
      static final CacheDisposable[] EMPTY = new CacheDisposable[0];
  
      @SuppressWarnings("rawtypes")
      static final CacheDisposable[] TERMINATED = new CacheDisposable[0];
  
      final AtomicReference<MaybeSource<T>> source;
  
      final AtomicReference<CacheDisposable<T>[]> observers;
  
      T value;
  
      Throwable error;
  
      @SuppressWarnings("unchecked")
      public MaybeCache(MaybeSource<T> source) {
          this.source = new AtomicReference<>(source);
          this.observers = new AtomicReference<>(EMPTY);
      }
  
      @Override
      protected void subscribeActual(MaybeObserver<? super T> observer) {
          CacheDisposable<T> parent = new CacheDisposable<>(observer, this);
          observer.onSubscribe(parent);
  
          if (add(parent)) {
              if (parent.isDisposed()) {
                  remove(parent);
                  return;
              }
          } else {
              if (!parent.isDisposed()) {
                  Throwable ex = error;
                  if (ex != null) {
                      observer.onError(ex);
                  } else {
                      T v = value;
                      if (v != null) {
                          observer.onSuccess(v);
                      } else {
                          observer.onComplete();
                      }
                  }
              }
              return;
          }
  
          MaybeSource<T> src = source.getAndSet(null);
          if (src != null) {
              src.subscribe(this);
          }
      }
  
      @Override
      public void onSubscribe(Disposable d) {
          // deliberately ignored
      }
  
      @SuppressWarnings("unchecked")
      @Override
      public void onSuccess(T value) {
          this.value = value;
          for (CacheDisposable<T> inner : observers.getAndSet(TERMINATED)) {
              if (!inner.isDisposed()) {
                  inner.downstream.onSuccess(value);
              }
          }
      }
  
      @SuppressWarnings("unchecked")
      @Override
      public void onError(Throwable e) {
          this.error = e;
          for (CacheDisposable<T> inner : observers.getAndSet(TERMINATED)) {
              if (!inner.isDisposed()) {
                  inner.downstream.onError(e);
              }
          }
      }
  
      @SuppressWarnings("unchecked")
      @Override
      public void onComplete() {
          for (CacheDisposable<T> inner : observers.getAndSet(TERMINATED)) {
              if (!inner.isDisposed()) {
                  inner.downstream.onComplete();
              }
          }
      }
  
      boolean add(CacheDisposable<T> inner) {
          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] = inner;
              if (observers.compareAndSet(a, b)) {
                  return true;
              }
          }
      }
  
      @SuppressWarnings("unchecked")
      void remove(CacheDisposable<T> inner) {
          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] == inner) {
                      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;
              }
          }
      }
  
      static final class CacheDisposable<T>
      extends AtomicReference<MaybeCache<T>>
      implements Disposable {
  
          private static final long serialVersionUID = -5791853038359966195L;
  
          final MaybeObserver<? super T> downstream;
  
          CacheDisposable(MaybeObserver<? super T> actual, MaybeCache<T> parent) {
              super(parent);
              this.downstream = actual;
          }
  
          @Override
          public void dispose() {
              MaybeCache<T> mc = getAndSet(null);
              if (mc != null) {
                  mc.remove(this);
              }
          }
  
          @Override
          public boolean isDisposed() {
              return get() == null;
          }
      }
  }
  