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.flowable;
  
  import java.util.*;
  import java.util.concurrent.Semaphore;
  import java.util.concurrent.atomic.AtomicReference;
  
  import org.reactivestreams.Publisher;
  
  import io.reactivex.rxjava3.core.*;
  import io.reactivex.rxjava3.internal.util.*;
  import io.reactivex.rxjava3.plugins.RxJavaPlugins;
  import io.reactivex.rxjava3.subscribers.DisposableSubscriber;
  
  /**
   * Wait for and iterate over the latest values of the source observable. If the source works faster than the
   * iterator, values may be skipped, but not the {@code onError} or {@code onComplete} events.
   * @param <T> the value type emitted
   */
  public final class BlockingFlowableLatest<T> implements Iterable<T> {
  
      final Publisher<? extends T> source;
  
      public BlockingFlowableLatest(Publisher<? extends T> source) {
          this.source = source;
      }
  
      @Override
      public Iterator<T> iterator() {
          LatestSubscriberIterator<T> lio = new LatestSubscriberIterator<>();
          Flowable.<T>fromPublisher(source).materialize().subscribe(lio);
          return lio;
      }
  
      /** Subscriber of source, iterator for output. */
      static final class LatestSubscriberIterator<T> extends DisposableSubscriber<Notification<T>> implements Iterator<T> {
          final Semaphore notify = new Semaphore(0);
          // observer's notification
          final AtomicReference<Notification<T>> value = new AtomicReference<>();
  
          // iterator's notification
          Notification<T> iteratorNotification;
  
          @Override
          public void onNext(Notification<T> args) {
              boolean wasNotAvailable = value.getAndSet(args) == null;
              if (wasNotAvailable) {
                  notify.release();
              }
          }
  
          @Override
          public void onError(Throwable e) {
              RxJavaPlugins.onError(e);
          }
  
          @Override
          public void onComplete() {
              // not expected
          }
  
          @Override
          public boolean hasNext() {
              if (iteratorNotification != null && iteratorNotification.isOnError()) {
                  throw ExceptionHelper.wrapOrThrow(iteratorNotification.getError());
              }
              if (iteratorNotification == null || iteratorNotification.isOnNext()) {
                  if (iteratorNotification == null) {
                      try {
                          BlockingHelper.verifyNonBlocking();
                          notify.acquire();
                      } catch (InterruptedException ex) {
                          dispose();
                          iteratorNotification = Notification.createOnError(ex);
                          throw ExceptionHelper.wrapOrThrow(ex);
                      }
  
                      Notification<T> n = value.getAndSet(null);
                      iteratorNotification = n;
                      if (n.isOnError()) {
                          throw ExceptionHelper.wrapOrThrow(n.getError());
                      }
                  }
              }
              return iteratorNotification.isOnNext();
          }
  
          @Override
          public T next() {
              if (hasNext()) {
                  if (iteratorNotification.isOnNext()) {
                      T v = iteratorNotification.getValue();
                      iteratorNotification = null;
                      return v;
                  }
              }
              throw new NoSuchElementException();
          }
  
          @Override
          public void remove() {
              throw new UnsupportedOperationException("Read-only iterator.");
          }
  
      }
  }
  